Abstract:
An object is to improve luminous efficiency of a light emitting element using triplet exciton energy effectively. Another object is to reduce power consumption of a light emitting element, a light emitting device, and an electronic device. Triplet exciton energy generated in a light emitting layer which exhibits short wavelength fluorescence can be effectively utilized by use of a structure in which the light emitting layers which exhibit short wavelength fluorescence are sandwiched between light emitting layers each including a phosphorescent compound. Further, the emission balance can be improved between the light emitting layer including a phosphorescent compound and the light emitting layer which exhibits fluorescence by the devising of the structure of the light emitting layer which exhibits fluorescence.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to light emitting elements using electroluminescence. In addition, the present invention relates to a light emitting device and an electronic device having the light emitting element. 
         [0003]    2. Description of the Related Art 
         [0004]    In recent years, research and development has been extensively conducted on light emitting elements using electroluminescence. In a basic structure of these light emitting elements, a substance having a light emitting property is interposed between a pair of electrodes. By application of voltage to these elements, light emission can be obtained from the substance having a light emitting property. 
         [0005]    Since such a light emitting element is of self-light emitting type, it is considered that the light emitting element has advantages over a liquid crystal display in that visibility of pixels is high, backlight is not required, and the like and is therefore suitable for a flat panel display element. Another major advantage of such a light emitting element is that it can be manufactured to be thin and lightweight. In addition, extremely high response speed is also a feature. 
         [0006]    Since the light emitting element can be formed into a film shape, planar light emission can be easily obtained by forming a large-area element. This is a feature that is hard to be obtained in point sources typified by an incandescent lamp and an LED or linear sources typified by a fluorescent light. Therefore, the light emitting element has a high utility value as a surface light source that can be applied to lighting and the like. 
         [0007]    Light emitting elements using electroluminescence are classified broadly according to whether they use an organic compound or an inorganic compound as a substance having a light emitting property. 
         [0008]    When an organic compound is used as a substance having a light emitting property, electrons and holes are injected into a layer including an organic compound having a light emitting property from a pair of electrodes by voltage application to a light emitting element, so that current flows therethrough. Then, the carriers (electrons and holes) are recombined, and thus, the organic compound having a light emitting property is excited. The organic compound having a light emitting property returns to a ground state from the excited state, thereby emitting light. Owing to this mechanism, such a light emitting element is referred to as a current-excitation light emitting element. 
         [0009]    Note that the excited state generated by an organic compound can be types of a singlet excited state and a triplet excited state, and 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. 
         [0010]    In improving the element characteristics of such a light emitting element, there are many problems caused by the material, and in order to solve such problems, an improvement of the element structure, a development of materials, and the like have been carried out. 
         [0011]    For example, in Non-Patent Document 1, a light emitting element with high efficiency is realized by using a method called Triplet Harvesting. 
       [Reference] 
     [Non-Patent Document 1] 
       [0012]    M. E. Kondakova, et al., SID 08 DIGEST, pp. 219-222 (2008) 
         [0013]    However, as for the structure disclosed in Non-Patent Document 1, a light-emitting layer (Yellow LEL) containing a yellow emissive phosphorescent compound is provided on a cathode side of a light-emitting layer (Blue LEL) containing a blue emissive fluorescent compound. Therefore, a part of the triplet excitation energy of the blue emissive fluorescent compound is transferred to the cathode side, which allows the yellow emissive phosphorescent compound in the Yellow LEL to emit light. On the other hand, since an electron blocking layer (EBL) having greater triplet-excitation energy than that in the Blue LEL is provided on the anode side of the Blue LEL, the transfer of the triplet excitation energy of the blue emissive fluorescent compound to an anode side is impossible. Thus, a part of the triplet excitation energy of the blue emissive fluorescent compound is consumed through the nonradiative process and does not contribute to the light emission. 
         [0014]    Thus, it is an object of one embodiment of the present invention to improve luminous efficiency of a light emitting element by using triplet exciton energy more effectively. 
         [0015]    In addition, it is another object of one embodiment of the present invention to reduce power consumption of a light emitting element, a light emitting device, and an electronic device. 
       SUMMARY OF THE INVENTION 
       [0016]    The present inventors found that triplet exciton energy generated in a light emitting layer which exhibits short wavelength fluorescence can be effectively utilized by use of a structure in which the light emitting layers which exhibit short wavelength fluorescence are sandwiched between light emitting layers each including a substance which exhibits phosphorescence (hereinafter referred to as a phosphorescent compound). In addition, when light emitting layers which simply exhibit short wavelength fluorescence are sandwiched only by light emitting layers each including a phosphorescent compound, carriers go through the light emitting layer which exhibits fluorescence, and the emission intensity balance collapses. However, they found that the emission intensity balance is improved between the light emitting layer including a phosphorescent compound and the light emitting layer which exhibits fluorescence by the devising of the structure of the light emitting layer which exhibits fluorescence. 
         [0017]    Therefore, a light emitting element according one feature of an embodiment of the present invention includes a first layer, a second layer, a third layer, and a fourth layer which are sequentially provided on an anode side between the anode and a cathode; the first layer and the second layer each include a hole transporting property; the third layer and the fourth layer each include an electron transporting property; the first layer includes a first phosphorescent compound and a first organic compound having a hole transporting property; the second layer includes a first fluorescent compound and a second organic compound having a hole transporting property; the third layer includes a second fluorescent compound and a first organic compound having an electron transporting property; and the fourth layer includes a second phosphorescent compound and a second organic compound having an electron transporting property. The triplet excitation energy of the second organic compound having a hole transporting property is higher than or equal to the triplet excitation energy of the first organic compound having a hole transporting property, and the triplet excitation energy of the first organic compound having an electron transporting property is higher than or equal to the triplet excitation energy of the second organic compound having an electron transporting property. 
         [0018]    In the above structure, it is preferable that the first organic compound having a hole transporting property and the second organic compound having a hole transporting property be the same organic compound. Since the first organic compound having a hole transporting property and the second organic compound having a hole transporting property are the same organic compound, an energy barrier due to carrier transfer is reduced. 
         [0019]    In the above structure, it is preferable that the first organic compound having an electron transporting property and the second organic compound having an electron transporting property be the same organic compound. Since the first organic compound having an electron transporting property and the second organic compound having an electron transporting property are the same organic compound, an energy barrier due to carrier transfer is reduced. 
         [0020]    In the above structure, it is preferable that a spacing layer formed using one or both of the first organic compound having a hole transporting property and the second organic compound having a hole transporting property be provided between the first layer and the second layer. In addition, it is preferable that a spacing layer formed using one or both of the first organic compound having an electron transporting property and the second organic compound having an electron transporting property be provided between the third layer and the fourth layer. By provision of the spacing layers, energy transfer from the second layer to the first layer and from the third layer to the fourth layer can be adjusted. 
         [0021]    In the above structure, the total thickness of the second layer and the third layer is preferably from 5 nm to 20 nm. When the total thickness of the second layer and the third layer is too large, light emission from the first layer and the fourth layer is reduced, and when the total thickness of the second layer and the third layer is too small, light emission from the second layer and the third layer is reduced. The thickness lies within the range, whereby light emission from each layer of the first layer, the second layer, the third layer, and the fourth layer can be balanced well. 
         [0022]    In the above structure, the concentration of the first fluorescent compound in the second layer is preferably from 0.1 wt % to 10 wt %. In addition, the concentration of the second fluorescent compound in the third layer is preferably from 0.1 wt % to 10 wt %. The concentration lies within the range, whereby strong light emission of the second layer or the third layer can be prevented and weak light emission of the first layer or the fourth layer can be prevented, so that light emission from each layer of the first layer, the second layer, the third layer, and the fourth layer can be balanced well. 
         [0023]    In the above structure, the first fluorescent organic compound and the second fluorescent organic compound are preferably the same organic compound. When the first fluorescent organic compound and the second fluorescent organic compound are the same organic compound, a light emitting element is easily manufactured. 
         [0024]    In the above structure, the emission color of each of the first fluorescent organic compound and the second fluorescent organic compound is preferably blue, and the emission color of the first phosphorescent compound is preferably green and the emission color of the second phosphorescent compound is preferably red. With such a structure, a white light emitting element can be obtained. 
         [0025]    In the above structure, the first phosphorescent compound and the second phosphorescent compound are preferably the same organic compound. When the first phosphorescent compound and the second phosphorescent compound are the same organic compound, a light emitting element is easily manufactured. 
