Patent Publication Number: US-9843002-B2

Title: Organometallic complex, light-emitting element, light-emitting device, electronic device, and lighting device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     One embodiment of the present invention relates to an organometallic complex. In particular, one embodiment of the present invention relates to an organometallic complex that can convert triplet excitation energy into light emission. In addition, one embodiment of the present invention relates to a light-emitting element, a light-emitting device, an electronic device, and a lighting device each including the organometallic complex. Note that one embodiment of the present invention is not limited to the above technical field. The technical field of one embodiment of the invention disclosed in this specification and the like relates to an object, a method, or a manufacturing method. Furthermore, one embodiment of the present invention relates to a process, a machine, manufacture, or a composition of matter. Specific examples of the technical field of one embodiment of the present invention disclosed in this specification include, in addition to the above, a semiconductor device, a display device, a liquid crystal display device, a power storage device, a memory device, a method for driving any of them, and a method for manufacturing any of them. 
     2. Description of the Related Art 
     A display including a light-emitting element having a structure in which an organic compound that is a light-emitting substance is provided between a pair of electrodes (also referred to as an organic EL element) has attracted attention as a next-generation flat panel display element in terms of characteristics of the light-emitting element, such as being thin and light in weight, high-speed response, and low voltage driving. When a voltage is applied to this light-emitting element, electrons and holes injected from the electrodes recombine to put the light-emitting substance into an excited state, and then light is emitted in returning from the excited state to the ground state. The excited state can be a singlet excited state (S*) and a triplet excited state (T*). Light emission from a singlet excited state is referred to as fluorescence, and light emission from a triplet excited state is referred to as phosphorescence. The statistical generation ratio thereof in the light-emitting element is considered to be S*:T*=1:3. 
     Among the above light-emitting substances, a compound capable of converting singlet excitation energy into light emission is called a fluorescent compound (fluorescent material), and a compound capable of converting triplet excitation energy into light emission is called a phosphorescent compound (phosphorescent material). 
     Accordingly, on the basis of the above generation ratio, the internal quantum efficiency (the ratio of the number of generated photons to the number of injected carriers) of a light-emitting element including a fluorescent material is thought to have a theoretical limit of 25%, while the internal quantum efficiency of a light-emitting element including a phosphorescent material is thought to have a theoretical limit of 75%. 
     In other words, a light-emitting element including a phosphorescent material has higher efficiency than a light-emitting element including a fluorescent material. Thus, various kinds of phosphorescent materials have been actively developed in recent years. An organometallic complex that contains iridium or the like as a central metal is particularly attracting attention because of its high phosphorescence quantum yield (see Patent Document 1, for example). 
     REFERENCE 
     Patent Document 
     
         
         [Patent Document 1] Japanese Published Patent Application No. 2009-023938 
       
    
     SUMMARY OF THE INVENTION 
     Although phosphorescent materials exhibiting excellent characteristics have been actively developed as disclosed in Patent Document 1, development of novel materials with better characteristics has been desired. 
     In view of the above, according to one embodiment of the present invention, a novel organometallic complex is provided. According to one embodiment of the present invention, a novel organometallic complex having high color purity is provided. According to one embodiment of the present invention, a novel organometallic complex that can be used in a light-emitting element is provided. According to one embodiment of the present invention, a novel organometallic complex that can be used in an EL layer of a light-emitting element is provided. According to one embodiment of the present invention, a novel light-emitting element is provided. In addition, according to one embodiment of the present invention, a novel light-emitting device, a novel electronic device, or a novel lighting device is provided. Note that the descriptions of these objects do not disturb the existence of other objects. In one embodiment of the present invention, there is no need to achieve all the objects. Other objects will be apparent from and can be derived from the description of the specification, the drawings, the claims, and the like. 
     One embodiment of the present invention is an organometallic complex including iridium and a ligand. The ligand includes a pyrido[2,3-b]indole skeleton and a pyrimidine skeleton bonded to the 3-position of the pyrido[2,3-b]indole skeleton. The 2-position of the pyrido[2,3-b]indole skeleton and the pyrimidine skeleton are each bonded to the iridium. 
     Another embodiment of the present invention is an organometallic complex including iridium, and first and second ligands bonded to the iridium. The first ligand includes a pyrido[2,3-b]indole skeleton and a pyrimidine skeleton bonded to the 3-position of the pyrido[2,3-b]indole skeleton. The second ligand is a monoanionic bidentate chelate ligand having a β-diketone structure, a monoanionic bidentate chelate ligand having a carboxyl group, a monoanionic bidentate chelate ligand having a phenolic hydroxyl group, a monoanionic bidentate chelate ligand in which two ligand elements are both nitrogen, or an aromatic heterocyclic bidentate ligand which can form a metal-carbon bonding with iridium by cyclometalation. The 2-position of the pyrido[2,3-b]indole skeleton and the pyrimidine skeleton are each bonded to the iridium. 
     In each of the above structures, the 3-position of the pyrimidine skeleton is bonded to the iridium. 
     Another embodiment of the present invention is an organometallic complex having a structure represented by the following general formula (G1). 
     
       
         
         
             
             
         
       
     
     Note that in the general formula (G1), R 1  to R 9  each independently represent any of hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and a substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms. 
     Another embodiment of the present invention is an organometallic complex represented by the following general formula (G2). 
     
       
         
         
             
             
         
       
     
     Note that in the general formula (G2), R 1  to R 9  each independently represent any of hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and a substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms; and L represents a monoanionic ligand. 
     In the above structure, the monoanionic ligand is a monoanionic bidentate chelate ligand having a β-diketone structure, a monoanionic bidentate chelate ligand having a carboxyl group, a monoanionic bidentate chelate ligand having a phenolic hydroxyl group, a monoanionic bidentate chelate ligand in which two ligand elements are both nitrogen, or an aromatic heterocyclic bidentate ligand which can form a metal-carbon bonding with iridium by cyclometalation. 
     In each of the above-described structures, the monoanionic ligand is represented by any one of the following general formulae (L1) to (L7). 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In the general formulae (L1) to (L7), R 71  to R 109  each independently represent any of hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a halogen group, a vinyl group, a substituted or unsubstituted haloalkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 6 carbon atoms, and a substituted or unsubstituted alkylthio group having 1 to 6 carbon atoms. Each of A 1  to A 3  independently represents nitrogen, sp 2  hybridized carbon bonded to hydrogen, or sp 2  hybridized carbon having a substituent. The substituent is an alkyl group having 1 to 6 carbon atoms, a halogen group, a haloalkyl group having 1 to 6 carbon atoms, or a phenyl group. 
     Another embodiment of the present invention is an organometallic complex represented by the following general formula (G3). 
     
       
         
         
             
             
         
       
     
     Note that in the general formula (G3), R 1  to R 9  each independently represent any of hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and a substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms. 
     Another embodiment of the present invention is an organometallic complex represented by the following general formula (G4). 
     
       
         
         
             
             
         
       
     
     Note that in the general formula (G4), R 1  to R 9  each independently represent any of hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and a substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms. 
     Any of the above organometallic complexes each of which is one embodiment of the present invention has a structure in which the 3-position of the pyrido[2,3-b]indole skeleton and the pyrimidine skeleton included in the ligand are bonded to each other and the 2-position of the pyrido[2,3-b]indole skeleton and the pyrimidine skeleton are each bonded to the iridium which is the central metal. In the case where a pyridine ring included in the pyrido[2,3-b]indole skeleton is bonded to the iridium which is the central metal, the HOMO level and the LUMO level tend to be low. An organometallic complex with a low HOMO level has a problem of a low hole-injection property when it is used in an EL element, which results in reduction of the light-emitting efficiency of the light-emitting element. However, since the pyrido[2,3-b]indole skeleton of the organometallic complex of one embodiment of the present invention includes a nitrogen atom in a five-membered ring included in the skeleton, the HOMO level which tends to be too low due to the pyridine ring can be high. Accordingly, the hole-injection property can be prevented from decreasing. Furthermore, the high HOMO level of the organometallic complex can narrow the band gap. When the organometallic complex with a narrow band gap is used for an EL layer or the like of a light-emitting element, carriers (electrons or holes) can be easily injected and transported, and the driving voltage can be reduced. In addition, an emission spectrum of the organometallic complex of one embodiment of the present invention is shifted to a short wavelength side owing to the structure in which the 2-position of the pyrido[2,3-b]indole skeleton is bonded to the iridium which is the central metal, and the emission spectrum is comparatively narrowed. This is preferable because highly efficient light emission and green light with high color purity can be achieved. 
     Another embodiment of the present invention is an organometallic complex represented by the following structural formula (100). 
     
       
         
         
             
             
         
       
     
     Another embodiment of the present invention is an organometallic complex represented by the following structural formula (112). 
     
       
         
         
             
             
         
       
     
     The organometallic complex which is one embodiment of the present invention is very effective for the following reason: the organometallic complex can emit phosphorescence, that is, it can provide luminescence from a triplet excited state, and can exhibit light emission, and therefore higher efficiency is possible when the organometallic complex is used in a light-emitting element. Thus, one embodiment of the present invention also includes a light-emitting element in which the organometallic complex of one embodiment of the present invention is used. 
     Another embodiment of the present invention is a light-emitting element including an EL layer between a pair of electrodes. The EL layer includes a light-emitting layer. The light-emitting layer includes any of the above organometallic complexes. 
     Another embodiment of the present invention is a light-emitting element including an EL layer between a pair of electrodes. The EL layer includes a light-emitting layer. The light-emitting layer includes a plurality of organic compounds. One of the plurality of organic compounds includes any of the above organometallic complexes. 
     One embodiment of the present invention includes, in its scope, not only a light-emitting device including the light-emitting element but also a lighting device including the light-emitting device. The light-emitting device in this specification refers to an image display device and a light source (e.g., a lighting device). In addition, the light-emitting device includes, in its category, all of a module in which a connector such as a flexible printed circuit (FPC) or a tape carrier package (TCP) is connected to a light-emitting device, a module in which a printed wiring board is provided on the tip of a TCP, and a module in which an integrated circuit (IC) is directly mounted on a light emitting element by a chip on glass (COG) method. 
     According to one embodiment of the present invention, a novel organometallic complex can be provided. According to one embodiment of the present invention, a novel organometallic complex having high color purity can be provided. According to one embodiment of the present invention, a novel organometallic complex that can be used in a light-emitting element can be provided. According to one embodiment of the present invention, a novel organometallic complex that can be used in an EL layer of a light-emitting element can be provided. According to one embodiment of the present invention, a novel light-emitting element including a novel organometallic complex can be provided. According to one embodiment of the present invention, a novel light-emitting device, a novel electronic device, or a novel lighting device can be provided. Note that the description of these effects does not preclude the existence of other effects. One embodiment of the present invention does not necessarily achieve all the effects listed above. Other effects will be apparent from and can be derived from the description of the specification, the drawings, the claims, and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIGS. 1A and 1B  illustrate structures of light-emitting elements; 
         FIGS. 2A and 2B  illustrate structures of light-emitting elements; 
         FIGS. 3A to 3C  illustrate light-emitting devices; 
         FIGS. 4A and 4B  illustrate a light-emitting device; 
         FIGS. 5A, 5B, 5C, 5D, 5D ′- 1 , and  5 D′- 2  illustrate electronic devices; 
         FIGS. 6A to 6C  illustrate an electronic device; 
         FIGS. 7A and 7B  illustrate an automobile; 
         FIGS. 8A to 8D  illustrate lighting devices; 
         FIG. 9  illustrates lighting devices; 
         FIGS. 10A and 10B  illustrate an example of a touch panel; 
         FIGS. 11A and 11B  illustrate an example of a touch panel; 
         FIGS. 12A and 12B  illustrate an example of a touch panel; 
         FIGS. 13A and 13B  are a block diagram and a timing chart of a touch sensor; 
         FIG. 14  is a circuit diagram of a touch sensor; 
         FIGS. 15A ,  15 B 1 , and  15 B 2  illustrate block diagrams of a display device; 
         FIG. 16  illustrates a circuit configuration of a display device; 
         FIG. 17  illustrates a cross-sectional structure of a display device; 
         FIG. 18  is a  1 H-NMR chart of an organometallic complex represented by the structural formula (100); 
         FIG. 19  shows the ultraviolet-visible absorption spectrum and the emission spectrum of the organometallic complex represented by the structural formula (100); 
         FIG. 20  is a  1 H-NMR chart of an organometallic complex represented by the structural formula (112); 
         FIG. 21  shows the ultraviolet-visible absorption spectrum and the emission spectrum of the organometallic complex represented by the structural formula (112); 
         FIG. 22  illustrates a light-emitting element; 
         FIG. 23  shows the current density-luminance characteristics of a light-emitting element 1 and a light-emitting element 2; 
         FIG. 24  shows the voltage-luminance characteristics of the light-emitting element 1 and the light-emitting element 2; 
         FIG. 25  shows the luminance-current efficiency characteristics of the light-emitting element 1 and the light-emitting element 2; 
         FIG. 26  shows the voltage-current characteristics of the light-emitting element 1 and the light-emitting element 2; and 
         FIG. 27  shows emission spectra of the light-emitting element 1 and the light-emitting element 2. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments and examples of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following description, and the mode and details can be variously changed unless departing from the scope and spirit of the present invention. Thus, the present invention should not be construed as being limited to the description in the following embodiments and examples. 
     Note that the terms “film” and “layer” can be interchanged with each other depending on the case or circumstances. For example, the term “conductive layer” can be changed into the term “conductive film” in some cases. Also, the term “insulating film” can be changed into the term “insulating layer” in some cases. 
     Embodiment 1 
     In this embodiment, organometallic complexes, each of which is one embodiment of the present invention, will be described. 
     An organometallic complex described in this embodiment includes iridium which is a central metal and a ligand. The ligand includes a pyrido[2,3-b]indole skeleton and a pyrimidine skeleton bonded to the 3-position of the pyrido[2,3-b]indole skeleton. The 2-position of the pyrido[2,3-b]indole skeleton and the pyrimidine skeleton are each bonded to the iridium. 
     An organometallic complex described in this embodiment includes iridium which is a central metal, and first and second ligands bonded to the iridium. The first ligand includes a pyrido[2,3-b]indole skeleton and a pyrimidine skeleton bonded to the 3-position of the pyrido[2,3-b]indole skeleton. The second ligand is a monoanionic bidentate chelate ligand having a β-diketone structure, a monoanionic bidentate chelate ligand having a carboxyl group, a monoanionic bidentate chelate ligand having a phenolic hydroxyl group, a monoanionic bidentate chelate ligand in which two ligand elements are both nitrogen, or an aromatic heterocyclic bidentate ligand which can form a metal-carbon bonding with iridium by cyclometalation. The 2-position of the pyrido[2,3-b]indole skeleton and the pyrimidine skeleton are each bonded to the iridium. 
     In each of the above structures, the 3-position of the pyrimidine skeleton is bonded to the iridium. 
     An organometallic complex described in this embodiment includes a structure represented by the following general formula (G1). 
     
       
         
         
             
             
         
       
     
     Note that in the general formula (G1), R 1  to R 9  each independently represent any of hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and a substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms. 
     An organometallic complex described in this embodiment is represented by following general formula (G2). 
     
       
         
         
             
             
         
       
     
     Note that in the general formula (G2), R 1  to R 9  each independently represent any of hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and a substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms; and L represents a monoanionic ligand. 
     In the above structure, the monoanionic ligand is a monoanionic bidentate chelate ligand having a β-diketone structure, a monoanionic bidentate chelate ligand having a carboxyl group, a monoanionic bidentate chelate ligand having a phenolic hydroxyl group, a monoanionic bidentate chelate ligand in which two ligand elements are both nitrogen, or an aromatic heterocyclic bidentate ligand which can form a metal-carbon bonding with iridium by cyclometalation. 
     In each of the above-described structures, the monoanionic ligand is represented by any one of the following general formulae (L1) to (L7). 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In the general formulae (L1) to (L7), R 71  to R 109  each independently represent any of hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a halogen group, a vinyl group, a substituted or unsubstituted haloalkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted alkoxy group having 1 to 6 carbon atoms, and a substituted or unsubstituted alkylthio group having 1 to 6 carbon atoms. Each of A 1  to A 3  independently represents nitrogen, sp 2  hybridized carbon bonded to hydrogen, or sp 2  hybridized carbon having a substituent. The substituent is an alkyl group having 1 to 6 carbon atoms, a halogen group, a haloalkyl group having 1 to 6 carbon atoms, or a phenyl group. 
     An organometallic complex described in this embodiment is represented by the following general formula (G3). 
     
       
         
         
             
             
         
       
     
     Note that in the general formula (G3), R 1  to R 9  each independently represent any of hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and a substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms. 
     An organometallic complex described in this embodiment is represented by the following general formula (G4). 
     
