A novel dibenzocarbazole compound with which a light-emitting element having low power consumption, high reliability, and high color purity can be fabricated is provided. In the dibenzocarbazole compound, an aryl group which has 14 to 30 carbon atoms and at least an anthracene skeleton is bonded to nitrogen of a dibenzo[a,g]carbazole skeleton or a dibenzo[a,i]carbazole skeleton. Furthermore, a light-emitting element including the dibenzocarbazole compound is provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

One embodiment of the present invention relates to a dibenzocarbazole compound. One embodiment of the present invention also relates to a light-emitting element, and a light-emitting device, a display device, an electronic device, and a lighting device each including the light-emitting element.

2. Description of the Related Art

In recent years, research and development have been extensively conducted on light-emitting elements using electroluminescence (EL). In a basic structure of such a light-emitting element, a layer containing a light-emitting material (an EL layer) is interposed between a pair of electrodes. By applying a voltage between the pair of electrodes of this element, light emission from the light-emitting material can be obtained.

Since the above light-emitting element is of a self-luminous type, a display device using this light-emitting element has advantages such as high visibility, no necessity of a backlight, low power consumption, and the like. Furthermore, the display device also has advantages in that it can be formed to be thin and lightweight, and has high response speed.

In a light-emitting element (e.g., an organic EL element) whose EL layer contains an organic material as a light-emitting material and is provided between a pair of electrodes, application of a voltage between the pair of electrodes causes injection of electrons from a cathode and holes from an anode into the EL layer having a light-emitting property and thus a current flows. By recombination of the injected electrons and holes, the organic material having a light-emitting property is brought into an excited state to provide light emission.

Note that an excited state formed by an organic material can be a singlet excited state (S*) or a triplet excited state (T*). Light emission from the singlet excited state is referred to as fluorescence, and light emission from the triplet excited state is referred to as phosphorescence. The statistical generation ratio of the excited states in the light-emitting element is considered to be S*:T*=1:3. In other words, a light-emitting element including a material that emits phosphorescence (a phosphorescent material) has higher emission efficiency than a light-emitting element including a material that emits fluorescence (a fluorescent material). Therefore, light-emitting elements containing phosphorescent materials capable of converting energy of the triplet excited state into light emission have been actively developed in recent years.

Among light-emitting elements including phosphorescent materials, a light-emitting element that emits blue light has not been put into practical use yet because it is difficult to develop a stable material having a high triplet excitation energy level. For this reason, a light-emitting element including a more stable fluorescent material has been developed for a light-emitting element that emits blue light and a material for increasing the emission efficiency and lifetime of a light-emitting element including a fluorescent material has been searched.

Note that the performance of a light-emitting element, such as emission efficiency or lifetime, is significantly affected by not only the performance of a light-emitting material but also the performance of a host material for exciting the light-emitting material or a carrier-transport material for transporting a carrier. Therefore, materials having a variety of molecular structures have been proposed in order to increase the emission efficiency and the lifetime of a light-emitting element (for example, Patent Documents 1 and 2).

In particular, as for a light-emitting element that emits deep blue light, not only a light-emitting material but also a host material for exciting the light-emitting material needs to have high excitation energy. Accordingly, development of a highly stable host material which can excite a light-emitting material efficiently has been required.

REFERENCE

Patent Document

[Patent Document 1] United States Published Patent Application No. 2008/0122344[Patent Document 2] PCT International Publication No. 2010/114264

SUMMARY OF THE INVENTION

As an example of a material which can be used as a host material of a light-emitting element that emits blue fluorescence, 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA) can be given. By using CzPA as a host material, a light-emitting element that emits blue fluorescence and has excellent characteristics in terms of emission efficiency and driving lifetime can be fabricated.

However, in recent years, display devices with low power consumption and high color reproducibility have been required with demand for higher performance. Therefore, light-emitting elements that emits light with higher color purity and has higher emission efficiency have been required. In particular, light-emitting elements that have high efficiency and long lifetime and emit deep blue light have been required. Note that although many light-emitting element materials have been proposed so far, it is difficult to develop a material with which a light-emitting element having high emission efficiency and long lifetime and emitting deep blue light can be achieved.

An object of one embodiment of the present invention is to provide a novel compound. Another object of one embodiment of the present invention is to provide a novel compound with which a light-emitting element having high emission efficiency can be achieved. Another object of one embodiment of the present invention is to provide a novel compound with which a light-emitting element having lower power consumption can be achieved. Another object of one embodiment of the present invention is to provide a novel compound with which a light-emitting element having long lifetime can be achieved. Another object of one embodiment of the present invention is to provide a novel compound with which a novel light-emitting element can be achieved. Another object of one embodiment of the present invention is to provide a light-emitting element including a novel compound. Another object of one embodiment of the present invention is to provide a light-emitting element with high emission efficiency. Another object of one embodiment of the present invention is to provide a light-emitting element which emits blue light with high emission efficiency. Another object of one embodiment of the present invention is to provide a light-emitting element with long lifetime. Another object of one embodiment of the present invention is to provide a novel light-emitting device. Another object of one embodiment of the present invention is to provide a novel display device. Another object of one embodiment of the present invention is to provide a novel electronic device. Another object of one embodiment of the present invention is to provide a novel lighting device.

Note that the description of the above objects does not disturb the existence of other objects. In one embodiment of the present invention, there is no need to achieve all the objects. Other objects are apparent from and can be derived from the description of the specification and the like.

The present inventors synthesized a novel dibenzocarbazole compound including a dibenzo[a,g]carbazole skeleton or a dibenzo[a,i]carbazole skeleton and an anthracene skeleton and have found that a light-emitting element having excellent characteristics can be provided when the dibenzocarbazole compound is used.

That is, one embodiment of the present invention is a dibenzocarbazole compound in which an aryl group is bonded to a dibenzo[a,g]carbazole skeleton or a dibenzo[a,i]carbazole skeleton and the aryl group is an aryl group which has 14 to 30 carbon atoms and at least an anthracene skeleton.

Another embodiment of the present invention is a dibenzocarbazole compound in which an aryl group is bonded to the 7-position of a dibenzo[a,g]carbazole skeleton or the 11-position of a dibenzo[a,i]carbazole skeleton and the aryl group is an aryl group which has 14 to 30 carbon atoms and at least an anthracene skeleton.

Another embodiment of the present invention is a dibenzocarbazole compound in which the 7-position of a dibenzo[a,g]carbazole skeleton or the 11-position of a dibenzo[a,i]carbazole skeleton is bonded to an anthracene skeleton through a phenylene group.

Another embodiment of the present invention is a dibenzocarbazole compound in which the 7-position of a dibenzo[a,g]carbazole skeleton or the 11-position of a dibenzo[a,i]carbazole skeleton is bonded to the 9-position of an anthracene skeleton through a phenylene group.

Another embodiment of the present invention is a dibenzocarbazole compound in which the 7-position of a dibenzo[a,g]carbazole skeleton or the 11-position of a dibenzo[a,i]carbazole skeleton is bonded to a substituted or unsubstituted anthryl phenyl group having 20 to 30 carbon atoms.

Another embodiment of the present invention is a dibenzocarbazole compound in which the 7-position of a dibenzo[a,g]carbazole skeleton or the 11-position of a dibenzo[a,i]carbazole skeleton is bonded to a substituted or unsubstituted (9-anthryl)phenyl group having 20 to 30 carbon atoms.

Another embodiment of the present invention is a dibenzocarbazole compound represented by General Formula (G1).

In General Formula (G1), R11to R22each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and Ar represents a substituted or unsubstituted aryl group which has 14 to 30 carbon atoms and at least an anthracene skeleton.

Another embodiment of the present invention is a dibenzocarbazole compound represented by General Formula (G2).

In General Formula (G2), R11to R22each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; X represents a substituted or unsubstituted arylene group having 6 to 13 carbon atoms; and Y represents a substituted or unsubstituted anthryl group.

In the above structure, the total number of carbon atoms of X and Y is preferably 20 to 30.

Another embodiment of the present invention is a dibenzocarbazole compound represented by General Formula (G3).

In General Formula (G3), R1to R8each independently represent hydrogen or an alkyl group having 1 to 4 carbon atoms; R9represents any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 10 carbon atoms; R11to R22each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and X represents a substituted or unsubstituted arylene group having 6 to 13 carbon atoms.

In the above structure, the total number of carbon atoms of R1to R9and X is preferably 6 to 16.

In any of the above structures, X preferably represents a substituted or unsubstituted phenylene group.

Another embodiment of the present invention is a dibenzocarbazole compound represented by General Formula (G4).

In General Formula (G4), R9represents any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 10 carbon atoms; R11to R22each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and X represents a substituted or unsubstituted phenylene group.

Another embodiment of the present invention is a dibenzocarbazole compound represented by General Formula (G5).

In General Formula (G5), R9represents any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 10 carbon atoms; and X represents a substituted or unsubstituted phenylene group.

In any of the above structures, the total number of carbon atoms of R9and X is preferably 6 to 16.

Another embodiment of the present invention is a dibenzocarbazole compound represented by Structural Formula (100).

Another embodiment of the present invention is a dibenzocarbazole compound represented by General Formula (G6).

In General Formula (G6), R31to R42each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and Ar represents a substituted or unsubstituted aryl group which has 14 to 30 carbon atoms and at least an anthracene skeleton.

Another embodiment of the present invention is a dibenzocarbazole compound represented by General Formula (G7).

In General Formula (G7), R31to R42each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; X represents a substituted or unsubstituted arylene group having 6 to 13 carbon atoms; and Y represents a substituted or unsubstituted anthryl group.

In the above structure, the total number of carbon atoms of X and Y is preferably 20 to 30.

Another embodiment of the present invention is a dibenzocarbazole compound represented by General Formula (G8).

In General Formula (G8), R1to R8each independently represent hydrogen or an alkyl group having 1 to 4 carbon atoms; R9represents any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 10 carbon atoms; R31to R42each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and X represents a substituted or unsubstituted arylene group having 6 to 13 carbon atoms.

In the above structure, the total number of carbon atoms of R1to R9and X is preferably 6 to 16.

In any of the above structures, X preferably represents a substituted or unsubstituted phenylene group.

Another embodiment of the present invention is a dibenzocarbazole compound represented by General Formula (G9).

In General Formula (G9), R9represents any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 10 carbon atoms; R31to R42each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and X represents a substituted or unsubstituted phenylene group.

Another embodiment of the present invention is a dibenzocarbazole compound represented by General Formula (G10).

In General Formula (G10), R9represents any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 10 carbon atoms; and X represents a substituted or unsubstituted phenylene group.

In any of the above structures, the total number of carbon atoms of R9and X is preferably 6 to 16.

Another embodiment of the present invention is a dibenzocarbazole compound represented by Structural Formula (136).

Another embodiment of the present invention is a light-emitting element including the dibenzocarbazole compound having any of the above structures.

Another embodiment of the present invention is a light-emitting element that includes a light-emitting layer and an electron-transport layer each including the dibenzocarbazole compound having any of the above structures.

Another embodiment of the present invention is a light-emitting element that includes a host material and a guest material. The host material is the dibenzocarbazole compound having any of the above structures.

In the above structure, the guest material preferably has a function of emitting fluorescence. Fluorescence emitted from the guest material is preferably blue. The guest material preferably emits light whose chromaticity y in CIE 1931 chromaticity coordinates is greater than or equal to 0.01 and less than or equal to 0.15.

In any of the above structures, it is preferable that the weight ratio of the guest material to the host material be greater than 0 and less than 0.03.

Another embodiment of the present invention is a light-emitting device including the light-emitting element with any of the above structures and a transistor. Another embodiment of the present invention is a display device including the light-emitting element with any of the above structures and a driving circuit. Another embodiment of the present invention is an electronic device including the light-emitting element with any of the above structures and at least one of a sensor, an operation button, a speaker, and a microphone. Another embodiment of the present invention is a lighting device including the light-emitting element with any of the above structures and at least one of a housing and a touch sensor. The category of one embodiment of the present invention includes not only a light-emitting device including a light-emitting element but also an electronic device including a light-emitting device. Accordingly, a light-emitting device in this specification refers to an image display device or a light source (including a lighting device). A display module in which a connector such as a flexible printed circuit (FPC) or a tape carrier package (TCP) is connected to a light-emitting device, a display module in which a printed wiring board is provided on the tip of a TCP, and a display module in which an integrated circuit (IC) is directly mounted on a light-emitting element by a chip on glass (COG) method are also embodiments of the present invention.

One embodiment of the present invention can provide a novel compound. One embodiment of the present invention can provide a novel compound with which a light-emitting element having high emission efficiency can be achieved. One embodiment of the present invention can provide a novel compound with which a light-emitting element having lower power consumption can be achieved. One embodiment of the present invention can provide a novel compound with which a light-emitting element having long lifetime can be achieved. One embodiment of the present invention can provide a novel compound with which a novel light-emitting element can be achieved. One embodiment of the present invention can provide a light-emitting element including the novel compound. One embodiment of the present invention can provide a light-emitting element with high emission efficiency. One embodiment of the present invention can provide a light-emitting element that emits blue light with high emission efficiency. One embodiment of the present invention can provide a light-emitting element with long lifetime. One embodiment of the present invention can provide a novel light-emitting device. One embodiment of the present invention can provide a novel display device. One embodiment of the present invention can provide a novel electronic device. One embodiment of the present invention can provide a novel lighting device.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to description to be given below, and modes and details thereof can be variously modified without departing from the purpose and the scope of the present invention. Accordingly, the present invention should not be interpreted as being limited to the content of the embodiments and examples below.

Note that the position, the size, the range, or the like of each structure illustrated in drawings and the like is not accurately represented in some cases for simplification. Therefore, the disclosed invention is not necessarily limited to the position, the size, the range, or the like disclosed in the drawings and the like.

Note that the ordinal numbers such as “first”, “second”, and the like in this specification and the like are used for convenience and do not denote the order of steps or the stacking order of layers. Therefore, for example, description can be made even when “first” is replaced with “second” or “third”, as appropriate. In addition, the ordinal numbers in this specification and the like are not necessarily the same as those which specify one embodiment of the present invention.

In the description of modes of the present invention in this specification and the like with reference to the drawings, the same components in different diagrams are commonly denoted by the same reference numeral in some cases.

In this specification and the like, a singlet excited state (S*) refers to a singlet state having excited energy. Among singlet excited states, an excited state having the lowest energy is referred to as the lowest singlet excited state. Furthermore, a singlet excited energy level means an energy level in a singlet excited state. Among singlet excited energy levels, the lowest excited energy level is referred to as the lowest singlet excited energy (S1) level. Note that in this specification and the like, simple expressions “singlet excited state” and “singlet excitation energy level” mean the lowest singlet excited state and the S1level, respectively, in some cases.

In this specification and the like, a triplet excited state (T*) means a triplet state having excited energy. Among triplet excited states, an excited state having the lowest energy is referred to as the lowest triplet excited state. Furthermore, a triplet excitation energy level means an energy level in a triplet excited state. Among triplet excitation energy levels, the lowest excitation energy level is referred to as the lowest triplet excitation energy (T1) level. Note that in this specification and the like, simple expressions “triplet excited state” and “triplet excitation energy level” mean the lowest triplet excited state and the T1level, respectively, in some cases.

In this specification and the like, a fluorescent material refers to a material that emits light in the visible light region when the relaxation from the singlet excited state to the ground state occurs. A phosphorescent material refers to a material that emits light in the visible light region at room temperature when the relaxation from the triplet excited state to the ground state occurs. That is, a phosphorescent material refers to a material that can convert triplet excitation energy into visible light.

Note that in this specification and the like, “room temperature” refers to a temperature higher than or equal to 0° C. and lower than or equal to 40° C.

In this specification and the like, a wavelength range of blue refers to a wavelength range of greater than or equal to 400 nm and less than or equal to 550 nm, and blue light has at least one peak in that range in an emission spectrum.

In this embodiment, a compound that can suitably be used in a light-emitting element of one embodiment of the present invention is described below.

A compound of one embodiment of the present invention is a dibenzocarbazole compound in which an aryl group having at least an anthracene skeleton is bonded to a dibenzo[a,g]carbazole skeleton or a dibenzo[a,i]carbazole skeleton. The dibenzo[a,g]carbazole skeleton, the dibenzo[a,i]carbazole skeleton, and the aryl group including an anthracene skeleton have a high carrier-transport property, and thus a light-emitting element including the dibenzocarbazole compound can have a low driving voltage. Furthermore, the dibenzocarbazole compound has a wide band gap, and thus a light-emitting element including the dibenzocarbazole compound can have high emission efficiency. In particular, a light-emitting element that emits blue light with high emission efficiency can be fabricated. In addition, since the dibenzocarbazole compound is highly resistant to repetition of oxidation and reduction, a light-emitting element including the dibenzocarbazole compound can have a long lifetime, in particular, a long driving lifetime. As described above, a light-emitting element including the compound of one embodiment of the present invention can have excellent emission characteristics and high performance.

When the number of carbon atoms of the aryl group is 14 to 30, the dibenzocarbazole compound is a low molecular compound with a relatively low molecular weight and accordingly has a structure suitable for vacuum evaporation (capable of being vacuum-evaporated at relatively low temperature). In general, a lower molecular weight tends to diminish heat resistance after film formation. However, the dibenzocarbazole compound has an advantage in that sufficient heat resistance can be ensured even with a low molecular weight because of the effect of the rigid dibenzo[a,g]carbazole skeleton, dibenzo[a,i]carbazole skeleton, and anthracene skeleton. Note that the dibenzo[a,g]carbazole skeleton or the dibenzo[a,i]carbazole skeleton is preferably bonded to the anthracene skeleton through an arylene group such as a phenylene group or a naphthylene group.

When nitrogen included in the dibenzo[a,g]carbazole skeleton and the dibenzo[a,i]carbazole skeleton is bonded to a substituent, the dibenzo[a,g]carbazole skeleton and the dibenzo[a,i]carbazole skeleton each have a wider band gap and thus can be favorably used for a light-emitting element that emits high-energy light such as blue light. Accordingly, a dibenzocarbazole compound in which the 7-position of a dibenzo[a,g]carbazole skeleton or the 11-position of the dibenzo[a,i]carbazole skeleton is bonded to an anthracene skeleton through an arylene group can be favorably used for a light-emitting element that emits blue light. Note that it is preferable that a phenylene group be used as the arylene group because the dibenzocarbazole compound can be stable and have a low molecular weight.

When the dibenzo[a,g]carbazole skeleton or the dibenzo[a,i]carbazole skeleton is bonded to the 9-position of an anthracene skeleton through an arylene group, the dibenzocarbazole compound has a high carrier-transport property. Accordingly, a light-emitting element including the dibenzocarbazole compound can be driven at low voltage. Note that it is preferable that a phenylene group be used as the arylene group because of its stability and its low molecular weight.

For the above reason, the dibenzocarbazole compound in which the 7-position of the dibenzo[a,g]carbazole skeleton or the 11-position of the dibenzo[a,i]carbazole skeleton is bonded to the 9-position of an anthracene skeleton through an arylene group has a wide band gap and a high carrier-transport property, and thus a light-emitting element including the dibenzocarbazole compound can have low driving voltage and emit blue light with high emission efficiency. Note that it is preferable that a phenylene group be used as the arylene group because of its stability and its low molecular weight.

In other words, the above dibenzocarbazole compound is a dibenzocarbazole compound in which an arylanthracene derivative is bonded to the dibenzo[a,g]carbazole skeleton or the dibenzo[a,i]carbazole skeleton. The dibenzocarbazole compound can be easily synthesized with high purity, so that element deterioration due to impurities can be suppressed. Note that the number of carbon atoms of the arylanthracene derivative bonded to the dibenzo[a,g]carbazole skeleton or the dibenzo[a,i]carbazole skeleton is preferably 20 to 30 in terms of stability of element characteristics and driving lifetime. In this case, the dibenzocarbazole compound can be vacuum-evaporated at relatively low temperature as described above and accordingly is unlikely to deteriorate due to pyrolysis or the like at evaporation. In addition, the compound is excellent in not only driving lifetime but also drive voltage. This is also because of electrochemical stability and high carrier-transport property owing to the molecular structure of the dibenzocarbazole compound in which an anthracene skeleton is bonded to the 7-position of the dibenzo[a,g]carbazole skeleton or the 11-position of the dibenzo[a,i]carbazole skeleton through an arylene group. Note that it is preferable that an anthrylphenyl group be used as the arylanthracene derivative because the dibenzocarbazole compound can be stable and have a low molecular weight.

Furthermore, for the above reason, a dibenzocarbazole compound in which the 9-position of an anthracene skeleton is bonded to the 7-position of the dibenzo[a,g]carbazole skeleton or the 11-position of the dibenzo[a,i]carbazole skeleton through an arylene group is more preferable. It can also be said that a dibenzocarbazole compound in which a (9-anthryl)aryl group is bonded to the 7-position of the dibenzo[a,g]carbazole skeleton or the 11-position of the dibenzo[a,i]carbazole skeleton is more preferable. Note that the number of carbon atoms of a (9-anthryl)aryl group bonded to the 7-position of the dibenzo[a,g]carbazole skeleton or the 11-position of the dibenzo[a,i]carbazole skeleton is preferably 20 to 30 in terms of stability of the compound and the light-emitting element. Thus, the dibenzocarbazole compound has a wide band gap which is a feature due to the effect of the skeleton of the (9-anthryl)aryl group, in addition to the high suitability for evaporation, electrochemical stability, and carrier-transport property described above. Hence, this compound is effective in a structure of a light-emitting element in which the dibenzocarbazole compound is used as a host material of a light-emitting layer and a light-emitting material is added as a guest material to the light-emitting layer. This compound is suitably used as a host material particularly in a blue light-emitting element. Note that it is preferable that a phenyl group be used as an aryl group of the (9-anthryl)aryl group because the dibenzocarbazole compound can be stable and have a low molecular weight. That is, it is preferable that a (9-anthryl)phenyl group be used as the (9-anthryl)aryl group.

The most stable molecular structures of compounds including the dibenzo[a,g]carbazole skeleton or the dibenzo[a,i]carbazole skeleton which is one embodiment of the present invention were derived from quantum chemistry calculation. For comparison, a compound including a dibenzo[c,g]carbazole skeleton was also subjected to quantum chemistry calculation. The compounds which were subjected to the calculation were 7-phenyl-7H-dibenzo[a,g]carbazole (abbreviation: agDBCz), 11-phenyl-11H-dibenzo[a,i]carbazole (abbreviation: aiDBCz), and 7-phenyl-7H-dibenzo[c,g]carbazole (abbreviation: cgDBCz). Molecular structures of the compounds are shown below.

The most stable structure of each of the compounds in a singlet ground state was calculated using the density functional theory (DFT). Note that Gaussian 09 was used as the quantum chemistry computational program. A high performance computer (ICE X, manufactured by SGI Japan, Ltd.) was used for the calculation. As a basis function, 6-311G(d,p) was used, and as a functional, B3LYP was used. In the DFT, the total energy is represented as the sum of potential energy, electrostatic energy between electrons, electronic kinetic energy, and exchange-correlation energy including all the complicated interactions between electrons. Also in the DFT, an exchange-correlation interaction is approximated by a functional (a function of another function) of one electron potential represented in terms of electron density to enable high-accuracy calculations.

FIGS. 1A to 1Fshow calculation results.FIGS. 1A and 1Bshow the result of agDBCz,FIGS. 1C and 1Dshow the result of aiDBCz, andFIGS. 1E and 1Fshow the result of cgDBCz. Note that inFIGS. 1A to 1F, a pyrrole ring included in each of the compounds is shown so as to be provided on an x-y plane.FIGS. 1A, 1C, and 1Eshow the most stable structures of the compounds seen from the x-y plane.FIGS. 1B, 1D, and 1Fshow the most stable structures of the compounds seen from a y-z plane.

As shown inFIGS. 1B and 1D, the dibenzo[a,g]carbazole skeleton in agDBCz is provided over the x-y plane and the dibenzo[a,i]carbazole skeleton in aiDBCz is provided over the x-y plane. As shown inFIG. 1F, in cgDBCz, hydrogen at the 1-position and hydrogen at the 12-position of the dibenzo[c,g]carbazole skeleton encounter steric hindrance, and thus the dibenzo[c,g]carbazole skeleton on the x-y plane is distorted in the z-axis direction.

That is, it can be said that the molecular structure distortion of the dibenzo[a,g]carbazole skeleton and the dibenzo[a,i]carbazole skeleton is smaller than that of the dibenzo[c,g]carbazole skeleton, and thus the dibenzo[a,g]carbazole skeleton and the dibenzo[a,i]carbazole skeleton are stable skeletons. Accordingly, the dibenzo[a,g]carbazole skeleton or the dibenzo[a,i]carbazole skeleton is used, whereby a stable dibenzocarbazole compound can be formed. A light-emitting element including the dibenzocarbazole compound can have long driving lifetime.

Furthermore, the lowest triplet excitation energy levels (T1 levels) of the above compounds were calculated. For the calculation of the T1 levels of the compounds, the most stable structures of the compounds in a singlet excited state and a triplet excited state were calculated using the density functional theory (DFT). As a basis function, 6-311G(d,p) was used, and as a functional, B3LYP was used. In addition, vibrational levels were calculated, and energy in electron transition between the lowest vibrational levels (0-0 transition) in the singlet excited state and the triplet excited state was calculated, whereby the T1 levels were calculated.

As a result of the calculation, the triplet excitation energy levels of agDBCz, aiDBCz, and cgDBCz were 2.44 eV, 2.60 eV, and 2.28 eV, respectively. That is, agDBCz and aiDBCz have higher triplet excitation energy than cgDBCz. Accordingly, the dibenzo[a,g]carbazole skeleton and the dibenzo[a,i]carbazole skeleton are favorably combined with a benzo[a]anthracene skeleton or the like having higher triplet excitation energy than an anthracene skeleton.

Example 1 of Compound

The above dibenzocarbazole compound which is one embodiment of the present invention is a dibenzocarbazole compound represented by General Formula (G1).

In General Formula (G1), Ar represents a substituted or unsubstituted aryl group which has 14 to 30 carbon atoms and at least an anthracene skeleton. In the case where the aryl group has a substituent, as the substituent, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 12 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of a cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a naphthyl group, and a biphenyl group.

Furthermore, R11to R22each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of a cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 13 carbon atoms include a phenyl group, a naphthyl group, a biphenyl group, and a fluorenyl group. The above aryl group may include one or more substituents, and the substituents may be bonded to each other to form a ring. As the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a naphthyl group, and a biphenyl group.

Example 2 of Compound

A dibenzocarbazole compound of one embodiment of the present invention, in which the 7-position of the dibenzo[a,g]carbazole skeleton is bonded to the aryl group having at least an anthracene skeleton, has a wide band gap and thus can be favorably used for a light-emitting element that emits high-energy light such as blue light, which is preferable. Furthermore, since the dibenzocarbazole compound has a high carrier-transport property, a light-emitting element including the compound can be driven at low voltage, which is preferable. The above dibenzocarbazole compound is a dibenzocarbazole compound represented by General Formula (G2).

In General Formula (G2), X represents a substituted or unsubstituted arylene group having 6 to 13 carbon atoms. Specific examples of the arylene group having 6 to 13 carbon atoms include a phenylene group, a naphthylene group, a biphenylene group, and a fluorenylene group. In the case where the arylene group has a substituent, as the substituent, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 10 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of a cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group.

Y represents a substituted or unsubstituted anthryl group. In the case where the anthryl group has a substituent, as the substituent, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 10 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group.

Furthermore, R11to R22each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of a cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 13 carbon atoms include a phenyl group, a naphthyl group, a biphenyl group, and a fluorenyl group. The above alkyl group may include one or more substituents, and the substituents may be bonded to each other to form a ring. As the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a naphthyl group, and a biphenyl group.

Note that the total number of carbon atoms of X and Y is preferably 20 to 30 in General Formula (G2), in which case the dibenzocarbazole compound is a low molecular compound with a relatively low molecular weight and accordingly has a structure suitable for vacuum evaporation (capable of being vacuum-evaporated at a relatively low temperature).

X is preferably a substituted or unsubstituted phenylene group in General Formula (G2), in which case the dibenzocarbazole compound is stable and has a low molecular weight.

Example 3 of Compound

A dibenzocarbazole compound of one embodiment of the present invention, in which the 7-position of the dibenzo[a,g]carbazole skeleton is bonded to the 9-position of an anthracene skeleton through an arylene group, has a high carrier-transport property, and thus a light-emitting element including the compound can be driven at low voltage, which is preferable. The above dibenzocarbazole compound is a dibenzocarbazole compound represented by General Formula (G3).

In General Formula (G3), X represents a substituted or unsubstituted arylene group having 6 to 13 carbon atoms. Specific examples of the arylene group having 6 to 13 carbon atoms include a phenylene group, a naphthylene group, a biphenylene group, and a fluorenylene group. In the case where the arylene group has a substituent, as the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 10 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group.

R1to R8each independently represent hydrogen or an alkyl group having 1 to 4 carbon atoms. Specific examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group.

R9represents any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 10 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of a cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group. The above aryl group may include a substituent. An alkyl group having 1 to 4 carbon atoms can be selected as the substituent. Specific examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group.

Furthermore, R11to R22each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of a cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 13 carbon atoms include a phenyl group, a naphthyl group, a biphenyl group, a fluorenyl group, and the like. The above aryl group may include one or more substituents, and the substituents may be bonded to each other to form a ring. As the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a naphthyl group, a biphenyl group, and the like.

Note that the total number of carbon atoms of R1to R9and X is preferably 6 to 16 in General Formula (G3), in which case the dibenzocarbazole compound is a low molecular compound with a relatively low molecular weight and accordingly has a structure suitable for vacuum evaporation (capable of being vacuum-evaporated at a relatively low temperature).

X is preferably a substituted or unsubstituted phenylene group in General Formula (G3), in which case the dibenzocarbazole compound is stable and has a low molecular weight.

Example 4 of Compound

In the case where each of R1to R8represents hydrogen in General Formula (G3), the compound is advantageous in terms of easiness of synthesis and material cost and has a relatively low molecular weight to be suitable for vacuum evaporation, which is particularly preferable. The dibenzocarbazole compound is a dibenzocarbazole compound represented by General Formula (G4).

In General Formula (G4), X represents a substituted or unsubstituted arylene group having 6 to 13 carbon atoms. Specific examples of the arylene group having 6 to 13 carbon atoms include a phenylene group, a naphthylene group, a biphenylene group, and a fluorenylene group. In the case where the arylene group has a substituent, as the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 10 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group.

R9represents any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 10 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of a cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group. The above aryl group may include a substituent. An alkyl group having 1 to 4 carbon atoms can be selected as the substituent. Specific examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group.

Furthermore, R11to R22each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of a cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 13 carbon atoms include a phenyl group, a naphthyl group, a biphenyl group, and a fluorenyl group. The above aryl group may include one or more substituents, and the substituents may be bonded to each other to form a ring. As the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a naphthyl group, and a biphenyl group.

Note that X is preferably a substituted or unsubstituted phenylene group in General Formula (G4), in which case the dibenzocarbazole compound is stable and has a low molecular weight.

Note that the total number of carbon atoms of R9and X is preferably 6 to 16 in General Formula (G4), in which case the dibenzocarbazole compound is a low molecular compound with a relatively low molecular weight and accordingly has a structure suitable for vacuum evaporation (capable of being vacuum-evaporated at a relatively low temperature).

Example 5 of Compound

In the case where each of R11to R22represents hydrogen in General Formula (G4), the compound is advantageous in terms of easiness of synthesis and material cost and has a relatively low molecular weight to be suitable for vacuum evaporation, which is particularly preferable. The dibenzocarbazole compound is a dibenzocarbazole compound represented by General Formula (G5).