         [0026]    In the above structure, it is preferable that the first fluorescent organic compound and the second fluorescent organic compound be the same organic compound, the first phosphorescent compound and the second phosphorescent compound be the same organic compound, and the emission color of the first phosphorescent compound and the second phosphorescent compound, the emission color of the first fluorescent compound and the second fluorescent compound be made to be complementary colors. With such a structure, a white light emitting element can be obtained. 
         [0027]    Moreover, an embodiment of the present invention includes a light emitting device having the above-described light emitting element. The light emitting device in this specification includes an image display device, a light emitting device, or a light source (including a lighting device). Further, the following are all included in a light emitting device: a module in which a connector, for example, a flexible printed circuit (FPC), a tape automated bonding (TAB) tape, or a tape carrier package (TCP) is attached to a panel provided with a light emitting element; a module provided with a printed wiring board at the end of the TAB tape or the TCP; and a module in which an integrated circuit (IC) is directly mounted to a light emitting element by a chip on glass (COG) method. 
         [0028]    Further, an electronic device using the light emitting element according to an embodiment of the present invention in a display portion is also included in the scope of the present invention. Consequently, one feature of an electronic device according to an embodiment of the present invention is to include a display portion, in which the display portion is provided with the above-described light emitting element and a control means to control light emission of the light emitting element. 
         [0029]    By application of an embodiment of the present invention, the singlet exciton and the triplet exciton which are generated in the light emitting layer can be effectively used, and a light emitting element with high luminous efficiency can be realized. 
         [0030]    In addition, by application of an embodiment of the present invention, power consumption of a light emitting element, a light emitting device, and an electronic device can be reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  illustrates a light emitting element according to an embodiment of the present invention. 
           [0032]      FIG. 2  is a band diagram illustrating a light emitting element according to an embodiment of the present invention. 
           [0033]      FIG. 3  is a band diagram illustrating a light emitting element according to an embodiment of the present invention. 
           [0034]      FIG. 4  illustrates a light emitting element according to an embodiment of the present invention. 
           [0035]      FIGS. 5A to 5C  illustrate a light emitting element according to an embodiment of the present invention. 
           [0036]      FIG. 6  illustrates a light emitting element according to an embodiment of the present invention. 
           [0037]      FIG. 7  illustrates a light emitting element according to an embodiment of the present invention. 
           [0038]      FIGS. 8A and 8B  illustrate a light emitting device according to an embodiment of the present invention. 
           [0039]      FIGS. 9A and 9B  illustrate a light emitting device according to an embodiment of the present invention. 
           [0040]      FIGS. 10A to 10D  each illustrate an electronic device according to an embodiment of the present invention. 
           [0041]      FIG. 11  illustrates an electronic device according to an embodiment of the present invention. 
           [0042]      FIG. 12  illustrates an electronic device according to an embodiment of the present invention. 
           [0043]      FIG. 13  illustrates an electronic device according to an embodiment of the present invention. 
           [0044]      FIG. 14  illustrates a lighting device according to an embodiment of the present invention. 
           [0045]      FIG. 15  illustrates a lighting device according to an embodiment of the present invention. 
           [0046]      FIGS. 16A to 16C  illustrate an electronic device according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0047]    Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, embodiment of the present invention is not limited to the following description, and various changes and modifications for the modes and details thereof will be apparent to those skilled in the art unless such changes and modifications depart from the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited to what is described in the embodiments described below. Note that like portions or portions having a similar function are denoted by the same reference numerals through drawings, and therefore, description thereof is omitted. 
       Embodiment 1 
       [0048]    A mode of a light emitting element according to an embodiment of the present invention is described with reference to  FIGS. 1 ,  2 ,  3 , and  4 . 
         [0049]    The light emitting element according to an embodiment of the present invention has a plurality of layers between a pair of electrodes. In this specification, the plurality of layers formed between the pair of electrodes is collectively referred to as an EL layer. The EL layer has at least a light emitting layer. 
         [0050]    In this embodiment, the light emitting element includes a first electrode  102 , a second electrode  104 , and an EL layer  103  formed between the first electrode  102  and the second electrode  104 , as illustrated in  FIG. 1 . Note that in this embodiment, the first electrode  102  serves as an anode and the second electrode  104  serves as a cathode. In other words, when voltage is applied to the first electrode  102  and the second electrode  104  such that potential of the first electrode  102  is higher than that of the second electrode  104 , light emission can be obtained. Such a case is described below. 
         [0051]    A substrate  101  is used as a support of the light emitting element. The substrate  101  can be formed with, for example, glass, plastic, or the like. Note that materials other than glass or plastic can be used as long as they can function as a support of the light emitting element. 
         [0052]    The first electrode  102  is preferably formed using a metal, an alloy, an electrically conductive compound, a mixture of these, or the like each having a high work function (specifically, a work function of 4.0 eV or higher is preferable). Specifically, indium tin oxide (ITO), indium tin oxide including silicon or silicon oxide, indium zinc oxide (IZO), indium oxide including tungsten oxide and zinc oxide (IWZO), or the like can be used. These conductive metal oxide films are generally formed by sputtering; however, the films may be manufactured by applying a sol-gel method. For example, indium zinc oxide (IZO) can be formed by a sputtering method using indium oxide into which 1 wt % to 20 wt % of zinc oxide is added, as a target. Indium oxide including tungsten oxide and zinc oxide (IWZO) can be formed by a sputtering method using a target in which 0.5 wt % to 5 wt % of tungsten oxide and 0.1 wt % to 1 wt % of zinc oxide are mixed with indium oxide. In addition, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), nitride of a metal material (such as titanium nitride), and the like can be given. 
         [0053]    The second electrode  104  can be formed using a metal, an alloy, an electrically conductive compound, a mixture of these, or the like each having a low work function (specifically, a work function of 3.8 eV or lower is preferable). As a specific example of such a cathode material, an element belonging to Group 1 or Group 2 in the periodic table, that is, an alkali metal such as lithium (Li) or cesium (Cs); an alkaline earth metal such as magnesium (Mg), calcium (Ca), or strontium (Sr); an alloy including any of these (MgAg, AlLi); a rare-earth metal such as europium (Eu) or ytterbium (Yb); an alloy of these; and the like can be given. However, when an electron injecting layer is provided between the second electrode  104  and an electron transporting layer, the second electrode  104  can be formed using various conductive materials such as Al, Ag, ITO, or indium tin oxide including silicon or silicon oxide regardless of its work function. 
         [0054]    There is no particular limitation on the stacked structure of the EL layer  103 , and layers formed with substances having a high electron transporting property, a substance having a high hole transporting property, a substance having a high electron injecting property, a substance having a high hole injecting property, a bipolar substance (a substance having high electron transporting and hole transporting properties) and/or the like may be combined with the light emitting layer described in this embodiment, as appropriate. For example, a hole injecting layer, a hole transporting layer, a hole blocking layer, an electron transporting layer, an electron injecting layer, and the like may be combined as appropriate with the light emitting layer described in Embodiment 1. Specific materials to form each of the layers are given below.  FIG. 1  illustrates a structure in which the first electrode  102 , a hole transporting layer  112 , a light emitting layer  113 , an electron transporting layer  114 , and the second electrode  104  are sequentially stacked, as an example. 
         [0055]    The hole transporting layer  112  is a layer including a substance having a high hole transporting property. As examples of the substance having a high hole transporting property, there are aromatic amine compounds such as 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (abbreviation: TPD), 4,4′,4″-tris(carbazol-9-yl)triphenylamine (abbreviation: TCTA), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA), 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbreviation: MTDATA), and 4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB), and the like. The substances described here are mainly substances having a hole mobility of 10 −6  cm 2 /Vs or more. Note that any other substance having a hole transporting property which is higher than an electron transporting property may be used. Note that the layer including a substance having a high hole transporting property is not limited to a single layer, and two or more layers including the above-described substances may be stacked. 
         [0056]    Furthermore, for the hole transporting layer  112 , a high molecular compound can be used. Examples of high molecular compounds include poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA), poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide] (abbreviation: PTPDMA), poly[N,N-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine (abbreviation: Poly-TPD), and the like. 
         [0057]    The light emitting layer  113  is a layer including a substance having a high light emitting property. In the light emitting element according to an embodiment of the present invention, the light emitting layer  113  includes a first layer  121 , a second layer  122 , a third layer  123 , and a fourth layer  124  which are sequentially provided from the side of the first electrode  102  that functions as an anode. 
         [0058]    The first layer  121  has a hole transporting property and includes a first substance which exhibits phosphorescence (hereinafter referred to as a phosphorescent compound) and a first organic compound having a hole transporting property. The triplet excitation energy of the first phosphorescent compound is the same as or lower than the triplet excitation energy of the first organic compound having a hole transporting property. 
