Patent Publication Number: US-2023139475-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. 10-2021-0144966, filed on Oct. 27, 2021, in the Korean Intellectual Property Office, the disclosure of which is incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Field 
     One or more embodiments relate to a light-emitting device and an electronic apparatus including the same. 
     2. Description of the Related Art 
     Organic light-emitting devices are self-emissive devices that, as compared with devices of the related art, have wide viewing angles, high contrast ratios, short response times, and excellent or suitable characteristics in terms of luminance, driving voltage, and response speed, and produce full-color images. 
     Organic light-emitting devices may include a first electrode located on a substrate, and a hole transport region, an emission layer, an electron transport region, and a second electrode sequentially stacked on the first electrode. Holes provided from the first electrode may move toward the emission layer through the hole transport region, and electrons provided from the second electrode may move toward the emission layer through the electron transport region. The holes and the electrons, which are carriers, recombine in the emission layer to produce excitons. These excitons transit from an excited state to a ground state, thereby generating light. 
     SUMMARY 
     Aspects according to one or more embodiments of the present disclosure are directed toward a light-emitting device and an electronic apparatus including the same, the light-emitting device having improved efficiency and lifespan characteristics by including a certain compound combination in an emission layer. 
     Additional aspects 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, wherein 
     the interlayer includes a first emission layer and a second emission layer, 
     the first emission layer includes a first hole transport host, a first electron transport host, and a first phosphorescent dopant, 
     the second emission layer includes a second hole transport host, a second electron transport host, and a second phosphorescent dopant, and wherein 
     (i) hole mobility of the first emission layer is faster than electron mobility of the first emission layer, or 
     (ii) hole mobility of the first hole transport host in the first emission layer is faster than electron mobility of the first electron transport host in the first emission layer. 
     According to one or more embodiments, an electronic apparatus includes the light-emitting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and enhancements 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 diagram of a structure of a light-emitting device according to an embodiment; 
         FIG.  2    is a schematic diagram of a structure of a light-emitting device according to an embodiment; 
         FIG.  3    is a schematic diagram of a structure of a light-emitting device according to an embodiment; 
         FIG.  4    is a schematic diagram of a structure of a light-emitting device according to an embodiment; 
         FIG.  5    is a schematic diagram of a structure of an electronic apparatus according to an embodiment; 
         FIG.  6    is a schematic diagram of a structure of an electronic apparatus according to an embodiment; 
         FIG.  7    is a driving voltage-current density graph of a hole-only device, utilizing a host compound of a light-emitting device according to an embodiment; and 
         FIG.  8    is a driving voltage-current density graph of an electron-only device, utilizing a host compound of a light-emitting device according to an 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, and duplicative descriptions thereof may not be provided. 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, by referring to the drawings, to explain aspects of the present description. As utilized herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Throughout the disclosure, the expression “at least one of a, b or c” indicates only a, only b, only c, both (e.g., simultaneously) a and b, both (e.g., simultaneously) a and c, both (e.g., simultaneously) b and c, all of a, b, and c, or variations thereof. 
     Because the disclosure may have diverse modified embodiments, embodiments are illustrated in the drawings and are described in the detailed description. An effect and a characteristic of the disclosure, and a method of accomplishing these will be apparent when referring to embodiments described with reference to the drawings. The disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. 
     Hereinafter, embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. The same or corresponding components will be denoted by the same reference numerals, and thus redundant description thereof will not be provided. 
     It will be understood that although the terms “first,” “second,” etc. may be utilized herein to describe one or more suitable components, these components should not be limited by these terms. These components are only utilized to distinguish one component from another. 
     An expression utilized in the singular encompasses the expression of the plural, unless it has a clearly different meaning in the context. 
     As utilized herein, the terms “include”, “include”, “have”, and/or the like, specify the presence of stated features, integers, processes, operations, elements, components, and/or combinations thereof but do not preclude the presence or addition of one or more other features, integers, processes, operations, elements, components, and/or combinations thereof. 
     Sizes of elements in the drawings may be exaggerated for convenience of explanation. In other words, because sizes and thicknesses of components in the drawings are arbitrarily illustrated for convenience of explanation, the following embodiments are not limited thereto. 
     When a certain embodiment is implemented differently, a specific process order may be performed differently from the described order. For example, two processes described in succession may be performed substantially concurrently (e.g., simultaneously), or may be performed in an order opposite to the described order. 
     It will be understood that when a layer, region, or component is referred to as being “connected to” another layer, region, or component, the layer, region, or component may be directly connected to the other layer, region, or component, or indirectly connected to the other layer, region, or component with the presence of one or more intervening layers, regions, or components. For example, it will be understood that when a layer, region, or component is referred to as being “electrically connected to” another layer, region, or component, the layer, region, or component may be directly electrically connected to the other layer, region, or component, or indirectly electrically connected to the other layer, region, or component with the presence of one or more intervening layers, regions, or components. 
     The term “interlayer” as used herein refers to a single layer and/or all layers between a first electrode and a second electrode of a light-emitting device. 
     A light-emitting device according to an embodiment includes: a first electrode; 
     a second electrode facing the first electrode; and 
     an interlayer located between the first electrode and the second electrode, wherein 
     the interlayer includes a first emission layer and a second emission layer, 
     the first emission layer includes a first hole transport host, a first electron transport host, and a first phosphorescent dopant, 
     the second emission layer includes a second hole transport host, a second electron transport host, and a second phosphorescent dopant. 
     In an embodiment, (i) hole mobility of the first emission layer may be faster than electron mobility of the first emission layer. 
     Hole mobility of the first emission layer refers to hole mobility of a host material in the first emission layer. For example, hole mobility of the first emission layer may refer to hole mobility of the first hole transport host and the first electron transport host. 
     Electron mobility of the first emission layer refers to electron mobility of a host material in the first emission layer. For example, electron mobility of the first emission layer may refer to electron mobility of the first hole transport host and the first electron transport host. 
     According to an embodiment, (ii) hole mobility of the first hole transport host in the first emission layer may be faster than electron mobility of the first electron transport host in the first emission layer. 
     In the present specification, “hole mobility” of a compound (indicated as “Compound” in the structure below) was measured at a room temperature of 25° C. by driving a hole-only device (HOD) having a structure of ITO (1,500 Å)/HT3:PD1 (1 wt %) (100 Å)/HT3 (500 Å)/Compound (1,000 Å)/PD1 (100 Å)/Yb (13 Å)/Ag:Mg (10 wt %) (600 Å) by utilizing source meter units of a Keithley 2400 and a high impedance electrometer Keithley 6514, and 100 Hz was set (e.g., utilized) to measure capacitance by utilizing HP4294A. 
     In the present specification, “electron mobility” of a compound (indicated as “Compound” in the structure below) was measured at a room temperature of 25° C. by driving an electron-only device (EOD) having a structure of ITO (1,500 Å)/Ag:Mg (300 Å)/Yb (13 Å)/TPM-TAZ:LiQ (50 wt %) (300 Å)/Compound (1,000 Å)/TPM-TAZ:LiQ (50 wt %) (300 Å)/Yb (13 Å)/Ag:Mg (10 wt %) (600 Å) utilizing source meter units of a Keithley 2400 and a high impedance electrometer Keithley 6514, and 100 Hz was set (e.g., utilized) to measure capacitance by utilizing HP4294A. 
     
       
         
         
             
             
         
       
     
     In an embodiment, a “hole transport host” may be a compound including a hole transport moiety. 
     In an embodiment, an “electron transport host” may be a compound having bipolar properties as well as a compound including an electron transport moiety. 
     In the present specification, the “hole transport host” and the “electron transport host” may be understood according to relative difference between hole mobility and electron mobility. For example, even when the electron transport host does not include an electron transport moiety, a bipolar compound exhibiting relatively higher electron mobility than the hole transport host may be understood as an electron transport host. 
     In the light-emitting device, (i) hole mobility of the first emission layer is faster than electron mobility thereof, or (ii) hole mobility of the first hole transport host in the first emission layer is faster than electron mobility of the first electron transport host, and thus, hole injection characteristics may be stable, and an exciton-polaron quenching phenomenon occurring in a high field direction may be prevented or reduced. Thus, in the light-emitting device, a roll-off phenomenon may be reduced, and efficiency and lifespan characteristics may be improved. 
     In an embodiment, a ratio (HM 1 :EM 1 ) of hole mobility (HM 1 ) of the first emission layer to electron mobility (EM 1 ) of the first emission layer may satisfy a range of 2:1 to 1,000:1, for example, 5:1 to 500:1. 
     For example, hole mobility of the first emission layer may satisfy a range of 1.0×10 −5  Vs/cm 2  to 5.0×10 −2  Vs/cm 2  or 1.0×10 −5  Vs/cm 2  to 1.0×10 −2  Vs/cm 2 , and electron mobility of the first emission layer may satisfy a range of 1.0×10 −7  Vs/cm 2  to 5.0×10 −2  Vs/cm 2  or 1.0×10 −7  Vs/cm 2  to 5.0×10 −3  Vs/cm 2 . 
     In an embodiment, a ratio (HM 1A :EM 1B ) of hole mobility (HM 1A ) of the first hole transport host in the first emission layer to electron mobility (EM 1B ) of the first electron transport host in the first emission layer may satisfy a range of 2:1 to 1,000:1, for example, 5:1 to 500:1. 
     For example, hole mobility of the first hole transport host in the first emission layer may satisfy a range of 1.0×10 −5  Vs/cm 2  to 1.0×10 −2  Vs/cm 2 , and electron mobility of the first electron transport host in the first emission layer may satisfy a range of 1.0×10 −7  Vs/cm 2  to 5.0×10 −3  Vs/cm 2 . 
     In an embodiment, electron mobility of the second emission layer may be slower than electron mobility of the first emission layer. 
     Electron mobility of the second emission layer refers to electron mobility of a host material in the second emission layer. For example, electron mobility of the second emission layer may refer to electron mobility of the second hole transport host and the second electron transport host. 
     In the light-emitting device, electron mobility of the second emission layer is slower than electron mobility of the first emission layer, and thus, electron injection characteristics of the second emission layer may be lower and an energy barrier may be formed, and an exciton-polaron quenching phenomenon occurring in a high field direction may be prevented or reduced. Thus, in the light-emitting device according to one or more embodiments, a roll-off phenomenon may be reduced, and efficiency and lifespan characteristics may be improved. 
     In an embodiment, a ratio (EM 2 :EM 1 ) of electron mobility (EM 2 ) of the second emission layer to electron mobility (EM 1 ) of the first emission layer may be 1.0×10 −1  Vs/cm 2  to 1.0×10 −3  Vs/cm 2 . That is, electron mobility (EM 2 ) of the second emission layer may be slower than electron mobility (EM 1 ) of the first emission layer by 1.0×10 −1  Vs/cm 2  to 1.0×10 −3  Vs/cm 2 . 
     In an embodiment, a ratio (EM 2 :EM 1 ) of electron mobility (EM 2 ) of the second emission layer to electron mobility (EM 1 ) of the first emission layer may be 1:1,000 to 1:2, for example, 1:100 to 1:5. 
     For example, electron mobility of the second emission layer may satisfy a range of 1.0×10 −7  Vs/cm 2  to 5.0×10 −2  Vs/cm 2  or 1.0×10 −6  Vs/cm 2  to 1.0×10 −3  Vs/cm 2 , and electron mobility of the first emission layer may satisfy a range of 1.0×10 −7  Vs/cm 2  to 5.0×10 −2  Vs/cm 2 , 1.0×10 −7  Vs/cm 2  to 5.0×10 −3  Vs/cm 2  or 1.0×10 −6  Vs/cm 2  to 5.0×10 −3  Vs/cm 2 . 
     In an embodiment, the first hole transport host and the second hole transport host may be different from each other, and 
     the first electron transport host and the second electron transport host may be different from each other. 
     For example, the light-emitting device include the first hole transport host, the second hole transport host, the first electron transport host, and the second electron transport host, which have different structures, and thus, may include at least four different types (kinds) of hosts. 
     In an embodiment, the first hole transport host and the second hole transport host may satisfy Inequality 1 below: 
       0.01 eV&lt;|LUMO(HT1)|−|LUMO(HT2)|&lt;0.05 eV  Inequality 1
 
     wherein, in Inequality 1, 
     LUMO(HT1) is a lowest unoccupied molecular orbital (LUMO) level of the first hole transport host, and 
     LUMO(HT2) is a LUMO level of the second hole transport host. 
     For example, a LUMO level of the first hole transport host may be deeper than a LUMO level of the second hole transport host. 
     Also, in an embodiment, the first electron transport host and the second electron transport host may satisfy Inequality 2: 
       0.01 eV&lt;|LUMO(ET1)|−|LUMO(ET2)|&lt;0.05 eV  Inequality 2
 