In General Formula (G5), X represents a substituted or unsubstituted arylene group having 6 to 13 carbon atoms. Specific examples of the arylene group having 6 to 13 carbon atoms include a phenylene group, a naphthylene group, a biphenylene group, and a fluorenylene group. In the case where the arylene group has a substituent, as the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 10 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group.

R9represents any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 10 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of a cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group. The above aryl group may include a substituent. An alkyl group having 1 to 4 carbon atoms can be selected as the substituent. Specific examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group.

Note that X is preferably a substituted or unsubstituted phenylene group in General Formula (G5), in which case the dibenzocarbazole compound is stable and has a low molecular weight.

Note that the total number of carbon atoms of R9and X is preferably 6 to 16 in General Formula (G5), in which case the dibenzocarbazole compound is a low molecular compound with a relatively low molecular weight and accordingly has a structure suitable for vacuum evaporation (capable of being vacuum-evaporated at a relatively low temperature).

Note that each of R9and X is preferably a phenylene group in General Formula (G5), in which case the dibenzocarbazole compound is stable and has a low molecular weight. Furthermore, the compound is advantageous in terms of easiness of synthesis and material cost.

Example 6 of Compound

The above dibenzocarbazole compound which is one embodiment of the present invention is a dibenzocarbazole compound represented by General Formula (G6).

In General Formula (G1), Ar represents a substituted or unsubstituted aryl group which has 14 to 30 carbon atoms and at least an anthracene skeleton. In the case where the aryl group has a substituent, as the substituent, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 12 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of a cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a naphthyl group, and a biphenyl group.

Furthermore, R31to R42each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of a cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 13 carbon atoms include a phenyl group, a naphthyl group, a biphenyl group, and a fluorenyl group. The above aryl group may include one or more substituents, and the substituents may be bonded to each other to form a ring. As the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a naphthyl group, and a biphenyl group.

Example 7 of Compound

A dibenzocarbazole compound of one embodiment of the present invention, in which the 11-position of the dibenzo[a,i]carbazole skeleton is bonded to the aryl group having at least an anthracene skeleton, has a wide band gap and thus can be favorably used for a light-emitting element which emits high-energy light such as blue light, which is preferable. Furthermore, since the dibenzocarbazole compound has a high carrier-transport property, a light-emitting element including the compound can be driven at low voltage, which is preferable. The above dibenzocarbazole compound is a dibenzocarbazole compound represented by General Formula (G7).

In General Formula (G7), X represents a substituted or unsubstituted arylene group having 6 to 13 carbon atoms. Specific examples of the arylene group having 6 to 13 carbon atoms include a phenylene group, a naphthylene group, a biphenylene group, and a fluorenylene group. In the case where the arylene group has a substituent, as the substituent, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 10 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group.

Y represents a substituted or unsubstituted anthryl group. In the case where the anthryl group has a substituent, as the substituent, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 10 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group.

Furthermore, R31to R42each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of a cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 13 carbon atoms include a phenyl group, a naphthyl group, a biphenyl group, and a fluorenyl group. The above aryl group may include one or more substituents, and the substituents may be bonded to each other to form a ring. As the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a naphthyl group, and a biphenyl group.

Note that the total number of carbon atoms of X and Y is preferably 20 to 30 in General Formula (G7), in which case the dibenzocarbazole compound is a low molecular compound with a relatively low molecular weight and accordingly has a structure suitable for vacuum evaporation (capable of being vacuum-evaporated at a relatively low temperature).

Note that X is preferably a substituted or unsubstituted phenylene group in General Formula (G7), in which case the dibenzocarbazole compound is stable and has a low molecular weight.

Example 8 of Compound

A dibenzocarbazole compound of one embodiment of the present invention, in which the 11-position of the dibenzo[a,i]carbazole skeleton is bonded to the 9-position of an anthracene skeleton through an arylene group, has a high carrier-transport property, and thus a light-emitting element including the compound can be driven at low voltage, which is preferable. The above dibenzocarbazole compound is a dibenzocarbazole compound represented by General Formula (G8).

In General Formula (G8), X represents a substituted or unsubstituted arylene group having 6 to 13 carbon atoms. Specific examples of the arylene group having 6 to 13 carbon atoms include a phenylene group, a naphthylene group, a biphenylene group, and a fluorenylene group. In the case where the arylene group has a substituent, as the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 10 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group.

R1to R8each independently represent hydrogen or an alkyl group having 1 to 4 carbon atoms. Specific examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group.

R9represents any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 10 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group. The above aryl group may include a substituent. An alkyl group having 1 to 4 carbon atoms can be selected as the substituent. Specific examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group.

Furthermore, R31to R42each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of a cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 13 carbon atoms include a phenyl group, a naphthyl group, a biphenyl group, and a fluorenyl group. The above aryl group may include one or more substituents, and the substituents may be bonded to each other to form a ring. As the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a naphthyl group, and a biphenyl group.

Note that the total number of carbon atoms of R1to R9and X is preferably 6 to 16 in General Formula (G8), in which case the dibenzocarbazole compound is a low molecular compound with a relatively low molecular weight and accordingly has a structure suitable for vacuum evaporation (capable of being vacuum-evaporated at a relatively low temperature).

X is preferably a substituted or unsubstituted phenylene group in General Formula (G8), in which case the dibenzocarbazole compound is stable and has a low molecular weight.

Example 9 of Compound

In the case where each of R1to R8represents hydrogen in General Formula (G8), the compound is advantageous in terms of easiness of synthesis and material cost and has a relatively low molecular weight to be suitable for vacuum evaporation, which is particularly preferable. The dibenzocarbazole compound is a dibenzocarbazole compound represented by General Formula (G9).

In General Formula (G9), X represents a substituted or unsubstituted arylene group having 6 to 13 carbon atoms. Specific examples of the arylene group having 6 to 13 carbon atoms include a phenylene group, a naphthylene group, a biphenylene group, and a fluorenylene group. In the case where the arylene group has a substituent, as the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 10 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group.

R9represents any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 10 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group. The above aryl group may include a substituent. An alkyl group having 1 to 4 carbon atoms can be selected as the substituent. Specific examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group.

Furthermore, R31to R42each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of a cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 13 carbon atoms include a phenyl group, a naphthyl group, a biphenyl group, and a fluorenyl group. The above aryl group may include one or more substituents, and the substituents may be bonded to each other to form a ring. As the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 12 carbon atoms include a phenyl group, a naphthyl group, and a biphenyl group.

X is preferably a substituted or unsubstituted phenylene group in General Formula (G9), in which case the dibenzocarbazole compound is stable and has a low molecular weight.

Note that the total number of carbon atoms of R9and X is preferably 6 to 16 in General Formula (G9), in which case the dibenzocarbazole compound is a low molecular compound with a relatively low molecular weight and accordingly has a structure suitable for vacuum evaporation (capable of being vacuum-evaporated at a relatively low temperature).

Example 10 of Compound

In the case where each of R31to R42represents hydrogen in General Formula (G9), the compound is advantageous in terms of easiness of synthesis and material cost and has a relatively low molecular weight to be suitable for vacuum evaporation, which is particularly preferable. The dibenzocarbazole compound is a dibenzocarbazole compound represented by General Formula (G10).

In General Formula (G10), X represents a substituted or unsubstituted arylene group having 6 to 13 carbon atoms. Specific examples of the arylene group having 6 to 13 carbon atoms include a phenylene group, a naphthylene group, a biphenylene group, and a fluorenylene group. In the case where the arylene group has a substituent, as the substituent, an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 6 carbon atoms, or an aryl group having 6 to 10 carbon atoms can also be selected. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group.

R9represents any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 10 carbon atoms. Specific examples of the alkyl group having 1 to 6 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a tert-butyl group, and an n-hexyl group. Specific examples of the cycloalkyl group having 3 to 6 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, and a cyclohexyl group. Specific examples of the aryl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group. The above aryl group may include a substituent. An alkyl group having 1 to 4 carbon atoms can be selected as the substituent. Specific examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group.

X is preferably a substituted or unsubstituted phenylene group in General Formula (G10), in which case the dibenzocarbazole compound is stable and has a low molecular weight.

Note that the total number of carbon atoms of R9and X is preferably 6 to 16 in General Formula (G10), in which case the dibenzocarbazole compound is a low molecular compound with a relatively low molecular weight and accordingly has a structure suitable for vacuum evaporation (capable of being vacuum-evaporated at a relatively low temperature).

Note that each of R9and X is preferably a phenylene group in General Formula (G10), in which case the dibenzocarbazole compound is stable and has a low molecular weight. Furthermore, the compound is advantageous in terms of easiness of synthesis and material cost.

Examples of Substituents

As an aryl group represented by Ar in General Formulae (G1) and (G6), which has 14 to 30 carbon atoms and at least an anthracene skeleton, and is, any of groups represented by Structural Formulae (Ant-1) to (Ant-53) can be used, for example. Note that the group Ar may include a substituent and is not limited to the following.

In General Formulae (G2) and (G7), as an anthryl group represented by Y, any of groups represented by Structural Forumlae (Ant-1) to (Ant-16) and (Ant-42) to (Ant-45) can be used, for example. Note that the group Y may include a substituent and is not limited to the following.

In General Formulae (G2) to (G5) and General Formulae (G7) to (G10), as an arylene group represented by X, any of groups represented by Structural Formulae (Ar-1) to (Ar-15) can be used, for example. Note that the group X may include a substituent and is not limited to the following.

As hydrogen, an alkyl group, or an aryl group represented by R11to R22in General Formulae (G1) to (G4) and R31to R42in General Formulae (G6) and (G9), any of groups represented by Structural Formulae (R-1) to (R-29) can be used, for example. Note that the alkyl group or the aryl group may include a substituent and is not limited to the following.

As an alkyl group or an aryl group represented by R9in General Formulae (G3) to (G5) and General Formulae (G8) to (G10), any of the groups represented by Structural Formulae (R-1) to (R-19) can be used, for example. Note that the alkyl group or the aryl group may include a substituent and is not limited to the following.

As hydrogen or an alkyl group represented by R1to R8in General Formulae (G3) and (G8), any of the groups represented by Structural Formulae (R-1) to (R-9) can be used, for example. Note that the alkyl group is not limited to the above.

Specific Examples of Compounds

Specific examples of structures of the dibenzocarbazole compounds represented by General Formulae (G1) to (G10) are compounds represented by Structural Formulae (100) to (171). Note that the dibenzocarbazole compounds represented by General Formulae (G1) to (G10) are not limited to the following examples.

As described above, the dibenzocarbazole compound which is one embodiment of the present invention has a wide band gap and thus is preferably used as a host material or a carrier-transport material particularly in a light-emitting element that emits blue light. In that case, the blue light-emitting element can have high emission efficiency. Furthermore, the dibenzocarbazole compound which is one embodiment of the present invention has a high carrier-transport property and thus is preferably used as a host material or a carrier-transport material in a light-emitting element. Accordingly, a light-emitting element with low drive voltage can be manufactured. Moreover, since the dibenzocarbazole compound which is one embodiment of the present invention is highly resistant to repetition of oxidation and reduction, a light-emitting element including the dibenzocarbazole compound can have a long lifetime. Therefore, the dibenzocarbazole compound which is one embodiment of the present invention is a material suitably used in a light-emitting element.

Note that the dibenzocarbazole compound which is one embodiment of the present invention can be deposited by an evaporation method (including a vacuum evaporation method), an ink-jet method, a coating method, a gravure printing method, or the like.

Note that the compound described in this embodiment can be used in combination with any of the structures described in the other embodiments as appropriate.

In this embodiment, methods for synthesizing the dibenzocarbazole compounds represented by General Formulae (G1) and (G6) are described. A variety of reactions can be applied to each of the methods for synthesizing the dibenzocarbazole compounds. For example, synthesis reactions described below enable the synthesis of the dibenzocarbazole compounds represented by General Formulae (G1) and (G6). Note that the methods for synthesizing the dibenzocarbazole compound which is one embodiment of the present invention are not limited to the following.

<Example of Method for Synthesizing Dibenzo[a,g]Carbazole Compound Represented by General Formula (G1)>

The dibenzo[a,g]carbazole compound represented by General Formula (G1) can be synthesized as in Synthesis Scheme (A-1). That is, a halide of an anthracene derivative (a1) is coupled with a dibenzo[a,g]carbazole derivative (a2) by using a metal catalyst, a metal, or a metal compound in the presence of a base, whereby the dibenzo[a,g]carbazole compound represented by General Formula (G1) can be obtained.

In Synthesis Scheme (A-1), R11to R22each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and Ar represents a substituted or unsubstituted aryl group which has 14 to 30 carbon atoms and at least an anthracene skeleton.

In the case where the Hartwig-Buchwald reaction is performed in Synthesis Scheme (A-1), Z represents a halogen or a triflate group. As the halogen, iodine, bromine, or chlorine is preferable. In this reaction, a palladium catalyst including a palladium compound or a palladium complex such as bis(dibenzylideneacetone)palladium(0) or palladium(II) acetate and a ligand that coordinates to the palladium complex or the palladium compound, such as tri(tert-butyl)phosphine, tri(n-hexyl)phosphine, or tricyclohexylphosphine, is used. Examples of the base include organic bases such as sodium tert-butoxide, inorganic bases such as a potassium carbonate, and the like. In the case where a solvent is used, toluene, xylene, benzene, tetrahydrofuran, or the like can be used.

In the case where an Ullmann reaction is performed in Synthesis Scheme (A-1), Z represents a halogen. As the halogen, iodine, bromine, or chlorine is preferable. As a catalyst, copper or a copper compound is used. In the case where a copper compound is used as the catalyst, R23and R24in Synthesis Scheme (A-1) individually represent a halogen, an acetyl group, or the like. As the halogen, chlorine, bromine, or iodine can be given. Note that copper(I) iodide where R23is iodine or copper(II) acetate where R24is an acetyl group is preferably used. As the base which is used, an inorganic base such as potassium carbonate can be given. As a solvent, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU), toluene, xylene, benzene, and the like can be employed. Note that the solvent is not limited thereto. In an Ullmann reaction, DMPU or xylene, which has a high boiling point, is preferably used, in which case the object of the synthesis can be obtained in a shorter time and a higher yield at a reaction temperature of 100° C. or more. A reaction temperature of 150° C. or more is further preferred and accordingly DMPU is more preferably used.

<Example of Method for Synthesizing Dibenzo[a,i]Carbazole Compound Represented by General Formula (G6)>

The dibenzo[a,i]carbazole compound represented by General Formula (G6) can be synthesized as in Synthesis Scheme (B-1). That is, a halide of an anthracene derivative (a1) is coupled with a dibenzo[a,i]carbazole derivative (a3) by using a metal catalyst, a metal, or a metal compound in the presence of a base, whereby the dibenzo[a,i]carbazole compound represented by General Formula (G6) can be obtained.

In Synthesis Scheme (B-1), R31to R42each independently represent any of hydrogen, an alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 6 carbon atoms, and a substituted or unsubstituted aryl group having 6 to 13 carbon atoms; and Ar represents a substituted or unsubstituted aryl group which has 14 to 30 carbon atoms and at least an anthracene skeleton.

In the case where the Hartwig-Buchwald reaction is performed in Synthesis Scheme (B-1), Z represents a halogen or a triflate group. As the halogen, iodine, bromine, or chlorine is preferable. In this reaction, a palladium catalyst including a palladium compound or a palladium complex such as bis(dibenzylideneacetone)palladium(0) or palladium(II) acetate and a ligand that coordinates to the palladium complex or the palladium compound, such as tri(tert-butyl)phosphine, tri(n-hexyl)phosphine, or tricyclohexylphosphine, is used. Examples of the base include organic bases such as sodium tert-butoxide, inorganic bases such as a potassium carbonate, and the like. In the case where a solvent is used, toluene, xylene, benzene, tetrahydrofuran, or the like can be used.

In the case where an Ullmann reaction is performed in Synthesis Scheme (B-1), Z represents a halogen. As the halogen, iodine, bromine, or chlorine is preferable. As a catalyst, copper or a copper compound is used. In the case where a copper compound is used as the catalyst, R23and R24in Synthesis Scheme (B-1) individually represent a halogen, an acetyl group, or the like. As the halogen, chlorine, bromine, or iodine can be given. Note that copper(I) iodide where R23is iodine or copper(II) acetate where R24is an acetyl group is preferably used. As the base which is used, an inorganic base such as potassium carbonate can be given. As a solvent, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU), toluene, xylene, benzene, and the like can be employed. Note that the solvent is not limited thereto. In an Ullmann reaction, DMPU or xylene, which has a high boiling point, is preferably used, in which case the object of the synthesis can be obtained in a shorter time and a higher yield at a reaction temperature of 100° C. or more. A reaction temperature of 150° C. or more is further preferred and accordingly DMPU is more preferably used.

In the above manner, the dibenzocarbazole compounds represented by General Formulae (G1) and (G6) can be synthesized.

Note that the compound described in this embodiment can be used in combination with any of the structures described in the other embodiments as appropriate.

In this embodiment, structure examples of a light-emitting element including any of the dibenzocarbazole compounds described in Embodiment 1 will be described with reference toFIGS. 2A to 2C.

Structure Example 1 of Light-Emitting Element

FIG. 2Ais a schematic cross-sectional view of a light-emitting element150of one embodiment of the present invention.

The light-emitting element150includes a pair of electrodes (an electrode101and an electrode102) and an EL layer100therebetween. Any of the layers in the EL layer100includes any of the dibenzocarbazole compounds described in Embodiment 1.

The EL layer100includes at least a light-emitting layer120.

The EL layer100illustrated inFIG. 2Aincludes functional layers such as a hole-injection layer111, a hole-transport layer112, an electron-transport layer113, and an electron-injection layer114, in addition to the light-emitting layer120.

Note that in this embodiment, although description is given assuming that the electrode101and the electrode102of the pair of electrodes serve as an anode and a cathode, respectively, they are not limited thereto for the structure of the light-emitting element150. That is, the electrode101may be a cathode, the electrode102may be an anode, and the stacking order of the layers between the electrodes may be reversed. In other words, the hole-injection layer111, the hole-transport layer112, the light-emitting layer120, the electron-transport layer113, and the electron-injection layer114may be stacked in this order from the anode side.

Note that the structure of the EL layer100is not limited to the structure illustrated inFIG. 2A, and a structure including at least one layer selected from the hole-injection layer111, the hole-transport layer112, the electron-transport layer113, and the electron-injection layer114may be employed. Alternatively, the EL layer100may include a functional layer which is capable of lowering a hole- or electron-injection barrier, improving a hole- or electron-transport property, inhibiting transport of holes or electrons, or suppressing a quenching phenomenon by an electrode, for example. Note that the light-emitting layer120and the functional layers may each be a single layer or stacked layers.

FIG. 2Bis a schematic cross-sectional view illustrating an example of the light-emitting layer120inFIG. 2A. The light-emitting layer120inFIG. 2Bincludes at least a host material121and a guest material122.

The dibenzocarbazole compounds described in Embodiment 1 have a high carrier-transport property and thus are suitable for the hole-transport layer112or the electron-transport layer113. In addition, the dibenzocarbazole compound has a high carrier-transport property and a wide band gap, and thus is suitable as the host material121. That is, when any of the dibenzocarbazole compounds described in Embodiment 1 is used for at least one of the host material121, the hole-transport layer112, and the electron-transport layer113of the light-emitting element150, a light-emitting element with a low drive voltage can be fabricated. When the dibenzocarbazole compound is used as the host material121of the light-emitting element150, a light-emitting element with a high emission efficiency can be fabricated. Note that the dibenzocarbazole compound is suitable for the host material and the carrier-transport material of a blue light-emitting element because of its wide band gap. Thus, with the structure illustrated in this embodiment, a light-emitting element that emits blue light and has a high emission efficiency can be fabricated. Furthermore, since the dibenzocarbazole compound is highly resistant to repetition of oxidation and reduction, a light-emitting element with a long driving lifetime can be fabricated.

Note that the dibenzocarbazole compounds described in Embodiment 1 have a wide band gap and thus are particularly suitable for a light-emitting element that emits deep blue light. In this specification and the like, deep blue refers to color having a chromaticity y of 0.01 to 0.15 on the CIE 1931 chromaticity coordinate.

Structure Example 2 of Light-Emitting Element

Next, a particularly preferable structure of the light-emitting element illustrated inFIGS. 2A and 2Bwill be described below with reference toFIG. 2C.

In the light-emitting element150illustrated inFIG. 2A, any of the dibenzocarbazole compounds described in Embodiment 1 is used as at least the host material121.

The host material121preferably has a function of converting triplet excitation energy into singlet excitation energy by causing triplet-triplet annihilation (TTA), so that the triplet excitation energy generated in the light-emitting layer120can be partly converted into singlet excitation energy by TTA in the host material121. The singlet excitation energy can be transferred to the guest material122and extracted as fluorescence. In order to achieve this, the lowest level of the singlet excitation energy (S1 level) of the host material121is preferably higher than the S1 level of the guest material122. In addition, the lowest level of the triplet excitation energy (T1 level) of the host material121is preferably lower than the T1 level of the guest material122.

Note that the host material121may be composed of a single compound or a plurality of compounds. The guest material122may be a light-emitting organic material, and the light-emitting organic material is preferably a material capable of emitting fluorescence (hereinafter also referred to as a fluorescent material). A structure in which a fluorescent material is used as the guest material122will be described below. The guest material122may be rephrased as the fluorescent material.

First, the light emission mechanism of the light-emitting element150is described below.

In the light-emitting element150of one embodiment of the present invention, voltage application between the pair of electrodes (the electrodes101and102) causes electrons and holes to be injected from the cathode and the anode, respectively, into the EL layer100and thus current flows. By recombination of the injected electrons and holes, excitons are formed. The ratio of singlet excitons to triplet excitons (hereinafter referred to as exciton generation probability) which are generated by carrier recombination is approximately 1:3 according to the statistically obtained probability. Hence, the probability of formation of singlet excitons is 25%.

Note that the term “exciton” refers to a carrier (electron and hole) pair. Since excitons have excitation energy, a material where excitons are generated is brought into an excited state.

Through the following two processes, singlet excitons are formed in the EL layer100and light emission from the guest material122can be obtained.(α) Direct formation process(β) TTA process.
<<(α) Direct Formation Process>>

Described first is the case where carriers (electrons and holes) recombine in the light-emitting layer120included in the EL layer100to form a singlet exciton.

When the carriers recombine in the host material121, excitons are formed to bring the host material121into an excited state (a singlet excited state or a triplet excited state). At this time, in the case where the excited state of the host material121is a singlet excited state, singlet excitation energy transfers from the S1 level of the host material121to the S1 level of the guest material122, thereby forming the singlet excited state of the guest material122. Note that the case where the excited state of the host material121is a triplet excited state is described later in (β) TTA process.

When the carriers recombine in the guest material122, excitons are formed to bring the guest material122into an excited state (a singlet excited state or a triplet excited state).

In the case where the formed excited state of the guest material122is a singlet excited state, light emission is obtained from the singlet excited state of the guest material122. To obtain a high emission efficiency in this case, the fluorescence quantum yield of the guest material122is preferably high, specifically, 50% or higher, further preferably 70% or higher, and still further preferably 90% or higher.

In the case where the formed excited state of the guest material122is a triplet excited state, the triplet excited state of the guest material122is thermally deactivated and does not contribute to light emission because the guest material122is a fluorescent material. However, if the T1 level of the host material121is lower than the T1 level of the guest material122, the triplet excitation energy of the guest material122can be transferred from the T1 level of the guest material122to the T1 level of the host material121. In this case, the triplet excitation energy can be converted into singlet excitation energy by (β) TTA process described later.

Described next is the case where a singlet exciton is formed from triplet excitons formed in the carrier recombination process in the light-emitting layer120.

Here, the case where the T1 level of the host material121is lower than the T1 level of the guest material122is described. The correlation of energy levels in this case is schematically shown inFIG. 2C. What terms and numerals inFIG. 2Crepresent are listed below. Note that the T1 level of the host material121may be higher than the T1 level of the guest material122.Host (121): the host material121Guest (122): the guest material122(fluorescent material)SFH: the S1 level of the host material121TFH: the T1 level of the host material121SFG: the S1 level of the guest material122(fluorescent material)TFG: the T1 level of the guest material122(fluorescent material)

Carriers recombine in the host material121and excitons are formed to bring the host material121into an excited state. At this time, in the case where the formed excitons are triplet excitons and two of the formed triplet excitons approach each other, a reaction in which part of their triplet excitation energy is converted into singlet excitation energy and the triplet excitons are converted into a singlet exciton having energy of the S1 level (SFH) of the host material121might be caused (see TTA inFIG. 2C). This is represented by General Formula (G11) or (G12).
3H+3H→1H*+1H(G11)
3H+3H→3H*+1H(G12)

General Formula (G11) represents a reaction in the host material121in which a singlet exciton (1H*) is formed from two triplet excitons (3H) with a total spin quantum number of 0. General Formula (G12) represents a reaction in the host material121in which an electronically or oscillatorily excited triplet exciton (3H*) is formed from two triplet excitons (3H) with a total spin quantum number of 1 (atomic unit). In General Formulae (G11) and (G12),1H represents the singlet ground state of the host material121.

Although the reactions in General Formulae (G11) and (G12) occur at the same probability, there are three times as many pairs of triplet excitons with a total spin quantum number of 1 (atomic unit) as pairs of triplet excitons with a total spin quantum number of 0. In other words, when an exciton is formed from two triplet excitons, the singlet-triplet exciton formation ratio is 1:3 according to the statistically obtained probability. In the case where the density of the triplet excitons in the light-emitting layer120is sufficiently high (e.g., 1×10−12cm−3or more), only the reaction of two triplet excitons approaching each other can be considered whereas deactivation of a single triplet exciton is ignored.

Thus, by one reaction in General Formula (G11) and three reactions in General Formula (G12), one singlet exciton (1H*) and three triplet excitons (3H*) which are electronically or oscillatorily excited are formed from eight triplet excitons (3H). This is represented by General Formula (G13).
83H→1H*+33H*+41H(G13)

The electronically or oscillatorily excited triplet excitons (3H*), which are formed as General Formula (G13), become triplet excitons (3H) by relaxation and then repeat the reaction in General Formula (G13) again with other triplet excitons. Hence, in General Formula (G13), if all the triplet excitons (3H) are converted into singlet excitons (1H*), five triplet excitons (3H) form one singlet exciton (1H*) (General Formula (G14)).
53H→1H*+41H(G14)

The ratio of singlet excitons (1H*) to triplet excitons (3H) which are directly formed by recombination of carriers injected from a pair of electrodes is statistically as follows:1H*:3H=1:3. That is, the probability of singlet excitons being directly formed by recombination of carriers injected from a pair of electrodes is 25%.

When the singlet excitons directly formed by recombination of carriers injected from a pair of electrodes and the singlet excitons formed by TTA are put together, eight singlet excitons can be formed from twenty excitons (the sum of singlet excitons and triplet excitons) directly formed by recombination of carriers injected from a pair of electrodes (General Formula (G15)). That is, TTA can increase the probability of singlet exciton formation from 25%, which is the conventional value, to at most 40% (=8/20).
51H*+153H→51H*+(31H*+121H)  (G15)

In the singlet excited state of the host material121which is formed by the singlet excitons formed through the above process, energy is transferred from the S1 level (SFH) of the host material121to the S1 level (SFG) of the guest material122, which is lower than SFH(see Route E1inFIG. 2C). Then, the guest material122brought into a singlet excited state emits fluorescence.

In the case where carriers recombine in the guest material122and an excited state formed by the formed excitons is a triplet excited state, if the T1 level (TFH) of the host material121is lower than the T1 level (TFG) of the guest material122, triplet excitation energy of TFGis not deactivated and transferred to TFH(see Route E2inFIG. 2C) to contribute to TTA.

In the case where the T1 level (TFG) of the guest material122is lower than the T1 level (TFH) of the host material121, the weight percentage of the guest material122is preferably lower than that of the host material121. Specifically, the weight ratio of the guest material122to the host material121is preferably greater than 0 and less than or equal to 0.05, which reduces the probability of carrier recombination in the guest material122. In addition, the probability of energy transfer from the T1 level (TFH) of the host material121to the T1 level (TFG) of the guest material122can be reduced.

In the case where a guest material emitting blue light is used, the weight ratio of the guest material122to the host material121is preferably greater than 0 and less than 0.03, which allows deeper blue light to be emitted.

As described above, triplet excitons formed in the light-emitting layer120can be converted into singlet excitons by TTA, so that light emitted from the guest material122can be efficiently obtained.

Since TTA can increase the probability of formation of singlet excitons and the emission efficiency of a light-emitting element as described above, increasing the probability of occurrence of TTA (also referred to as TTA efficiency) is important for high emission efficiency. That is, it is important that a delayed fluorescence component due to TTA account for a large proportion of light emitted from the light-emitting element.

To increase the probability of occurrence of TTA, the host material121preferably has a higher singlet excitation energy and a lower triplet excitation energy than the guest material122. Thus, the host material121is preferably a compound having a condensed aromatic ring skeleton, further preferably, a compound including an aryl group having at least an anthracene skeleton.

In a light-emitting element that emits blue light, a compound with high excitation energy needs to be used as the host material121. That is, a compound including an aryl group having at least an anthracene skeleton is preferably used as the compound that emits delayed fluorescence due to TTA and can be used as a light-emitting material or the host material121in the light-emitting element that emits blue light.

When holes and electrons are injected from the anode and the cathode, respectively, into an EL layer so that current flows, the holes and the electrons are respectively injected to the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of a compound included in the EL layer, and then transferred.

In the case where the injected holes and electrons recombine in the host material and for example, the HOMO and the LUMO in the host material have molecular orbitals in the same region, an exciton to be generated has energy equivalent to the energy gap between the HOMO level and the LUMO level.

Hence, the compound preferably has a hole-transport skeleton and an electron-transport skeleton each with a wide band gap.

Any of the dibenzocarbazole compounds described in Embodiment 1 is preferably used as the above compound.

Benzo[a]anthracene skeleton is a tetracyclic aromatic hydrocarbon but has an S1 level and a T1 level that are approximately as high as those of anthracene, which is a tricyclic aromatic hydrocarbon. Thus, the dibenzocarbazole compound having the benzo[a]anthracene skeleton is suitable for the light-emitting element with a high TTA efficiency.

Note that a factor of delayed fluorescence in a light-emitting element, which is other than TTA, may be thermally activated delayed fluorescence due to reverse intersystem crossing from the triplet excited state to the singlet excited state. To efficiently cause reverse intersystem crossing, an energy difference between the S1 level and the T1 level is preferably 0.2 eV or less. In other words, an energy difference greater than 0.2 eV between the S1 level and the T1 level hardly causes reverse intersystem crossing. Therefore, to efficiently cause TTA, an energy difference between the lowest singlet excitation energy level and lowest triplet excitation energy level of a compound in which TTA occurs is preferably greater than 0.2 eV, further preferably greater than or equal to 0.5 eV.

The lowest singlet excitation energy level of an organic compound can be observed from an absorption spectrum at a transition from the singlet ground state to the lowest singlet excited state in the organic compound. Alternatively, the lowest singlet excitation energy level may be estimated from a peak wavelength of a fluorescence spectrum of the organic compound. Furthermore, the lowest triplet excitation energy level can be observed from an absorption spectrum at a transition from the singlet ground state to the lowest triplet excited state in the organic compound, but is difficult to observe in some cases because this transition is a forbidden transition. In such cases, the lowest triplet excitation energy level may be estimated from a peak wavelength of a phosphorescence spectrum of the organic compound. Thus, a difference in equivalent energy value between the peak wavelengths of the fluorescence and phosphorescence spectra of the organic compound is preferably greater than 0.2 eV, further preferably greater than or equal to 0.5 eV.

Next, components of a light-emitting element of one embodiment of the present invention are described in detail.