         [0059]    The second layer  122  has a hole transporting property and includes a first substance which exhibits fluorescence (hereinafter referred to as a fluorescent compound) and a second organic compound having a hole transporting property. The singlet excitation energy of the first fluorescent compound is the same as or lower than the singlet excitation energy of the second organic compound having a hole transporting property. 
         [0060]    The third layer  123  has an electron transporting property and includes a second fluorescent compound and a first organic compound having an electron transporting property. The singlet excitation energy of the second fluorescent compound is the same as or lower than the singlet excitation energy of the first organic compound having an electron transporting property. 
         [0061]    The fourth layer  124  has an electron transporting property and includes a second phosphorescent compound and a second organic compound having an electron transporting property. The triplet excitation energy of the second phosphorescent compound is the same as or lower than the triplet excitation energy of the second organic compound having an electron transporting property. 
         [0062]    With such a structure, when voltage is applied to the first electrode  102  and the second electrode  104  such that the potential of the first electrode  102  is higher than that of the second electrode  104 , a recombination region is formed in the vicinity of the interface between the second layer  122  and the third layer  123 . 
         [0063]    In other words, as illustrated in  FIG. 2 , holes injected from the first electrode  102  are transported through the hole transporting layer  112  to the first layer  121 . Because the first layer  121  has a hole transporting property, the holes are transported through the first layer  121  to the second layer  122 . Because the second layer  122  also has a hole transporting property, the holes are transported to the vicinity of the interface between the second layer  122  and the third layer  123 . On the other hand, electrons injected from the second electrode  104  are transported through the electron transporting layer  114  to the fourth layer  124 . Because the fourth layer  124  has an electron transporting property, the electrons are transported through the fourth layer  124  to the third layer  123 . Because the third layer  123  also has an electron transporting property, the electrons are transported to the vicinity of the interface between the third layer  123  and the second layer  122 . Then, in the vicinity of the interface between the second layer  122  and the third layer  123 , the holes and the electrons are recombined. In this recombination region  131 , an exciton of a singlet excited state (S*) and an exciton of a triplet excited state (T*) are generated, and the statistical generation ratio is thought to be S*:T*=1:3. The energy of the exciton of a singlet excited state is transferred to a singlet excited state of the first fluorescent compound included in the second layer  122  and a singlet excited state of the second fluorescent compound included in the third layer  123 , whereby the first fluorescent compound and the second fluorescent compound emit light. 
         [0064]    On the other hand, in a conventional light emitting element, an exciton of a triplet excited state generated in the recombination region  131  is deactivated without contribution to light emission, or only a part is used as disclosed in Non-Patent Document 1. 
         [0065]    In the light emitting element according to an embodiment of the present invention, the triplet excitation energy (an energy difference between a ground state and a triplet excited state) of the second organic compound having a hole transporting property is the same as or higher than the triplet excitation energy of the first organic compound having a hole transporting property. The triplet excitation energy of the first organic compound having an electron transporting property is the same as or higher than the triplet excitation energy of the second organic compound having an electron transporting property. With such a structure, exciton energy of a triplet excited state generated in the recombination region  131  can be transferred through the second layer to the first layer  121 , and the energy of the exciton can be transferred to the triplet excited state of the first organic compound having a hole transporting property included in the first layer  121 . In addition, exciton energy of a triplet excited state generated in the recombination region  131  can be transferred through the third layer to the fourth layer  124 , and the energy of the exciton can be transferred to a triplet excited state of a second organic compound having an electron transporting property included in the fourth layer  124 . 
         [0066]    As a result, energy is transferred from the triplet excited state of the first organic compound having a hole transporting property to the triplet excited state of the first phosphorescent compound, whereby the first phosphorescent compound emits light. In addition, energy is transferred from the triplet excited state of the second organic compound having an electron transporting property to the triplet excited state of the second phosphorescent compound, whereby the second phosphorescent compound emits light. 
         [0067]    In other words, by application of an embodiment of the present invention, the exciton of the singlet excited state and the exciton of the triplet excited state which are generated in the recombination region  131  can be effectively used for light emission. 
         [0068]    As for the light emitting element according to an embodiment of the present invention, the above-mentioned structure of the light emitting layer  113  is adopted, whereby the recombination region  131  can be limited to the vicinity of the center of the light emitting layer  113 , and carrier penetration can be suppressed, so that the emission intensity balance can be improved. In addition, the thickness of each layer (the first layer  121 , the second layer  122 , the third layer  123 , and the fourth layer  124 ) is adjusted, whereby the distance from the recombination region  131  to each layer can be adjusted; therefore, the emission balance can be improved. 
         [0069]    In the above structure, it is preferable that the first organic compound having a hole transporting property included in the first layer  121  and the second organic compound having a hole transporting property included in the second layer  122  be the same organic compound. By use of the same organic compound, the excitons of the triplet excited state generated in the recombination region  131  are easily diffused, and the energy is more smoothly transferred to the triplet excited state of the first organic compound having a hole transporting property included in the first layer  121 . In addition, manufacture of a light emitting element also becomes easy. 
         [0070]    In a similar manner, it is preferable that the first organic compound having an electron transporting property included in the third layer  123  and the second organic compound having an electron transporting property included in the fourth layer  124  be the same organic compound. By use of the same organic compound, the excitons of the triplet excited state generated in the recombination region  131  are easily diffused, and the energy is more smoothly transferred to the triplet excited state of the second organic compound having an electron transporting property included in the fourth layer  124 . In addition, manufacture of a light emitting element also becomes easy. 
         [0071]    As illustrated in  FIG. 3 , it is preferable that a spacing layer  141  formed using one or both of the first organic compound having a hole transporting property and the second organic compound having a hole transporting property be provided between the first layer  121  and the second layer  122 . In  FIG. 3 , the spacing layer  141  formed using the second organic compound having a hole transporting property is illustrated as an example. By provision of the spacing layer  141 , the distance between the recombination region  131  and the first layer  121  is easily adjusted, whereby light emission intensity from the first layer  121  is easily adjusted in accordance with the transfer of the energy from the triplet excited state. In addition, the singlet excitation energy of the first fluorescent compound included in the second layer  122  can be prevented from transferring to the first phosphorescent compound included in the first layer  121  due to the energy transfer by the Forster mechanism. Further, one or both of the first organic compound having a hole transporting property and the second organic compound having a hole transporting property is used for the spacing layer  141 , whereby the energy from the triplet excited state can be smoothly transferred. In addition, the spacing layer can be easily formed. 
         [0072]    In a similar manner, it is preferable that a spacing layer formed using one or both of the first organic compound having an electron transporting property and the second organic compound having an electron transporting property be provided between the third layer  123  and the fourth layer  124 . In  FIG. 3 , a spacing layer  142  formed using the first organic compound having an electron transporting property is illustrated as an example. By provision of the spacing layer, the distance between the recombination region  131  and the fourth layer  124  is easily adjusted, whereby light emission intensity from the fourth layer  124  is easily adjusted in accordance with the transfer of the energy from the triplet excited state. In addition, the singlet excitation energy of the second fluorescent compound included in the third layer  123  can be prevented from transferring to the second phosphorescent compound included in the fourth layer  124  due to the energy transfer by the Forster mechanism. Further, one or both of the first organic compound having an electron transporting property and the second organic compound having an electron transporting property is used for the spacing layer, whereby the energy from the triplet excited state can be smoothly transferred. In addition, a spacing layer can be easily formed. 
         [0073]    Further, the total thickness of the second layer  122  and the third layer  123  is preferably greater than or equal to 5 nm and less than or equal to 20 nm. When the total thickness of the second layer  122  and the third layer  123  is too small, carriers penetrate, and the recombination region expands. When the total thickness of the second layer  122  and the third layer  123  is too large, the triplet excitation energy from the recombination region is not transferred to the first layer  121  and the fourth layer  124 , so that the first phosphorescent compound and the second phosphorescent compound do not emit light. Therefore, the total thickness of the second layer  122  and the third layer  123  is preferably greater than or equal to 5 nm and less than or equal to 20 nm. 
         [0074]    In addition, the concentration of the first fluorescent organic compound in the second layer  122  is preferably greater than or equal to 0.1 wt % and less than or equal to 10 wt %. When the concentration of the first fluorescent organic compound is too low, light emission from the first fluorescent organic compound is reduced. Further, when the concentration of the first fluorescent organic compound is too high, the energy from the triplet excitation energy from the recombination region is received by the first fluorescent organic compound, thereby deactivating excitons without light emission. Therefore, the concentration of the first fluorescent organic compound in the second layer  122  is preferably greater than or equal to 0.1 wt % and less than or equal to 10 wt %. 