     wherein, in Inequality 2, 
     LUMO(ET1) is a LUMO level of the first electron transport host, and 
     LUMO(ET2) is a LUMO level of the second electron transport host. 
     For example, a LUMO level of the first electron transport host may be deeper than a LUMO level of the second electron transport host. 
     Because the light-emitting device according to an embodiment satisfies Inequalities 1 and 2, an energy barrier may be formed in the second emission layer, and thus, an exciton-polaron quenching phenomenon occurring in a high field direction may be prevented or reduced. Thus, in the light-emitting device, a roll-off phenomenon may be reduced, and efficiency and lifespan characteristics may be improved. 
     In an embodiment, the first hole transport host and the second hole transport host may each independently be represented by one of Formulae 311-1 to 311-6, and 
     the first electron transport host and the second electron transport host may each independently be represented by one of Formulae 312-1 to 312-4 and 313: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae 311-1 to 311-6, 312-1 to 312-4, 313, and 313A, 
     Ar 301  may 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 , 
     A 301  to A 304  may each independently be a C 3 -C 60  carbocyclic group or a C 1 -C 60  heterocyclic group, 
     X 301  may be O, S, N-[(L 304 ) xb4 -R 304 ], C[(L 304 ) xb4 -R 304 ][(L 305 ) xb5 -R 305 ], or Si[(L 304 ) xb4 -R 304 ][(L 305 ) xb5 -R 305] , 
     X 302 , Y 301 , and Y 302  may each independently be a single bond, O, S, N-[(L 305 ) xb5 -R 305 ], C[(L 304 ) xb4 -R 304 ][(L 305 ) xb5 -R 305 ], Si[(L 304 ) xb4 -R 304 ][(L 305 ) xb5 -R 305 ], or S(═O) 2 , 
     xb1 to xb5 may each independently be 0, 1, 2, 3, 4, or 5, 
     xb6 may be 1, 2, 3, 4, or 5, 
     X 321  to X 328  may each independently be N or C[(L 324 )xb24-R 324 ], 
     Y 321  may be *—O—*′, *—S—*′, *—N[(L 325 ) xb25 -R 325 ]—*′, *—C[(L 325 ) xb25 -R 325 ][(L 326 ) xb26 -R 326 ]—*′, *—C[(L 325 ) xb25 -R 325 ]═C[(L 326 ) xb26 -R 326 ]—*′, *—C[(L 325 ) xb25 -R 325 ]═N—*′, or *—N═C[(L 326 ) xb26 -R 326 ]—*, 
     k21 may be 0, 1, or 2, wherein Y 321  is not present when k21 is 0, 
     xb21 to xb26 may each independently be 0, 1, 2, 3, 4, or 5, 
     A 31 , A 32 , and A 34  may each independently be a C 3 -C 60  carbocyclic group or a C 1 -C 30  heterocyclic group, 
     A 33  may be a group represented by Formula 313A, 
     X 31  may be N[(L 335 ) xb35 -(R 335 )], O, S, Se, C[(L 335 ) xb35 -(R 335 )][(L 336 ) xb36 -(R 336 )], or Si[(L 335 ) xb35 -(R 335 )][(L 336 ) xb36 -(R 336 )], 
     xb31 to xb36 may each independently be 0, 1, 2, 3, 4, or 5, 
     xb42 to xb44 may each independently be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, 
     L 301  to L 306 , L 321  to L 326 , and L 331  to L 336  may each independently be a single bond, a C 1 -C 20  alkylene group unsubstituted or substituted with at least one R 10a , a C 1 -C 20  alkenylene group unsubstituted or substituted with at least one R 10a , a C 1 -C 20  alkynylene group unsubstituted or substituted with at least one R 10a , a C 3 -C 10  cycloalkylene group unsubstituted or substituted with at least one R 10a , a C 1 -C 10  heterocycloalkylene group unsubstituted or substituted with at least one R 10a , a C 3 -C 10  cycloalkenylene group unsubstituted or substituted with at least one R 10a , a C 1 -C 10  heterocycloalkenylene group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  arylene group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroarylene group unsubstituted or substituted with at least one R 10a , a divalent non-aromatic condensed polycyclic group unsubstituted or substituted with at least one R 10a , or a divalent non-aromatic condensed heteropolycyclic group unsubstituted or substituted with at least one R 10a , 
     R 301  to R 305 , R 311  to R 314 , R 321  to R 326 , and R 331  to R 336  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono 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 10  cycloalkyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 10  heterocycloalkyl group unsubstituted or substituted with at least one R 10a , a C 3 -C 10  cycloalkenyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 10  heterocycloalkenyl group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  aryl group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  aryloxy group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  arylthio group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroaryl group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroaryloxy group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroarylthio group unsubstituted or substituted with at least one R 10a , a monovalent non-aromatic condensed polycyclic group unsubstituted or substituted with at least one R 10a , a monovalent non-aromatic condensed heteropolycyclic group unsubstituted or substituted with at least one R 10a , —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 1 )(Q 2 ), —N(Q 1 )(Q 2 ), —P(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O)(Q 1 ), —S(═O) 2 (Q 1 ), —P(═O)(Q 1 )(Q 2 ), or —P(═S)(Q 1 )(Q 2 ), 
     two or more substituents of R 321  to R 324  may optionally be bonded together to form 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 10a  may be: 
     deuterium, —F, —Cl, —Br, —I, 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, —I, 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 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio 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 1 -C 60  heteroaryloxy group, or a C 1 -C 60  heteroarylthio group, each unsubstituted or substituted with 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, 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 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio 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 ), and 
     Q 1  to Q 3 , Q 11  to Q 13 , Q 21  to Q 23 , Q 31  to Q 33 , Q 41  to Q 43 , Q 301  to Q 303 , Q 321  to Q 323 , and Q 331  to Q 333  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 or a C 1 -C 60  heterocyclic group, each 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. 
     In an embodiment, Ar 301  and A 301  to A 304  may each independently be a benzene group, a naphthalene group, a phenanthrene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, an indene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, a dibenzofluorene group, an indole group, a pyridine group, a pyrimidine group, a carbazole group, a benzocarbazole group, a dibenzocarbazole group, an azacarbazole group, a furan group, a benzofuran group, a dibenzofuran group, an azadibenzofuran group, a naphthofuran group, a benzonaphthofuran group, a dinaphthofuran group, a thiophene group, a benzothiophene group, a dibenzothiophene group, an azadibenzothiophene group, a naphthothiophene group, a benzonaphthothiophene group, or a dinaphthothiophene group. 
     In an embodiment, L 301  to L 306 , L 321  to L 326 , and L 331  to L 336  may each independently be: a single bond, a phenylene group, a pentalenylene group, an indenylene group, a naphthylene group, an azulenylene group, a heptalenylene group, an indacenylene group, an acenaphthylene group, a fluorenylene group, a spiro-bifluorenylene group, a spiro-fluorene-benzofluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenalenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a naphthacenylene group, a picenylene group, a perylenylene group, a pentaphenylene group, a hexacenylene group, a pentacenylene group, a rubicenylene group, a coronenylene group, an ovalenylene group, a pyrrolylene group, a thiophenylene group, a furanylene group, an imidazolylene group, a pyrazolylene group, a thiazolylene group, an isothiazolylene group, an oxazolylene group, an isoxazolylene group, a pyridinylene group, a pyrazinylene group, a pyrimidinylene group, a pyridazinylene group, an isoindolylene group, an indolylene group, an indazolylene group, a purinylene group, a quinolinylene group, an isoquinolinylene group, a benzoquinolinylene group, a phthalazinylene group, a naphthyridinylene group, a quinoxalinylene group, a quinazolinylene group, a cinnolinylene group, a carbazolylene group, a phenanthridinylene group, an acridinylene group, a phenanthrolinylene group, a phenazinylene group, a benzimidazolylene group, a benzofuranylene group, a benzothiophenylene group, a benzoisothiazolylene group, a benzoxazolylene group, an isobenzoxazolylene group, a triazolylene group, a tetrazolylene group, an oxadiazolylene group, a triazinylene group, a dibenzofuranylene group, a dibenzothiophenylene group, dibenzosilolylene group, a benzocarbazolylene group, a dibenzocarbazolylene group, a thiadiazolylene group, an imidazopyridinylene group, or an imidazopyrimidinylene group; or 
     a phenylene group, a pentalenylene group, an indenylene group, a naphthylene group, an azulenylene group, a heptalenylene group, an indacenylene group, an acenaphthylene group, a fluorenylene group, a spiro-bifluorenylene group, a spiro-fluorene-benzofluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenalenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a naphthacenylene group, a picenylene group, a perylenylene group, a pentaphenylene group, a hexacenylene group, a pentacenylene group, a rubicenylene group, a coronenylene group, an ovalenylene group, a pyrrolylene group, a thiophenylene group, a furanylene group, an imidazolylene group, a pyrazolylene group, a thiazolylene group, an isothiazolylene group, an oxazolylene group, an isooxazolylene group, a pyridinylene group, a pyrazinylene group, a pyrimidinylene group, a pyridazinylene group, an isoindolylene group, an indolylene group, an indazolylene group, a purinylene group, a quinolinylene group, an isoquinolinylene group, a benzoquinolinylene group, a phthalazinylene group, a naphthyridinylene group, a quinoxalinylene group, a quinazolinylene group, a cinnolinylene group, a carbazolylene group, a phenanthridinylene group, an acridinylene group, a phenanthrolinylene group, a phenazinylene group, a benzimidazolylene group, a benzofuranylene group, a benzothiophenylene group, a benzoisothiazolylene group, a benzoxazolylene group, an isobenzoxazolylene group, a triazolylene group, a tetrazolylene group, an oxadiazolylene group, a triazinylene group, a dibenzofuranylene group, a dibenzothiophenylene group, a dibenzosilolylene group, a benzocarbazolylene group, a dibenzocarbazolylene group, a thiadiazolylene group, an imidazopyridinylene group, or an imidazopyrimidinylene group, each substituted with deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzoimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzoisothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolylene group, a benzocarbazolyl group, a dibenzocarbazolyl group, a thiadiazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, —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 ), —P(═O)(Q 31 )(Q 32 ), or any combination thereof, 
     wherein Q 31  to Q 33  may each independently be a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a phenyl group substituted with a C 1 -C 10  alkyl group, a biphenyl group, a terphenyl group, a naphthyl group, a pyridinyl group, a pyrimidyl group, a triazinyl group, a quinolinyl group, or an isoquinolinyl group. 
     In an embodiment, L 301  to L 306 , L 321  to L 326 , and L 331  to L 336  may each independently be a group represented by one of Formulae 3-1 to 3-26: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae 3-1 to 3-26, 
     Z 11  to Z 14  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a triazinyl group, a benzoimidazolyl group, a phenanthrolinyl group, or —Si(Q 31 )(Q 32 )(Q 33 ), 
     Q 31  to Q 33  may each independently be a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, or a naphthyl group, 
     d2 may be 0, 1, or 2, 
     d3 may be 0, 1, 2, or 3, 
     d4 may be 0, 1, 2, 3, or 4, 
     d5 may be 0, 1, 2, 3, 4, or 5, 
     d6 may be 0, 1, 2, 3, 4, 5, or 6, 
     d8 may be 0, 1, 2, 3, 4, 5, 6, 7, or 8, and 
     * and *′ each indicate a binding site to a neighboring atom. 
     In Formulae 311-1 to 311-6, 312-1 to 312-4, 313, and 313A, xb21 to xb26 and xb31 to xb36 may each independently be 0, 1, 2, 3, 4, or 5. 
     In an embodiment, xb21 to xb26 and xb31 to xb36 may each independently be 0, 1, or 2. 
     For example, xb21 to xb26 and xb31 to xb36 may each independently be 0 or 1. 
     In an embodiment, R 301  to R 305 , R 311  to R 314 , R 321  to R 324 , and R 331  to R 336  may each independently be: hydrogen, deuterium, —F —Cl, —Br, —I, a hydroxyl group, or a cyano group; 
     a C 1 -C 20  alkyl group, a C 2 -C 20  alkenyl group, a C 2 -C 20  alkynyl group, or a C 1-20  alkoxy group; 
     a C 1 -C 20  alkyl group, a C 2 -C 20  alkenyl group, a C 2 -C 20  alkynyl group, or a C 1 -C 20  alkoxy group, each substituted with deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, —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 ), —P(═O)(Q 31 )(Q 32 ), or any combination thereof; 
     a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a furanyl group, a thiophenyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzothiazolyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, or an imidazopyrimidinyl group; or 
     a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a furanyl group, a thiophenyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a benzoimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzothiazolyl group, a benzoisothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, or an imidazopyrimidinyl group, each substituted with deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, a C 2 -C 20  alkenyl group, a C 2 -C 20  alkynyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a furanyl group, a thiophenyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a benzoimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzothiazolyl group, a benzoisothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, —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 ), —P(═O)(Q 31 )(Q 32 ), or any combination thereof, 
     wherein Q 31  to Q 33  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a cyano group, a C 1 -C 20  alkyl group, a C 2 -C 20  alkenyl group, a C 2 -C 20  alkynyl group, a C 1 -C 20  alkoxy group, 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 20  aryl group, a C 1 -C 20  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, or a terphenyl group. 
     In an embodiment, R 301  to R 305 , R 311  to R 314 , R 321  to R 324 , and R 331  to R 336  may each independently be: hydrogen, deuterium, —F —Cl, —Br, —I, a hydroxyl group, or a cyano group; a C 1 -C 20  alkyl group or a C 1 -C 20  alkoxy group, each substituted with deuterium, —F, —Cl, —Br, —I, a cyano group, a phenyl group, a biphenyl group, or any combination thereof; or a group represented by one of Formulae 5-1 to 5-26 and 6-1 to 6-55: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae 5-1 to 5-26 and 6-1 to 6-55, 
     Y 31  and Y 32  may each independently be O, S, C(Z 33 )(Z 34 ), N(Z 33 ), or Si(Z 33 )(Z 34 ), 
     Z 31  to Z 34  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, a C 2 -C 20  alkenyl group, a C 2 -C 20  alkynyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyridinyl group, a pyrimidinyl group, a carbazolyl group, or a triazinyl group, 
     e2 may be 1 or 2, 
     e3 may be 1, 2, or 3, 
     e4 may be 1, 2, 3, or 4, 
     e5 may be 1, 2, 3, 4, or 5, 
     e6 may be 1, 2, 3, 4, 5, or 6, 
     e7 may be 1, 2, 3, 4, 5, 6, or 7, 
     e9 may be 1, 2, 3, 4, 5, 6, 7, 8, or 9, and 
     * indicates a binding site to a neighboring atom. 
     In an embodiment, xb42 to xb44 may each independently be 0, 1, 2, 3, 4, 5, 6, 7, or 8. 
     For example, xb42 to xb44 may each independently be 0, 1, 2, 3, or 4. 
     For example, xb42 to xb44 may each independently be 0, 1, or 2. 
     In an embodiment, the first hole transport host and the second hole transport host may each independently be selected from Compounds HH-1 to HH-21: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In an embodiment, the first electron transport host and the second electron transport host may each independently be selected from Compounds EH-1 to EH-24: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In an embodiment, the first hole transport host and the first electron transport host may form an exciplex. 
     In an embodiment, the second hole transport host and the second electron transport host may form an exciplex. 
     In an embodiment, the first phosphorescent dopant and the second phosphorescent dopant may be identical to or different from each other. 
     In an embodiment, the first phosphorescent dopant and the second phosphorescent dopant may each independently have a maximum emission wavelength of about 490 nm to about 580 nm. 
     For example, the first phosphorescent dopant and the second phosphorescent dopant may each be a green dopant. 
     In an embodiment, the first phosphorescent dopant and the second phosphorescent dopant may each independently have a maximum emission wavelength of about 510 nm to about 545 nm. 
     In an embodiment, a maximum emission wavelength of the first phosphorescent dopant may be about 520 nm to about 540 nm. 
     In an embodiment, a difference between a maximum emission wavelength of the first phosphorescent dopant and a maximum emission wavelength of the second phosphorescent dopant may be about 10 nm or less, for example, about 5 nm or less or about 3 nm or less. 
     In an embodiment, a coincidence ratio between an emission spectrum of the first phosphorescent dopant and an emission spectrum of the second phosphorescent dopant may be about 80% or more. For example, a coincidence ratio between an emission spectrum of the first phosphorescent dopant and an emission spectrum of the second phosphorescent dopant may be about 85% or more or about 90% or more and about 100% or less. 
     For example, an area of a region where an emission spectrum of the first phosphorescent dopant and an emission spectrum of the second phosphorescent dopant overlap each other may be about 80% or more of an area of an emission spectrum region of the first phosphorescent dopant. For example, an area of a region where an emission spectrum of the first phosphorescent dopant and an emission spectrum of the second phosphorescent dopant overlap each other may be about 85% or more or about 90% or more and about 100% or less of an area of an emission spectrum region of the first phosphorescent dopant. 
     In an embodiment, the first phosphorescent dopant and the second phosphorescent dopant may each independently be a compound represented by Formula 411 or 412: 
     