In the light-emitting layer120, the weight percentage of the host material121is higher than that of at least the guest material122, and the guest material122(fluorescent material) is dispersed in the host material121. Any of the dibenzocarbazole compounds described in Embodiment 1 is preferably used as the host material121in the light-emitting layer120. Note that in the light-emitting layer120, the host material121may be composed of one kind of compound or a plurality of compounds.

In the light-emitting layer120, the guest material122is preferably, but not particularly limited to, an anthracene derivative, a tetracene derivative, a chrysene derivative, a phenanthrene derivative, a pyrene derivative, a perylene derivative, a stilbene derivative, an acridone derivative, a coumarin derivative, a phenoxazine derivative, a phenothiazine derivative, or the like, and for example, any of the following materials can be used.

Note that the light-emitting layer120may include a material other than the host material121and the guest material122.

Note that the light-emitting layer120can have a structure in which two or more layers are stacked. For example, in the case where the light-emitting layer120is formed by stacking a first light-emitting layer and a second light-emitting layer in this order from the hole-transport layer side, the first light-emitting layer is formed using a substance having a hole-transport property as the host material and the second light-emitting layer is formed using a substance having an electron-transport property as the host material. Also in such a case, at least one light-emitting layer preferably includes any of the dibenzocarbazole compounds described in Embodiment 1.

Next, details of other components of the light-emitting element150inFIG. 2Aare described.

The hole-injection layer111has a function of reducing a barrier for hole injection from one of the pair of electrodes (the electrode101or the electrode102) to promote hole injection and is formed using, for example, a transition metal oxide, a phthalocyanine derivative, or an aromatic amine. As the transition metal oxide, molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, manganese oxide, or the like can be given. As the phthalocyanine derivative, phthalocyanine, metal phthalocyanine, or the like can be given. As the aromatic amine, a benzidine derivative, a phenylenediamine derivative, or the like can be given. It is also possible to use a high molecular compound such as polythiophene or polyaniline; a typical example thereof is poly(ethylenedioxythiophene)/poly(styrenesulfonic acid), which is self-doped polythiophene.

As the hole-injection layer111, a layer containing a composite material of a hole-transport material and a material having a property of accepting electrons from the hole-transport material can also be used. Alternatively, a stack of a layer containing a material having an electron accepting property and a layer containing a hole-transport material may also be used. In a steady state or in the presence of an electric field, electric charge can be transferred between these materials. As examples of the material having an electron-accepting property, organic acceptors such as a quinodimethane derivative, a chloranil derivative, and a hexaazatriphenylene derivative can be given. A specific example is a compound having an electron-withdrawing group (a halogen group or a cyano group), such as 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F4-TCNQ), chloranil, or 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (abbreviation: HAT-CN). Alternatively, a transition metal oxide such as an oxide of a metal from Group 4 to Group 8 can also be used. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, rhenium oxide, or the like can be used. In particular, molybdenum oxide is preferable because it is stable in the air, has a low hygroscopic property, and is easily handled.

A material having a property of transporting more holes than electrons can be used as the hole-transport material, and a material having a hole mobility of 1×10−6cm2/Vs or higher is preferable. Specifically, an aromatic amine, a carbazole derivative, an aromatic hydrocarbon, a stilbene derivative, or the like can be used. Furthermore, the hole-transport material may be a high molecular compound.

The aromatic hydrocarbon may have a vinyl skeleton. Examples of the aromatic hydrocarbon having a vinyl group are 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi), and 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA).

The hole-transport layer112is a layer containing a hole-transport material and can be formed using any of the materials given as examples of the material of the hole-injection layer111. In order that the hole-transport layer112has a function of transporting holes injected into the hole-injection layer111to the light-emitting layer120, the highest occupied molecular orbital (HOMO) level of the hole-transport layer112is preferably equal or close to the HOMO level of the hole-injection layer111.

As the hole-transport material, a substance having a hole mobility of 1×10 cm2/Vs or higher is preferably used. Note that any substance other than the substances listed here may be used as long as the hole-transport property is higher than the electron-transport property. The layer including a substance having a high hole-transport property is not limited to a single layer, and two or more layers containing the aforementioned substances may be stacked.

Any of the dibenzocarbazole compounds described in Embodiment 1 may be used as a material included in the hole-transport layer112.

The electron-transport layer113has a function of transporting, to the light-emitting layer120, electrons injected from the other of the pair of electrodes (the electrode101or the electrode102) through the electron-injection layer114. A material having a property of transporting more electrons than holes can be used as an electron-transport material, and a material having an electron mobility of 1×10−6cm2/Vs or higher is preferred. As the compound which easily accepts electrons (the material having an electron-transport property), a π-electron deficient heteroaromatic compound such as a nitrogen-containing heteroaromatic compound, a metal complex, or the like can be used. Specific examples include a metal complex having a quinoline ligand, a benzoquinoline ligand, an oxazole ligand, or a thiazole ligand; an oxadiazole derivative; a triazole derivative; a benzimidazole derivative; a quinoxaline derivative; a dibenzoquinoxaline derivative; a phenanthroline derivative; a pyridine derivative; a bipyridine derivative; a pyrimidine derivative; and a triazine derivative. Note that a substance other than the above substances may be used as long as it has a higher electron-transport property than a hole-transport property. The electron-transport layer113is not limited to a single layer, and may include stacked two or more layers containing the aforementioned substances.

Any of the dibenzocarbazole compounds described in Embodiment 1 can also be used suitably. Note that a substance other than the above substances may be used as long as it has a higher electron-transport property than a hole-transport property. The electron-transport layer113is not limited to a single layer, and may include stacked two or more layers containing the aforementioned substances.

Between the electron-transport layer113and the light-emitting layer120, a layer that controls the transport of electron carriers may be provided. This is a layer formed by the addition of a small amount of a substance having a high electron-trapping property to the aforementioned material having a high electron-transport property, and the layer is capable of adjusting carrier balance by retarding the transport of electron carriers. Such a structure is very effective in preventing a problem (such as a reduction in element lifetime) caused when electrons pass through the light-emitting layer.

An n-type compound semiconductor may also be used, and an oxide such as titanium oxide, zinc oxide, silicon oxide, tin oxide, tungsten oxide, tantalum oxide, barium titanate, barium zirconate, zirconium oxide, hafnium oxide, aluminum oxide, yttrium oxide, or zirconium silicate; a nitride such as silicon nitride; cadmium sulfide; zinc selenide; or zinc sulfide can be used, for example.

The electron-injection layer114has a function of reducing a barrier for electron injection from the electrode102to promote electron injection and can be formed using a Group 1 metal or a Group 2 metal, or an oxide, a halide, or a carbonate of any of the metals, for example. Alternatively, a composite material containing an electron-transport material (described above) and a material having a property of donating electrons to the electron-transport material can also be used. As the material having an electron-donating property, a Group 1 metal, a Group 2 metal, an oxide of any of the metals, or the like can be given. Specifically, an alkali metal, an alkaline earth metal, or a compound thereof, such as lithium fluoride, sodium fluoride, cesium fluoride, calcium fluoride, or lithium oxide, can be used. Alternatively, a rare earth metal compound like erbium fluoride can be used. Electride may also be used for the electron-injection layer114. Examples of the electride include a substance in which electrons are added at high concentration to calcium oxide-aluminum oxide. The electron-injection layer114can be formed using the substance that can be used for the electron-transport layer113.

A composite material in which an organic compound and an electron donor (donor) are mixed may also be used for the electron-injection layer114. Such a composite material is excellent in an electron-injection property and an electron-transport property because electrons are generated in the organic compound by the electron donor. In this case, the organic compound is preferably a material that is excellent in transporting the generated electrons. Specifically, the above-listed substances for forming the electron-transport layer113(e.g., the metal complexes and heteroaromatic compounds) can be used, for example. As the electron donor, a substance showing an electron-donating property with respect to the organic compound may be used. Specifically, an alkali metal, an alkaline earth metal, and a rare earth metal are preferred; for example, lithium, sodium, cesium, magnesium, calcium, erbium, and ytterbium are given. In addition, an alkali metal oxide or an alkaline earth metal oxide is preferred; for example, lithium oxide, calcium oxide, and barium oxide are given. A Lewis base such as magnesium oxide can also be used. An organic compound such as tetrathiafulvalene (abbreviation: TTF) can also be used.

Note that the light-emitting layer, the hole-injection layer, the hole-transport layer, the electron-transport layer, and the electron-injection layer described above can each be formed by an evaporation method (including a vacuum evaporation method), an inkjet method, a coating method, a gravure printing method, or the like. Besides the above-mentioned materials, an inorganic compound such as a quantum dot or a high molecular compound (e.g., an oligomer, a dendrimer, or a polymer) may be used in the light-emitting layer, the hole-injection layer, the hole-transport layer, the electron-transport layer, and the electron-injection layer.

A quantum dot is a semiconductor nanocrystal with a size of several nanometers to several tens of nanometers and contains approximately 1×103to 1×106atoms. Since the energy shift of quantum dots depends on their size, quantum dots made of the same substance emit light with different wavelengths depending on their size; thus, emission wavelengths can be easily adjusted by changing the size of quantum dots.

A quantum dot has an emission spectrum with a narrow peak, leading to emission with high color purity. In addition, a quantum dot is said to have a theoretical internal quantum efficiency of approximately 100%, which far exceeds that of a fluorescent organic compound, i.e., 25%, and is comparable to that of a phosphorescent organic compound. Therefore, a quantum dot can be used as a light-emitting material to obtain a light-emitting element having high light-emitting efficiency. Furthermore, since a quantum dot which is an inorganic material has high inherent stability, a light-emitting element which is favorable also in terms of lifetime can be obtained.

Examples of a material of a quantum dot include a Group 14 element, a Group element, a Group 16 element, a compound of a plurality of Group 14 elements, a compound of an element belonging to any of Groups 4 to 14 and a Group 16 element, a compound of a Group 2 element and a Group 16 element, a compound of a Group 13 element and a Group 15 element, a compound of a Group 13 element and a Group 17 element, a compound of a Group 14 element and a Group 15 element, a compound of a Group 11 element and a Group 17 element, iron oxides, titanium oxides, spinel chalcogenides, and semiconductor clusters.

As the quantum dot, any of a core-type quantum dot, a core-shell quantum dot, a core-multishell quantum dot, and the like can be used. Note that when a core is covered with a shell formed of another inorganic material having a wider band gap, the influence of defects and dangling bonds existing at the surface of a nanocrystal can be reduced. Since such a structure can significantly improve the quantum efficiency of light emission, it is preferable to use a core-shell or core-multishell quantum dot. Examples of the material of a shell include zinc sulfide and zinc oxide.

Quantum dots have a high proportion of surface atoms and thus have high reactivity and easily cohere together. For this reason, it is preferable that a protective agent be attached to, or a protective group be provided at the surfaces of quantum dots. The attachment of the protective agent or the provision of the protective group can prevent cohesion and increase solubility in a solvent. It can also reduce reactivity and improve electrical stability. Examples of the protective agent (or the protective group) include polyoxyethylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, and polyoxyethylene oleyl ether, trialkylphosphines such as tripropylphosphine, tributylphosphine, trihexylphosphine, and trioctylphoshine; polyoxyethylene alkylphenyl ethers such as polyoxyethylene n-octylphenyl ether and polyoxylethylene n-nonylphenyl ether, tertiary amines such as tri(n-hexyl)amine, tri(n-octyl)amine, and tri(n-decyl)amine; organophosphorus compounds such as tripropylphosphine oxide, tributylphosphine oxide, trihexylphosphine oxide, trioctylphosphine oxide, and tridecylphosphine oxide; polyethylene glycol diesters such as polyethylene glycol dilaurate and polyethylene glycol distearate; organic nitrogen compounds such as nitrogen-containing aromatic compounds, e.g., pyridines, lutidines, collidines, and quinolones; animoalkanes such as hexylamine, octylamine, decylamine, dodecylamine, tetradecylamine, hexadecylamine, and octadecylamine; dialkylsulfides such as dibutylsulfide; dialkylsulfoxides such as dimethylsulfoxide and dibutylsulfoxide; organic sulfur compounds such as sulfur-containing aromatic compounds, e.g., thiophene; higher fatty acids such as a palmitin acid, a stearic acid, and an oleic acid; alcohols; sorbitan fatty acid esters; fatty acid modified polyesters; tertiary amine modified polyurethanes; and polyethyleneimines.

Since quantum dots with a smaller size have a wider band gap, the size is adjusted as appropriate so that light with a desired wavelength can be obtained. Light emission from the quantum dots shifts to a blue color side, i.e., a high energy side, as the crystal size decreases; thus, the emission wavelengths of the quantum dots can be adjusted over a wavelength region of a spectrum of an ultraviolet region, a visible light region, and an infrared region by changing the size of the quantum dots. The range of size (diameter) of quantum dots which is usually used is 0.5 nm to 20 nm, preferably 1 nm to 10 nm. The emission spectra are narrowed as the size distribution of the quantum dots gets smaller, and thus light with high color purity can be obtained. The shape of the quantum dots is not particularly limited and may be a spherical shape, a rod shape, a circular shape, or the like. Quantum rods which are rod-like shape quantum dots have a function of emitting directional light; thus, quantum rods can be used as a light-emitting material to obtain a light-emitting element with higher external quantum efficiency.

In most organic EL elements, light-emitting materials are dispersed in host materials so that the concentration quenching of the light-emitting materials is suppressed to improve emission efficiency. The host material needs to have a singlet excitation energy level or a triplet excitation energy level higher than or equal to that of the light-emitting material. Particularly in the case where a blue phosphorescent material is used as a light-emitting material, it is not easy to develop a host material having a long lifetime and a triplet excitation energy level higher than or equal to that of the blue phosphorescent material. With use of quantum dots, a light-emitting layer can be obtained with no host material used while the emission efficiency is maintained, thereby offering a light-emitting element which is favorable in terms of a lifetime. In the case where the light-emitting layer is composed of only quantum dots, core-shell quantum dots (including core-multishell quantum dots) are preferably used.

In the case where quantum dots are used as the light-emitting material in the light-emitting layer, the thickness of the light-emitting layer is set to 3 nm to 100 nm, preferably 10 nm to 100 nm, and the light-emitting layer is made to contain 1 volume % to 100 volume % of the quantum dots. Note that it is preferable that the light-emitting layer be composed of only the quantum dots. To form a light-emitting layer in which the quantum dots are dispersed as light-emitting materials in host materials, the quantum dots may be dispersed in the host materials, or the host materials and the quantum dots may be dissolved or dispersed in an appropriate liquid medium, and then a wet process (e.g., a spin coating method, a casting method, a die coating method, blade coating method, a roll coating method, an ink-jet method, a printing method, a spray coating method, a curtain coating method, or a Langmuir-Blodgett method) may be performed. For a light-emitting layer containing a phosphorescent material, a vacuum evaporation method, as well as the wet process, can be suitably employed.

An example of the liquid medium used for the wet process is an organic solvent of ketones such as methyl ethyl ketone and cyclohexanone; fatty acid esters such as ethyl acetate; halogenated hydrocarbons such as dichlorobenzene; aromatic hydrocarbons such as toluene, xylene, mesitylene, and cyclohexylbenzene; aliphatic hydrocarbons such as cyclohexane, decalin, and dodecane; dimethylformamide (DMF); dimethyl sulfoxide (DMSO); or the like.

The electrodes101and102function as an anode and a cathode of each light-emitting element. The electrodes101and102can be formed using a metal, an alloy, or a conductive compound, a mixture or a stack thereof, or the like.

One of the electrodes101and102is preferably formed using a conductive material having a function of reflecting light. Examples of the conductive material include aluminum (Al) and an alloy containing Al. Examples of the alloy containing Al include an alloy containing Al and L (L represents one or more of titanium (Ti), neodymium (Nd), nickel (Ni), and lanthanum (La)), such as an alloy containing Al and Ti and an alloy containing Al, Ni, and La. Aluminum has low resistance and high light reflectivity. Aluminum is included in earth's crust in large amount and is inexpensive; therefore, a light-emitting element with aluminum can be manufactured at low costs. Alternatively, silver (Ag), an alloy of Ag and N (N represents one or more of yttrium (Y), Nd, magnesium (Mg), ytterbium (Yb), Al, Ti, gallium (Ga), zinc (Zn), indium (In), tungsten (W), manganese (Mn), tin (Sn), iron (Fe), Ni, copper (Cu), palladium (Pd), iridium (Ir), or gold (Au)), or the like can be used. Examples of the alloy containing silver include an alloy containing silver, palladium, and copper, an alloy containing silver and copper, an alloy containing silver and magnesium, an alloy containing silver and nickel, an alloy containing silver and gold, an alloy containing silver and ytterbium, and the like. Besides, a transition metal such as tungsten, chromium (Cr), molybdenum (Mo), copper, or titanium can be used.

Light emitted from the light-emitting layer is extracted through the electrode101and/or the electrode102. Thus, at least one of the electrodes101and102is preferably formed using a conductive material having a function of transmitting light. Examples of the conductive material include a conductive material having a visible light transmittance higher than or equal to 40% and lower than or equal to 100%, preferably higher than or equal to 60% and lower than or equal to 100%, and a resistivity lower than or equal to 1×10−2Ω·cm.

The electrodes101and102may each be formed using a conductive material having functions of transmitting light and reflecting light. Examples of the conductive material include a conductive material having a visible light reflectivity higher than or equal to 20% and lower than or equal to 80%, preferably higher than or equal to 40% and lower than or equal to 70%, and a resistivity lower than or equal to 1×10−2Ω·cm. For example, one or more kinds of conductive metals and alloys, conductive compounds, and the like can be used. Specifically, a metal oxide such as indium tin oxide (hereinafter, referred to as ITO), indium tin oxide containing silicon or silicon oxide (ITSO), indium oxide-zinc oxide (indium zinc oxide), indium oxide-tin oxide containing titanium, indium titanium oxide, or indium oxide containing tungsten oxide and zinc oxide can be used. A metal thin film having a thickness that allows transmission of light (preferably, a thickness greater than or equal to 1 nm and less than or equal to 30 nm) can also be used. As the metal, Ag, an alloy of Ag and Al, an alloy of Ag and Mg, an alloy of Ag and Au, an alloy of Ag and Yb, or the like can be used.

In this specification and the like, the material transmitting light may be a material that transmits visible light and has conductivity. Examples of the material include, in addition to the above-described oxide conductor typified by ITO, an oxide semiconductor and an organic conductor containing an organic substance. Examples of the organic conductor containing an organic substance include a composite material in which an organic compound and an electron donor (donor material) are mixed and a composite material in which an organic compound and an electron acceptor (acceptor material) are mixed. Alternatively, an inorganic carbon-based material such as graphene may be used. The resistivity of the material is preferably lower than or equal to 1×105Ω·cm, further preferably lower than or equal to 1×104Ω·cm.

Alternatively, the electrode101and/or the electrode102may be formed by stacking two or more of these materials.

Furthermore, to increase light extraction efficiency, a material having a higher refractive index than an electrode that has a function of transmitting light may be formed in contact with the electrode. Such a material may be a conductive material or a non-conductive material as long as having a function of transmitting visible light. For example, in addition to the above-described oxide conductor, an oxide semiconductor and an organic material are given as examples. As examples of the organic material, materials of the light-emitting layer, the hole-injection layer, the hole-transport layer, the electron-transport layer, and the electron-injection layer are given. Alternatively, an inorganic carbon-based material or a metal film thin enough to transmit light can be used. A plurality of layers each of which is formed using the material having a high refractive index and has a thickness of several nanometers to several tens of nanometers may be stacked.

In the case where the electrode101or the electrode102functions as the cathode, the electrode preferably contains a material having a low work function (lower than or equal to 3.8 eV). The examples include an element belonging to Group 1 or 2 of the periodic table (e.g., an alkali metal such as lithium, sodium, or cesium, an alkaline earth metal such as calcium or strontium, or magnesium), an alloy containing any of these elements (e.g., Ag—Mg or Al—Li), a rare earth metal such as europium (Eu) or Yb, an alloy containing any of these rare earth metals, and an alloy containing aluminum and silver.

In the case where the electrode101or the electrode102is used as an anode, a material having a high work function (higher than or equal to 4.0 eV) is preferably used.

Alternatively, the electrodes101and102may each be a stack of a conductive material having a function of reflecting light and a conductive material having a function of transmitting light. Such a structure is preferable because the electrodes101and102can each have a function of adjusting the optical path length so that desired light emitted from each light-emitting layer resonates and is intensified.

As the method for forming the electrodes101and102, a sputtering method, an evaporation method, a printing method, a coating method, a molecular beam epitaxy (MBE) method, a CVD method, a pulsed laser deposition method, an atomic layer deposition (ALD) method, or the like can be used as appropriate.

A light-emitting element in one embodiment of the present invention may be formed over a substrate of glass, plastic, or the like. As the way of stacking layers over the substrate, layers may be sequentially stacked from the electrode101side or sequentially stacked from the electrode102side.

For the substrate over which the light-emitting element of one embodiment of the present invention can be formed, glass, quartz, plastic, or the like can be used, for example. Alternatively, a flexible substrate can be used. The flexible substrate means a substrate that can be bent, such as a plastic substrate made of polycarbonate or polyarylate, for example. Alternatively, a film, an inorganic vapor deposition film, or the like can be used. Another material may be used as long as the substrate functions as a support in a manufacturing process of the light-emitting element or an optical element as long as it has a function of protecting the light-emitting element or the optical element.

In the present invention and the like, a light-emitting element can be formed using any of a variety of substrates, and there is no particular limitation on the type of substrate. Examples of the substrate include a semiconductor substrate (e.g., a single crystal substrate or a silicon substrate), an SOI substrate, a glass substrate, a quartz substrate, a plastic substrate, a metal substrate, a stainless steel substrate, a substrate including stainless steel foil, a tungsten substrate, a substrate including tungsten foil, a flexible substrate, an attachment film, paper which include a fibrous material, and a base material film. Examples of a glass substrate include a barium borosilicate glass substrate, an aluminoborosilicate glass substrate, and a soda lime glass substrate. Examples of the flexible substrate, the attachment film, the base material film, and the like are substrates of plastics typified by polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), and polytetrafluoroethylene (PTFE). Another example is a resin such as acrylic. Alternatively, polypropylene, polyester, polyvinyl fluoride, polyvinyl chloride, or the like can be used. Further alternatively, polyamide, polyimide, aramid, epoxy, an inorganic vapor deposition film, paper, or the like can be used.

Alternatively, a flexible substrate may be used as the substrate such that the light-emitting element is provided directly on the flexible substrate. Further alternatively, a separation layer may be provided between the substrate and the light-emitting element. The separation layer can be used when part or the whole of a light-emitting element formed over the separation layer is separated from the substrate and transferred onto another substrate. In such a case, the light-emitting element can be transferred to a substrate having low heat resistance or a flexible substrate as well. Note that the above separation layer may have a structure in which inorganic films of a tungsten film and a silicon oxide film are stacked, a structure in which a resin film of polyimide or the like is formed over a substrate, or the like.

In other words, after the light-emitting element is formed using a substrate, the light-emitting element may be transferred to another substrate. Example of the substrate to which the light-emitting element is transferred are, in addition to the above substrates, a cellophane substrate, a stone substrate, a wood substrate, a cloth substrate (including a natural fiber (e.g., silk, cotton, and hemp), a synthetic fiber (e.g., nylon, polyurethane, and polyester), a regenerated fiber (e.g., acetate, cupra, rayon, and regenerated polyester), and the like), a leather substrate, and a rubber substrate. When such a substrate is used, a light-emitting element with high durability, high heat resistance, reduced weight, or reduced thickness can be formed.

The light-emitting element150may be formed over an electrode electrically connected to a field-effect transistor (FET), for example, which is formed over any of the above-described substrates. Accordingly, an active matrix display device in which the FET controls the driving of the light-emitting element150can be manufactured.

In this embodiment, one embodiment of the present invention has been described. Other embodiments of the present invention are described in the other embodiments. Note that one embodiment of the present invention is not limited to the above examples. In other words, various embodiments of the invention are described in this embodiment and the other embodiments, and one embodiment of the present invention is not limited to a particular embodiment. An example in which one embodiment of the present invention is used in a light-emitting element is described; however, one embodiment of the present invention is not limited thereto. Depending on circumstances or conditions, one embodiment of the present invention is not necessarily used in a light-emitting element, for example. For another example, one embodiment is not limited to the example in which the EL layer includes the dibenzocarbazole compound. Depending on circumstances, the EL layer does not necessarily include the dibenzocarbazole compound.

The structure described above in this embodiment can be combined with any of the other embodiments as appropriate.

In this embodiment, a light-emitting element having a structure different from that described in Embodiment 3 will be described below with reference toFIGS. 3A to 4C. InFIGS. 3A to 4C, a portion having a function similar to that inFIG. 2Ais represented by the same hatch pattern as inFIG. 2Aand not especially denoted by a reference numeral in some cases. In addition, common reference numerals are used for portions having similar functions, and a detailed description of the portions is omitted in some cases.

Structure Example 1 of Light-Emitting Element

FIG. 3Ais a schematic cross-sectional view of a light-emitting element250.

The light-emitting element250illustrated inFIG. 3Aincludes a plurality of light-emitting units (a light-emitting unit106and a light-emitting unit108inFIG. 3A) between a pair of electrodes (the electrode101and the electrode102). One of the light-emitting units preferably has the same structure as the EL layer100illustrated inFIGS. 2A to 2C. That is, it is preferable that the light-emitting element150illustrated inFIGS. 2A to 2Cinclude one light-emitting unit while the light-emitting element250include a plurality of light-emitting units. Note that the electrode101functions as an anode and the electrode102functions as a cathode in the following description of the light-emitting element250; however, the functions may be interchanged in the light-emitting element250.

In the light-emitting element250illustrated inFIG. 3A, the light-emitting unit106and the light-emitting unit108are stacked, and a charge-generation layer115is provided between the light-emitting unit106and the light-emitting unit108. Note that the light-emitting unit106and the light-emitting unit108may have the same structure or different structures. For example, it is preferable that the EL layer100illustrated inFIGS. 2A to 2Cbe used in the light-emitting unit106.

The charge-generation layer115may have either a structure in which an acceptor substance that is an electron acceptor is added to a hole-transport material or a structure in which a donor substance that is an electron donor is added to an electron-transport material. Alternatively, both of these structures may be stacked.

In the case where the charge-generation layer115contains a composite material of an organic compound and an acceptor substance, the composite material that can be used for the hole-injection layer111described in Embodiment 3 may be used for the composite material. As the organic compound, a variety of compounds such as an aromatic amine compound, a carbazole compound, an aromatic hydrocarbon, and a high molecular compound (such as an oligomer, a dendrimer, or a polymer) can be used. A material having a hole mobility of 1×10−6cm2/Vs or higher is preferably used as the organic compound. Note that any other material may be used as long as it has a property of transporting more holes than electrons. Since the composite material of an organic compound and an acceptor substance has excellent carrier-injection and carrier-transport properties, low-voltage driving or low-current driving can be realized. Note that when a surface of a light-emitting unit on the anode side is in contact with the charge-generation layer115as in the light-emitting unit108, the charge-generation layer115can also serve as a hole-injection layer or a hole-transport layer of the light-emitting unit; thus, a hole-injection layer or a hole-transport layer is not necessarily included in the light-emitting unit.

The charge-generation layer115may have a stacked structure of a layer containing the composite material of an organic compound and an acceptor substance and a layer containing another material. For example, the charge-generation layer115may be formed using a combination of a layer containing the composite material of an organic compound and an acceptor substance with a layer containing one compound selected from among electron-donating materials and a compound having a high electron-transport property. Furthermore, the charge-generation layer115may be formed using a combination of a layer containing the composite material of an organic compound and an acceptor substance with a layer containing a transparent conductive film.

The charge-generation layer115provided between the light-emitting unit106and the light-emitting unit108is configured so that electrons are injected into one of the light-emitting units and holes are injected into the other light-emitting unit when a voltage is applied between the electrode101and the electrode102. For example, inFIG. 3A, the charge-generation layer115injects electrons into the light-emitting unit106and holes into the light-emitting unit108when a voltage is applied such that the potential of the electrode101is higher than that of the electrode102.

Note that in terms of light extraction efficiency, the charge-generation layer115preferably has a visible light transmittance (specifically, a visible light transmittance of higher than or equal to 40%). The charge-generation layer115functions even when having lower conductivity than the pair of electrodes (the electrodes101and102).

The charge-generation layer115formed by using any of the above materials can suppress an increase in drive voltage caused by the stack of the light-emitting layers.

AlthoughFIG. 3Aillustrates the light-emitting element including the two light-emitting units, the light-emitting element can include three or more light-emitting units stacked. With a plurality of light-emitting units between a pair of electrodes, which are partitioned by the charge-generation layer as in the light-emitting element250, it is possible to provide a light-emitting element which can emit high-luminance light with the current density kept low, has a long lifetime, and consumes low power.

When the structure described in Embodiment 3 is used for at least one of the plurality of units, a light-emitting element with a high emission efficiency can be provided.

When any of the dibenzocarbazole compounds described in Embodiment 1 is used for at least one of the light-emitting layers, a light-emitting element with a high emission efficiency can be provided.

In this embodiment, the light-emitting layer120included in the light-emitting unit106has a structure similar to that of the light-emitting layer120illustrated inFIG. 2B. That is, the light-emitting layer120includes the host material121and the guest material122.

The light-emitting layer140included in the light-emitting unit108includes a host material141and a guest material142as illustrated inFIG. 3B. The host material141includes an organic compound141_1and an organic compound141_2. Note that the guest material142is described below as a phosphorescent material.

The light emission mechanism of the light-emitting layer140is described below.

The organic compound141_1and the organic compound141_2which are included in the light-emitting layer140form an exciplex.

Although it is acceptable as long as the combination of the organic compound141_1and the organic compound141_2can form an exciplex, preferably, one of them is a compound having a hole-transport property and the other is a compound having an electron-transport property.

FIG. 3Cshows a correlation between the energy levels of the organic compound141_1, the organic compound141_2, and the guest material142in the light-emitting layer140. The following explains what terms and numerals inFIG. 3Crepresent:Host (141_1): the organic compound141_1(host material);Host (141_2): the organic compound141_2(host material);Guest (142): the guest material142(phosphorescent material);SPH1: the S1 level of the organic compound141_1(host material);TPH1: the T1 level of the organic compound141_1(host material);SPH2: the S1 level of the organic compound141_2(host material);TPH2: the T1 level of the organic compound141_2(host material);TPG: the T1 level of the guest material142(phosphorescent material);SE: the S1 level of the exciplex; andTE: the T1 level of the exciplex.

The organic compound141_1and the organic compound141_2form an exciplex, and the S1 level (SE) and the T1 level (TE) of the exciplex are energy levels adjacent to each other (see Route E7inFIG. 3C).

One of the organic compound141_1and the organic compound141_2receives a hole and the other receives an electron to readily form an exciplex. Alternatively, when one of the organic compounds is brought into an excited state, it immediately interacts with the other to form an exciplex. Consequently, most excitons in the light-emitting layer140exist as exciplexes. Because the excitation energy levels (SEor TE) of the exciplex are lower than the S1 levels (SPH1and SPH2) of the host materials (the organic compounds141_1and141_2) that form the exciplex, the excited state of the host material141can be formed with lower excitation energy. This can reduce the drive voltage of the light-emitting element.

Both of the energies SEand TEof the exciplex are then transferred to the T1 level of the guest material142(the phosphorescent material); thus, light emission is obtained (see Routes E8and E9inFIG. 3C).

Note that the T1 level (TE) of the exciplex is preferably higher than the T1 level (TPG) of the guest material142. In that case, the singlet excitation energy and the triplet excitation energy of the formed exciplex can be transferred from the S1 level (SE) and the T1 level (TE) of the exciplex to the T1 level (TPG) of the guest material142.

