Patent Publication Number: US-2022216419-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. 10-2021-0001928, filed on Jan. 7, 2021, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     One or more aspects of embodiments of the present disclosure relate to a light-emitting device and an electronic apparatus including the same. 
     2. Description of the Related Art 
     Self-emissive light-emitting devices may have wide viewing angles, high contrast ratios, short response times, and/or excellent or suitable characteristics in terms of luminance, driving voltage, and/or response speed. 
     In an example light-emitting device, a first electrode is located on a substrate, and a hole transport region, an emission layer, an electron transport region, and a second electrode are sequentially arranged 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. Carriers (such as the holes and the electrons) may recombine in the emission layer to produce excitons. The excitons may transition from an excited state to a ground state to thereby generate light. 
     SUMMARY 
     One or more aspects of embodiments of the present disclosure are directed toward a light-emitting device having a low driving voltage, high luminescence efficiency, and/or long lifespan, and an electronic apparatus including the light-emitting device. 
     Additional aspects will be set forth in part in the description that follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments of the disclosure. 
     One or more embodiments of the present disclosure provide a light-emitting device including: 
     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 an emission layer and an electron transport region, 
     the electron transport region is located between the emission layer and the second electrode, 
     the electron transport region includes an electron transport layer, 
     the electron transport layer includes a first material and a second material, 
     the first material is a heterocyclic compound represented by Formula 1, and 
     the second material includes a first metal in the form of an element of the first metal, a halide of the first metal, a complex including the first metal, or any combination thereof: 
     
       
         
         
             
             
         
       
     
     wherein, in Formulae 1, 2A, 2B, and 2C, 
     Ar 1  may be a group represented by Formula 2A, a group represented by Formula 2B, or a group represented by Formula 2C, 
     X 1  may be N or C-[(L 1 ) a1 -(R 1 ) b1 ], and X 2  may be N or C-[(L 2 ) a2 -(R 2 ) b2 ], 
     T 1  and T 2  may each independently be C or N, 
     T 3  may be N or C(R 6 ), 
     ring CY 1  may be a C 1 -C 60  heterocyclic group, 
     L 1  to L 5  may each independently be a single bond, a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 1a , or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 1a , 
     a1 to a5 may each independently be an integer from 1 to 5, 
     R 1  to R 4  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 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 , 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 7 -C 60  aryl alkyl group unsubstituted or substituted with at least one R 10a , a C 2 -C 60  heteroaryl alkyl group unsubstituted or substituted with at least one R 10a , a group represented by Formula 2A, a group represented by Formula 2B, a group represented by Formula 2C, —Si(Q 1 )(Q 2 )(Q 3 ), —N(Q 1 )(Q 2 ), —B(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O) 2 (Q 1 ), or —P(═O)(Q 1 )(Q 2 ), 
     R 5  and R 6  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 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 , 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 7 -C 60  aryl alkyl group unsubstituted or substituted with at least one R 10a , a C 2 -C 60  heteroaryl alkyl group unsubstituted or substituted with at least one R 10a , —Si(Q 1 )(Q 2 )(Q 3 ), —N(Q 1 )(Q 2 ), —B(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O) 2 (Q 1 ), or —P(═O)(Q 1 )(Q 2 ), 
     b1 to b5 and c5 may each independently be an integer from 1 to 20, 
     R 1a  is the same as described in connection with R 1 , 
     * in Formulae 2A to 2C indicates a binding site to a neighboring atom, 
     the heterocyclic compound represented by Formula 1 may satisfy Conditions 1 and 2: 
     Condition 1 
     Formula 1 does not include a benzo[k]fluoranthene group, 
     Condition 2 
     When ring CY 1  in Formulae 2A and 2B is a benzimidazole group, at least one of X 1  and X 2  is N, and 
     R 10a  may be: 
     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  aryl alkyl group, a C 2 -C 60  heteroaryl alkyl 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 6  heterocyclic group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 7 -C 60  aryl alkyl group, or a C 2 -C 60  heteroaryl alkyl 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  aryl alkyl group, a C 2 -C 60  heteroaryl alkyl 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 1  to Q 3 , Q 11  to Q 13 , Q 21  to Q 23 , and Q 31  to Q 33  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 7 -C 60  aryl alkyl group, or a C 2 -C 60  heteroaryl alkyl group, or 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 6  alkoxy group, a phenyl group, a biphenyl group, or any combination thereof. 
     One or more embodiments of the present disclosure provide an electronic apparatus including the light-emitting device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic view of a light-emitting device according to an embodiment; and 
         FIGS. 2 and 3  are each a schematic view of an electronic apparatus 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 the specification, 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 with reference 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. 
     It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. Thus, a first element could be termed a second element without departing from the teachings of the present invention. Similarly, a second element could be termed a first element. As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. 
     As used herein, the terms “use,” “using,” and “used” may be considered synonymous with the terms “utilize,” “utilizing,” and “utilized,” respectively. As used herein, expressions such as “at least one of,” “one of,” and “selected from,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Further, the use of “may” when describing embodiments of the present disclosure refers to “one or more embodiments of the present disclosure”. 
     It will be understood that when an element is referred to as being “on,” “connected to,” or “coupled to” another element, it may be directly on, connected, or coupled to the other element or one or more intervening elements may also be present. 
     When an element is referred to as being “directly on,” “directly connected to,” or “directly coupled to” another element, there are no intervening elements present. 
     A light-emitting device according to an embodiment of the present disclosure may include: a first electrode; a second electrode facing the first electrode; and an interlayer located between the first electrode and the second electrode. 
     The interlayer may include an emission layer and an electron transport region, and the electron transport region may be located between the emission layer and the second electrode. 
     The electron transport region may include an electron transport layer. 
     The electron transport layer may include a first material and a second material. 
     The first material in the electron transport layer may be a heterocyclic compound represented by Formula 1: 
     