         [0075]    In a similar manner, the concentration of the second fluorescent organic compound in the third layer  123  is preferably greater than or equal to 0.1 wt % and less than or equal to 10 wt %. When the concentration of the second fluorescent organic compound is too low, light emission from the second fluorescent organic compound is reduced. In addition, when the concentration of the second fluorescent organic compound is too high, the energy from the triplet excitation energy from the recombination region is received by the second fluorescent organic compound, thereby deactivating excitons without light emission. Therefore, the concentration of the second fluorescent organic compound in the third layer  123  is preferably greater than or equal to 0.1 wt % and less than or equal to 10 wt %. 
         [0076]    It is preferable that the first fluorescent organic compound included in the second layer  122  and the second fluorescent organic compound included in the third layer  123  be the same organic compound. By use of the same organic compound, the energy of the exciton generated from the recombination region  131  is more equally transferred to the second layer  122  and the third layer  123 . Therefore, the emission balance can be improved. In addition, manufacture of a light emitting element also becomes easy. 
         [0077]    Since light emission can be obtained from a plurality of substances each having a high light emitting property, the light emitting element according to an embodiment of the present invention is suitable for a white light emitting element. The light emitting element according to an embodiment of the present invention is applied to the white light emitting element, whereby a white light emitting element with high efficiency can be obtained. 
         [0078]    For example, the emission color of the first fluorescent organic compound and the emission color of the first phosphorescent compound are made to be complementary colors, whereby a white light emitting element can be obtained. In addition, the emission color of the second fluorescent organic compound and the emission color of the second phosphorescent compound are made to be complementary colors, whereby a white light emitting element with an excellent color rendering property can be obtained. 
         [0079]    Note that “complementary color” means a relation between colors which becomes an achromatic color when they are mixed. That is, white light emission can be obtained by mixture of light from substances whose emission colors are complementary colors. 
         [0080]    In addition, for example, the emission color of the first fluorescent organic compound and the emission color of the second phosphorescent compound are made to be complementary colors, whereby a white light emitting element can be obtained. Further, the emission color of the second fluorescent organic compound and the emission color of the first phosphorescent compound are made to be complementary colors, whereby a white light emitting element with an excellent color rendering property can be obtained. 
         [0081]    The emission color of the first fluorescent organic compound and that of the second fluorescent organic compound are blue, and the emission color of the first phosphorescent compound is green and the emission color of the second phosphorescent compound is red, whereby a white light emitting element with an excellent color rendering property can be obtained. 
         [0082]    When the first fluorescent organic compound and the second fluorescent organic compound are the same organic compound, and the first phosphorescent compound and the second phosphorescent compound are the same organic compound, the emission color of the first phosphorescent compound and the second phosphorescent compound and the emission color of the first fluorescent organic compound and the second fluorescent organic compound are made to be complementary colors, whereby a white light emitting element can be obtained. Since the first fluorescent organic compound and the second fluorescent organic compound are the same organic compound, the energy from the recombination region to the second layer  122  and the third layer  123  is more equally transferred, whereby the emission balance can be improved. In addition, manufacture of a light emitting element also becomes easy. Further, when the first phosphorescent compound and the second phosphorescent compound are the same organic compound, a white light emitting element can be more easily formed. 
         [0083]    Various kinds of materials can be used for the phosphorescent compounds of the second layer  122  and the third layer  123 . For example, as a blue light emitting phosphorescent compound, organometallic complexes such as bis[2-(4′,6′-difluorophenyl)pyridinato-N,C 2′ ]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6), bis[2-(4′,6′-difluorophenyl)pyridinato-N,C 2′ ]iridium(III)picolinate (abbreviation: FIrpic), bis[2-(3′,5′bistrifluoromethylphenyl)pyridinato-NC 2′ ]iridium(III)picolinate (abbreviation: Ir(CF 3 ppy) 2 (pic)), and bis[2-(4′,6′-difluorophenyl)pyridinato-N,C 2′ ]iridium(III)acetylacetonate (abbreviation: FIr(acac)) can be given. As a green light emitting phosphorescent compound, organometallic complexes such as tris(2-phenylpyridinato-N,C 2′ )iridium(III) (abbreviation: Ir(ppy) 3 ), bis(2-phenylpyridinato-N,C 2′ )iridium(III)acetylacetonate (abbreviation: Ir(ppy) 2 (acac)), bis(1,2-diphenyl-1H-benzimidazolato)iridium(III)acetylacetonate (abbreviation: Ir(pbi) 2 (acac)), and bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: Ir(bzq) 2 (acac)), can be given. As a yellow light emitting phosphorescent compound, organometallic complexes such as bis(2,4-diphenyl-1,3-oxazolato-N,C 2′ )iridium(III)acetylacetonate (abbreviation: Ir(dpo) 2 (acac)), bis[2-(4′-(perfluorophenylphenyl)pyridinato]iridium(III) acetylacetonate (abbreviation: Ir(p-PF-ph) 2 (acac)), and bis(2-phenylbenzothiazolato-N,C 2′ )iridium(III)acetylacetonate (abbreviation: Ir(bt) 2 (acac)) can be given. As an orange light emitting phosphorescent compound, organometallic complexes such as tris(2-phenylquinolinato-N,C 2 )iridium(III) (abbreviation: Ir(pq) 3 ), bis(2-phenylquinolinato-N,C 2 )iridium(III)acetylacetonate (abbreviation: Ir(pq) 2 (acac)), and (acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium(III) (abbreviation: [Ir(mppr-Me) 2 (acac)] can be given. As a red light emitting phosphorescent compound, organometallic complexes such as bis[2-(2′-benzo[4,5-a]thienyl)pyridinato-N,C 3′ )iridium(III) acetylacetonate (abbreviation: Ir(btp) 2 (acac)), bis(1-phenylisoquinolinato-N, C 2′ )iridium(III)acetylacetonate (abbreviation: Ir(piq) 2 (acac)), (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: Ir(Fdpq) 2 (acac)), and 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinplatinum(II) (abbreviation: PtOEP) can be given. In addition, a rare-earth metal complex such as tris(acetylacetonato)(monophenanthroline)terbium(II) (abbreviation: Tb(acac) 3 (Phen)); tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviation: Eu(DBM) 3 (Phen)); or tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: Eu(TTA) 3 (Phen)) performs light emission (electron transition between different multiplicities) from a rare-earth metal ion; therefore, such a rare-earth metal complex can be used as the phosphorescent compound. 
         [0084]    Various kinds of materials can be used for the fluorescent compounds of the first layer  121  and the fourth layer  124 . For example, as a blue light emitting fluorescent compound, there are N,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N-diphenylstilbene-4,4′-diamine (abbreviation: YGA2S), 4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine (abbreviation: YGAPA), 2,5,8,11-tetra(tert-butyl)perylene (abbreviation: TBP), and the like. As a green light emitting fluorescent compound, there are N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine (abbreviation: 2PCAPA), N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine (abbreviation: 2PCABPhA), N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPA), N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine (abbreviation: 2DPABPhA), 9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine (abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine (abbreviation: DPhAPhA), and the like. As a yellow light emitting fluorescent compound, there are rubrene, 5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT), and the like. As a red light emitting fluorescent compound, there are N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation: p-mPhTD), 7,13-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine (abbreviation: p-mPhAFD), and the like. 
         [0085]    Various kinds of materials can be used for the organic compound having a hole transporting property in each of the first layer  121  and the second layer  122 . For example, an aromatic amine compound such as 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB or α-NPD), N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (abbreviation: TPD), 4,4′,4″-tris(carbazol-9-yl)triphenylamine (abbreviation: TCTA), 4,4′,4″-tris(N,N′-diphenylamino)triphenylamine (abbreviation: TDATA), 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (abbreviation: MTDATA), or 4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl (abbreviation: BSPB), or the like can be used. The substances described here are mainly substances having a hole mobility of 10 −6  cm 2 /Vs or more. Note that any other substance having a hole transporting property which is higher than an electron transporting property may be used. A high molecular compound such as poly(N-vinylcarbazole) (abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA), poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide] (abbreviation: PTPDMA); or poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation: Poly-TPD) can be used. 
