Patent Publication Number: US-2023147748-A1

Title: Light-emitting device and electronic apparatus including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2021-0151666, filed on Nov. 5, 2021, in the Korean Intellectual Property Office, the entire content of which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     1. Field 
     One or more embodiments of the present disclosure relate to a light-emitting device and an electronic apparatus including the same. 
     2. Description of the Related Art 
     Light-emitting devices are self-emissive devices that, as compared with other devices of the related art, have wide viewing angles, high contrast ratios, short response times, and excellent characteristics in terms of luminance, driving voltage, and response speed. 
     In an example, a light-emitting device may have a structure in which a first electrode is arranged on a substrate, and a hole transport region, an emission layer, an electron transport region, and a second electrode are sequentially formed on the first electrode. Holes provided from the first electrode move toward the emission layer through the hole transport region, and electrons provided from the second electrode move toward the emission layer through the electron transport region. Carriers, such as holes and electrons, recombine in the emission layer to produce light. 
     SUMMARY 
     One or more embodiments of the present disclosure include a light-emitting device having improved efficiency. 
     Additional aspects of embodiments will be set forth in part in the description, which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments of the disclosure. 
     According to one or more embodiments, a light-emitting device includes 
     a first electrode, 
     a second electrode facing the first electrode, and 
     an interlayer between the first electrode and the second electrode and including an emission layer, wherein: 
     the emission layer includes a layer including a platinum (Pt) complex, and 
     a thickness of the layer is greater than 0 Å and less than 10 Å. 
     According to one or more embodiments, an electronic apparatus includes 
     the light-emitting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects and features of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    is a schematic view of a light-emitting device according to an embodiment; 
         FIG.  2    is a cross-sectional view of an electronic apparatus according to an embodiment; and 
         FIG.  3    is a cross-sectional view of an electronic apparatus according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in more detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout the specification. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects of embodiments of the present description. As used herein, the term “and/or” includes any and all combinations of one or more of the same associated listed items. Throughout the disclosure, the expression “at least one of a, b or c” indicates only a, only b, only c, both a and b, both a and c, both b and c, all of a, b, and c, or variations thereof. 
     An aspect of embodiments of the present disclosure provides a light-emitting device including: 
     a first electrode; 
     a second electrode facing the first electrode; and 
     an interlayer arranged between the first electrode and the second electrode and including an emission layer, wherein: 
     the emission layer includes a layer including a platinum (Pt) complex, and 
     a thickness of the layer is greater than 0 Å and less than 10 Å. 
     In an embodiment, the Pt complex may be a dopant. 
     In an embodiment, the emission layer may include the layer including (or consisting of) the Pt complex. For example, the emission layer may include the layer including only the Pt complex which is a dopant. In some embodiments, the emission layer consists of the Pt complex such that the emission layer is substantially free of other components, which are present in the emission layer, if at all, only as an incidental impurity. In some embodiments, the emission layer consists of the Pt complex such that the emission layer is completely free of other components. 
     In the related art, an emission layer formed by doping a host with a dopant had a difficulty in maintaining uniformity. 
     However, in the light-emitting device according to an embodiment of the present disclosure, the emission layer includes, as a single film, a dopant layer including only the Pt complex, thereby easily maintaining uniformity. 
     In the light-emitting device according to an embodiment of the present disclosure, when a thickness of the layer including the Pt complex in the emission layer is 10 Å or more, exciton quenching occurs, thereby decreasing efficiency. 
     In an embodiment, the emission layer may include: a first layer including a first host; and a second layer including a second host. 
     In an embodiment, the first electrode may be an anode, and the second electrode may be a cathode, and the interlayer may further include a hole transport region that is arranged between the first electrode and the emission layer and includes: an electron-blocking layer; and a hole injection layer, a hole transport layer or any combination thereof. 
     In an embodiment, the first electrode may be an anode, and the second electrode may be a cathode, and the interlayer may further include an electron transport region that is arranged between the second electrode and the emission layer and includes: a hole-blocking layer; and an electron transport layer, an electron injection layer or any combination thereof. 
     In an embodiment, the light-emitting device may further include an electron-blocking layer and a hole-blocking layer. 
     In an embodiment, the emission layer may emit blue light. 
     In an embodiment, the emission layer may include: the first layer including the first host; and the second layer including the second host, and the layer including the Pt complex may be arranged between the first layer and the second layer. 
     For example, the emission layer may have a structure including (or consisting of) first host-including first layer/Pt complex-including layer/second host-including second layer. For example, the emission layer may have a structure including (or consisting of) second host-including second layer/Pt complex-including layer/first host-including first layer structure. 
     In an embodiment, the first host and/or the second host may be a mixed host of an electron-transporting host and a hole-transporting host. 
     For example, the first host may be a mixed host of an electron-transporting host and a hole-transporting host. For example, the second host may be a mixed host of an electron-transporting host and a hole-transporting host. 
     For example, the first host and the second host may each be a mixed host of an electron-transporting host and a hole-transporting host. In this case, each of the electron-transporting host and the hole-transporting host in the first host may be identical to or different from each of the electron-transporting host and the hole-transporting host in the second host. 
     In an embodiment, a weight ratio of the electron-transporting host to the hole-transporting host may be in a range of about 1:9 to about 9:1. For example, the weight ratio of the electron-transporting host to the hole-transporting host may be in a range of about 3:7 to about 7:3. For example, the weight ratio of the electron-transporting host to the hole-transporting host is in a range of about 4:5 to about 5:4. 
     In the case where the first host and/or the second host is a mixed host of the electron-transporting host and the hole-transporting host, the transport of holes and electrons may be achieved in a suitable or desirable balance when the weight ratio of the electron-transporting host to the hole-transporting host is within the ranges above. 
     Examples for the electron-transporting host and the hole-transporting host are further described herein below. 
     In an embodiment, the first host and/or the second host may be a single host. The term “single host” refers to a host that transports both holes and electrons to an equal extent (e.g., a substantially equal extent). 
     For example, the first host may be a single host. For example, the second host may be a single host. For example, the first host and the second host may each be a single host. 
     For example, the first host may be a single host, and the second host may be a mixed host of the electron-transporting host and the hole-transporting host. For example, the first host may be a mixed host of the electron-transporting host and the hole-transporting host, and the second host may be a single host. 
     Examples of the single host are further described herein below. 
     In an embodiment, a thickness of the first layer may be in a range of about 100 Å to about 300 Å. 
     In an embodiment, a thickness of the second layer may be in a range of about 100 Å to about 300 Å. 
     When the thicknesses of the first layer and the second layer are within these ranges, excellent luminescence characteristics may be obtained without a substantial increase in driving voltage. 
     In an embodiment, the interlayer may further include an electron-blocking layer, wherein the electron-blocking layer may be in contact (e.g., physical contact) with the emission layer. 
     In an embodiment, the interlayer may further include a hole-blocking layer, wherein the hole-blocking layer may be in contact (e.g., physical contact) with the emission layer. 
     In an embodiment, the interlayer may further include an electron-blocking layer and a hole-blocking layer, wherein the electron-blocking layer may be in contact (e.g., physical contact) with the first layer or the second layer, and the hole-blocking layer may be in contact (e.g., physical contact) with the first layer or the second layer. 
     For example, the emission layer may have a structure including (or consisting of) electron-blocking layer/first host-including first layer/Pt complex-including layer/second host-including second layer/hole-blocking layer. For example, the first host and the second host may each be a mixed host of an electron-transporting host and a hole-transporting host. For example, the first host and the second host may be both a single host. For example, the first host may be a single host, and the second host may be a mixed host of the electron-transporting host and the hole-transporting host. For example, the first host may be a mixed host of the electron-transporting host and the hole-transporting host, and the second host may be a single host. 
     The host(s) and the dopant may respectively be the same as described herein. 
     Another aspect of embodiments of the present disclosure provides an electronic apparatus including the light-emitting device. 
     In an embodiment, the electron apparatus may further include a thin-film transistor, 
     wherein the thin-film transistor may include a source electrode and a drain electrode, and 
     the first electrode of the light-emitting device may be electrically connected to at least one of the source and drain electrodes of the thin-film transistor. 
     In an embodiment, the electronic apparatus may further include a color filter, a color conversion layer, a touch screen layer, a polarizing layer, or any combination thereof. 
     The term “interlayer,” as used herein, refers to a single layer and/or all of a plurality of layers arranged between the first electrode and the second electrode of the light-emitting device. 
     Description of FIG.  1   
       FIG.  1    is a schematic cross-sectional view of a light-emitting device  10  according to an embodiment. The light-emitting device  10  includes a first electrode  110 , an interlayer  130 , and a second electrode  150 . 
     Hereinafter, the structure of the light-emitting device  10  according to an embodiment and a method of manufacturing the light-emitting device  10  will be described with reference to  FIG.  1   . First electrode  110   
     In  FIG.  1   , a substrate may be additionally arranged under the first electrode  110  and/or above the second electrode  150 . In an embodiment, as the substrate, a glass substrate and/or a plastic substrate may be used. In one or more embodiments, the substrate may be a flexible substrate, and for example, may include plastics having excellent heat resistance and durability, such as polyimide, polyethylene terephthalate (PET), polycarbonate, polyethylene naphthalate, polyarylate (PAR), polyetherimide, or any combination thereof. 
     The first electrode  110  may be formed by, for example, depositing and/or sputtering a material for forming the first electrode  110  on the substrate. When the first electrode  110  is an anode, a material for forming the first electrode  110  may be a high-work function material that facilitates injection of holes. 
     The first electrode  110  may be a reflective electrode, a semi-transmissive electrode, or a transmissive electrode. In an embodiment, when the first electrode  110  is a transmissive electrode, a material for forming the first electrode  110  may include indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO 2 ), zinc oxide (ZnO), or any combination thereof. In one or more embodiments, when the first electrode  110  is a semi-transmissive electrode or a reflective electrode, a material for forming the first electrode  110  may include magnesium (Mg), silver (Ag), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), or any combination thereof. 
     The first electrode  110  may have a single-layered structure consisting of a single layer or a multi-layered structure including a plurality of layers. For example, the first electrode  110  may have a three-layered structure of ITO/Ag/ITO. 
     Interlayer  130   
     The interlayer  130  is arranged on the first electrode  110 . The interlayer  130  may include an emission layer. 
     The interlayer  130  may further include a hole transport region between the first electrode  110  and the emission layer, and an electron transport region between the emission layer and the second electrode  150 . 
     The interlayer  130  may further include, in addition to various suitable organic materials, a metal-containing compound, such as an organometallic compound, an inorganic material, such as a quantum dot, and/or the like. 
     In one or more embodiments, the interlayer  130  may include i) two or more emission layers sequentially stacked between the first electrode  110  and the second electrode  150 , and ii) a charge generation layer arranged between the two or more emission layers. When the interlayer  130  includes the emission layers and the charge generation layer as described above, the light-emitting device  10  may be a tandem light-emitting device. 
     Hole Transport Region in Interlayer  130   
     The hole transport region may have: i) a single-layered structure consisting of a single layer consisting of a single material; ii) a single-layered structure consisting of a single layer consisting of a plurality of different materials; or iii) a multi-layered structure including a plurality of layers including different materials. 
     The hole transport region may include: an electron-blocking layer; a hole injection layer; a hole transport layer; or any combination thereof. 
     For example, the hole transport region may have a multi-layered structure, such as a hole injection layer/hole transport layer/electron-blocking layer structure, a hole injection layer/electron-blocking layer structure, or a hole transport layer/electron-blocking layer structure, wherein constituting layers for each structure are sequentially stacked from the first electrode  110 . 
     The hole transport region may include a compound represented by Formula  201 , a compound represented by Formula  202 , or any combination thereof: 
     