       
         
         
             
             
         
       
     
     wherein, in Formula 1, Ar 1  may be a group represented by Formula 2A, a group represented by Formula 2B, or a group represented by Formula 2C: 
     
       
         
         
             
             
         
       
     
     Formulae 2A to 2C are described in more detail below. 
     In Formula 1, X 1  may be N or C-[(L 1 ) a1 -(R 1 ) b1 ], and X 2  may be N or C-[(L 2 ) a2 -(R 2 ) b2 ]. 
     In an embodiment, in Formula 1, 
     i) X 1  may be C-[(L 1 ) a1 -(R 1 ) b1 ], and X 2  may be C-[(L 2 ) a2 -(R 2 ) b2 ]; 
     ii) X 1  may be N, and X 2  may be C-[(L 2 ) a2 -(R 2 ) b2 ]; 
     iii) X 1  may be C-[(L 1 ) a1 -(R 1 ) b1 ], and X 2  may be N; or 
     iv) X 1  may be N, and X 2  may be N. 
     T 1  and T 2  in Formulae 2A and 2B may each independently be C or N. 
     In an embodiment, T 1  and T 2  in Formulae 2A and 2B may each be C. 
     T 3  in Formula 2C may be N or C(R 6 ). 
     In an embodiment, T 3  in Formula 2C may be C(R 6 ). 
     ring CY 1  in Formulae 2A and 2B may be a C 1 -C 6  heterocyclic group. 
     In an embodiment, ring CY 1  in Formulae 2A and 2B may be 
     i) a first group, 
     ii) a condensed cyclic group in which a first group and at least one second group are condensed with each other, 
     iii) a condensed cyclic group in which a first group and at least one third group are condensed with each other, or 
     iv) a condensed cyclic group in which a first group, at least one second group, and at least one third group are condensed with each other, 
     where the first group may be a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a pyrazole group, an imidazole group, a triazole group, an oxazole group, an isoxazole group, a thiazole group, or an isothiazole group, each including T 1  and T 2  in Formulae 2A and 2B as a ring-forming atom, 
     the second group may be a benzene group, a pyrrole group, a furan group, or a thiophene group, and 
     the third group may be a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a pyrazole group, an imidazole group, a triazole group, an oxazole group, an isoxazole group, a thiazole group, or an isothiazole group. 
     In an embodiment, ring CY 1  in Formulae 2A and 2B may be a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a quinazoline group, a quinoxaline group, a naphthyridine group, a benzoquinoline group, a benzoisoquinoline group, a benzoquinazoline group, a benzoquinoxaline group, a benzonaphthyridine group, a pyridoquinoline group (for example, a phenanthroline group), a pyridoisoquinoline group, a pyridoquinazoline group, a pyridoquinoxaline group, a pyridonaphthyridine group, a benzopyrazole group, a benzimidazole group, a benzoxazole group, a benzothiazole group, a pyridopyrazole group, a pyridoimidazole group, a pyridooxazole group, a pyridothiazole group, a pyridopyrrole group, a pyridofuran group, or a pyridothiophene group. 
     In one or more embodiments, ring CY 1  in Formulae 2A and 2B may be a group represented by one of Formulae 2(1) to 2(11): 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae 2(1) to 2(11), 
     Y 1  to Y 8  may each independently be C or N, 
     Y 9  may be O, S, or N(R 59 ), 
     R 59  may be the same as described in connection with R 5 , and 
     * indicates a binding site to a neighboring atom. 
     In some embodiments, a case in which all of Y 1  to Y 8  in Formulae 2(1) to 2(9) are N may be excluded, and in some embodiments, a case in which all of Y 1  to Y 8  in Formulae 2(10) and 2(11) are N may be excluded. 
     In an embodiment, all of Y 1  to Y 8  in Formulae 2(1) to 2(9) may be C (e.g., simultaneously), and in an embodiment, all of Y 1  to Y 8  in Formulae 2(10) and 2(11) may be C (e.g., simultaneously). 
     In one or more embodiments, one or two of Y 1  to Y 4  in Formulae 2(1) and 2(7) to 2(9) may be N, one or two of Y 1  to Y 6  in Formulae 2(2), 2(3), and 2(10) may be N, and one or two of Y 1  to Y 8  in Formulae 2(4) to 2(6) and 2(11) may be N. 