       
         
         
             
             
         
       
     
     In Formulae 411 and 412, 
     M 41  and M 42  may each independently be platinum (Pt), palladium (Pd), copper(Cu), silver (Ag), gold (Au), rhodium (Rh), iridium (Ir), ruthenium (Ru), osmium (Os), titanium (Ti), zirconium (Zr), hafnium (Hf), europium (Eu), terbium (Tb), or thulium (Tm); 
     n41 may be 1, 2, or 3, 
     Ln 42  may be an organic ligand, and n42 may be 0, 1, or 2, 
     Y 41  to Y 46  may each independently be N or C, 
     A 41  to A 46  may each independently be a C 3 -C 60  carbocyclic group or a C 1 -C 60  heterocyclic group, 
     T 41  to T 46  may each independently be a single bond, *—O—*′, or *—S—*′, 
     L 41  to L 45  may each independently be a single bond, *—O—*′, *—S—*′, *—C(R 47 )(R 48 )—*′, *—C(R 47 )═*′, *═C(R 47 )—*′, *—C(R 47 )═C(R 48 )—*′, —C(═O)—′, *—C(═S)—*′, *—C≡C—*′, *—B(R 47 )—*′, *—N(R 47 )—*′, *—P(R 47 )—*′, *—Si(R 47 )(R 48 )—*′, *—P(═O)(R 47 )—*′, or *—Ge(R 47 )(R 48 )—*′, 
     m41 to m45 may each independently be 0, 1, 2, or 3, 
     R 41  to R 48  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono 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 10  cycloalkyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 10  heterocycloalkyl group unsubstituted or substituted with at least one R 10a , a C 3 -C 10  cycloalkenyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 10  heterocycloalkenyl group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  aryl group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  aryloxy group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  arylthio group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroaryl group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroaryloxy group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroarylthio group unsubstituted or substituted with at least one R 10a , a monovalent non-aromatic condensed polycyclic group unsubstituted or substituted with at least one R 10a , a monovalent non-aromatic condensed heteropolycyclic group unsubstituted or substituted with at least one R 10a , —Si(Q 41 )(Q 42 )(Q 43 ), —N(Q 41 )(Q 42 ), —B(Q 41 )(Q 42 ), —C(═O)(Q 41 ), —S(═O) 2 (Q 41 ), or —P(═O)(Q 41 )(Q 42 ), 
     R 47  and R 41 ; R 47  and R 42 ; R 47  and R 43 ; or R 47  and R 44  may optionally be bonded together to form 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 , 
     b41 to b46 may each independently be 1, 2, 3, 4, 5, 6, 7, or 8, 
     * and *′ each indicate a binding site to a neighboring atom, and 
     R 10a  may be: 
     deuterium, —F, —Cl, —Br, —I, 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, —I, 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 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio 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, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio group, or a C 2 -C 60  heteroarylalkyl group, each unsubstituted or substituted with 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, 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 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio 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 ), 
     wherein Q 11  to Q 13 , Q 21  to Q 23 , Q 31  to Q 33 , and Q 41  to Q 43  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 or a C 1 -C 60  heterocyclic group, each 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. 
     In an embodiment, R 41  to R 48  may each independently be: 
     hydrogen, deuterium, —F —Cl, —Br, —I, a hydroxyl group, or a cyano group; 
     a C 1 -C 20  alkyl group, a C 2 -C 20  alkenyl group, a C 2 -C 20  alkynyl group, or a C 1-20  alkoxy group; 
     a C 1 -C 20  alkyl group, a C 2 -C 20  alkenyl group, a C 2 -C 20  alkynyl group, or a C 1 -C 20  alkoxy group, each substituted with deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, —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 ), —P(═O)(Q 31 )(Q 32 ), or any combination thereof; 
     a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a furanyl group, a thiophenyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzothiazolyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, or an imidazopyrimidinyl group; or 
     a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a furanyl group, a thiophenyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a benzoimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzothiazolyl group, a benzoisothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, or an imidazopyrimidinyl group, each substituted with deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, a C 2 -C 20  alkenyl group, a C 2 -C 20  alkynyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group, a norbornenyl group, a cyclopentenyl group, a cyclohexenyl group, a cycloheptenyl group, a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a furanyl group, a thiophenyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a benzoimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzothiazolyl group, a benzoisothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, —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 ), —P(═O)(Q 31 )(Q 32 ), or any combination thereof, 
     wherein Q 31  to Q 33  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a cyano group, a C 1 -C 20  alkyl group, a C 2 -C 20  alkenyl group, a C 2 -C 20  alkynyl group, a C 1 -C 20  alkoxy group, 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 20  aryl group, a C 1 -C 20  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, or a terphenyl group. 
     In an embodiment, R 41  to R 48  may each independently be: hydrogen, deuterium, —F —Cl, —Br, —I, a hydroxyl group, or a cyano group; a C 1 -C 20  alkyl group or a C 1 -C 20  alkoxy group, each substituted with deuterium, —F, —Cl, —Br, —I, a cyano group, a phenyl group, a biphenyl group, or any combination thereof; or a group represented by one of Formulae 5-1 to 5-26 and 6-1 to 6-55: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae 5-1 to 5-26 and 6-1 to 6-55, 
     Y 31  and Y 32  may each independently be O, S, C(Z 33 )(Z 34 ), N(Z 33 ), or Si(Z 33 )(Z 34 ), 
     Z 31  to Z 34  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, a C 2 -C 20  alkenyl group, a C 2 -C 20  alkynyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyridinyl group, a pyrimidinyl group, a carbazolyl group, or a triazinyl group, 
     e2 may be 1 or 2, 
     e3 may be 1, 2, or 3, 
     e4 may be 1, 2, 3, or 4, 
     e5 may be 1, 2, 3, 4, or 5, 
     e6 may be 1, 2, 3, 4, 5, or 6, 
     e7 may be 1, 2, 3, 4, 5, 6, or 7, 
     e9 may be 1, 2, 3, 4, 5, 6, 7, 8, or 9, and 
     * indicates a binding site to a neighboring atom. 
     In an embodiment, b41 to b46 may each independently be 1, 2, 3, 4, 5, 6, 7, or 8. 
     For example, b41 to b46 may each independently be 1, 2, 3, or 4. 
     For example, b41 to b46 may each independently be 1 or 2. 
     In an embodiment, the first phosphorescent dopant and the second phosphorescent dopant may each independently be selected from Compounds G-1 to G-12: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In an embodiment, based on 100 parts by weight of the first emission layer, an amount of the first hole transport host may be from about 0.1 parts by weight to about 99 parts by weight, for example, about 0.5 parts by weight to about 95 parts by weight, or 0.1 parts by weight to about 90 parts by weight, and an amount of the first electron transport host may be from about 0.1 parts by weight to about 99 parts by weight, for example, about 0.5 parts by weight to about 95 parts by weight, or 0.1 parts by weight to about 90 parts by weight. 
     In an embodiment, an amount of the first phosphorescent dopant may be from about 0.1 parts by weight to about 40 parts by weight, based on 100 parts by weight of the first emission layer. For example, an amount of the first phosphorescent dopant may be from about 0.5 parts by weight to about 30 parts by weight, or about 0.1 parts by weight to about 20 parts by weight, based on 100 parts by weight of the first emission layer. 
     In an embodiment, an amount of the first hole transport host and an amount of the first electron transport host may be substantially equal to each other based on a weight of the first emission layer, or an amount of the first hole transport host may be greater than an amount of the first electron transport host, or an amount of the first electron transport host may be greater than an amount of the first hole transport host. 
     In an embodiment, based on 100 parts by weight of the second emission layer, an amount of the second hole transport host may be from about 0.1 parts by weight to about 99 parts by weight, for example, about 0.5 parts by weight to about 95 parts by weight, or 0.1 parts by weight to about 90 parts by weight, and an amount of the second electron transport host may be from about 0.1 parts by weight to about 99 parts by weight, for example, about 0.5 parts by weight to about 95 parts by weight, or 0.1 parts by weight to about 90 parts by weight. 
     In an embodiment, an amount of the second phosphorescent dopant may be from about 0.1 parts by weight to about 40 parts by weight, based on 100 parts by weight of the second emission layer. For example, an amount of the second phosphorescent dopant may be from about 0.5 parts by weight to about 30 parts by weight, about 0.1 parts by weight to about 20 parts by weight, or about 0.5 parts by weight to about 15 parts by weight, based on 100 parts by weight of the second emission layer. 
     In an embodiment, an amount of the second hole transport host and an amount of the second electron transport host may be substantially equal to each other based on a weight of the second emission layer, or an amount of the second hole transport host may be greater than an amount of the second electron transport host, or an amount of the second electron transport host may be greater than an amount of the second hole transport host. 
     In an embodiment, the first emission layer and the second emission layer may be in direct contact with each other. 
     In an embodiment, the light-emitting device may be to emit green light having a maximum emission wavelength of about 490 nm to about 580 nm. 
     In an embodiment, the first electrode of the light-emitting device may be an anode, 
     the second electrode of the light-emitting device may be a cathode, 
     the interlayer may further include a hole transport region between the first electrode and the emission layer and an electron transport region between the emission layer and the second electrode, 
     the hole transport region may further include a hole injection layer, a hole transport layer, an electron blocking layer, or any combination thereof, and 
     the electron transport region may further include a hole blocking layer, an electron control layer, an electron transport layer, an electron injection layer, or any combination thereof. 
     In an embodiment, the first emission layer may be in direct contact with the hole transport region, and the second emission layer may be in direct contact with the electron transport region. 
     In an embodiment, the interlayer may include m emitting units and m−1 charge-generating units between neighboring emitting units, and 
     one of the m emitting units may include the first emission layer and the second emission layer. The first emission layer and the second emission layer are respectively the same as those described in the present specification. 
     The light-emitting device includes m−1 charge-generating units between neighboring emitting units among the m emitting units. 
     In an embodiment, an m−1 th  charge-generating unit is included between an m th  emitting unit and an m−1 th  emitting unit. m may be a natural number of 2 or more. For example, m may be a natural number from 2 to 10. 
     For example, when m is 2, a first electrode, a first emitting unit, a first charge-generating unit, and a second emitting unit may be sequentially arranged. In this case, the first emitting unit may be to emit a first-color light, the second emitting unit may be to emit a second-color light, and a maximum emission wavelength of the first-color light and a maximum emission wavelength of the second-color light may be identical to or different from each other. 
     In an embodiment, when m is 3, a first electrode, a first emitting unit, a first charge-generating unit, a second emitting unit, a second charge-generating unit, and a third emitting unit may be sequentially arranged. In this case, the first emitting unit may be to emit a first-color light, the second emitting unit may be to emit a second-color light, the third emitting unit may be to emit a third-color light, and a maximum emission wavelength of the first-color light, a maximum emission wavelength of the second-color light, and a maximum emission wavelength of the third-color light may be identical to or different from each other. 
     In an embodiment, when m is 4, a first electrode, a first emitting unit, a first charge-generating unit, a second emitting unit, a second charge-generating unit, a third emitting unit, a third charge-generating unit, and a fourth emitting unit may be sequentially arranged. In this case, the first emitting unit may be to emit a first-color light, the second emitting unit may be to emit a second-color light, the third emitting unit may be to emit a third-color light, the fourth emitting unit may be to emit a fourth-color light, and a maximum emission wavelength of the first-color light, a maximum emission wavelength of the second-color light, a maximum emission wavelength of the third-color light, and a maximum emission wavelength of the fourth-color light may be identical to or different from each other. 
     In an embodiment, a maximum emission wavelength of light emitted from at least one emitting unit among the m emitting units may be different from a maximum emission wavelength of light emitted from at least another one emitting unit among the remaining emitting units. 
     In the light-emitting device according to an embodiment, at least one of the m emitting units may include the first emission layer and the second emission layer. 
     For example, an m th  emitting unit which is the m th  closest to the first electrode may include a hole transport region, an emission region, and an electron transport region, and the emission region may include the first emission layer and the second emission layer. 
     Referring to  FIGS.  3  and  4   , among the m emitting units, an emitting unit which is the m th  closest to the first electrode may be referred to as an m th  emitting unit. 
     An emitting unit which is the closest to the first electrode among the m emitting units is referred to as a first emitting unit, an emitting unit which is the farthest from the first electrode is referred to as an m th  emitting unit, and the first emitting unit to the m th  emitting unit are sequentially arranged. For example, an m−1 th  emitting unit is arranged between the first emitting unit and the m th  emitting unit. 
     At least one of the m−1 charge-generating units may include an n-type or kind charge generation layer, a p-type or kind charge generation layer, and/or a p-type or kind hole injection layer. 
     In an embodiment, among the m−1 charge-generating units, a charge-generating unit which is the m−1 th  closest to the first electrode may be referred to as an m−1 th  charge-generating unit. 
     In an embodiment, the m−1 th  charge-generating unit may include an m−1 th  n-type or kind charge generation layer, an m−1 th  p-type or kind charge generation layer, and/or an m−1 th  p-type or kind hole injection layer. 
     For example, in the m−1 th  charge-generating unit, the m−1 th  n-type or kind charge generation layer, the m−1 th  p-type or kind charge generation layer, and the m−1 th  p-type or kind hole injection layer may be sequentially stacked. 
     In an embodiment, the m−1 th  p-type or kind charge generation layer (pCGL(m−1)) may be in direct contact with the m−1 th  n-type or kind charge generation layer (nCGL(m−1)) and the m−1 th  p-type or kind hole injection layer (pHIL(m−1)). 
     According to another embodiment, an electronic apparatus may include the light-emitting device as described above. The electronic apparatus may further include a thin-film transistor. In some embodiments, the electronic apparatus may further include a thin-film transistor including a source electrode and a drain electrode, wherein the first electrode of the light-emitting device may be electrically connected to the source electrode or the drain electrode. 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. More details for the electronic apparatus may be the same as those described in the present specification. 
     Description of FIGS.  1  to  4   
       FIGS.  1  and  2    are each 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 , and the interlayer  130  includes a first emission layer  135 A and a second emission layer  135 B. 
     Also, referring to  FIGS.  3  and  4   , the interlayer  130  of the light-emitting device  10  may include m emitting units  145 ( 1 ) . . .  145 ( m −1), and  145 ( m ), and m−1 charge-generating units  144 ( 1 ) . . .  144 ( m −1) arranged between neighboring emitting units, and one of the m emitting units  145 ( 1 ) . . .  145 ( m −1), and  145 ( m ) may include the first emission layer  135 A and the second emission layer  135 B. 
     Hereinafter, a structure of the light-emitting device  10  according to an embodiment and a method of manufacturing the light-emitting device  10  will be described in connection with  FIGS.  1  to  4   . 
     First Electrode  110   
     In  FIG.  1   , a substrate may be additionally located under the first electrode  110  or above the second electrode  150 . As the substrate, a glass substrate or a plastic substrate may be utilized. In an embodiment, the substrate may be a flexible substrate, and may include plastics with excellent or suitable 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 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. 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 combinations thereof. In an embodiment, when the first electrode  110  is a semi-transmissive electrode or a reflective electrode, magnesium (Mg), silver (Ag), aluminum (AI), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), or any combinations thereof may be utilized as a material for forming the first electrode  110 . 
     The first electrode  110  may have a single-layered structure consisting of a single layer or a multilayer 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  may be located 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 one or more metal-containing compounds such as one or more organometallic compounds, one or more inorganic materials such as quantum dots, and/or the like, in addition to one or more suitable organic materials. 
     In an embodiment, the interlayer  130  may include, i) two or more emitting units sequentially stacked between the first electrode  110  and the second electrode  150 , and ii) a charge generation layer located between the two or more emitting units. When the interlayer  130  includes two or more emitting units and a 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 including (e.g., 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 a hole injection layer, a hole transport layer, an emission auxiliary layer, an electron blocking layer, or any combination thereof. 
     For example, the hole transport region may have a multi-layered structure including a hole injection layer/hole transport layer structure, a hole injection layer/hole transport layer/emission auxiliary layer structure, a hole injection layer/emission auxiliary layer structure, a hole transport layer/emission auxiliary layer structure, or a hole injection layer/hole transport layer/electron blocking layer structure, the layers of each structure being stacked sequentially from the first electrode  110  in the respective stated order. 
     The hole transport region may include a compound represented by Formula 201, a compound represented by Formula 202, or any combination thereof: 
     