       
         
         
             
             
         
       
     
     Note that in the general formula (G4), R 1  to R 9  each independently represent any of hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and a substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms. 
     Note that in the case where the substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, the substituted or unsubstituted aryl group having 6 to 13 carbon atoms, or the substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms in any of the above general formulae (G1) to (G4) has a substituent, examples of the substituent include an alkyl group having 1 to 6 carbon atoms, such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, or a hexyl group; a cycloalkyl group having 5 to 7 carbon atoms, such as a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a 1-norbornyl group, or a 2-norbornyl group; and an aryl group having 6 to 12 carbon atoms, such as a phenyl group or a biphenyl group. 
     Specific examples of the alkyl group having 1 to 6 carbon atoms in R 1  to R 9  in each of the general formulae (G1) to (G4) include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, a pentyl group, an isopentyl group, a sec-pentyl group, a tert-pentyl group, a neopentyl group, a hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, a neohexyl group, a 3-methylpentyl group, a 2-methylpentyl group, a 2-ethylbutyl group, a 1,2-dimethylbutyl group, a 2,3-dimethylbutyl group, and a trifluoromethyl group. 
     Specific examples of the aryl group having 6 to 13 carbon atoms in R 1  to R 9  in each of the general formulae (G1) to (G4) include a phenyl group, a tolyl group (an o-tolyl group, an m-tolyl group, and a p-tolyl group), a naphthyl group (a 1-naphthyl group and a 2-naphthyl group), a biphenyl group (a biphenyl-2-yl group, a biphenyl-3-yl group, and a biphenyl-4-yl group), a xylyl group, a pentalenyl group, an indenyl group, a fluorenyl group, and a phenanthryl group. Note that the above substituents may be bonded to each other and form a ring. In such a case, for example, a spirofluorene skeleton is formed in such a manner that carbon at the 9-position of a fluorenyl group has two phenyl groups as substituents and these phenyl groups are bonded to each other. 
     Specific examples of the heteroaryl group having 3 to 12 carbon atoms in R 1  to R 9  in each of the general formulae (G1) to (G4) include an imidazolyl group, a pyrazolyl group, a pyridyl group, a pyridazyl group, a triazyl group, a benzimidazolyl group, and a quinolyl group. 
     Any of the organometallic complexes represented by the general formulae (G1) to (G4), each of which is one embodiment of the present invention, has a structure in which the 3-position of the pyrido[2,3-b]indole skeleton and the pyrimidine skeleton included in the ligand are bonded to each other and the 2-position of the pyrido[2,3-b]indole skeleton and the pyrimidine skeleton are each bonded to the iridium which is the central metal. In the case where a pyridine ring included in the pyrido[2,3-b]indole skeleton is bonded to the iridium which is the central metal, the HOMO level and the LUMO level tend to be low. An organometallic complex with a low HOMO level has a problem of a low hole-injection property when it is used in an EL element, which results in reduction of the light-emitting efficiency of the light-emitting element. However, since the pyrido[2,3-b]indole skeleton of the organometallic complex of one embodiment of the present invention includes a nitrogen atom in a five-membered ring included in the skeleton, the HOMO level which tends to be too low due to the pyridine ring can be high. Accordingly, the hole-injection property can be prevented from decreasing. Furthermore, the high HOMO level of the organometallic complex can narrow the band gap. When the organometallic complex with a narrow band gap is used for an EL layer or the like of a light-emitting element, carriers (electrons or holes) can be easily injected and transported, and the driving voltage can be reduced. In addition, an emission spectrum of the organometallic complex of one embodiment of the present invention is shifted to a short wavelength side owing to the structure in which the 2-position of the pyrido[2,3-b]indole skeleton is bonded to the iridium which is the central metal, and the emission spectrum is comparatively narrowed. This is preferable because highly efficient light emission and green light with high color purity can be achieved. 
     Next, specific structural formulae of the above-described organometallic complexes, each of which is one embodiment of the present invention, are shown below. Note that the present invention is not limited to these formulae. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The organometallic complexes represented by the structural formulae (100) to (121) are novel substances capable of emitting phosphorescence. There can be geometrical isomers and stereoisomers of these substances depending on the type of the ligand. Each of the organometallic complexes which are embodiments of the present invention includes all of these isomers. 
     Next, an example of a method for synthesizing the organometallic complex which is one embodiment of the present invention and represented by the general formula (G1) is described. 
     &lt;&lt;Synthesis Method of Pyrimidine Derivative Represented by General Formula (G0)&gt;&gt; 
     A pyrimidine derivative represented by the following general formula (G0) can be synthesized by a simple synthesis scheme (A) or (A′) as follows. In the synthesis scheme (A), Q represents halogen; R 31  represents a single bond, a methylene group, an ethylidene group, a propylidene group, an isopropylidene group, or the like; each of R 32  to R 35  is the same or different from one another and represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms; and R 33  and R 35  may be bonded to each other through a carbon chain to form a ring. 
     
       
         
         
             
             
         
       
     
     In the general formula (G0), R 1  to R 9  each independently represent any of hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and a substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms. 
     For example, as illustrated in the scheme (A), the pyrimidine derivative represented by the general formula (G0) can be obtained by coupling a boronic acid, a boronate ester, or a cyclic-triolborate salt (A1) with a halogenated pyrimidine compound (A2) and then coupling the obtained product with an organic halide (A3). As the cyclic-triolborate salt, a potassium salt, a lithium salt, a sodium salt, or the like can be used. 
     
       
         
         
             
             
         
       
     
     Alternatively, as illustrated in the scheme (A′), the pyrimidine derivative represented by the general formula (G0) can be obtained by reacting a 1,3-diketone (A1′) which is a pyrido[2,3-b]indole derivative with amidine (A2′). 
     
       
         
         
             
             
         
       
     
     Since a wide variety of the compounds (A1), (A2), (A1′), and (A2′) are commercially available or their synthesis is feasible, a great variety of the pyrimidine derivative represented by the general formula (G0) can be synthesized. Accordingly, the organometallic complexes described in this embodiment have wider variations of ligands. 
     &lt;&lt;Synthesis Method of Organometallic Complex Represented by General Formula (G2)&gt;&gt; 
     Next, a method for synthesizing the organometallic complex which is one embodiment of the present invention and represented by the general formula (G2) is described. First, as shown in the following synthesis scheme (B-1), the pyrimidine derivative represented by the general formula (G0) and an iridium metal compound containing halogen (e.g., iridium chloride, iridium bromide, iridium iodide, iridium acetate, or ammonium hexachloroiridate) are heated in an inert gas atmosphere by using no solvent, an alcohol-based solvent (e.g., glycerol, ethylene glycol, 2-methoxyethanol, or 2-ethoxyethanol) alone, or a mixed solvent of water and one or more kinds of such alcohol-based solvents, whereby a novel dinuclear complex (P), which is one type of organometallic complex having a halogen-bridged structure, can be obtained. There is no particular limitation on a heating means, and an oil bath, a sand bath, an aluminum block, or the like can be used. Alternatively, microwaves can be used as the heating means. 
     
       
         
         
             
             
         
       
     
     In the synthesis scheme (B-1), Q represents halogen, and R 1  to R 9  each independently represent any of hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and a substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms. 
     Then, as shown in the following synthesis scheme (B-2), the dinuclear complex (P) obtained in the synthesis scheme (B-1) is reacted with HL which is a material of a monoanionic ligand in an inert gas atmosphere, whereby a proton of HL is separated and L coordinates to the central metal, iridium. Thus, the organometallic complex represented by the general formula (G2) can be obtained. 
     
       
         
         
             
             
         
       
     
     In the synthesis scheme (B-2), L represents a monoanionic ligand, Q represents halogen, and R 1  to R 9  each independently represent any of hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and a substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms. In the above structure, the monoanionic ligand is a monoanionic bidentate chelate ligand having a β-diketone structure, a monoanionic bidentate chelate ligand having a carboxyl group, a monoanionic bidentate chelate ligand having a phenolic hydroxyl group, a monoanionic bidentate chelate ligand in which two ligand elements are both nitrogen, or an aromatic heterocyclic bidentate ligand which can form a metal-carbon bonding with iridium by cyclometalation. 
     &lt;&lt;Synthesis Method of Organometallic Complex Represented by General Formula (G3)&gt;&gt; 
     Next, a method for synthesizing the organometallic complex which is one embodiment of the present invention and represented by the general formula (G3) is described. As shown in a synthesis scheme (C), an iridium compound containing halogen (e.g., iridium chloride hydrate, iridium bromide, iridium iodide, iridium acetate, or ammonium hexachloroiridate) or an organoiridium complex compound (e.g., an acetylacetonato complex, a diethylsulfide complex, a di-μ-chloro bridged dinuclear complex, or a di-μ-hydroxo bridged dinuclear complex) is mixed with the pyrimidine derivative represented by the general formula (G0), the mixture is dissolved in an alcohol-based solvent (e.g., glycerol, ethylene glycol, 2-methoxyethanol, or 2-ethoxyethanol) or not dissolved in any solvent, and heating is performed. Thus, the organometallic complex represented by the general formula (G3) can be obtained. 
     
       
         
         
             
             
         
       
     