       
         
         
             
             
         
       
     
     In Formulae 201 and 202, 
     L 201  to L 204  may each independently be a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a  or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a , 
     L 205  may be *—O—*′, *—S—*′, *—N(Q 201 )—*′, a C 1 -C 20  alkylene group unsubstituted or substituted with at least one R 10a , a C 2 -C 20  alkenylene group unsubstituted or substituted with at least one R 10a , a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a , or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a , 
     xa1 to xa4 may each independently be an integer from 0 to 5, 
     xa5 may be an integer from 1 to 10, 
     R 201  to R 204  and Q 201  may each independently be a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a  or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a , 
     R 201  and R 202  may optionally be linked to each other via a single bond, a C 1 -C 5  alkylene group unsubstituted or substituted with at least one R 10a , or a C 2 -C 5  alkenylene group unsubstituted or substituted with at least one R 10a , to form a C 8 -C 60  polycyclic group (for example, a carbazole group or the like) unsubstituted or substituted with at least one R 10a  (for example, Compound HT16), 
     R 203  and R 204  may optionally be linked to each other via a single bond, a C 1 -C 5  alkylene group unsubstituted or substituted with at least one R 10a , or a C 2 -C 5  alkenylene group unsubstituted or substituted with at least one R 10a , to form a C 8 -C 60  polycyclic group unsubstituted or substituted with at least one R 10a , and 
     na1 may be an integer from 1 to 4. 
     For example, each of Formulae 201 and 202 may include at least one of groups represented by Formulae CY201 to CY217: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae CY201 to CY217, R 10b  and R 10c  may each be the same as described in connection with R 10a , ring CY 201  to ring CY 204  may each independently be a C 3 -C 20  carbocyclic group or a C 1 -C 20  heterocyclic group, and at least one hydrogen in Formulae CY201 to CY217 may be unsubstituted or substituted with R 10a . 
     In one or more embodiments, ring CY 201  to ring CY 204  in Formulae CY201 to CY217 may each independently be a benzene group, a naphthalene group, a phenanthrene group, or an anthracene group. 
     In one or more embodiments, each of Formulae 201 and 202 may include at least one of groups represented by Formulae CY201 to CY203. 
     In one or more embodiments, Formula 201 may include at least one of groups represented by Formulae CY201 to CY203 and at least one of groups represented by Formulae CY204 to CY217. 
     In one or more embodiments, in Formula 201, xa1 may be 1, R 201  may be a group represented by one of Formulae CY201 to CY203, xa2 may be 0, and R 202  may be a group represented by one of Formulae CY204 to CY207. 
     In one or more embodiments, each of Formulae 201 and 202 may not include groups represented by Formulae CY201 to CY203. 
     In one or more embodiments, each of Formulae 201 and 202 may not include groups represented by Formulae CY201 to CY203, and may include at least one of groups represented by Formulae CY204 to CY217. 
     In one or more embodiments, each of Formulae 201 and 202 may not include groups represented by Formulae CY201 to CY217. 
     For example, the hole transport region may include one of Compounds HT1 to HT46, m-MTDATA, TDATA, 2-TNATA, NPB(NPD), β-NPB, TPD, Spiro-TPD, Spiro-NPB, methylated NPB, TAPC, HMTPD, 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA), polyaniline/dodecylbenzenesulfonic acid (PANI/DBSA), poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS), polyaniline/camphor sulfonic acid (PANI/CSA), polyaniline/poly(4-styrenesulfonate) (PANI/PSS), or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A thickness of the hole transport region may be in a range of about 50 Å to about 10,000 Å, for example, about 100 Å to about 4,000 Å. When the hole transport region includes a hole injection layer, a hole transport layer, or any combination thereof, a thickness of the hole injection layer may be in a range of about 100 Å to about 9,000 Å, for example, about 100 Å to about 1,000 Å, and a thickness of the hole transport layer may be in a range of about 50 Å to about 2,000 Å, for example, about 100 Å to about 1,500 Å. When the thicknesses of the hole transport region, the hole injection layer, and the hole transport layer are within these ranges, suitable or satisfactory hole transporting characteristics may be obtained without a substantial increase in driving voltage. 
     The electron-blocking layer may be a layer that prevents or reduces electron leakage from the emission layer to the hole transport region. Materials that may be included in the hole transport region may be included in the electron-blocking layer. 
     A thickness of the electron-blocking layer may be in a range of about 50 Å to about 300 Å, for example, about 100 Å to about 200 Å. When the thickness of the electron-blocking layer is within the ranges above, electron-blocking characteristics may be increased or optimized. 
     p-Dopant 
     The hole transport region may further include, in addition to these materials, a charge-generation material for the improvement of conductive properties (e.g., electrically conductive properties). The charge-generation material may be uniformly or non-uniformly dispersed in the hole transport region (for example, in the form of a single layer consisting of a charge-generation material). 
     The charge-generation material may be, for example, a p-dopant. 
     For example, the p-dopant may have a lowest unoccupied molecular orbital (LUMO) energy level of about −3.5 eV or less. 
     In an embodiment, the p-dopant may include a quinone derivative, a cyano group-containing compound, a compound including element EL1 and element EL2, or any combination thereof. 
     Examples of the quinone derivative include TCNQ, F4-TCNQ, and the like. 
     Examples of the cyano group-containing compound include HAT-CN, a compound represented by Formula 221, and the like: 
     
       
         
         
             
             
         
       
     