       
         
         
             
             
         
       
     
     wherein, 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 and/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. 
     In an embodiment, each of Formulae 201 and 202 may include at least one of the groups represented by Formulae CY201 to CY217: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae CY201 to CY217, R 10b  and R 10c  may each independently be the same as described with respect to 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  as described above. 
     In an embodiment, 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 an embodiment, each of Formulae 201 and 202 may include at least one of the groups represented by Formulae CY201 to CY203. 
     In an embodiment, Formula 201 may include at least one of groups represented by Formulae CY201 to CY203 and at least one of the groups represented by Formulae CY204 to CY217. 
     In an embodiment, xa1 in Formula 201 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 an embodiment, each of Formulae 201 and 202 may not include(e.g., may exclude) any of the groups represented by Formulae CY201 to CY203. 
     In an embodiment, each of Formulae 201 and 202 may not include(e.g., may exclude) any of the groups represented by Formulae CY201 to CY203, and may include at least one of the groups represented by Formulae CY204 to CY217. 
     In an embodiment, each of Formulae 201 and 202 may not include(e.g., may exclude) any of the groups represented by Formulae CY201 to CY217. 
     In an embodiment, the hole transport region may include at least one of Compounds HT1 to HT46, m-MTDATA, TDATA, 2-TNATA, NPB(NPD), p-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, satisfactory hole-transporting characteristics may be obtained without a substantial increase in driving voltage. 
     The emission auxiliary layer may increase light-emission efficiency by compensating for an optical resonance distance according to the wavelength of light emitted by an emission layer, and the electron blocking layer may block or reduce the leakage of electrons from an emission layer to a hole transport region. Materials that may be included in the hole transport region may be included in the emission auxiliary layer and the electron blocking layer. 
     p-Dopant 
     The hole transport region may further include, in addition to these materials, a charge-generation material for the improvement of 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. 
     In an embodiment, a lowest unoccupied molecular orbital (LUMO) energy level of the p-dopant may be about −3.5 eV or less. 
     In an embodiment, the p-dopant may include a quinone derivative, a cyano group-containing compound, a compound containing element EL1 and element EL2, or any combination thereof. 
     Examples of the quinone derivative may include TCNQ, F4-TCNQ, and/or the like. 
     Examples of the cyano group-containing compound may include HAT-CN, a compound represented by Formula 221, and/or 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 containing element EL1 and element EL2, element EL1 may be a metal, a metalloid, or a combination thereof, and element EL2 may be a non-metal, a metalloid, or a combination thereof. 
     Examples of the metal may include: an alkali metal (for example, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), etc.); an alkaline earth metal (for example, beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), etc.); a 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), etc.); a post-transition metal (for example, zinc (Zn), indium (In), tin (Sn), etc.); and a 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), etc.). 
     Examples of the metalloid may include silicon (Si), antimony (Sb), and tellurium (Te). 
     Examples of the non-metal may include oxygen (O) and halogen (for example, F, Cl, Br, I, etc.). 
     In an embodiment, examples of the compound containing element EL1 and element EL2 may include a metal oxide, a metal halide (for example, a metal fluoride, a metal chloride, a metal bromide, or a metal iodide), a metalloid halide (for example, a metalloid fluoride, a metalloid chloride, a metalloid bromide, or a metalloid iodide), a metal telluride, or any combination thereof. 
     Examples of the metal oxide may include tungsten oxide (for example, WO, W 2 O 3 , WO 2 , WO 3 , W 2 O 5 , etc.), vanadium oxide (for example, VO, V 2 O 3 , VO 2 , V 2 O 5 , etc.), molybdenum oxide (MoO, Mo 2 O 3 , MoO 2 , MoO 3 , Mo 2 O 5 , etc.), and rhenium oxide (for example, ReO 3 , etc.). 
     Examples of the metal halide may include an alkali metal halide, an alkaline earth metal halide, a transition metal halide, a post-transition metal halide, and a lanthanide metal halide. 
     Examples of the alkali metal halide may include LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, and CsI. 
     Examples of the alkaline earth metal halide may 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 , and BaI 2 . 
     Examples of the transition metal halide may include titanium halide (for example, TiF 4 , TiCl 4 , TiBr 4 , TiI 4 , etc.), zirconium halide (for example, ZrF 4 , ZrCl 4 , ZrBr 4 , ZrI 4 , etc.), hafnium halide (for example, HfF 4 , HfCl 4 , HfBr 4 , HfI 4 , etc.), vanadium halide (for example, VF 3 , VCl 3 , VBr 3 , VI 3 , etc.), niobium halide (for example, NbF 3 , NbCl 3 , NbBr 3 , NbI 3 , etc.), tantalum halide (for example, TaF 3 , TaCl 3 , TaBr 3 , TaI 3 , etc.), chromium halide (for example, CrF 3 , CrCl 3 , CrBr 3 , CrI 3 , etc.), molybdenum halide (for example, MoF 3 , MoCl 3 , MoBr 3 , MoI 3 , etc.), tungsten halide (for example, WF 3 , WCl 3 , WBr 3 , WI 3 , etc.), manganese halide (for example, MnF 2 , MnCl 2 , MnBr 2 , MnI 2 , etc.), technetium halide (for example, TcF 2 , TcCl 2 , TcBr 2 , TcI 2 , etc.), rhenium halide (for example, ReF 2 , ReCl 2 , ReBr 2 , ReI 2 , etc.), iron halide (for example, FeF 2 , FeCl 2 , FeBr 2 , FeI 2 , etc.), ruthenium halide (for example, RuF 2 , RuCl 2 , RuBr 2 , RuI 2 , etc.), osmium halide (for example, OsF 2 , OsCl 2 , OsBr 2 , OsI 2 , etc.), cobalt halide (for example, CoF 2 , CoCl 2 , CoBr 2 , CoI 2 , etc.), rhodium halide (for example, RhF 2 , RhCl 2 , RhBr 2 , RhI 2 , etc.), iridium halide (for example, IrF 2 , IrCl 2 , IrBr 2 , IrI 2 , etc.), nickel halide (for example, NiF 2 , NiCl 2 , NiBr 2 , NiI 2 , etc.), palladium halide (for example, PdF 2 , PdCl 2 , PdBr 2 , PdI 2 , etc.), platinum halide (for example, PtF 2 , PtCl 2 , PtBr 2 , PtI 2 , etc.), copper halide (for example, CuF, CuCl, CuBr, CuI, etc.), silver halide (for example, AgF, AgCl, AgBr, AgI, etc.), and gold halide (for example, AuF, AuCl, AuBr, AuI, etc.). 
     Examples of the post-transition metal halide may include zinc halide (for example, ZnF 2 , ZnCl 2 , ZnBr 2 , ZnI 2 , etc.), indium halide (for example, InI 3 , etc.), and tin halide (for example, SnI 2 , etc.). 
     Examples of the lanthanide metal halide may 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 , and SmI 3 . 
     Examples of the metalloid halide may include antimony halide (for example, SbCl 5 , etc.). 
     Examples of the metal telluride may include alkali metal telluride (for example, Li 2 Te, Na 2 Te, K 2 Te, Rb 2 Te, Cs 2 Te, etc.), alkaline earth metal telluride (for example, BeTe, MgTe, CaTe, SrTe, BaTe, etc.), 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, etc.), post-transition metal telluride (for example, ZnTe, etc.), and lanthanide metal telluride (for example, LaTe, CeTe, PrTe, NdTe, PmTe, EuTe, GdTe, TbTe, DyTe, HoTe, ErTe, TmTe, YbTe, LuTe, etc.). 
     Emission Layer in Interlayer  130   
     The light-emitting device according to an embodiment may include an emission layer in an interlayer. The emission layer may be the same as described above, or as described in connection with the light-emitting device. 
     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 sub-pixel. In an embodiment, the emission layer may have a stacked structure of two or more layers of a red emission layer, a green emission layer, and a blue emission layer, in which the two or more layers contact each other or are separated from each other. In an embodiment, the emission layer may include two or more materials selected from a red light-emitting material, a green light-emitting material, and a blue light-emitting material, in which the two or more materials are mixed with each other in a single layer to emit white light. 
     The emission layer may include a host and a dopant. The dopant may include a phosphorescent dopant, a fluorescent dopant, or any combination thereof. 
     An amount of the dopant in the emission layer may be from about 0.01 to about 15 parts by weight based on 100 parts by weight of the host. 
     In an embodiment, the emission layer may include a quantum dot. 
     In some embodiments, the emission layer may include a delayed fluorescence dopant. The delayed fluorescence dopant may act (e.g., serve) as a host or a dopant in the emission layer. 
     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, excellent or suitable light-emission characteristics may be obtained without a substantial increase in driving voltage. 
     Host 
     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 independently be the same as described in connection with Q 1 . 
     In an embodiment, when xb11 in Formula 301 is 2 or more, two or more of Ar 301  (s) may be linked to each other via a single bond. 
     In an embodiment, the host may include a compound represented by Formula 301-1, a compound represented by Formula 301-2, or any combination thereof: 
     