     In the synthesis scheme (C), R 1  to R 9  each independently represent any of hydrogen, a substituted or unsubstituted alkyl group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group having 6 to 13 carbon atoms, and a substituted or unsubstituted heteroaryl group having 3 to 12 carbon atoms. 
     The above is the description on the examples of methods for synthesizing the organometallic complexes of embodiments of the present invention; however, the present invention is not limited thereto and any other synthesis method may be employed. 
     The above-described organometallic complexes each of which is one embodiment of the present invention can emit phosphorescence and thus can be used as a light-emitting material or a light-emitting substance of a light-emitting element. 
     With the use of any of the organometallic complexes each of which is one embodiment of the present invention, a light-emitting element, a light-emitting device, an electronic device, or a lighting device with high emission efficiency can be obtained. Alternatively, it is possible to obtain a light-emitting element, a light-emitting device, an electronic device, or a lighting device with low power consumption. 
     In Embodiment 1, one embodiment of the present invention has been described. Other embodiments of the present invention are described in Embodiments 2 to 9. Note that one embodiment of the present invention is not limited to the above examples. In other words, various embodiments of the invention are described in this embodiment and the other embodiments, and one embodiment of the present invention is not limited to a particular embodiment. The example in which one embodiment of the present invention is used in a light-emitting element is described; however, one embodiment of the present invention is not limited thereto. Depending on circumstances or conditions, one embodiment of the present invention may be used in objects other than a light-emitting element. 
     The structures described in this embodiment can be used in appropriate combination with any of the structures described in the other embodiments. 
     Embodiment 2 
     In this embodiment, a light-emitting element which is one embodiment of the present invention will be described with reference to  FIGS. 1A and 1B . 
     In the light-emitting element described in this embodiment, an EL layer  102  including a light-emitting layer  113  is interposed between a pair of electrodes (a first electrode (anode)  101  and a second electrode (cathode)  103 ), and the EL layer  102  includes a hole-injection layer  111 , a hole-transport layer  112 , an electron-transport layer  114 , an electron-injection layer  115 , and the like in addition to the light-emitting layer  113 . 
     When a voltage is applied to the light-emitting element, holes injected from the first electrode  101  side and electrons injected from the second electrode  103  side recombine in the light-emitting layer  113 ; with energy generated by the recombination, a light-emitting substance such as the organometallic complex that is contained in the light-emitting layer  113  emits light. 
     The hole-injection layer  111  in the EL layer  102  can inject holes into the hole-transport layer  112  or the light-emitting layer  113  and can be formed of, for example, a substance having a high hole-transport property and a substance having an acceptor property, in which case electrons are extracted from the substance having a high hole-transport property by the substance having an acceptor property to generate holes. Thus, holes are injected from the hole-injection layer  111  into the light-emitting layer  113  through the hole-transport layer  112 . For the hole-injection layer  111 , a substance having a high hole-injection property can also be used. For example, molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, manganese oxide, or the like can be used. Alternatively, the hole-injection layer  111  can be formed using a phthalocyanine-based compound such as phthalocyanine (abbreviation: H 2 Pc) and copper phthalocyanine (CuPc), an aromatic amine compound such as 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB) and N,N′-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (abbreviation: DNTPD), or a high molecular compound such as poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS). 
     A preferred specific example in which the light-emitting element described in this embodiment is fabricated is described below. 
     For the first electrode (anode)  101  and the second electrode (cathode)  103 , a metal, an alloy, an electrically conductive compound, a mixture thereof, and the like can be used. Specific examples are indium oxide-tin oxide (indium tin oxide), indium oxide-tin oxide containing silicon or silicon oxide, indium oxide-zinc oxide (indium zinc oxide), indium oxide containing tungsten oxide and zinc oxide, gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), and titanium (Ti). In addition, an element belonging to Group 1 or Group 2 of the periodic table, for example, an alkali metal such as lithium (Li) or cesium (Cs), an alkaline earth metal such as calcium (Ca) or strontium (Sr), magnesium (Mg), an alloy containing such an element (MgAg or AlLi), a rare earth metal such as europium (Eu) or ytterbium (Yb), an alloy containing such an element, graphene, and the like can be used. The first electrode (anode)  101  and the second electrode (cathode)  103  can be formed by, for example, a sputtering method or an evaporation method (including a vacuum evaporation method). 
     As the substance having a high hole-transport property which is used for the hole-injection layer  111  and the hole-transport layer  112 , any of a variety of organic compounds such as aromatic amine compounds, carbazole derivatives, aromatic hydrocarbons, and high molecular compounds (e.g., oligomers, dendrimers, or polymers) can be used. Specifically, a substance having a hole mobility of 1×10 −6  cm 2 /Vs or more is preferably used. The layer formed using the substance having a high hole-transport property is not limited to a single layer and may be formed by stacking two or more layers. Organic compounds that can be used as the substance having a hole-transport property are specifically given below. 
     Examples of the aromatic amine compounds are N,N′-di(p-tolyl)-N,N′-diphenyl-p-phenylenediamine (abbreviation: DTDPPA), 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB), DNTPD, 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene (abbreviation: DPA3B), 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. 
     Specific examples of the carbazole derivatives are 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. Other examples are 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]-9H-carbazole (abbreviation: CzPA), 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene, and the like. 
     Examples of the aromatic hydrocarbons are 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), 2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene, 9,10-bis[2-(1-naphthyl)phenyl]anthracene, 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. Besides, pentacene, coronene, or the like can also be used. The aromatic hydrocarbon which has a hole mobility of 1×10 −6  cm 2 /Vs or more and which has 14 to 42 carbon atoms is particularly preferable. The aromatic hydrocarbons may have a vinyl skeleton. Examples of the aromatic hydrocarbon having a vinyl group are 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi) and 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (abbreviation: DPVPA). 
     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 also be used. 
     Examples of the substance having an acceptor property which is used for the hole-injection layer  111  and the hole-transport layer  112  are compounds having an electron-withdrawing group (a halogen group or a cyano group) such as 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F 4 -TCNQ), chloranil, and 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HAT-CN). In particular, a compound in which electron-withdrawing groups are bonded to a condensed aromatic ring having a plurality of hetero atoms, like HAT-CN, is thermally stable and preferable. Oxides of metals belonging to Groups 4 to 8 of 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 their high electron-accepting properties. Among these, molybdenum oxide is especially preferable since it is stable in the air, has a low hygroscopic property, and is easy to handle. 
     The light-emitting layer  113  contains a light-emitting substance, which may be a fluorescent substance or a phosphorescent substance. In the light-emitting element which is one embodiment of the present invention, the organometallic complex described in Embodiment 1 is preferably used as the light-emitting substance in the light-emitting layer  113 . The light-emitting layer  113  preferably contains, as a host material, a substance having higher triplet excitation energy than this organometallic complex (guest material). Alternatively, the light-emitting layer  113  may contain, in addition to the light-emitting substance, two kinds of organic compounds that can form an excited complex (also called an exciplex) at the time of recombination of carriers (electrons and holes) in the light-emitting layer  113  (the two kinds of organic compounds may be any of the host materials as described above). In order to form an exciplex efficiently, it is particularly preferable to combine a compound which easily accepts electrons (a material having an electron-transport property) and a compound which easily accepts holes (a material having a hole-transport property). In the case where the combination of a material having an electron-transport property and a material having a hole-transport property which form an exciplex is used as a host material as described above, the carrier balance between holes and electrons in the light-emitting layer can be easily optimized by adjustment of the mixture ratio of the material having an electron-transport property and the material having a hole-transport property. The optimization of the carrier balance between holes and electrons in the light-emitting layer can prevent a region in which electrons and holes are recombined from existing on one side in the light-emitting layer. By preventing the region in which electrons and holes are recombined from existing on one side, the reliability of the light-emitting element can be improved. 
     As the compound that is preferably used to form the above exciplex and easily accepts electrons (the material having an electron-transport property), a π-electron deficient heteroaromatic compound such as a nitrogen-containing heteroaromatic compound, a metal complex, or the like can be used. Specific examples include metal complexes such as bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq 2 ), bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq), bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), and bis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ); heterocyclic compounds having polyazole skeletons, such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation: PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (abbreviation: TAZ), 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]-9H-carbazole (abbreviation: CO11), 2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole) (abbreviation: TPBI), and 2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (abbreviation: mDBTBIm-II); heterocyclic compounds having diazine skeletons, such as 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTPDBq-II), 2-[3′-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mDBTBPDBq-II), 2-[3′-(9H-carbazol-9-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (abbreviation: 2mCzBPDBq), 2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 2CzPDBq-III), 7-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 7mDBTPDBq-II), 6-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (abbreviation: 6mDBTPDBq-II), 4,6-bis[3-(phenanthren-9-yl)phenyl]pyrimidine (abbreviation: 4,6mPnP2Pm), 4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (abbreviation: 4,6mDBTP2Pm-II), and 4,6-bis[3-(9H-carbazol-9-yl)-phenyl]pyrimidine (abbreviation: 4,6mCzP2Pm); a heterocyclic compound having a triazine skeleton, such as 2-{4-[3-(N-phenyl-9H-carbazol-3-yl)-9H-carbazol-9-yl]phenyl}-4,6-diphenyl-1,3,5-triazine (abbreviation: PCCzPTzn); and heterocyclic compounds having pyridine skeletons, such as 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (abbreviation: 35DCzPPy) and 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (abbreviation: TmPyPB). Among the above materials, the heterocyclic compounds having diazine skeletons, those having triazine skeletons, and those having pyridine skeletons are highly reliable and preferred. In particular, the heterocyclic compounds having diazine (pyrimidine or pyrazine) skeletons and those having triazine skeletons have a high electron-transport property and contribute to a decrease in drive voltage. 
     As the compound that is preferably used to form the above exciplex and easily accepts holes (the material having a hole-transport property), a π-electron rich heteroaromatic compound (e.g., a carbazole derivative or an indole derivative), an aromatic amine compound, or the like can be favorably used. Specific examples include compounds having aromatic amine skeletons, such as 2-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]spiro-9,9′-bifluorene (abbreviation: PCASF), 4,4′,4″-tris[N-(1-naphthyl)-N-phenylamino]triphenylamine (abbreviation: 1′-TNATA), 2,7-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-spiro-9,9′-bifluorene (abbreviation: DPA2SF), N,N′-bis(9-phenylcarbazol-3-yl)-N,N′-diphenylbenzene-1,3-diamine (abbreviation: PCA2B), N-(9,9-dimethyl-2-diphenylamino-9H-fluoren-7-yl)diphenylamine (abbreviation: DPNF), N,N′,N″-triphenyl-N,N′,N″-tris(9-phenylcarbazol-3-yl)benzene-1,3,5-triamine (abbreviation: PCA3B), 2-[N-(4-diphenylaminophenyl)-N-phenylamino]spiro-9,9′-bifluorene (abbreviation: DPASF), N,N′-bis[4-(carbazol-9-yl)phenyl]-N,N′-diphenyl-9,9-dimethylfluorene-2,7-diamine (abbreviation: YGA2F), NPB, N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine (abbreviation: TPD), 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation: DPAB), BSPB, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP), 4-phenyl-3′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: mBPAFLP), N-(9,9-dimethyl-9H-fluoren-2-yl)-N-{9,9-dimethyl-2-[N′-phenyl-N′-(9,9-dimethyl-9H-fluoren-2-yl)amino]-9H-fluoren-7-yl}phenylamine (abbreviation: DFLADFL), PCzPCA1, 3-[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzDPA1), 3,6-bis[N-(4-diphenylaminophenyl)-N-phenylamino]-9-phenylcarbazole (abbreviation: PCzDPA2), DNTPD, 3,6-bis[N-(4-diphenylaminophenyl)-N-(1-naphthyflamino]-9-phenylcarbazole (abbreviation: PCzTPN2), PCzPCA2, 4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBA1BP), 4,4′-diphenyl-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBBi1BP), 4-(1-naphthyl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBANB), 4,4′-di(1-naphthyl)-4″-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBNBB), 3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (abbreviation: PCzPCN1), 9,9-dimethyl-N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]fluoren-2-amine (abbreviation: PCBAF), N-phenyl-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]spiro-9,9′-bifluoren-2-amine (abbreviation: PCBASF), N-(4-biphenyl)-N-(9,9-dimethyl-9H-fluoren-2-yl)-9-phenyl-9H-carbazol-3-amine (abbreviation: PCBiF), and N-(1,1′-biphenyl-4-yl)-N-[4-(9-phenyl-9H-carbazol-3-yl)phenyl]-9,9-dimethyl-9H-fluoren-2-amine (abbreviation: PCBBiF); compounds having carbazole skeletons, such as 1,3-bis(N-carbazolyl)benzene (abbreviation: mCP), CBP, 3,6-bis(3,5-diphenylphenyl)-9-phenylcarbazole (abbreviation: CzTP), and 9-phenyl-9H-3-(9-phenyl-9H-carbazol-3-yl)carbazole (abbreviation: PCCP); compounds having thiophene skeletons, such as 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzothiophene) (abbreviation: DBT3P-II), 2,8-diphenyl-4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]dibenzothiophene (abbreviation: DBTFLP-III), and 4-[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-6-phenyldibenzothiophene (abbreviation: DBTFLP-IV); and compounds having furan skeletons, such as 4,4′,4″-(benzene-1,3,5-triyl)tri(dibenzofuran) (abbreviation: DBF3P-II) and 4-{3-[3-(9-phenyl-9H-fluoren-9-yl)phenyl]phenyl}dibenzofuran (abbreviation: mmDBFFLBi-II). Among the above materials, the compounds having aromatic amine skeletons and the compounds having carbazole skeletons are preferred because these compounds are highly reliable, have a high hole-transport property, and contribute to a reduction in drive voltage. 
     Note that in the case where the light-emitting layer  113  contains the above-described organometallic complex (guest material) and the host material, phosphorescence with high emission efficiency can be obtained from the light-emitting layer  113 . 
     In the light-emitting element, the light-emitting layer  113  does not necessarily have the single-layer structure shown in  FIG. 1A  and may have a stacked-layer structure including two or more layers as shown in  FIG. 1B . In that case, each layer in the stacked-layer structure emits light. For example, fluorescence is obtained from a first light-emitting layer  113 ( a   1 ), and phosphorescence is obtained from a second light-emitting layer  113 ( a   2 ) stacked over the first light-emitting layer. Note that the stacking order may be reversed. It is preferable that light emission due to energy transfer from an exciplex to a dopant be obtained from the layer that emits phosphorescence. The emission color of one layer and that of the other layer may be the same or different. In the case where the emission colors are different, a structure in which, for example, blue light from one layer and orange or yellow light or the like from the other layer can be obtained can be formed. Each layer may contain various kinds of dopants. 
     Note that in the case where the light-emitting layer  113  has a stacked-layer structure, for example, the organometallic complex described in Embodiment 1, a light-emitting substance converting singlet excitation energy into light emission, and a light-emitting substance converting triplet excitation energy into light emission can be used alone or in combination. In that case, the following substances can be used. 
     As an example of the light-emitting substance converting singlet excitation energy into light emission, a substance which emits fluorescence (a fluorescent compound) can be given. 
     Examples of the substance which emits fluorescence 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), 4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine (abbreviation: 2YGAPPA), N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: PCAPA), perylene, 2,5,8,11-tetra(tert-butyl)perylene (abbreviation: TBP), 4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation: PCBAPA), N,N″-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N′,N′-triphenyl-1,4-phenylenediamine] (abbreviation: DPABPA), N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine (abbreviation: 2PCAPPA), N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N′-triphenyl-1,4-phenylenediamine (abbreviation: 2DPAPPA), N,N,N′,N′,N″,N″,N′″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine (abbreviation: DBC1), coumarin 30, 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), coumarin 545T, N,N′-diphenylquinacridone (abbreviation: DPQd), rubrene, 5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT), 2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile (abbreviation: DCM1), 2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCM2), N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation: p-mPhTD), 7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine (abbreviation: p-mPhAFD), {2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTI), {2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: DCJTB), 2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile (abbreviation: BisDCM), 2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile (abbreviation: BisDCJTM), and the like. 
     Examples of the light-emitting substance converting triplet excitation energy into light emission are a substance which emits phosphorescence (a phosphorescent compound) and a thermally activated delayed fluorescent (TADF) material which emits thermally activated delayed fluorescence. Note that “delayed fluorescence” exhibited by the TADF material refers to light emission having the same spectrum as normal fluorescence and an extremely long lifetime. The lifetime is 1×10 −6  seconds or longer, preferably 1×10 −3  seconds or longer. 
     Examples of the substance which emits phosphorescence are bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C 2′ }iridium(III) picolinate (abbreviation: [Ir(CF 3 ppy) 2 (pic)]), bis[2-(4′,6′-difluorophenyl)pyridinato-N,C 2′ ]iridium(III) acetylacetonate (abbreviation: FIracac), tris(2-phenylpyridinato)iridium(III) (abbreviation: [Ir(ppy) 3 ]), bis(2-phenylpyridinato)iridium(III) acetylacetonate (abbreviation: [Ir(ppy) 2 (acac)]), tris(acetylacetonato)(monophenanthroline)terbium(III) (abbreviation: [Tb(acac) 3 (Phen)]), bis(benzo[h]quinolinato)iridium(III) acetylacetonate (abbreviation: [Ir(bzq) 2 (acac)]), bis(2,4-diphenyl-1,3-oxazolato-N,C 2′ )iridium(III) acetylacetonate (abbreviation: [Ir(dpo) 2 (acac)]), bis{2-[4′-(perfluorophenyephenyl]pyridinato-N,C 2′ }iridium(III) acetylacetonate (abbreviation: [Ir(p-PF-ph) 2 (acac)]), bis(2-phenylbenzothiazolato-N,C 2′ )iridium(III) acetylacetonate (abbreviation: [Ir(bt) 2 (acac)]), 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)]), (acetylacetonato)bis(3,5-dimethyl-2-phenylpyrazinato)iridium (III) (abbreviation: [Ir(mppr-Me) 2 (acac)]), (acetylacetonato)bis(5-isopropyl-3-methyl-2-phenylpyrazinato)iridium(III) (abbreviation: [Ir(mppr-iPr) 2 (acac)]), (acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III) (abbreviation: [Ir(tppr) 2 (acac)]), bis(2,3,5-triphenylpyrazinato)(dipivaloylmethanato)iridium(III) (abbreviation: [Ir(tppr) 2 (dpm)]), (acetylacetonato)bis(6-tert-butyl-4-phenylpyrimidinato)iridium(III) (abbreviation: [Ir(tBuppm) 2 (acac)]), (acetylacetonato)bis(4,6-diphenylpyrimidinato)iridium(III) (abbreviation: [Ir(dppm) 2 (acac)]), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) (abbreviation: PtOEP), tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III) (abbreviation: [Eu(DBM) 3 (Phen)]), tris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III) (abbreviation: [Eu(TTA) 3 (Phen)]), and the like. 
     Examples of the TADF material are fullerene, a derivative thereof, an acridine derivative such as proflavine, eosin, and the like. Other examples are a metal-containing porphyrin, such as a porphyrin containing magnesium (Mg), zinc (Zn), cadmium (Cd), tin (Sn), platinum (Pt), indium (In), or palladium (Pd). Examples of the metal-containing porphyrin are a protoporphyrin-tin fluoride complex (abbreviation: SnF 2 (Proto IX)), a mesoporphyrin-tin fluoride complex (abbreviation: SnF 2 (Meso IX)), a hematoporphyrin-tin fluoride complex (abbreviation: SnF 2 (Hemato IX)), a coproporphyrin tetramethyl ester-tin fluoride complex (abbreviation: SnF 2 (Copro III-4Me)), an octaethylporphyrin-tin fluoride complex (abbreviation: SnF 2 (OEP)), an etioporphyrin-tin fluoride complex (abbreviation: SnF 2 (Etio I)), an octaethylporphyrin-platinum chloride complex (abbreviation: PtCl 2 OEP), and the like. Alternatively, a heterocyclic compound including a π-electron rich heteroaromatic ring and a π-electron deficient heteroaromatic ring can be used, such as 2-(biphenyl-4-yl)-4,6-bis(12-phenylindolo[2,3-a]carbazol-11-yl)-1,3,5-triazine (abbreviation: PIC-TRZ). Note that a material in which the π-electron rich heteroaromatic ring is directly bonded to the π-electron deficient heteroaromatic ring is particularly preferably used because both the donor property of the π-electron rich heteroaromatic ring and the acceptor property of the π-electron deficient heteroaromatic ring are increased and the energy difference between the S1 level and the T1 level becomes small. 
     The light-emitting layer  113  can be formed using a quantum dot (QD) having unique optical characteristics. Note that QD means a nanoscale semiconductor crystal. Specifically, the nanoscale semiconductor crystal has a diameter of several nanometers to several tens of nanometers. Furthermore, by using a crystal having a different size, the optical characteristics and the electronic characteristics can be changed, and thus an emission color or the like can be adjusted easily. A quantum dot has an emission spectrum with a narrow peak, and thus emission of light with high color purity can be obtained. 
     Examples of a material forming a quantum dot include a Group 14 element in the periodic table, a Group 15 element in the periodic table, a Group 16 element in the periodic table, a compound of a plurality of Group 14 elements in the periodic table, a compound of an element belonging to any of Groups 4 to 14 in the periodic table and a Group 16 element in the periodic table, a compound of a Group 2 element in the periodic table and a Group 16 element in the periodic table, a compound of a Group 13 element in the periodic table and a Group 15 element in the periodic table, a compound of a Group 13 element in the periodic table and a Group 17 element in the periodic table, a compound of a Group 14 element in the periodic table and a Group 15 element in the periodic table, a compound of a Group 11 element in the periodic table and a Group 17 element in the periodic table, iron oxides, titanium oxides, spinel chalcogenides, and semiconductor clusters. 
     Specific examples include, but are not limited to, cadmium selenide; cadmium sulfide; cadmium telluride; zinc selenide; zinc oxide; zinc sulfide; zinc telluride; mercury sulfide; mercury selenide; mercury telluride; indium arsenide; indium phosphide; gallium arsenide; gallium phosphide; indium nitride; gallium nitride; indium antimonide; gallium antimonide; aluminum phosphide; aluminum arsenide; aluminum antimonide; lead selenide; lead telluride; lead sulfide; indium selenide; indium telluride; indium sulfide; gallium selenide; arsenic sulfide; arsenic selenide; arsenic telluride; antimony sulfide; antimony selenide; antimony telluride; bismuth sulfide; bismuth selenide; bismuth telluride; silicon; silicon carbide; germanium; tin; selenium; tellurium; boron; carbon; phosphorus; boron nitride; boron phosphide; boron arsenide; aluminum nitride; aluminum sulfide; barium sulfide; barium selenide; barium telluride; calcium sulfide; calcium selenide; calcium telluride; beryllium sulfide; beryllium selenide; beryllium telluride; magnesium sulfide; magnesium selenide; germanium sulfide; germanium selenide; germanium telluride; tin sulfide; tin selenide; tin telluride; lead oxide; copper fluoride; copper chloride; copper bromide; copper iodide; copper oxide; copper selenide; nickel oxide; cobalt oxide; cobalt sulfide; iron oxide; iron sulfide; manganese oxide; molybdenum sulfide; vanadium oxide; tungsten oxide; tantalum oxide; titanium oxide; zirconium oxide; silicon nitride; germanium nitride; aluminum oxide; barium titanate; a compound of selenium, zinc, and cadmium; a compound of indium, arsenic, and phosphorus; a compound of cadmium, selenium, and sulfur; a compound of cadmium, selenium, and tellurium; a compound of indium, gallium, and arsenic; a compound of indium, gallium, and selenium; a compound of indium, selenium, and sulfur; a compound of copper, indium, and sulfur; and combinations thereof. What is called an alloyed quantum dot, whose composition is represented by a given ratio, may be used. For example, an alloyed quantum dot of cadmium, selenium, and sulfur is an effective material to obtain blue light because the emission wavelength can be changed by changing the percentages of the elements. 