         [0086]    Various kinds of materials can be used for the organic compound having an electron transporting property in each of the third layer  123  and the fourth layer  124 . For example, a metal complex having a quinoline or benzoquinoline skeleton, such as tris(8-quinolinolato)aluminum (abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq 3 ), bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq 2 ), or bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation: BAlq), or the like can be used. Alternatively, a metal complex having an oxazole-based or thiazole-based ligand, such as bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX) 2 ) or bis[2-(2-hydroxyphenyl)-benzothiazolato]zinc (abbreviation: Zn(BTZ) 2 ), or the like can be used. Further alternatively, besides the metal complexes, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]carbazole (abbreviation: CO11), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), or the like can be used. The substances described here are mainly substances having an electron mobility of 10 −6  cm 2 /Vs or more. Note that any other substance having an electron transporting property which is higher than a hole transporting property may be used. Alternatively, a high molecular compound such as poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)] (abbreviation: PF-Py) or poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-pyridine-6,6′-diyl)] (abbreviation: PF-BPy) can be used. 
         [0087]    A white light emitting element to which an embodiment of the present invention is applied can be obtained by using the following example. As the first phosphorescent compound in the first layer, (acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III) (abbreviation: Ir(Fdpq) 2 (acac)) which emits red light is used. As the first organic compound having a hole transporting property, 4,4′,4″-tris(carbazol-9-yl)triphenylamine (abbreviation: TCTA) is used. As the first fluorescent compound in the second layer, 2,5,8,11-tetra(tert-butyl)perylene (abbreviation: TBP) which emits blue light is used. As the second compound having a hole transporting property, TCTA which is the same as that used for the first compound having a hole transporting property is used. As the second fluorescent compound in the third layer, TBP which is the same as that used for the first fluorescent compound is used. As the first organic compound having an electron transporting property, 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]carbazole (abbreviation: CO11) is used. As the second phosphorescent compound in the fourth layer, bis(2-phenylpyridinato-N,C 2′ )iridium(III)acetylacetonate (abbreviation: Ir(ppy) 2 (acac)) which emits green light is used. As the second organic compound having an electron transporting property, CO11 which is the same as that used for the first organic compound having an electron transporting property is used. 
         [0088]    The electron transporting layer  114  is a layer including a substance having a high electron transporting property. For example, a metal complex having a quinoline or benzoquinoline skeleton, such as tris(8-quinolinolato)aluminum (abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq 3 ), bis(10-hydroxybenzo[h]-quinolinato)beryllium (abbreviation: BeBq 2 ), or bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation: BAlq), or the like can be used. Alternatively, a metal complex having an oxazole-based or thiazole-based ligand, such as bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX) 2 ) or bis[2-(2-hydroxyphenyl)-benzothiazolato]zinc (abbreviation: Zn(BTZ) 2 ), or the like can be used. Further alternatively, besides the metal complexes, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis[5-[(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (abbreviation: OXD-7), 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]carbazole (abbreviation: CO11), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-biphenylyl)-1,2,4-triazole (abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), or the like can be used. The substances described here are mainly substances having an electron mobility of 10 −6  cm 2 /Vs or more. Note that any other substance having an electron transporting property which is higher than a hole transporting property may be used. Furthermore, the electron transporting layer is not limited to a single layer, and two or more layers made of the above-described substances may be stacked. 
         [0089]    Alternatively, as the electron transporting layer  114 , a high molecular compound such as poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)] (abbreviation: PF-Py) or poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-pyridine-6,6′-diyl)] (abbreviation: PF-BPy) can be used. 
         [0090]    As illustrated in  FIG. 4 , a hole injecting layer  111  may be provided between the first electrode  102  and the hole transporting layer  112 . As the substance having a high hole injecting property, molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, manganese oxide, or the like can be used. In addition, it is possible to use a phthalocyanine-based compound such as phthalocyanine (abbreviation: H 2 Pc) or copper phthalocyanine (abbreviation: CuPc), a high molecule such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS), or the like to form the hole injecting layer. 
         [0091]    Alternatively, a composite material in which an acceptor substance is included in a substance having a high hole transporting property can be used for the hole injecting layer  111 . Note that, by using the substance in which an acceptor substance is included in a substance having a high hole transporting property, a material used to form an electrode can be selected regardless of its work function. In other words, besides a material with a high work function, a material with a low work function can also be used as the first electrode  102 . As the acceptor substance, 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F 4 -TCNQ), chloranil, and the like can be given. In addition, transition metal oxide can be given. Further, oxide of metals that belong to Group 4 to Group 8 in the periodic table can be given. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are preferable because of a high electron accepting property. Among these, molybdenum oxide is especially preferable since it is stable in the air and its hygroscopic property is low so that it can be easily treated. 
         [0092]    Note that, in this specification, “composition” means not only a simple mixture of two materials but also a mixture of a plurality of materials in a condition where electric charge is given and received among the materials. 
         [0093]    As the organic compound used for the composite material, various compounds such as an aromatic amine compound, a carbazole derivative, aromatic hydrocarbon, and a high molecular compound (oligomer, dendrimer, polymer, or the like) can be used. Note that the organic compound used for the composite material is preferably an organic compound having a high hole transporting property. Specifically, a substance having a hole mobility of 10 −6  cm 2 /Vs or more is preferably used. Note that any other substance having a hole transporting property which is higher than an electron transporting property may be used. The organic compound that can be used for the composite material is specifically given below. 
         [0094]    For example, the followings can be given as the aromatic amine compound: N,N′-bis(4-methylphenyl)-N,N′-diphenyl-p-phenylenediamine (abbreviation: DTDPPA); 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB); 4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (abbreviation: DNTPD); 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene (abbreviation: DPA3B); and the like. 
         [0095]    As specific examples of the carbazole derivative which can be used as the composite material, the following can be given: 3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA1); 3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzPCA2); 3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPCN1); and the like. 
         [0096]    Moreover, as carbazole derivatives which can be used for the composite material, 4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP); 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB); 9-[4-(10-phenyl-9-anthracenyl)phenyl]- 9 H-carbazole (abbreviation: CZPA); 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene; or the like can also be used. 
         [0097]    As aromatic hydrocarbon which can be used for the composite material, the following can be given for example: 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA); 2-tert-butyl-9,10-di(1-naphthyl)anthracene, 9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA); 2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA); 9,10-di(2-naphthyl)anthracene (abbreviation: DNA); 9,10-diphenylanthracene (abbreviation: DPAnth); 2-tert-butylanthracene (abbreviation: t-BuAnth); 9,10-bis(4-methyl-1-naphthyl)anthracene (abbreviation: DMNA); 9,10-bis[2-(1-naphthyl)phenyl]-2-tert-butylanthracene; 9,10-bis[2-(1-naphthyl)phenylanthracene; 2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene; 2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene; 9,9′-bianthryl; 10,10′-diphenyl-9,9′-bianthryl; 10,10′-bis(2-phenylphenyl)-9,9′-bianthryl; 10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl; anthracene; tetracene; rubrene; perylene; 2,5,8,11-tetra(tert-butyl)perylene; and the like. In addition, pentacene, coronene, or the like can also be used. As these aromatic hydrocarbons listed here, an aromatic hydrocarbon having a hole mobility of 1×10 −6  cm 2 /Vs or more and having 14 to 42 carbon atoms is more preferable. 
         [0098]    Note that aromatic hydrocarbon that can be used for the composite material may have a vinyl skeleton. As an aromatic hydrocarbon having a vinyl group, for example, 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi), 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA), and the like can be given. 
         [0099]    In addition, a high molecular compound such as poly(N-vinylcarbazole) (abbreviation: PVK) or poly(4-vinyl triphenylamine) (abbreviation: PVTPA) can also be used. 
         [0100]    As illustrated in  FIG. 4 , an electron injecting layer  115  may be provided between the electron transporting layer  114  and the second electrode  104 . As the electron injecting layer  115 , an alkali metal, an alkaline earth metal, or a compound of these such as lithium fluoride (LiF), cesium fluoride (CsF), or calcium fluoride (CaF 2 ) can be used. For example, a layer formed using a substance having an electron transporting property including an alkali metal, an alkaline earth metal, or a compound of these, such as Alq which includes magnesium (Mg), can be used. When a layer formed using a substance having an electron transporting property including an alkali metal or an alkaline earth metal is used as the electron injecting layer  115 , electrons can be efficiently injected from the second electrode  104 , which is preferable. 
         [0101]    As a formation method of the EL layer  103 , various methods can be employed, and either a wet process or a dry process can be used. For example, a vacuum evaporation method, an inkjet method, a spin coating method, or the like may be used. Further, each electrode or each layer may be formed by a different method. 
         [0102]    In the light emitting element according to an embodiment of the present invention having the above structure, to allow current to flow due to a potential difference between the first electrode  102  and the second electrode  104  and holes and electrons are recombined in the EL layer  103  so that light is emitted. More specifically, a light emitting region is formed in the light emitting layer  113  in the EL layer  103 . 