In order to efficiently transfer excitation energy from the exciplex to the guest material142, the T1 level (TE) of the exciplex is preferably lower than or equal to the T1 levels (TPH1and TPH2) of the organic compounds (the organic compound141_1and the organic compound141_2) which form the exciplex. Thus, quenching of the triplet excitation energy of the exciplex due to the organic compounds (the organic compounds141_1and141_2) is less likely to occur, resulting in efficient energy transfer from the exciplex to the guest material142.

In order that the organic compound141_1and the organic compound141_2efficiently form an exciplex, it is preferable to satisfy the following: the HOMO level of one of the organic compound141_1and the organic compound141_2is higher than that of the other and the LUMO level of the one of the organic compound141_1and the organic compound141_2is higher than that of the other. For example, when the organic compound141_1has a hole-transport property and the organic compound141_2has an electron-transport property, it is preferable that the HOMO level of the organic compound141_1be higher than the HOMO level of the organic compound141_2and the LUMO level of the organic compound141_1be higher than the LUMO level of the organic compound141_2. Alternatively, when the organic compound141_2has a hole-transport property and the organic compound141_1has an electron-transport property, it is preferable that the HOMO level of the organic compound141_2be higher than the HOMO level of the organic compound141_1and the LUMO level of the organic compound141_2be higher than the LUMO level of the organic compound141_1. Specifically, the energy difference between the HOMO level of the organic compound141_1and the HOMO level of the organic compound141_2is preferably greater than or equal to 0.05 eV, further preferably greater than or equal to 0.1 eV, and still further preferably greater than or equal to 0.2 eV. Alternatively, the energy difference between the LUMO level of the organic compound141_1and the LUMO level of the organic compound141_2is preferably greater than or equal to 0.05 eV, more preferably greater than or equal to 0.1 eV, and still more preferably greater than or equal to 0.2 eV.

In the case where the combination of the organic compounds141_1and141_2is a combination of a compound having a hole-transport property and a compound having an electron-transport property, the carrier balance can be easily controlled by adjusting the mixture ratio. Specifically, the weight ratio of the compound having a hole-transport property to the compound having an electron-transport property is preferably within a range of 1:9 to 9:1. Since the carrier balance can be easily controlled with the structure, a carrier recombination region can also be controlled easily.

Next, factors controlling the processes of intermolecular energy transfer between the host material141and the guest material142will be described. As mechanisms of the intermolecular energy transfer, two mechanisms, i.e., Förster mechanism (dipole-dipole interaction) and Dexter mechanism (electron exchange interaction), have been proposed. Although the intermolecular energy transfer process between the host material141and the guest material142is described below, the same applies to the case where the host material141is an exciplex.

In Förster mechanism, energy transfer does not require direct contact between molecules and energy is transferred through a resonant phenomenon of dipolar oscillation between the host material141and the guest material142. By the resonant phenomenon of dipolar oscillation, the host material141provides energy to the guest material142, and thus, the host material141in an excited state is brought to a ground state and the guest material142in a ground state is brought to an excited state. Note that the rate constant kh*→gof Förster mechanism is expressed by Formula (1).

In Formula (1), ν denotes a frequency, f′h(ν) denotes a normalized emission spectrum of the host material141(a fluorescent spectrum in energy transfer from a singlet excited state, and a phosphorescent spectrum in energy transfer from a triplet excited state), εg(ν) denotes a molar absorption coefficient of the guest material142, N denotes Avogadro's number, n denotes a refractive index of a medium, R denotes an intermolecular distance between the host material141and the guest material142, τ denotes a measured lifetime of an excited state (fluorescence lifetime or phosphorescence lifetime), c denotes the speed of light, ϕ denotes an emission quantum yield (a fluorescence quantum yield in energy transfer from a singlet excited state, and a phosphorescence quantum yield in energy transfer from a triplet excited state), and K2denotes a coefficient (0 to 4) of orientation of a transition dipole moment between the host material141and the guest material142. Note that K2is ⅔ in random orientation.

In Dexter mechanism, the host material141and the guest material142are close to a contact effective range where their orbitals overlap, and the host material141in an excited state and the guest material142in a ground state exchange their electrons, which leads to energy transfer. Note that the rate constant kh*→gof Dexter mechanism is expressed by Formula (2).

In Formula (2), h denotes a Planck constant, K denotes a constant having an energy dimension, ν denotes a frequency, f′h(ν) denotes a normalized emission spectrum of the host material141(a fluorescent spectrum in energy transfer from a singlet excited state, and a phosphorescent spectrum in energy transfer from a triplet excited state), ε′g(ν) denotes a normalized absorption spectrum of the guest material142, L denotes an effective molecular radius, and R denotes an intermolecular distance between the host material141and the guest material142.

Here, the efficiency of energy transfer from the host material141to the guest material142(energy transfer efficiency ϕET) is expressed by Formula (3). In the formula, krdenotes a rate constant of a light-emission process (fluorescence in energy transfer from a singlet excited state, and phosphorescence in energy transfer from a triplet excited state) of the host material141, kndenotes a rate constant of a non-light-emission process (thermal deactivation or intersystem crossing) of the host material141, and τ denotes a measured lifetime of an excited state of the host material141.

According to Formula (3), it is found that the energy transfer efficiency ϕETcan be increased by increasing the rate constant kh*→gof energy transfer so that another competing rate constant kr+kn(=1/τ) becomes relatively small.

<<Concept for Promoting Energy Transfer>>

In energy transfer by Förster mechanism, high energy transfer efficiency ϕETis obtained when emission quantum yield ϕ (a fluorescence quantum yield in energy transfer from a singlet excited state, and a phosphorescence quantum yield in energy transfer from a triplet excited state) is high. Furthermore, it is preferable that the emission spectrum (the fluorescence spectrum in energy transfer from the singlet excited state) of the host material141largely overlap with the absorption spectrum (absorption corresponding to the transition from the singlet ground state to the triplet excited state) of the guest material142. Moreover, it is preferable that the molar absorption coefficient of the guest material142be also high. This means that the emission spectrum of the host material141overlaps with the absorption band of the guest material142that is on the longest wavelength side.

In energy transfer by Dexter mechanism, in order to increase the rate constant kh*→g, it is preferable that an emission spectrum of the host material141(a fluorescent spectrum in energy transfer from a singlet excited state, and a phosphorescent spectrum in energy transfer from a triplet excited state) largely overlap with an absorption spectrum of the guest material142(absorption corresponding to transition from a singlet ground state to a triplet excited state). Therefore, the energy transfer efficiency can be optimized by making the emission spectrum of the host material141overlap with the absorption band of the guest material142which is on the longest wavelength side.

In a manner similar to that of the energy transfer from the host material141to the guest material142, the energy transfer by both Förster mechanism and Dexter mechanism also occurs in the energy transfer process from the exciplex to the guest material142.

That is, the host material141includes the organic compounds141_1and141_2which are a combination for forming an exciplex functioning as an energy donor capable of efficiently transferring energy to the guest material142. The excitation energy for forming the exciplex by the organic compounds141_1and141_2can be lower than the excitation energy of the organic compound141_1in the excited state and lower than the excitation energy of the organic compound141_2in the excited state. This results in a reduction in the driving voltage of the light-emitting element.

Furthermore, in order to facilitate the energy transfer from the S1 level of the exciplex to the T1 level of the guest material142serving as an energy acceptor, it is preferable that the emission spectrum of the exciplex overlap with the absorption band of the guest material142which is on the longest wavelength side (lowest energy side). Thus, the efficiency of generating the triplet excited state of the guest material142can be increased.

The exciplex generated in the light-emitting layer140has a feature in that the singlet excitation energy level is close to the triplet excitation energy level. Therefore, by overlapping the emission spectrum of the exciplex and the absorption band of the guest material142which is on the longest wavelength side (lowest energy side), energy can be easily transferred from the triplet excitation energy level of the exciplex to the triplet excitation energy level of the guest material142.

When the light-emitting layer140has the above-described structure, light emission from the guest material142(the phosphorescent material) of the light-emitting layer140can be obtained efficiently.

Note that the above-described processes through Routes E7to E9may be referred to as exciplex-triplet energy transfer (ExTET) in this specification and the like. In other words, in the light-emitting layer140, excitation energy is transferred from the exciplex to the guest material142. In this case, the efficiency of reverse intersystem crossing from TEto SEand the emission quantum yield from SEare not necessarily high; thus, materials can be selected from a wide range of options.

Note that in each of the above-described structures, the emission colors of the guest materials used in the light-emitting unit106and the light-emitting unit108may be the same or different. In the case where the same guest materials emitting light of the same color are used for the light-emitting units106and108, the light-emitting element250can exhibit a high emission luminance at a small current value, which is preferable. In the case where guest materials emitting light of different colors are used for the light-emitting units106and108, the light-emitting element250can exhibit multi-color light emission, which is preferable. In that case, when a plurality of light-emitting materials with different emission wavelengths are used in one or both of the light-emitting layers120and140, the light-emitting element250emits light obtained by synthesizing lights with different emission peaks. That is, the emission spectrum of the light-emitting element250has at least two local maximum values.

The above structure is also suitable for obtaining white light emission. When the light-emitting layer120and the light-emitting layer140emit light of complementary colors, white light emission can be obtained. It is particularly favorable to select the guest materials so that white light emission with high color rendering properties or light emission of at least red, green, and blue can be obtained.

One or both of the light-emitting layers120and140may be divided into layers and each of the divided layers may contain a different light-emitting material. That is, one or both of the light-emitting layers120and140may consist of two or more layers. For example, in the case where the light-emitting layer is formed by stacking a first light-emitting layer and a second light-emitting layer in this order from the hole-transport layer side, the first light-emitting layer is formed using a substance having a hole-transport property as the host material and the second light-emitting layer is formed using a substance having an electron-transport property as the host material. In that case, a light-emitting material included in the first light-emitting layer may be the same as or different from a light-emitting material included in the second light-emitting layer. In addition, the materials may have functions of emitting light of the same color or light of different colors. White light emission with a high color rendering property that is formed of three primary colors or four or more colors can be obtained by using a plurality of light-emitting materials emitting light of different colors.

In the case where the light-emitting units106and108contain guest materials whose emission colors are different, light emitted from the light-emitting layer120preferably has an emission peak on the shorter wavelength side than light emitted from the light-emitting layer140. The luminance of a light-emitting element using a material having a high triplet excitation energy level tends to degrade quickly; thus, any of the dibenzocarbazole compounds described in Embodiment 1 is used in the light-emitting layer emitting light of a short wavelength so that a light-emitting element with less degradation of luminance can be provided.

Structure Example 2 of Light-Emitting Element

Next, a structure example different from that of the light-emitting element illustrated inFIGS. 3A to 3Cwill be described below with reference toFIGS. 4A to 4C.

FIG. 4Ais a schematic cross-sectional view of a light-emitting element252.

In the light-emitting element252shown inFIG. 4A, an EL layer110is between a pair of electrodes (the electrodes101and102). Note that the electrode101functions as an anode and the electrode102functions as a cathode in the following description of the light-emitting element252; however, the functions may be interchanged in the light-emitting element252.

The EL layer110includes a light-emitting layer180. The light-emitting layer180includes the light-emitting layer120and the light-emitting layer140. In the light-emitting element252, as the EL layer110, the hole-injection layer111, the hole-transport layer112, the electron-transport layer113, and the electron-injection layer114are illustrated in addition to the light-emitting layers. However, this stacked structure is an example, and the structure of the EL layer110in the light-emitting element252is not limited thereto. For example, the stacking order of the above layers of the EL layer110may be changed. Alternatively, in the EL layer110, another functional layer other than the above layers may be provided. The functional layer may have a function of lowering a hole- or electron-injection barrier, a function of improving a hole- or electron-transport property, a function of inhibiting transport of holes or electrons, or a function of generating holes or electrons, for example.

As illustrated inFIG. 4B, the light-emitting layer120contains the host material121and the guest material122. The light-emitting layer140contains the host material141and the guest material142. The host material141includes the organic compound141_1and the organic compound141_2. Note that in the description below, the guest material122is a fluorescent material and the guest material142is a phosphorescent material.

The light emission mechanism of the light-emitting layer120is similar to that of the light-emitting layer120illustrated inFIGS. 2B and 2C. The light emission mechanism of the light-emitting layer140is similar to that of the light-emitting layer140illustrated inFIGS. 3B and 3C.

In the case where the light-emitting layers120and140are in contact with each other as illustrated inFIG. 4A, even when energy (in particular, triplet excitation energy) is transferred from the exciplex of the light-emitting layer140to the host material121of the light-emitting layer120at an interface between the light-emitting layer120and the light-emitting layer140, triplet excitation energy can be converted into light emission in the light-emitting layer120.

Note that the T1 level of the host material121of the light-emitting layer120is preferably lower than the T1 levels of the organic compounds141_1and141_2of the light-emitting layer140. In the light-emitting layer120, the S1 level of the host material121is preferably higher than the S1 level of the guest material122(fluorescent material) while the T1 level of the host material121is preferably lower than the T1 level of the guest material122(fluorescent material).

FIG. 4Cshows a correlation of energy levels in the case where TTA is utilized in the light-emitting layer120and ExTET is utilized in the light-emitting layer140. The following explains what terms and numerals inFIG. 4Crepresent:

Host (121): the host material121;

Host (141_1): the host material (the organic compound141_1);

SFH: the S1 level of the host material121;

TFH: the T1 level of the host material121;

SFG: the S1 level of the guest material122(fluorescent material);

TFG: the T1 level of the guest material122(fluorescent material);

SPH: the S1 level of the host material (the organic compound141_1);

TPH: the T1 level of the host material (the organic compound141_1);

TPG: the T1 level of the guest material142(phosphorescent material);

SE: the S1 level of the exciplex; and

TE: the T1 level of the exciplex.

As shown inFIG. 4C, the exciplex exists only in an excited state; thus, exciton diffusion between the exciplexes is less likely to occur. In addition, because the excitation energy levels (SEand TE) of the exciplex are lower than the excitation energy levels (SPHand TPH) of the organic compound141_1(i.e., the host material of the phosphorescent material) of the light-emitting layer140, energy diffusion from the exciplex to the organic compound141_1does not occur. That is, the efficiency of the phosphorescent light-emitting layer (the light-emitting layer140) can be maintained because an exciton diffusion distance of the exciplex is short in the phosphorescent light-emitting layer (the light-emitting layer140). In addition, even when part of the triplet excitation energy of the exciplex of the phosphorescent light-emitting layer (the light-emitting layer140) diffuses into the fluorescent light-emitting layer (the light-emitting layer120) through the interface between the fluorescent light-emitting layer (the light-emitting layer120) and the phosphorescent light-emitting layer (the light-emitting layer140), energy loss can be reduced because the triplet excitation energy in the fluorescent light-emitting layer (the light-emitting layer120) caused by the diffusion is converted into light emission through TTA.

As described above, ExTET is utilized in the light-emitting layer140and TTA is utilized in the light-emitting layer120; thus, the light-emitting element252can have a reduced energy loss and a high emission efficiency. Furthermore, in the case where the light-emitting layer120and the light-emitting layer140are in contact with each other as in the light-emitting element252, the number of the EL layers110as well as the energy loss can be reduced. Therefore, a light-emitting element with low manufacturing costs can be obtained.

Note that the light-emitting layer120and the light-emitting layer140are not necessarily in contact with each other. In that case, it is possible to prevent energy transfer by the Dexter mechanism (in particular, triplet energy transfer) from the organic compound141_1in an excited state, the organic compound141_2in an excited state, or the guest material142(phosphorescent material) in an excited state which is generated in the light-emitting layer140to the host material121or the guest material122(fluorescent material) in the light-emitting layer120. Therefore, the thickness of a layer provided between the light-emitting layer120and the light-emitting layer140may be several nanometers. Specifically, the thickness is preferably more than or equal to 1 nm and less than or equal to 5 nm, in which case an increase in driving voltage can be inhibited.

The layer provided between the light-emitting layer120and the light-emitting layer140may contain a single material or both a hole-transport material and an electron-transport material. In the case of a single material, a bipolar material may be used. The bipolar material here refers to a material in which the ratio between the electron mobility and the hole mobility is 100 or less. Alternatively, the hole-transport material, the electron-transport material, or the like may be used. At least one of materials contained in the layer may be the same as the host material (the organic compound141_1or141_2) of the light-emitting layer140. This facilitates the manufacture of the light-emitting element and reduces the driving voltage. Furthermore, the hole-transport material and the electron-transport material may form an exciplex, which effectively prevents exciton diffusion. Specifically, it is possible to prevent energy transfer from the host material (the organic compound141_1or141_2) in an excited state or the guest material142(phosphorescent material) in an excited state of the light-emitting layer140to the host material121or the guest material122(fluorescent material) in the light-emitting layer120.

In the light-emitting element252, the light-emitting layer120and the light-emitting layer140have been described as being positioned on the hole-transport layer112side and the electron-transport layer113side, respectively; however, the light-emitting element of one embodiment of the present invention is not limited to this structure. The light-emitting layer120and the light-emitting layer140may be positioned on the electron-transport layer113side and the hole-transport layer112side, respectively.

Note that in the light-emitting element252, a carrier recombination region is preferably distributed to some extent. Therefore, it is preferable that the light-emitting layer120or140have an appropriate degree of carrier-trapping property. It is particularly preferable that the guest material142(phosphorescent material) in the light-emitting layer140have an electron-trapping property. Alternatively, the guest material122(fluorescent material) in the light-emitting layer120preferably has a hole-trapping property.

Note that light emitted from the light-emitting layer120preferably has an emission peak on the shorter wavelength side than light emitted from the light-emitting layer140. The luminance of a light-emitting element using a phosphorescent material emitting light with a short wavelength tends to degrade quickly. By using fluorescence with a short wavelength, a light-emitting element with less degradation of luminance can be provided.

Furthermore, the light-emitting layer120and the light-emitting layer140may be made to emit light with different emission wavelengths, so that the light-emitting element can be a multicolor light-emitting element. In that case, the emission spectrum of the light-emitting element is formed by combining light having different emission peaks, and thus has at least two local maximum values.

The above structure is also suitable for obtaining white light emission. When the light-emitting layer120and the light-emitting layer140emit light of complementary colors, white light emission can be obtained.

In addition, white light emission with a high color rendering property that is formed of three primary colors or four or more colors can be obtained by using a plurality of light-emitting materials emitting light of different emission wavelengths for one of the light-emitting layers120and140or both. In that case, the light-emitting layer may be divided into layers and each of the divided layers may contain a light-emitting material different from the others.

<Example of Material that can be Used in Light-Emitting Layers>

Next, materials that can be used in the light-emitting layers120and140are described.

<<Material that can be Used in Light-Emitting Layer120>>

In the light-emitting layer120, the host material121is present in the largest proportion by weight, and the guest material122(fluorescent material) is dispersed in the host material121. The S1 level of the host material121is preferably higher than the S1 level of the guest material122(fluorescent material) while the T1 level of the host material121is preferably lower than the T1 level of the guest material122(fluorescent material).

Any of the dibenzocarbazole compounds described in Embodiment 1 is preferably used as the host material121. This allows the fabrication of a light-emitting element with a high emission efficiency.

In the light-emitting layer120, the guest material122is preferably, but not particularly limited to, an anthracene derivative, a tetracene derivative, a chrysene derivative, a phenanthrene derivative, a pyrene derivative, a perylene derivative, a stilbene derivative, an acridone derivative, a coumarin derivative, a phenoxazine derivative, a phenothiazine derivative, or the like. For example, any of the materials described in Embodiment 3 can be used.

Note that the light-emitting layer120can have a structure in which two or more layers are stacked. For example, in the case where the light-emitting layer120is formed by stacking a first light-emitting layer and a second light-emitting layer in this order from the hole-transport layer side, the first light-emitting layer is formed using a substance having a hole-transport property as the host material and the second light-emitting layer is formed using a substance having an electron-transport property as the host material.

In the light-emitting layer120, the host material121may be composed of a single compound or a plurality of compounds. The light-emitting layer120may include a material other than the host material121and the guest material122.

<<Material that can be Used in Light-Emitting Layer140>>

In the light-emitting layer140, the host material141is present in the largest proportion by weight, and the guest material142(fluorescent material) is dispersed in the host material141. The T1 level of the host material141(organic compounds141_1and141_2) is preferably higher than the T1 level of the guest material142in the light-emitting layer140.

Examples of the organic compound141_1include a zinc- or aluminum-based metal complex, an oxadiazole derivative, a triazole derivative, a benzimidazole derivative, a quinoxaline derivative, a dibenzoquinoxaline derivative, a dibenzothiophene derivative, a dibenzofuran derivative, a pyrimidine derivative, a triazine derivative, a pyridine derivative, a bipyridine derivative, and a phenanthroline derivative. Other examples are an aromatic amine and a carbazole derivative. Specifically, the electron-transport material and the hole-transport material described in Embodiment 3 can be used.

As the organic compound141_2, a substance which can form an exciplex together with the organic compound141_1is preferably used. Specifically, the electron-transport material and the hole-transport material described in Embodiment 3 can be used. In that case, it is preferable that the organic compound141_1, the organic compound141_2, and the guest material142(phosphorescent material) be selected such that the emission peak of the exciplex formed by the organic compounds141_1and141_2overlaps with an absorption band, specifically an absorption band on the longest wavelength side, of a triplet metal to ligand charge transfer (MLCT) transition of the guest material142(phosphorescent material). This makes it possible to provide a light-emitting element with a drastically improved emission efficiency. Note that in the case where a thermally activated delayed fluorescence material is used instead of the phosphorescent material, it is preferable that the absorption band on the longest wavelength side be a singlet absorption band.

As the guest material142(phosphorescent material), an iridium-, rhodium-, or platinum-based organometallic complex or metal complex can be used; in particular, an organoiridium complex such as an iridium-based ortho-metalated complex is preferable. As an ortho-metalated ligand, a 4H-triazole ligand, a 1H-triazole ligand, an imidazole ligand, a pyridine ligand, a pyrimidine ligand, a pyrazine ligand, an isoquinoline ligand, and the like can be given. As the metal complex, a platinum complex having a porphyrin ligand and the like can be given.

Examples of the substance that has an emission peak in the yellow or red wavelength range include organometallic iridium complexes having a pyrimidine skeleton, such as (diisobutyrylmethanato)bis[4,6-bis(3-methylphenyl)pyrimidinato]iridium(III) (abbreviation: Ir(5mdppm)2(dibm)), bis[4,6-bis(3-methylphenyl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: Ir(5mdppm)2(dpm)), and bis[4,6-di(naphthalen-1-yl)pyrimidinato](dipivaloylmethanato)iridium(III) (abbreviation: Ir(d1npm)2(dpm)); organometallic iridium complexes having a pyrazine skeleton, such as (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(I) (abbreviation: Ir(tppr)2(acac)), bis(2,3,5-triphenylpyrazinato) (dipivaloylmethanato)iridium(III) (abbreviation: Ir(tpprh)2(dpm)), and (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: Ir(Fdpq)2(acac)); organometallic iridium complexes having a pyridine skeleton, such as tris(1-phenylisoquinolinato-N,C2′)iridium(III) (abbreviation: Ir(piq)3) and bis(1-phenylisoquinolinato-N,C2′)iridium(III) acetylacetonate (abbreviation: Ir(piq)2(acac)); a platinum complex such as 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) (abbreviation: PtOEP); and rare earth metal complexes such as tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(II) (abbreviation: Eu(DBM)3(Phen)) and tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: Eu(TTA)3(Phen)). Among the materials given above, the organometallic iridium complexes having a pyrimidine skeleton have distinctively high reliability and emission efficiency and are thus particularly preferable. Further, the organometallic iridium complexes having a pyrazine skeleton can provide red light emission with favorable chromaticity.

Any material can be used as the light-emitting organic material included in the light-emitting layer as long as the material can convert the triplet excitation energy into light emission. As an example of the material that can convert triplet excitation energy into light emission, a thermally activated delayed fluorescence (TADF) material can be given in addition to the phosphorescent material. Therefore, the term “phosphorescent material” in the description can be rephrased as the term “thermally activated delayed fluorescence material”. The thermally activated delayed fluorescence material is a material having a small energy difference between the singlet excitation energy level and the triplet excitation energy level and has a function of converting the triplet excitation energy into the singlet excitation energy by reverse intersystem crossing. Thus, the thermally activated delayed fluorescence material can up-convert a triplet excited state into a singlet excited state (i.e., reverse intersystem crossing is possible) using a little thermal energy and efficiently exhibit light emission (fluorescence) from the singlet excited state. Conditions for efficiently obtaining thermally activated delayed fluorescence are as follows: the energy difference between the singlet excitation energy level and the triplet excitation energy level is preferably greater than 0 eV and less than or equal to 0.2 eV, more preferably greater than 0 eV and less than or equal to 0.1 eV.

As examples of the thermally activated delayed fluorescence material, any of the following materials can be used. First, a fullerene, a derivative thereof, an acridine derivative such as proflavine, eosin, and the like can be given. Furthermore, a metal-containing porphyrin, such as a porphyrin containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd), can be given. Examples of the metal-containing porphyrin include a protoporphyrin-tin fluoride complex (SnF2(Proto IX)), a mesoporphyrin-tin fluoride complex (SnF2(Meso IX)), a hematoporphyrin-tin fluoride complex (SnF2(Hemato IX)), a coproporphyrin tetramethyl ester-tin fluoride complex (SnF2(Copro III-4Me)), an octaethylporphyrin-tin fluoride complex (SnF2(OEP)), an etioporphyrin-tin fluoride complex (SnF2(Etio I)), and an octaethylporphyrin-platinum chloride complex (PtCl2(OEP)).

As the thermally activated delayed fluorescence material composed of one kind of material, a heterocyclic compound including a π-electron rich heteroaromatic ring and a π-electron deficient heteroaromatic ring can also be used. Specifically, 2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine (abbreviation: PIC-TRZ), 2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: PCCzPTzn), 2-[4-(10 OH-phenoxazin-10-yl)phenyl]-4,6-diphenyl-1,3,5-triazine (abbreviation: PXZ-TRZ), 3-[4-(5-phenyl-5,10-dihydrophenazin-10-yl)phenyl]-4,5-diphenyl-1,2,4-triazole (abbreviation: PPZ-3TPT), 3-(9,9-dimethyl-9H-acridin-10-yl)-9H-xanthen-9-one (abbreviation: ACRXTN), bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (abbreviation: DMAC-DPS), or 10-phenyl-10H,10′H-spiro[acridin-9,9′-anthracen]-10′-one (abbreviation: ACRSA) can be used. The heterocyclic compound is preferably used because of having the π-electron rich heteroaromatic ring and the π-electron deficient heteroaromatic ring, for which the electron-transport property and the hole-transport property are high. Note that a substance in which the π-electron rich heteroaromatic ring is directly bonded to the π-electron deficient heteroaromatic ring is particularly preferable because the donor property of the π-electron rich heteroaromatic ring and the acceptor property of the π-electron deficient heteroaromatic ring are both increased and the difference between the level of the singlet excited state and the level of the triplet excited state becomes small. Note that an aromatic ring to which an electron-withdrawing group such as a cyano group is bonded may be used instead of the π-electron deficient heteroaromatic ring.

There is no limitation on the emission colors of the light-emitting materials contained in the light-emitting layers120and140, and they may be the same or different. Light emitted from the light-emitting materials is mixed and extracted out of the element; therefore, for example, in the case where their emission colors are complementary colors, the light-emitting element can emit white light. In consideration of the reliability of the light-emitting element, the emission peak wavelength of the light-emitting material included in the light-emitting layer120is preferably shorter than that of the light-emitting material included in the light-emitting layer140.

Note that the light-emitting units106and108and the charge-generation layer115can be formed by an evaporation method (including a vacuum evaporation method), an ink-jet method, a coating method, gravure printing, or the like.

In this embodiment, examples of light-emitting elements having structures different from those described in Embodiments 3 and 4 are described below with reference toFIGS. 5A and 5B,FIGS. 6A and 6B,FIGS. 7A to 7C, andFIGS. 8A to 8C.

Structure Example 1 of Light-Emitting Element

FIGS. 5A and 5Bare cross-sectional views each illustrating a light-emitting element of one embodiment of the present invention. InFIGS. 5A and 5B, a portion having a function similar to that inFIG. 2Ais represented by the same hatch pattern as inFIG. 2Aand not especially denoted by a reference numeral in some cases. In addition, common reference numerals are used for portions having similar functions, and a detailed description of the portions is omitted in some cases.

Light-emitting elements260aand260binFIGS. 5A and 5Bmay have a bottom-emission structure in which light is extracted through the substrate200or may have a top-emission structure in which light emitted from the light-emitting element is extracted in the direction opposite to the substrate200. However, one embodiment of the present invention is not limited to this structure, and a light-emitting element having a dual-emission structure in which light emitted from the light-emitting element is extracted in both top and bottom directions of the substrate200may be used.

In the case where the light-emitting elements260aand260beach have a bottom emission structure, the electrode101preferably has a function of transmitting light and the electrode102preferably has a function of reflecting light. Alternatively, in the case where the light-emitting elements260aand260beach have a top emission structure, the electrode101preferably has a function of reflecting light and the electrode102preferably has a function of transmitting light.

The light-emitting elements260aand260beach include the electrode101and the electrode102over the substrate200. Between the electrodes101and102, a light-emitting layer123B, a light-emitting layer123G, and a light-emitting layer123R are provided. The hole-injection layer111, the hole-transport layer112, the electron-transport layer113, and the electron-injection layer114are also provided.

The light-emitting element260bincludes, as part of the electrode101, a conductive layer101a, a conductive layer101bover the conductive layer101a, and a conductive layer101cunder the conductive layer101a. In other words, the light-emitting element260bincludes the electrode101having a structure in which the conductive layer101ais sandwiched between the conductive layer101band the conductive layer101c.

In the light-emitting element260b, the conductive layer101band the conductive layer101cmay be formed of different materials or the same material. The conductive layers101band101care preferably formed of the same conductive material, in which case patterning by etching in the process for forming the electrode101can be performed easily.

In the light-emitting element260b, the electrode101may include one of the conductive layer101band the conductive layer101c.

For each of the conductive layers101a,101b, and101c, which are included in the electrode101, the structure and materials of the electrode101or102described in Embodiment 3 can be used.

InFIGS. 5A and 5B, a partition wall145is provided between a region221B, a region221G, and a region221R, which are sandwiched between the electrode101and the electrode102. The partition wall145has an insulating property. The partition wall145covers end portions of the electrode101and has openings overlapping with the electrode. With the partition wall145, the electrode101provided over the substrate200in the regions can be divided into island shapes.

Note that the light-emitting layer123B and the light-emitting layer123G may overlap with each other in a region where they overlap with the partition wall145. The light-emitting layer123G and the light-emitting layer123R may overlap with each other in a region where they overlap with the partition wall145. The light-emitting layer123R and the light-emitting layer123B may overlap with each other in a region where they overlap with the partition wall145.

The partition wall145has an insulating property and is formed using an inorganic or organic material. Examples of the inorganic material include silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, aluminum oxide, and aluminum nitride. Examples of the organic material include photosensitive resin materials such as an acrylic resin and a polyimide resin.

Note that a silicon oxynitride film refers to a film in which the proportion of oxygen is higher than that of nitrogen. The silicon oxynitride film preferably contains oxygen, nitrogen, silicon, and hydrogen in the ranges of 55 atomic % to 65 atomic %, 1 atomic % to 20 atomic %, 25 atomic % to 35 atomic %, and 0.1 atomic % to 10 atomic %, respectively. A silicon nitride oxide film refers to a film in which the proportion of nitrogen is higher than that of oxygen. The silicon nitride oxide film preferably contains nitrogen, oxygen, silicon, and hydrogen in the ranges of 55 atomic % to 65 atomic %, 1 atomic % to 20 atomic %, 25 atomic % to 35 atomic %, and 0.1 atomic % to 10 atomic %, respectively.