     As a structure of a quantum dot, a core structure, a core-shell structure, a core-multishell structure, or the like can be given, and any of the structures may be used. Note that a core-shell quantum dot or a core-multishell quantum dot where a shell covers a core is preferable because a shell formed of an inorganic material having a wider band gap than an inorganic material used as the core can reduce the influence of defects and dangling bonds existing at the surface of the nanocrystal and significantly improve the quantum efficiency of light emission. 
     Moreover, QD can be dispersed into a solution, and thus the light-emitting layer  113  can be formed by a coating method, an inkjet method, a printing method, or the like. Note that QD can emit not only light with bright and vivid color but also light with a wide range of wavelengths and has high efficiency and long lifetime. Thus, when QD is included in the light-emitting layer  113 , the element characteristics can be improved. 
     The electron-transport layer  114  is a layer containing a substance having a high electron-transport property (also referred to as an electron-transport compound). For the electron-transport layer  114 , a metal complex such as tris(8-quinolinolato)aluminum (abbreviation: Alq 3 ), tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq 3 ), BeBq 2 , BAlq, bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX) 2 ), or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ) 2 ) can be used. Alternatively, a heteroaromatic compound such as PBD, OXD-7, TAZ, 3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole (abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproine (abbreviation: BCP), or 4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs) can also be used. A high molecular compound such as poly(2,5-pyridinediyl) (abbreviation: PPy), 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′-bipyridine-6,6′-diyl)] (abbreviation: PF-BPy) can also be used. The substances listed here are mainly ones that have an electron mobility of 1×10 −6  cm 2 /Vs or higher. Note that any substance other than the substances listed here may be used for the electron-transport layer  114  as long as the electron-transport property is higher than the hole-transport property. 
     The electron-transport layer  114  is not limited to a single layer, and may be a stack of two or more layers each containing any of the substances listed above. 
     The electron-injection layer  115  is a layer containing a substance having a high electron-injection property. For the electron-injection layer  115 , an alkali metal, an alkaline earth metal, or a compound thereof, such as lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF 2 ), or lithium oxide (LiO x ) can be used. A rare earth metal compound like erbium fluoride (ErF 3 ) can also be used. An electride may also be used for the electron-injection layer  115 . Examples of the electride include a substance in which electrons are added at high concentration to calcium oxide-aluminum oxide. Any of the substances for forming the electron-transport layer  114 , which are given above, can be used. 
     A composite material in which an organic compound and an electron donor (donor) are mixed may also be used for the electron-injection layer  115 . Such a composite material is excellent in an electron-injection property and an electron-transport property because electrons are generated in the organic compound by the electron donor. In this case, the organic compound is preferably a material that is excellent in transporting the generated electrons. Specifically, for example, the substances for forming the electron-transport layer  114  (e.g., a metal complex or a heteroaromatic compound), which are given above, can be used. As the electron donor, a substance showing an electron-donating property with respect to the organic compound may be used. Specifically, an alkali metal, an alkaline earth metal, and a rare earth metal are preferable, and lithium, cesium, magnesium, calcium, erbium, ytterbium, and the like are given. In addition, an alkali metal oxide or an alkaline earth metal oxide is preferable, and lithium oxide, calcium oxide, barium oxide, and the like are given. A Lewis base such as magnesium oxide can also be used. An organic compound such as tetrathiafulvalene (abbreviation: TTF) can also be used. 
     Note that each of the hole-injection layer  111 , the hole-transport layer  112 , the light-emitting layer  113 , the electron-transport layer  114 , and the electron-injection layer  115  can be formed by any one or any combination of the following methods: an evaporation method (including a vacuum evaporation method), a printing method (such as relief printing, intaglio printing, gravure printing, planography printing, and stencil printing), an ink jet method, a coating method, and the like. Besides the above-mentioned materials, an inorganic compound such as a quantum dot or a high molecular compound (e.g., an oligomer, a dendrimer, or a polymer) may be used for the hole-injection layer  111 , the hole-transport layer  112 , the light-emitting layer  113 , the electron-transport layer  114 , and the electron-injection layer  115 , which are described above. 
     In the above-described light-emitting element, current flows due to a potential difference applied between the first electrode  101  and the second electrode  103  and holes and electrons recombine in the EL layer  102 , whereby light is emitted. Then, the emitted light is extracted outside through one or both of the first electrode  101  and the second electrode  103 . Thus, one or both of the first electrode  101  and the second electrode  103  are electrodes having light-transmitting properties. 
     The above-described light-emitting element can emit phosphorescence originating from the organometallic complex and thus can have higher efficiency than a light-emitting element using only a fluorescent compound. 
     The structure described in this embodiment can be used in appropriate combination with any of the structures described in the other embodiments. 
     Embodiment 3 
     In this embodiment, a light-emitting element (hereinafter referred to as a tandem light-emitting element) which is one embodiment of the present invention and includes a plurality of EL layers is described. 
     A light-emitting element described in this embodiment is a tandem light-emitting element including, between a pair of electrodes (a first electrode  201  and a second electrode  204 ), a plurality of EL layers (a first EL layer  202 ( 1 ) and a second EL layer  202 ( 2 )) and a charge-generation layer  205  provided therebetween, as illustrated in  FIG. 2A . 
     In this embodiment, the first electrode  201  functions as an anode, and the second electrode  204  functions as a cathode. Note that the first electrode  201  and the second electrode  204  can have structures similar to those described in Embodiment 2. In addition, either or both of the EL layers (the first EL layer  202 ( 1 ) and the second EL layer  202 ( 2 )) may have structures similar to those described in Embodiment 2. In other words, the structures of the first EL layer  202 ( 1 ) and the second EL layer  202 ( 2 ) may be the same or different from each other. When the structures are the same, Embodiment 2 can be referred to. 
     The charge-generation layer  205  provided between the plurality of EL layers (the first EL layer  202 ( 1 ) and the second EL layer  202 ( 2 )) has a function of injecting electrons into one of the EL layers and injecting holes into the other of the EL layers when a voltage is applied between the first electrode  201  and the second electrode  204 . In this embodiment, when a voltage is applied such that the potential of the first electrode  201  is higher than that of the second electrode  204 , the charge-generation layer  205  injects electrons into the first EL layer  202 ( 1 ) and injects holes into the second EL layer  202 ( 2 ). 
     Note that in terms of light extraction efficiency, the charge-generation layer  205  preferably has a property of transmitting visible light (specifically, the charge-generation layer  205  has a visible light transmittance of 40% or more). The charge-generation layer  205  functions even when it has lower conductivity than the first electrode  201  or the second electrode  204 . 
     The charge-generation layer  205  may have either a structure in which an electron acceptor (acceptor) is added to an organic compound having a high hole-transport property or a structure in which an electron donor (donor) is added to an organic compound having a high electron-transport property. Alternatively, both of these structures may be stacked. 
     In the case of the structure in which an electron acceptor is added to an organic compound having a high hole-transport property, as the organic compound having a high hole-transport property, the substances having a high hole-transport property which are given in Embodiment 2 as the substances used for the hole-injection layer  111  and the hole-transport layer  112  can be used. For example, an aromatic amine compound such as NPB, TPD, TDATA, MTDATA, or BSPB, or the like can be used. The substances listed here are mainly ones that have a hole mobility of 1×10 4  cm 2 Ns or higher. Note that any organic compound other than the compounds listed here may be used as long as the hole-transport property is higher than the electron-transport property. 
     As the electron acceptor, 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation: F 4 -TCNQ), chloranil, and the like can be given. Oxides of metals belonging to Groups 4 to 8 of the periodic table can also be given. Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, and rhenium oxide are preferable because of their high electron-accepting properties. Among these, molybdenum oxide is especially preferable since it is stable in the air, has a low hygroscopic property, and is easy to handle. 
     In the case of the structure in which an electron donor is added to an organic compound having a high electron-transport property, as the organic compound having a high electron-transport property, the substances having a high electron-transport property which are given in Embodiment 2 as the substances used for the electron-transport layer  114  can be used. For example, a metal complex having a quinoline skeleton or a benzoquinoline skeleton, such as Alq, Almq 3 , BeBq 2 , or BAlq, or the like can be used. Alternatively, a metal complex having an oxazole-based ligand or a thiazole-based ligand, such as Zn(BOX) 2  or Zn(BTZ) 2  can be used. Alternatively, in addition to such a metal complex, PBD, OXD-7, TAZ, Bphen, BCP, or the like can be used. The substances listed here are mainly ones that have an electron mobility of 1×10 −6  cm 2 /Vs or higher. Note that any organic compound other than the compounds listed here may be used as long as the electron-transport property is higher than the hole-transport property. 
     As the electron donor, it is possible to use an alkali metal, an alkaline earth metal, a rare earth metal, metals belonging to Groups 2 and 13 of the periodic table, or an oxide or carbonate thereof. Specifically, lithium (Li), cesium (Cs), magnesium (Mg), calcium (Ca), ytterbium (Yb), indium (In), lithium oxide, cesium carbonate, or the like is preferably used. Alternatively, an organic compound such as tetrathianaphthacene may be used as the electron donor. 
     Note that forming the charge-generation layer  205  by using any of the above materials can suppress a drive voltage increase caused by the stack of the EL layers. The charge-generation layer  205  can be formed by any one or any combination of the following methods: an evaporation method (including a vacuum evaporation method), a printing method (such as relief printing, intaglio printing, gravure printing, planography printing, and stencil printing), an ink-jet method, a coating method, and the like. 
     Although the light-emitting element including two EL layers is described in this embodiment, the present invention can be similarly applied to a light-emitting element in which n EL layers ( 202 ( 1 ) to  202 ( n )) (n is three or more) are stacked as illustrated in  FIG. 2B . In the case where a plurality of EL layers are included between a pair of electrodes as in the light-emitting element according to this embodiment, by providing charge-generation layers ( 205 ( 1 ) to  205 ( n− 1)) between the EL layers, light emission in a high luminance region can be obtained with current density kept low. Since the current density can be kept low, the element can have a long lifetime. 
     When the EL layers have different emission colors, a desired emission color can be obtained from the whole light-emitting element. For example, in a light-emitting element having two EL layers, when an emission color of the first EL layer and an emission color of the second EL layer are complementary colors, the light-emitting element can emit white light as a whole. Note that “complementary colors” refer to colors that can produce an achromatic color when mixed. In other words, mixing light of complementary colors allows white light emission to be obtained. Specifically, a combination in which blue light emission is obtained from the first EL layer and yellow or orange light emission is obtained from the second EL layer is given as an example. In that case, it is not necessary that both of blue light emission and yellow (or orange) light emission are fluorescence, and the both are not necessarily phosphorescence. For example, a combination in which blue light emission is fluorescence and yellow (or orange) light emission is phosphorescence or a combination in which blue light emission is phosphorescence and yellow (or orange) light emission is fluorescence may be employed. 
     The same can be applied to a light-emitting element having three EL layers. For example, the light-emitting element as a whole can provide white light emission when the emission color of the first EL layer is red, the emission color of the second EL layer is green, and the emission color of the third EL layer is blue. 
     Note that the structure described in this embodiment can be combined as appropriate with any of the structures described in the other embodiments. 
     Embodiment 4 
     In this embodiment, a light-emitting device which is one embodiment of the present invention is described. 
     The light-emitting device may be either a passive matrix light-emitting device or an active matrix light-emitting device. Any of the light-emitting elements described in other embodiments can be used for the light-emitting device described in this embodiment. 
     In this embodiment, first, an active matrix light-emitting device is described with reference to  FIGS. 3A to 3C . 
     Note that  FIG. 3A  is a top view illustrating a light-emitting device and  FIG. 3B  is a cross-sectional view taken along the chain line A-A′ in  FIG. 3A . The light-emitting device according to this embodiment includes a pixel portion  302  provided over an element substrate  301 , a driver circuit portion (a source line driver circuit)  303 , and driver circuit portions (gate line driver circuits)  304   a  and  304   b . The pixel portion  302 , the driver circuit portion  303 , and the driver circuit portions  304   a  and  304   b  are sealed between the element substrate  301  and a sealing substrate  306  with a sealant  305 . 
     In addition, over the element substrate  301 , a lead wiring  307  for connecting an external input terminal, through which a signal (e.g., a video signal, a clock signal, a start signal, or a reset signal) or a potential from the outside is transmitted to the driver circuit portion  303  and the driver circuit portions  304   a  and  304   b , is provided. Here, an example is described in which a flexible printed circuit (FPC)  308  is provided as the 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 in this specification includes, in its category, not only the light-emitting device itself but also the light-emitting device provided with the FPC or the PWB. 
     Next, a cross-sectional structure is described with reference to  FIG. 3B . The driver circuit portions and the pixel portion are formed over the element substrate  301 ; the driver circuit portion  303  that is the source line driver circuit and the pixel portion  302  are illustrated here. 
     The driver circuit portion  303  is an example in which an FET  309  and an FET  310  are combined. Note that the driver circuit portion  303  may be formed with a circuit including transistors having the same conductivity type (either n-channel transistors or p-channel transistors) or a CMOS circuit including an n-channel transistor and a p-channel transistor. Although this embodiment shows a driver integrated type in which the driver circuit is formed over the substrate, the driver circuit is not necessarily formed over the substrate, and may be formed outside the substrate. 
     The pixel portion  302  includes a switching FET (not shown) and a current control FET  312 , and a wiring of the current control FET  312  (a source electrode or a drain electrode) is electrically connected to first electrodes (anodes) ( 313   a  and  313   b ) of light-emitting elements  317   a  and  317   b . Although the pixel portion  302  includes two FETs (the switching FET and the current control FET  312 ) in this embodiment, one embodiment of the present invention is not limited thereto. The pixel portion  302  may include, for example, three or more FETs and a capacitor in combination. 
     As the FETs  309 ,  310 , and  312 , for example, a staggered transistor or an inverted staggered transistor can be used. Examples of a semiconductor material that can be used for the FETs  309 ,  310 , and  312  include Group 13 semiconductors, Group 14 semiconductors (e.g., silicon), compound semiconductors, oxide semiconductors, and organic semiconductors. In addition, there is no particular limitation on the crystallinity of the semiconductor, and an amorphous semiconductor or a crystalline semiconductor can be used. In particular, an oxide semiconductor is preferably used for the FETs  309 ,  310 , and  312 . Examples of the oxide semiconductor are In—Ga oxides, In-M-Zn oxides (M is Al, Ga, Y, Zr, La, Ce, Hf, or Nd), and the like. For example, an oxide semiconductor that has an energy gap of 2 eV or more, preferably 2.5 eV or more, further preferably 3 eV or more is used for the FETs  309 ,  310 , and  312 , so that the off-state current of the transistors can be reduced. 
     In addition, conductive films ( 320   a  and  320   b ) for optical adjustment are stacked over the first electrodes  313   a  and  313   b . For example, as illustrated in  FIG. 3B , in the case where the wavelengths of light extracted from the light-emitting elements  317   a  and  317   b  are different from each other, the thicknesses of the conductive films  320   a  and  320   b  are different from each other. In addition, an insulator  314  is formed to cover end portions of the first electrodes ( 313   a  and  313   b ). In this embodiment, the insulator  314  is formed using a positive photosensitive acrylic resin. The first electrodes ( 313   a  and  313   b ) are used as anodes in this embodiment. 
     The insulator  314  preferably has a surface with curvature at an upper end portion or a lower end portion thereof. This enables the coverage with a film to be formed over the insulator  314  to be favorable. The insulator  314  can be formed using, for example, either a negative photosensitive resin or a positive photosensitive resin. The material for the insulator  314  is not limited to an organic compound and an inorganic compound such as silicon oxide, silicon oxynitride, or silicon nitride can also be used. 
     An EL layer  315  and a second electrode  316  are stacked over the first electrodes ( 313   a  and  313   b ). In the EL layer  315 , at least a light-emitting layer is provided. In the light-emitting elements ( 317   a  and  317   b ) including the first electrodes ( 313   a  and  313   b ), the EL layer  315 , and the second electrode  316 , an end portion of the EL layer  315  is covered with the second electrode  316 . The structure of the EL layer  315  may be the same as or different from the single-layer structure and the stacked layer structure described in Embodiments 2 and 3. Furthermore, the structure may differ between the light-emitting elements. 
     For the first electrodes ( 313   a  and  313   b ), the EL layer  315 , and the second electrode  316 , any of the materials given in Embodiment 2 can be used. The first electrodes ( 313   a  and  313   b ) of the light-emitting elements ( 317   a  and  317   b ) are electrically connected to the lead wiring  307  in a region  321 , so that an external signal is input through the FPC  308 . The second electrode  316  in the light-emitting elements ( 317   a  and  317   b ) is electrically connected to a lead wiring  323  in a region  322 , so that an external signal is input through the FPC  308  that is not illustrated in the figure. 
     Although the cross-sectional view in  FIG. 3B  illustrates only the two light-emitting elements ( 317   a  and  317   b ), a plurality of light-emitting elements are arranged in a matrix in the pixel portion  302 . Specifically, in the pixel portion  302 , light-emitting elements that emit light of two kinds of colors (e.g., B and Y), light-emitting elements that emit light of three kinds of colors (e.g., R, G, and B), light-emitting elements that emit light of four kinds of colors (e.g., (R, G, B, and Y) or (R, G, B, and W)), or the like are formed so that a light-emitting device capable of full color display can be obtained. In such cases, full color display may be achieved as follows: materials different according to the emission colors or the like of the light-emitting elements are used to form light-emitting layers (so-called separate coloring formation); alternatively, the plurality of light-emitting elements share one light-emitting layer formed using the same material and further include color filters. Thus, the light-emitting elements that emit light of a plurality of kinds of colors are used in combination, so that effects such as an improvement in color purity and a reduction in power consumption can be achieved. Furthermore, the light-emitting device may have improved emission efficiency and reduced power consumption by combination with quantum dots. 
     The sealing substrate  306  is attached to the element substrate  301  with the sealant  305 , whereby the light-emitting elements  317   a  and  317   b  are provided in a space  318  surrounded by the element substrate  301 , the sealing substrate  306 , and the sealant  305 . 
     The sealing substrate  306  is provided with coloring layers (color filters)  324 , and a black layer (black matrix)  325  is provided between adjacent coloring layers. Note that one or both of the adjacent coloring layers (color filters)  324  may be provided so as to partly overlap with the black layer (black matrix)  325 . Light emission obtained from the light-emitting elements  317   a  and  317   b  is extracted through the coloring layers (color filters)  324 . 
     Note that the space  318  may be filled with an inert gas (such as nitrogen or argon) or the sealant  305 . In the case where the sealant is applied for attachment of the substrates, one or more of UV treatment, heat treatment, and the like are preferably performed. 
     An epoxy-based resin or glass frit is preferably used for the sealant  305 . The material preferably allows as little moisture and oxygen as possible to penetrate. As the sealing substrate  306 , a glass substrate, a quartz substrate, or a plastic substrate formed of fiber-reinforced plastic (FRP), poly(vinyl fluoride) (PVF), polyester, an acrylic resin, or the like can be used. In the case where glass frit is used as the sealant, the element substrate  301  and the sealing substrate  306  are preferably glass substrates for high adhesion. 
     Structures of the FETs electrically connected to the light-emitting elements may be different from those in  FIG. 3B  in the position of a gate electrode; that is, the structures may be the same as those of an FET  326 , an FET  327 , and an FET  328 , as illustrated in  FIG. 3C . The coloring layer (color filter)  324  with which the sealing substrate  306  is provided may be provided as illustrated in  FIG. 3C  such that, at a position where the coloring layer (color filter)  324  overlaps with the black layer (black matrix)  325 , the coloring layer (color filter)  324  further overlaps with an adjacent coloring layer (color filter)  324 . 
     As described above, the active matrix light-emitting device can be obtained. 
     The light-emitting device which is one embodiment of the present invention may be of the passive matrix type, instead of the active matrix type described above. 
       FIGS. 4A and 4B  illustrate a passive matrix light-emitting device.  FIG. 4A  is a top view of the passive matrix light-emitting device, and  FIG. 4B  is a cross-sectional view thereof. 
     As illustrated in  FIGS. 4A and 4B , light-emitting elements  405  including a first electrode  402 , EL layers ( 403   a ,  403   b , and  403   c ), and second electrodes  404  are formed over a substrate  401 . Note that the first electrode  402  has an island-like shape, and a plurality of the first electrodes  402  are formed in one direction (the lateral direction in  FIG. 4A ) to form a striped pattern. An insulating film  406  is formed over part of the first electrode  402 . A partition  407  formed using an insulating material is provided over the insulating film  406 . The sidewalls of the partition  407  slope so that the distance between one sidewall and the other sidewall gradually decreases toward the surface of the substrate as illustrated in  FIG. 4B . 
     Since the insulating film  406  includes openings over the part of the first electrode  402 , the EL layers ( 403   a ,  403   b , and  403   c ) and second electrodes  404  which are divided as desired can be formed over the first electrode  402 . In the example in  FIGS. 4A and 4B , a mask such as a metal mask and the partition  407  over the insulating film  406  are employed to form the EL layers ( 403   a ,  403   b , and  403   c ) and the second electrodes  404 . In this example, the EL layer  403   a , the EL layer  403   b , and the EL layer  403   c  emit light of different colors (e.g., red, green, blue, yellow, orange, and white). 
     After the formation of the EL layers ( 403   a ,  403   b , and  403   c ), the second electrodes  404  are formed. Thus, the second electrodes  404  are formed over the EL layers ( 403   a ,  403   b , and  403   c ) without contact with the first electrode  402 . 