     In one or more embodiments, ring CY 1  in Formulae 2A and 2B may be a group represented by one of Formulae 2-1 to 2-67: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae 2-1 to 2-67, 
     Y 9  may be O, S, or N(R 59 ), 
     R 59  may be the same as described in connection with R 5 , and 
     * indicates a binding site to a neighboring atom. 
     L 1  to L 5  in Formulae 1, 2A, and 2B may each independently be a single bond, a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 1a , or a C 1 -C 6  heterocyclic group unsubstituted or substituted with at least one R 1a . 
     In an embodiment, L 1  to L 5  may each independently be: 
     a single bond; or 
     a benzene group, a naphthalene group, a phenanthrene group, a pyrene group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a quinazoline group, a quinoxaline group, a naphthyridine group, a benzoquinoline group, a benzoisoquinoline group, a benzoquinazoline group, a benzoquinoxaline group, a benzonaphthyridine group, a pyridoquinoline group, a pyridoisoquinoline group, a pyridoquinazoline group, a pyridoquinoxaline group, a pyridonaphthyridine group, a benzopyrazole group, a benzimidazole group, a benzoxazole group, a benzothiazole group, a pyridopyrazole group, a pyridoimidazole group, a pyridooxazole group, a pyridothiazole group, a pyridopyrrole group, a pyridofuran group, or a pyridothiophene group, each unsubstituted or substituted with deuterium, a C 1 -C 20  alkyl group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a phenanthrenyl group, a pyrenyl group, a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a quinazolinyl group, a quinoxalinyl group, a naphthyridinyl group, a benzoquinolinyl group, a benzoisoquinolinyl group, a benzoquinazolinyl group, a benzoquinoxalinyl group, a benzonaphthyridinyl group, a pyridoquinolinyl group, a pyridoisoquinolinyl group, a pyridoquinazolinyl group, a pyridoquinoxalinyl group, a pyridonaphthyridinyl group, a benzopyrazolyl group, a benzimidazolyl group, a benzoxazolyl group, a benzothiazolyl group, a pyridopyrazolyl group, a pyridoimidazolyl group, a pyridooxazolyl group, a pyridothiazolyl group, a pyridopyrrolyl group, a pyridofuranyl group, a pyridothiophenyl group, or any combination thereof. 
     In one or more embodiments, L 1  to L 5  may each independently be: 
     a single bond; or 
     a benzene group, a naphthalene group, a phenanthrene group, or a pyrene group, each unsubstituted or substituted with deuterium, a C 1 -C 20  alkyl group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a phenanthrenyl group, a pyrenyl group, or any combination thereof. 
     a1 to a5 in Formulae 1, 2A, and 2B may respectively indicate the numbers of L 1  to L 5 , and may each independently be an integer from 1 to 5 (for example, 1, 2, or 3). When a1 is 2 or more, two or more Li(s) may be identical to or different from each other, when a2 is 2 or more, two or more L 2 (s) may be identical to or different from each other, when a3 is 2 or more, two or more L 3 (s) may be identical to or different from each other, when a4 is 2 or more, two or more L 4 (s) may be identical to or different from each other, and when a5 is 2 or more, two or more L 5 (s) may be identical to or different from each other. 
     In Formulae 1, 2A, 2B, and 2C, 
     R 1  to R 4  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 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 , 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 7 -C 60  aryl alkyl group unsubstituted or substituted with at least one R 10a , a C 2 -C 60  heteroaryl alkyl group unsubstituted or substituted with at least one R 10a , a group represented by Formula 2A, a group represented by Formula 2B, a group represented by Formula 2C, —Si(Q 1 )(Q 2 )(Q 3 ), —N(Q 1 )(Q 2 ), —B(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O) 2 (Q 1 ), or —P(═O)(Qi)(Q 2 ), and 