The light-emitting layers123R,123G, and123B preferably contain light-emitting materials having functions of emitting light of different colors. For example, when the light-emitting layer123R contains a light-emitting material having a function of emitting red, the region221R emits red light. When the light-emitting layer123G contains a light-emitting material having a function of emitting green, the region221G emits green light. When the light-emitting layer123B contains a light-emitting material having a function of emitting blue, the region221B emits blue light. The light-emitting element260aor260bhaving such a structure is used in a pixel of a display device, whereby a full-color display device can be fabricated. The thicknesses of the light-emitting layers may be the same or different.

One or more of the light-emitting layer123B, the light-emitting layer123G, and the light-emitting layer123R preferably have at least one of the structures of the light-emitting layer120described in Embodiment 3. In that case, a light-emitting element with high emission efficiency can be fabricated.

One or more of the light-emitting layers123B,123G, and123R may include two or more stacked layers.

When at least one light-emitting layer includes the light-emitting layer described in Embodiment 3 and the light-emitting element260aor260bincluding the light-emitting layer is used in pixels in a display device, a display device with high emission efficiency can be fabricated. The display device including the light-emitting element260aor260bcan thus have reduced power consumption.

By providing an optical element (e.g., a color filter, a polarizing plate, and an anti-reflection film) on the light extraction side of the electrode through which light is extracted, the color purity of each of the light-emitting elements260aand260bcan be improved. Therefore, the color purity of a display device including the light-emitting element260aor260bcan be improved. Alternatively, the reflection of external light by each of the light-emitting elements260aand260bcan be reduced. Therefore, the contrast ratio of a display device including the light-emitting element260aor260bcan be improved.

For the other components of the light-emitting elements260aand260b, the components of the light-emitting element in Embodiments 3 and 4 may be referred to.

Structure Example 2 of Light-Emitting Element

Next, structure examples different from the light-emitting elements illustrated inFIGS. 5A and 5Bwill be described below with reference toFIGS. 6A and 6B.

FIGS. 6A and 6Bare cross-sectional views of a light-emitting element of one embodiment of the present invention. InFIGS. 6A and 6B, a portion having a function similar to that inFIGS. 5A and 5Bis represented by the same hatch pattern as inFIGS. 5A and 5Band not especially denoted by a reference numeral in some cases. In addition, common reference numerals are used for portions having similar functions, and a detailed description of such portions is not repeated in some cases.

FIGS. 6A and 6Billustrate structure examples of a light-emitting element including the light-emitting layer between a pair of electrodes. A light-emitting element262aillustrated inFIG. 6Ahas a top-emission structure in which light is extracted in a direction opposite to the substrate200, and a light-emitting element262billustrated inFIG. 6Bhas a bottom-emission structure in which light is extracted to the substrate200side. However, one embodiment of the present invention is not limited to these structures and may have a dual-emission structure in which light emitted from the light-emitting element is extracted in both top and bottom directions with respect to the substrate200over which the light-emitting element is formed.

The light-emitting elements262aand262beach include the electrode101, the electrode102, an electrode103, and an electrode104over the substrate200. At least a light-emitting layer170, a light-emitting layer190, and the charge-generation layer115are provided between the electrode101and the electrode102, between the electrode102and the electrode103, and between the electrode102and the electrode104. The hole-injection layer111, the hole-transport layer112, the electron-transport layer113, the electron-injection layer114, the hole-injection layer116, the hole-transport layer117, the electron-transport layer118, and the electron-injection layer119are further provided.

The electrode101includes a conductive layer101aand a conductive layer101bover and in contact with the conductive layer101a. The electrode103includes a conductive layer103aand a conductive layer103bover and in contact with the conductive layer103a. The electrode104includes a conductive layer104aand a conductive layer104bover and in contact with the conductive layer104a.

The light-emitting element262aillustrated inFIG. 6Aand the light-emitting element262billustrated inFIG. 6Beach include a partition wall145between a region222B sandwiched between the electrode101and the electrode102, a region222G sandwiched between the electrode102and the electrode103, and a region222R sandwiched between the electrode102and the electrode104. The partition wall145has an insulating property. The partition wall145covers end portions of the electrodes101,103, and104and has openings overlapping with the electrodes. With the partition wall145, the electrodes provided over the substrate200in the regions can be separated into island shapes.

The charge-generation layer115can be formed with a material obtained by adding an electron acceptor (acceptor) to a hole-transport material or a material obtained by adding an electron donor (donor) to an electron-transport material. Note that when the conductivity of the charge-generation layer115is as high as that of the pair of electrodes, carriers generated in the charge-generation layer115might transfer to an adjacent pixel and light emission might occur in the pixel. In order to prevent such false light emission from an adjacent pixel, the charge-generation layer115is preferably formed with a material whose conductivity is lower than that of the pair of electrodes.

The light-emitting elements262aand262beach include a substrate220provided with an optical element224B, an optical element224G, and an optical element224R in the direction in which light emitted from the region222B, light emitted from the region222G, and light emitted from the region222R are extracted. The light emitted from each region is emitted outside the light-emitting element through each optical element. In other words, the light from the region222B, the light from the region222G, and the light from the region222R are emitted through the optical element224B, the optical element224G, and the optical element224R, respectively.

The optical elements224B,224G, and224R each have a function of selectively transmitting light of a particular color out of incident light. For example, the light emitted from the region222B through the optical element224B is blue light, the light emitted from the region222G through the optical element224G is green light, and the light emitted from the region222R through the optical element224R is red light.

For example, a coloring layer (also referred to as color filter), a band pass filter, a multilayer filter, or the like can be used for the optical elements224R,224G, and224B. Alternatively, color conversion elements can be used as the optical elements. A color conversion element is an optical element that converts incident light into light having a longer wavelength than the incident light. As the color conversion elements, quantum-dot elements can be favorably used. The usage of the quantum dot can increase color reproducibility of the display device.

One or more optical elements may be stacked over each of the optical elements224R,224G, and224B. As another optical element, a circularly polarizing plate, an anti-reflective film, or the like can be provided, for example. A circularly polarizing plate provided on the side where light emitted from the light-emitting element of the display device is extracted can prevent a phenomenon in which light entering from the outside of the display device is reflected inside the display device and returned to the outside. An anti-reflective film can weaken external light reflected by a surface of the display device. This leads to clear observation of light emitted from the display device.

Note that inFIGS. 6A and 6B, blue light (B), green light (G), and red light (R) emitted from the regions through the optical elements are schematically illustrated by arrows of dashed lines.

A light-blocking layer223is provided between the optical elements. The light-blocking layer223has a function of blocking light emitted from the adjacent regions. Note that a structure without the light-blocking layer223may also be employed.

The light-blocking layer223has a function of reducing the reflection of external light. The light-blocking layer223has a function of preventing mixture of light emitted from an adjacent light-emitting element. As the light-blocking layer223, a metal, a resin containing black pigment, carbon black, a metal oxide, a composite oxide containing a solid solution of a plurality of metal oxides, or the like can be used.

Note that the optical element224B and the optical element224G may overlap with each other in a region where they overlap with the light-blocking layer223. In addition, the optical element224G and the optical element224R may overlap with each other in a region where they overlap with the light-blocking layer223. In addition, the optical element224R and the optical element224B may overlap with each other in a region where they overlap with the light-blocking layer223.

As for the structures of the substrate200and the substrate220provided with the optical elements, Embodiment 3 can be referred to.

Light emitted from the light-emitting layer170and the light-emitting layer190resonates between a pair of electrodes (e.g., the electrode101and the electrode102). The light-emitting layer170and the light-emitting layer190are formed at such a position as to intensify the light of a desired wavelength among light to be emitted. For example, by adjusting the optical length from a reflective region of the electrode101to the light-emitting region of the light-emitting layer170and the optical length from a reflective region of the electrode102to the light-emitting region of the light-emitting layer170, the light of a desired wavelength among light emitted from the light-emitting layer170can be intensified. By adjusting the optical length from the reflective region of the electrode101to the light-emitting region of the light-emitting layer190and the optical length from the reflective region of the electrode102to the light-emitting region of the light-emitting layer190, the light of a desired wavelength among light emitted from the light-emitting layer190can be intensified. In the case of a light-emitting element in which a plurality of light-emitting layers (here, the light-emitting layers170and190) are stacked, the optical lengths of the light-emitting layers170and190are preferably optimized.

In each of the light-emitting elements262aand262b, by adjusting the thicknesses of the conductive layers (the conductive layer101b, the conductive layer103b, and the conductive layer104b) in each region, the light of a desired wavelength among light emitted from the light-emitting layers170and190can be increased. Note that the thickness of at least one of the hole-injection layer111and the hole-transport layer112or at least one of the electron-injection layer119and the electron-transport layer118may differ between the regions to increase the light emitted from the light-emitting layers170and190.

For example, in the case where the refractive index of the conductive material having a function of reflecting light in the electrodes101to104is lower than the refractive index of the light-emitting layer170or190, the thickness of the conductive layer101bof the electrode101is adjusted so that the optical length between the electrode101and the electrode102is mBλB/2 (mBis a natural number and λBis the wavelength of light intensified in the region222B). Similarly, the thickness of the conductive layer103bof the electrode103is adjusted so that the optical length between the electrode103and the electrode102is mGλG/2 (mGis a natural number and λGis the wavelength of light intensified in the region222G). Furthermore, the thickness of the conductive layer104bof the electrode104is adjusted so that the optical length between the electrode104and the electrode102is mRλR/2 (mRis a natural number and λRis the wavelength of light intensified in the region222R).

In the case where it is difficult to precisely determine the reflective regions of the electrodes101to104, the optical length for increasing the intensity of light emitted from the light-emitting layer170or the light-emitting layer190may be derived on the assumption that certain regions of the electrodes101to104are the reflective regions. In the case where it is difficult to precisely determine the light-emitting regions of the light-emitting layer170and the light-emitting layer190, the optical length for increasing the intensity of light emitted from the light-emitting layer170and the light-emitting layer190may be derived on the assumption that certain regions of the light-emitting layer170and the light-emitting layer190are the light-emitting regions.

In the above manner, with the microcavity structure, in which the optical length between the pair of electrodes in the respective regions is adjusted, scattering and absorption of light in the vicinity of the electrodes can be suppressed, resulting in high light extraction efficiency.

In the above structure, the conductive layers101b,103b, and104bpreferably have a function of transmitting light. The materials of the conductive layers101b,103b, and104bmay be the same or different. It is preferable to use the same material for the conductive layer101b, the conductive layer103b, and the conductive layer104bbecause patterning by etching in the formation process of the electrode101, the electrode103, and the electrode104can be performed easily. Each of the conductive layers101b,103b, and104bmay have a stacked structure of two or more layers.

Since the light-emitting element262aillustrated inFIG. 6Ahas a top-emission structure, it is preferable that the conductive layer101a, the conductive layer103a, and the conductive layer104ahave a function of reflecting light. In addition, it is preferable that the electrode102have functions of transmitting light and reflecting light.

Since the light-emitting element262billustrated inFIG. 6Bhas a bottom-emission structure, it is preferable that the conductive layer101a, the conductive layer103a, and the conductive layer104ahave functions of transmitting light and reflecting light. In addition, it is preferable that the electrode102have a function of reflecting light.

In each of the light-emitting elements262aand262b, the conductive layers101a,103a, and104amay be formed of different materials or the same material. When the conductive layers101a,103a, and104aare formed of the same material, manufacturing cost of the light-emitting elements262aand262bcan be reduced. Note that each of the conductive layers101a,103a, and104amay have a stacked structure including two or more layers.

At least one of the structures described in Embodiments 3 and 4 is preferably used for at least one of the light-emitting layers170and190included in the light-emitting elements262aand262b. In this way, the light-emitting elements can have high emission efficiency.

Either or both of the light-emitting layers170and190may have a stacked structure of two layers like the light-emitting layers190aand190b, for example. Two kinds of light-emitting materials (a first compound and a second compound) for emitting light of different colors are used in the two light-emitting layers, so that light of a plurality of colors can be obtained at the same time. It is particularly preferable to select the light-emitting materials of the light-emitting layers so that white light can be obtained by combining light emissions from the light-emitting layers170and190.

Either or both of the light-emitting layers170and190may have a stacked structure of three or more layers, in which a layer not including a light-emitting material may be included.

In the above-described manner, by using the light-emitting element262aor262bincluding the light-emitting layer having at least one of the structures described in Embodiments 3 and 4 in pixels in a display device, a display device with high emission efficiency can be fabricated. Accordingly, the display device including the light-emitting element262aor262bcan have low power consumption.

For the other components of the light-emitting elements262aand262b, the components of the light-emitting element260aor260bor the light-emitting element in Embodiments 3 and 4 may be referred to.

Next, a method for fabricating a light-emitting element of one embodiment of the present invention is described below with reference toFIGS. 7A to 7CandFIGS. 8A to 8C. Here, a method for fabricating the light-emitting element262aillustrated inFIG. 6Ais described.

FIGS. 7A to 7CandFIGS. 8A to 8Care cross-sectional views illustrating a method for fabricating the light-emitting element of one embodiment of the present invention.

The method for fabricating the light-emitting element262adescribed below includes first to seventh steps.

In the first step, the electrodes (specifically the conductive layer101aof the electrode101, the conductive layer103aof the electrode103, and the conductive layer104aof the electrode104) of the light-emitting elements are formed over the substrate200(seeFIG. 7A).

In this embodiment, a conductive layer having a function of reflecting light is formed over the substrate200and processed into a desired shape; whereby the conductive layers101a,103a, and104aare formed. As the conductive layer having a function of reflecting light, an alloy film of silver, palladium, and copper (also referred to as an Ag—Pd—Cu film or APC) is used. The conductive layers101a,103a, and104aare preferably formed through a step of processing the same conductive layer, because the manufacturing cost can be reduced.

Note that a plurality of transistors may be formed over the substrate200before the first step. The plurality of transistors may be electrically connected to the conductive layers101a,103a, and104a.

In the second step, the conductive layer101bhaving a function of transmitting light is formed over the conductive layer101aof the electrode101, the conductive layer103bhaving a function of transmitting light is formed over the conductive layer103aof the electrode103, and the conductive layer104bhaving a function of transmitting light is formed over the conductive layer104aof the electrode104(seeFIG. 7B).

In this embodiment, the conductive layers101b,103b, and104beach having a function of transmitting light are formed over the conductive layers101a,103a, and104aeach having a function of reflecting light, respectively, whereby the electrode101, the electrode103, and the electrode104are formed. As the conductive layers101b,103b, and104b, ITSO films are used.

The conductive layers101b,103b, and104bhaving a function of transmitting light may be formed in a plurality of steps. When the conductive layers101b,103b, and104bhaving a function of transmitting light are formed in a plurality of steps, they can be formed to have thicknesses which enable microcavity structures appropriate in the respective regions.

In the third step, the partition wall145that covers end portions of the electrodes of the light-emitting element is formed (seeFIG. 7C).

The partition wall145includes an opening overlapping with the electrode. The conductive film exposed by the opening functions as the anode of the light-emitting element. As the partition wall145, a polyimide-based resin is used in this embodiment.

In the first to third steps, since there is no possibility of damaging the EL layer (a layer containing an organic compound), a variety of film formation methods and micromachining technologies can be employed. In this embodiment, a reflective conductive layer is formed by a sputtering method, a pattern is formed over the conductive layer by a lithography method, and then the conductive layer is processed into an island shape by a dry etching method or a wet etching method to form the conductive layer101aof the electrode101, the conductive layer103aof the electrode103, and the conductive layer104aof the electrode104. Then, a transparent conductive film is formed by a sputtering method, a pattern is formed over the transparent conductive film by a lithography method, and then the transparent conductive film is processed into island shapes by a wet etching method to form the electrodes101,103, and104.

The hole-injection layer111can be formed by co-evaporating a hole-transport material and a material containing an acceptor substance. Note that a co-evaporation method is an evaporation method in which a plurality of different substances are concurrently vaporized from respective different evaporation sources. The hole-transport layer112can be formed by evaporating a hole-transport material.

The light-emitting layer190can be formed by evaporating a guest material that emits light of at least one color selected from violet, blue, blue green, green, yellow green, yellow, orange, and red. As the guest material, a fluorescent or phosphorescent organic material can be used. The structure of the light-emitting layer described in Embodiments 3 and 4 is preferably employed. The light-emitting layer190may have a two-layer structure. In such a case, the two light-emitting layers each preferably contain a light-emitting material that emits light of a different color.

The electron-transport layer113can be formed by evaporating a substance having a high electron-transport property. The electron-injection layer114can be formed by evaporating a substance having a high electron-injection property.

The charge-generation layer115can be formed by evaporating a material obtained by adding an electron acceptor (acceptor) to a hole-transport material or a material obtained by adding an electron donor (donor) to an electron-transport material.

In the fifth step, the hole-injection layer116, the hole-transport layer117, the light-emitting layer170, the electron-transport layer118, the electron-injection layer119, and the electrode102are formed (seeFIG. 8B).

The hole-injection layer116can be formed by using a material and a method which are similar to those of the hole-injection layer111. The hole-transport layer117can be formed by using a material and a method which are similar to those of the hole-transport layer112.

The light-emitting layer170can be formed by evaporating a guest material that emits light of at least one color selected from violet, blue, blue green, green, yellow green, yellow, orange, and red. As the guest material, a fluorescent or phosphorescent organic compound can be used. The structure of the light-emitting layer described in Embodiments 3 and 4 is preferably employed. Note that at least one of the light-emitting layer170and the light-emitting layer190preferably includes any of the dibenzocarbazole compounds described in Embodiment 1. The light-emitting layer170and the light-emitting layer190preferably include light-emitting organic compounds exhibiting light of different colors.

The electron-transport layer118can be formed by using a material and a method which are similar to those of the electron-transport layer113. The electron-injection layer119can be formed by using a material and a method which are similar to those of the electron-injection layer114.

The electrode102can be formed by stacking a reflective conductive film and a light-transmitting conductive film. The electrode102may have a single-layer structure or a stacked-layer structure.

Through the above-described steps, the light-emitting element including the region222B, the region222G, and the region222R over the electrode101, the electrode103, and the electrode104, respectively, are formed over the substrate200.

In the sixth step, the light-blocking layer223, the optical element224B, the optical element224G, and the optical element224R are formed over the substrate220(seeFIG. 8C).

As the light-blocking layer223, a resin film containing black pigment is formed in a desired region. Then, the optical element224B, the optical element224G, and the optical element224R are formed over the substrate220and the light-blocking layer223. As the optical element224B, a resin film containing blue pigment is formed in a desired region. As the optical element224G, a resin film containing green pigment is formed in a desired region. As the optical element224R, a resin film containing red pigment is formed in a desired region.

In the seventh step, the light-emitting element formed over the substrate200is attached to the light-blocking layer223, the optical element224B, the optical element224G, and the optical element224R formed over the substrate220, and sealed with a sealant (not illustrated).

This embodiment shows an example of a mode where any of the dibenzocarbazole compounds described in Embodiment 1 is used in an active layer of a vertical transistor (a static induction transistor (SIT)), which is a kind of an organic semiconductor element.

In an element structure, between a source electrode301and a drain electrode302, a thin-film active layer330including any of the dibenzocarbazole compounds described in Embodiment 1 is provided and gate electrodes303are embedded in the active layer330, as illustrated inFIG. 9. The gate electrodes303are electrically connected to a means for applying a gate voltage, and the source electrode301and the drain electrode302are electrically connected to a means for controlling a voltage between the source electrode and the drain electrode.

In such an element structure, when a voltage is applied between the source electrode and the drain electrode without applying a voltage to the gate electrodes303, a current flows (the element is turned on). Then, when a voltage is applied to the gate electrodes303in that state, a depletion layer is formed in the periphery of the gate electrodes303, so that the current ceases flowing (the element is turned off). With such a mechanism, an organic semiconductor element300operates as a transistor.

In a vertical transistor, a material having both a carrier-transport property and a favorable film quality is required for an active layer like in a light-emitting element. Since each of the dibenzocarbazole compounds described in Embodiment 1 sufficiently meets these requirements, it can be suitably used.

In this embodiment, a display device of one embodiment of the present invention will be described below with reference toFIGS. 10A and 10B,FIGS. 11A and 11B,FIG. 12,FIGS. 13A and 13B,FIGS. 14A and 14B,FIG. 15,FIGS. 16A and 16B,FIG. 17, andFIGS. 18A and 18B.

Structure Example 1 of Display Device

FIG. 10Ais a top view illustrating a display device600andFIG. 10Bis a cross-sectional view taken along the dashed-dotted line A-B and the dashed-dotted line C-D inFIG. 10A. The display device600includes driver circuit portions (a signal line driver circuit portion601and a scan line driver circuit portion603) and a pixel portion602. Note that the signal line driver circuit portion601, the scan line driver circuit portion603, and the pixel portion602have a function of controlling light emission from a light-emitting element.

The display device600also includes an element substrate610, a sealing substrate604, a sealant605, a region607surrounded by the sealant605, a lead wiring608, and an FPC609.

Note that the lead wiring608is a wiring for transmitting signals to be input to the signal line driver circuit portion601and the scan line driver circuit portion603and for receiving a video signal, a clock signal, a start signal, a reset signal, and the like from the FPC609serving as an external input terminal. Although only the FPC609is illustrated here, the FPC609may be provided with a printed wiring board (PWB).

As the signal line driver circuit portion601, a CMOS circuit in which an n-channel transistor623and a p-channel transistor624are combined is formed. As the signal line driver circuit portion601or the scan line driver circuit portion603, various types of circuits such as a CMOS circuit, a PMOS circuit, or an NMOS circuit can be used. Although a driver in which a driver circuit portion is formed and a pixel are formed over the same surface of a substrate in the display device of this embodiment, the driver circuit portion is not necessarily formed over the substrate and can be formed outside the substrate.

The pixel portion602includes a switching transistor611, a current control transistor612, and a lower electrode613electrically connected to a drain of the current control transistor612. Note that a partition wall614is formed to cover end portions of the lower electrode613. As the partition wall614, for example, a positive type photosensitive acrylic resin film can be used.

In order to obtain favorable coverage, the partition wall614is formed to have a curved surface with curvature at its upper or lower end portion. For example, in the case of using a positive photosensitive acrylic as a material of the partition wall614, it is preferable that only the upper end portion of the partition wall614have a curved surface with curvature (the radius of the curvature being 0.2 μm to 3 μm). As the partition wall614, either a negative photosensitive resin or a positive photosensitive resin can be used.

Note that there is no particular limitation on a structure of each of the transistors (the transistors611,612,623, and624). For example, a staggered transistor can be used. In addition, there is no particular limitation on the polarity of these transistors. For these transistors, n-channel and p-channel transistors may be used, or either n-channel transistors or p-channel transistors may be used, for example. Furthermore, there is no particular limitation on the crystallinity of a semiconductor film used for these transistors. For example, an amorphous semiconductor film or a crystalline semiconductor film may be used. Examples of a semiconductor material include Group 14 semiconductors (e.g., a semiconductor including silicon), compound semiconductors (including oxide semiconductors), organic semiconductors, and the like. For example, it is preferable to use an oxide semiconductor that has an energy gap of 2 eV or more, preferably 2.5 eV or more and further preferably 3 eV or more, for the transistors, so that the off-state current of the transistors can be reduced. Examples of the oxide semiconductor include an In—Ga oxide and an In-M-Zn oxide (M is aluminum (Al), gallium (Ga), yttrium (Y), zirconium (Zr), lanthanum (La), cerium (Ce), tin (Sn), hafnium (Hf), or neodymium (Nd)).

An EL layer616and an upper electrode617are formed over the lower electrode613. Here, the lower electrode613functions as an anode and the upper electrode617functions as a cathode.

In addition, the EL layer616is formed by various methods such as an evaporation method with an evaporation mask, an ink-jet method, or a spin coating method. As another material included in the EL layer616, a low molecular compound or a high molecular compound (including an oligomer or a dendrimer) may be used.

Note that a light-emitting element618is formed with the lower electrode613, the EL layer616, and the upper electrode617. The light-emitting element618preferably has any of the structures described in Embodiments 3 to 5. In the case where the pixel portion includes a plurality of light-emitting elements, the pixel portion may include both any of the light-emitting elements described in Embodiments 3 to 5 and a light-emitting element having a different structure.

When the sealing substrate604and the element substrate610are attached to each other with the sealant605, the light-emitting element618is provided in the region607surrounded by the element substrate610, the sealing substrate604, and the sealant605. The region607is filled with a filler. In some cases, the region607is filled with an inert gas (nitrogen, argon, or the like) or filled with an ultraviolet curable resin or a thermosetting resin which can be used for the sealant605. For example, a polyvinyl chloride (PVC)-based resin, an acrylic-based resin, a polyimide-based resin, an epoxy-based resin, a silicone-based resin, a polyvinyl butyral (PVB)-based resin, or an ethylene vinyl acetate (EVA)-based resin can be used. It is preferable that the sealing substrate be provided with a recessed portion and a desiccant be provided in the recessed portion, in which case deterioration due to influence of moisture can be inhibited.

An optical element621is provided below the sealing substrate604to overlap with the light-emitting element618. A light-blocking layer622is provided below the sealing substrate604. The structures of the optical element621and the light-blocking layer622can be the same as those of the optical element and the light-blocking layer in Embodiment 5, respectively.

An epoxy-based resin or glass frit is preferably used for the sealant605. It is preferable that such a material do not transmit moisture or oxygen as much as possible. As the sealing substrate604, a glass substrate, a quartz substrate, or a plastic substrate formed of fiber reinforced plastic (FRP), poly(vinyl fluoride) (PVF), polyester, acrylic, or the like can be used.

In the above-described manner, the display device including any of the light-emitting elements and the optical elements which are described in Embodiments 3 to 5 can be obtained.

Structure Example 2 of Display Device

Next, another example of the display device is described with reference toFIGS. 11A and 11BandFIG. 12. Note thatFIGS. 11A and 11BandFIG. 12are each a cross-sectional view of a display device of one embodiment of the present invention.

InFIG. 11A, a substrate1001, a base insulating film1002, a gate insulating film1003, gate electrodes1006,1007, and1008, a first interlayer insulating film1020, a second interlayer insulating film1021, a peripheral portion1042, a pixel portion1040, a driver circuit portion1041, lower electrodes1024R,1024G, and1024B of light-emitting elements, a partition wall1025, an EL layer1028, an upper electrode1026of the light-emitting elements, a sealing layer1029, a sealing substrate1031, a sealant1032, and the like are illustrated.

InFIG. 11A, examples of the optical elements, coloring layers (a red coloring layer1034R, a green coloring layer1034G, and a blue coloring layer1034B) are provided on a transparent base material1033. Further, a light-blocking layer1035may be provided. The transparent base material1033provided with the coloring layers and the light-blocking layer is positioned and fixed to the substrate1001. Note that the coloring layers and the light-blocking layer are covered with an overcoat layer1036. In the structure inFIG. 11A, red light, green light, and blue light transmit the coloring layers, and thus an image can be displayed with the use of pixels of three colors.

FIG. 11Billustrates an example in which, as examples of the optical elements, the coloring layers (the red coloring layer1034R, the green coloring layer1034G, and the blue coloring layer1034B) are provided between the gate insulating film1003and the first interlayer insulating film1020. As in this structure, the coloring layers may be provided between the substrate1001and the sealing substrate1031.

FIG. 12illustrates an example in which, as examples of the optical elements, the coloring layers (the red coloring layer1034R, the green coloring layer1034G, and the blue coloring layer1034B) are provided between the first interlayer insulating film1020and the second interlayer insulating film1021. As in this structure, the coloring layers may be provided between the substrate1001and the sealing substrate1031.

The above-described display device has a structure in which light is extracted from the substrate1001side where the transistors are formed (a bottom-emission structure), but may have a structure in which light is extracted from the sealing substrate1031side (a top-emission structure).

Structure Example 3 of Display Device

FIGS. 13A and 13Bare each an example of a cross-sectional view of a display device having a top emission structure. Note thatFIGS. 13A and 13Bare each a cross-sectional view illustrating the display device of one embodiment of the present invention, and the driver circuit portion1041, the peripheral portion1042, and the like, which are illustrated inFIGS. 11A and 11BandFIG. 12, are not illustrated therein.

In this case, as the substrate1001, a substrate that does not transmit light can be used. The process up to the step of forming a connection electrode which connects the transistor and the anode of the light-emitting element is performed in a manner similar to that of the display device having a bottom-emission structure. Then, a third interlayer insulating film1037is formed to cover an electrode1022. This insulating film may have a planarization function. The third interlayer insulating film1037can be formed using a material similar to that of the second interlayer insulating film, or can be formed using any other various materials.

The lower electrodes1024R,1024G, and1024B of the light-emitting elements each function as an anode here, but may function as a cathode. Further, in the case of a display device having a top-emission structure as illustrated inFIGS. 13A and 13B, the lower electrodes1024R,1024G, and1024B preferably have a function of reflecting light. The upper electrode1026is provided over the EL layer1028. It is preferable that the upper electrode1026have a function of reflecting light and a function of transmitting light and that a microcavity structure be used between the upper electrode1026and the lower electrodes1024R,1024G, and1024B, in which case the intensity of light having a specific wavelength is increased.

In the case of a top-emission structure as illustrated inFIG. 13A, sealing can be performed with the sealing substrate1031on which the coloring layers (the red coloring layer1034R, the green coloring layer1034G, and the blue coloring layer1034B) are provided. The sealing substrate1031may be provided with the light-blocking layer1035which is positioned between pixels. Note that a light-transmitting substrate is favorably used as the sealing substrate1031.

FIG. 13Aillustrates the structure provided with the light-emitting elements and the coloring layers for the light-emitting elements as an example; however, the structure is not limited thereto. For example, as shown inFIG. 13B, a structure including the red coloring layer1034R and the blue coloring layer1034B but not including a green coloring layer may be employed to achieve full color display with the three colors of red, green, and blue. The structure as illustrated inFIG. 13Awhere the light-emitting elements are provided with the coloring layers is effective to suppress reflection of external light. In contrast, the structure as illustrated inFIG. 13Bwhere the light-emitting elements are provided with the red coloring layer and the blue coloring layer and without the green coloring layer is effective to reduce power consumption because of small energy loss of light emitted from the green light-emitting element.

Structure Example 4 of Display Device

Although a display device including sub-pixels of three colors (red, green, and blue) is described above, the number of colors of sub-pixels may be four (red, green, blue, and yellow, or red, green, blue, and white).FIGS. 14A and 14B,FIG. 15, andFIGS. 16A and 16Billustrate structures of display devices each including the lower electrodes1024R,1024G,1024B, and1024Y.FIGS. 14A and 14BandFIG. 15each illustrate a display device having a structure in which light is extracted from the substrate1001side on which transistors are formed (bottom-emission structure), andFIGS. 16A and 16Beach illustrate a display device having a structure in which light is extracted from the sealing substrate1031side (top-emission structure).

FIG. 14Aillustrates an example of a display device in which optical elements (the coloring layer1034R, the coloring layer1034G, the coloring layer1034B, and a coloring layer1034Y) are provided on the transparent base material1033.FIG. 14Billustrates an example of a display device in which optical elements (the coloring layer1034R, the coloring layer1034G, and the coloring layer1034B) are provided between the gate insulating film1003and the first interlayer insulating film1020.FIG. 15illustrates an example of a display device in which optical elements (the coloring layer1034R, the coloring layer1034G, the coloring layer1034B, and the coloring layer1034Y) are provided between the first interlayer insulating film1020and the second interlayer insulating film1021.