         [0103]    The emitted light is extracted out through one or both of the first electrode  102  and the second electrode  104 . Accordingly, one or both of the first electrode  102  and the second electrode  104  is/are an electrode having a light transmitting property. When only the first electrode  102  is an electrode having a light transmitting property, light is extracted from the substrate side through the first electrode  102  as illustrated by an arrow in  FIG. 5A . In addition, when only the second electrode  104  is an electrode having a light transmitting property, light is extracted from the opposite side to the substrate side through the second electrode  104  as illustrated by an arrow in  FIG. 5B . Further, when the first electrode  102  and the second electrode  104  are both electrodes having light transmitting properties, light is extracted to opposite sides, i.e., the substrate side and the opposite side, through the first electrode  102  and the second electrode  104  as illustrated by an arrow in  FIG. 5C . 
         [0104]    The structure of EL layer  103  provided between the first electrode  102  and the second electrode  104  is not limited to the above example. A structure other than the above-described one may also be used as long as a light emitting region in which holes and electrons are recombined is provided in a portion apart from the first electrode  102  and the second electrode  104  so that quenching caused by the light emitting region and the first electrode  102  or the second electrode  104  coming close to each other is suppressed, and moreover, as long as the light emitting layer  113  includes the above structure. 
         [0105]    In other words, there are no particular limitations on the stacked structure of the EL layer  103 , and layers formed using a substance having a high electron transporting property, a substance having a high hole transporting property, a substance having a high electron injecting property, a substance having a high hole injecting property, a bipolar substance (a substance having high electron transporting and hole transporting properties), a hole block material, and the like may be freely combined with the light emitting layer  113  of an embodiment of the present invention. 
         [0106]    The light emitting element illustrated in  FIG. 6  has a structure in which the second electrode  104  functioning as the cathode, the EL layer  103 , and the first electrode  102  functioning as the anode are sequentially stacked over the substrate  101 . The EL layer  103  has the hole transporting layer  112 , the light emitting layer  113 , and the electron transporting layer  114 . In the light emitting layer  113 , the first layer  121 , the second layer  122 , the third layer  123 , and the fourth layer  124  are sequentially stacked from the first electrode  102  side. 
         [0107]    In this embodiment, the light emitting element is manufactured over a substrate formed with glass, plastic, or the like. By formation of a plurality of such light emitting elements over a substrate, a passive matrix light emitting device can be manufactured. Alternatively, for example, a thin film transistor (TFT) may be formed over a substrate formed with glass, plastic, or the like, and a light emitting element may be manufactured over an electrode that is electrically connected to the TFT. Thus, an active matrix light emitting device which controls the driving of a light emitting element by a TFT can be manufactured. Note that a structure of the TFT is not particularly limited. The TFT may be either of staggered type or inverted staggered type. As for a driver circuit formed on the TFT substrate also, one or both of n-channel transistors and p-channel transistors may be used. In addition, the crystallinity of a semiconductor film used for the TFT is not particularly limited. Either an amorphous semiconductor film or a crystalline semiconductor film may be used. 
         [0108]    The light emitting element according to an embodiment of the present invention can achieve high luminous efficiency by efficiently using an exciton of a singlet excited state and an exciton of a triplet excited state which are generated in the recombination region. 
         [0109]    Since high luminous efficiency is obtained, power consumption of the light emitting element can be reduced. 
         [0110]    Note that this embodiment can be combined with any of other embodiments, as appropriate. 
       Embodiment 2 
       [0111]    In this embodiment, a light emitting element (a stacked type element) in which a plurality of light emitting units according to an embodiment of the present invention is stacked will be described with reference to  FIG. 7 . This light emitting element is a light emitting element having a plurality of light emitting units between a first electrode and a second electrode. As the light emitting units, at least a light emitting layer may be included, and a structure similar to that of the EL layer described in Embodiment 1 can be used. In other words, the light emitting element described in Embodiment 1 is a light emitting element having one light emitting unit, and a light emitting element having a plurality of light emitting units will be described in this embodiment. 
         [0112]    In  FIG. 7 , a first light emitting unit  511  and a second light emitting unit  512  are stacked between a first electrode  501  and a second electrode  502 . A charge generation layer  513  is provided between the first light emitting unit  511  and the second light emitting unit  512 . To the first electrode  501  and the second electrode  502 , similar electrodes to those described in Embodiment 1 can be applied. The first light emitting unit  511  and the second light emitting unit  512  may have the same structure or different structures, and the structures, described in Embodiment 1 can be applied. 
         [0113]    The charge generation layer  513  includes a composite material of an organic compound and metal oxide. The composite material of an organic compound and metal oxide is the composite material described in Embodiment 1, and includes an organic compound and metal oxide such as vanadium oxide, molybdenum oxide, or tungsten oxide. As the organic compound, various compounds such as an aromatic amine compound, a carbazole derivative, aromatic hydrocarbon, and a high molecular compound (oligomer, dendrimer, polymer, or the like) can be used. Note that the organic compound having a hole mobility of 10 −6  cm 2 /Vs or more is preferably used as an organic compound having a hole transporting property. Note that any other substance having a hole transporting property which is higher than an electron transporting property may be used. The composite material of an organic compound and metal oxide is superior in carrier injecting property and carrier transporting property, and accordingly, low-voltage driving and low-current driving can be realized. 
         [0114]    Note that the charge generation layer  513  may be formed with a combination of a composite material of an organic compound and metal oxide and other materials. For example, the charge generation layer  513  may be formed with a combination of a layer including the composite material of an organic compound and metal oxide and a layer including a compound having a high electron transporting property and an electron donating substance with respect to the compound having the high electron transporting property. Further, the charge generation layer  513  may be formed with a combination of a layer including the composite material of an organic compound and metal oxide and a transparent conductive film. 
         [0115]    In any cases, the charge generation layer  513  interposed between the first light emitting unit  511  and the second light emitting unit  512  is acceptable as long as electrons are injected to a light emitting unit on one side and holes are injected to a light emitting unit on the other side when voltage is applied to the first electrode  501  and the second electrode  502 . For example, in  FIG. 7 , any layer can be employed as the charge generation layer  513  as long as the layer injects electrons into the first light emitting unit  511  and holes into the second light emitting unit  512  when voltage is applied so that the potential of the first electrode  501  is higher than that of the second electrode  502 . 
         [0116]    In this embodiment, the light emitting element having two light emitting units is described; however, similarly, an embodiment can be applied to a light emitting element in which three or more light emitting units are stacked. When a plurality of light emitting units is arranged to be partitioned from each other with a charge generation layer between a pair of electrodes, like the light emitting element according to this embodiment, light emission from a region of high luminance can be realized at a low current density, and thus, an element with a long life can be achieved. 
         [0117]    Note that this embodiment can be combined with any of other embodiments, as appropriate. 
       Embodiment 3 
       [0118]    In this embodiment, a light emitting device having a light emitting element according to an embodiment of the present invention will be described. 
         [0119]    A light emitting device having the light emitting element according to an embodiment of the prevent invention in a pixel portion will be described in this embodiment with reference to  FIGS. 8A and 8B .  FIG. 8A  is a top view illustrating the light emitting device, and  FIG. 8B  is a cross sectional view taken along line A-A′ and line B-B′ of  FIG. 8A . This light emitting device includes a driver circuit portion (source side driver circuit)  601 , a pixel portion  602 , and a driver circuit portion (gate side driver circuit)  603  which are illustrated by dotted lines in order to control the light emission of the light emitting element. Reference numeral  604  denotes a sealing substrate; reference numeral  605  denotes a sealing material; and a portion surrounded by the sealing material  605  corresponds to a space  607 . 
         [0120]    Note that a leading wiring  608  is a wiring for transmitting signals input in the source side driver circuit  601  and the gate side driver circuit  603 . The leading wiring  608  receives video signals, clock signals, start signals, reset signals, and the like from a flexible printed circuit (FPC)  609  that serves as an external input terminal. Although only the FPC is illustrated here, the FPC may be provided with a printed wiring board (PWB). The light emitting device according to this specification includes not only a light emitting device body but also a state in which an FPC or a PWB is attached thereto. 
         [0121]    Next, the sectional structure will be described with reference to  FIG. 8B . The driver circuit portion and the pixel portion are formed over an element substrate  610 , and the source side driver circuit  601 , which is one of the driver circuit portions, and one pixel in the pixel portion  602  are illustrated. 
         [0122]    Note that as the source side driving circuit  601 , a CMOS circuit in which an n-channel TFT  623  and a p-channel TFT  624  are combined is formed. The driver circuit may be formed by various CMOS circuits, PMOS circuits, or NMOS circuits. Although a driver-integration type device, in which a driver circuit is formed over the substrate provided with the pixel portion, is described in this embodiment, a driver circuit is not necessarily formed over the substrate provided with the pixel portion, but can be formed outside a substrate. 