     In Formula 221, 
     R 221  to R 223  may each independently be a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a  or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a , and 
     at least one of R 221  to R 223  may each independently be a C 3 -C 60  carbocyclic group or a C 1 -C 60  heterocyclic group, each substituted with: a cyano group; —F; —Cl; —Br; —I; a C 1 -C 20  alkyl group substituted with a cyano group, —F, —Cl, —Br, —I, or any combination thereof; or any combination thereof. 
     In the compound including element EL 1  and element EL 2 , element EL 1  may be metal, metalloid, or any combination thereof, and element EL 2  may be non-metal, metalloid, or any combination thereof. 
     Examples of the metal include an alkali metal (for example, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and the like); alkaline earth metal (for example, beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and the like); transition metal (for example, titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), and the like); post-transition metal (for example, zinc (Zn), indium (In), tin (Sn), and the like); lanthanide metal (for example, lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), and the like); and the like. 
     Examples of the metalloid include silicon (Si), antimony (Sb), tellurium (Te), and the like. 
     Examples of the non-metal include oxygen (O), halogen (for example, F, Cl, Br, I, and the like), and the like. 
     Examples of the compound including element EL 1  and element EL 2  include metal oxide, metal halide (for example, metal fluoride, metal chloride, metal bromide, metal iodide, and the like), metalloid halide (for example, metalloid fluoride, metalloid chloride, metalloid bromide, metalloid iodide, and the like), metal telluride, or any combination thereof. 
     Examples of the metal oxide include tungsten oxide (for example, WO, W 2 O 3 , WO 2 , WO 3 , W 2 O 5 , and the like), vanadium oxide (for example, VO, V 2 O 3 , VO 2 , V 2 O 5 , and the like), molybdenum oxide (MoO, Mo 2 O 3 , MoO 2 , MoO 3 , Mo 2 O 5 , and the like), rhenium oxide (for example, ReO 3  and the like), and the like. 
     Examples of the metal halide include alkali metal halide, alkaline earth metal halide, transition metal halide, post-transition metal halide, lanthanide metal halide, and the like. 
     Examples of the alkali metal halide include LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, CsI, and the like. 
     Examples of the alkaline earth metal halide include BeF 2 , MgF 2 , CaF 2 , SrF 2 , BaF 2 , BeCl 2 , MgCl 2 , CaCl 2 , SrCl 2 , BaCl 2 , BeBr 2 , MgBr 2 , CaBr 2 , SrBr 2 , BaBr 2 , BeI 2 , MgI 2 , CaI 2 , SrI 2 , BaI 2 , and the like. 
     Examples of the transition metal halide include titanium halide (for example, TiF 4 , TiCl 4 , TiBr 4 , TiI 4 , and the like), zirconium halide (for example, ZrF 4 , ZrCl 4 , ZrBr 4 , ZrI 4 , and the like), hafnium halide (for example, HfF 4 , HfCl 4 , HfBr 4 , HfI 4 , and the like), vanadium halide (for example, VF 3 , VCl 3 , VBr 3 , VI 3 , and the like), niobium halide (for example, NbF 3 , NbCl 3 , NbBr 3 , NbI 3 , and the like), tantalum halide (for example, TaF 3 , TaCl3, TaBr3, Tai3, and the like), chromium halide (for example, CrF 3 , CrCl 3 , CrBr 3 , CrI 3 , and the like), molybdenum halide (for example, MoF 3 , MoCl 3 , MoBr 3 , MoI 3 , and the like), tungsten halide (for example, WF 3 , WCl 3 , WBr 3 , WI 3 , and the like), manganese halide (for example, MnF 2 , MnCl 2 , MnBr 2 , MnI 2 , and the like), technetium halide (for example, TcF 2 , TcCl 2 , TcBr 2 , TcI 2 , and the like), rhenium halide (for example, ReF 2 , ReCl 2 , ReBr 2 , ReI 2 , and the like), iron halide (for example, FeF 2 , FeCl 2 , FeBr 2 , FeI 2 , and the like), ruthenium halide (for example, RuF 2 , RuCl 2 , RuBr 2 , RuI 2 , and the like), osmium halide (for example, OsF 2 , OsCl 2 , OsBr 2 , OsI 2 , and the like), cobalt halide (for example, CoF 2 , CoCl 2 , CoBr 2 , CoI 2 , and the like), rhodium halide (for example, RhF 2 , RhCl 2 , RhBr 2 , RhI 2 , and the like), iridium halide (for example, IrF 2 , IrCl 2 , IrBr 2 , IrI 2 , and the like), nickel halide (for example, NiF 2 , NiCl 2 , NiBr 2 , NiI 2 , and the like), palladium halide (for example, PdF 2 , PdCl 2 , PdBr 2 , PdI 2 , and the like), platinum halide (for example, PtF 2 , PtCl 2 , PtBr 2 , PtI 2 , and the like), copper halide (for example, CuF, CuCl, CuBr, CuI, and the like), silver halide (for example, AgF, AgCl, AgBr, AgI, and the like), gold halide (for example, AuF, AuCl, AuBr, AuI, and the like), and the like 
     Examples of the post-transition metal halide include zinc halide (for example, ZnF 2 , ZnCl 2 , ZnBr 2 , ZnI 2 , and the like), indium halide (for example, InI 3  and the like), tin halide (for example, SnI 2  and the like), and the like 
     Examples of the lanthanide metal halide include YbF, YbF 2 , YbF 3 , SmF 3 , YbCl, YbCl 2 , YbCl 3  SmCl 3 , YbBr, YbBr 2 , YbBr 3  SmBr 3 , YbI, YbI 2 , YbI 3 , SmI 3 , and the like. 
     Examples of the metalloid halide include antimony halide (for example, SbCl 5  and the like) and the like. 
     Examples of the metal telluride include alkali metal telluride (for example, Li 2 Te, Na 2 Te, K 2 Te, Rb 2 Te, Cs 2 Te, and the like), alkaline earth metal telluride (for example, BeTe, MgTe, CaTe, SrTe, BaTe, and the like), transition metal telluride (for example, TiTe 2 , ZrTe 2 , HfTe 2 , V 2 Te 3 , Nb 2 Te 3 , Ta 2 Te 3 , Cr 2 Te 3 , Mo 2 Te 3 , W 2 Te 3 , MnTe, TcTe, ReTe, FeTe, RuTe, OsTe, CoTe, RhTe, IrTe, NiTe, PdTe, PtTe, Cu 2 Te, CuTe, Ag 2 Te, AgTe, Au 2 Te, and the like), post-transition metal telluride (for example, ZnTe, and the like), lanthanide metal telluride (for example, LaTe, CeTe, PrTe, NdTe, PmTe, EuTe, GdTe, TbTe, DyTe, HoTe, ErTe, TmTe, YbTe, LuTe, and the like), and the like. 
     Emission Layer in Interlayer  130   
     When the light-emitting device  10  is a full-color light-emitting device, the emission layer may be patterned into a red emission layer, a green emission layer, and/or a blue emission layer, according to a subpixel. In an embodiment, the emission layer may have a stacked structure in which two or more layers among a red emission layer, a green emission layer, and a blue emission layer contact (e.g., physically contact) each other or are spaced apart from each other to emit white light. In one or more embodiments, the emission layer may have a structure in which two or more materials among a red light-emitting material, a green light-emitting material, and a blue light-emitting material are mixed with each other in a single layer to emit white light. 
     In an embodiment, the emission layer may include a host and a dopant. The dopant may include a phosphorescent dopant. The phosphorescent dopant may be the Pt complex. 
     A thickness of the emission layer may be in a range of about 100 Å to about 1,000 Å, for example, about 200 Å to about 600 Å. When the thickness of the emission layer is within the ranges above, excellent luminescence characteristics may be obtained without a substantial increase in driving voltage. 
     Host 
     The hole-transporting host may be a compound having strong hole properties. The expression “a compound having strong hole properties” refers to a compound that is easy to accept holes, and such properties may be obtained by including a hole-receiving moiety (also, referred to as a hole-transporting moiety). 
     Such a hole-receiving moiety may include, for example, a π-electron-rich heteroaromatic compound (for example, a carbazole derivative or an indole derivative), or an aromatic amine compound. 
     The electron-transporting host may be a compound having strong electron properties. The expression “a compound having strong electron properties” refers to a compound that is easy to accept electrons, and such properties may be obtained by including an electron-receiving moiety (also, referred to as an electron-transporting moiety). 
     Such an electron-receiving moiety may include, for example, a π electron-deficient heteroaromatic compound. For example, the electron-receiving may include a nitrogen-containing heteroaromatic compound. 
     When a compound includes only a hole-transporting moiety or only an electron-transporting moiety, it is clear whether the nature of the compound has hole-transporting properties or electron-transporting properties. 
     In an embodiment, a compound may include both a hole-transporting moiety and an electron-transporting moiety. In this case, a simple comparison between the total number of the hole-transporting moieties and the total number of the electron-transporting moieties in the compound may be a criterion for predicting whether the compound is a hole-transporting compound or an electron-transporting compound, but it cannot be a sole or an absolute criterion. One of the reasons why such a simple comparison cannot be a sole or an absolute criterion is that one hole-transporting moiety and one electron-transporting moiety do not respectively have exactly the same ability to attract holes and electrons. 
     Therefore, a relatively reliable way to determine whether a compound having a certain structure is a hole-transporting compound or an electron-transporting compound is to directly implement the compound in a device and observe the hole-transporting compound or electron-transporting properties of the compound. 
     In the emission layer of the light-emitting device according to an embodiment of the present disclosure, the first layer may include a first host, and the second layer may include a second host. 
     The first host and/or the second host may be a mixed host of the electron-transporting host and the hole-transporting host. 
     The first host and/or the second host may be a single host. In this regard, the single host may include both a hole-transporting moiety and an electron-transporting moiety, and refers to a host that transports both holes and electrons to the same extent. 
     In an embodiment, the host may include a compound represented by Formula 301: 
       [Ar 301 ] xb11 -[(L 301 ) xb1 -R 301 ] xb21    Formula 301
 
     wherein, in Formula 301, 
     Ar 301  and L 301  may each independently be a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a  or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a , 
     xb11 may be 1, 2, or 3, 
     xb1 may be an integer from 0 to 5, 
     R 301  may be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 60  alkyl group unsubstituted or substituted with at least one R 10a , a C 2 -C 60  alkenyl group unsubstituted or substituted with at least one R 10a , a C 2 -C 60  alkynyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  alkoxy group unsubstituted or substituted with at least one R 10a , a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a , —Si(Q 301 )(Q 302 )(Q 303 ), —N(Q 301 )(Q 302 ), —B(Q 301 )(Q 302 ), —C(═O)(Q 301 ), —S(═O) 2 (Q 301 ), or —P(═O)(Q 301 )(Q 302 ), 
     xb21 may be an integer from 1 to 5, and 
     Q 301  to Q 303  may each be the same as described in connection with Q 1 . 
     For example, when xb11 in Formula 301 is 2 or more, two or more of Ar 301  may be linked together via a single bond. 
     In one or more embodiments, the host may include a compound represented by Formula 301-1, a compound represented by Formula 301-2, or any combination thereof: 
     
       
         
         
             
             
         
       
     
     In Formulae 301-1 and 301-2, 
     ring A 301  to ring A 304  may each independently be a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a  or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a , 
     X 301  may be O, S, N-[(L 304 ) xb4 -R 304 ], C(R 304 )(R 305 ), or Si(R 304 )(R 305 ), 
     xb22 and xb23 may each independently be 0, 1, or 2, 
     L 301 , xb1, and R 301  may each be the same as described herein, 
     L 302  to L 304  may each independently be the same as described in connection with L 301 , 
     xb2 to xb4 may each independently be the same as described in connection with xb1, and 
     R 302  to R 305  and R 311  to R 314  may each be the same as described in connection with R 301 . 
     In one or more embodiments, the host may include an alkaline earth-metal complex. In one or more embodiments, the host may include a Be complex (for example, Compound H55), an Mg complex, a Zn complex, or any combination thereof. 
     In an embodiment, the host may include one of Compounds H1 to H126, 9,10-di(2-naphthyl)anthracene (ADN), 2-methyl-9,10-bis(naphthalen-2-yl)anthracene (MADN), 9,10-di-(2-naphthyl)-2-t-butyl-anthracene (TBADN), 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP), 1,3-di-9-carbazolylbenzene (mCP), 1,3,5-tri(carbazol-9-yl)benzene (TCP) or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Phosphorescent Dopant 
     The phosphorescent dopant may include at least one transition metal atom as a central metal atom. 
     The phosphorescent dopant may include a monodentate ligand, a bidentate ligand, a tridentate ligand, a tetradentate ligand, a pentadentate ligand, a hexadentate ligand, or any combination thereof. 
     The phosphorescent dopant may be electrically neutral. 
     For example, the phosphorescent dopant may include an organometallic compound represented by Formula 401: 
     
       
         
         
             
             
         
       
     
     In Formulae 401 and 402, 
     M may be Pt, 
     L 401  may be a ligand represented by Formula 402, and xc1 may be 1, 2, or 3, wherein, when xc1 is 2 or more, two or more of L 401  may be identical to or different from each other, 
     L 402  may be an organic ligand, and xc2 may be 0, 1, 2, 3, or 4, wherein, when xc2 is 2 or more, two or more of L 402  may be identical to or different from each other, 
     X 401  and X 402  may each independently be nitrogen or carbon, 
     ring A 401  and ring A 402  may each independently be a C 3 -C 60  carbocyclic group or a C 1 -C 60  heterocyclic group, 
     T 401  may be a single bond, —O—, —S—, —C(═O)—, —N(Q 411 )—, —C(Q 411 )(Q 412 )—, —C(Q 411 )═C(Q 412 )—, —C(Q 411 )═, or ═C═, 
     X 403  and X 404  may each independently be a chemical bond (for example, a covalent bond or a coordinate bond), O, S, N(Q 413 ), B(Q 413 ), P(Q 413 ), C(Q 413 )(Q 414 ), or Si(Q 413 )(Q 414 ), 
     Q 411  to Q 414  may each be the same as described in connection with Q 1 , 
     R 401  and R 402  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 20  alkyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 20  alkoxy group unsubstituted or substituted with at least one R 10a , a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a , —Si(Q 401 )(Q 402 )(Q 403 ), —N(Q 401 )(Q 402 ), —B(Q 401 )(Q 402 ), —C(═O)(Q 401 ), —S(═O) 2 (Q 401 ), or —P(═O)(Q 401 )(Q 402 ), 
     Q 401  to Q 403  may each be the same as described in connection with 
     xc11 and xc12 may each independently be an integer from 0 to 10, and 
     * and *′ in Formula 402 each indicate a binding site to M in Formula 401. 
     For example, in Formula 402, i) X 401  may be nitrogen, and X 402  may be carbon, or ii) each of X 401  and X 402  may be nitrogen. 
     In an embodiment, when xc1 in Formula 401 is 2 or more, two ring A 401 (s) among two or more of L 401  may optionally be linked to each other via T 402 , which is a linking group, and two ring A 402 (s) among two or more of L 401  may optionally be linked to each other via T 403 , which is a linking group (see Compounds PD1 to PD4 and PD7). T 402  and T 403  may each be the same as described in connection with T 401 . 
     In Formula 401, L 402  may be an organic ligand. For example, L 402  may include a halogen group, a diketone group (for example, an acetylacetonate group), a carboxylic acid group (for example, a picolinate group), —C(═O), an isonitrile group, a —CN group, a phosphorus group (for example, a phosphine group, a phosphite group, and the like), or any combination thereof. 
     The phosphorescent dopant may include, for example, one of Compounds PD1 to PD43, or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Electron Transport Region in Interlayer  130   
     The electron transport region may have: i) a single-layered structure consisting of a single layer consisting of a single material, ii) a single-layered structure consisting of a single layer consisting of a plurality of different materials, or iii) a multi-layered structure including a plurality of layers including different materials. 
     The electron transport region may include: a hole-blocking layer; an electron transport layer; an electron injection layer; or any combination thereof. 
     For example, the electron transport region may have a hole-blocking layer/electron transport layer structure, a hole-blocking layer/electron injection layer structure, or a hole-blocking layer/electron transport layer/electron injection layer structure, wherein constituting layers for each structure are sequentially stacked from the emission layer. 
     In an embodiment, the electron transport region (for example, the hole-blocking layer, or the electron transport layer in the electron transport region) may include a metal-free compound including at least one π electron-deficient nitrogen-containing C 1 -C 60  cyclic group. 
     For example, the electron transport region  160  may include a compound represented by Formula 601: 
       [Ar 601 ] xe11 —[(L 601 ) xe1 —R 601 ] xe21    Formula 601
 