     R 5  and R 6  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 6  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 , 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 7 -C 60  aryl alkyl group unsubstituted or substituted with at least one R 10a , a C 2 -C 60  heteroaryl alkyl group unsubstituted or substituted with at least one R 10a , —Si(Q 1 )(Q 2 )(Q 3 ), —N(Q 1 )(Q 2 ), —B(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O) 2 (Q 1 ), or —P(═O)(Q 1 )(Q 2 ). Q 1  to Q 3  may be the same as described in the present specification. 
     In an embodiment, R 3  and R 4  may each independently be: 
     a phenyl group, a naphthyl group, a phenanthrenyl group, a pyrenyl group, a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a quinazolinyl group, a quinoxalinyl group, a naphthyridinyl group, a benzoquinolinyl group, a benzoisoquinolinyl group, a benzoquinazolinyl group, a benzoquinoxalinyl group, a benzonaphthyridinyl group, a pyridoquinolinyl group, a pyridoisoquinolinyl group, a pyridoquinazolinyl group, a pyridoquinoxalinyl group, a pyridonaphthyridinyl group, a benzopyrazolyl group, a benzimidazolyl group, a benzoxazolyl group, a benzothiazolyl group, a pyridopyrazolyl group, a pyridoimidazolyl group, a pyridooxazolyl group, a pyridothiazolyl group, a pyridopyrrolyl group, a pyridofuranyl group, or a pyridothiophenyl group, each unsubstituted or substituted with deuterium, a C 1 -C 20  alkyl group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a phenanthrenyl group, a pyrenyl group, a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a quinazolinyl group, a quinoxalinyl group, a naphthyridinyl group, a benzoquinolinyl group, a benzoisoquinolinyl group, a benzoquinazolinyl group, a benzoquinoxalinyl group, a benzonaphthyridinyl group, a pyridoquinolinyl group, a pyridoisoquinolinyl group, a pyridoquinazolinyl group, a pyridoquinoxalinyl group, a pyridonaphthyridinyl group, a benzopyrazolyl group, a benzimidazolyl group, a benzoxazolyl group, a benzothiazolyl group, a pyridopyrazolyl group, a pyridoimidazolyl group, a pyridooxazolyl group, a pyridothiazolyl group, a pyridopyrrolyl group, a pyridofuranyl group, a pyridothiophenyl group, or any combination thereof; or 
     a group represented by Formula 2A, a group represented by Formula 2B, or a group represented by Formula 2C. 
     In an embodiment, R 1 , R 2 , R 5 , and R 6  may each independently be: 
     hydrogen, deuterium, or a C 1 -C 20  alkyl group; or 
     a phenyl group, a naphthyl group, a phenanthrenyl group, a pyrenyl group, a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a quinazolinyl group, a quinoxalinyl group, a naphthyridinyl group, a benzoquinolinyl group, a benzoisoquinolinyl group, a benzoquinazolinyl group, a benzoquinoxalinyl group, a benzonaphthyridinyl group, a pyridoquinolinyl group, a pyridoisoquinolinyl group, a pyridoquinazolinyl group, a pyridoquinoxalinyl group, a pyridonaphthyridinyl group, a benzopyrazolyl group, a benzimidazolyl group, a benzoxazolyl group, a benzothiazolyl group, a pyridopyrazolyl group, a pyridoimidazolyl group, a pyridooxazolyl group, a pyridothiazolyl group, a pyridopyrrolyl group, a pyridofuranyl group, or a pyridothiophenyl group, each unsubstituted or substituted with deuterium, a C 1 -C 20  alkyl group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a phenanthrenyl group, a pyrenyl group, a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a quinazolinyl group, a quinoxalinyl group, a naphthyridinyl group, a benzoquinolinyl group, a benzoisoquinolinyl group, a benzoquinazolinyl group, a benzoquinoxalinyl group, a benzonaphthyridinyl group, a pyridoquinolinyl group, a pyridoisoquinolinyl group, a pyridoquinazolinyl group, a pyridoquinoxalinyl group, a pyridonaphthyridinyl group, a benzopyrazolyl group, a benzimidazolyl group, a benzoxazolyl group, a benzothiazolyl group, a pyridopyrazolyl group, a pyridoimidazolyl group, a pyridooxazolyl group, a pyridothiazolyl group, a pyridopyrrolyl group, a pyridofuranyl group, a pyridothiophenyl group, or any combination thereof. 