       
         
         
             
             
         
       
     
     wherein, 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 respectively the same as those described in the present specification, 
     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 independently be the same as described in connection with R 301 . 
     In an embodiment, the host may include an alkali earth metal complex, a post-transition metal complex, or any combination thereof. In an embodiment, 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 at least one of Compounds H1 to H124, 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 as a central metal. 
     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. 
     In an embodiment, the phosphorescent dopant may include an organometallic compound represented by Formula 401: 
     
       
         
         
             
             
         
       
     
     wherein, in Formulae 401 and 402, 
     M may be a transition metal (for example, iridium (Ir), platinum (Pt), palladium (Pd), osmium (Os), titanium (Ti), gold (Au), hafnium (Hf), europium (Eu), terbium (Tb), rhodium (Rh), rhenium (Re), or thulium (Tm), 
     L 401  may be a ligand represented by Formula 402, and xc1 may be 1, 2, or 3, wherein, when xc1 is two or more, two or more of L 401 (s) 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 (s) 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 independently 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 independently be the same as described in connection with Q 1 , 
     xc11 and xc12 may each independently be an integer from 0 to 10, and 
     * and *′ in Formula 402 each indicates a binding site to M in Formula 401. 
     In an embodiment, 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  in two or more of L 401 (s) may be optionally linked to each other via T 402 , which is a linking group, and two ring A 402  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 independently be the same as described in connection with T 401 . 
     L 402  in Formula 401 may be an organic ligand. In an embodiment, 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, —CN group, a phosphorus group (for example, a phosphine group, a phosphite group, etc.), or any combination thereof. 
     The phosphorescent dopant may include, for example, one of compounds PD1 to PD25, or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Fluorescent Dopant 
     The fluorescent dopant may include an amine group-containing compound, a styryl group-containing compound, or any combination thereof. 
     In an embodiment, the fluorescent dopant may include a compound represented by Formula 501: 
     
       
         
         
             
             
         
       
     
     wherein, in Formula 501, 
     Ar 501 , L 501  to L 503 , R 501 , and R 502  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 , 
     xd1 to xd3 may each independently be 0, 1, 2, or 3, and 
     xd4 may be 1, 2, 3, 4, 5, or 6. 
     In an embodiment, Ar 501  in Formula 501 may be a condensed cyclic group (for example, an anthracene group, a chrysene group, or a pyrene group) in which three or more monocyclic groups are condensed together. 
     In an embodiment, xd4 in Formula 501 may be 2. 
     For example, the fluorescent dopant may include: at least one of Compounds FD1 to FD36; DPVBi; DPAVBi; or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Delayed Fluorescence Dopant 
     The emission layer may include a delayed fluorescence dopant. 
     In the present specification, the delayed fluorescence dopant may be selected from compounds capable of emitting delayed fluorescence based on a delayed fluorescence emission mechanism. 
     The delayed fluorescence dopant included in the emission layer may act (e.g., serve) as a host or a dopant depending on the type or kind of other materials included in the emission layer. 
     In an embodiment, a difference between a triplet energy level (eV) of the delayed fluorescence dopant and a singlet energy level (eV) of the delayed fluorescence dopant may be greater than or equal to 0 eV and less than or equal to 0.5 eV. When the difference between the triplet energy level (eV) of the delayed fluorescence dopant and the singlet energy level (eV) of the delayed fluorescence dopant satisfies the above-described range, up-conversion from the triplet state to the singlet state of the delayed fluorescence dopants may effectively occur, and thus, the luminescence efficiency of the light-emitting device  10  may be improved. 
     In an embodiment, the delayed fluorescence dopant may include i) a material including at least one electron donor (for example, a π electron-rich C 3 -C 60  cyclic group, such as a carbazole group) and at least one electron acceptor (for example, a sulfoxide group, a cyano group, or a π electron-deficient nitrogen-containing C 1 -C 60  cyclic group), and ii) a material including a C 8 -C 60  polycyclic group in which two or more cyclic groups are condensed while sharing boron (B). 
     Examples of the delayed fluorescence dopant may include at least one of Compounds DF1 to DF9: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Quantum Dot 
     The emission layer may include a quantum dot. 
     In the present specification, the term “quantum dot” as used herein refers to a crystal of a semiconductor compound, and may include any suitable material capable of emitting light of one or more suitable emission wavelengths according to the size of the crystal. 
     A diameter of the quantum dot may be, for example, in a range of about 1 nm to about 10 nm. 
     The quantum dot may be synthesized by a wet chemical process, a metal organic (e.g., organometallic) chemical vapor deposition process, a molecular beam epitaxy process, and/or any similar process. 
     In the wet chemical process, a precursor material is mixed with an organic solvent to grow a quantum dot particle crystal. When the crystal grows, the organic solvent naturally acts (e.g., serves) as a dispersant coordinated on the surface of the quantum dot crystal and controls the growth of the crystal so that the growth of quantum dot particles can be controlled or selected through a low cost process, which is more easily performed than vapor deposition methods, such as metal organic chemical vapor deposition (MOCVD) and/or molecular beam epitaxy (MBE). 
     The quantum dot may include: a Group II-VI semiconductor compound; a Group III-V semiconductor compound; a Group III-VI semiconductor compound; a Group I-III-VI semiconductor compound; a Group IV-VI semiconductor compound; a Group IV element or compound; or any combination thereof. 
     Examples of the Group II-VI semiconductor compound may include: a binary compound, such as CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, and/or MgS; a ternary compound, such as CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, and/or MgZnS; a quaternary compound, such as CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, and/or HgZnSTe; or any combination thereof. 
     Examples of the Group III-V semiconductor compound may include: a binary compound, such as GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, and/or InSb; a ternary compound, such as GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InGaP, InNP, InAlP, InNAs, InNSb, InPAs, and/or InPSb; a quaternary compound, such as GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, and/or InAlPSb; or any combination thereof. In an embodiment, the Group III-V semiconductor compound may further include one or more Group II elements. Examples of the Group III-V semiconductor compound further including one or more Group II elements may include InZnP, InGaZnP, InAlZnP, and/or the like. 
     Examples of the Group III-VI semiconductor compound may include: a binary compound, such as GaS, GaSe, Ga 2 Se 3 , GaTe, InS, InSe, In 2 S 3 , In 2 Se 3 , and/or InTe; a ternary compound, such as InGaS 3 , and/or InGaSe 3 ; or any combination thereof. 
     Examples of the Group I-III-VI semiconductor compound may include: a ternary compound, such as AgInS, AgInS 2 , CuInS, CuInS 2 , CuGaO 2 , AgGaO 2 , and/or AgAlO 2 ; or any combination thereof. 
     Examples of the Group IV-VI semiconductor compound may include: a binary compound, such as SnS, SnSe, SnTe, PbS, PbSe, PbTe, and/or the like; a ternary compound, such as SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, and/or the like; a quaternary compound, such as SnPbSSe, SnPbSeTe, SnPbSTe, and/or the like; or any combination thereof. 
     The Group IV element or compound may include: a single element compound, such as Si and/or Ge; a binary compound, such as SiC and/or SiGe; or any combination thereof. 
     Each element included in a multi-element compound such as the binary compound, the ternary compound and the quaternary compound, may exist in a particle with a substantially uniform concentration or a non-substantially uniform concentration. 
     In an embodiment, the quantum dot may have a single structure or a dual core-shell structure. In the case of the quantum dot having a single structure, the concentration of each element included in the corresponding quantum dot is substantially uniform. In an embodiment, in a quantum dot with a core-shell dual structure, the material contained in the core and the material contained in the shell may be different from each other. 
     The shell of the quantum dot may act (e.g., serve) as a protective layer to prevent or reduce chemical degeneration of the core to maintain semiconductor characteristics and/or as a charging layer to impart electrophoretic characteristics to the quantum dot. The shell may be a single layer or a multi-layer. The element presented in the interface between the core and the shell of the quantum dot may have a concentration gradient that decreases toward the center of the quantum dot. 
     Examples of the shell of the quantum dot may be an oxide of metal, metalloid, and/or non-metal, a semiconductor compound, and any combination thereof. Examples of the oxide of metal, metalloid, and/or non-metal may include: a binary compound, such as SiO 2 , Al 2 O 3 , TiO 2 , ZnO, MnO, Mn 2 O 3 , Mn 3 O 4 , CuO, FeO, Fe 2 O 3 , Fe 3 O 4 , CoO, Co 3 O 4 , and/or NiO; a ternary compound, such as MgAl 2 O 4 , CoFe 2 O 4 , NiFe 2 O 4 , and/or CoMn 2 O 4 ; or any combination thereof. Examples of the semiconductor compound may include, as described herein, a Group II-VI semiconductor compound, a Group III-V semiconductor compound, a Group III-VI semiconductor compound, a Group I-III-VI semiconductor compound, a Group IV-VI semiconductor compound, or any combination thereof. In some embodiments, the semiconductor compound may include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnSeS, ZnTeS, GaAs, GaP, GaSb, HgS, HgSe, HgTe, InAs, InP, InGaP, InSb, AlAs, AlP, AlSb, or any combination thereof. 
     A full width at half maximum (FWHM) of an emission wavelength spectrum of the quantum dot may be about 45 nm or less, for example, about 40 nm or less, for example, about 30 nm or less, and within these ranges, color purity or color reproducibility may be increased. In some embodiments, because the light emitted through the quantum dot is emitted in all directions, the wide viewing angle may be improved. 
     In some embodiments, the quantum dot may be a spherical particle, a pyramidal particle, a multi-arm particle, a cubic nanoparticle, a nanotube particle, a nanowire particle, a nanofiber particle, or a nanoplate particle. 
     Because the energy band gap can be adjusted by controlling the size of the quantum dot, light having one or more suitable wavelength bands may be obtained from the quantum dot emission layer. Therefore, by utilizing quantum dots of different sizes, a light-emitting device that emits light of one or more suitable wavelengths may be implemented. In an embodiment, the size of the quantum dot may be selected to emit red, green and/or blue light. In some embodiments, the size of the quantum dot may be configured to emit white light by combining light of one or more suitable colors. 
     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 including (e.g., 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 buffer layer, a hole blocking layer, an electron control layer, an electron transport layer, an electron injection layer, or any combination thereof. 
     For example, the electron transport region may have an electron transport layer/electron injection layer structure, a hole-blocking layer/electron transport layer/electron injection layer structure, an electron control layer/electron transport layer/electron injection layer structure, or a buffer layer/electron transport layer/electron injection layer structure, with the constituting layers of each structure being sequentially stacked from an emission layer in the respective stated order. 
     In an embodiment, the electron transport region (for example, the buffer layer, the hole-blocking layer, the electron control 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. 
     In an embodiment, the electron transport region 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 independently 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 , or 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 (s) may be linked to each other via a single bond. 
     In an embodiment, Ar 601  in Formula 601 may be a substituted or unsubstituted anthracene group. 
     In an embodiment, the electron transport region may include a compound represented by Formula 601-1: 
     
       
         
         
             
             
         