     wherein, in Formula 601, 
     Ar 601  and L 601  may each independently be a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a  or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a , 
     xe11 may be 1, 2, or 3, 
     xe1 may be 0, 1, 2, 3, 4, or 5, 
     R 601  may be a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a , —Si(Q 601 )(Q 602 )(Q 603 ), —C(═O)(Q 601 ), —S(═O) 2 (Q 601 ), or —P(═O)(Q 601 )(Q 602 ), 
     Q 601  to Q 603  may each be the same as described in connection with Q 1 , 
     xe21 may be 1, 2, 3, 4, or 5, and 
     at least one of Ar 601 , L 601 , and R 601  may each independently be a π electron-deficient nitrogen-containing C 1 -C 60  cyclic group unsubstituted or substituted with at least one R 10a . 
     In an embodiment, when xe11 in Formula 601 is 2 or more, two or more of Ar 601  may be bonded together via a single bond. 
     In one or more embodiments, Ar 601  in Formula 601 may be a substituted or unsubstituted anthracene group. 
     In one or more embodiments, the electron transport region may include a compound represented by Formula 601-1: 
     
       
         
         
             
             
         
       
     
     In Formula 601-1, 
     X 614  may be N or C(R 614 ), X 615  may be N or C(R 615 ), X 616  may be N or C(R 616 ), and at least one of X 614  to X 616  may be N, 
     L 611  to L 613  may each be the same as described in connection with L 601 , 
     xe611 to xe613 may each be the same as described in connection with xe1, 
     R 611  to R 613  may each be the same as described in connection with R 601 , and 
     R 614  to R 616  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a , or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a . 
     For example, xe1 and xe611 to xe613 in Formulae 601 and 601-1 may each independently be 0, 1, or 2. 
     The electron transport region may include one of Compounds ET1 to ET45, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), 4,7-diphenyl-1,10-phenanthroline (Bphen), Alq 3 , BAlq, TAZ, NTAZ, H125, H126, or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A thickness of the electron transport region may be in a range of about 100 Å to about 5,000 Å, for example, about 160 Å to about 4,000 Å. When the electron transport region includes the hole-blocking layer, the electron transport layer, or any combination thereof, a thickness of the hole-blocking layer or electron transport layer may be in a range of about 20 Å to about 1,000 Å, for example, about 30 Å to about 300 Å, and a thickness of the electron transport layer may be in a range of about 100 Å to about 1,000 Å, for example, about 150 Å to about 500 Å. When the thicknesses of the hole-blocking layer and/or the electron transport layer are within these ranges, suitable or satisfactory electron transporting characteristics may be obtained without a substantial increase in driving voltage. 
     The electron transport region (for example, the electron transport layer in the electron transport region) may further include, in addition to the materials described above, a metal-containing material. 
     The metal-containing material may include an alkali metal complex, an alkaline earth metal complex, or any combination thereof. The metal ion of an alkali metal complex may be a Li ion, a Na ion, a K ion, a Rb ion, or a Cs ion, and the metal ion of an alkaline earth metal complex may be a Be ion, a Mg ion, a Ca ion, a Sr ion, or a Ba ion. A ligand coordinated with the metal ion of the alkali metal complex or the alkaline earth-metal complex may include a hydroxyquinoline, a hydroxyisoquinoline, a hydroxybenzoquinoline, a hydroxyacridine, a hydroxyphenanthridine, a hydroxyphenyloxazole, a hydroxyphenylthiazole, a hydroxyphenyloxadiazole, a hydroxyphenylthiadiazole, a hydroxyphenylpyridine, a hydroxyphenylbenzimidazole, a hydroxyphenylbenzothiazole, a bipyridine, a phenanthroline, a cyclopentadiene, or any combination thereof. 
     For example, the metal-containing material may include a Li complex. The Li complex may include, for example, Compound ET-D1 (LiQ) or ET-D2: 
     
       
         
         
             
             
         
       
     