     In Formulae 1, 2A, and 2B, b1 to b5 may respectively indicate the numbers of R 1  to R 5 , c5 may indicate the number of groups represented by *-[(L 5 ) a5 -(R 5 ) b5 ], and b1 to b5 and c5 may each independently be an integer from 1 to 20 (for example 0, 1, 2, or 3). When b1 is 2 or more, two or more R 1 (s) may be identical to or different from each other, when b2 is 2 or more, two or more R 2 (s) may be identical to or different from each other, when b3 is 2 or more, two or more R 3 (s) may be identical to or different from each other, when b4 is 2 or more, two or more R 4 (s) may be identical to or different from each other, when b5 is 2 or more, two or more R 5 (s) may be identical to or different from each other, and when c5 is 2 or more, two or more groups represented by *-[(L 5 ) a5 -(R 5 ) b5 ] may be identical to or different from each other. 
     In an embodiment, in Formula 1, 
     ) L 3  may be a single bond, b3 may be 1, and R 3  may be a group represented by Formula 2A, a group represented by Formula 2B, or a group represented by Formula 2C, 
     ii) L 4  may be a single bond, b4 may be 1, and R 4  may be a group represented by Formula 2A, a group represented by Formula 2B, or a group represented by Formula 2C, or 
     iii) L 3  and L 4  may each be a single bond, b3 and b4 may each be 1, and R 3  and R 4  may each independently be a group represented by Formula 2A, a group represented by Formula 2B, or a group represented by Formula 2C. For example, Formula 1 may be described according to cases (i) and/or (ii) above. 
     R 1a  may be the same as described in connection with R 1 . 
     * in Formulae 2A to 2C indicates a binding site to a neighboring atom. 
     The heterocyclic compound represented by Formula 1 may satisfy Conditions 1 and 2: 
     Condition 1 
     Formula 1 does not include a benzo[k]fluoranthene group 
     Condition 2 
     When ring CY 1  in Formulae 2A and 2B is a benzimidazole group, at least one of X 1  and X 2  is N 
     In an embodiment, the first material may include one of Compounds 1 to 74, or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In one or more embodiments, the second material in the electron transport layer may include a first metal in the form of an element of the first metal (e.g., an elemental substance), a halide of the first metal, a complex including the first metal, or any combination thereof. 
     The first metal included in the second material may be an alkali metal, an alkaline earth metal, a rare earth metal, a Group 3 transition metal, or any combination thereof. The term “first metal included in a second material” as utilized herein refers to not only the “first metal”, but also the “first metal” included in the halide of the first metal and the “first metal” included in the complex including the first metal. 
     In an embodiment, the first metal included in the second material may be lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), radium (Ra), scandium (Sc), yttrium (Y), 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), or any combination thereof. 
     The halide of the first metal may include a fluoride of the first metal, a chloride of the first metal, a bromide of the first metal, an iodide of the first metal, or any combination thereof. 
     In an embodiment, the halide of the first metal may include LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, CsI, BeF 2 , MgF 2 , CaF 2 , SrF 2 , BaF 2 , BeCl 2 , MgCl 2 , CaCl 2 ), SrCl 2 , BaCl 2 , BeBr 2 , MgBr 2 , CaBr 2 , SrBr 2 , BaBr 2 , BeI 2 , MgI 2 , CaI 2 , SrI 2 , BaI 2 , YbF, YbF 2 , YbF 3 , SmF 3 , YbCl, YbCl 2 , YbCl 3 , SmCl 3 , YbBr, YbBr 2 , YbBr 3  SmBr 3 , YbI, YbI 2 , YbI 3 , SmI 3 , ScF 3 , GdF 3 , TbF 3 , YbI 3 , ScI 3 , TbI 3 , or any combination thereof. 
     The complex including the first metal may further include a ligand in the number of n (e.g., having a multiplicity of n) bonded to the first metal, wherein n may be an integer from 1 to 6, and at least one of the ligand in the number of n (e.g., at least one of the n ligand(s)) may be a group represented by Formulae 3-1 or 3-2: 
     