       
     
     wherein, 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 independently be the same as described in connection with L 601 , 
     xe611 to xe613 may each independently be the same as described in connection with xe1, 
     R 611  to R 613  may each independently 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 . 
     In an embodiment, 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 at least 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, or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A thickness of the electron transport region may be from about 100 Å to about 5,000 Å, for example, from about 100 Å to about 4,000 Å, from about 160 Å to about 5,000 Å, or from about 160 Å to about 4,000 Å. When the electron transport region includes a buffer layer, a hole blocking layer, an electron control layer, an electron transport layer, or any combination thereof, the thickness of the buffer layer, the hole blocking layer, or the electron control layer may each independently be from about 20 Å to about 1000 Å, for example, about 30 Å to about 300 Å, and the thickness of the electron transport layer may be from about 100 Å to about 1000 Å, for example, about 150 Å to about 500 Å. When the thickness of the buffer layer, the hole blocking layer, the electron control layer, the electron transport layer, and/or the electron transport region are within these ranges, 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. A metal ion of the alkali metal complex may be a Li ion, a Na ion, a K ion, a Rb ion, or a Cs ion, and a metal ion of the 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. 
     In an embodiment, 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 be in direct contact with 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 including (e.g., 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, 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. 
     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 include one or more oxides, halides (for example, fluorides, chlorides, bromides, and/or iodides), and/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 one or more alkali metal oxides, such as Li 2 O, Cs 2 O, and/or K 2 O, alkali metal halides, such as LiF, NaF, CsF, KF, LiI, NaI, CsI, and/or KI, 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 (x is a real number satisfying the condition of 0&lt;x&lt;1), Ba x Ca 1-x O (x is a real number satisfying the condition of 0&lt;x&lt;1), and/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. In an embodiment, the rare earth metal-containing compound may include lanthanide metal telluride. Examples of the lanthanide metal telluride may 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 , and Lu 2 Te 3 . 
     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 and ii), as a ligand bonded to the metal ion, for example, a hydroxyquinoline, a hydroxyisoquinoline, a hydroxybenzoquinoline, a hydroxyacridine, a hydroxyphenanthridine, a hydroxyphenyloxazole, a hydroxyphenylthiazole, a hydroxyphenyloxadiazole, a hydroxyphenylthiadiazole, a hydroxyphenylpyridine, a hydroxyphenyl benzimidazole, a hydroxyphenylbenzothiazole, a bipyridine, a phenanthroline, a cyclopentadiene, or any combination thereof. 
     The electron injection layer may include (e.g., 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 an embodiment, the electron injection layer may further include an organic material (for example, a compound represented by Formula 601). 
     In an embodiment, the electron injection layer may include (e.g., 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 an embodiment, 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, the alkali metal, the alkaline earth metal, the rare earth metal, the alkali metal-containing compound, the alkaline earth metal-containing compound, the rare earth metal-containing compound, the alkali metal complex, the alkaline earth-metal complex, the rare earth metal complex, or any combination thereof may be homogeneously or non-homogeneously 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, and, for example, about 3 Å to about 90 Å. When the thickness of the electron injection layer is within the ranges described above, satisfactory electron injection characteristics may be obtained without a substantial increase in driving voltage. 
     Second Electrode  150   
     The second electrode  150  may be located on the interlayer  130  having a structure as described above. The second electrode  150  may be a cathode, which is an electron injection electrode, and as the material for the second electrode  150 , a metal, an alloy, an electrically conductive compound, or any combination thereof, each having a low work function, may be utilized. 
     In an embodiment, the second electrode  150  may include lithium (Li), silver (Ag), magnesium (Mg), aluminum (AI), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), ytterbium (Yb), silver-ytterbium (Ag—Yb), ITO, IZO, or a combination thereof. The second electrode  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 two or more layers. 
     Capping Layer 
     A first capping layer may be located outside the first electrode  110 , and/or a second capping layer may be located 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 this 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 this 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 this stated order. 
     In one or more embodiments, light generated in an emission layer of the interlayer  130  of the light-emitting device  10  may be extracted (e.g., emitted) 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 an emission layer of the interlayer  130  of the light-emitting device  10  may be extracted (e.g., emitted) 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  is increased, so that the emission efficiency of the light-emitting device  10  may be improved. 
     Each of the first capping layer and the second capping layer may include a material having a refractive index (at 589 nm) of 1.6 or more. 
     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. 
     At least one of the first capping layer or the second capping layer may each independently include one or more carbocyclic compounds, one or more heterocyclic compounds, one or more amine group-containing compounds, one or more porphyrin derivatives, one or more phthalocyanine derivatives, one or more naphthalocyanine derivatives, one or more alkali metal complexes, one or more alkaline earth metal complexes, or any combination thereof. The carbocyclic compound, the heterocyclic compound, and the amine group-containing compound may be optionally substituted with a substituent containing O, N, S, Se, Si, F, Cl, Br, I, or any combination thereof. 
     In an embodiment, at least one of the first capping layer or the second capping layer may each independently include an amine group-containing compound. 
     In an embodiment, at least one of the first capping layer or 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 an embodiment, at least one of the first capping layer or the second capping layer may each independently include at least one of Compounds HT28 to HT33, at least one of Compounds CP1 to CP6, β-NPB, or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Film 
     According to another embodiment, a film includes one or more of the above disclosed compounds. The film may be, for example, an optical member (or a light control member or means) (for example, a color filter, a color conversion member, a capping layer, a light extraction efficiency enhancement layer, a selective light absorbing layer, a polarizing layer, a quantum dot-containing layer, and/or like), a light-blocking member (for example, a light reflective layer, a light absorbing layer, and/or the like), and/or a protective member (for example, an insulating layer, a dielectric layer, and/or the like). 
     Electronic Apparatus 
     The light-emitting device may be included in one or more suitable electronic apparatuses. In an embodiment, the 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) a color filter and a color conversion layer. The color filter and/or the color conversion layer may be located in at least one traveling direction of light emitted from the light-emitting device. In some embodiments, the light emitted from the light-emitting device may be blue light or white light. The light-emitting device may be the same as described above. In an embodiment, the color conversion layer may include quantum dots. The quantum dot may be, for example, a quantum dot as described herein. 
     The electronic apparatus may include a first substrate. The first substrate may include a plurality of subpixel regions, the color filter may include a plurality of color filter regions respectively corresponding to the subpixel regions, and the color conversion layer may include a plurality of color conversion regions respectively corresponding to the subpixel regions. 
     A pixel-defining film may be located among (e.g., between) the subpixel regions to define each of the subpixel regions. 
     The color filter may further include a plurality of color filter regions and light-shielding patterns located among (e.g., between) the color filter regions, and the color conversion layer may include a plurality of color conversion regions and light-shielding patterns located among (e.g., between) the color conversion regions. 
     The color filter regions (or the color conversion regions) may include a first region emitting a first color light, a second region emitting a second color light, and/or a third region emitting a third color light, and the first color light, the second color light, and/or the third color light may have different maximum emission wavelengths from one another. In an embodiment, 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. In an embodiment, the color filter regions (or the color conversion regions) may include quantum dots. For example, the first region may include a red quantum dot, the second region may include a green quantum dot, and the third region may not include (e.g., may exclude) a quantum dot. The quantum dot is the same as described in the present specification. The first region, the second region, and/or the third region may each further include a scatterer. 
     In an embodiment, the light-emitting device may be to emit a first light, the first region may be to absorb the first light to emit a first first-color light, the second region may be to absorb the first light to emit second a first-color light, and the third region may be to absorb the first light to emit a third first-color light. In this regard, the first first-color light, the second first-color light, and the third first-color light may have different maximum emission wavelengths. For example, 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 light-emitting device as described above. The thin-film transistor may include a source electrode, a drain electrode, and an activation layer, wherein the source electrode or the drain electrode may be electrically connected to the first electrode or the second electrode of the light-emitting device. 
     The thin-film transistor may further include a gate electrode, a gate insulating film, etc. 
     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 and/or the color conversion layer may be located between the color filter and the light-emitting device. The sealing portion allows light from the light-emitting device to be extracted (e.g., emitted) to the outside, while concurrently (e.g., simultaneously) preventing or reducing ambient air and/or moisture from penetrating into the light-emitting device. The sealing portion may be a sealing substrate including a transparent glass substrate or a plastic substrate. The sealing portion may be a thin-film encapsulation layer including at least one layer 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 located on the sealing portion, in addition to the color filter and/or the color conversion layer, according to the usage of the electronic apparatus. The functional layers may include a touch screen layer, a polarizing layer, and/or 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 utilizing biometric information of a living body (for example, fingertips, pupils, etc.). 
     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 one or more suitable displays, light sources, lighting, personal computers (for example, a mobile personal computer), mobile phones, digital cameras, electronic diaries (e.g., 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, one or more suitable measuring instruments, meters (for example, meters for a vehicle, an aircraft, and/or a vessel), projectors, and/or the like. 
     Description of FIGS.  5  and  6   
       FIG.  5    is a cross-sectional view of a light-emitting apparatus according to an embodiment of the present disclosure. 
     The light-emitting apparatus of  FIG.  5    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, 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 located 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 and/or polysilicon, an organic semiconductor, and/or an oxide semiconductor, and may include a source region, a drain region and a channel region. 
     A gate insulating film  230  for insulating the activation layer  220  from the gate electrode  240  may be located on the activation layer  220 , and the gate electrode  240  may be located on the gate insulating film  230 . 
     An interlayer insulating film  250  is located on the gate electrode  240 . The interlayer insulating film  250  may be placed between the gate electrode  240  and the source electrode  260  to insulate the gate electrode  240  from the source electrode  260  and between the gate electrode  240  and the drain electrode  270  to insulate the gate electrode  240  from the drain electrode  270 . 
     The source electrode  260  and the drain electrode  270  may be located 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 in contact with the exposed portions of the source region and the drain region of the activation layer  220 . 
     The TFT is electrically connected to a light-emitting device to drive the light-emitting device, and is covered by 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 is provided on the passivation layer  280 . The light-emitting device may include a first electrode  110 , an interlayer  130 , and a second electrode  150 . 
     The first electrode  110  may be arranged on the passivation layer  280 . The passivation layer  280  does not completely cover the drain electrode  270  and exposes a portion of the drain electrode  270 , and the first electrode  110  is connected to the exposed portion of the drain electrode  270 . 
     A pixel-defining layer  290  containing an insulating material may be located on the first electrode  110 . The pixel-defining layer  290  exposes a 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 and/or polyacrylic organic film. In one or more embodiments, at least some layers of the interlayer  130  may extend beyond the upper portion of the pixel-defining layer  290  to be located in the form of a common layer. 
     The second electrode  150  may be located 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 located on the capping layer  170 . The encapsulation portion  300  may be located 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 a combination thereof; or a combination of the inorganic film and the organic film. 
       FIG.  6    is a cross-sectional view of a light-emitting apparatus according to an embodiment of the disclosure. 
     The light-emitting apparatus of  FIG.  6    is the same as the light-emitting apparatus of  FIG.  5   , except that a light-shielding pattern  500  and a functional region  400  are additionally located on the encapsulation portion  300 . The functional region  400  may be i) a color filter region, ii) a color conversion region, or iii) a combination of the color filter region and the color conversion region. In an embodiment, the light-emitting device included in the light-emitting apparatus of  FIG.  6    may be a tandem light-emitting device. 
     Manufacturing Method 
     Respective layers included in the hole transport region, the emission layer, and respective layers included in the electron transport region may be formed in a certain region by utilizing one or more suitable methods selected from vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) deposition, ink-jet printing, laser-printing, and laser-induced thermal imaging. 
     When respective layers included in the hole transport region, the emission layer, and respective layers included in the electron transport region are formed by vacuum deposition, the deposition may be performed at a deposition temperature of about 100° C. to about 500° C., a vacuum degree of about 10 −8  torr to about 10 −3  torr, and a deposition speed 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. 
     Definition of Terms 
     The term “C 3 -C 60  carbocyclic group” as used herein refers to a cyclic group consisting of only 3 to 60 carbon atoms as ring-forming atoms, and the term “C 1 -C 60  heterocyclic group” as used herein refers to a cyclic group that has, in addition to one to sixty carbon atoms, a heteroatom as a ring-forming atom. The C 3 -C 60  carbocyclic group and the C 1 -C 60  heterocyclic group may each independently be a monocyclic group consisting of one ring or a polycyclic group in which two or more rings are condensed with each other. In an embodiment, the C 1 -C 60  heterocyclic group has 3 to 61 ring-forming atoms. 
     The term “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 three to sixty 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 one to sixty carbon atoms and includes *—N═*′ as a ring-forming moiety. 
     In an embodiment, 
     the C 3 -C 60  carbocyclic group may be i) group T1 or ii) a condensed cyclic group in which two or more groups T1 are condensed with each other (for example, the C 3 -C 60  carbocyclic group may be 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, and/or an indenoanthracene group), 
     the C 1 -C 60  heterocyclic group may be i) group T2, ii) a condensed cyclic group in which two or more groups T2 are condensed with each other, or iii) a condensed cyclic group in which at least one group T2 and at least one group T1 are condensed with each other (for example, the C 1 -C 60  heterocyclic group may be 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, etc.), 
     the π electron-rich C 3 -C 60  cyclic group may be i) group T1, ii) a condensed cyclic group in which two or more groups T1 are condensed with each other, iii) group T3, iv) a condensed cyclic group in which two or more groups T3 are condensed with each other, or v) a condensed cyclic group in which at least one group T3 and at least one group T1 are condensed with each other (for example, the π electron-rich C 3 -C 60  cyclic group may be 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, etc.), 
     the π electron-deficient nitrogen-containing C 1 -C 60  cyclic group may be i) group T4, ii) a condensed cyclic group in which two or more group T4 are condensed with each other, iii) a condensed cyclic group in which at least one group T4 and at least one group T1 are condensed with each other, iv) a condensed cyclic group in which at least one group T4 and at least one group T3 are condensed with each other, or v) a condensed cyclic group in which at least one group T4, at least one group T1, and at least one group T3 are condensed with one another (for example, the π electron-deficient nitrogen-containing C 1 -C 60  cyclic group may be 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, etc.), 
     group T1 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 a 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, 
     group T2 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, 
     group T3 may be a furan group, a thiophene group, a 1H-pyrrole group, a silole group, or a borole group, and 
     group T4 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 term “cyclic group”, “C 3 -C 60  carbocyclic group”, “C 1 -C 60  heterocyclic group”, “π electron-rich C 3 -C 60  cyclic group”, or “π electron-deficient nitrogen-containing C 1 -C 60  cyclic group” as used herein refers 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, etc.), depending on the structure of a formula in connection with which the terms are used. In an embodiment, “a benzene group” may be a benzo group, a phenyl group, a phenylene group, and/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, and 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 one to sixty carbon atoms, and examples thereof may 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, and a tert-decyl group. The term “C 1 -C 60  alkylene group” as used herein refers to a divalent group having 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 in the middle and/or at a terminal end (e.g., the terminus) of the C 2 -C 60  alkyl group, and examples thereof may include an ethenyl group, a propenyl group, and a butenyl group. The term “C 2 -C 60  alkenylene group” as used herein refers to a divalent group having 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 in the middle and/or at a terminal end (e.g., the terminus) of the C 2 -C 60  alkyl group, and examples thereof may include an ethynyl group and a propynyl group. The term “C 2 -C 60  alkynylene group” as used herein refers to a divalent group having 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 may include a methoxy group, an ethoxy group, and an isopropyloxy group. 
     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 may 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, and a bicyclo[2.2.2]octyl group. The term “C 3 -C 10  cycloalkylene group” as used herein refers to a divalent group having 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 that further includes, in addition to 1 to 10 carbon atoms, at least one heteroatom as a ring-forming atom, and examples thereof may include a 1,2,3,4-oxatriazolidinyl group, a tetrahydrofuranyl group, and a tetrahydrothiophenyl group. The term “C 1 -C 10  heterocycloalkylene group” as used herein refers to a divalent group having 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, and examples thereof may include a cyclopentenyl group, a cyclohexenyl group, and a cycloheptenyl group. The term “C 3 -C 10  cycloalkenylene group” as used herein refers to a divalent group having 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 that has, in addition to 1 to 10 carbon atoms, at least one heteroatom as a ring-forming atom, and at least one double bond (e.g., carbon-carbon double bond) in the cyclic structure thereof. Examples of the C 1 -C 10  heterocycloalkenyl group may include a 4,5-dihydro-1,2,3,4-oxatriazolyl group, a 2,3-dihydrofuranyl group, and a 2,3-dihydrothiophenyl group. The term “C 1 -C 10  heterocycloalkenylene group” as used herein refers to a divalent group having 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 having six to sixty carbon atoms, and the term “C 6 -C 60  arylene group” as used herein refers to a divalent group having a carbocyclic aromatic system having six to sixty carbon atoms. Examples of the C 6 -C 60  aryl group may include 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, and an ovalenyl group. When the C 6 -C 60  aryl group and the C 6 -C 60  arylene group each independently include two or more rings, the rings may be condensed with each other. 
     The term “C 1 -C 60  heteroaryl group” as used herein refers to a monovalent group having a heterocyclic aromatic system that has, in addition to 1 to 60 carbon atoms, at least one heteroatom as a ring-forming atom. The term “C 1 -C 60  heteroarylene group” as used herein refers to a divalent group having a heterocyclic aromatic system that has, in addition to 1 to 60 carbon atoms, at least one heteroatom as a ring-forming atom. Examples of the C 1 -C 60  heteroaryl group may include 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 carbazolyl group, a dibenzofuranyl group, a dibenzothiophenyl group, and a naphthyridinyl group. When the C 1 -C 60  heteroaryl group and the C 1 -C 60  heteroarylene group each independently include two or more rings, the rings may be condensed with each other. 
     The term “monovalent non-aromatic condensed polycyclic group” as used herein refers to a monovalent group having two or more rings condensed to each other, only carbon atoms (for example, having 8 to 60 carbon atoms) as ring-forming atoms, and no aromaticity in its entire molecular structure when considered as a whole. Examples of the monovalent non-aromatic condensed polycyclic group may include an indenyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, an indenophenanthrenyl group, an adamantyl group, and an indeno anthracenyl group. The term “divalent non-aromatic condensed polycyclic group” as used herein refers to a divalent group having the same structure as a monovalent non-aromatic condensed polycyclic group. 
     The term “monovalent non-aromatic condensed heteropolycyclic group” as used herein refers to a monovalent group having two or more rings condensed to each other, 1 to 60 carbon atoms and at least one heteroatom as a ring-forming atom, and no aromaticity in its entire molecular structure when considered as a whole. Examples of the monovalent non-aromatic condensed heteropolycyclic group may include (e.g., may be) 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 benzonaphtho silolyl group, a benzofurodibenzofuranyl group, a benzofurodibenzothiophenyl group, and a benzothienodibenzothiophenyl group. The term “divalent non-aromatic condensed heteropolycyclic group” as used herein refers to a divalent group having the same structure as a monovalent non-aromatic condensed heteropolycyclic group. 
     The term “C 6 -C 60  aryloxy group” as used herein refers to a monovalent group represented by -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 refers to a monovalent group represented by -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 monovalent group represented by -A 104 A 105  (where A 104  may be a C 1 -C 54  alkylene group, and A 105  may be a C 6 -C 59  aryl group), and the term “C 2 -C 60  heteroarylalkyl group” as used herein refers to a monovalent group represented by -A 106 A 107  (where A 106  may be a C 1 -C 59  alkylene group, and A 107  may be a C 1 -C 59  heteroaryl group). 
     The term “R 10a ” as used herein refers to: 
     Deuterium (D), —F, —Cl, —Br, —I, 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, —I, 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, —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, 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 ). 
     Q 1  to Q 3 , Q 11  to Q 13 , Q 21  to Q 23 , and Q 31  to Q 33  as used herein 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; a C 3 -C 60  carbocyclic group or a C 1 -C 60  heterocyclic group, each 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; a C 7 -C 60  arylalkyl group; or a C 2 -C 60  heteroarylalkyl group. 
     The term “hetero atom” as used herein refers to any atom other than a carbon atom. Examples of the heteroatom may include O, S, N, P, Si, B, Ge, Se, or any combination thereof. 
     The term “the third-row transition metal” as used herein may include hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), and/or the like. 
     The term “Ph” as used herein refers to a phenyl group, the term “Me” as used herein refers to a methyl group, the term “Et” as used herein refers to an ethyl group, the term “ter-Bu,” “ t Bu, or “Bu t ” as used herein refers to a tert-butyl group, and the term “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. 
     * and *′ as used herein, unless defined otherwise, each refer to a binding site to a neighboring atom in a corresponding formula or moiety. 
     Hereinafter, a compound according to embodiments and a light-emitting device according to embodiments will be described in more detail with reference to Examples. The expression “B was utilized instead of A” used in describing Examples refers to that an identical molar equivalent of B was utilized in place of A. 
     EXAMPLES 
     Evaluation Example 1: Hole Mobility and Electron Mobility Evaluation 
     By driving a hole-only device and an electron-only device utilizing source measurement units of Keithley 2400 and high impedance electrometer Keithley 6514, the hole mobility and the electron mobility of compounds shown in Table 1 were measured at room temperature (25° C.). The results are shown in  FIGS.  7  and  8   . The structures of the hole-only device and the electron-only device utilized for evaluation are as follows. 
     Hole-Only Device 
     ITO (1,500 Å)/HT3:PD1 (1 wt %) (100 Å)/HT3 (500 Å)/Compound (1,000 Å)/PD1 (100 Å)/Yb (13 Å)/Ag:Mg (10 wt %) (600 Å) 
     Electron-Only Device 
     ITO (1,500 Å)/Ag:Mg (300 Å)/Yb (13 Å)/TPM-TAZ:LiQ (50 wt %) (300 Å)/Compound (1,000 Å)/TPM-TAZ:LiQ (50 wt %) (300 Å)/Yb (13 Å)/Ag:Mg (10 wt %) (600 Å) 
     