     The electron transport region may include an electron injection layer that facilitates the injection of electrons from the second electrode  150 . The electron injection layer may directly contact the second electrode  150 . 
     The electron injection layer may have: i) a single-layered structure consisting of a single layer consisting of a single material, ii) a single-layered structure consisting of a single layer consisting of a plurality of different materials, or iii) a multi-layered structure including a plurality of layers including different materials. 
     The electron injection layer may include an alkali metal, alkaline earth metal, a rare earth metal, an alkali metal-containing compound, alkaline earth metal-containing compound, a rare earth metal-containing compound, an alkali metal complex, an alkaline earth metal complex, a rare earth metal complex, or any combination thereof. 
     The alkali metal may include Li, Na, K, Rb, Cs, or any combination thereof. The alkaline earth metal may include Mg, Ca, Sr, Ba, or any combination thereof. The rare earth metal may include Sc, Y, Ce, Tb, Yb, Gd, or any combination thereof. 
     The alkali metal-containing compound, the alkaline earth metal-containing compound, and the rare earth metal-containing compound may be oxides, halides (for example, fluorides, chlorides, bromides, iodides, and the like), or tellurides of the alkali metal, the alkaline earth metal, and the rare earth metal, or any combination thereof. 
     The alkali metal-containing compound may include alkali metal oxides, such as Li 2 O, Cs 2 O, K 2 O, and/or the like, alkali metal halides, such as LiF, NaF, CsF, KF, LiI, NaI, CsI, KI, and/or the like, or any combination thereof. The alkaline earth metal-containing compound may include an alkaline earth metal compound, such as BaO, SrO, CaO, Ba x Sr 1−x O (wherein x is a real number satisfying the condition of 0&lt;x&lt;1), Ba x Ca 1−x O (wherein x is a real number satisfying the condition of 0&lt;x&lt;1), or the like. The rare earth metal-containing compound may include YbF 3 , ScF 3 , Sc 2 O 3 , Y 2 O 3 , Ce 2 O 3 , GdF 3 , TbF 3 , YbI 3 , ScI 3 , TbI 3 , or any combination thereof. For example, the rare earth metal-containing compound may include lanthanide metal telluride. Examples of the lanthanide metal telluride include LaTe, CeTe, PrTe, NdTe, PmTe, SmTe, EuTe, GdTe, TbTe, DyTe, HoTe, ErTe, TmTe, YbTe, LuTe, La 2 Te 3 , Ce 2 Te 3 , Pr 2 Te 3 , Nd 2 Te 3 , Pm 2 Te 3 , Sm 2 Te 3 , Eu 2 Te 3 , Gd 2 Te 3 , Tb 2 Te 3 , Dy 2 Te 3 , Ho 2 Te 3 , Er 2 Te 3 , Tm 2 Te 3 , Yb 2 Te 3 , Lu 2 Te 3 , and the like. 
     The alkali metal complex, the alkaline earth-metal complex, and the rare earth metal complex may include: i) one of ions of the alkali metal, the alkaline earth metal, and the rare earth metal, respectively; and ii), as a ligand bonded to the metal ion, for example, hydroxyquinoline, hydroxyisoquinoline, hydroxybenzoquinoline, hydroxyacridine, hydroxyphenanthridine, hydroxyphenyloxazole, hydroxyphenylthiazole, hydroxyphenyloxadiazole, hydroxyphenylthiadiazole, hydroxyphenylpyridine, hydroxyphenyl benzimidazole, hydroxyphenylbenzothiazole, bipyridine, phenanthroline, cyclopentadiene, or any combination thereof. 
     In an embodiment, the electron injection layer may include (or consist of) an alkali metal, an alkaline earth metal, a rare earth metal, an alkali metal-containing compound, an alkaline earth metal-containing compound, a rare earth metal-containing compound, an alkali metal complex, an alkaline earth metal complex, a rare earth metal complex, or any combination thereof, as described above. In one or more embodiments, the electron injection layer may further include an organic material (for example, the compound represented by Formula 601). 
     In one or more embodiments, the electron injection layer may include (or consist of): i) an alkali metal-containing compound (for example, an alkali metal halide); or ii) a) an alkali metal-containing compound (for example, an alkali metal halide), and b) an alkali metal, an alkaline earth metal, a rare earth metal, or any combination thereof. In one or more embodiments, the electron injection layer may be a KI:Yb co-deposited layer, an RbI:Yb co-deposited layer, and/or the like. 
     When the electron injection layer further includes an organic material, alkali metal, alkaline earth metal, rare earth metal, an alkali metal-containing compound, an alkaline earth metal-containing compound, a rare earth metal-containing compound, an alkali metal complex, an alkaline earth-metal complex, a rare earth metal complex, or any combination thereof may be uniformly or non-uniformly dispersed in a matrix including the organic material. 
     A thickness of the electron injection layer may be in a range of about 1 Å to about 100 Å, for example, about 3 Å to about 90 Å. When the thickness of the electron injection layer is within these ranges, suitable or satisfactory electron injection characteristics may be obtained without a substantial increase in driving voltage. 
     Second electrode  150   
     The second electrode  150  is arranged on the above-described interlayer  130 . The second electrode  150  may be a cathode, which is an electron injection electrode, and as a material for forming the second electrode  150 , a metal, an alloy, an electrically conductive compound, or any combination thereof, each having a low work function, may be used. 
     The anode  150  may include lithium (Li), silver (Ag), magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), ytterbium (Yb), silver-ytterbium (Ag—Yb), ITO, IZO, or any combination thereof. The anode  150  may be a transmissive electrode, a semi-transmissive electrode, or a reflective electrode. 
     The second electrode  150  may have a single-layered structure or a multi-layered structure including a plurality of layers. 
     Capping Layer 
     A first capping layer may be arranged outside the first electrode  110 , and/or a second capping layer may be arranged outside the second electrode  150 . In more detail, the light-emitting device  10  may have a structure in which the first capping layer, the first electrode  110 , the interlayer  130 , and the second electrode  150  are sequentially stacked in the stated order, a structure in which the first electrode  110 , the interlayer  130 , the second electrode  150 , and the second capping layer are sequentially stacked in the stated order, or a structure in which the first capping layer, the first electrode  110 , the interlayer  130 , the second electrode  150 , and the second capping layer are sequentially stacked in the stated order. 
     In an embodiment, light generated in the emission layer of the interlayer  130  of the light-emitting device  10  may be extracted toward the outside through the first electrode  110 , which is a semi-transmissive electrode or a transmissive electrode, and the first capping layer. In one or more embodiments, light generated in the emission layer of the interlayer  130  of the light-emitting device  10  may be extracted toward the outside through the second electrode  150 , which is a semi-transmissive electrode or a transmissive electrode, and the second capping layer. 
     The first capping layer and the second capping layer may increase external emission efficiency according to the principle of constructive interference. Accordingly, the light extraction efficiency of the light-emitting device  10  may be increased, so that the luminescence efficiency of the light-emitting device  10  may be also improved. 
     Each of the first capping layer and the second capping layer may include a material having a refractive index of 1.6 or more (at a wavelength of 589 nm). 
     The first capping layer and the second capping layer may each independently be an organic capping layer including an organic material, an inorganic capping layer including an inorganic material, or an organic-inorganic composite capping layer including an organic material and an inorganic material. 
     In an embodiment, at least one of the first capping layer and the second capping layer may each independently include a carbocyclic compound, a heterocyclic compound, an amine group-containing compound, a porphine derivative, a phthalocyanine derivative, a naphthalocyanine derivative, an alkali metal complex, an alkaline earth metal complex, or any combination thereof. The carbocyclic compound, the heterocyclic compound, and the amine group-containing compound may each optionally be substituted with a substituent including O, N, S, Se, Si, F, CI, Br, I, or any combination thereof. In one or more embodiments, at least one of the first capping layer and the second capping layer may each independently include an amine group-containing compound. 
     In one or more embodiments, at least one of the first capping layer and the second capping layer may each independently include a compound represented by Formula 201, a compound represented by Formula 202, or any combination thereof. 
     In one or more embodiments, at least one of the first capping layer and the second capping layer may each independently include one of Compounds CP1 to CP6, β-NPB, or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Electronic Apparatus 
     The light-emitting device may be included in various suitable electronic apparatuses. For example, an electronic apparatus including the light-emitting device may be a light-emitting apparatus, an authentication apparatus, and/or the like. 
     The electronic apparatus (for example, a light-emitting apparatus) may further include, in addition to the light-emitting device, i) a color filter, ii) a color conversion layer, or iii) both a color filter and a color conversion layer. The color filter and/or the color conversion layer may be arranged in at least one traveling direction of light emitted from the light-emitting device. For example, the light emitted from the light-emitting device may be blue light. Further details for the light-emitting device are the same as described herein. In an embodiment, the color conversion layer may include a quantum dot. 
     The electronic apparatus may include a first substrate. The first substrate may include a plurality of subpixel areas, the color filter may include a plurality of color filter areas respectively corresponding to the subpixel areas, and the color conversion layer may include a plurality of color conversion areas respectively corresponding to the subpixel areas. 
     A pixel-defining film may be arranged among the subpixel areas to define each of the subpixel areas. 
     The color filter may further include a plurality of color filter areas and light-shielding patterns arranged among the color filter areas, and the color conversion layer may further include a plurality of color conversion areas and light-shielding patterns arranged among the color conversion areas. 
     The plurality of color filter areas (or the plurality of color conversion areas) may include a first area to emit a first-color light, a second area to emit a second-color light, and/or a third area to emit a third-color light, wherein the first-color light, the second-color light, and/or the third-color light may have different maximum emission wavelengths from one another. For example, the first-color light may be red light, the second-color light may be green light, and the third-color light may be blue light. For example, the plurality of color filter areas (or the plurality of color conversion areas) may include quantum dots. For example, the first region may include red quantum dots, the second region may include green quantum dots, and the third region may not include quantum dots. Further details for the quantum dots may be the same as described herein. The first region, the second region, and/or the third region may each further include a scatterer (e.g., a light scatterer). 
     For example, the light-emitting device may emit a first light, the first region may absorb the first light and emit a first-first color light, the second region may absorb the first light and emit a second-first color light, and the third region may absorb the first light and emit a third-first color light. Here, the first-first color light, the second-first color light, and the third-first color light may have different maximum emission wavelengths from each other. In more detail, the first light may be blue light, the first-first color light may be red light, the second-first color light may be green light, and the third-first color light may be blue light. 
     The electronic apparatus may further include a thin-film transistor in addition to the above-described light-emitting device. The thin-film transistor may include a source electrode, a drain electrode, and an activation layer, wherein any one of the source electrode and the drain electrode may be electrically connected to any one of the first electrode and the second electrode of the light-emitting device. 
     The thin-film transistor may further include a gate electrode, a gate insulating film, and/or the like. 
     The activation layer may include crystalline silicon, amorphous silicon, an organic semiconductor, an oxide semiconductor, and/or the like. 
     The electronic apparatus may further include a sealing portion for sealing the light-emitting device. The sealing portion may be arranged between the color filter and the light-emitting device and/or between the color conversion layer and the light-emitting device. The sealing portion allows light from the light-emitting device to be extracted to the outside, and concurrently (e.g., simultaneously) prevents or reduces penetration of ambient air and/or moisture into the light-emitting device. The sealing portion may be a sealing substrate including a transparent glass substrate and/or a plastic substrate. The sealing portion may be a thin-film encapsulation layer including at least one of an organic layer and/or an inorganic layer. When the sealing portion is a thin-film encapsulation layer, the electronic apparatus may be flexible. 
     Various suitable functional layers may be additionally arranged on the sealing portion, in addition to the color filter and/or the color conversion layer, according to use of the electronic apparatus. Examples of the functional layer include a touch screen layer, a polarizing layer, and the like. The touch screen layer may be a pressure-sensitive touch screen layer, a capacitive touch screen layer, and/or an infrared touch screen layer. The authentication apparatus may be, for example, a biometric authentication apparatus that authenticates an individual by using biometric information of a living body (for example, fingertips, pupils, and the like). 
     The authentication apparatus may further include, in addition to the light-emitting device as described above, a biometric information collector. 
     The electronic apparatus may be applied to various suitable displays, light sources, lighting, personal computers (for example, a mobile personal computer), mobile phones, digital cameras, electronic organizers, electronic dictionaries, electronic game machines, medical instruments (for example, electronic thermometers, sphygmomanometers, blood glucose meters, pulse measurement devices, pulse wave measurement devices, electrocardiogram displays, ultrasonic diagnostic devices, and/or endoscope displays), fish finders, various suitable measuring instruments, meters (for example, meters for a vehicle, an aircraft, and/or a vessel), projectors, and/or the like. 
     Description of FIGS.  2  and  3   
       FIG.  2    is a cross-sectional view of an electronic apparatus according to an embodiment. 
     The electronic apparatus of  FIG.  2    includes a substrate  100 , a thin-film transistor (TFT), a light-emitting device, and an encapsulation portion  300  that seals the light-emitting device. 
     The substrate  100  may be a flexible substrate, a glass substrate, and/or a metal substrate. A buffer layer  210  may be arranged on the substrate  100 . The buffer layer  210  may prevent or reduce penetration of impurities through the substrate  100  and may provide a flat surface on the substrate  100 . 
     A TFT may be arranged on the buffer layer  210 . The TFT may include an activation layer  220 , a gate electrode  240 , a source electrode  260 , and a drain electrode  270 . 
     The activation layer  220  may include an inorganic semiconductor such as silicon or polysilicon, an organic semiconductor, or an oxide semiconductor, and may include a source region, a drain region, and a channel region. 
     A gate insulating film  230  for electrically insulating the activation layer  220  from the gate electrode  240  may be arranged on the activation layer  220 , and the gate electrode  240  may be arranged on the gate insulating film  230 . 
     An interlayer insulating film  250  may be arranged on the gate electrode  240 . 
     The interlayer insulating film  250  may be arranged between the gate electrode  240  and the source electrode  260  and between the gate electrode  240  and the drain electrode  270 , to electrically insulate them from one another. 
     The source electrode  260  and the drain electrode  270  may be arranged on the interlayer insulating film  250 . The interlayer insulating film  250  and the gate insulating film  230  may be formed to expose the source region and the drain region of the activation layer  220 , and the source electrode  260  and the drain electrode  270  may be arranged in contact (e.g., physical contact) with the exposed portions of the source region and the drain region of the activation layer  220 . 