       
         
         
             
             
         
       
     
     wherein, in Formulae 3-1 and 3-2, 
     A 1  and A 2  may each independently be C or N, 
     A 3  may be O or S, 
     ring CY 11  and ring CY 12  may each independently be a C 5 -C 60  carbocyclic group or a C 3 -C 60  heterocyclic group, 
     Z 1  and Z 2  may each independently be the same as described in connection with R 1 , 
     d1 and d2 may each independently be an integer from 0 to 20, and 
     * and *′ each indicate a binding site to the first metal. 
     In an embodiment, ring CY 11  and ring CY 12  in Formulae 3-1 and 3-2 may each independently be a benzene group, a naphthalene group, a pyridine group, a pyrimidine group, a benzimidazole group, a benzoxazole group, or a benzothiazole group. 
     In an embodiment, at least one of the n ligand(s) may be hydroxy quinoline, hydroxy isoquinoline, hydroxy benzoquinoline, hydroxy acridine, hydroxy phenanthridine, hydroxy phenyloxazole, hydroxy phenylthiazole, hydroxy phenyloxadiazole, hydroxy phenylthiadiazole, hydroxy phenylpyridine, hydroxy phenylbenzimidazole, hydroxy phenylbenzothiazole, bipyridine, phenanthroline, or cyclopentadiene. 
     In an embodiment, the complex including the first metal may be one of Compounds M1-1 to M1-4: 
     
       
         
         
             
             
         
       
     
     M in Compounds M1-1 to M1-4 may be an alkali metal (for example, Li, Na, K, Rb, etc.). 
     The electron transport layer may further include, in addition to the first material and the second material as described above, an organometallic compound in which a first metal derived from the second material and Ar included in the first material are bonded to each other. The term “first metal derived from the second material” refers to not only the “first metal included in the second material” as described above, but also ions of the first metal, the first metal separated from a halogen ion in the halide of the first metal (for example, ions of the first metal), and the first metal separated from the ligand in the complex including the first metal (for example, ions of the first metal). Accordingly, the organometallic compound may not be a material that is additionally utilized when forming the electron transport layer, and for example may be derived from (e.g., a reaction product of) the first material and the second material as described herein during and/or after the formation of the electron transport layer. In an embodiment, the electron transport layer may be formed by: 1) co-depositing the first material and the second material, and/or 2) coating and baking a mixture including the first material, the second material, and a solvent. 
     In an embodiment, a cyclometalated ring including the first metal in the organometallic compound may be a 5-membered ring (see Formulae 1A to 1C). For example, the organometallic compound may include a 5-membered cyclometalated ring including an atom of the first metal as a ring member. 
     In an embodiment, the organometallic compound in which the first metal derived from the second material and Ar included in the first material are bonded to each other may include an organometallic compound represented by Formula 1A, an organometallic compound represented by Formula 1B, an organometallic compound represented by Formula 1C, or any combination thereof: 
     
       
         
         
             
             
         
       
     