       
         
         
             
             
         
       
     
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Compound 
                 Hole mobility 
                 Electron mobility 
               
               
                   
                   
               
             
            
               
                   
                 HH-1 
                 3.8 × 10 −3  Vs/cm 2   
                 1.5 × 10 −6  Vs/cm 2   
               
               
                   
                 EH-8 
                 3.4 × 10 −6  Vs/cm 2   
                 2.4 × 10 −4  Vs/cm 2   
               
               
                   
                 HH-19 
                 5.6 × 10 −4  Vs/cm 2   
                 3.8 × 10 −6  Vs/cm 2   
               
               
                   
                 EH-1 
                 8.4 × 10 −6  Vs/cm 2   
                 1.1 × 10 −5  Vs/cm 2   
               
               
                   
                 HH-1 + EH-8 
                 2.3 × 10 −3  Vs/cm 2   
                 1.1 × 10 −4  Vs/cm 2   
               
               
                   
                 HH-19 + EH-1 
                 4.3 × 10 −4  Vs/cm 2   
                 1.0 × 10 −5  Vs/cm 2   
               
               
                   
                   
               
            
           
         
       
     
     Examples 1 and 2 and Comparative Examples 1 to 10 
     An ITO glass substrate was cut to a size of 50 mm×50 mm×0.7 mm, ultrasonically cleaned with isopropyl alcohol and pure water for 10 minutes each, and then cleaned by irradiation of ultraviolet rays and exposure of ozone thereto for 10 minutes. Then, the ITO glass substrate was loaded onto a vacuum deposition apparatus. First, HAT-CN was vacuum-deposited on the substrate to form a hole injection layer having a thickness of 50 Å, and then NPB and TCTA were vacuum-deposited thereon to form a hole transport layer and a hole injection layer having a thickness of 600 Å/50 Å. 
     First emission layer materials shown in Table 2 were co-deposited on the hole transport layer and the hole injection layer at a weight ratio of 5:5 to form a first emission layer having a thickness of 200 Å. Second emission layer materials shown in Table 2 were co-deposited on the first emission layer at a weight ratio of 5:5 to form a second emission layer having a thickness of 200 Å. 
     Subsequently, T2T was vacuum-deposited on the second emission layer to form a hole blocking layer having a thickness of 50 Å. TPM-TAZ was vacuum-deposited on the hole blocking layer to form an electron transport layer having a thickness of 300 Å. 
     Ag:Mg (10 wt %) were vacuum-deposited on the electron transport layer to form an Ag:Mg electrode having a thickness of 100 Å, and CPL was vacuum-deposited on the Ag:Mg (10 wt %) electrode to form a capping layer having a thickness of 700 Å, thereby completing manufacture of the light-emitting devices of Table 1. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Evaluation Example 2: Evaluation of Light-Emitting Devices of Examples 1 and 2 and Comparative Examples 1 to 10 
     The driving voltage, luminescence efficiency, and lifespan (T 95 ) of the light-emitting devices manufactured according to Examples 1 and 2 and Comparative Examples 1 to 8 were measured utilizing a Keithley SMU 236 and a luminance meter PR650, and the results are shown in Table 2. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                 Driving 
                   
                 Efficiency 
                 Efficiency 
                 Lifespan 
               
               
                   
                 Host + dopant 
                 Host_dopant 
                 voltage 
                   
                 @1,000 
                 @10,000 
                 @10,000 
               
               
                 Light- 
                 in first 
                 in second 
                 @100 nit 
                 Efficiency 
                 nit 
                 nit 
                 nit 
               
               
                 emitting 
                 emission 
                 emission 
                 (relative 
                 (relative 
                 (relative 
                 (relative 
                 (T 95 , 
               
               
                 device 
                 layer 
                 layer 
                 value) 
                 value) 
                 value) 
                 value) 
                 hour) 
               
               
                   
               
             
            
               
                 Example 
                 HH-1 + EH-8 
                 HH-19 + EH-1 
                 100% 
                 100% 
                 98% 
                 95% 
                 680 
               
               
                 1 
                 (weight ratio 
                 (weight ratio 
                   
                   
                   
                   
                   
               
               
                   
                 5:5), G-1 
                 5:5), G-2 
                   
                   
                   
                   
                   
               
               
                 Example 
                 HH-1 + EH-8 
                 HH-19 + EH-1 
                 104% 
                  93% 
                 91% 
                 87% 
                 450 
               
               
                 2 
                 (weight ratio 
                 (weight ratio 
                   
                   
                   
                   
                   
               
               
                   
                 5:5), G-2 
                 5:5), G-1 
                   
                   
                   
                   
                   
               
               
                 Compara- 
                 HH-19 + EH-1 
                 HH-1 + EH-8 
                 105% 
                 100% 
                 89% 
                 69% 
                 300 
               
               
                 tive 
                 (weight ratio 
                 (weight ratio 
                   
                   
                   
                   
                   
               
               
                 Example 
                 5:5), 
                 5:5), 
                   
                   
                   
                   
                   
               
               
                 1 
                 G-2 
                 G-1 
                   
                   
                   
                   
                   
               
               
                 Compara- 
                 HH-19 + EH-1 
                 HH-1 + EH-8 
                 105% 
                  93% 
                 82% 
                 62% 
                 250 
               
               
                 tive 
                 (weight ratio 
                 (weight ratio 
                   
                   
                   
                   
                   
               
               
                 Example 
                 5:5), 
                 5:5), 
                   
                   
                   
                   
                   
               
               
                 2 
                 G-1 
                 G-2 
                   
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Compara- 
                 HH-1 + EH-8 (weight ratio 
                 100% 
                 100% 
                 89% 
                 68% 
                 300 
               
               
                 tive 
                 5:5), 
                   
                   
                   
                   
                   
               
               
                 Example 
                 G-1 
                   
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 3 
                   
                   
                   