         [0123]    The pixel portion  602  has a plurality of pixels, each of which includes a switching TFT  611 , a current control TFT  612 , and a first electrode  613  which is electrically connected to a drain of the current control TFT  612 . Note that an insulator  614  is formed so as to cover an end portion of the first electrode  613 . Here, the insulator  614  is formed using a positive photosensitive acrylic resin film. 
         [0124]    In order to prevent adverse influence on a light-emitting element  618 , the insulator  614  is provided such that either an upper end portion or a lower end portion of the insulator has a curved surface with a curvature. For example, in the case of using positive photosensitive acrylic as a material for the insulator  614 , it is preferable that the insulator  614  be formed so as to have a curved surface with a curvature radius (0.2 μm to 3 μm) the upper end portion of the insulator  614 . Note that the insulator  614  can be formed using either negative photosensitive acrylic that becomes insoluble in an etchant due to light irradiation, or positive photosensitive acrylic that becomes soluble in an etchant due to light irradiation. 
         [0125]    An EL layer  616  and a second electrode  617  are formed over the first electrode  613 . Here, the first electrode  613  can be formed with various metals, alloys, electrically conductive compounds, or mixture thereof. If the first electrode  613  is used as an anode, it is preferable to use a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like with a high work function (a work function of 4.0 eV or higher) among such materials. For example, a stacked-layer structure of a film including a titanium nitride film and a film including aluminum as its main component, a three-layer structure of a titanium nitride film, a film including aluminum as its main component, and a titanium nitride film, or the like can be used in addition to a single layer of indium tin oxide including silicon, indium zinc oxide, a titanium nitride film, a chromium film, a tungsten film, a Zn film, a Pt film, or the like. 
         [0126]    The EL layer  616  is formed by various methods such as an evaporation method using an evaporation mask, an inkjet method, a spin coating method, or the like. The EL layer  616  has the light emitting layer described in Embodiment 1. Further, the EL layer  616  may be formed using another material including a low molecular compound or a high molecular compound (including oligomer and dendrimer). As the material for the EL layer  616 , not only an organic compound but also an inorganic compound may be used. 
         [0127]    The second electrode  617  can be formed with various metals, alloys, electrically conductive compounds, or mixtures of these. If the second electrode is used as a cathode, it is preferable to use a metal, an alloy, an electrically conductive compound, a mixture of these, or the like with a low work function (a work function of 3.8 eV or lower) among such materials. As an example, an element belonging to Group 1 or Group 2 in the periodic table, that is, an alkali metal such as lithium (Li) or cesium (Cs); an alkaline earth metal such as magnesium (Mg), calcium (Ca), or strontium (Sr); an alloy including any of these (MgAg, AlLi); and the like can be given. In the case where light generated in the EL layer  616  is transmitted through the second electrode  617 , the second electrode  617  can be formed using a stacked layer of a metal thin film whose thickness is made small, and a transparent conductive film (indium tin oxide (ITO), indium tin oxide including silicon or silicon oxide, indium zinc oxide (IZO), indium oxide including tungsten oxide and zinc oxide (IWZO), or the like). 
         [0128]    By attaching the sealing substrate  604  to the element substrate  610  with the sealing material  605 , a light emitting element  618  is provided in the space  607  which is surrounded by the element substrate  610 , the sealing substrate  604 , and the sealing material  605 . Note that the space  607  is filled with a filler and may be filled with an inert gas (such as nitrogen or argon), the sealing material  605 , or the like. 
         [0129]    As the sealing material  605 , an epoxy resin is preferably used. In addition, it is desirable to use a material that allows permeation of moisture or oxygen as little as possible. As the sealing substrate  604 , a plastic substrate formed with Fiberglass-Reinforced Plastics (FRP), polyvinyl fluoride (PVF), polyester, acrylic, or the like can be used besides a glass substrate or a quartz substrate. 
         [0130]    As described above, the light emitting device having the light emitting element according to an embodiment of the present invention can be obtained. 
         [0131]    The light emitting device according to an embodiment of the present invention includes the light emitting element described in Embodiment 1 or Embodiment 2. Therefore, a light emitting device with high luminous efficiency can be obtained. In addition, power consumption of the light emitting device can be reduced. 
         [0132]    Although an active matrix light emitting device in which driving of a light emitting element is controlled by thin film transistors is described in this embodiment as described above, the light emitting device may be replaced with a passive matrix light emitting device.  FIGS. 9A and 9B  illustrate a passive matrix light emitting device which is manufactured by application of an embodiment of the present invention. Note that  FIG. 9A  is a perspective view illustrating the light emitting device, and  FIG. 9B  is a cross-sectional view of  FIG. 9A  taken along line X-Y. In  FIGS. 9A and 9B , over a substrate  951 , an EL layer  955  is provided between an electrode  952  and an electrode  956 . The end portion of the electrode  952  is covered with an insulating layer  953 . A partition layer  954  is provided over the insulating layer  953 . The sidewalls of the partition layer  954  are aslope so that a distance between both sidewalls is gradually narrowed toward the surface of the substrate. That is, a cross section in the direction of a narrow side of the partition layer  954  has a trapezoidal shape, and a lower side (which faces a surface of the insulating layer  953  and is in contact with the insulating layer  953 ) is shorter than an upper side (which faces the surface of the insulating layer  953  and is not in contact with the insulating layer  953 ). A cathode can be patterned by providing the partition layer  954  in this manner. In addition, in a passive matrix light emitting device, a light emitting device with low power consumption can be obtained by including a light emitting element with high luminous efficiency according to an embodiment of the present invention. 
         [0133]    Note that this embodiment can be combined with any of other embodiments, as appropriate. 
       Embodiment 4 
       [0134]    In this embodiment, an electronic device according to an embodiment of the present invention including the light emitting device described in Embodiment 3 as part thereof will be described. The electronic device according to an embodiment of the present invention has the light emitting element described in Embodiment 1 or Embodiment 2, and a display portion with high luminous efficiency. Moreover, a display portion having low power consumption is included. 
         [0135]    As an electronic device manufactured using the light emitting device according to an embodiment of the present invention, a camera such as a video camera or a digital camera, a goggle type display, a navigation system, an audio reproducing device (car audio set, audio component set, or the like), a computer, a game machine, a portable information terminal (mobile computer, cellular phone, portable game machine, e-book reader, or the like), and an image reproducing device provided with a recording medium (specifically, a device provided with a display device that can reproduce a recording medium and display the image such as a Digital Versatile Disc (DVD)), and the like can be given. Specific examples of these electronic devices are illustrated in  FIGS. 10A to 10D . 
         [0136]      FIG. 10A  illustrates a television device according to this embodiment, which includes a housing  9101 , a support base  9102 , a display portion  9103 , a speaker portion  9104 , a video input terminal  9105 , and the like. In the display portion  9103  of this television device, the light emitting elements described in Embodiment 1 or Embodiment 2 are arranged in matrix. One feature of the light emitting element is that luminous efficiency is high and power consumption is low. Since the display portion  9103  constructed of such light emitting elements has similar characteristics, this television device consumes less power. With such characteristics, the number or scale of power supply circuits in the television device can be drastically reduced, and therefore, the size and weight of the housing  9101  and the support base  9102  can be reduced. In the television device according to this embodiment, reduction in power consumption and reduction in size and weight are achieved; therefore, a product which is suitable for living environment can be provided. 
         [0137]      FIG. 10B  illustrates a computer according to this embodiment, which includes a main body  9201 , a housing  9202 , a display portion  9203 , a keyboard  9204 , an external connection port  9205 , a pointing device  9206 , and the like. In the display portion  9203  of this computer, the light emitting elements described in Embodiment 1 or Embodiment 2 are arranged in matrix. One feature of the light emitting element is that luminous efficiency is high and power consumption is low. Since the display portion  9203  constructed of such light emitting elements has similar characteristics, this computer consumes less power. With such characteristics, the number or scale of power supply circuits in the computer can be drastically reduced, and therefore, the size and weight of the main body  9201  and the housing  9202  can be reduced. In the computer according to this embodiment, reduction in power consumption and reduction in size and weight are achieved; therefore, a product which is suitable for environment can be provided. 