     Note that sealing can be performed by a method similar to that used for the active matrix light-emitting device, and description thereof is not made. 
     As described above, the passive matrix light-emitting device can be obtained. 
     Note that in this specification and the like, a transistor or a light-emitting element can be formed using any of a variety of substrates, for example. The type of substrate is not limited to a certain type. As the substrate, a semiconductor substrate (e.g., a single crystal substrate or a silicon substrate), an SOI substrate, a glass substrate, a quartz substrate, a plastic substrate, a metal substrate, a stainless steel substrate, a substrate including stainless steel foil, a tungsten substrate, a substrate including tungsten foil, a flexible substrate, an attachment film, paper including a fibrous material, a base material film, or the like can be used, for example. As an example of a glass substrate, a barium borosilicate glass substrate, an aluminoborosilicate glass substrate, a soda lime glass substrate, or the like can be given. Examples of the flexible substrate, the attachment film, the base material film, and the like are substrates of plastics typified by polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), and polytetrafluoroethylene (PTFE). Another example is a synthetic resin such as acrylic. Alternatively, polypropylene, polyester, polyvinyl fluoride, polyvinyl chloride, or the like can be used. Alternatively, polyamide, polyimide, aramid, epoxy, an inorganic vapor deposition film, paper, or the like can be used. Specifically, the use of semiconductor substrates, single crystal substrates, SOI substrates, or the like enables the manufacture of small-sized transistors with a small variation in characteristics, size, shape, or the like and with high current supply capability. A circuit using such transistors achieves lower power consumption of the circuit or higher integration of the circuit. 
     Alternatively, a flexible substrate may be used as the substrate, and a transistor or a light-emitting element may be provided directly on the flexible substrate. Still alternatively, a separation layer may be provided between the substrate and the transistor or the light-emitting element. The separation layer can be used when part or the whole of a semiconductor device formed over the separation layer is separated from the substrate and transferred onto another substrate. In such a case, the transistor or the light-emitting element can be transferred to a substrate having low heat resistance or a flexible substrate. For the separation layer, a stack including inorganic films, which are a tungsten film and a silicon oxide film, or an organic resin film of polyimide or the like formed over a substrate can be used, for example. 
     In other words, a transistor or a light-emitting element may be formed using one substrate, and then transferred to another substrate. Examples of a substrate to which a transistor or a light-emitting element is transferred are, in addition to the above-described substrates over which a transistor or a light-emitting element can be formed, a paper substrate, a cellophane substrate, an aramid film substrate, a polyimide film substrate, a stone substrate, a wood substrate, a cloth substrate (including a natural fiber (e.g., silk, cotton, or hemp), a synthetic fiber (e.g., nylon, polyurethane, or polyester), a regenerated fiber (e.g., acetate, cupra, rayon, or regenerated polyester), or the like), a leather substrate, a rubber substrate, and the like. When such a substrate is used, a transistor with excellent characteristics or a transistor with low power consumption can be formed, a device with high durability or high heat resistance can be provided, or a reduction in weight or thickness can be achieved. 
     Note that the structure described in this embodiment can be combined as appropriate with any of the structures described in other embodiments. 
     Embodiment 5 
     In this embodiment, examples of a variety of electronic devices and an automobile manufactured using a light-emitting device which is one embodiment of the present invention are described. 
     Examples of the electronic device including the light-emitting device are television devices (also referred to as TV or television receivers), monitors for computers and the like, cameras such as digital cameras and digital video cameras, digital photo frames, cellular phones (also referred to as mobile phones or portable telephone devices), portable game consoles, portable information terminals, audio playback devices, large game machines such as pachinko machines, and the like. Specific examples of the electronic devices are illustrated in  FIGS. 5A, 5B, 5C, 5D, 5D ′- 1 , and  5 D′- 2  and  FIGS. 6A to 6C . 
       FIG. 5A  illustrates an example of a television device. In the television device  7100 , a display portion  7103  is incorporated in a housing  7101 . The display portion  7103  can display images and may be a touch panel (an input/output device) including a touch sensor (an input device). Note that the light-emitting device which is one embodiment of the present invention can be used for the display portion  7103 . In addition, here, the housing  7101  is supported by a stand  7105 . 
     The television device  7100  can be operated by an operation switch of the housing  7101  or a separate remote controller  7110 . With operation keys  7109  of the remote controller  7110 , channels and volume can be controlled and images displayed on the display portion  7103  can be controlled. Furthermore, the remote controller  7110  may be provided with a display portion  7107  for displaying data output from the remote controller  7110 . 
     Note that the television device  7100  is provided with a receiver, a modem, and the like. With the use of the receiver, general television broadcasts can be received. Moreover, when the television device is connected to a communication network with or without wires via the modem, one-way (from a sender to a receiver) or two-way (between a sender and a receiver or between receivers) information communication can be performed. 
       FIG. 5B  illustrates a computer, which includes a main body  7201 , a housing  7202 , a display portion  7203 , a keyboard  7204 , an external connection port  7205 , a pointing device  7206 , and the like. Note that this computer can be manufactured using the light-emitting device which is one embodiment of the present invention for the display portion  7203 . The display portion  7203  may be a touch panel (an input/output device) including a touch sensor (an input device). 
       FIG. 5C  illustrates a smart watch, which includes a housing  7302 , a display portion  7304 , operation buttons  7311  and  7312 , a connection terminal  7313 , a band  7321 , a clasp  7322 , and the like. 
     The display portion  7304  mounted in the housing  7302  serving as a bezel includes a non-rectangular display region. The display portion  7304  can display an icon  7305  indicating time, another icon  7306 , and the like. The display portion  7304  may be a touch panel (an input/output device) including a touch sensor (an input device). 
     The smart watch illustrated in  FIG. 5C  can have a variety of functions, such as a function of displaying a variety of information (e.g., a still image, a moving image, and a text image) on a display portion, a touch panel function, a function of displaying a calendar, date, time, and the like, a function of controlling processing with a variety of software (programs), a wireless communication function, a function of being connected to a variety of computer networks with a wireless communication function, a function of transmitting and receiving a variety of data with a wireless communication function, and a function of reading a program or data stored in a recording medium and displaying the program or data on a display portion. 
     The housing  7302  can include a speaker, a sensor (a sensor having a function of measuring force, displacement, position, speed, acceleration, angular velocity, rotational frequency, distance, light, liquid, magnetism, temperature, chemical substance, sound, time, hardness, electric field, current, voltage, electric power, radiation, flow rate, humidity, gradient, oscillation, odor, or infrared rays), a microphone, and the like. Note that the smart watch can be manufactured using the light-emitting device for the display portion  7304 . 
       FIGS. 5D, 5D ′- 1 , and  5 D′- 2  illustrate an example of a cellular phone (e.g., smartphone). A cellular phone  7400  includes a housing  7401  provided with a display portion  7402 , a microphone  7406 , a speaker  7405 , a camera  7407 , an external connection portion  7404 , an operation button  7403 , and the like. In the case where a light-emitting device is manufactured by forming the light-emitting element of one embodiment of the present invention over a flexible substrate, the light-emitting device can be used for the display portion  7402  having a curved surface as illustrated in  FIG. 5D . 
     When the display portion  7402  of the cellular phone  7400  illustrated in  FIG. 5D  is touched with a finger or the like, data can be input to the cellular phone  7400 . In addition, operations such as making a call and composing e-mail can be performed by touch on the display portion  7402  with a finger or the like. 
     There are mainly three screen modes of the display portion  7402 . The first mode is a display mode mainly for displaying an image. The second mode is an input mode mainly for inputting data such as characters. The third mode is a display-and-input mode in which two modes of the display mode and the input mode are combined. 
     For example, in the case of making a call or composing e-mail, a character input mode mainly for inputting characters is selected for the display portion  7402  so that characters displayed on the screen can be input. In this case, it is preferable to display a keyboard or number buttons on almost the entire screen of the display portion  7402 . 
     When a detection device such as a gyroscope or an acceleration sensor is provided inside the cellular phone  7400 , display on the screen of the display portion  7402  can be automatically changed by determining the orientation of the cellular phone  7400  (whether the cellular phone is placed horizontally or vertically for a landscape mode or a portrait mode). 
     The screen modes are changed by touch on the display portion  7402  or operation with the operation button  7403  of the housing  7401 . The screen modes can be switched depending on the kind of images displayed on the display portion  7402 . For example, when a signal of an image displayed on the display portion is a signal of moving image data, the screen mode is switched to the display mode. When the signal is a signal of text data, the screen mode is switched to the input mode. 
     Moreover, in the input mode, if a signal detected by an optical sensor in the display portion  7402  is detected and the input by touch on the display portion  7402  is not performed for a certain period, the screen mode may be controlled so as to be changed from the input mode to the display mode. 
     The display portion  7402  may function as an image sensor. For example, an image of a palm print, a fingerprint, or the like is taken by touch on the display portion  7402  with the palm or the finger, whereby personal authentication can be performed. In addition, by providing a backlight or a sensing light source that emits near-infrared light in the display portion, an image of a finger vein, a palm vein, or the like can be taken. 
     The light-emitting device can be used for a cellular phone having a structure illustrated in  FIG. 5D ′- 1  or  FIG. 5D ′- 2 , which is another structure of the cellular phone (e.g., a smartphone). 
     Note that in the case of the structure illustrated in  FIG. 5D ′- 1  or  FIG. 5D ′- 2 , text data, image data, or the like can be displayed on second screens  7502 ( 1 ) and  7502 ( 2 ) of housings  7500 ( 1 ) and  7500 ( 2 ) as well as first screens  7501 ( 1 ) and  7501 ( 2 ). Such a structure enables a user to easily see text data, image data, or the like displayed on the second screens  7502 ( 1 ) and  7502 ( 2 ) while the cellular phone is placed in user&#39;s breast pocket. 
     Another electronic device including a light-emitting device is a foldable portable information terminal illustrated in  FIGS. 6A to 6C .  FIG. 6A  illustrates a portable information terminal  9310  which is opened.  FIG. 6B  illustrates the portable information terminal  9310  which is being opened or being folded.  FIG. 6C  illustrates the portable information terminal  9310  which is folded. The portable information terminal  9310  is highly portable when folded. The portable information terminal  9310  is highly browsable when opened because of a seamless large display region. 
     A display portion  9311  is supported by three housings  9315  joined together by hinges  9313 . Note that the display portion  9311  may be a touch panel (an input/output device) including a touch sensor (an input device). By bending the display portion  9311  at a connection portion between two housings  9315  with the use of the hinges  9313 , the portable information terminal  9310  can be reversibly changed in shape from an opened state to a folded state. The light-emitting device of one embodiment of the present invention can be used for the display portion  9311 . A display region  9312  in the display portion  9311  is a display region that is positioned at a side surface of the portable information terminal  9310  which is folded. On the display region  9312 , information icons, file shortcuts of frequently used applications or programs, and the like can be displayed, and confirmation of information and start of application can be smoothly performed. 
       FIGS. 7A and 7B  illustrate an automobile including a light-emitting device. The light-emitting device can be incorporated in the automobile, and specifically, can be included in lights  5101  (including lights of the rear part of the car), a wheel  5102  of a tire, a part or whole of a door  5103 , or the like on the outer side of the automobile which is illustrated in  FIG. 7A . The light-emitting device can also be included in a display portion  5104 , a steering wheel  5105 , a gear lever  5106 , a sheet  5107 , an inner rearview mirror  5108 , or the like on the inner side of the automobile which is illustrated in  FIG. 7B , or in a part of a glass window. 
     As described above, the electronic devices and automobiles can be obtained using the light-emitting device which is one embodiment of the present invention. Note that the light-emitting device can be used for electronic devices and automobiles in a variety of fields without being limited to the electronic devices described in this embodiment. 
     Note that the structure described in this embodiment can be combined as appropriate with any of the structures described in other embodiments. 
     Embodiment 6 
     In this embodiment, a structure of a lighting device fabricated using the light-emitting element which is one embodiment of the present invention is described with reference to  FIGS. 8A to 8D . 
       FIGS. 8A to 8D  are examples of cross-sectional views of lighting devices.  FIGS. 8A and 8B  illustrate bottom-emission lighting devices in which light is extracted from the substrate side, and  FIGS. 8C and 8D  illustrate top-emission lighting devices in which light is extracted from the sealing substrate side. 
     A lighting device  4000  illustrated in  FIG. 8A  includes a light-emitting element  4002  over a substrate  4001 . In addition, the lighting device  4000  includes a substrate  4003  with unevenness on the outside of the substrate  4001 . The light-emitting element  4002  includes a first electrode  4004 , an EL layer  4005 , and a second electrode  4006 . 
     The first electrode  4004  is electrically connected to an electrode  4007 , and the second electrode  4006  is electrically connected to an electrode  4008 . In addition, an auxiliary wiring  4009  electrically connected to the first electrode  4004  may be provided. Note that an insulating layer  4010  is formed over the auxiliary wiring  4009 . 
     The substrate  4001  and a sealing substrate  4011  are bonded to each other by a sealant  4012 . A desiccant  4013  is preferably provided between the sealing substrate  4011  and the light-emitting element  4002 . The substrate  4003  has the unevenness illustrated in  FIG. 8A , whereby the extraction efficiency of light emitted from the light-emitting element  4002  can be increased. 
     Instead of the substrate  4003 , a diffusion plate  4015  may be provided on the outside of the substrate  4001  as in a lighting device  4100  illustrated in  FIG. 8B . 
     A lighting device  4200  illustrated in  FIG. 8C  includes a light-emitting element  4202  over a substrate  4201 . The light-emitting element  4202  includes a first electrode  4204 , an EL layer  4205 , and a second electrode  4206 . 
     The first electrode  4204  is electrically connected to an electrode  4207 , and the second electrode  4206  is electrically connected to an electrode  4208 . An auxiliary wiring  4209  electrically connected to the second electrode  4206  may be provided. An insulating layer  4210  may be provided under the auxiliary wiring  4209 . 
     The substrate  4201  and a sealing substrate  4211  with unevenness are bonded to each other by a sealant  4212 . A barrier film  4213  and a planarization film  4214  may be provided between the sealing substrate  4211  and the light-emitting element  4202 . The sealing substrate  4211  has the unevenness illustrated in  FIG. 8C , whereby the extraction efficiency of light emitted from the light-emitting element  4202  can be increased. 
     Instead of the sealing substrate  4211 , a diffusion plate  4215  may be provided over the light-emitting element  4202  as in a lighting device  4300  illustrated in  FIG. 8D . 
     The EL layers  4005  and  4205  in this embodiment can each include any of the organometallic complexes which are embodiments of the present invention. In that case, a lighting device with low power consumption can be provided. 
     Note that the structure described in this embodiment can be combined as appropriate with any of the structures described in other embodiments. 
     Embodiment 7 
     In this embodiment, examples of a lighting device to which the light-emitting device of one embodiment of the present invention is applied are described with reference to  FIG. 9 . 
       FIG. 9  illustrates an example in which the light-emitting device is used as an indoor lighting device  8001 . Since the light-emitting device can have a large area, it can be used for a lighting device having a large area. In addition, with the use of a housing with a curved surface, a lighting device  8002  in which a light-emitting region has a curved surface can also be obtained. A light-emitting element included in the light-emitting device described in this embodiment is in a thin film form, which allows the housing to be designed more freely. Thus, the lighting device can be elaborately designed in a variety of ways. In addition, a wall of the room may be provided with a lighting device  8003 . 
     Besides the above examples, when the light-emitting device is used as part of furniture in a room, a lighting device that functions as the furniture can be obtained. 
     As described above, a variety of lighting devices that include the light-emitting device can be obtained. Note that these lighting devices are also embodiments of the present invention. 
     Note that the structure described in this embodiment can be combined as appropriate with any of the structures described in other embodiments. 
     Embodiment 8 
     In this embodiment, touch panels including the light-emitting element of one embodiment of the present invention or the light-emitting device of one embodiment of the present invention will be described with reference to  FIGS. 10A and 10B ,  FIGS. 11A and 11B ,  FIGS. 12A and 12B ,  FIGS. 13A and 13B , and  FIG. 14 . 
       FIGS. 10A and 10B  are perspective views of a touch panel  2000 . Note that  FIGS. 10A and 10B  illustrate typical components of the touch panel  2000  for simplicity. 
     The touch panel  2000  includes a display panel  2501  and a touch sensor  2595  (see  FIG. 10B ). Furthermore, the touch panel  2000  includes substrates  2510 ,  2570 , and  2590 . 
     The display panel  2501  includes a plurality of pixels over the substrate  2510 , and a plurality of wirings  2511  through which signals are supplied to the pixels. The plurality of wirings  2511  are led to a peripheral portion of the substrate  2510 , and part of the plurality of wirings  2511  forms a terminal  2519 . The terminal  2519  is electrically connected to an FPC  2509 ( 1 ). 
     The substrate  2590  includes the touch sensor  2595  and a plurality of wirings  2598  electrically connected to the touch sensor  2595 . The plurality of wirings  2598  are led to a peripheral portion of the substrate  2590 , and part of the plurality of wirings  2598  forms a terminal  2599 . The terminal  2599  is electrically connected to an FPC  2509 ( 2 ). Note that in  FIG. 10B , electrodes, wirings, and the like of the touch sensor  2595  provided on the back side of the substrate  2590  (the side facing the substrate  2510 ) are indicated by solid lines for clarity. 
     As the touch sensor  2595 , a capacitive touch sensor can be used, for example. Examples of the capacitive touch sensor are a surface capacitive touch sensor, a projected capacitive touch sensor, and the like. 
     Examples of the projected capacitive touch sensor are a self-capacitive touch sensor, a mutual capacitive touch sensor, and the like, which differ mainly in the driving method. The use of a mutual capacitive touch sensor is preferable because multiple points can be sensed simultaneously. 
     First, an example of using a projected capacitive touch sensor is described with reference to  FIG. 10B . Note that in the case of a projected capacitive touch sensor, a variety of sensors that can sense the approach or contact of an object such as a finger can be used. 
     The projected capacitive touch sensor  2595  includes electrodes  2591  and  2592 . The electrodes  2591  are electrically connected to any of the plurality of wirings  2598 , and the electrodes  2592  are electrically connected to any of the other wirings  2598 . The electrodes  2592  each have a shape of a plurality of quadrangles arranged in one direction with one corner of a quadrangle connected to one corner of another quadrangle with a wiring  2594  in one direction, as illustrated in  FIGS. 10A and 10B . In the same manner, the electrodes  2591  each have a shape of a plurality of quadrangles arranged with one corner of a quadrangle connected to one corner of another quadrangle; however, the direction in which the electrodes  2591  are connected is a direction crossing the direction in which the electrodes  2592  are connected. Note that the direction in which the electrodes  2591  are connected and the direction in which the electrodes  2592  are connected are not necessarily perpendicular to each other, and the electrodes  2591  may be arranged to intersect with the electrodes  2592  at an angle greater than 0° and less than 90°. 
     The intersecting area of the wiring  2594  and one of the electrodes  2592  is preferably as small as possible. Such a structure allows a reduction in the area of a region where the electrodes are not provided, reducing unevenness in transmittance. As a result, unevenness in the luminance of light passing through the touch sensor  2595  can be reduced. 
     Note that the shapes of the electrodes  2591  and  2592  are not limited to the above-described shapes and can be any of a variety of shapes. For example, the plurality of electrodes  2591  may be provided so that a space between the electrodes  2591  are reduced as much as possible, and the plurality of electrodes  2592  may be provided with an insulating layer sandwiched between the electrodes  2591  and  2592 . In that case, it is preferable to provide, between two adjacent electrodes  2592 , a dummy electrode which is electrically insulated from these electrodes because the area of a region having a different transmittance can be reduced. 
     Next, the touch panel  2000  is described in detail with reference to  FIGS. 11A  and  11 B.  FIGS. 11A and 11B  are cross-sectional views taken along the dashed-dotted line X 1 -X 2  in  FIG. 10A . 
     The touch panel  2000  includes the touch sensor  2595  and the display panel  2501 . 
     The touch sensor  2595  includes the electrodes  2591  and  2592  that are provided in a staggered arrangement and in contact with the substrate  2590 , an insulating layer  2593  covering the electrodes  2591  and  2592 , and the wiring  2594  that electrically connects the adjacent electrodes  2591  to each other. Between the adjacent electrodes  2591 , the electrode  2592  is provided. 
     The electrodes  2591  and  2592  can be formed using a light-transmitting conductive material. As a light-transmitting conductive material, a conductive oxide such as indium oxide, indium tin oxide, indium zinc oxide, zinc oxide, or zinc oxide to which gallium is added can be used. A graphene compound may be used as well. When a graphene compound is used, it can be formed, for example, by reducing a graphene oxide film. As a reducing method, a method with application of heat, a method with laser irradiation, or the like can be employed. 
     For example, the electrodes  2591  and  2592  can be formed by depositing a light-transmitting conductive material on the substrate  2590  by a sputtering method and then removing an unneeded portion by any of various patterning techniques such as photolithography. 
     Examples of a material for the insulating layer  2593  are a resin such as an acrylic resin or an epoxy resin, a resin having a siloxane bond, and an inorganic insulating material such as silicon oxide, silicon oxynitride, or aluminum oxide. 
     The adjacent electrodes  2591  are electrically connected to each other with the wiring  2594  formed in part of the insulating layer  2593 . Note that a material for the wiring  2594  preferably has higher conductivity than materials for the electrodes  2591  and  2592  to reduce electrical resistance. 
     One wiring  2598  is electrically connected to any of the electrodes  2591  and  2592 . Part of the wiring  2598  serves as a terminal. For the wiring  2598 , a metal material such as aluminum, gold, platinum, silver, nickel, titanium, tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium or an alloy material containing any of these metal materials can be used. 
     Through the terminal  2599 , the wiring  2598  and the FPC  2509 ( 2 ) are electrically connected to each other. The terminal  2599  can be formed using any of various kinds of anisotropic conductive films (ACF), anisotropic conductive pastes (ACP), and the like. 