The coloring layer1034R transmits red light, the coloring layer1034G transmits green light, and the coloring layer1034B transmits blue light. The coloring layer1034Y transmits yellow light or transmits light of a plurality of colors selected from blue, green, yellow, and red. When the coloring layer1034Y can transmit light of a plurality of colors selected from blue, green, yellow, and red, light released from the coloring layer1034Y may be white light. Since the light-emitting element which transmits yellow or white light has high emission efficiency, the display device including the coloring layer1034Y can have lower power consumption.

In the top-emission display devices illustrated inFIGS. 16A and 16B, a light-emitting element including the lower electrode1024Y preferably has a microcavity structure between the lower electrode1024Y and the upper electrode1026as in the display device illustrated inFIG. 13A. In the display device illustrated inFIG. 16A, sealing can be performed with the sealing substrate1031on which the coloring layers (the red coloring layer1034R, the green coloring layer1034G, the blue coloring layer1034B, and the yellow coloring layer1034Y) are provided.

Light emitted through the microcavity and the yellow coloring layer1034Y has an emission spectrum in a yellow region. Since yellow is a color with a high luminosity factor, a light-emitting element emitting yellow light has high emission efficiency. Therefore, the display device ofFIG. 16Acan reduce power consumption.

FIG. 16Aillustrates the structure provided with the light-emitting elements and the coloring layers for the light-emitting elements as an example; however, the structure is not limited thereto. For example, as shown inFIG. 16B, a structure including the red coloring layer1034R, the green coloring layer1034G, and the blue coloring layer1034B but not including a yellow coloring layer may be employed to achieve full color display with the four colors of red, green, blue, and yellow or of red, green, blue, and white. The structure as illustrated inFIG. 16Awhere the light-emitting elements are provided with the coloring layers is effective to suppress reflection of external light. In contrast, the structure as illustrated inFIG. 16Bwhere the light-emitting elements are provided with the red coloring layer, the green coloring layer, and the blue coloring layer and without the yellow coloring layer is effective to reduce power consumption because of small energy loss of light emitted from the yellow or white light-emitting element.

Structure Example 5 of Display Device

Next, a display device of another embodiment of the present invention is described with reference toFIG. 17.FIG. 17is a cross-sectional view taken along the dashed-dotted line A-B and the dashed-dotted line C-D inFIG. 10A. Note that inFIG. 17, portions having functions similar to those of portions inFIG. 10Bare given the same reference numerals as inFIG. 10B, and a detailed description of the portions is omitted.

The display device600inFIG. 17includes a sealing layer607a, a sealing layer607b, and a sealing layer607cin a region607surrounded by the element substrate610, the sealing substrate604, and the sealant605. For one or more of the sealing layer607a, the sealing layer607b, and the sealing layer607c, a resin such as a polyvinyl chloride (PVC) based resin, an acrylic-based resin, a polyimide-based resin, an epoxy-based resin, a silicone-based resin, a polyvinyl butyral (PVB) based resin, or an ethylene vinyl acetate (EVA) based resin can be used. Alternatively, an inorganic material such as silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, aluminum oxide, or aluminum nitride can be used. The formation of the sealing layers607a,607b, and607ccan prevent deterioration of the light-emitting element618due to impurities such as water, which is preferable. In the case where the sealing layers607a,607b, and607care formed, the sealant605is not necessarily provided.

Alternatively, any one or two of the sealing layers607a,607b, and607cmay be provided or four or more sealing layers may be formed. When the sealing layer has a multilayer structure, the impurities such as water can be effectively prevented from entering the light-emitting element618which is inside the display device from the outside of the display device600. In the case where the sealing layer has a multilayer structure, a resin and an inorganic material are preferably stacked.

Structure Example 6 of Display Device

Although the display devices in the structure examples 1 to 4 in this embodiment each have a structure including optical elements, one embodiment of the present invention does not necessarily include an optical element.

FIGS. 18A and 18Beach illustrate a display device having a structure in which light is extracted from the sealing substrate1031side (a top-emission display device).FIG. 18Aillustrates an example of a display device including a light-emitting layer1028R, a light-emitting layer1028G, and a light-emitting layer1028B.FIG. 18Billustrates an example of a display device including a light-emitting layer1028R, a light-emitting layer1028G, a light-emitting layer1028B, and a light-emitting layer1028Y.

The light-emitting layer1028R has a function of exhibiting red light, the light-emitting layer1028G has a function of exhibiting green light, and the light-emitting layer1028B has a function of exhibiting blue light. The light-emitting layer1028Y has a function of exhibiting yellow light or a function of exhibiting light of a plurality of colors selected from blue, green, and red. The light-emitting layer1028Y may exhibit white light. Since the light-emitting element which exhibits yellow or white light has high light emission efficiency, the display device including the light-emitting layer1028Y can have lower power consumption.

Each of the display devices inFIGS. 18A and 18Bdoes not necessarily include coloring layers serving as optical elements because EL layers exhibiting light of different colors are included in sub-pixels.

For the sealing layer1029, a resin such as a polyvinyl chloride (PVC) based resin, an acrylic-based resin, a polyimide-based resin, an epoxy-based resin, a silicone-based resin, a polyvinyl butyral (PVB) based resin, or an ethylene vinyl acetate (EVA) based resin can be used. Alternatively, an inorganic material such as silicon oxide, silicon oxynitride, silicon nitride oxide, silicon nitride, aluminum oxide, or aluminum nitride can be used. The formation of the sealing layer1029can prevent deterioration of the light-emitting element due to impurities such as water, which is preferable.

Alternatively, the sealing layer1029may have a single-layer or two-layer structure, or four or more sealing layers may be formed as the sealing layer1029. When the sealing layer has a multilayer structure, the impurities such as water can be effectively prevented from entering the inside of the display device from the outside of the display device. In the case where the sealing layer has a multilayer structure, a resin and an inorganic material are preferably stacked.

Note that the sealing substrate1031has a function of protecting the light-emitting element. Thus, for the sealing substrate1031, a flexible substrate or a film can be used.

The structures described in this embodiment can be combined as appropriate with any of the other structures in this embodiment and the other embodiments.

In this embodiment, a display device including a light-emitting element of one embodiment of the present invention will be described with reference toFIGS. 19A and 19B,FIGS. 20A and 20B, andFIGS. 21A and 21B.

FIG. 19Ais a block diagram illustrating the display device of one embodiment of the present invention, andFIG. 19Bis a circuit diagram illustrating a pixel circuit of the display device of one embodiment of the present invention.

<Description of Display Device>

The display device illustrated inFIG. 19Aincludes a region including pixels of display elements (the region is hereinafter referred to as a pixel portion802), a circuit portion provided outside the pixel portion802and including circuits for driving the pixels (the portion is hereinafter referred to as a driver circuit portion804), circuits having a function of protecting elements (the circuits are hereinafter referred to as protection circuits806), and a terminal portion807. Note that the protection circuits806are not necessarily provided.

A part or the whole of the driver circuit portion804is preferably formed over a substrate over which the pixel portion802is formed, in which case the number of components and the number of terminals can be reduced. When a part or the whole of the driver circuit portion804is not formed over the substrate over which the pixel portion802is formed, the part or the whole of the driver circuit portion804can be mounted by COG or tape automated bonding (TAB).

The pixel portion802includes a plurality of circuits for driving display elements arranged in X rows (X is a natural number of 2 or more) and Y columns (Y is a natural number of 2 or more) (such circuits are hereinafter referred to as pixel circuits801). The driver circuit portion804includes driver circuits such as a circuit for supplying a signal (scan signal) to select a pixel (the circuit is hereinafter referred to as a scan line driver circuit804a) and a circuit for supplying a signal (data signal) to drive a display element in a pixel (the circuit is hereinafter referred to as a signal line driver circuit804b).

The scan line driver circuit804aincludes a shift register or the like. Through the terminal portion807, the scan line driver circuit804areceives a signal for driving the shift register and outputs a signal. For example, the scan line driver circuit804areceives a start pulse signal, a clock signal, or the like and outputs a pulse signal. The scan line driver circuit804ahas a function of controlling the potentials of wirings supplied with scan signals (such wirings are hereinafter referred to as scan lines GL_1to GL_X). Note that a plurality of scan line driver circuits804amay be provided to control the scan lines GL_1to GL_X separately. Alternatively, the scan line driver circuit804ahas a function of supplying an initialization signal. Without being limited thereto, the scan line driver circuit804acan supply another signal.

The signal line driver circuit804bincludes a shift register or the like. The signal line driver circuit804breceives a signal (image signal) from which a data signal is derived, as well as a signal for driving the shift register, through the terminal portion807. The signal line driver circuit804bhas a function of generating a data signal to be written to the pixel circuit801which is based on the image signal. In addition, the signal line driver circuit804bhas a function of controlling output of a data signal in response to a pulse signal produced by input of a start pulse signal, a clock signal, or the like. Furthermore, the signal line driver circuit804bhas a function of controlling the potentials of wirings supplied with data signals (such wirings are hereinafter referred to as data lines DL_1to DL_Y). Alternatively, the signal line driver circuit804bhas a function of supplying an initialization signal. Without being limited thereto, the signal line driver circuit804bcan supply another signal.

The signal line driver circuit804bincludes a plurality of analog switches or the like, for example. The signal line driver circuit804bcan output, as the data signals, signals obtained by time-dividing the image signal by sequentially turning on the plurality of analog switches. The signal line driver circuit804bmay include a shift register or the like.

A pulse signal and a data signal are input to each of the plurality of pixel circuits801through one of the plurality of scan lines GL supplied with scan signals and one of the plurality of data lines DL supplied with data signals, respectively. Writing and holding of the data signal to and in each of the plurality of pixel circuits801are controlled by the scan line driver circuit804a. For example, to the pixel circuit801in the m-th row and the n-th column (m is a natural number of less than or equal to X, and n is a natural number of less than or equal to Y), a pulse signal is input from the scan line driver circuit804athrough the scan line GL_m, and a data signal is input from the signal line driver circuit804bthrough the data line DL_n in accordance with the potential of the scan line GL_m.

The protection circuit806shown inFIG. 19Ais connected to, for example, the scan line GL between the scan line driver circuit804aand the pixel circuit801. Alternatively, the protection circuit806is connected to the data line DL between the signal line driver circuit804band the pixel circuit801. Alternatively, the protection circuit806can be connected to a wiring between the scan line driver circuit804aand the terminal portion807. Alternatively, the protection circuit806can be connected to a wiring between the signal line driver circuit804band the terminal portion807. Note that the terminal portion807means a portion having terminals for inputting power, control signals, and image signals to the display device from external circuits.

The protection circuit806is a circuit that electrically connects a wiring connected to the protection circuit to another wiring when a potential out of a certain range is applied to the wiring connected to the protection circuit.

As illustrated inFIG. 19A, the protection circuits806are connected to the pixel portion802and the driver circuit portion804, so that the resistance of the display device to overcurrent generated by electrostatic discharge (ESD) or the like can be improved. Note that the configuration of the protection circuits806is not limited to that, and for example, a configuration in which the protection circuits806are connected to the scan line driver circuit804aor a configuration in which the protection circuits806are connected to the signal line driver circuit804bmay be employed. Alternatively, the protection circuits806may be configured to be connected to the terminal portion807.

InFIG. 19A, an example in which the driver circuit portion804includes the scan line driver circuit804aand the signal line driver circuit804bis shown; however, the structure is not limited thereto. For example, only the scan line driver circuit804amay be formed and a separately prepared substrate where a signal line driver circuit is formed (e.g., a driver circuit substrate formed with a single crystal semiconductor film or a polycrystalline semiconductor film) may be mounted.

Structure Example of Pixel Circuit

Each of the plurality of pixel circuits801inFIG. 19Acan have a structure illustrated inFIG. 19B, for example.

One of a source electrode and a drain electrode of the transistor852is electrically connected to a wiring to which a data signal is supplied (a data line DL_n). A gate electrode of the transistor852is electrically connected to a wiring to which a gate signal is supplied (a scan line GL_m).

The transistor852has a function of controlling whether to write a data signal.

One of a pair of electrodes of the capacitor862is electrically connected to a wiring to which a potential is supplied (hereinafter referred to as a potential supply line VL_a), and the other is electrically connected to the other of the source electrode and the drain electrode of the transistor852.

The capacitor862functions as a storage capacitor for storing written data.

One of a source electrode and a drain electrode of the transistor854is electrically connected to the potential supply line VL_a. Furthermore, a gate electrode of the transistor854is electrically connected to the other of the source electrode and the drain electrode of the transistor852.

One of an anode and a cathode of the light-emitting element872is electrically connected to a potential supply line VL_b, and the other is electrically connected to the other of the source electrode and the drain electrode of the transistor854.

As the light-emitting element872, any of the light-emitting elements described in Embodiments 3 to 5 can be used.

Note that a high power supply potential VDD is supplied to one of the potential supply line VL_a and the potential supply line VL_b, and a low power supply potential VSS is supplied to the other.

In the display device including the pixel circuits801inFIG. 19B, the pixel circuits801are sequentially selected row by row by the scan line driver circuit804ainFIG. 19A, for example, whereby the transistors852are turned on and a data signal is written.

When the transistors852are turned off, the pixel circuits801in which the data has been written are brought into a holding state. Furthermore, the amount of current flowing between the source electrode and the drain electrode of the transistor854is controlled in accordance with the potential of the written data signal. The light-emitting element872emits light with a luminance corresponding to the amount of flowing current. This operation is sequentially performed row by row; thus, an image is displayed.

Alternatively, the pixel circuit can have a function of compensating variation in threshold voltages or the like of a transistor.FIGS. 20A and 20BandFIGS. 21A and 21Billustrate examples of the pixel circuit.

The pixel circuit illustrated inFIG. 20Aincludes six transistors (transistors303_1to303_6), a capacitor304, and a light-emitting element305. The pixel circuit illustrated inFIG. 20Ais electrically connected to wirings301_1to301_5and wirings302_1and302_2. Note that as the transistors303_1to303_6, for example, p-channel transistors can be used.

The pixel circuit shown inFIG. 20Bhas a configuration in which a transistor303_7is added to the pixel circuit shown inFIG. 20A. The pixel circuit illustrated inFIG. 20Bis electrically connected to wirings301_6and301_7. The wirings301_5and301_6may be electrically connected to each other. Note that as the transistor303_7, for example, a p-channel transistor can be used.

The pixel circuit shown inFIG. 21Aincludes six transistors (transistors308_1to308_6), the capacitor304, and the light-emitting element305. The pixel circuit illustrated inFIG. 21Ais electrically connected to wirings306_1to306_3and wirings307_1to307_3. The wirings306_1and306_3may be electrically connected to each other. Note that as the transistors308_1to308_6, for example, p-channel transistors can be used.

The pixel circuit illustrated inFIG. 21Bincludes two transistors (transistors309_1and309_2), two capacitors (capacitors304_1and304_2), and the light-emitting element305. The pixel circuit illustrated inFIG. 21Bis electrically connected to wirings311_1to311_3and wirings312_1and312_2. With the configuration of the pixel circuit illustrated inFIG. 21B, the pixel circuit can be driven by a voltage inputting current driving method (also referred to as CVCC). Note that as the transistors309_1and309_2, for example, p-channel transistors can be used.

A light-emitting element of one embodiment of the present invention can be used for an active matrix method in which an active element is included in a pixel of a display device or a passive matrix method in which an active element is not included in a pixel of a display device.

In the active matrix method, as an active element (a non-linear element), not only a transistor but also a variety of active elements (non-linear elements) can be used. For example, a metal insulator metal (MIM), a thin film diode (TFD), or the like can also be used. Since these elements can be formed with a smaller number of manufacturing steps, manufacturing cost can be reduced or yield can be improved. Alternatively, since the size of these elements is small, the aperture ratio can be improved, so that power consumption can be reduced and higher luminance can be achieved.

As a method other than the active matrix method, the passive matrix method in which an active element (a non-linear element) is not used can also be used. Since an active element (a non-linear element) is not used, the number of manufacturing steps is small, so that manufacturing cost can be reduced or yield can be improved. Alternatively, since an active element (a non-linear element) is not used, the aperture ratio can be improved, so that power consumption can be reduced or higher luminance can be achieved, for example.

In this embodiment, a display device including a light-emitting element of one embodiment of the present invention and an electronic device in which the display device is provided with an input device will be described with reference toFIGS. 22A and 22B,FIGS. 23A to 23C,FIGS. 24A and 24B,FIGS. 25A and 25B, andFIG. 26.

In this embodiment, a touch panel2000including a display device and an input device will be described as an example of an electronic device. In addition, an example in which a touch sensor is included as an input device will be described.

FIGS. 22A and 22Bare perspective views of the touch panel2000. Note thatFIGS. 22A and 22Billustrate only main components of the touch panel2000for simplicity.

The touch panel2000includes a display device2501and a touch sensor2595(seeFIG. 22B). The touch panel2000also includes a substrate2510, a substrate2570, and a substrate2590. The substrate2510, the substrate2570, and the substrate2590each have flexibility. Note that one or all of the substrates2510,2570, and2590may be inflexible.

The display device2501includes a plurality of pixels over the substrate2510and a plurality of wirings2511through which signals are supplied to the pixels. The plurality of wirings2511are led to a peripheral portion of the substrate2510, and parts of the plurality of wirings2511form a terminal2519. The terminal2519is electrically connected to an FPC2509(1). The plurality of wirings2511can supply signals from a signal line driver circuit2503s(1) to the plurality of pixels.

The substrate2590includes the touch sensor2595and a plurality of wirings2598electrically connected to the touch sensor2595. The plurality of wirings2598are led to a peripheral portion of the substrate2590, and parts of the plurality of wirings2598form a terminal. The terminal is electrically connected to an FPC2509(2). Note that inFIG. 22B, electrodes, wirings, and the like of the touch sensor2595provided on the back side of the substrate2590(the side facing the substrate2510) are indicated by solid lines for clarity.

As the touch sensor2595, a capacitive touch sensor can be used. Examples of the capacitive touch sensor are a surface capacitive touch sensor and a projected capacitive touch sensor.

Examples of the projected capacitive touch sensor are a self capacitive touch sensor and a mutual capacitive touch sensor, which differ mainly in the driving method. The use of a mutual capacitive type is preferable because multiple points can be sensed simultaneously.

Note that the touch sensor2595illustrated inFIG. 22Bis an example of using a projected capacitive touch sensor.

Note that a variety of sensors that can sense proximity or touch of a sensing target such as a finger can be used as the touch sensor2595.

The projected capacitive touch sensor2595includes electrodes2591and electrodes2592. The electrodes2591are electrically connected to any of the plurality of wirings2598, and the electrodes2592are electrically connected to any of the other wirings2598.

The electrodes2592each have a shape of a plurality of quadrangles arranged in one direction with one corner of a quadrangle connected to one corner of another quadrangle as illustrated inFIGS. 22A and 22B.

The electrodes2591each have a quadrangular shape and are arranged in a direction intersecting with the direction in which the electrodes2592extend.

A wiring2594electrically connects two electrodes2591between which the electrode2592is positioned. The intersecting area of the electrode2592and the wiring2594is preferably as small as possible. Such a structure allows a reduction in the area of a region where the electrodes are not provided, reducing variation in transmittance. As a result, variation in luminance of light passing through the touch sensor2595can be reduced.

Note that the shapes of the electrodes2591and the electrodes2592are not limited thereto and can be any of a variety of shapes. For example, a structure may be employed in which the plurality of electrodes2591are arranged so that gaps between the electrodes2591are reduced as much as possible, and the electrodes2592are spaced apart from the electrodes2591with an insulating layer interposed therebetween to have regions not overlapping with the electrodes2591. In this case, it is preferable to provide, between two adjacent electrodes2592, a dummy electrode electrically insulated from these electrodes because the area of regions having different transmittances can be reduced.

<Description of Display Device>

Next, the display device2501will be described in detail with reference toFIG. 23A.FIG. 23Acorresponds to a cross-sectional view taken along dashed-dotted line X1-X2inFIG. 22B.

The display device2501includes a plurality of pixels arranged in a matrix. Each of the pixels includes a display element and a pixel circuit for driving the display element.

In the following description, an example of using a light-emitting element that emits white light as a display element will be described; however, the display element is not limited to such an element. For example, light-emitting elements that emit light of different colors may be included so that the light of different colors can be emitted from adjacent pixels.

For the substrate2510and the substrate2570, for example, a flexible material with a vapor permeability of lower than or equal to 1×10−5g·m−2·day−1, preferably lower than or equal to 1×10−6g·m−2·day−1can be favorably used. Alternatively, materials whose thermal expansion coefficients are substantially equal to each other are preferably used for the substrate2510and the substrate2570. For example, the coefficients of linear expansion of the materials are preferably lower than or equal to 1×10−3/K, further preferably lower than or equal to 5×10−5/K, and still further preferably lower than or equal to 1×10−5/K.

Note that the substrate2510is a stacked body including an insulating layer2510afor preventing impurity diffusion into the light-emitting element, a flexible substrate2510b, and an adhesive layer2510cfor attaching the insulating layer2510aand the flexible substrate2510bto each other. The substrate2570is a stacked body including an insulating layer2570afor preventing impurity diffusion into the light-emitting element, a flexible substrate2570b, and an adhesive layer2570cfor attaching the insulating layer2570aand the flexible substrate2570bto each other.

For the adhesive layer2510cand the adhesive layer2570c, for example, polyester, polyolefin, polyamide (e.g., nylon, aramid), polyimide, polycarbonate, or an acrylic resin, polyurethane, or an epoxy resin can be used. Alternatively, a material that includes a resin having a siloxane bond such as silicone can be used.

A sealing layer2560is provided between the substrate2510and the substrate2570. The sealing layer2560preferably has a refractive index higher than that of air. In the case where light is extracted to the sealing layer2560side as illustrated inFIG. 23A, the sealing layer2560can also serve as an optical adhesive layer.

A sealant may be formed in the peripheral portion of the sealing layer2560. With the use of the sealant, a light-emitting element2550R can be provided in a region surrounded by the substrate2510, the substrate2570, the sealing layer2560, and the sealant. Note that an inert gas (such as nitrogen and argon) may be used instead of the sealing layer2560. A drying agent may be provided in the inert gas so as to adsorb moisture or the like. A resin such as an acrylic resin or an epoxy resin may be used. An epoxy-based resin or a glass frit is preferably used as the sealant. As a material used for the sealant, a material which is impermeable to moisture and oxygen is preferably used.

The display device2501includes a pixel2502R. The pixel2502R includes a light-emitting module2580R.

The pixel2502R includes the light-emitting element2550R and a transistor2502tthat can supply electric power to the light-emitting element2550R. Note that the transistor2502tfunctions as part of the pixel circuit. The light-emitting module2580R includes the light-emitting element2550R and a coloring layer2567R.

The light-emitting element2550R includes a lower electrode, an upper electrode, and an EL layer between the lower electrode and the upper electrode. As the light-emitting element2550R, any of the light-emitting elements described in Embodiments3to 5 can be used.

A microcavity structure may be employed between the lower electrode and the upper electrode so as to increase the intensity of light having a specific wavelength.

In the case where the sealing layer2560is provided on the light extraction side, the sealing layer2560is in contact with the light-emitting element2550R and the coloring layer2567R.

The coloring layer2567R is positioned in a region overlapping with the light-emitting element2550R. Accordingly, part of light emitted from the light-emitting element2550R passes through the coloring layer2567R and is emitted to the outside of the light-emitting module2580R as indicated by an arrow in the drawing.

The display device2501includes a light-blocking layer2567BM on the light extraction side. The light-blocking layer2567BM is provided so as to surround the coloring layer2567R.

The coloring layer2567R is a coloring layer having a function of transmitting light in a particular wavelength region. For example, a color filter for transmitting light in a red wavelength region, a color filter for transmitting light in a green wavelength region, a color filter for transmitting light in a blue wavelength region, a color filter for transmitting light in a yellow wavelength region, or the like can be used. Each color filter can be formed with any of various materials by a printing method, an inkjet method, an etching method using a photolithography technique, or the like.

An insulating layer2521is provided in the display device2501. The insulating layer2521covers the transistor2502t. Note that the insulating layer2521has a function of covering unevenness caused by the pixel circuit. The insulating layer2521may have a function of suppressing impurity diffusion. This can prevent the reliability of the transistor2502tor the like from being lowered by impurity diffusion.

The light-emitting element2550R is formed over the insulating layer2521. A partition2528is provided so as to overlap with an end portion of the lower electrode of the light-emitting element2550R. Note that a spacer for controlling the distance between the substrate2510and the substrate2570may be formed over the partition2528.

A scan line driver circuit2503g(1) includes a transistor2503tand a capacitor2503c. Note that the driver circuit can be formed in the same process and over the same substrate as those of the pixel circuits.

The wirings2511through which signals can be supplied are provided over the substrate2510. The terminal2519is provided over the wirings2511. The FPC2509(1) is electrically connected to the terminal2519. The FPC2509(1) has a function of supplying a video signal, a clock signal, a start signal, a reset signal, or the like. Note that the FPC2509(1) may be provided with a PWB.

In the display device2501, transistors with any of a variety of structures can be used.FIG. 23Aillustrates an example of using bottom-gate transistors; however, the present invention is not limited to this example, and top-gate transistors may be used in the display device2501as illustrated inFIG. 23B.

In addition, there is no particular limitation on the polarity of the transistor2502tand the transistor2503t. For these transistors, n-channel and p-channel transistors may be used, or either n-channel transistors or p-channel transistors may be used, for example. Furthermore, there is no particular limitation on the crystallinity of a semiconductor film used for the transistors2502tand2503t. For example, an amorphous semiconductor film or a crystalline semiconductor film may be used. Examples of semiconductor materials include Group 14 semiconductors (e.g., a semiconductor including silicon), compound semiconductors (including oxide semiconductors), organic semiconductors, and the like. An oxide semiconductor that has an energy gap of 2 eV or more, preferably 2.5 eV or more, further preferably 3 eV or more is preferably used for one of the transistors2502tand2503tor both, so that the off-state current of the transistors can be reduced. Examples of the oxide semiconductors include an In—Ga oxide, an In-M-Zn oxide (M represents Al, Ga, Y, Zr, La, Ce, Sn, Hf, or Nd), and the like.

<Description of Touch Sensor>

Next, the touch sensor2595will be described in detail with reference toFIG. 23C.FIG. 23Ccorresponds to a cross-sectional view taken along dashed-dotted line X3-X4inFIG. 22B.

The touch sensor2595includes the electrodes2591and the electrodes2592provided in a staggered arrangement on the substrate2590, an insulating layer2593covering the electrodes2591and the electrodes2592, and the wiring2594that electrically connects the adjacent electrodes2591to each other.

The electrodes2591and the electrodes2592are formed using a light-transmitting conductive material. As a light-transmitting conductive material, a conductive oxide such as indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zinc oxide to which gallium is added can be used. Note that a film including graphene may be used as well. The film including graphene can be formed, for example, by reducing a film containing graphene oxide. As a reducing method, a method with application of heat or the like can be employed.

The electrodes2591and the electrodes2592may be formed by, for example, depositing a light-transmitting conductive material on the substrate2590by a sputtering method and then removing an unnecessary portion by any of various pattern forming techniques such as photolithography.

Examples of a material for the insulating layer2593are a resin such as an acrylic resin or an epoxy resin, a resin having a siloxane bond such as silicone, and an inorganic insulating material such as silicon oxide, silicon oxynitride, or aluminum oxide.

Openings reaching the electrodes2591are formed in the insulating layer2593, and the wiring2594electrically connects the adjacent electrodes2591. A light-transmitting conductive material can be favorably used as the wiring2594because the aperture ratio of the touch panel can be increased. Moreover, a material with higher conductivity than the conductivities of the electrodes2591and2592can be favorably used for the wiring2594because electric resistance can be reduced.

One electrode2592extends in one direction, and a plurality of electrodes2592are provided in the form of stripes. The wiring2594intersects with the electrode2592.

Adjacent electrodes2591are provided with one electrode2592provided therebetween. The wiring2594electrically connects the adjacent electrodes2591.

Note that the plurality of electrodes2591are not necessarily arranged in the direction orthogonal to one electrode2592and may be arranged to intersect with one electrode2592at an angle of more than 0 degrees and less than 90 degrees.

The wiring2598is electrically connected to any of the electrodes2591and2592. Part of the wiring2598functions as a terminal. For the wiring2598, a metal material such as aluminum, gold, platinum, silver, nickel, titanium, tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium or an alloy material containing any of these metal materials can be used.

Note that an insulating layer that covers the insulating layer2593and the wiring2594may be provided to protect the touch sensor2595.

A connection layer2599electrically connects the wiring2598to the FPC2509(2).

As the connection layer2599, any of various anisotropic conductive films (ACF), anisotropic conductive pastes (ACP), or the like can be used.

Next, the touch panel2000will be described in detail with reference toFIG. 24A.FIG. 24Acorresponds to a cross-sectional view taken along dashed-dotted line X5-X6inFIG. 22A.

In the touch panel2000illustrated inFIG. 24A, the display device2501described with reference toFIG. 23Aand the touch sensor2595described with reference toFIG. 23Care attached to each other.

The touch panel2000illustrated inFIG. 24Aincludes an adhesive layer2597and an anti-reflective layer2567pin addition to the components described with reference toFIGS. 23A and 23C.

The adhesive layer2597is provided in contact with the wiring2594. Note that the adhesive layer2597attaches the substrate2590to the substrate2570so that the touch sensor2595overlaps with the display device2501. The adhesive layer2597preferably has a light-transmitting property. A heat curable resin or an ultraviolet curable resin can be used for the adhesive layer2597. For example, an acrylic resin, a urethane-based resin, an epoxy-based resin, or a siloxane-based resin can be used.

The anti-reflective layer2567pis positioned in a region overlapping with pixels. As the anti-reflective layer2567p, a circularly polarizing plate can be used, for example.

Next, a touch panel having a structure different from that illustrated inFIG. 24Awill be described with reference toFIG. 24B.

FIG. 24Bis a cross-sectional view of a touch panel2001. The touch panel2001illustrated inFIG. 24Bdiffers from the touch panel2000illustrated inFIG. 24Ain the position of the touch sensor2595relative to the display device2501. Different parts are described in detail below, and the above description of the touch panel2000is referred to for the other similar parts.

The coloring layer2567R is positioned in a region overlapping with the light-emitting element2550R. The light-emitting element2550R illustrated inFIG. 24Bemits light to the side where the transistor2502tis provided. Accordingly, part of light emitted from the light-emitting element2550R passes through the coloring layer2567R and is emitted to the outside of the light-emitting module2580R as indicated by an arrow inFIG. 24B.

The touch sensor2595is provided on the substrate2510side of the display device2501.

The adhesive layer2597is provided between the substrate2510and the substrate2590and attaches the touch sensor2595to the display device2501.

As illustrated inFIG. 24A or 24B, light may be emitted from the light-emitting element through one or both of the substrate2510and the substrate2570.

<Description of Method for Driving Touch Panel>

Next, an example of a method for driving a touch panel will be described with reference toFIGS. 25A and 25B.

FIG. 25Ais a block diagram illustrating the structure of a mutual capacitive touch sensor.FIG. 25Aillustrates a pulse voltage output circuit2601and a current sensing circuit2602. Note that inFIG. 25A, six wirings X1to X6represent the electrodes2621to which a pulse voltage is applied, and six wirings Y1to Y6represent the electrodes2622that detect changes in current.FIG. 25Aalso illustrates capacitors2603that are each formed in a region where the electrodes2621and2622overlap with each other. Note that functional replacement between the electrodes2621and2622is possible.

The pulse voltage output circuit2601is a circuit for sequentially applying a pulse voltage to the wirings X1to X6. By application of a pulse voltage to the wirings X1to X6, an electric field is generated between the electrodes2621and2622of the capacitor2603. When the electric field between the electrodes is shielded, for example, a change occurs in the capacitor2603(mutual capacitance). The approach or contact of a sensing target can be sensed by utilizing this change.