     The TFT may be electrically connected to a light-emitting device to drive the light-emitting device, and may be protected by being covered with a passivation layer  280 . The passivation layer  280  may include an inorganic insulating film, an organic insulating film, or any combination thereof. A light-emitting device may be provided on the passivation layer  280 . The light-emitting device may include the first electrode  110 , the interlayer  130 , and the second electrode  150 . 
     The first electrode  110  may be arranged on the passivation layer  280 . The passivation layer  280  may be arranged to expose a portion of the drain electrode  270  without fully covering the drain electrode  270 , and the first electrode  110  may be arranged to be connected to the exposed portion of the drain electrode  270 . 
     A pixel defining layer  290  including an insulating material (e.g., an electrically insulating material) may be arranged on the first electrode  110 . The pixel defining layer  290  may expose a certain region of the first electrode  110 , and an interlayer  130  may be formed in the exposed region of the first electrode  110 . The pixel defining layer  290  may be a polyimide-based organic film and/or a polyacrylic-based organic film. In some embodiments, at least some layers of the interlayer  130  may extend beyond the upper portion of the pixel defining layer  290  to be arranged in the form of a common layer. 
     The second electrode  150  may be arranged on the interlayer  130 , and a capping layer  170  may be additionally formed on the second electrode  150 . The capping layer  170  may be formed to cover the second electrode  150 . 
     The encapsulation portion  300  may be arranged on the capping layer  170 . The encapsulation portion  300  may be arranged on a light-emitting device to protect the light-emitting device from moisture and/or oxygen. The encapsulation portion  300  may include: an inorganic film including silicon nitride (SiNx), silicon oxide (SiOx), indium tin oxide, indium zinc oxide, or any combination thereof; an organic film including polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyimide, polyethylene sulfonate, polyoxymethylene, polyarylate, hexamethyldisiloxane, an acrylic resin (for example, polymethyl methacrylate, polyacrylic acid, and/or the like), an epoxy-based resin (for example, aliphatic glycidyl ether (AGE), and/or the like), or any combination thereof; or any combination of the inorganic films and the organic films. 
       FIG.  3    is a cross-sectional view of an electronic apparatus according to another embodiment of the present disclosure. 
     The electronic apparatus of  FIG.  3    is substantially the same as the electronic apparatus of  FIG.  2   , except that a light-shielding pattern  500  and a functional region  400  are additionally arranged on the encapsulation portion  300 . The functional region  400  may be i) a color filter area, ii) a color conversion area, or iii) a combination of the color filter area and the color conversion area. In one or more embodiments, the light-emitting device included in the light-emitting apparatus of  FIG.  3    may be a tandem light-emitting device. 
     Manufacturing Method 
     The layers included in the hole transport region, the emission layer, and the layers included in the electron transport region may be formed in a certain region by using various suitable methods such as vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) deposition, ink-jet printing, laser-printing, laser-induced thermal imaging, and/or the like. 
     When the layers constituting the hole transport are included in the hole transport region, the emission layer, and the layers included in the electron transport region are formed by vacuum deposition, the deposition may be performed at a deposition temperature in a range of about 100° C. to about 500° C., a vacuum degree in a range of about 10 −8  torr to about 10 −3  torr, and a deposition speed in a range of about 0.01 Å/sec to about 100 Å/sec, depending on a material to be included in a layer to be formed and the structure of a layer to be formed. 
     When layers constituting the hole transport region, an emission layer, and layers constituting the electron transport region are formed by spin coating, the spin coating may be performed at a coating speed of about 2,000 rpm to about 5,000 rpm and at a heat treatment temperature of about 80° C. to about 200° C. by taking into account a material to be included in a layer to be formed and the structure of a layer to be formed. 
     General Definition of Substituents 
     The term “C 3 -C 60  carbocyclic group,” as used herein, refers to a cyclic group consisting of carbon atoms only as a ring-forming atom and having 3 to 60 carbon atoms, and the term “C 1 -C 60  heterocyclic group,” as used herein, refers to a cyclic group that has 1 to 60 carbon atoms and further has, in addition to carbon, a heteroatom as a ring-forming atom. The C 3 -C 60  carbocyclic group and the C 1 -C 60  heterocyclic group may each be a monocyclic group consisting of one ring or a polycyclic group in which two or more rings are condensed together with each other. For example, the C 1 -C 60  heterocyclic group has 3 to 61 ring-forming atoms. 
     The “cyclic group,” as used herein, may include the C 3 -C 60  carbocyclic group and the C 1 -C 60  heterocyclic group. 
     The term “π electron-rich C 3 -C 60  cyclic group,” as used herein, refers to a cyclic group that has 3 to 60 carbon atoms and does not include *—N═*′ as a ring-forming moiety, and the term “π electron-deficient nitrogen-containing C 1 -C 60  cyclic group,” as used herein, refers to a heterocyclic group that has 1 to 60 carbon atoms and includes *—N═*&#39; as a ring-forming moiety. 
     For example, 
     the C 3 -C 60  carbocyclic group may be i) a T1 group or ii) a condensed cyclic group in which two or more T1 groups are condensed together with each other (for example, a cyclopentadiene group, an adamantane group, a norbornane group, a benzene group, a pentalene group, a naphthalene group, an azulene group, an indacene group, an acenaphthylene group, a phenalene group, a phenanthrene group, an anthracene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, a perylene group, a pentaphene group, a heptalene group, a naphthacene group, a picene group, a hexacene group, a pentacene group, a rubicene group, a coronene group, an ovalene group, an indene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, an indenophenanthrene group, or an indenoanthracene group), 
     the C 1 -C 60  heterocyclic group may be i) a T2 group, ii) a condensed cyclic group in which two or more T2 groups are condensed together with each other, or iii) a condensed cyclic group in which at least one T2 group and at least one T1 group are condensed together with each other (for example, a pyrrole group, a thiophene group, a furan group, an indole group, a benzoindole group, a naphthoindole group, an isoindole group, a benzoisoindole group, a naphthoisoindole group, a benzosilole group, a benzothiophene group, a benzofuran group, a carbazole group, a dibenzosilole group, a dibenzothiophene group, a dibenzofuran group, an indenocarbazole group, an indolocarbazole group, a benzofurocarbazole group, a benzothienocarbazole group, a benzosilolocarbazole group, a benzoindolocarbazole group, a benzocarbazole group, a benzonaphthofuran group, a benzonaphthothiophene group, a benzonaphthosilole group, a benzofurodibenzofuran group, a benzofurodibenzothiophene group, a benzothienodibenzothiophene group, a pyrazole group, an imidazole group, a triazole group, an oxazole group, an isoxazole group, an oxadiazole group, a thiazole group, an isothiazole group, a thiadiazole group, a benzopyrazole group, a benzimidazole group, a benzoxazole group, a benzoisoxazole group, a benzothiazole group, a benzoisothiazole group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a benzoquinoline group, a benzoisoquinoline group, a quinoxaline group, a benzoquinoxaline group, a quinazoline group, a benzoquinazoline group, a phenanthroline group, a cinnoline group, a phthalazine group, a naphthyridine group, an imidazopyridine group, an imidazopyrimidine group, an imidazotriazine group, an imidazopyrazine group, an imidazopyridazine group, an azacarbazole group, an azafluorene group, an azadibenzosilole group, an azadibenzothiophene group, an azadibenzofuran group, and the like), 
     the π electron-rich C 3 -C 60  cyclic group may be i) a T1 group, ii) a condensed cyclic group in which two or more T1 groups are condensed together with each other, iii) a T3 group, iv) a condensed cyclic group in which two or more T3 groups are condensed together with each other, or v) a condensed cyclic group in which at least one T3 group and at least one T1 group are condensed together with each other (for example, the C 3 -C 60  carbocyclic group, a 1H-pyrrole group, a silole group, a borole group, a 2H-pyrrole group, a 3H-pyrrole group, a thiophene group, a furan group, an indole group, a benzoindole group, a naphthoindole group, an isoindole group, a benzoisoindole group, a naphthoisoindole group, a benzosilole group, a benzothiophene group, a benzofuran group, a carbazole group, a dibenzosilole group, a dibenzothiophene group, a dibenzofuran group, an indenocarbazole group, an indolocarbazole group, a benzofurocarbazole group, a benzothienocarbazole group, a benzosilolocarbazole group, a benzoindolocarbazole group, a benzocarbazole group, a benzonaphthofuran group, a benzonaphthothiophene group, a benzonaphthosilole group, a benzofurodibenzofuran group, a benzofurodibenzothiophene group, a benzothienodibenzothiophene group, and the like), 
     the π electron-deficient nitrogen-containing C 1 -C 60  cyclic group may be i) a T4 group, ii) a condensed cyclic group in which two or more T4 groups are condensed together with each other, iii) a condensed cyclic group in which at least one T4 group and at least one T1 group are condensed together with each other, iv) a condensed cyclic group in which at least one T4 group and at least one T3 group are condensed together with each other, or v) a condensed cyclic group in which at least one T4 group, at least one T1 group, and at least one T3 group are condensed together with one another (for example, a pyrazole group, an imidazole group, a triazole group, an oxazole group, an isoxazole group, an oxadiazole group, a thiazole group, an isothiazole group, a thiadiazole group, a benzopyrazole group, a benzimidazole group, a benzoxazole group, a benzoisoxazole group, a benzothiazole group, a benzoisothiazole group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a benzoquinoline group, a benzoisoquinoline group, a quinoxaline group, a benzoquinoxaline group, a quinazoline group, a benzoquinazoline group, a phenanthroline group, a cinnoline group, a phthalazine group, a naphthyridine group, an imidazopyridine group, an imidazopyrimidine group, an imidazotriazine group, an imidazopyrazine group, an imidazopyridazine group, an azacarbazole group, an azafluorene group, an azadibenzosilole group, an azadibenzothiophene group, an azadibenzofuran group, and the like), 
     the T1 group may be a cyclopropane group, a cyclobutane group, a cyclopentane group, a cyclohexane group, a cycloheptane group, a cyclooctane group, a cyclobutene group, a cyclopentene group, a cyclopentadiene group, a cyclohexene group, a cyclohexadiene group, a cycloheptene group, an adamantane group, a norbornane (or bicyclo[2.2.1]heptane) group, a norbornene group, a bicyclo[1.1.1]pentane group, a bicyclo[2.1.1]hexane group, a bicyclo[2.2.2]octane group, or a benzene group, 
     the T2 group may be a furan group, a thiophene group, a 1H-pyrrole group, a silole group, a borole group, a 2H-pyrrole group, a 3H-pyrrole group, an imidazole group, a pyrazole group, a triazole group, a tetrazole group, an oxazole group, an isoxazole group, an oxadiazole group, a thiazole group, an isothiazole group, a thiadiazole group, an azasilole group, an azaborole group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a tetrazine group, a pyrrolidine group, an imidazolidine group, a dihydropyrrole group, a piperidine group, a tetrahydropyridine group, a dihydropyridine group, a hexahydropyrimidine group, a tetrahydropyrimidine group, a dihydropyrimidine group, a piperazine group, a tetrahydropyrazine group, a dihydropyrazine group, a tetrahydropyridazine group, or a dihydropyridazine group, 
     the T3 group may be a furan group, a thiophene group, a 1H-pyrrole group, a silole group, or a borole group, and 
     the T4 group may be a 2H-pyrrole group, a 3H-pyrrole group, an imidazole group, a pyrazole group, a triazole group, a tetrazole group, an oxazole group, an isoxazole group, an oxadiazole group, a thiazole group, an isothiazole group, a thiadiazole group, an azasilole group, an azaborole group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, or a tetrazine group. 
     The terms “the cyclic group,” “the C 3 -C 60  carbocyclic group,” “the C 1 -C 60  heterocyclic group,” “the π electron-rich C 3 -C 60  cyclic group,” or “the π electron-deficient nitrogen-containing C 1 -C 60  cyclic group,” as used herein, refer to a group condensed to any cyclic group, a monovalent group, or a polyvalent group (for example, a divalent group, a trivalent group, a tetravalent group, and the like) according to the structure of a formula for which the corresponding term is used. For example, the “benzene group” may be a benzo group, a phenyl group, a phenylene group, or the like, which may be easily understood by one of ordinary skill in the art according to the structure of a formula including the “benzene group.” 
     Examples of the monovalent C 3 -C 60  carbocyclic group and the monovalent C 1 -C 60  heterocyclic group may include a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group. Examples of the divalent C 3 -C 60  carbocyclic group and the divalent C 1 -C 60  heterocyclic group may include a C 3 -C 10  cycloalkylene group, a C 1 -C 10  heterocycloalkylene group, a C 3 -C 10  cycloalkenylene group, a C 1 -C 10  heterocycloalkenylene group, a C 6 -C 60  arylene group, a C 1 -C 60  heteroarylene group, a divalent non-aromatic condensed polycyclic group, and a divalent non-aromatic condensed heteropolycyclic group. 
     The term “C 1 -C 60  alkyl group,” as used herein, refers to a linear or branched aliphatic hydrocarbon monovalent group that has 1 to 60 carbon atoms, and examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, a tert-pentyl group, a neopentyl group, an isopentyl group, a sec-pentyl group, a 3-pentyl group, a sec-isopentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an n-heptyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an n-octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an n-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an n-decyl group, an isodecyl group, a sec-decyl group, a tert-decyl group, and the like. The term “C 1 -C 60  alkylene group,” as used herein, refers to a divalent group having substantially the same structure as the C 1 -C 60  alkyl group. 
     The term “C 2 -C 60  alkenyl group,” as used herein, refers to a monovalent hydrocarbon group having at least one carbon-carbon double bond at a main chain (e.g., in the middle) or at a terminal end (e.g., the terminus) of the C 2 -C 60  alkyl group, and examples thereof include an ethenyl group, a propenyl group, a butenyl group, and the like. The term “C 2 -C 60  alkenylene group,” as used herein, refers to a divalent group having substantially the same structure as the C 2 -C 60  alkenyl group. 
     The term “C 2 -C 60  alkynyl group,” as used herein, refers to a monovalent hydrocarbon group having at least one carbon-carbon triple bond at a main chain (e.g., in the middle) or at a terminal end (e.g., the terminus) of the C 2 -C 60  alkyl group, and examples thereof include an ethynyl group, a propynyl group, and the like. The term “C 2 -C 60  alkynylene group,” as used herein, refers to a divalent group having substantially the same structure as the C 2 -C 60  alkynyl group. 
     The term “C 1 -C 60  alkoxy group,” as used herein, refers to a monovalent group represented by —OA 101  (wherein A 101  is the C 1 -C 60  alkyl group), and examples thereof include a methoxy group, an ethoxy group, an isopropyloxy group, and the like. 
     The term “C 3 -C 10  cycloalkyl group,” as used herein, refers to a monovalent saturated hydrocarbon cyclic group having 3 to 10 carbon atoms, and examples thereof include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group (or a bicyclo[2.2.1]heptyl group), a bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, a bicyclo[2.2.2]octyl group, and the like. The term “C 3 -C 10  cycloalkylene group,” as used herein, refers to a divalent group having substantially the same structure as the C 3 -C 10  cycloalkyl group. 
     The term “C 1 -C 10  heterocycloalkyl group,” as used herein, refers to a monovalent cyclic group of 1 to 10 carbon atoms, further including, in addition to carbon atoms, at least one heteroatom, as ring-forming atoms, and examples thereof include a 1,2,3,4-oxatriazolidinyl group, a tetrahydrofuranyl group, a tetrahydrothiophenyl group, and the like. The term “C 1 -C 10  heterocycloalkylene group,” as used herein, refers to a divalent group having substantially the same structure as the C 1 -C 10  heterocycloalkyl group. 