     An adhesive layer  2597  is provided in contact with the wiring  2594 . That is, the touch sensor  2595  is attached to the display panel  2501  so that they overlap with each other with the adhesive layer  2597  provided therebetween. Note that the substrate  2570  as illustrated in  FIG. 11A  may be provided over the surface of the display panel  2501  that is in contact with the adhesive layer  2597 ; however, the substrate  2570  is not always needed. 
     The adhesive layer  2597  has a light-transmitting property. For example, a thermosetting resin or an ultraviolet curable resin can be used; specifically, a resin such as an acrylic-based resin, a urethane-based resin, an epoxy-based resin, or a siloxane-based resin can be used. 
     The display panel  2501  in  FIG. 11A  includes, between the substrate  2510  and the substrate  2570 , a plurality of pixels arranged in a matrix and a driver circuit. Each pixel includes a light-emitting element and a pixel circuit driving the light-emitting element. 
     In  FIG. 11A , a pixel  2502 R is shown as an example of the pixel of the display panel  2501 , and a scan line driver circuit  2503   g  is shown as an example of the driver circuit. 
     The pixel  2502 R includes a light-emitting element  2550 R and a transistor  2502   t  that can supply electric power to the light-emitting element  2550 R. 
     The transistor  2502   t  is covered with an insulating layer  2521 . The insulating layer  2521  covers unevenness caused by the transistor and the like that have been already formed to provide a flat surface. The insulating layer  2521  may serve also as a layer for preventing diffusion of impurities. That is preferable because a reduction in the reliability of the transistor or the like due to diffusion of impurities can be prevented. 
     The light-emitting element  2550 R is electrically connected to the transistor  2502   t  through a wiring. It is one electrode of the light-emitting element  2550 R that is directly connected to the wiring. An end portion of the one electrode of the light-emitting element  2550 R is covered with an insulator  2528 . 
     The light-emitting element  2550 R includes an EL layer between a pair of electrodes. A coloring layer  2567 R is provided to overlap with the light-emitting element  2550 R, and part of light emitted from the light-emitting element  2550 R is transmitted through the coloring layer  2567 R and extracted in the direction indicated by an arrow in the drawing. A light-blocking layer  2567 BM is provided at an end portion of the coloring layer, and a sealing layer  2560  is provided between the light-emitting element  2550 R and the coloring layer  2567 R. 
     Note that when the sealing layer  2560  is provided on the side from which light from the light-emitting element  2550 R is extracted, the sealing layer  2560  preferably has a light-transmitting property. The sealing layer  2560  preferably has a higher refractive index than the air. 
     The scan line driver circuit  2503   g  includes a transistor  2503   t  and a capacitor  2503   c . Note that the driver circuit and the pixel circuits can be formed in the same process over the same substrate. Thus, in a manner similar to that of the transistor  2502   t  in the pixel circuit, the transistor  2503   t  in the driver circuit (scan line driver circuit  2503   g ) is also covered with the insulating layer  2521 . 
     The wirings  2511  through which a signal can be supplied to the transistor  2503   t  are provided. The terminal  2519  is provided in contact with the wiring  2511 . The terminal  2519  is electrically connected to the FPC  2509 ( 1 ), and the FPC  2509 ( 1 ) has a function of supplying signals such as an image signal and a synchronization signal. Note that a printed wiring board (PWB) may be attached to the FPC  2509 ( 1 ). 
     Although the case where the display panel  2501  illustrated in  FIG. 11A  includes a bottom-gate transistor is described, the structure of the transistor is not limited thereto, and any of transistors with various structures can be used. In each of the transistors  2502   t  and  2503   t  illustrated in  FIG. 11A , a semiconductor layer containing an oxide semiconductor can be used for a channel region. Alternatively, a semiconductor layer containing amorphous silicon or a semiconductor layer containing polycrystalline silicon that is obtained by crystallization process such as laser annealing can be used for a channel region. 
       FIG. 11B  illustrates the structure of the display panel  2501  that includes a top-gate transistor instead of the bottom-gate transistor illustrated in  FIG. 11A . The kind of the semiconductor layer that can be used for the channel region does not depend on the structure of the transistor. 
     In the touch panel  2000  illustrated in  FIG. 11A , an anti-reflection layer  2567   p  overlapping with at least the pixel is preferably provided on a surface of the touch panel on the side from which light from the pixel is extracted, as illustrated in  FIG. 11A . As the anti-reflection layer  2567   p , a circular polarizing plate or the like can be used. 
     For the substrates  2510 ,  2570 , and  2590  in  FIG. 11A , for example, a flexible material having a vapor permeability of 1×10 −5  g/(m 2 ·day) or lower, preferably 1×10 −6  g/(m 2 ·day) or lower, can be favorably used. Alternatively, it is preferable to use the materials that make these substrates have substantially the same coefficient of thermal expansion. For example, the coefficients of linear expansion of the materials are 1×10 −3 /K or lower, preferably 5×10 −5 /K or lower, and further preferably 1×10 −5 /K or lower. 
     Next, a touch panel  2000 ′ having a structure different from that of the touch panel  2000  illustrated in  FIGS. 11A and 11B  is described with reference to  FIGS. 12A and 12B . It can be used as a touch panel as well as the touch panel  2000 . 
       FIGS. 12A and 12B  are cross-sectional views of the touch panel  2000 ′. In the touch panel  2000 ′ illustrated in  FIGS. 12A and 12B , the position of the touch sensor  2595  relative to the display panel  2501  is different from that in the touch panel  2000  illustrated in  FIGS. 11A and 11B . Only different structures are described below, and the above description of the touch panel  2000  can be referred to for the other similar structures. 
     The coloring layer  2567 R overlaps with the light-emitting element  2550 R. Light from the light-emitting element  2550 R illustrated in  FIG. 12A  is emitted to the side where the transistor  2502   t  is provided. That is, (part of) light emitted from the light-emitting element  2550 R passes through the coloring layer  2567 R and is extracted in the direction indicated by an arrow in  FIG. 12A . Note that the light-blocking layer  2567 BM is provided at an end portion of the coloring layer  2567 R. 
     The touch sensor  2595  is provided on the transistor  2502   t  side (the far side from the light-emitting element  2550 R) of the display panel  2501  (see  FIG. 12A ). 
     The adhesive layer  2597  is in contact with the substrate  2510  of the display panel  2501  and attaches the display panel  2501  and the touch sensor  2595  to each other in the structure illustrated in  FIG. 12A . The substrate  2510  is not necessarily provided between the display panel  2501  and the touch sensor  2595  that are attached to each other by the adhesive layer  2597 . 
     As in the touch panel  2000 , transistors with a variety of structures can be used for the display panel  2501  in the touch panel  2000 ′. Although a bottom-gate transistor is used in  FIG. 12A , a top-gate transistor may be used as illustrated in  FIG. 12B . 
     An example of a driving method of the touch panel is described with reference to  FIGS. 13A and 13B . 
       FIG. 13A  is a block diagram illustrating the structure of a mutual capacitive touch sensor.  FIG. 13A  illustrates a pulse voltage output circuit  2601  and a current sensing circuit  2602 . Note that in the example of  FIG. 13A , six wirings X 1 -X 6  represent electrodes  2621  to which a pulse voltage is supplied, and six wirings Y 1 -Y 6  represent electrodes  2622  that sense a change in current.  FIG. 13A  also illustrates a capacitor  2603  which is formed in a region where the electrodes  2621  and  2622  overlap with each other. Note that functional replacement between the electrodes  2621  and  2622  is possible. 
     The pulse voltage output circuit  2601  is a circuit for sequentially applying a pulse voltage to the wirings X 1  to X 6 . By application of a pulse voltage to the wirings X 1  to X 6 , an electric field is generated between the electrodes  2621  and  2622  of the capacitor  2603 . When the electric field between the electrodes is shielded, for example, a change occurs in the capacitor  2603  (mutual capacitance). The approach or contact of a sensing target can be sensed by utilizing this change. 
     The current sensing circuit  2602  is a circuit for sensing changes in current flowing through the wirings Y 1  to Y 6  that are caused by the change in mutual capacitance in the capacitor  2603 . No change in current value is sensed in the wirings Y 1  to Y 6  when there is no approach or contact of a sensing target, whereas a decrease in current value is sensed when mutual capacitance is decreased owing to the approach or contact of a sensing target. Note that an integrator circuit or the like is used for sensing of current. 
       FIG. 13B  is a timing chart showing input and output waveforms in the mutual capacitive touch sensor illustrated in  FIG. 13A . In  FIG. 13B , sensing of a sensing target is performed in all the rows and columns in one frame period.  FIG. 13B  shows a period when a sensing target is not sensed (not touched) and a period when a sensing target is sensed (touched). Sensed current values of the wirings Y 1  to Y 6  are shown as the waveforms of voltage values. 
     A pulse voltage is sequentially applied to the wirings X 1  to X 6 , and the waveforms of the wirings Y 1  to Y 6  change in accordance with the pulse voltage. When there is no approach or contact of a sensing target, the waveforms of the wirings Y 1  to Y 6  change uniformly in accordance with changes in the voltages of the wirings X 1  to X 6 . The current value is decreased at the point of approach or contact of a sensing target and accordingly the waveform of the voltage value changes. By sensing a change in mutual capacitance in this manner, the approach or contact of a sensing target can be sensed. 
     Although  FIG. 13A  illustrates a passive touch sensor in which only the capacitor  2603  is provided at the intersection of wirings as a touch sensor, an active touch sensor including a transistor and a capacitor may be used.  FIG. 14  is a sensor circuit included in an active touch sensor. 
     The sensor circuit illustrated in  FIG. 14  includes the capacitor  2603  and transistors  2611 ,  2612 , and  2613 . 
     A signal G 2  is input to a gate of the transistor  2613 . A voltage VRES is applied to one of a source and a drain of the transistor  2613 , and one electrode of the capacitor  2603  and a gate of the transistor  2611  are electrically connected to the other of the source and the drain of the transistor  2613 . One of a source and a drain of the transistor  2611  is electrically connected to one of a source and a drain of the transistor  2612 , and a voltage VSS is applied to the other of the source and the drain of the transistor  2611 . A signal G 1  is input to a gate of the transistor  2612 , and a wiring ML is electrically connected to the other of the source and the drain of the transistor  2612 . The voltage VSS is applied to the other electrode of the capacitor  2603 . 
     Next, the operation of the sensor circuit illustrated in  FIG. 14  is described. First, a potential for turning on the transistor  2613  is supplied as the signal G 2 , and a potential with respect to the voltage VRES is thus applied to a node n connected to the gate of the transistor  2611 . Then, a potential for turning off the transistor  2613  is applied as the signal G 2 , whereby the potential of the node n is maintained. Then, mutual capacitance of the capacitor  2603  changes owing to the approach or contact of a sensing target such as a finger; accordingly, the potential of the node n is changed from VRES. 
     In reading operation, a potential for turning on the transistor  2612  is supplied as the signal G 1 . A current flowing through the transistor  2611 , that is, a current flowing through the wiring ML is changed in accordance with the potential of the node n. By sensing this current, the approach or contact of a sensing target can be sensed. 
     In each of the transistors  2611 ,  2612 , and  2613 , an oxide semiconductor layer is preferably used as a semiconductor layer in which a channel region is formed. In particular, such a transistor is preferably used as the transistor  2613 , so that the potential of the node n can be held for a long time and the frequency of operation of resupplying VRES to the node n (refresh operation) can be reduced. 
     Note that the structure described in this embodiment can be used in appropriate combination with any of the structures described in other embodiments. 
     Embodiment 9 
     In this embodiment, as a display device including any of the light-emitting elements which are embodiments of the present invention, a display device which includes a reflective liquid crystal element and a light-emitting element and is capable of performing display both in a transmissive mode and a reflective mode is described with reference to  FIGS. 15A ,  15 B 1 , and  15 B 2 ,  FIG. 16 , and  FIG. 17 . Such a display device can also be referred to as an emissive OLED and reflective LC hybrid display (ER-hybrid display). 
     The display device described in this embodiment can be driven with extremely low power consumption for display using the reflective mode in a bright place such as outdoors. Meanwhile, in a dark place such as indoors or at night, image can be displayed at an optimal luminance with the use of the transmissive mode. Thus, by combination of these modes, the display device can display an image with lower power consumption and a higher contrast compared to a conventional display panel. 
     As an example of the display device of this embodiment, description is made on a display device in which a liquid crystal element provided with a reflective electrode and a light-emitting element are stacked and an opening of the reflective electrode is provided in a position overlapping with the light-emitting element. Visible light is reflected by the reflective electrode in the reflective mode and light emitted from the light-emitting element is emitted through the opening of the reflective electrode in the transmissive mode. Note that transistors used for driving these elements (the liquid crystal element and the light-emitting element) are preferably formed on the same plane. It is preferable that the liquid crystal element and the light-emitting element be stacked through an insulating layer. 
       FIG. 15A  is a block diagram illustrating a display device described in this embodiment. A display device  500  includes a circuit (G)  501 , a circuit (S)  502 , and a display portion  503 . In the display portion  503 , a plurality of pixels  504  are arranged in an R direction and a C direction in a matrix. A plurality of wirings G 1 , wirings G 2 , wirings ANO, and wirings CSCOM are electrically connected to the circuit (G)  501 . These wirings are also electrically connected to the plurality of pixels  504  arranged in the R direction. A plurality of wirings S 1  and wirings S 2  are electrically connected to the circuit (S)  502 , and these wirings are also electrically connected to the plurality of pixels  504  arranged in the C direction. 
     Each of the plurality of pixels  504  includes a liquid crystal element and a light-emitting element. The liquid crystal element and the light-emitting element include portions overlapping with each other. 
     FIG.  15 B 1  shows the shape of a conductive film  505  serving as a reflective electrode of the liquid crystal element included in the pixel  504 . Note that an opening  507  is provided in a position  506  which is part of the conductive film  505  and which overlaps with the light-emitting element. That is, light emitted from the light-emitting element is emitted through the opening  507 . 
     The pixels  504  in FIG.  15 B 1  are arranged such that adjacent pixels  504  in the R direction exhibit different colors. Furthermore, the openings  507  are provided so as not to be arranged in a line in the R direction. Such arrangement has an effect of suppressing crosstalk between the light-emitting elements of adjacent pixels  504 . 
     The opening  507  can have a polygonal shape, a quadrangular shape, an elliptical shape, a circular shape, a cross shape, a stripe shape, or a slit-like shape, for example. 
     FIG.  15 B 2  illustrates another example of the arrangement of the conductive films  505 . 
     The ratio of the opening  507  to the total area of the conductive film  505  (excluding the opening  507 ) affects the display of the display device. That is, a problem is caused in that as the area of the opening  507  is larger, the display using the liquid crystal element becomes darker; in contrast, as the area of the opening  507  is smaller, the display using the light-emitting element becomes darker. Furthermore, in addition to the problem of the ratio of the opening, a small area of the opening  507  itself also causes a problem in that extraction efficiency of light emitted from the light-emitting element is decreased. The ratio of opening  507  to the total area of the conductive film  505  (other than the opening  507 ) is preferably 5% or more and 60% or less for maintaining display quality at the time of combination of the liquid crystal element and the light-emitting element. 
     Next, an example of a circuit configuration of the pixel  504  is described with reference to  FIG. 16 .  FIG. 16  shows two adjacent pixels  504 . 
     The pixel  504  includes a transistor SW 1 , a capacitor C 1 , a liquid crystal element  510 , a transistor SW 2 , a transistor M, a capacitor C 2 , a light-emitting element  511 , and the like. Note that these components are electrically connected to any of the wiring G 1 , the wiring G 2 , the wiring ANO, the wiring CSCOM, the wiring S 1 , and the wiring S 2  in the pixel  504 . The liquid crystal element  510  and the light-emitting element  511  are electrically connected to a wiring VCOM 1  and a wiring VCOM 2 , respectively. 
     A gate of the transistor SW 1  is connected to the wiring G 1 . One of a source and a drain of the transistor SW 1  is connected to the wiring S 1 , and the other of the source and the drain is connected to one electrode of the capacitor C 1  and one electrode of the liquid crystal element  510 . The other electrode of the capacitor C 1  is connected to the wiring CSCOM. The other electrode of the liquid crystal element  510  is connected to the wiring VCOM 1 . 
     A gate of the transistor SW 2  is connected to the wiring G 2 . One of a source and a drain of the transistor SW 2  is connected to the wiring S 2 , and the other of the source and the drain is connected to one electrode of the capacitor C 2  and a gate of the transistor M. The other electrode of the capacitor C 2  is connected to one of a source and a drain of the transistor M and the wiring ANO. The other of the source and the drain of the transistor M is connected to one electrode of the light-emitting element  511 . Furthermore, the other electrode of the light-emitting element  511  is connected to the wiring VCOM 2 . 
     Note that the transistor M includes two gates between which a semiconductor is provided and which are electrically connected to each other. With such a structure, the amount of current flowing through the transistor M can be increased. 
     The on/off state of the transistor SW 1  is controlled by a signal from the wiring G 1 . A predetermined potential is supplied from the wiring VCOM 1 . Furthermore, orientation of liquid crystals of the liquid crystal element  510  can be controlled by a signal from the wiring S 1 . A predetermined potential is supplied from the wiring CSCOM. 
     The on/off state of the transistor SW 2  is controlled by a signal from the wiring G 2 . By the difference between the potentials applied from the wiring VCOM 2  and the wiring ANO, the light-emitting element  511  can emit light. Furthermore, the on/off state of the transistor M is controlled by a signal from the wiring S 2 . 
     Accordingly, in the structure of this embodiment, in the case of the reflective mode, the liquid crystal element  510  is controlled by the signals supplied from the wiring G 1  and the wiring S 1  and optical modulation is utilized, whereby display can be performed. In the case of the transmissive mode, the light-emitting element  511  can emit light when the signals are supplied from the wiring G 2  and the wiring S 2 . In the case where both modes are performed at the same time, desired driving can be performed on the basis of the signals from the wiring G 1 , the wiring G 2 , the wiring S 1 , and the wiring S 2 . 
     Next, specific description will be given with reference to  FIG. 17 , a schematic cross-sectional view of the display device  500  described in this embodiment. 
     The display device  500  includes a light-emitting element  523  and a liquid crystal element  524  between substrates  521  and  522 . Note that the light-emitting element  523  and the liquid crystal element  524  are formed with an insulating layer  525  positioned therebetween. That is, the light-emitting element  523  is positioned between the substrate  521  and the insulating layer  525 , and the liquid crystal element  524  is positioned between the substrate  522  and the insulating layer  525 . 
     A transistor  515 , a transistor  516 , a transistor  517 , a coloring layer  528 , and the like are provided between the insulating layer  525  and the light-emitting element  523 . 
     A bonding layer  529  is provided between the substrate  521  and the light-emitting element  523 . The light-emitting element  523  includes a conductive layer  530  serving as one electrode, an EL layer  531 , and a conductive layer  532  serving as the other electrode which are stacked in this order over the insulating layer  525 . In the light-emitting element  523  that is a bottom emission light-emitting element, the conductive layer  532  and the conductive layer  530  contain a material that reflects visible light and a material that transmits visible light, respectively. Light emitted from the light-emitting element  523  is transmitted through the coloring layer  528  and the insulating layer  525  and then transmitted through the liquid crystal element  524  via an opening  533 , thereby being emitted to the outside of the substrate  522 . 
     In addition to the liquid crystal element  524 , a coloring layer  534 , a light-blocking layer  535 , an insulating layer  546 , a structure  536 , and the like are provided between the insulating layer  525  and the substrate  522 . The liquid crystal element  524  includes a conductive layer  537  serving as one electrode, a liquid crystal  538 , a conductive layer  539  serving as the other electrode, alignment films  540  and  541 , and the like. Note that the liquid crystal element  524  is a reflective liquid crystal element and the conductive layer  539  serves as a reflective electrode; thus, the conductive layer  539  is formed using a material with high reflectivity. Furthermore, the conductive layer  537  serves as a transparent electrode, and thus is formed using a material that transmits visible light. Alignment films  540  and  541  may be provided on the conductive layers  537  and  539  and in contact with the liquid crystal  538 . The insulating layer  546  is provided so as to cover the coloring layer  534  and the light-blocking layer  535  and serves as an overcoat layer. Note that the alignment films  540  and  541  are not necessarily provided. 
     The opening  533  is provided in part of the conductive layer  539 . A conductive layer  543  is provided in contact with the conductive layer  539 . Since the conductive layer  543  has a light-transmitting property, a material transmitting visible light is used for the conductive layer  543 . 
     The structure  536  serves as a spacer that prevents the substrate  522  from coming closer to the insulating layer  525  than required. The structure  536  is not necessarily provided. 
     One of a source and a drain of the transistor  515  is electrically connected to the conductive layer  530  in the light-emitting element  523 . For example, the transistor  515  corresponds to the transistor M in  FIG. 16 . 
     One of a source and a drain of the transistor  516  is electrically connected to the conductive layer  539  and the conductive layer  543  in the liquid crystal element  524  through a terminal portion  518 . That is, the terminal portion  518  electrically connects the conductive layers provided on both surfaces of the insulating layer  525 . The transistor  516  corresponds to the transistor SW 1  in  FIG. 16 . 
     A terminal portion  519  is provided in a region where the substrates  521  and  522  do not overlap with each other. Similarly to the terminal portion  518 , the terminal portion  519  electrically connects the conductive layers provided on both surfaces of the insulating layer  525 . The terminal portion  519  is electrically connected to a conductive layer obtained by processing the same conductive film as the conductive layer  543 . Thus, the terminal portion  519  and the FPC  544  can be electrically connected to each other through a conductive layer  545 . 
     A connection portion  547  is provided in part of a region where a bonding layer  542  is provided. In the connection portion  547 , the conductive layer obtained by processing the same conductive film as the conductive layer  543  and part of the conductive layer  537  are electrically connected with a connector  548 . Accordingly, a signal or a potential input from the FPC  544  can be supplied to the conductive layer  537  through the connector  548 . 
     The structure  536  is provided between the conductive layer  537  and the conductive layer  543 . The structure  536  maintains a cell gap of the liquid crystal element  524 . 
     As the conductive layer  543 , a metal oxide, a metal nitride, or an oxide such as an oxide semiconductor whose resistance is reduced is preferably used. In the case of using an oxide semiconductor, a material in which at least one of the concentrations of hydrogen, boron, phosphorus, nitrogen, and other impurities and the number of oxygen vacancies is made to be higher than those in a semiconductor layer of a transistor is used for the conductive layer  543 . 
     Note that the structure described in this embodiment can be combined as appropriate with any of the structures described in other embodiments. 
     Example 1 
     Synthesis Example 1 
     This example shows a method for synthesizing an organometallic complex bis{9-ethyl-3-[6-(2-methylpropyl)-4-pyrimidinyl-κN3]-9H-pyrido[2,3-b]indol-2-yl-κC}(2,4-pentanedionato-κ 2 O,O′)iridium(III) (abbreviation: [Ir(iBuidrpypm) 2 (acac)]), which is one embodiment of the present invention and represented by the structural formula (100) in Embodiment 1. A structure of [Ir(iBuidrpypm) 2 (acac)] is shown below. 
     