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Compara- 
                 HH-19 + EH-1 (weight ratio 
                 100% 
                 100% 
                 90% 
                 70% 
                 300 
               
               
                 tive 
                 5:5), 
                   
                   
                   
                   
                   
               
               
                 Example 
                 G-2 
                   
                   
                   
                   
                   
               
               
                 4 
                   
                   
                   
                   
                   
                   
               
               
                 Compara- 
                 HH-1 + EH-8 (weight ratio 
                 104% 
                  94% 
                 85% 
                 66% 
                 260 
               
               
                 tive 
                 5:5), 
                   
                   
                   
                   
                   
               
               
                 Example 
                 G-2 
                   
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 5 
                   
                   
                   
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Compara- 
                 HH-19 + EH-1 (weight ratio 
                 105% 
                  92% 
                 83% 
                 64% 
                 250 
               
               
                 tive 
                 5:5), 
                   
                   
                   
                   
                   
               
               
                 Example 
                 G-1 
                   
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 6 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Compara- 
                 HH-1 + EH-8 
                 HH-19 + EH-1 
                 100% 
                 102% 
                 98% 
                 95% 
                 610 
               
               
                 tive 
                 (weight ratio 
                 (weight ratio 
                   
                   
                   
                   
                   
               
               
                 Example 
                 3:7), 
                 5:5), 
                   
                   
                   
                   
                   
               
               
                 7 
                 G-1 
                 G-2 
                   
                   
                   
                   
                   
               
               
                 Compara- 
                 HH-1 + EH-8 
                 HH-19 + EH-1 
                 100% 
                  99% 
                 95% 
                 91% 
                 510 
               
               
                 tive 
                 (weight ratio 
                 (weight ratio 
                   
                   
                   
                   
                   
               
               
                 Example 
                 7:3), 
                 5:5), 
                   
                   
                   
                   
                   
               
               
                 8 
                 G-1 
                 G-2 
                   
                   
                   
                   
                   
               
               
                 Compara- 
                 HH-1 + EH-8 
                 HH-19 + EH-1 
                 100% 
                 100% 
                 96% 
                 94% 
                 720 
               
               
                 tive 
                 (weight ratio 
                 (weight ratio 
                   
                   
                   
                   
                   
               
               
                 Example 
                 5:5), 
                 7:3), 
                   
                   
                   
                   
                   
               
               
                 9 
                 G-1 
                 G-2 
                   
                   
                   
                   
                   
               
               
                 Compara- 
                 HH-1 + EH-8 
                 HH-19 + EH-1 
                 101% 
                  98% 
                 95% 
                 92% 
                 510 
               
               
                 tive 
                 (weight ratio 
                 (weight ratio 
                   
                   
                   
                   
                   
               
               
                 Example 
                 5:5), 
                 7:3), 
                   
                   
                   
                   
                   
               
               
                 10  
                 G-1 
                 G-2 
               
               
                   
               
               
                 
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                 
               
            
           
         
       
     
     Examples 3 and 4 and Comparative Examples 11 to 20 
     A glass substrate with a 15 Ω/cm 2  (800 Å) ITO/Ag/ITO anode formed thereon (a product of Corning Inc.) was cut to a size of 50 mm×50 mm×0.7 mm, sonicated with isopropyl alcohol and pure water for 5 minutes each, and then cleaned by irradiation of ultraviolet rays and exposure of ozone thereto for 15 minutes. The resultant glass substrate was loaded onto a vacuum deposition apparatus. 
     HAT-CN was deposited on the ITO/Ag/ITO anode of the glass substrate to form a hole injection layer having a thickness of 50 Å, NPB was deposited on the hole injection layer to form a hole transport layer having a thickness of 650 Å, TCTA was deposited on the hole transport layer to form an electron blocking layer having a thickness of 50 Å, HT56 and FD23 were co-deposited at a volume ratio of 97:3 on the electron blocking layer to form an emission layer having a thickness of 200 Å, T2T was deposited on the emission layer to form a hole blocking layer having a thickness of 50 Å, and TPM-TAZ and LiQ were co-deposited at a volume ratio of 1:1 on the hole blocking layer to form an electron transport layer having a thickness of 200 Å, thereby forming a first emitting unit. 
     BCP and Li were co-deposited at a volume ratio of 99:1 on the first emitting unit to form an n-type or kind charge generation layer having a thickness of 150 Å, and HAT-CN was deposited on the n-type or kind charge generation layer to form a p-type or kind charge generation layer having a thickness of 50 Å, thereby forming a first charge-generating unit. 
     NPB was deposited on the first charge-generating unit to form a hole transport layer having a thickness of 500 Å, TCTA was deposited on the hole transport layer to form an electron blocking layer having a thickness of 50 Å, HT56 and FD23 were co-deposited at a volume ratio of 97:3 on the electron blocking layer to form an emission layer having a thickness of 200 Å, T2T was deposited on the emission layer to form a hole blocking layer having a thickness of 50 Å, and TPM-TAZ and LiQ were co-deposited at a volume ratio of 1:1 on the hole blocking layer to form an electron transport layer having a thickness of 200 Å, thereby forming a second emitting unit. 
     BCP and Li were co-deposited at a volume ratio of 99:1 on the second emitting unit to form an n-type or kind charge generation layer having a thickness of 150 Å, and HAT-CN was deposited on the n-type or kind charge generation layer to form a p-type or kind charge generation layer having a thickness of 50 Å, thereby forming a second charge-generating unit. 
     NPB was deposited on the second charge-generating unit to form a hole transport layer having a thickness of 400 Å, TCTA was deposited on the hole transport layer to form an electron blocking layer having a thickness of 50 Å, HT56 and FD23 were co-deposited at a volume ratio of 97:3 on the electron blocking layer to form an emission layer having a thickness of 200 Å, T2T was deposited on the emission layer to form a hole blocking layer having a thickness of 50 Å, and TPM-TAZ and LiQ were co-deposited at a volume ratio of 1:1 on the hole blocking layer to form an electron transport layer having a thickness of 200 Å, thereby forming a third emitting unit. 
     BCP and Li were co-deposited at a volume ratio of 99:1 on the third emitting unit to form an n-type or kind charge generation layer having a thickness of 150 Å, and HAT-CN was deposited on the n-type or kind charge generation layer to form a p-type or kind charge generation layer having a thickness of 50 Å, thereby forming a third charge-generating unit. 
     NPB was deposited on the third charge-generating unit to form a hole transport layer having a thickness of 600 Å, TCTA was deposited on the hole transport layer to form an electron blocking layer having a thickness of 50 Å, first emission layer materials shown in Table 3 were co-deposited on the electron blocking layer to form a first emission layer having a thickness of 200 Å. Second emission layer materials shown in Table 3 were co-deposited on the first emission layer to form a second emission layer having a thickness of 200 Å. TPM-TAZ and LiQ were co-deposited on the emission layer at a volume ratio of 1:1 to form an electron transport layer having a thickness of 300 Å, thereby forming a fourth emitting unit. 
     Yb was deposited on the fourth emitting unit to a thickness of 10 Å, and then Ag and Mg were co-deposited thereon at a volume ratio of 9:1 to form a cathode having a thickness of 100 Å, thereby completing manufacture of a tandem light-emitting device. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Evaluation Example 3: Evaluation of Light-Emitting Devices of Examples 3 and 4 and Comparative Examples 11 to 20 
     The driving voltage, luminescence efficiency, and lifespan (T 95 ) of the light-emitting devices manufactured according to Examples 3 and 4 and Comparative Examples 11 to 20 were measured utilizing a Keithley SMU 236 and a luminance meter PR650, and the results are shown in Table 3. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                 Driving 
                   
                   
                   
                   
               
               
                   
                   
                   
                 voltage 
                 Efficiency 
                 Efficiency 
                 Efficiency 
                 Lifespan 
               
               
                   
                 Host + dopant 
                 Host + dopant 
                 @100 
                 @100 
                 @1,000 
                 @10,000 
                 @10,000 
               
               
                 Light- 
                 in first 
                 in second 
                 nit 
                 nit 
                 nit 
                 nit 
                 nit 
               
               
                 emitting 
                 emission 
                 emission 
                 (relative 
                 (relative 
                 (relative 
                 (relative 
                 (T 95 , 
               
               
                 device 
                 layer 
                 layer 
                 value) 
                 value) 
                 value) 
                 value) 
                 hour) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Example 3 
                 HH-1 + EH-8 
                 HH-19 + EH-1 
                 100% 
                 100% 
                 99% 
                 97% 
                 750 
               
               
                   
                 (weight ratio 
                 (weight ratio 
               
               
                   
                 5:5), G-1 
                 5:5), G-7 
               
               
                 Example 4 
                 HH-1 + EH-8 
                 HH-19 + EH-1 
                 105% 
                  94% 
                 92% 
                 90% 
                 560 
               
               
                   
                 (weight ratio 
                 (weight ratio 
               
               
                   
                 5:5), G-7 
                 5:5), G-1 
               
               
                 Comparative 
                 HH-19 + EH-1 
                 HH-1 + EH-8 
                 105% 
                 100% 
                 89% 
                 75% 
                 410 
               
               
                 Example 11 
                 (weight ratio 
                 (weight ratio 
               
               
                   
                 5:5), G-7 
                 5:5), G-1 
               
               
                 Comparative 
                 HH-19 + EH-1 
                 HH-1 + EH-8 
                 106% 
                  93% 
                 84% 
                 73% 
                 320 
               
               
                 Example 12 
                 (weight ratio 
                 (weight ratio 
               
               
                   
                 5:5), G-1 
                 5:5), G-7 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Comparative 
                 HH-1 + EH-8 
                 100% 
                 100% 
                 91% 
                 75% 
                 400 
               
               
                 Example 13 
                 (weight ratio 
               
               
                   
                 5:5), G-1 
               
               
                 Comparative 
                 HH-19 + EH-1 
                 100% 
                 100% 
                 90% 
                 77% 
                 400 
               
               
                 Example 14 
                 (weight ratio 
               
               
                   
                 5:5), G-7 
               
               
                 Comparative 
                 HH-1 + EH-8 
                 105% 
                  94% 
                 86% 
                 69% 
                 310 
               
               
                 Example 15 
                 (weight ratio 
               
               
                   
                 5:5), G-7 
               
               
                 Comparative 
                 HH-19 + EH-1 
                 106% 
                  93% 
                 85% 
                 71% 
                 300 
               
               
                 Example 16 
                 (weight ratio 
               
               
                   
                 5:5), G-1 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Comparative 
                 HH-1 + EH-8 
                 HH-19 + EH-1 
                 100% 
                 100% 
                 98% 
                 96% 
                 710 
               
               
                 Example 17 
                 (weight ratio 
                 (weight ratio 
               
               
                   
                 3:7), G-1 
                 5:5), G-2 
               
               
                 Comparative 
                 HH-1 + EH-8 
                 HH-19 + EH-1 
                 101% 
                 100% 
                 94% 
                 90% 
                 580 
               
               
                 Example 18 
                 (weight ratio 
                 (weight ratio 
               
               
                   
                 7:3), G-1 
                 5:5), G-2 
               
               
                 Comparative 
                 HH-1 + EH-8 
                 HH-19 + EH-1 
                 101% 
                 100% 
                 97% 
                 95% 
                 750 
               
               
                 Example 19 
                 (weight ratio 
                 (weight ratio 
               
               
                   
                 5:5), G-1 
                 7:3), G-2 
               
               
                 Comparative 
                 HH-1 + EH-8 
                 HH-19 + EH-1 
                 102% 
                 100% 
                 96% 
                 93% 
                 620 
               
               
                 Example 20 
                 (weight ratio 
                 (weight ratio 
               
               
                   
                 5:5), G-1 
                 7:3), G-2 
               
               
                   
               
            
           
         
       
     
     Referring to Tables 2 and 3, it was confirmed that the light-emitting devices according to an embodiment had driving voltages which are lower than or equal to those of the light-emitting devices of Comparative Examples, and had excellent or suitable luminescence efficiency and lifespan characteristics. For example, it was confirmed that the light-emitting devices according to an embodiment had significantly superior luminescence efficiency and lifespan characteristics at high luminance to those of the light-emitting devices of Comparative Examples. 
     A light-emitting device according to an embodiment has excellent or suitable luminescence efficiency and lifespan characteristics. 
     The electronic apparatus and/or any other relevant devices or components according to embodiments of the present invention described herein may be implemented utilizing any suitable hardware, firmware (e.g. an application-specific integrated circuit), software, or a combination of software, firmware, and hardware. For example, the various components of the apparatus may be formed on one integrated circuit (IC) chip or on separate IC chips. Further, the various components of the [device] may be implemented on a flexible printed circuit film, a tape carrier package (TCP), a printed circuit board (PCB), or formed on one substrate. Further, the various components of the apparatus may be a process or thread, running on one or more processors, in one or more computing devices, executing computer program instructions and interacting with other system components for performing the various functionalities described herein. The computer program instructions are stored in a memory which may be implemented in a computing device using a standard memory device, such as, for example, a random access memory (RAM). The computer program instructions may also be stored in other non-transitory computer readable media such as, for example, a CD-ROM, flash drive, or the like. Also, a person of skill in the art should recognize that the functionality of various computing devices may be combined or integrated into a single computing device, or the functionality of a particular computing device may be distributed across one or more other computing devices without departing from the scope of the embodiments. 
     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 other embodiments. While one or more embodiments have been described with reference to the drawings, it will be understood by those of ordinary skill in the art that one or more suitable changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims and equivalents thereof.