     wherein, in Formulae 1A to 1C, 
     M may be the first metal derived from the second material, 
     X 1 , X 2 , T 1  to T 3 , ring CY 1 , L 1  to L 5 , a1 to a5, R 1  to R 5 , b1 to b5, and c5 may each independently be the same as described in the present specification. 
     A weight ratio of the first material to the second material in the electron transport layer may be in the range of about 9.9:0.1 to about 3:7, for example, about 9.9:0.1 to about 5:5. When the weight ratio of the first material to the second material is within this range, the electron transport layer may have excellent or suitable electron transporting characteristics. 
     In an embodiment, when the second material is the complex including the first metal, the weight ratio of the first material to the second material in the electron transport layer may be in the range of about 9.9:0.1 to about 5:5 (for example, 5:5). 
     In an embodiment, when the second material is the first metal or the halide of the first metal, the weight ratio of the first material to the second material in the electron transport layer may be in the range of about 9.9:0.1 to about 7:3 (for example, 9:1). 
     Because the electron transport layer includes the first material and the second material as described herein, excellent or suitable electron transport and injection characteristics may be obtained. In one or more embodiments, the first metal included in the second material may be converted into an ionic form (e.g., may be present as cation(s), ionic complexes, and/or metal salts) in the electron transport layer, and there is a risk that ions of the first metal may move to a neighboring layer, for example, the emission layer, the electron injection layer, and/or the second electrode (cathode) to partially bond to (with) materials included in the neighboring layer, resulting in a decrease in the stability of the light-emitting device and an increase in the driving voltage thereof. However, because the first material in the electron transport layer includes “Ar 1 ” as described herein, an organometallic compound in which the first metal derived from the second material and Ar included in the first material are bonded to each other may be additionally formed (e.g., may instead be formed at a higher reaction rate), and thus, the ions of the first metal may be substantially prevented or reduced from moving to the neighboring layer. As a result, the stability of the light-emitting device may be improved, thereby improving the driving voltage, luminescence efficiency, and/or lifespan of the light-emitting device. 
     In one or more embodiments, although not limited by the correctness of any theory or explanation set forth herein, i) when the heterocyclic compound represented by Formula 1 satisfies Condition 1, steric hindrance characteristics of the first material may be reduced, thereby increasing the probability and/or rate of contact (e.g., reaction) between the first material and the second material, and ii) when the heterocyclic compound represented by Formula 1 satisfies Condition 2, the electron transport layer may have a better electron transport capability. 
     The electron transport region may further include a buffer layer located between the emission layer and the electron transport layer. 
     The electron transport region may further include, in addition to the electron transport layer and the buffer layer as described above, a hole blocking layer, an electron control layer, an electron injection layer, or any combination thereof. 
     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, and 
     the interlayer may further include a hole transport region located between the first electrode and the emission layer. 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. 
     In one or more embodiments, the light-emitting device may include a capping layer located outside of the first electrode or outside of the second electrode (e.g., on the side of either electrode that faces oppositely away from the emission layer). 
     In an embodiment, the light-emitting device may further include at least one of a first capping layer located outside the first electrode and a second capping layer located outside the second electrode, and the heterocyclic compound represented by Formula 1 may be included in at least one of the first capping layer and the second capping layer. The first capping layer and/or second capping layer may each independently be the same as described in the present specification. 
     The term “interlayer” as utilized herein may refer to a single layer and/or all of a plurality of layers located between a first electrode and a second electrode of a light-emitting device. 
     According to another aspect of the present disclosure, provided is an electronic apparatus including the light-emitting device. The electronic apparatus may further include a thin-film transistor. In one or more embodiments, the electronic apparatus may further include a thin-film transistor including a source electrode and a drain electrode, and 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 on the electronic apparatus may be the same as described in the present specification. 
     Description of FIG.  1   
       FIG. 1  is a schematic cross-sectional view of a light-emitting device  10  according to an embodiment. The light-emitting device  10  includes a first electrode  110 , an interlayer  130 , and a second electrode  150 . 
     Hereinafter, the structure of the light-emitting device  10  according to an embodiment and a method of manufacturing the light-emitting device  10  will be described in connection with  FIG. 1 . 
     First Electrode  110   
     In  FIG. 1 , a substrate may be additionally located under the first electrode  110  or above the second electrode  150 . A glass substrate and/or a plastic substrate may be utilized as the substrate. In one or more embodiments, 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 and/or sputtering a material for forming the first electrode  110  on the substrate. When the first electrode  110  is an anode, a material for forming the first electrode  110  may be a high work function material that facilitates injection of holes. 
     The first electrode  110  may be a reflective electrode, a semi-transmissive electrode, or a transmissive electrode. When the first electrode  110  is a transmissive electrode, a material for forming the first electrode  110  may include indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO 2 ), zinc oxide (ZnO), or any combination thereof. In one or more embodiments, when the first electrode  110  is a semi-transmissive electrode or a reflective electrode, magnesium (Mg), silver (Ag), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), or any combination thereof may be utilized as a material for forming a first electrode. 
     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 located between the first electrode  110  and the emission layer and an electron transport region located between the emission layer and the second electrode  150 . 
     The interlayer  130  may further include metal-containing compounds (such as organometallic compounds), inorganic materials (such as quantum dots), and/or the like, in addition to various suitable organic materials. 
     In one or more embodiments, 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 emitting units. When the interlayer  130  includes the emitting unit and the charge generation layer as described above, the light-emitting device  10  may be a tandem light-emitting device. 
     Hole Transport Region in Interlayer  130   
     The hole transport region may have: i) a single-layered structure including (e.g., consisting of) a single layer including (e.g., consisting of) a single material, ii) a single-layered structure including (e.g., 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, where the layers of each structure are stacked sequentially from the first electrode  110 . 
     The hole transport region may include a compound represented by Formula 201, a compound represented by Formula 202, or any combination thereof: 
     
       
         
         
             
             
         
       
     