       
         
         
             
             
         
       
     
     Step 1: Synthesis of 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-pyrido[2,3-b]indole 
     First, in a 200 mL three-neck flask were put 2.01 g of 3-chloro-9H-pyrido[2,3-b]indole, 3.02 g of bis(pinacolato)diboron, 1.52 g of potassium acetate, and 99 mL of dry acetonitrile, and the air in the flask was replaced with nitrogen. 
     The mixture in the flask was degassed by being stirred under reduced pressure, 1.4 mL of tricyclohexylphosphine (abbreviation: P(C 6 H 11 ) 3 ) (a 0.6M toluene solution) and 0.37 g of tris(dibenzylideneacetone)dipalladium(0) (abbreviation: Pd 2 (dba) 3 ) were added to the mixture, and stirring was performed at 85° C. for 12 hours. Furthermore, 0.7 mL of P(C 6 H 11 ) 3  and 0.19 g of Pd 2 (dba) 3  were added thereto, and the mixture was stirred at 85° C. for seven hours. Then, 0.7 mL of P(C 6 H 11 ) 3  and 0.19 g of Pd 2 (dba) 3  were added thereto, and the mixture was stirred at 85° C. for seven hours. 
     After that, water was added to this solution, and an organic layer was extracted with ethyl acetate. The extracted solution was washed with saturated saline, and magnesium sulfate was added for drying. The solution obtained by the drying was filtrated. The solvent of this solution was distilled off, and then the obtained residue was purified by silica gel column chromatography using hexane and ethyl acetate as a developing solvent in a volume ratio of 2:1 to give a target white powder in a yield of 41%. The synthesis scheme of Step 1 is shown in (a-1). 
     
       
         
         
             
             
         
       
     
     Step 2: Synthesis of 3-[6-(2-methylpropyl)-4-pyrimidinyl]-9H-pyrido[2,3-b]indole 
     Next, in a 100-mL round-bottom flask equipped with a reflux pipe were put 1.82 g of 3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-pyrido[2,3-b]indole obtained in Step 1, 0.87 g of 4-chloro-6-(2-methylpropyl)pyrimidine, 7.7 mL of a 1 M aqueous solution of potassium acetate, 7.7 mL of a 1 M aqueous solution of sodium carbonate, and 16 mL of acetonitrile, and the air in the flask was replaced with argon. To this mixture, 0.35 g of tetrakis(triphenylphosphine)palladium(0) was added, and the reaction container was heated by irradiation with microwaves (2.45 GHz, 400 W) for an hour. Then, the precipitated solid was subjected to suction filtration and washed with water and ethanol. The obtained solid was purified by silica gel column chromatography using dichloromethane and ethyl acetate as a developing solvent in a volume ratio of 2:1 to give a target white powder in a yield of 91%. The synthesis scheme of Step 2 is shown in (a-2). 
     
       
         
         
             
             
         
       
     
     Step 3: Synthesis of 9-ethyl-3-[6-(2-methylpropyl)-4-pyrimidinyl]-9H-pyrido[2,3-b]indole 
     Next, in a 100 mL three-neck flask were put 1.71 g of 3-[6-(2-methylpropyl)-4-pyrimidinyl]-9H-pyrido[2,3-b]indole obtained in Step 2 and 50 mL of dry DMF, and the air in the flask was replaced with nitrogen. Then, 0.68 g of sodium hydride (60% in mineral oil) was added to this mixture, and stirring was performed at room temperature for an hour. After that, 0.96 mL of iodoethane was added dropwise, and the mixture was stirred at room temperature for 20 and a half hours. The obtained reaction solution was poured into 150 mL of water, and an organic layer was extracted with dichloromethane. The extracted solution was washed with saturated saline, and magnesium sulfate was added for drying. The solution obtained by the drying was filtrated. The solvent of this solution was distilled off, and then the obtained residue was purified by silica gel column chromatography using hexane and ethyl acetate as a developing solvent in a volume ratio of 5:1 to give yellow oil of the target pyrimidine derivative HiBuidrpypm (abbreviation) in a yield of 86%. The synthesis scheme of Step 3 is shown in (a-3). 
     
       
         
         
             
             
         
       
     
     Step 4: Synthesis of di-μ-chloro-tetrakis{9-ethyl-3-[6-(2-methylpropyl)-4-pyrimidinyl-κN3]-9H-pyrido[2,3-b]indol-2-yl-κC}diiridium(III) (abbreviation: [Ir(iBuidrpypm) 2 Cl] 2 ) 
     Next, in a recovery flask equipped with a reflux pipe were put 15 mL of 2-ethoxyethanol, 5 mL, of water, 1.60 g of HiBuidrpypm (abbreviation) obtained in Step 3, and 0.69 g of iridium chloride hydrate (IrCl 3 .nH 2 O) (produced by Furuya Metal Co., Ltd.), and the air in the flask was replaced with argon. After that, microwave irradiation (2.45 GHz, 100 W) was performed for an hour to cause a reaction. The solvent was distilled off, and then the obtained residue was subjected to suction filtration and washed with methanol to give a yellow-brown powder of a dinuclear complex [Ir(iBuidrpypm) 2 Cl] 2  (abbreviation) in a yield of 83%. Note that the microwave irradiation was performed using a microwave synthesis system (Discover, manufactured by CEM Corporation). The synthesis scheme of Step 4 is shown in (a-4). 
     