The current sensing circuit2602is a circuit for detecting changes in current flowing through the wirings Y1to Y6that are caused by the change in mutual capacitance in the capacitor2603. No change in current value is detected in the wirings Y1to Y6when there is no approach or contact of a sensing target, whereas a decrease in current value is detected when mutual capacitance is decreased owing to the approach or contact of a sensing target. Note that an integrator circuit or the like is used for sensing of current values.

FIG. 25Bis a timing chart showing input and output waveforms in the mutual capacitive touch sensor illustrated inFIG. 25A. InFIG. 25B, sensing of a sensing target is performed in all the rows and columns in one frame period.FIG. 25Bshows a period when a sensing target is not sensed (not touched) and a period when a sensing target is sensed (touched). InFIG. 25B, sensed current values of the wirings Y1to Y6are shown as the waveforms of voltage values.

A pulse voltage is sequentially applied to the wirings X1to X6, and the waveforms of the wirings Y1to Y6change in accordance with the pulse voltage. When there is no approach or contact of a sensing target, the waveforms of the wirings Y1to Y6change uniformly in accordance with changes in the voltages of the wirings X1to X6. The current value is decreased at the point of approach or contact of a sensing target and accordingly the waveform of the voltage value changes.

By detecting a change in mutual capacitance in this manner, the approach or contact of a sensing target can be sensed.

AlthoughFIG. 25Aillustrates a passive matrix type touch sensor in which only the capacitor2603is provided at the intersection of wirings as a touch sensor, an active matrix type touch sensor including a transistor and a capacitor may be used.FIG. 26illustrates an example of a sensor circuit included in an active matrix type touch sensor.

A signal G2is input to a gate of the transistor2613. A voltage VRES is applied to one of a source and a drain of the transistor2613, and one electrode of the capacitor2603and a gate of the transistor2611are electrically connected to the other of the source and the drain of the transistor2613. One of a source and a drain of the transistor2611is electrically connected to one of a source and a drain of the transistor2612, and a voltage VSS is applied to the other of the source and the drain of the transistor2611. A signal G1is input to a gate of the transistor2612, and a wiring ML is electrically connected to the other of the source and the drain of the transistor2612. The voltage VSS is applied to the other electrode of the capacitor2603.

Next, the operation of the sensor circuit inFIG. 26will be described. First, a potential for turning on the transistor2613is supplied as the signal G2, and a potential with respect to the voltage VRES is thus applied to the node n connected to the gate of the transistor2611. Then, a potential for turning off the transistor2613is applied as the signal G2, whereby the potential of the node n is maintained.

Then, mutual capacitance of the capacitor2603changes owing to the approach or contact of a sensing target such as a finger, and accordingly the potential of the node n is changed from VRES.

In reading operation, a potential for turning on the transistor2612is supplied as the signal G1. A current flowing through the transistor2611, that is, a current flowing through the wiring ML is changed in accordance with the potential of the node n. By sensing this current, the approach or contact of a sensing target can be sensed.

In each of the transistors2611,2612, and2613, an oxide semiconductor layer is preferably used as a semiconductor layer in which a channel region is formed. In particular, such a transistor is preferably used as the transistor2613so that the potential of the node n can be held for a long time and the frequency of operation of resupplying VRES to the node n (refresh operation) can be reduced.

In this embodiment, a display module and electronic devices including a light-emitting element of one embodiment of the present invention will be described with reference toFIG. 27,FIGS. 28A to 28G,FIGS. 29A to 29F,FIGS. 30A to 30D, andFIGS. 31A and 31B.

In a display module8000inFIG. 27, a touch sensor8004connected to an FPC8003, a display device8006connected to an FPC8005, a frame8009, a printed board8010, and a battery8011are provided between an upper cover8001and a lower cover8002.

The light-emitting element of one embodiment of the present invention can be used for the display device8006, for example.

The shapes and sizes of the upper cover8001and the lower cover8002can be changed as appropriate in accordance with the sizes of the touch sensor8004and the display device8006.

The touch sensor8004can be a resistive touch sensor or a capacitive touch sensor and may be formed to overlap with the display device8006. A counter substrate (sealing substrate) of the display device8006can have a touch sensor function. A photosensor may be provided in each pixel of the display device8006so that an optical touch sensor is obtained.

The frame8009protects the display device8006and also serves as an electromagnetic shield for blocking electromagnetic waves generated by the operation of the printed board8010. The frame8009may serve as a radiator plate.

The printed board8010has a power supply circuit and a signal processing circuit for outputting a video signal and a clock signal. As a power source for supplying power to the power supply circuit, an external commercial power source or the battery8011provided separately may be used. The battery8011can be omitted in the case of using a commercial power source.

The display module8000can be additionally provided with a member such as a polarizing plate, a retardation plate, or a prism sheet.

The electronic devices illustrated inFIGS. 28A to 28Gcan have a variety of functions, for example, a function of displaying a variety of data (a still image, a moving image, a text image, and the like) on the display portion, a touch sensor function, a function of displaying a calendar, date, time, and the like, a function of controlling a process with a variety of software (programs), a wireless communication function, a function of being connected to a variety of computer networks with a wireless communication function, a function of transmitting and receiving a variety of data with a wireless communication function, a function of reading a program or data stored in a memory medium and displaying the program or data on the display portion, and the like. Note that functions that can be provided for the electronic devices illustrated inFIGS. 28A to 28Gare not limited to those described above, and the electronic devices can have a variety of functions. Although not illustrated inFIGS. 28A to 28G, the electronic devices may include a plurality of display portions. The electronic devices may have a camera or the like and a function of taking a still image, a function of taking a moving image, a function of storing the taken image in a memory medium (an external memory medium or a memory medium incorporated in the camera), a function of displaying the taken image on the display portion, or the like.

The electronic devices illustrated inFIGS. 28A to 28Gwill be described in detail below.

FIG. 28Ais a perspective view of a portable information terminal9100. The display portion9001of the portable information terminal9100is flexible. Therefore, the display portion9001can be incorporated along a bent surface of a bent housing9000. In addition, the display portion9001includes a touch sensor, and operation can be performed by touching the screen with a finger, a stylus, or the like. For example, when an icon displayed on the display portion9001is touched, an application can be started.

FIG. 28Bis a perspective view of a portable information terminal9101. The portable information terminal9101functions as, for example, one or more of a telephone set, a notebook, and an information browsing system. Specifically, the portable information terminal can be used as a smartphone. Note that the speaker9003, the connection terminal9006, the sensor9007, and the like, which are not shown inFIG. 28B, can be positioned in the portable information terminal9101as in the portable information terminal9100shown inFIG. 28A. The portable information terminal9101can display characters and image information on its plurality of surfaces. For example, three operation buttons9050(also referred to as operation icons, or simply, icons) can be displayed on one surface of the display portion9001. Furthermore, information9051indicated by dashed rectangles can be displayed on another surface of the display portion9001. Examples of the information9051include display indicating reception of an incoming email, social networking service (SNS) message, call, and the like; the title and sender of an email and SNS message; the date; the time; remaining battery; and display indicating the strength of a received signal such as a radio wave. Instead of the information9051, the operation buttons9050or the like may be displayed on the position where the information9051is displayed.

As a material of the housing9000, an alloy, plastic, ceramic, or a material containing carbon fiber can be used. As the material containing carbon fiber, carbon fiber reinforced plastic (CFRP) has advantages of lightweight and corrosion-free; however, it is black and thus limits the exterior and design of the housing. The CFRP can be regarded as a kind of reinforced plastic, which may use glass fiber or aramid fiber. Since the fiber might be separated from a resin by high impact, the alloy is preferred. As the alloy, an aluminum alloy and a magnesium alloy can be given. An amorphous alloy (also referred to as metallic glass) containing zirconium, copper, nickel, and titanium especially has high elastic strength. This amorphous alloy has a glass transition region at room temperature, which is also referred to as a bulk-solidifying amorphous alloy and substantially has an amorphous atomic structure. An alloy material is molded in a mold of at least the part of the housing and coagulated by a solidification casting method, whereby part of the housing is formed with the bulk-solidifying amorphous alloy. The amorphous alloy may contain beryllium, silicon, niobium, boron, gallium, molybdenum, tungsten, manganese, iron, cobalt, yttrium, vanadium, phosphorus, carbon, or the like in addition to zirconium, copper, nickel, and titanium. The amorphous alloy may be formed by a vacuum evaporation method, a sputtering method, an electroplating method, an electroless plating method, or the like instead of the solidification casting method. The amorphous alloy may include a microcrystal or a nanocrystal as long as a state without a long-range order (a periodic structure) is maintained as a whole. Note that the term alloy includes both a complete solid solution alloy having a single solid-phase structure and a partial solution having two or more phases. The housing9000using the amorphous alloy can have high elastic strength. Even if the portable information terminal9101is dropped and the impact causes temporary deformation, the use of the amorphous alloy in the housing9000allows a return to the original shape; thus, the impact resistance of the portable information terminal9101can be improved.

FIG. 29Cis a perspective view of a portable information terminal9102. The portable information terminal9102has a function of displaying information on three or more surfaces of the display portion9001. Here, information9052, information9053, and information9054are displayed on different surfaces. For example, a user of the portable information terminal9102can see the display (here, the information9053) with the portable information terminal9102put in a breast pocket of his/her clothes. Specifically, a caller's phone number, name, or the like of an incoming call is displayed in a position that can be seen from above the portable information terminal9102. Thus, the user can see the display without taking out the portable information terminal9102from the pocket and decide whether to answer the call.

FIG. 28Dis a perspective view of a watch-type portable information terminal9200. The portable information terminal9200is capable of executing a variety of applications such as mobile phone calls, e-mailing, viewing and editing texts, music reproduction, Internet communication, and computer games. The display surface of the display portion9001is bent, and images can be displayed on the bent display surface. The portable information terminal9200can employ near field communication that is a communication method based on an existing communication standard. In that case, for example, mutual communication between the portable information terminal9200and a headset capable of wireless communication can be performed, and thus hands-free calling is possible. The portable information terminal9200includes the connection terminal9006, and data can be directly transmitted to and received from another information terminal via a connector. Power charging through the connection terminal9006is possible. Note that the charging operation may be performed by wireless power feeding without using the connection terminal9006.

FIGS. 28E, 28F, and 28Gare perspective views of a foldable portable information terminal9201.FIG. 28Eis a perspective view illustrating the portable information terminal9201that is opened.FIG. 28Fis a perspective view illustrating the portable information terminal9201that is being opened or being folded.FIG. 28Gis a perspective view illustrating the portable information terminal9201that is folded. The portable information terminal9201is highly portable when folded. When the portable information terminal9201is opened, a seamless large display region is highly browsable. The display portion9001of the portable information terminal9201is supported by three housings9000joined together by hinges9055. By folding the portable information terminal9201at a connection portion between two housings9000with the hinges9055, the portable information terminal9201can be reversibly changed in shape from an opened state to a folded state. For example, the portable information terminal9201can be bent with a radius of curvature of greater than or equal to 1 mm and less than or equal to 150 mm.

Examples of electronic devices are a television set (also referred to as a television or a television receiver), a monitor of a computer or the like, a camera such as a digital camera or a digital video camera, a digital photo frame, a mobile phone handset (also referred to as a mobile phone or a mobile phone device), a goggle-type display (head mounted display), a portable game machine, a portable information terminal, an audio reproducing device, and a large-sized game machine such as a pachinko machine.

Furthermore, the electronic device of one embodiment of the present invention may include a secondary battery. It is preferable that the secondary battery be capable of being charged by non-contact power transmission.

Examples of the secondary battery include a lithium ion secondary battery such as a lithium polymer battery using a gel electrolyte (lithium ion polymer battery), a lithium-ion battery, a nickel-hydride battery, a nickel-cadmium battery, an organic radical battery, a lead storage battery, an air secondary battery, a nickel-zinc battery, and a silver-zinc battery.

The electronic device of one embodiment of the present invention may include an antenna. When a signal is received by the antenna, the electronic device can display an image, data, or the like on a display portion. When the electronic device includes a secondary battery, the antenna may be used for non-contact power transmission.

FIG. 29Aillustrates a portable game machine including a housing7101, a housing7102, display portions7103and7104, a microphone7105, speakers7106, an operation key7107, a stylus7108, and the like. When the light-emitting device of one embodiment of the present invention is used as the display portion7103or7104, it is possible to provide a user-friendly portable game machine with quality that hardly deteriorates. Although the portable game machine illustrated inFIG. 29Aincludes two display portions, the display portions7103and7104, the number of display portions included in the portable game machine is not limited to two.

FIG. 29Billustrates a video camera including a housing7701, a housing7702, a display portion7703, operation keys7704, a lens7705, a joint7706, and the like. The operation keys7704and the lens7705are provided for the housing7701, and the display portion7703is provided for the housing7702. The housing7701and the housing7702are connected to each other with the joint7706, and the angle between the housing7701and the housing7702can be changed with the joint7706. Images displayed on the display portion7703may be switched in accordance with the angle at the joint7706between the housing7701and the housing7702.

FIG. 29Cillustrates a notebook personal computer including a housing7121, a display portion7122, a keyboard7123, a pointing device7124, and the like. Note that the display portion7122is small- or medium-sized but can perform 8 k display because it has greatly high pixel density and high resolution; therefore, a significantly clear image can be obtained.

FIG. 29Dis an external view of a head-mounted display7200.

The head-mounted display7200includes a mounting portion7201, a lens7202, a main body7203, a display portion7204, a cable7205, and the like. The mounting portion7201includes a battery7206.

Power is supplied from the battery7206to the main body7203through the cable7205. The main body7203includes a wireless receiver or the like to receive video data, such as image data, and display it on the display portion7204. The movement of the eyeball and the eyelid of a user is captured by a camera in the main body7203and then coordinates of the points the user looks at are calculated using the captured data to utilize the eye point of the user as an input means.

The mounting portion7201may include a plurality of electrodes so as to be in contact with the user. The main body7203may be configured to sense current flowing through the electrodes with the movement of the user's eyeball to recognize the direction of his or her eyes. The main body7203may be configured to sense current flowing through the electrodes to monitor the user's pulse. The mounting portion7201may include sensors, such as a temperature sensor, a pressure sensor, or an acceleration sensor, so that the user's biological information can be displayed on the display portion7204. The main body7203may be configured to sense the movement of the user's head or the like to move an image displayed on the display portion7204in synchronization with the movement of the user's head or the like.

FIG. 29Eis an external view of a camera7300. The camera7300includes a housing7301, a display portion7302, an operation button7303, a shutter button7304, a connection portion7305, and the like. A lens7306can be put on the camera7300.

The connection portion7305includes an electrode to connect with a finder7400, which is described below, a stroboscope, or the like.

Although the lens7306of the camera7300here is detachable from the housing7301for replacement, the lens7306may be included in the housing7301.

Images can be taken at the touch of the shutter button7304. In addition, images can be taken by operation of the display portion7302including a touch sensor.

In the display portion7302, the display device of one embodiment of the present invention or a touch sensor can be used.

The finder7400includes a housing7401, a display portion7402, and a button7403.

The housing7401includes a connection portion for engagement with the connection portion7305of the camera7300so that the finder7400can be connected to the camera7300. The connection portion includes an electrode, and an image or the like received from the camera7300through the electrode can be displayed on the display portion7402.

The button7403has a function of a power button, and the display portion7402can be turned on and off with the button7403.

Although the camera7300and the finder7400are separate and detachable electronic devices inFIGS. 29E and 29F, the housing7301of the camera7300may include a finder having a display device of one embodiment of the present invention or a touch sensor.

FIG. 30Aillustrates an example of a television set. In the television set9300, the display portion9001is incorporated into the housing9000. Here, the housing9000is supported by a stand9301.

The television set9300illustrated inFIG. 30Acan be operated with an operation switch of the housing9000or a separate remote controller9311. The display portion9001may include a touch sensor. The television set9300can be operated by touching the display portion9001with a finger or the like. The remote controller9311may be provided with a display portion for displaying data output from the remote controller9311. With operation keys or a touch panel of the remote controller9311, channels or volume can be controlled and images displayed on the display portion9001can be controlled.

The television set9300is provided with a receiver, a modem, or the like. A general television broadcast can be received with the receiver. When the television set is connected to a communication network with or without wires via the modem, one-way (from a transmitter to a receiver) or two-way (between a transmitter and a receiver or between receivers) data communication can be performed.

The electronic device or the lighting device of one embodiment of the present invention has flexibility and therefore can be incorporated along a curved inside/outside wall surface of a house or a building or a curved interior/exterior surface of a car.

FIG. 30Bis an external view of an automobile9700.FIG. 30Cillustrates a driver's seat of the automobile9700. The automobile9700includes a car body9701, wheels9702, a dashboard9703, lights9704, and the like. The display device, the light-emitting device, or the like of one embodiment of the present invention can be used in a display portion or the like of the automobile9700. For example, the display device, the light-emitting device, or the like of one embodiment of the present invention can be used in display portions9710to9715illustrated inFIG. 30C.

The display portion9710and the display portion9711are each a display device provided in an automobile windshield. The display device, the light-emitting device, or the like of one embodiment of the present invention can be a see-through display device, through which the opposite side can be seen, using a light-transmitting conductive material for its electrodes and wirings. Such a see-through display portion9710or9711does not hinder driver's vision during driving the automobile9700. Thus, the display device, the light-emitting device, or the like of one embodiment of the present invention can be provided in the windshield of the automobile9700. Note that in the case where a transistor or the like for driving the display device, the light-emitting device, or the like is provided, a transistor having a light-transmitting property, such as an organic transistor using an organic semiconductor material or a transistor using an oxide semiconductor, is preferably used.

The display portion9712is a display device provided on a pillar portion. For example, an image taken by an imaging unit provided in the car body is displayed on the display portion9712, whereby the view hindered by the pillar portion can be compensated. The display portion9713is a display device provided on the dashboard. For example, an image taken by an imaging unit provided in the car body is displayed on the display portion9713, whereby the view hindered by the dashboard can be compensated. That is, by displaying an image taken by an imaging unit provided on the outside of the automobile, blind areas can be eliminated and safety can be increased. Displaying an image to compensate for the area which a driver cannot see, makes it possible for the driver to confirm safety easily and comfortably.

FIG. 30Dillustrates the inside of a car in which bench seats are used for a driver seat and a front passenger seat. A display portion9721is a display device provided in a door portion. For example, an image taken by an imaging unit provided in the car body is displayed on the display portion9721, whereby the view hindered by the door can be compensated. A display portion9722is a display device provided in a steering wheel. A display portion9723is a display device provided in the middle of a seating face of the bench seat. Note that the display device can be used as a seat heater by providing the display device on the seating face or backrest and by using heat generation of the display device as a heat source.

The display portion9714, the display portion9715, and the display portion9722can provide a variety of kinds of information such as navigation data, a speedometer, a tachometer, a mileage, a fuel meter, a gearshift indicator, and air-condition setting. The content, layout, or the like of the display on the display portions can be changed freely by a user as appropriate. The information listed above can also be displayed on the display portions9710to9713,9721, and9723. The display portions9710to9715and9721to9723can also be used as lighting devices. The display portions9710to9715and9721to9723can also be used as heating devices.

A display device9500illustrated inFIGS. 31A and 31Bincludes a plurality of display panels9501, a hinge9511, and a bearing9512. The plurality of display panels9501each include a display region9502and a light-transmitting region9503.

Each of the plurality of display panels9501is flexible. Two adjacent display panels9501are provided so as to partly overlap with each other. For example, the light-transmitting regions9503of the two adjacent display panels9501can be overlapped each other. A display device having a large screen can be obtained with the plurality of display panels9501. The display device is highly versatile because the display panels9501can be wound depending on its use.

Moreover, although the display regions9502of the adjacent display panels9501are separated from each other inFIGS. 31A and 31B, without limitation to this structure, the display regions9502of the adjacent display panels9501may overlap with each other without any space so that a continuous display region9502is obtained, for example.

The electronic devices described in this embodiment each include the display portion for displaying some sort of data. Note that the light-emitting element of one embodiment of the present invention can also be used for an electronic device which does not have a display portion. The structure in which the display portion of the electronic device described in this embodiment is flexible and display can be performed on the bent display surface or the structure in which the display portion of the electronic device is foldable is described as an example; however, the structure is not limited thereto and a structure in which the display portion of the electronic device is not flexible and display is performed on a plane portion may be employed.

In this embodiment, a light-emitting device including the light-emitting element of one embodiment of the present invention will be described with reference toFIGS. 32A to 32CandFIGS. 33A to 33D.

FIG. 32Ais a perspective view of a light-emitting device3000shown in this embodiment, andFIG. 32Bis a cross-sectional view along dashed-dotted line E-F inFIG. 32A. Note that inFIG. 32A, some components are illustrated by broken lines in order to avoid complexity of the drawing.

The light-emitting device3000illustrated inFIGS. 32A and 32Bincludes a substrate3001, a light-emitting element3005over the substrate3001, a first sealing region3007provided around the light-emitting element3005, and a second sealing region3009provided around the first sealing region3007.

Light is emitted from the light-emitting element3005through one or both of the substrate3001and a substrate3003. InFIGS. 32A and 32B, a structure in which light is emitted from the light-emitting element3005to the lower side (the substrate3001side) is illustrated.

As illustrated inFIGS. 32A and 32B, the light-emitting device3000has a double sealing structure in which the light-emitting element3005is surrounded by the first sealing region3007and the second sealing region3009. With the double sealing structure, entry of impurities (e.g., water, oxygen, and the like) from the outside into the light-emitting element3005can be favorably suppressed. Note that it is not necessary to provide both the first sealing region3007and the second sealing region3009. For example, only the first sealing region3007may be provided.

Note that inFIG. 32B, the first sealing region3007and the second sealing region3009are each provided in contact with the substrate3001and the substrate3003. However, without limitation to such a structure, for example, one or both of the first sealing region3007and the second sealing region3009may be provided in contact with an insulating film or a conductive film provided on the substrate3001. Alternatively, one or both of the first sealing region3007and the second sealing region3009may be provided in contact with an insulating film or a conductive film provided on the substrate3003.

The substrate3001and the substrate3003can have structures similar to those of the substrate200and the substrate220described in the above embodiment, respectively. The light-emitting element3005can have a structure similar to that of any of the light-emitting elements described in the above embodiments.

For the first sealing region3007, a material containing glass (e.g., a glass fit, a glass ribbon, and the like) can be used. For the second sealing region3009, a material containing a resin can be used. With the use of the material containing glass for the first sealing region3007, productivity and a sealing property can be improved. Moreover, with the use of the material containing a resin for the second sealing region3009, impact resistance and heat resistance can be improved. However, the materials used for the first sealing region3007and the second sealing region3009are not limited to such, and the first sealing region3007may be formed using the material containing a resin and the second sealing region3009may be formed using the material containing glass.

As the above glass frits, for example, a frit paste is applied to a substrate and is subjected to heat treatment, laser light irradiation, or the like. The frit paste contains the glass frit and a resin (also referred to as a binder) diluted by an organic solvent. Note that an absorber which absorbs light having the wavelength of laser light may be added to the glass frit. For example, an Nd:YAG laser or a semiconductor laser is preferably used as the laser. The shape of laser light may be circular or quadrangular.

As the above material containing a resin, for example, polyester, polyolefin, polyamide (e.g., nylon, aramid), polyimide, polycarbonate, or an acrylic resin, polyurethane, or an epoxy resin can be used. Alternatively, a material that includes a resin having a siloxane bond such as silicone can be used.

Note that in the case where the material containing glass is used for one or both of the first sealing region3007and the second sealing region3009, the material containing glass preferably has a thermal expansion coefficient close to that of the substrate3001. With the above structure, generation of a crack in the material containing glass or the substrate3001due to thermal stress can be suppressed.

For example, the following advantageous effect can be obtained in the case where the material containing glass is used for the first sealing region3007and the material containing a resin is used for the second sealing region3009.

The second sealing region3009is provided closer to an outer portion of the light-emitting device3000than the first sealing region3007is. In the light-emitting device3000, distortion due to external force or the like increases toward the outer portion. Thus, the light-emitting device3000is sealed using the material containing a resin for the outer portion of the light-emitting device3000where a larger amount of distortion is generated, that is, the second sealing region3009, and the light-emitting device3000is sealed using the material containing glass for the first sealing region3007provided on an inner side of the second sealing region3009, whereby the light-emitting device3000is less likely to be damaged even when distortion due to external force or the like is generated.

Furthermore, as illustrated inFIG. 32B, a first region3011corresponds to the region surrounded by the substrate3001, the substrate3003, the first sealing region3007, and the second sealing region3009. A second region3013corresponds to the region surrounded by the substrate3001, the substrate3003, the light-emitting element3005, and the first sealing region3007.

The first region3011and the second region3013are preferably filled with, for example, an inert gas such as a rare gas or a nitrogen gas. Alternatively, the first region3011and the second region3013are preferably filled with a resin such as an acrylic resin or an epoxy resin. Note that for the first region3011and the second region3013, a reduced pressure state is preferred to an atmospheric pressure state.

FIG. 32Cillustrates a modification example of the structure inFIG. 32B.FIG. 32Cis a cross-sectional view illustrating the modification example of the light-emitting device3000.

FIG. 32Cillustrates a structure in which a desiccant3018is provided in a recessed portion provided in part of the substrate3003. The other components are the same as those of the structure illustrated inFIG. 32B.

As the desiccant3018, a substance which adsorbs moisture and the like by chemical adsorption or a substance which adsorbs moisture and the like by physical adsorption can be used. Examples of the substance that can be used as the desiccant3018include alkali metal oxides, alkaline earth metal oxide (e.g., calcium oxide, barium oxide, and the like), sulfate, metal halides, perchlorate, zeolite, silica gel, and the like.

Next, modification examples of the light-emitting device3000which is illustrated inFIG. 32Bare described with reference toFIGS. 33A to 33D. Note thatFIGS. 33A to 33Dare cross-sectional views illustrating the modification examples of the light-emitting device3000illustrated inFIG. 32B.

In each of the light-emitting devices illustrated inFIGS. 33A to 33D, the second sealing region3009is not provided but only the first sealing region3007is provided. Moreover, in each of the light-emitting devices illustrated inFIGS. 33A to 33D, a region3014is provided instead of the second region3013illustrated inFIG. 32B.

For the region3014, for example, polyester, polyolefin, polyamide (e.g., nylon, aramid), polyimide, polycarbonate, or an acrylic resin, polyurethane, or an epoxy resin can be used. Alternatively, a material that includes a resin having a siloxane bond such as silicone can be used.

When the above-described material is used for the region3014, what is called a solid-sealing light-emitting device can be obtained.

In the light-emitting device illustrated inFIG. 33B, a substrate3015is provided on the substrate3001side of the light-emitting device illustrated inFIG. 33A.

The substrate3015has unevenness as illustrated inFIG. 33B. With a structure in which the substrate3015having unevenness is provided on the side through which light emitted from the light-emitting element3005is extracted, the efficiency of extraction of light from the light-emitting element3005can be improved. Note that instead of the structure having unevenness and illustrated inFIG. 33B, a substrate having a function as a diffusion plate may be provided.

In the light-emitting device illustrated inFIG. 33C, light is extracted through the substrate3003side, unlike in the light-emitting device illustrated inFIG. 33A, in which light is extracted through the substrate3001side.

The light-emitting device illustrated inFIG. 33Cincludes the substrate3015on the substrate3003side. The other components are the same as those of the light-emitting device illustrated inFIG. 33B.

In the light-emitting device illustrated inFIG. 33D, the substrate3003and the substrate3015included in the light-emitting device illustrated inFIG. 33Care not provided but a substrate3016is provided.

The substrate3016includes first unevenness positioned closer to the light-emitting element3005and second unevenness positioned farther from the light-emitting element3005. With the structure illustrated inFIG. 33D, the efficiency of extraction of light from the light-emitting element3005can be further improved.

Thus, the use of the structure described in this embodiment can provide a light-emitting device in which deterioration of a light-emitting element due to impurities such as moisture and oxygen is suppressed. Alternatively, with the structure described in this embodiment, a light-emitting device having high light extraction efficiency can be obtained.

In this embodiment, examples in which the light-emitting element of one embodiment of the present invention is used for various lighting devices and electronic devices will be described with reference toFIGS. 34A to 34CandFIG. 35.

An electronic device or a lighting device that has a light-emitting region with a curved surface can be obtained with the use of the light-emitting element of one embodiment of the present invention which is manufactured over a substrate having flexibility.

Furthermore, a light-emitting device to which one embodiment of the present invention is applied can also be used for lighting for motor vehicles, examples of which are lighting for a dashboard, a windshield, a ceiling, and the like.

FIG. 34Ais a perspective view illustrating one surface of a multifunction terminal3500, andFIG. 34Bis a perspective view illustrating the other surface of the multifunction terminal3500. In a housing3502of the multifunction terminal3500, a display portion3504, a camera3506, lighting3508, and the like are incorporated. The light-emitting device of one embodiment of the present invention can be used for the lighting3508.

The lighting3508that includes the light-emitting device of one embodiment of the present invention functions as a planar light source. Thus, unlike a point light source typified by an LED, the lighting3508can provide light emission with low directivity. When the lighting3508and the camera3506are used in combination, for example, imaging can be performed by the camera3506with the lighting3508lighting or flashing. Because the lighting3508functions as a planar light source, a photograph as if taken under natural light can be taken.

Note that the multifunction terminal3500illustrated inFIGS. 34A and 34Bcan have a variety of functions as in the electronic devices illustrated inFIGS. 28A to 28G.

The housing3502can include a speaker, a sensor (a sensor having a function of measuring force, displacement, position, speed, acceleration, angular velocity, rotational frequency, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, gradient, oscillation, odor, or infrared rays), a microphone, and the like. When a detection device including a sensor for detecting inclination, such as a gyroscope or an acceleration sensor, is provided inside the multifunction terminal3500, display on the screen of the display portion3504can be automatically switched by determining the orientation of the multifunction terminal3500(whether the multifunction terminal is placed horizontally or vertically for a landscape mode or a portrait mode).

The display portion3504may function as an image sensor. For example, an image of a palm print, a fingerprint, or the like is taken when the display portion3504is touched with the palm or the finger, whereby personal authentication can be performed. Furthermore, by providing a backlight or a sensing light source which emits near-infrared light in the display portion3504, an image of a finger vein, a palm vein, or the like can be taken. Note that the light-emitting device of one embodiment of the present invention may be used for the display portion3504.

FIG. 34Cis a perspective view of a security light3600. The security light3600includes lighting3608on the outside of the housing3602, and a speaker3610and the like are incorporated in the housing3602. The light-emitting device of one embodiment of the present invention can be used for the lighting3608.

The security light3600emits light when the lighting3608is gripped or held, for example. An electronic circuit that can control the manner of light emission from the security light3600may be provided in the housing3602. The electronic circuit may be a circuit that enables light emission once or intermittently a plurality of times or may be a circuit that can adjust the amount of emitted light by controlling the current value for light emission. A circuit with which a loud audible alarm is output from the speaker3610at the same time as light emission from the lighting3608may be incorporated.

The security light3600can emit light in various directions; therefore, it is possible to intimidate a thug or the like with light, or light and sound. Moreover, the security light3600may include a camera such as a digital still camera to have a photography function.

FIG. 35illustrates an example in which the light-emitting element is used for an indoor lighting device8501. Since the light-emitting element can have a larger area, a lighting device having a large area can also be formed. In addition, a lighting device8502in which a light-emitting region has a curved surface can also be formed with the use of a housing with a curved surface. A light-emitting element described in this embodiment is in the form of a thin film, which allows the housing to be designed more freely. Therefore, the lighting device can be elaborately designed in a variety of ways. Furthermore, a wall of the room may be provided with a large-sized lighting device8503. Touch sensors may be provided in the lighting devices8501,8502, and8503to control the power on/off of the lighting devices.