     The term “C 3 -C 10  cycloalkenyl group,” as used herein, refers to a monovalent cyclic group that has three to ten carbon atoms and at least one carbon-carbon double bond in the ring thereof and no aromaticity (e.g., is not aromatic), and examples thereof include a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, and the like. The term “C 3 -C 10  cycloalkenylene group,” as used herein, refers to a divalent group having substantially the same structure as the C 3 -C 10  cycloalkenyl group. 
     The term “C 1 -C 10  heterocycloalkenyl group,” as used herein, refers to a monovalent cyclic group of 1 to 10 carbon atoms, further including, in addition to carbon atoms, at least one heteroatom, as ring-forming atoms, and having at least one carbon-carbon double bond in the cyclic structure thereof. Examples of the C 1 -C 10  heterocycloalkenyl group are a 4,5-dihydro-1,2,3,4-oxatriazolylgroup, a 2,3-dihydrofuranyl group, a 2,3-dihydrothiophenyl group, and the like. The term “C 1 -C 10  heterocycloalkenylene group,” as used herein, refers to a divalent group having substantially the same structure as the C 1 -C 10  heterocycloalkenyl group. 
     The term “C 6 -C 60  aryl group,” as used herein, refers to a monovalent group having a carbocyclic aromatic system of 6 to 60 carbon atoms, and the term “C 6 -C 60  arylene group” as used herein refers to a divalent group having a carbocyclic aromatic system of 6 to 60 carbon atoms. Examples of the C 6 -C 60  aryl group are a phenyl group, a pentalenyl group, a naphthyl group, an azulenyl group, an indacenyl group, an acenaphthyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a perylenyl group, a pentaphenyl group, a heptalenyl group, a naphthacenyl group, a picenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, and the like. When the C 6 -C 60  aryl group and the C 6 -C 60  arylene group each include two or more rings, the two or more rings may be condensed together with each other. 
     The term “C 1 -C 60  heteroaryl group,” as used herein, refers to a monovalent group having a heterocyclic aromatic system of 1 to 60 carbon atoms, further including, in addition to carbon atoms, at least one heteroatom, as ring-forming atoms. The term “C 1 -C 60  heteroarylene group,” as used herein, refers to a divalent group having a heterocyclic aromatic system of 1 to 60 carbon atoms, further including, in addition to carbon atoms, at least one heteroatom, as ring-forming atoms. Examples of the C 1 -C 60  heteroaryl group are a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, a benzoquinolinyl group, an isoquinolinyl group, a benzoisoquinolinyl group, a quinoxalinyl group, a benzoquinoxalinyl group, a quinazolinyl group, a benzoquinazolinyl group, a cinnolinyl group, a phenanthrolinyl group, a phthalazinyl group, a naphthyridinyl group, and the like. When the C 1 -C 60  heteroaryl group and the C 1 -C 60  heteroarylene group each include two or more rings, the rings may be condensed together with each other. 
     The term “monovalent non-aromatic condensed polycyclic group,” as used herein, refers to a monovalent group (for example, having 8 to 60 carbon atoms) having two or more rings condensed to each other, only carbon atoms as ring-forming atoms, and no aromaticity in its entire molecular structure (e.g., is not aromatic when considered as a whole). Examples of the monovalent non-aromatic condensed polycyclic group are an indenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, an indenophenanthrenyl group, and an indeno anthracenyl group. The term “divalent non-aromatic condensed polycyclic group,” as used herein, refers to a divalent group having substantially the same structure as the monovalent non-aromatic condensed polycyclic group described above. 
     The term “monovalent non-aromatic condensed heteropolycyclic group,” as used herein, refers to a monovalent group (for example, having 1 to 60 carbon atoms) having two or more rings condensed to each other, further including, in addition to carbon atoms, at least one heteroatom, as ring-forming atoms, and having non-aromaticity in its entire molecular structure (e.g., is not aromatic when considered as a whole). Examples of the monovalent non-aromatic condensed heteropolycyclic group are a pyrrolyl group, a thiophenyl group, a furanyl group, an indolyl group, a benzoindolyl group, a naphthoindolyl group, an isoindolyl group, a benzoisoindolyl group, a naphthoisoindolyl group, a benzosilolyl group, a benzothiophenyl group, a benzofuranyl group, a carbazolyl group, a dibenzosilolyl group, a dibenzothiophenyl group, a dibenzofuranyl group, an azacarbazolyl group, an azafluorenyl group, an azadibenzosilolyl group, an azadibenzothiophenyl group, an azadibenzofuranyl group, a pyrazolyl group, an imidazolyl group, a triazolyl group, a tetrazolyl group, an oxazolyl group, an isoxazolyl group, a thiazolyl group, an isothiazolyl group, an oxadiazolyl group, a thiadiazolyl group, a benzopyrazolyl group, a benzimidazolyl group, a benzoxazolyl group, a benzothiazolyl group, a benzoxadiazolyl group, a benzothiadiazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, an imidazotriazinyl group, an imidazopyrazinyl group, an imidazopyridazinyl group, an indeno carbazolyl group, an indolocarbazolyl group, a benzofurocarbazolyl group, a benzothienocarbazolyl group, a benzosilolocarbazolyl group, a benzoindolocarbazolyl group, a benzocarbazolyl group, a benzonaphthofuranyl group, a benzonaphthothiophenyl group, a benzonaphthosilolyl group, a benzofurodibenzofuranyl group, a benzofurodibenzothiophenyl group, a benzothienodibenzothiophenyl group, and the like. The term “divalent non-aromatic condensed heteropolycyclic group,” as used herein, refers to a divalent group having substantially the same structure as the monovalent non-aromatic condensed heteropolycyclic group described above. 
     The term “C 6 -C 60  aryloxy group,” as used herein, indicates —OA 102  (wherein A 102  is the C 6 -C 60  aryl group), and the term “C 6 -C 60  arylthio group,” as used herein, indicates —SA 103  (wherein A 103  is the C 6 -C 60  aryl group). 
     The term “C 7 -C 60  arylalkyl group,” as used herein, refers to -A 104 A 105  (where A 104  is a C 1 C 54  alkylene group, and A 105  is a C 6 -C 59  aryl group), and the term “C 2 -C 60  heteroarylalkyl group,” as used herein, refers to -A 106 A 107  (where A 106  is a C 1 -C 59  alkylene group, and A 107  is a C 1 -C 59  heteroaryl group). 
     The term “R 10a ,” as used herein, may be: 
     deuterium, —F, —Cl, —Br, a hydroxyl group, a cyano group, or a nitro group; 
     a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, or a C 1 -C 60  alkoxy group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, a hydroxyl group, a cyano group, a nitro group, a C 3 -C 60  carbocyclic group, a C 1 -C 60  heterocyclic group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 7 -C 60  arylalkyl group, a C 2 -C 60  heteroarylalkyl group, —Si(Q 11 )(Q 12 )(Q 13 ), —N(Q 11 )(Q 12 ), —B(Q 11 )(Q 12 ), —C(═O)(Q 11 ), —S(═O) 2 (Q 11 ), —P(═O)(Q 11 )(Q 12 ), or any combination thereof; 
     a C 3 -C 60  carbocyclic group, a C 1 -C 60  heterocyclic group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 7 -C 60  arylalkyl group, or a C 2 -C 60  heteroarylalkyl group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 3 -C 60  carbocyclic group, a C 1 -C 60  heterocyclic group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 7 -C 60  arylalkyl group, a C 2 -C 60  heteroarylalkyl group, —Si(Q 21 )(Q 22 )(Q 23 ), —N(Q 21 )(Q 22 ), —B(Q 21 )(Q 22 ), —C(═O)(Q 21 ), —S(═O) 2 (Q 21 ), —P(═O)(Q 21 )(Q 22 ), or any combination thereof; or 
     —Si(Q 31 )(Q 32 )(Q 33 ), —N(Q 31 )(Q 32 ), —B(Q 31 )(Q 32 ), —C(═O)(Q 31 ), —S(═O) 2 (Q 31 ), or —P(═O)(Q 31 )(Q 32 ). 
     In the present specification, Q 1  to Q 3 , Q 11  to Q 13 , Q 21  to Q 23 , and Q 31  to Q 33  may each independently be: hydrogen; deuterium; —F; —Cl; —Br; —I; a hydroxyl group; a cyano group; a nitro group; a C 1 -C 60  alkyl group; a C 2 -C 60  alkenyl group; a C 2 -C 60  alkynyl group; a C 1 -C 60  alkoxy group; or a C 3 -C 60  carbocyclic group; a C 1 -C 60  heterocyclic group; a C 7 -C 60  arylalkyl group; a C 2 -C 60  heteroarylalkyl group unsubstituted or substituted with deuterium, —F, a cyano group, a C 1 -C 60  alkyl group, a C 1 -C 60  alkoxy group, a phenyl group, a biphenyl group, or any combination thereof. 
     The term “heteroatom,” as used herein, refers to any atom other than a carbon atom. Examples of the heteroatom are O, S, N, P, Si, B, Ge, Se, or any combinations thereof. 
     The term “the third-row transition metal,” as used herein, includes hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), and the like. 
     “Ph,” as used herein, refers to a phenyl group, “Me,” as used herein, refers to a methyl group, “Et,” as used herein, refers to an ethyl group, “ter-Bu” or “Bu t ,” as used herein, refers to a tert-butyl group, and “OMe,” as used herein, refers to a methoxy group. 
     The term “biphenyl group,” as used herein, refers to “a phenyl group substituted with a phenyl group.” In other words, the “biphenyl group” is a substituted phenyl group having a C 6 -C 60  aryl group as a substituent. 
     The term “terphenyl group,” as used herein, refers to “a phenyl group substituted with a biphenyl group.” In other words, the “terphenyl group” is a substituted phenyl group having, as a substituent, a C 6 -C 60  aryl group substituted with a C 6 -C 60  aryl group. 
     The maximum number of carbon atoms in this substituent definition section is an example only. In an embodiment, the maximum carbon number of 60 in the C 1 -C 60  alkyl group is an example, and the definition of the alkyl group is equally applied to a C 1 -C 20  alkyl group. The same applies to other cases. 
     * and *′, as used herein, unless defined otherwise, each refer to a binding site to a neighboring atom in a corresponding formula. 
     Hereinafter, a compound and light-emitting device according to embodiments will be described in more detail with reference to Examples. 
     EXAMPLES 
     Manufacture of Light-Emitting Device 
     Comparative Example 1 
     A glass substrate (anode, ITO 300 Å/Ag 50 Å/ITO 300 Å) was cut to a size of 50 mm×50 mm×0.7 mm, cleaned by sonication with isopropyl alcohol and pure water each for 5 minutes, cleaned by irradiation of ultraviolet rays and exposure of ozone thereto for 30 minutes, and then loaded into a vacuum deposition apparatus. 
     HAT-CN was vacuum-deposited on the glass substrate to form a hole injection layer having a thickness of 150 Å. Subsequently, NPB as a hole-transporting compound was vacuum-deposited on the hole injection layer to form a hole transport layer having a thickness of 600 Å. 
     TCTA was vacuum-deposited on the hole transport layer to form an electron-blocking layer having a thickness of 100 Å. 
     CBP and H125 as hosts and PD43 as a dopant were deposited on the electron-blocking layer to form an emission layer having a thickness of 400 Å (wherein a weight ratio of CBP to H125 was 5:5, and a doping ratio of the dopant was 5 wt % based on 100 parts by weight of the sum of CBP and H125). 
     H125 was vacuum-deposited on the emission layer to form a hole-blocking layer having a thickness of 100 Å. 
     TPM-TAZ and LiQ were deposited at a weight ratio of 5:5 on the hole-blocking layer to form an electron transport layer having a thickness of 300 Å. 
     Yb was vacuum-deposited on the electron transport layer to a thickness of 10 Å, and subsequently, AgMg was vacuum-deposited thereon to a thickness of 100 Å (wherein a doping ratio of Mg was 5 wt %) to form a cathode. Then, CP1 was deposited on the cathode to form a capping layer having a thickness of 700 Å, thereby completing the manufacture of a light-emitting device. 
     Comparative Example 2 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 1, except that H40 as a host and PD43 as a dopant were deposited on the electron-blocking layer to form an emission layer having a thickness of 400 Å (wherein a doping ratio was 5 wt %). 
     Comparative Example 3 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 1, except that, in forming an emission layer, CBP and H125 as hosts were deposited on the electron-blocking layer to form a first layer having a thickness of 200 Å (wherein a weight ratio of CBP to H125 was 5:5), fac-Ir(dfpypy) 3  was deposited on the first layer to form a dopant layer having a thickness of 2 Å, and subsequently, CBP and H125 were deposited on the dopant layer to form a second layer having a thickness of 200 Å (wherein a weight ratio of CBP to H125 was 5:5). 
     Comparative Example 4 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 3, except that PD43 was used to form a dopant layer having a thickness of 12 Å. 
     Comparative Example 5 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 3, except that a dopant layer was formed by using PD43 to a thickness of 10 nm. 
     Example 1 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 1, except that, in forming an emission layer, CBP and H125 as hosts were deposited on the electron-blocking layer to form a first layer having a thickness of 200 Å (wherein a weight ratio of CBP to H125 was 5:5), PD43 was deposited on the first layer to form a dopant layer having a thickness of 1 Å, and subsequently, CBP and H125 were deposited on the dopant layer to form a second layer having a thickness of 200 Å (wherein a weight ratio of CBP to H125 was 5:5). 
     Example 2 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 1, except that, in forming an emission layer, H40 as a host was deposited on the electron-blocking layer to form a first layer having a thickness of 200 Å, PD43 was deposited on the first layer to form a dopant layer having a thickness of 1 Å, and subsequently, H40 was deposited on the dopant layer to form a second layer having a thickness of 200 Å. 
     Example 3 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 1, except that, in forming an emission layer, H40 as a host was deposited on the electron-blocking layer to form a first layer having a thickness of 200 Å, PD43 was deposited on the first layer to form a dopant layer having a thickness of 1 Å, and subsequently, CBP and H125 were deposited on the dopant layer to form a second layer having a thickness of 200 Å (wherein a weight ratio of CBP to H125 was 5:5). 
     Example 4 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 1, except that, in forming an emission layer, CBP and H125 as hosts were deposited on the electron-blocking layer to form a first layer having a thickness of 200 Å (wherein a weight ratio of CBP to H125 was 5:5), PD43 was deposited on the first layer to form a dopant layer having a thickness of 1 Å, and subsequently, H40 was deposited on the dopant layer to form a second layer having a thickness of 200 Å. 
     Example 5 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 1, except that, in forming an emission layer, CBP and H125 as hosts were deposited on the electron-blocking layer to form a first layer having a thickness of 200 Å (wherein a weight ratio of CBP to H125 was 5:5), PD43 was deposited on the first layer to form a dopant layer having a thickness of 2 Å, and subsequently, CBP and H125 were deposited on the dopant layer to form a second layer having a thickness of 200 Å (wherein a weight ratio of CBP to H125 was 5:5). 
     Example 6 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 1, except that, in forming an emission layer, H40 as a host was deposited on the electron-blocking layer to form a first layer having a thickness of 200 Å, PD43 was deposited on the first layer to form a dopant layer having a thickness of 2 Å, and subsequently, H40 was deposited on the dopant layer to form a second layer having a thickness of 200 Å. 
     Example 7 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 1, except that, in forming an emission layer, H40 as a host was deposited on the electron-blocking layer to form a first layer having a thickness of 200 Å, PD43 was deposited on the first layer to form a dopant layer having a thickness of 2 Å, and subsequently, CBP and H125 were deposited on the dopant layer to form a second layer having a thickness of 200 Å (wherein a weight ratio of CBP to H125 was 5:5). 
     Example 8 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 1, except that, in forming an emission layer, CBP and H125 as hosts were deposited on the electron-blocking layer to form a first layer having a thickness of 200 Å (wherein a weight ratio of CBP to H125 was 5:5), PD43 was deposited on the first layer to form a dopant layer having a thickness of 2 Å, and subsequently, H40 was deposited on the dopant layer to form a second layer having a thickness of 200 Å. 
     To evaluate characteristics of each of the light-emitting devices manufactured according to Comparative Examples 1 to 5 and Examples 1 to 8, current density, current efficiency, quantum efficiency, and power efficiency were measured, and results thereof are shown in Table 1. 
     The efficiency of the light-emitting device was measured by using a measurement device C9920-2-12 manufactured by Hamamatsu Photonics Inc. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Current 
                 Current 
                 Quantum 
                 Power 
               