         [0138]      FIG. 10C  illustrates a camera that includes a main body  9301 , a display portion  9302 , a housing  9303 , an external connection port  9304 , a remote control receiving portion  9305 , an image receiving portion  9306 , a battery  9307 , an audio input portion  9308 , operation keys  9309 , an eyepiece portion  9310 , and the like. In the display portion  9302  of this camera, the light emitting elements described in Embodiment 1 or Embodiment 2 are arranged in matrix. One feature of the light emitting element is that luminous efficiency is high and power consumption is low. Since the display portion  9302  constructed of such light emitting elements has similar characteristics, this camera consumes less power. With such characteristics, the number or scale of power supply circuits in the camera can be drastically reduced, and therefore, the size and weight of the main body  9301  can be reduced. In the camera according to this embodiment, reduction in power consumption and reduction in size and weight are achieved; therefore, a product which is suitable for being carried around can be provided. 
         [0139]      FIG. 10D  illustrates a cellular phone according to this embodiment, which includes a main body  9401 , a housing  9402 , a display portion  9403 , an audio input portion  9404 , an audio output portion  9405 , operation keys  9406 , an external connection port  9407 , an antenna  9408 , and the like. In the display portion  9403  of this cellular phone, the light emitting elements described in Embodiment 1 or Embodiment 2 are arranged in matrix. One feature of the light emitting element is that luminous efficiency is high and power consumption is low. Since the display portion  9403  constructed of such light emitting elements has similar characteristics, this cellular phone consumes less power. With such characteristics, the number or scale of power supply circuits in the cellular phone can be drastically reduced, and therefore, the size and weight of the main body  9401  and the housing  9402  can be reduced. In the cellular phone according to this embodiment, reduction in power consumption and reduction in size and weight are achieved; therefore, a product which is suitable for being carried around can be provided. 
         [0140]      FIGS. 16A to 16C  illustrate an example of a structure of a cellular phone, which is different from the structure of the cellular phone of  FIG. 10D .  FIG. 16A  is a front view,  FIG. 16B  is a rear view, and  FIG. 16C  is a development view. The cellular phone illustrated in  FIGS. 16A to 16C  is a so-called smartphone which has both a function as a phone and a function as a portable information terminal, and incorporates a computer to conduct a variety of data processing in addition to voice calls. 
         [0141]    The cellular phone illustrated in  FIGS. 16A to 16C  has two housings  1001  and  1002 . The housing  1001  includes a display portion  1101 , a speaker  1102 , a microphone  1103 , operation keys  1104 , a pointing device  1105 , a camera lens  1106 , an external connection terminal  1107 , and the like, while the housing  1002  includes a keyboard  1201 , an external memory slot  1202 , a camera lens  1203 , a light  1204 , an earphone terminal  1008 , and the like. In addition, an antenna is incorporated in the housing  1001 . 
         [0142]    In addition to the above structure, the cellular phone may incorporate a non-contact IC chip, a small size memory device, or the like. 
         [0143]    In the display portion  1101 , the light emitting device described in Embodiment  3  can be incorporated, and a display direction can be changed as appropriate depending on the usage mode. The cellular phone is provided with the camera lens  1106  on the same surface as the display portion  1101 , and thus it can be used as a video phone. Further, a still image and a moving image can be taken with the camera lens  1203  and the light  1204  by using the display portion  1101  as a viewfinder. The speaker  1102  and the microphone  1103  are not limited to use for verbal communication, and can be used for a videophone, recording, reproduction, and the like. With use of the operation keys  1104 , operation of incoming and outgoing calls, simple information input of electronic mails or the like, scrolling of a screen, cursor motion, and the like are possible. Furthermore, the housing  1001  and the housing  1002  ( FIG. 16A ), which are overlapped with each other, are slid to expose the housing  1002  as illustrated in  FIG. 16C , and can be used as a portable information terminal. In this case, smooth operation is possible with use of the keyboard  1201  and the pointing device  1105 . The external connection terminal  1107  can be connected to an AC adapter or a variety of cables such as a USB cable, and can be charged and perform data communication with a computer or the like. Moreover, a large amount of data can be stored by inserting a storage medium into the external memory slot  1202  and can be moved. 
         [0144]    In addition to the above-described functions, the cellular phone may also have an infrared communication function, a television reception function, or the like. 
         [0145]      FIG. 11  illustrates an audio reproducing device, specifically, a car audio system, which includes a main body  701 , a display portion  702 , and operation switches  703  and  704 . The display portion  702  can be realized by the (passive matrix or active matrix) light emitting device described in Embodiment 3. Further, the display portion  702  may employ a segment type light emitting device. In any case, the use of a light emitting element according to an embodiment of the present invention makes it possible to form a bright display portion while achieving low power consumption, with the use of a vehicle power source (12 V to 42 V). Although an in-car audio system is described in this embodiment, an embodiment may be used for a portable audio device or an audio device for household use. 
         [0146]      FIG. 12  illustrates a digital player as an example of an audio reproducing device. The digital player illustrated in  FIG. 12  includes a main body  710 , a display portion  711 , a memory portion  712 , an operation portion  713 , earphones  714 , and the like. Note that headphones or wireless earphones can be used instead of the earphones  714 . The display portion  711  can be realized by the (passive matrix or active matrix) light emitting device described in Embodiment 3. Further, the display portion  711  may employ a segment type light emitting device. In any case, the use of a light emitting element according to an embodiment of the present invention makes it possible to form a bright display portion which can display images even when using a secondary battery (a nickel-hydrogen battery or the like) while achieving low power consumption. As the memory portion  712 , a hard disk or a nonvolatile memory is used. For example, a NAND type nonvolatile memory with a recording capacity of 20 gigabytes (GB) to 200 gigabytes (GB) is used, and by operating the operation portion  713 , an image or sound (e.g., music) can be recorded and reproduced. Note that power consumption of the display portions  702  in  FIG. 11  and the display portion  711  in  FIG. 12  can be suppressed through display of white characters on the black background. This is particularly effective for portable audio systems. 
         [0147]    As described above, the applicable range of the light emitting device manufactured by applying an embodiment of the present invention is so wide that the light emitting device is applicable to electronic devices in various fields. By applying an embodiment of the present invention, an electronic device which has high luminous efficiency and a display portion consuming less power can be manufactured. 
         [0148]    The light emitting device according to an embodiment of the present invention can also be used as a lighting device. An example using the light emitting element according to an embodiment of the present invention as a lightning device will be described with reference to  FIG. 13 . 
         [0149]      FIG. 13  illustrates a liquid crystal display device using the light emitting device to which an embodiment of the present invention is applied as a backlight, as an example of the electronic device using a light emitting device according to an embodiment of the present invention as a lighting device. The liquid crystal display device illustrated in  FIG. 13  includes a housing  901 , a liquid crystal layer  902 , a backlight  903 , and a housing  904 . The liquid crystal layer  902  is connected to a driver IC  905 . The light emitting device to which an embodiment of the present invention is applied is used as the backlight  903 , and current is supplied through a terminal  906 . 
         [0150]    Since the light emitting device according to an embodiment of the present invention is thin and has high luminous efficiency and low power consumption, reduction in thickness and power consumption of a display device is possible by using a light emitting device according to an embodiment of the present invention as a backlight of the liquid crystal display device. Moreover, a light emitting device according to an embodiment of the present invention is a plane emission type lighting device and can have a large area. Thus, the backlight can have a large area, and a liquid crystal display device having a large area can also be obtained. 
         [0151]      FIG. 14  illustrates an example in which a light emitting device according to an embodiment of the present invention is used as a desk lamp, which is one of lighting devices. The desk lamp illustrated in  FIG. 14  includes a housing  2001  and a light source  2002 , and a light emitting device according to an embodiment of the present invention is used as the light source  2002 . The light emitting device according to an embodiment of the present invention have high luminous efficiency and low power consumption; thus, the desk lamp also has low power consumption. 
         [0152]      FIG. 15  illustrates an example of using the light emitting device, to which an embodiment of the present invention is applied, as an indoor lighting device  3001 . Because the light emitting device according to an embodiment of the present invention can have a large area, a light emitting device according to an embodiment of the present invention can be used as a lighting device having a large area. Moreover, because the light emitting device according to an embodiment of the present invention has high luminous efficiency and low power consumption, the light emitting device according to an embodiment of the present invention can be used as a lighting device which consumes less power. As illustrated in the drawing, a television device  3002  according to an embodiment of the present invention as illustrated in  FIG. 10A  may be set in a room where the light emitting device to which an embodiment of the present invention is applied is used as the indoor lighting device  3001 , and public broadcasting or movies can be appreciated there. In such a case, since both devices consume less power, environmental load can be reduced. 
         [0153]    Note that this embodiment can be combined with any of other embodiments, as appropriate. 
         [0154]    This application is based on Japanese Patent Application serial No. 2008-223217 filed with Japan Patent Office on Sep. 1, 2008, the entire contents of which are hereby incorporated by reference.