       
         
         
             
             
         
       
     
     Step 5: Synthesis of bis{9-ethyl-3-[6-(2-methylpropyl)-4-pyrimidinyl-κN3]-9H-pyrido[2,3-b]indol-2-yl-κC}(2,4-pentanedionato-κ 2 O,O′)iridium(III) (abbreviation: [Ir(iBuidrpypm) 2 (acac)]) 
     In a recovery flask equipped with a reflux pipe were put 20 mL of 2-ethoxyethanol, 1.28 g of the dinuclear complex [Ir(iBuidrpypm) 2 Cl] 2  (abbreviation) obtained in Step 4, 0.22 g of acetylacetone (abbreviation: Hacac), and 0.77 g of sodium carbonate, and the air in the flask was replaced with argon. After that, the mixture was heated by irradiation with microwaves (2.45 GHz, 120 W) for 60 minutes. The obtained reaction solution was subjected to suction filtration and the filtrate was concentrated, so that a yellow solid was obtained. The obtained solid was used for reaction. In a recovery flask equipped with a reflux pipe were put 0.94 g of the yellow solid, 0.16 g of Hacac, 0.56 g of sodium carbonate, and 20 mL of 2-ethoxyethanol, and the air in the flask was replaced with argon. After that, the mixture was heated by irradiation with microwaves (2.45 GHz, 120 W) for two hours. Here, 0.16 g of Hacac was further added, and the mixture was heated by irradiation with microwaves (2.45 GHz, 120 W) for two hours. The obtained reaction solution was subjected to suction filtration and washed with dichloromethane. The filtrate was concentrated, the obtained residue was purified by silica gel column chromatography using dichloromethane and ethyl acetate as a developing solvent in a volume ratio of 10:1, and recrystallization was performed with a mixed solvent of dichloromethane and ethanol. Thus, [Ir(iBuidrpypm) 2 (acac)] (abbreviation), which is the organometallic complex of the present invention, was obtained as a yellow powder in a yield of 19%. By a train sublimation method, 0.27 g of the obtained yellow powder solid was purified. In the sublimation purification, the solid was heated at 310° C. under a pressure of 2.6 Pa with an argon gas flow rate of 5 mL/min. After the sublimation purification, a target yellow solid was obtained in a yield of 78%. A synthetic scheme of Step 5 is shown in (a-5). 
     
       
         
         
             
             
         
       
     
     Analysis results by nuclear magnetic resonance spectrometry ( 1 H-NMR) of the compound obtained in Step 5 are shown below. The  1 H-NMR chart is shown in  FIG. 18 . The results demonstrate that the organometallic complex [Ir(iBuidrpypm) 2 (acac)] represented by the above structural formula (100) was obtained in this synthesis example. 
       1 H-NMR. δ(CDCl 3 ): 1.11-1.16 (m, 18H), 1.87 (s, 6H), 2.35-2.40 (m, 2H), 2.85-2.95 (m, 4H), 3.97-4.03 (m, 2H), 4.06-4.12 (m, 2H), 5.32 (s, 1H), 7.11 (t, 2H), 7.19 (d, 2H), 7.31 (t, 2H), 7.63 (s, 2H), 7.87 (d, 2H), 8.28 (s, 2H), 9.15 (s, 2H). 
     Next, an ultraviolet-visible absorption spectrum (hereinafter, simply referred to as an “absorption spectrum”) and an emission spectrum of a dichloromethane solution of [Ir(iBuidrpypm) 2 (acac)] were measured. The measurement of the absorption spectrum was conducted at room temperature, for which an ultraviolet-visible light spectrophotometer (V550 type manufactured by JASCO Corporation) was used and the dichloromethane solution (0.011 mmol/L) was put in a quartz cell. In addition, the measurement of the emission spectrum was performed at room temperature in such a manner that an absolute PL quantum yield measurement system (C11347-01 manufactured by Hamamatsu Photonics K. K.) was used and the deoxidized dichloromethane solution (0.011 mmol/L) was sealed in a quartz cell under a nitrogen atmosphere in a glove box (LABstar M13 (1250/780) manufactured by Bright Co., Ltd.). Analysis results of the obtained absorption and emission spectra are shown in  FIG. 19 , in which the horizontal axis represents wavelength and the vertical axes represent absorption intensity and emission intensity. In  FIG. 19 , two solid lines are shown; a thin line represents the absorption spectrum, and a thick line represents the emission spectrum. Note that the absorption spectrum in  FIG. 19  is the results obtained in such a way that the absorption spectrum measured by putting only dichloromethane in a quartz cell was subtracted from the absorption spectrum measured by putting the dichloromethane solution (0.011 mmol/L) in a quartz cell. 
     As shown in  FIG. 19 , the organometallic complex [Ir(iBuidrpypm) 2 (acac)] has an emission peak at 516 nm, and green light emission was observed from the dichloromethane solution. 
     Example 2 
     Synthesis Example 2 
     This example shows a method for synthesizing an organometallic complex tris{9-ethyl-3-[6-(2-methylpropyl)-4-pyrimidinyl-κN3]-9H-pyrido[2,3-b]indol-2-yl-κC}iridium(III) (abbreviation: [Ir(iBuidrpypm) 3 ]), which is one embodiment of the present invention and represented by the structural formula (112) in Embodiment 1. A structure of [Ir(iBuidrpypm) 3 ] is shown below. 
     
       
         
         
             
             
         
       
     
     Synthesis of [Ir(iBuidrpypm) 3 ] 
     First, in a 200 mL three-neck flask equipped with a reflux pipe were put 0.43 g of a dinuclear complex [Ir(iBuidrpypm) 2 Cl]) (abbreviation), 0.33 g of potassium carbonate, 0.39 g of HiBuidrpypm (abbreviation), and 4 g of phenol, and the air in the flask was replaced with nitrogen. Then, heating was performed at 195° C. for eight hours. After that, the obtained residue was irradiated with ultrasonic waves, subjected to suction filtration in methanol, and washed with water and methanol. The obtained solid was purified by silica gel column chromatography using dichloromethane and ethyl acetate as a developing solvent in a volume ratio of 1:2, and recrystallization was performed with a mixed solvent of toluene and hexane. Thus, a yellow powder of [Ir(iBuidrpypm) 3 ] (abbreviation) which is the organometallic complex of the present invention was obtained in a yield of 21%. The synthesis scheme is shown in (b-1). 
     
       
         
         
             
             
         
       
     
     Analysis results by nuclear magnetic resonance spectrometry ( 1 H-NMR) of the obtained yellow powder are shown below. The  1 H-NMR chart is shown in  FIG. 20 . The results demonstrate that the organometallic complex [Ir(iBuidrpypm) 3 ] represented by the above structural formula (112) was obtained in this synthesis example. 
       1 H NMR. δ(CDCl 3 ): 0.82-0.85 (m, 9H), 0.89-0.95 (m, 18H), 2.12-2.18 (m, 3H), 2.65 (d, 6H), 3.68-3.75 (m, 3H), 3.88-3.94 (m, 3H), 7.16-7.20 (m, 6H), 7.34 (t, 3H), 7.66 (s, 3H), 8.00 (d, 3H), 8.49 (s, 6H). 
     Next, an ultraviolet-visible absorption spectrum (hereinafter, simply referred to as an “absorption spectrum”) and an emission spectrum of a dichloromethane solution of [Ir(iBuidrpypm) 3 ] were measured. The measurement of the absorption spectrum was conducted at room temperature, for which an ultraviolet-visible light spectrophotometer (V550 type manufactured by JASCO Corporation) was used and the dichloromethane solution (9.7 μmol/L) was put in a quartz cell. In addition, the measurement of the emission spectrum was performed at room temperature in such a manner that an absolute PL quantum yield measurement system (C11347-01 manufactured by Hamamatsu Photonics K. K.) was used and the deoxidized dichloromethane solution (9.7 μmol/L) was sealed in a quartz cell under a nitrogen atmosphere in a glove box (LABstar M13 (1250/780) manufactured by Bright Co., Ltd.). 
     Analysis results of the obtained absorption and emission spectra are shown in  FIG. 21 , in which the horizontal axis represents wavelength and the vertical axes represent absorption intensity and emission intensity. In  FIG. 21 , two solid lines are shown; a thin line represents the absorption spectrum, and a thick line represents the emission spectrum. Note that the absorption spectrum in  FIG. 21  is the results obtained in such a way that the absorption spectrum measured by putting only dichloromethane in a quartz cell was subtracted from the absorption spectrum measured by putting the dichloromethane solution (9.7 μmol/L) in a quartz cell. 
     As shown in  FIG. 21 , the organometallic complex [Ir(iBuidrpypm) 3 ] has an emission peak at 519 nm, and green light emission was observed from the dichloromethane solution. 
     Example 3 
     In this example, a light-emitting element 1 including [Ir(iBuidrpypm) 2 (acac)] (structural formula (100)) which is the organometallic complex of one embodiment of the present invention, and a light-emitting element 2 including [Ir(iBuidrpypm) 3 ] (structural formula (112)) which is the organometallic complex of one embodiment of the present invention were fabricated. Note that the fabrication of the light-emitting elements 1 and 2 is described with reference to  FIG. 22 . Chemical formulae of materials used in this example are shown below. 
                                           
&lt;&lt;Fabrication of Light-Emitting Elements 1 and 2&gt;&gt;
 
     First, indium tin oxide (ITO) containing silicon oxide was deposited over a glass substrate  900  by a sputtering method, whereby a first electrode  901  functioning as an anode was formed. Note that the thickness was set to 110 nm and the electrode area was set to 2 mm×2 mm. 
     Next, as pretreatment for forming the light-emitting element over the substrate  900 , UV ozone treatment was performed for 370 seconds after washing of a surface of the substrate with water and baking that was performed at 200° C. for an hour. 
     After that, the substrate  900  was transferred into a vacuum evaporation apparatus where the pressure had been reduced to approximately 1×10 −4  Pa, and was subjected to vacuum baking at 170° C. for 30 minutes in a heating chamber of the vacuum evaporation apparatus. Then, the substrate  900  was cooled down for approximately 30 minutes. 
     Next, the substrate  900  was fixed to a holder provided in the vacuum evaporation apparatus so that a surface of the substrate over which the first electrode  901  was formed faced downward. In this example, a case is described in which a hole-injection layer  911 , a hole-transport layer  912 , a light-emitting layer  913 , an electron-transport layer  914 , and an electron-injection layer  915 , which are included in an EL layer  902 , are sequentially formed by a vacuum evaporation method. 
     After reducing the pressure of the vacuum evaporation apparatus to 1×10 −4  Pa, 1,3,5-tri(dibenzothiophen-4-yl)benzene (abbreviation: DBT3P-II) and molybdenum oxide were co-evaporated at a mass ratio of 4:2 (DBT3P-II: molybdenum oxide), whereby the hole-injection layer  911  was formed over the first electrode  901 . The thickness of the hole-injection layer  911  was 60 nm. Note that co-evaporation is an evaporation method in which a plurality of different substances are concurrently vaporized from different evaporation sources. 
     Then, 9-phenyl-9H-3-(9-phenyl-9H-carbazol-3-yl)carbazole (abbreviation: PCCP) was deposited by evaporation to a thickness of 20 nm, whereby the hole-transport layer  912  was formed. 
     Next, the light-emitting layer  913  was formed over the hole-transport layer  912 . 
     In the case of the light-emitting element 1, 9,9′-(pyrimidine-4,6-diyldi-3,1-phenylene)bis(9H-carbazole) (abbreviation: 4,6mCzP2Pm), PCCP, and [Ir(iBuidrpypm) 2 (acac)] were co-evaporated with a mass ratio of 4,6mCzP2Pm to PCCP and [Ir(iBuidrpypm) 2 (acac)] being 0.7:0.3:0.05, whereby the light-emitting layer  913  with a thickness of 40 nm was formed. 
     In the case of the light-emitting element 2, 4,6mCzP2Pm, PCCP, and [Ir(iBuidrpypm) 3 ] were co-evaporated with a mass ratio of 4,6mCzP2Pm to PCCP and [Ir(iBuidrpypm) 3 ] being 0.7:0.3:0.05, whereby the light-emitting layer  913  with a thickness of 40 nm was formed. 
     Next, over the light-emitting layer  913  of each of the light-emitting elements 1 and 2, 4,6mCzP2Pm was deposited by evaporation to a thickness of 20 nm, and then Bphen was deposited by evaporation to a thickness of 10 nm, whereby the electron-transport layer  914  was formed. 
     Furthermore, lithium fluoride was evaporated to a thickness of 1 nm over the electron-transport layer  914 , whereby the electron-injection layer  915  was formed. 
     Finally, aluminum was deposited to a thickness of 200 nm over the electron-injection layer  915 , whereby a second electrode  903  functioning as a cathode was formed. Thus, the light-emitting elements 1 and 2 were fabricated. Note that in all the above evaporation steps, evaporation was performed by a resistance-heating method. 
     Table 1 shows element structures of the light-emitting elements 1 and 2 fabricated as described above. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Hole- 
                 Hole- 
                 Light- 
                   
                 Electron- 
                   
               
               
                   
                 First 
                 injection 
                 transport 
                 emitting 
                 Electron- 
                 injection 
                 Second 
               
               
                   
                 electrode 
                 layer 
                 layer 
                 layer 
                 transport layer 
                 layer 
                 electrode 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Light- 
                 ITO 
                 DBT3P-II:MoO x   
                 PCCP 
                 * 
                 4,6mCzP2Pm 
                 Bphen 
                 LiF 
                 Al 
               
               
                 emitting 
                 (110 nm) 
                 (4:260 nm) 
                 (20 nm) 
                   
                 (20 nm) 
                 (10 nm) 
                 (1 nm) 
                 (200 nm) 
               
               
                 element 1 
               
               
                 Light- 
                 ITO 
                 DBT3P-II:MoO x   
                 PCCP 
                 ** 
                 4,6mCzP2Pm 
                 Bphen 
                 LiF 
                 Al 
               
               
                 emitting 
                 (110 nm) 
                 (4:260 nm) 
                 (20 nm) 
                   
                 (20 nm) 
                 (10 nm) 
                 (1 nm) 
                 (200 nm) 
               
               
                 element 2 
               
               
                   
               
               
                 * 4,6mCzP2Pm:PCCP:[Ir(iBuidrpypm) 2 (acac)] (0.7:0.3:0.05 40 nm) 
               
               
                 ** 4,6mCzP2Pm:PCCP:[Ir(iBuidrpypm) 3 ] (0.7:0.3:0.05 40 nm) 
               
            
           
         
       
     
     The fabricated light-emitting elements 1 and 2 were each sealed in a glove box containing a nitrogen atmosphere so as not to be exposed to the air (specifically, a sealant was applied to surround the elements, and at the time of sealing, UV treatment was performed first and then heat treatment was performed at 80° C. for an hour). 
     &lt;&lt;Operation Characteristics of Light-Emitting Elements 1 and 2&gt;&gt; 
     Measurement of the fabricated light-emitting elements 1 and 2 was performed. The measurement was carried out at room temperature (under an atmosphere where a temperature was maintained at 25° C.). 
       FIG. 23  shows the current density-luminance characteristics of the light-emitting elements 1 and 2;  FIG. 24  shows the voltage-luminance characteristics thereof;  FIG. 25  shows the luminance-current efficiency characteristics thereof and  FIG. 26  shows the voltage-current characteristics thereof. 
     Table 2 shows initial values of main characteristics of the light-emitting elements 1 and 2 at a luminance of about 1000 cd/m 2 . 
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                   
                 External 
               
               
                   
                   
                   
                 Current 
                   
                   
                 Current 
                 Power 
                 quantum 
               
               
                   
                 Voltage 
                 Current 
                 density 
                 Chromaticity 
                 Luminance 
                 efficiency 
                 efficiency 
                 efficiency 
               
               
                   
                 (V) 
                 (mA) 
                 (mA/cm 2 ) 
                 (x, y) 
                 (cd/m 2 ) 
                 (cd/A) 
                 (lm/W) 
                 (%) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Light- 
                 3.2 
                 0.043 
                 1.1 
                 (0.30, 0.64) 
                 980 
                 91 
                 89 
                 25 
               
               
                 emitting 
               
               
                 element 1 
               
               
                 Light- 
                 3.3 
                 0.080 
                 2.0 
                 (0.31, 0.64) 
                 1000 
                 53 
                 50 
                 14 
               
               
                 emitting 
               
               
                 element 2 
               
               
                   
               
            
           
         
       
     
       FIG. 27  shows emission spectra of the light-emitting elements 1 and 2 to which current was applied at a current density of 25 mA/cm 2 . As shown in  FIG. 27 , each of the emission spectra of the light-emitting elements 1 and 2 has a peak at around 520 nm, which indicates that the peaks are derived from green light emission of [Ir(iBuidrpypm) 2 (acac)] and [Ir(iBuidrpypm) 3 ] each of which is the organometallic complex of one embodiment of the present invention. 
     This application is based on Japanese Patent Application serial no. 2015-212831 filed with Japan Patent Office on Oct. 29, 2015, the entire contents of which are hereby incorporated by reference.