Moreover, when the light-emitting element is used on the surface side of a table, a lighting device8504which has a function as a table can be obtained. When the light-emitting element is used as part of other furniture, a lighting device which has a function as the furniture can be obtained.

As described above, lighting devices and electronic devices can be obtained by application of the light-emitting device of one embodiment of the present invention. Note that the light-emitting device can be used for electronic devices in a variety of fields without being limited to the lighting devices and the electronic devices described in this embodiment.

Described in this example is a method of synthesizing 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[a,g]carbazole (abbreviation: agDBCzPA, Structural Formula (100)), which is a dibenzocarbazole compound represented by General Formula (G1) described in Embodiment 1.

In a 200-mL three-neck flask were put 3.0 g (7.5 mmol) of 9-(4-bromophenyl)-10-phenylanthracene, 2.0 g (7.5 mol) of 7H-dibenzo[a,g]carbazole, and 1.4 g (15 mmol) of sodium tert-butoxide, and the air in the flask was replaced with nitrogen. To this mixture were added 38 mL of mesitylene and 0.30 mL of tri-tert-butylphosphine (10 wt % hexane solution), and the mixture was stirred to be degassed while the pressure in the flask was reduced. After the degassing, 43 mg (0.075 mol) of bis(dibenzylideneacetone)palladium(0) was added to the mixture, and the mixture was stirred at 150° C. for 6 hours under a nitrogen stream. After the stirring, the mixture was cooled to room temperature, and approximately 20 mL of water was added to the mixture and then stirred. Then, this mixture was suction-filtered to collect a solid. The collected solid was dissolved in approximately 50 mL of toluene heated, and the solution was suction-filtered through Celite, aluminum oxide, and Florisil. The obtained filtrate was concentrated to give a solid. The obtained solid was recrystallized from toluene, so that 3.5 g of a pale yellow powder, which was the object of the synthesis, was obtained with a yield of 78%. This reaction scheme is shown below.

Then, 3.5 g of the obtained pale yellow powdered solid was sublimated and purified by a train sublimation method. In the sublimation purification, agDBCzPA was heated at 290° C. under a pressure of 2.7 Pa with a flow rate of argon gas of 5.0 mL/min. After the sublimation purification, 3.3 g of a pale yellow solid of agDBCzPA was obtained at a collection rate of 96%.

The resulting substance was measured by1H NMR (nuclear magnetic resonance). The measurement data are shown below.

FIGS. 36A and 36Bare1H NMR charts.FIG. 36Bis an enlarged chart showing a range of 7.00 ppm to 9.50 ppm ofFIG. 36A. These results indicate that agDBCzPA, which is the dibenzocarbazole compound of one embodiment of the present invention represented by Structural Formula (100), was obtained.

Next, the obtained agDBCzPA was analyzed by liquid chromatography mass spectrometry (LC/MS).

The LC/MS analysis was carried out with Acquity UPLC (produced by Waters Corporation) and Xevo G2 Tof MS (produced by Waters Corporation).

In the MS analysis, ionization was carried out by an electrospray ionization (ESI) method. At this time, the capillary voltage and the sample cone voltage were set to 3.0 kV and 30 V, respectively, and detection was performed in a positive mode. A component which underwent the ionization under the above conditions was made to collide with an argon gas in a collision cell to dissociate into product ions. The energy (collision energy) for the collision with argon was 70 eV. The mass range in the measurement was m/z=100 to 1200.

FIG. 37shows the measurement results. According to the results inFIG. 37, product ions are detected mainly around m/z=596, m/z=330, and m/z=266 in agDBCzPA, which is the dibenzocarbazole compound of one embodiment of the present invention represented by Structural Formula (100). Note that the results inFIG. 37show typical features derived from agDBCzPA and therefore can be regarded as important data for identifying agDBCzPA contained in the mixture.

An N—C bond between dibenzo[a,g]carbazole and a phenylene group is cut and electric charge remains on the dibenzo[a,g]carbazole side; thus, the product ions around m/z=266 are useful because they probably include data on a state where the N—C bond between dibenzo[a,g]carbazole and a phenylene group of the compound represented by Structural Formula (100) is cut. In addition, the product ions around m/z=330 can be presumed to be product ions including diphenylanthracene, which indicates that agDBCzPA, which is the dibenzocarbazole compound of one embodiment of the present invention, includes dibenzo[a,g]carbazole and diphenylanthracene.

Thermogravimetry-differential thermal analysis (TG-DTA) was performed on the obtained agDBCzPA. The measurement was conducted by using a high vacuum differential type differential thermal balance (TG-DTA 2410SA, manufactured by Bruker AXS K.K.). The measurement was conducted under a nitrogen stream (flow rate: 200 mL/min) at normal pressure at a temperature increase rate of 10° C./min. It was found from the relationship between weight and temperature (thermogravimetry) that the 5% weight loss temperature of agDBCzPA was approximately 475° C. This indicates that agDBCzPA has high heat resistance.

Next, ultraviolet-visible absorption spectra (hereinafter simply referred to as “absorption spectra”) and emission spectra of a thin film of agDBCzPA and a toluene solution of agDBCzPA were measured.

The absorption spectrum of agDBCzPA in a toluene solution was obtained by subtraction of the absorption spectrum of toluene and a quartz cell from the absorption spectrum of the toluene solution of agDBCzPA put in the quartz cell. The absorption spectrum of the thin film was obtained by subtraction of the absorption spectrum of a quartz substrate from the absorption spectrum of a sample formed by vacuum evaporation of agDBCzPA on the quartz substrate. Note that the absorption spectra were measured using an ultraviolet-visible spectrophotometer (V-550 type manufactured by JASCO Corporation).

The emission spectra were measured with a fluorescence spectrophotometer (FS920 manufactured by Hamamatsu Photonics K.K.).

FIG. 38shows the measurement results of the absorption and emission spectra of agDBCzPA in the toluene solution, andFIG. 39shows the measurement results of the absorption and emission spectra of agDBCzPA in the thin film.

As shown inFIG. 38, in the toluene solution of agDBCzPA, the absorption maxima were observed at approximately 292 nm, 305 nm, 341 nm, 354 nm, 372 nm, and 396 nm, and the emission peaks were observed at 417 nm and 429 nm.

The ionization potential of the thin film of agDBCzPA was measured in the air with a photoelectron spectrometer (AC-3, produced by Riken Keiki, Co., Ltd.). The obtained value of the ionization potential was converted into a negative value, and the HOMO level of agDBCzPA was −5.93 eV. From the data of the absorption spectrum of the thin film inFIG. 39, the absorption edge of agDBCzPA, which was obtained from Tauc plot with an assumption of direct transition, was 2.95 eV. Thus, the optical energy gap of agDBCzPA in the solid state was estimated to be 2.95 eV; from the values of the HOMO level obtained above and this energy gap, the LUMO level of agDBCzPA can be estimated to be −2.98 eV. This reveals that agDBCzPA in the solid state has an energy gap as wide as 2.95 eV.

Then, the electrochemical characteristics (oxidation reaction characteristics and reduction reaction characteristics) of agDBCzPA were measured by cyclic voltammetry (CV) measurement. Note that for the measurement, an electrochemical analyzer (ALS model 600A or 600C, produced by BAS Inc.) was used, and the measurement was performed on a solution in which agDBCzPA is dissolved in N,N-dimethylformamide (abbreviation: DMF). In the measurement, the potential of a working electrode with respect to the reference electrode was changed within an appropriate range, so that the oxidation peak potential and the reduction peak potential were obtained. In addition, the HOMO and LUMO levels of agDBCzPA were calculated from the obtained peak potentials and the redox potential of the reference electrode estimated to be −4.94 eV.

According to the CV measurement results, the oxidation potential of agDBCzPA was 0.76 V and the reduction potential was −2.21 V. In addition, the HOMO level and LUMO level of agDBCzPA, which were calculated from the CV measurement results, were −5.70 eV and −2.74 eV, respectively. Thus, agDBCzPA was found to have a large energy difference between the HOMO level and the LUMO level.

Described in this example is a method of synthesizing 11-[4-(10-phenyl-9-anthryl)phenyl]-11H-dibenzo[a,i]carbazole (abbreviation: aiDBCzPA, Structural Formula (136)), which is a dibenzocarbazole compound represented by General Formula (G6) described in Embodiment 1.

In a 200-mL three-neck flask were put 3.0 g (7.5 mmol) of 9-(4-bromophenyl)-10-phenylanthracene, 2.0 g (7.5 mol) of 11H-dibenzo[a,i]carbazole, and 1.4 g (15 mmol) of sodium tert-butoxide, and the air in the flask was replaced with nitrogen. To this mixture were added 38 mL of mesitylene and 0.30 mL of tri(tert-butyl)phosphine (10 wt % hexane solution), and the mixture was stirred to be degassed while the pressure in the flask was reduced. After the degassing, 43 mg (0.075 mol) of bis(dibenzylideneacetone)palladium(0) was added to the mixture, and the mixture was stirred at 150° C. for 6 hours under a nitrogen stream. After the stirring, the aqueous layer of this mixture was subjected to extraction with toluene, and the solution of the extract and the organic layer were combined and washed with saturated brine. The organic layer was dried over magnesium sulfate, and after that, this mixture was gravity-filtered. A solid obtained by concentrating the obtained filtrate was dissolved in approximately 30 mL of toluene, and the resulting solution was purified by silica gel column chromatography (developing solvent, hexane:toluene=4:1) to give a solid. The solid obtained by the purification was recrystallized from toluene/hexane, so that 3.8 g of a pale yellow powder, which was the object of the synthesis, was obtained with a yield of 85%. This reaction scheme is shown below.

Then, 3.7 g of the obtained pale yellow powdered solid was sublimated and purified by a train sublimation method. In the sublimation purification, aiDBCzPA was heated at 280° C. under a pressure of 2.8 Pa with a flow rate of argon gas of 5.0 mL/min. After the sublimation purification, 2.0 g of a pale yellow solid of aiDBCzPA was obtained at a collection rate of 55%.

The resulting substance was measured by1H NMR (nuclear magnetic resonance). The measurement data are shown below.

FIGS. 40A and 40Bare1H NMR charts.FIG. 40Bis an enlarged chart showing a range of 7.00 ppm to 8.50 ppm ofFIG. 40A. These results indicate that aiDBCzPA, which is the dibenzocarbazole compound of one embodiment of the present invention represented by Structural Formula (136), was obtained.

Next, the obtained aiDBCzPA was analyzed by liquid chromatography mass spectrometry (LC/MS).

The LC/MS analysis was carried out with Acquity UPLC (produced by Waters Corporation) and Xevo G2 Tof MS (produced by Waters Corporation).

In the MS analysis, ionization was carried out by an electrospray ionization (ESI) method. At this time, the capillary voltage and the sample cone voltage were set to 3.0 kV and 30 V, respectively, and detection was performed in a positive mode. A component which underwent the ionization under the above conditions was made to collide with an argon gas in a collision cell to dissociate into product ions. The energy (collision energy) for the collision with argon was 70 eV. The mass range in the measurement was m/z=100 to 1200.

FIG. 41shows the measurement results. According to the results inFIG. 41, product ions are detected mainly around m/z=596, m/z=330, and m/z=266 in aiDBCzPA, which is the dibenzocarbazole compound of one embodiment of the present invention represented by Structural Formula (136). Note that the results inFIG. 41show typical features derived from aiDBCzPA and therefore can be regarded as important data for identifying aiDBCzPA contained in the mixture.

An N—C bond between dibenzo[a,i]carbazole and a phenylene group is cut and electric charge remains on the dibenzo[a,i]carbazole side; thus, the product ions around m/z=266 are useful because they probably include data on a state where the N—C bond between dibenzo[a,i]carbazole and a phenylene group of the compound represented by Structural Formula (136) is cut. In addition, the product ions around m/z=330 can be presumed to be product ions including diphenylanthracene, which indicates that aiDBCzPA, which is the dibenzocarbazole compound of one embodiment of the present invention, includes dibenzo[a,i]carbazole and diphenylanthracene.

Thermogravimetry-differential thermal analysis (TG-DTA) was performed on the obtained aiDBCzPA. The measurement was conducted by using a high vacuum differential type differential thermal balance (TG-DTA 2410SA, manufactured by Bruker AXS K.K.). The measurement was conducted under a nitrogen stream (flow rate: 200 ml/min) at normal pressure at a temperature increase rate of 10° C./min. It was found from the relationship between weight and temperature (thermogravimetry) that the 5% weight loss temperature of aiDBCzPA was approximately 442° C. This indicates that aiDBCzPA has high heat resistance.

Next, ultraviolet-visible absorption spectra (hereinafter simply referred to as “absorption spectra”) and emission spectra of a thin film of aiDBCzPA and a toluene solution of aiDBCzPA were measured. The measurement method is similar to that in Example 1.

FIG. 42shows the measurement results of the absorption and emission spectra of aiDBCzPA in the toluene solution, andFIG. 43shows the measurement results of the absorption and emission spectra of aiDBCzPA in the thin film.

As shown inFIG. 42, in the toluene solution of aiDBCzPA, the absorption maxima were observed at approximately 291 nm, 321 nm, 335 nm, 352 nm, 375 nm, and 396 nm, and the emission peaks were observed at 413 nm and 432 nm.

As shown inFIG. 43, in the thin film of aiDBCzPA, the absorption maxima were observed at approximately 228 nm, 264 nm, 294 nm, 324 nm, 335 nm, 381 nm, and 402 nm, and the emission peaks were observed at 429 nm and 442 nm (excitation wavelength: 381 nm).

The ionization potential of the thin film of aiDBCzPA was measured in the air with a photoelectron spectrometer (AC-3, produced by Riken Keiki, Co., Ltd.). The obtained value of the ionization potential was converted into a negative value, and the HOMO level of aiDBCzPA was −5.91 eV. From the data of the absorption spectrum of the thin film inFIG. 43, the absorption edge of aiDBCzPA, which was obtained from Tauc plot with an assumption of direct transition, was 2.95 eV. Thus, the optical energy gap of aiDBCzPA in the solid state was estimated to be 2.95 eV; from the values of the HOMO level obtained above and this energy gap, the LUMO level of aiDBCzPA can be estimated to be −2.96 eV. This reveals that aiDBCzPA in the solid state has an energy gap as wide as 2.95 eV.

Then, the electrochemical characteristics (oxidation reaction characteristics and reduction reaction characteristics) of aiDBCzPA were measured by cyclic voltammetry (CV) measurement. Note that the measurement method is similar to that in Example 1.

According to the CV measurement results, the oxidation potential of aiDBCzPA was 0.73 V and the reduction potential was −2.21 V. In addition, the HOMO level and LUMO level of aiDBCzPA, which were calculated from the CV measurement results, were −5.77 eV and −2.74 eV, respectively. Thus, aiDBCzPA was found to have a large energy difference between the HOMO level and the LUMO level.

In this example, a fabrication example of a light-emitting element including a compound of one embodiment of the present invention and the characteristics of the light-emitting element will be described.FIG. 2Acan be referred to for a schematic cross-sectional view of the light-emitting element fabricated in this example. Table 1 shows details of the element structure. In addition, structures and abbreviations of compounds used are given below. Note that the above examples are referred to for other compounds.

As the electrode101, an ITSO film was formed to a thickness of 70 nm over a substrate. The electrode area of the electrode101was set to 4 mm2(2 mm×2 mm).

Then, as the hole-injection layer111over the electrode101, 3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPPn) and molybdenum oxide (MoO3) were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCPPn to MoO3was 1:0.5. Note that co-evaporation is an evaporation method in which a plurality of different substances are concurrently vaporized from the respective evaporation sources.

Next, as the hole-transport layer112over the hole-injection layer111, PCPPn was deposited by evaporation to a thickness of 20 nm.

Next, as the light-emitting layer120over the hole-transport layer112, 7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[a,g]carbazole (abbreviation: agDBCzPA) and N,N′-bis(3-methylphenyl)-N,N-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]pyrene-1,6-diamine (abbreviation: 1,6mMemFLPAPrn) were deposited by co-evaporation to a thickness of 25 nm such that the weight ratio of agDBCzPA to 1,6mMemFLPAPrn was 1:0.01. Note that in the light-emitting layer120, agDBCzPA is a host material and 1,6mMemFLPAPrn is a guest material (fluorescent material).

Then, as the electron-transport layer113over the light-emitting layer120, agDBCzPA and bathophenanthroline (abbreviation: BPhen) were sequentially deposited by evaporation to thicknesses of 10 nm and 15 nm, respectively. After that, as the electron-injection layer114over the electron-transport layer113, lithium fluoride (LiF) was deposited by evaporation to a thickness of 1 nm.

Next, as the electrode102over the electron-injection layer114, aluminum (Al) was deposited to a thickness of 200 nm.

Next, in a glove box containing a nitrogen atmosphere, a sealing substrate was fixed to the substrate over which the organic materials were deposited using a sealant for an organic EL device, so that the light-emitting element 1 was sealed. Through the above steps, the light-emitting element 1 was obtained.

A light-emitting element 2 was fabricated through the same steps as those for the above-mentioned light-emitting element 1 except for the step of forming the light-emitting layer120.

As the light-emitting layer120in the light-emitting element 2, agDBCzPA and 1,6mMemFLPAPrn were deposited by co-evaporation to a thickness of 25 nm such that the weight ratio of agDBCzPA to 1,6mMemFLPAPrn was 1:0.03. Note that in the light-emitting layer120, agDBCzPA is a host material and 1,6mMemFLPAPrn is a guest material (fluorescent material).

A light-emitting element 3 was fabricated through the same steps as those for the above-mentioned light-emitting element 1 except for the steps of forming the light-emitting layer120and the electron-transport layer113.

As the light-emitting layer120in the light-emitting element 3,11-[4-(10-phenyl-9-anthryl)phenyl]-11H-dibenzo[a,i]carbazole (abbreviation: aiDBCzPA) and 1,6mMemFLPAPrn were deposited by co-evaporation to a thickness of 25 nm such that the weight ratio of aiDBCzPA to 1,6mMemFLPAPrn was 1:0.01. Note that in the light-emitting layer120, aiDBCzPA is a host material and 1,6mMemFLPAPrn is a guest material (fluorescent material).

As the electron-transport layer113in the light-emitting element 3, aiDBCzPA and BPhen were sequentially deposited by evaporation to thicknesses of 10 nm and 15 nm, respectively.

A light-emitting element 4 was fabricated through the same steps as those for the above-mentioned light-emitting element 3 except for the step of forming the light-emitting layer120.

As the light-emitting layer120in the light-emitting element 4, aiDBCzPA and 1,6mMemFLPAPrn were deposited by co-evaporation to a thickness of 25 nm such that the weight ratio of aiDBCzPA to 1,6mMemFLPAPrn was 1:0.03. Note that in the light-emitting layer120, aiDBCzPA is a host material and 1,6mMemFLPAPrn is a guest material (fluorescent material).

Next, the emission characteristics of the fabricated light-emitting elements 1 to 4 were measured. The luminance and CIE chromaticity were measured with a luminance colorimeter (BM-5A manufactured by TOPCON TECHNOHOUSE CORPORATION), and the electroluminescence spectrum was measured with a multi-channel spectrometer (PMA-11 manufactured by Hamamatsu Photonics K.K.). Note that the measurement was performed at room temperature (in an atmosphere maintained at 25° C.).

FIG. 44shows the current efficiency-luminance characteristics of the light-emitting elements 1 to 4,FIG. 45shows the luminance-voltage characteristics thereof, andFIG. 46shows the external quantum efficiency-luminance characteristics thereof.FIG. 47shows the electroluminescence spectra when a current with a current density of 2.5 mA/cm2was supplied to the light-emitting elements 1 to 4.

Table 2 shows the emission characteristics of the light-emitting elements at a luminance around 1000 cd/m2.

As shown inFIG. 47, the light-emitting elements 1 to 4 exhibited blue light emission derived from the guest material (1,6mMemFLPAPrn).

FIG. 44toFIG. 47and Table 2 show that the light-emitting elements 1 to 4, which include a fluorescent material as a light-emitting material, have a high current efficiency and a high external quantum efficiency. The light-emitting elements 1 to 4 also exhibited an external quantum efficiency as high as more than 9%.

Since the probability of formation of singlet excitons which are generated by recombination of carriers (holes and electrons) injected from a pair of electrodes is at most 25%, the external quantum efficiency in the case where the light extraction efficiency to the outside is 25% is at most 6.25%. The light-emitting elements 1 to 4 have an external quantum efficiency higher than 6.25%. This is because in addition to light emission derived from singlet excitons generated by recombination of carriers (holes and electrons) injected from a pair of electrodes, light emission derived from singlet excitons generated by TTA was obtained from the light-emitting elements 1 to 4.

Note that the light-emitting element 1 has a chromaticity y of 0.142, i.e., exhibits deeper blue emission than the light-emitting element 2 and also has a higher external quantum efficiency than the light-emitting element 2. In addition, the light-emitting element 3 has a chromaticity y of 0.135, i.e., exhibits deeper blue emission than the light-emitting element 4 and also has a higher external quantum efficiency than the light-emitting element 4.

In the light-emitting element that emits blue light, a high emission energy needs to be confined in the light-emitting layer, which makes it difficult to obtain a high emission efficiency particularly in the light-emitting element that exhibits deep blue emission. However, the light-emitting element including the dibenzocarbazole compound of one embodiment of the present invention as the host material emits deep blue light while exhibiting a high efficiency. This indicates that the dibenzocarbazole compound of one embodiment of the present invention can be suitably used for light-emitting elements that emit deep blue light.

Furthermore, the light-emitting elements 1 to 4 are driven at a low voltage and therefore consume low power. That is, a light-emitting element driven at a low voltage can be fabricated when the dibenzocarbazole compound of one embodiment of the present invention, which has a high carrier-transport property, is used as a host material and an electron-transport material.

Next, the driving lifetime of the light-emitting elements 1 to 4 was measured.FIG. 48shows the measurement results of the driving lifetime test. Note that the driving lifetime test was performed while each of the light-emitting elements 1 to 4 was continuously driven with a constant current density, which was set so that each light-emitting element had an initial luminance of 5000 cd.

As shown inFIG. 48, the light-emitting elements 1 to 4, which include a blue fluorescent material as a light-emitting material, have a long driving lifetime. In addition, the light-emitting element 1 has a longer driving lifetime than the light-emitting element 2, and the light-emitting element 3 has a longer driving lifetime than the light-emitting element 4.

In the light-emitting element that emits blue light, a high emission energy needs to be confined in the light-emitting layer, which makes it difficult to obtain a long driving lifetime particularly in the light-emitting element that exhibits deep blue emission. However, the light-emitting element including the dibenzocarbazole compound of one embodiment of the present invention as the host material emits deep blue light while exhibiting a long driving lifetime. This indicates that the dibenzocarbazole compound of one embodiment of the present invention can be suitably used for light-emitting elements that emit deep blue light. Specifically, the dibenzocarbazole compound of one embodiment of the present invention can be suitably used for a light-emitting element that emits deep blue having a chromaticity y of 0.01 to 0.15.

The above results also indicate that in the light-emitting element including the dibenzocarbazole compound of one embodiment of the present invention as the host material, the weight percentage of the guest material is preferably lower than that of the host material; specifically, the weight ratio of the guest material to the host material is preferably greater than 0 and less than 0.03.

As described above, the dibenzocarbazole compound of one embodiment of the present invention can be suitably used for a light-emitting element that emits deep blue light. With the dibenzocarbazole compound of one embodiment of the present invention, a light-emitting element with a high emission efficiency can be fabricated. With the dibenzocarbazole compound of one embodiment of the present invention, a light-emitting element with lower power consumption can be fabricated. With the dibenzocarbazole compound of one embodiment of the present invention, a light-emitting element with a long driving lifetime can be fabricated.

The structures described in this example can be used in combination with any of the structures described in the other embodiments as appropriate.

In this example, a fabrication example of light-emitting elements 5 and 6 including a compound of one embodiment of the present invention and the characteristics of the light-emitting elements will be described. For comparison, light-emitting elements 7 and 8 including a compound different from that of one embodiment of the present invention were also fabricated.FIG. 2Acan be referred to for a schematic cross-sectional view of the light-emitting element fabricated in this example. Table 3 shows details of the element structure. In addition, structures and abbreviations of compounds used are given below. Note that the above examples are referred to for other compounds.

As the electrode101, an ITSO film was formed to a thickness of 70 nm over a substrate. The electrode area of the electrode101was set to 4 mm2(2 mm×2 mm).

Then, as the hole-injection layer111over the electrode101, 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: PCzPA) and molybdenum oxide (MoO3) were deposited by co-evaporation to a thickness of 10 nm such that the weight ratio of PCzPA to MoO3was 1:0.5.

Next, as the hole-transport layer112over the hole-injection layer111, PCzPA was deposited by evaporation to a thickness of 20 nm.

Then, as the light-emitting layer120over the hole-transport layer112, agDBCzPA and 1,6mMemFLPAPrn were deposited by co-evaporation to a thickness of 25 nm such that the weight ratio of agDBCzPA to 1,6mMemFLPAPrn was 1:0.01. Note that in the light-emitting layer120, agDBCzPA is a host material and 1,6mMemFLPAPrn is a guest material (fluorescent material).

Then, as the electron-transport layer113over the light-emitting layer120, agDBCzPA and BPhen were sequentially deposited by evaporation to thicknesses of1Q nm and 15 nm, respectively. After that, as the electron-injection layer114over the electron-transport layer113, lithium fluoride (LiF) was deposited by evaporation to a thickness of 1 nm.

Next, as the electrode102over the electron-injection layer114, aluminum (Al) was deposited to a thickness of 200 nm.

Next, in a glove box containing a nitrogen atmosphere, a sealing substrate was fixed to the substrate over which the organic materials were deposited using a sealant for an organic EL device, so that the light-emitting element 5 was sealed. Through the above steps, the light-emitting element 5 was obtained.

The light-emitting element 6 was fabricated through the same steps as those for the above-mentioned light-emitting element 5 except for the steps of forming the light-emitting layer120and the electron-transport layer113.

As the light-emitting layer120in the light-emitting element 6, aiDBCzPA and 1,6mMemFLPAPrn were deposited by co-evaporation to a thickness of 25 nm such that the weight ratio of aiDBCzPA to 1,6mMemFLPAPrn was 1:0.01. Note that in the light-emitting layer120, aiDBCzPA is a host material and 1,6mMemFLPAPrn is a guest material (fluorescent material).

As the electron-transport layer113in the light-emitting element 6, aiDBCzPA and BPhen were sequentially deposited by evaporation to thicknesses of 10 nm and 15 nm, respectively.

The light-emitting element 7 for comparison was fabricated through the same steps as those for the above-mentioned light-emitting element 5 except for the steps of forming the light-emitting layer120and the electron-transport layer113.

As the light-emitting layer120in the light-emitting element 7,7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole (abbreviation: cgDBCzPA) and 1,6mMemFLPAPrn were deposited by co-evaporation to a thickness of 25 nm such that the weight ratio of cgDBCzPA to 1,6mMemFLPAPrn was 1:0.03. Note that in the light-emitting layer120, cgDBCzPA is a host material and 1,6mMemFLPAPrn is a guest material (fluorescent material).

As the electron-transport layer113in the light-emitting element 7, cgDBCzPA and BPhen were sequentially deposited by evaporation to thicknesses of 10 nm and 15 nm, respectively.

The light-emitting element 8 for comparison was fabricated through the same steps as those for the above-mentioned light-emitting element 5 except for the steps of forming the light-emitting layer120and the electron-transport layer113.

As the light-emitting layer120in the light-emitting element 8,9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA) and 1,6mMemFLPAPrn were deposited by co-evaporation to a thickness of 25 nm such that the weight ratio of CzPA to 1,6mMemFLPAPrn was 1:0.04. Note that in the light-emitting layer120, CzPA is a host material and 1,6mMemFLPAPrn is a guest material (fluorescent material).

As the electron-transport layer113in the light-emitting element 8, CzPA and BPhen were sequentially deposited by evaporation to thicknesses of 10 nm and 15 nm, respectively.

Next, the emission characteristics of the fabricated light-emitting elements 5 to 8 were measured. Note that the measurement was performed at room temperature (in an atmosphere maintained at 25° C.) as in Example 3.FIG. 49shows the current efficiency-luminance characteristics of the light-emitting elements 5 to 8,FIG. 50shows the luminance-voltage characteristics thereof, andFIG. 51shows the external quantum efficiency-luminance characteristics thereof.FIG. 52shows the electroluminescence spectra when a current with a current density of 2.5 mA/cm2was supplied to the light-emitting elements 5 to 8.

Table 4 shows the emission characteristics of the light-emitting elements at a luminance around 1000 cd/m2.

As shown inFIG. 52, the light-emitting elements 5 to 8 exhibited blue light emission derived from the guest material (1,6mMemFLPAPrn).

FIG. 49toFIG. 52and Table 4 show that the light-emitting elements 5 to 8, which include a fluorescent material as a light-emitting material, have a high current efficiency and a high external quantum efficiency.

The light-emitting elements 5 and 6 have a high current efficiency and a high external quantum efficiency although they exhibit deep blue emission with a chromaticity y of 0.143 and 0.135. That is, a light-emitting element including the dibenzocarbazole compound of one embodiment of the present invention as a host material can be suitably used for a light-emitting element that emits deep blue light.

Furthermore, the light-emitting elements 5 and 6 are driven at a low voltage and therefore consume low power. That is, a light-emitting element driven at a low voltage can be fabricated when the dibenzocarbazole compound of one embodiment of the present invention, which has a high carrier-transport property, is used as a host material and an electron-transport material.

Next, the driving lifetime of the light-emitting elements 5 to 8 was measured.FIG. 53shows the measurement results of the driving lifetime test. Note that the driving lifetime test was performed while the light-emitting elements 5 to 8 were continuously driven with a constant current density, which was set to 44.87 mA/cm2so that the light-emitting element 7 had an initial luminance of 5000 cd.

As shown inFIG. 53, the light-emitting elements 5 and 6, which include a blue fluorescent material as a light-emitting material, have a long driving lifetime. In addition, the light-emitting element 5 has a driving lifetime equal to that of the light-emitting element 7 and longer than that of the light-emitting element 8 although it emits deeper blue light than the light-emitting elements 7 and 8. The light-emitting element 6 has a longer driving lifetime than the light-emitting element 8 although it emits deeper blue light than the light-emitting element 8.

In the light-emitting element that emits blue light, a high emission energy needs to be confined in the light-emitting layer, which makes it difficult to obtain a long driving lifetime particularly in the light-emitting element that exhibits deep blue emission. However, the light-emitting element including the dibenzocarbazole compound of one embodiment of the present invention as the host material emits deep blue light while exhibiting a long driving lifetime. This indicates that the dibenzocarbazole compound of one embodiment of the present invention can be suitably used for light-emitting elements that emit deep blue light. Specifically, the dibenzocarbazole compound of one embodiment of the present invention can be suitably used for a light-emitting element that emits deep blue having a chromaticity y of 0.01 to 0.15.

As described above, the dibenzocarbazole compound of one embodiment of the present invention can be suitably used for a light-emitting element that emits deep blue light. With the dibenzocarbazole compound of one embodiment of the present invention, a light-emitting element with a high emission efficiency can be fabricated. With the dibenzocarbazole compound of one embodiment of the present invention, a light-emitting element with lower power consumption can be fabricated. With the dibenzocarbazole compound of one embodiment of the present invention, a light-emitting element with a long driving lifetime can be fabricated.

The structures described in this example can be used in combination with any of the structures described in the other embodiments as appropriate.

This application is based on Japanese Patent Application serial No. 2015-214392 filed with Japan Patent Office on Oct. 30, 2015, the entire contents of which are hereby incorporated by reference.