               
                   
                 density 
                 efficiency 
                 efficiency 
                 efficiency 
               
               
                   
                 (mA/cm 2 ) 
                 (cd/A) 
                 (%) 
                 (lm/W) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Comparative 
                 1.7 
                 22 
                 4 
                 10 
               
               
                 Example 1 
               
               
                 Comparative 
                 1.5 
                 20 
                 3 
                 9 
               
               
                 Example 2 
               
               
                 Comparative 
                 1.0 
                 15 
                 2 
                 5 
               
               
                 Example 3 
               
               
                 Comparative 
                 1.6 
                 21 
                 3 
                 9 
               
               
                 Example 4 
               
               
                 Comparative 
                 0.5 
                 5 
                 0.8 
                 0.9 
               
               
                 Example 5 
               
               
                 Example 1 
                 3.2 
                 44 
                 9 
                 24 
               
               
                 Example 2 
                 3.2 
                 44 
                 9 
                 24 
               
               
                 Example 3 
                 3.3 
                 45 
                 10 
                 25 
               
               
                 Example 4 
                 3.2 
                 44 
                 9 
                 24 
               
               
                 Example 5 
                 3.0 
                 43 
                 8 
                 23 
               
               
                 Example 6 
                 3.2 
                 44 
                 9 
                 24 
               
               
                 Example 7 
                 3.1 
                 43 
                 8 
                 24 
               
               
                 Example 8 
                 3.0 
                 42 
                 9 
                 23 
               
               
                   
               
            
           
         
       
     
     The hosts were doped with the dopant in Comparative Examples 1 and 2, the Ir complex was used to form the dopant layer in Comparative Example 3, and the thickness of the dopant layer was 10 Å or more in Comparative Examples 4 and 5. 
     Referring to Table 1, it can be seen that the light-emitting devices of Examples 1 to 8 showed excellent results compared to the light-emitting devices of Comparative Examples 1 to 5. 
     As described above, according to the one more embodiments, a light-emitting device may exhibit improved efficiency as compared with other devices in the related art. 
     It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects In one or more embodiments. While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the following claims, and equivalents thereof.