     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 0201 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 , and may thereby 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 one or more embodiments, each of Formulae 201 and 202 may include at least one of groups represented by Formulae CY201 to CY217. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     R 10b  and R 10c  in Formulae CY201 to CY217 may each independently be the same as described in connection with R 10a , ring CY 201  to ring CY 204  may each independently be a C 3 -C 20  carbocyclic group or a C 1 -C 20  heterocyclic group, and at least one hydrogen in Formulae CY201 to CY217 may be unsubstituted or substituted with R 10a . 
     In 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 one or more embodiments, each of Formulae 201 and 202 may include at least one of groups represented by Formulae CY201 to CY203. 
     In one or more embodiments, Formula 201 may include at least one of the groups represented by Formulae CY201 to CY203 and at least one of the groups represented by Formulae CY204 to CY217. 
     In one or more embodiments, 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 one or more embodiments, each of Formulae 201 and 202 may not include (e.g., may exclude) a group represented by one of Formulae CY201 to CY203. 
     In one or more embodiments, each of Formulae 201 and 202 may not include (e.g., may exclude) a group represented by one of Formulae CY201 to CY203, and may include at least one of groups represented by Formulae CY204 to CY217. 
     In one or more embodiments, each of Formulae 201 and 202 may not include (e.g., may exclude) a group represented by one of Formulae CY201 to CY217. 
     In an embodiment, the hole transport region may include one of Compounds HT1 to HT46, m-MTDATA, TDATA, 2-TNATA, NPB(NPD), β-NPB, TPD, Spiro-TPD, Spiro-NPB, methylated NPB, TAPC, HMTPD, 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA), polyaniline/dodecylbenzene sulfonic acid (PANI/DBSA), poly(3,4-ethylene dioxythiophene)/poly(4-styrene sulfonate) (PEDOT/PSS), polyaniline/camphor sulfonic acid (PANI/CSA), polyaniline/poly(4-styrene sulfonate) (PANI/PSS), HTM2, 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 of the wavelength of light emitted by an emission layer, and the electron blocking layer may block or reduce 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/or 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 substantially uniformly or non-uniformly dispersed in the hole-transporting 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 one or more embodiments, the lowest unoccupied molecular orbital (LUMO) energy level of the p-dopant may be −3.5 eV or less. 
     In one or more embodiments, 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, etc. 
     Examples of the cyano group-containing compound may include HAT-CN, and a compound represented by Formula 221 
     
       
         
         
             
             
         
       
     
     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 6  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 any combination thereof, and element EL2 may be a non-metal, a metalloid, or any 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 one or more embodiments, 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, and/or a metal iodide), metalloid halide (for example, a metalloid fluoride, a metalloid chloride, a metalloid bromide, and/or a metalloid iodide), a metal telluride, or any combination thereof. 
     Examples of the metal oxide may include a tungsten oxide (for example, WO, W 2 O 3 , WO 2 , WO 3 , W 2 O 5 , etc.), a vanadium oxide (for example, VO, V 2 O 3 , VO 2 , V 2 O 5 , etc.), a molybdenum oxide (MoO, Mo 2 O 3 , MoO 2 , MoO 3 , Mo 2 O 5 , etc.), and a 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 a titanium halide (for example, TiF 4 , TiCl 4 , TiBr 4 , TiI 4 , etc.), a zirconium halide (for example, ZrF 4 , ZrCl 4 , ZrBr 4 , ZrI 4 , etc.), a hafnium halide (for example, HfF 4 , HfCl 4 , HfBr 4 , HfI 4 , etc.), a vanadium halide (for example, VF 3 , VCl 3 , VBr 3 , VI 3 , etc.), a niobium halide (for example, NbF 3 , NbCl 3 , NbBr 3 , NbI 3 , etc.), a tantalum halide (for example, TaF 3 , TaCl 3 , TaBr 3 , TaI 3 , etc.), a chromium halide (for example, CrF 3 , CrCl 3 , CrBr 3 , CrI 3 , etc.), a molybdenum halide (for example, MoF 3 , MoCl 3 , MoBr 3 , MoI 3 , etc.), a tungsten halide (for example, WF 3 , WCl 3 , WBr 3 , WI 3 , etc.), a manganese halide (for example, MnF 2 , MnCl 2 , MnBr 2 , Mn 12 , etc.), a technetium halide (for example, TcF 2 , TcCl 2 , TcBr 2 , TcI 2 , etc.), a rhenium halide (for example, ReF 2 , ReCl 2 , ReBr 2 , ReI 2 , etc.), an iron halide (for example, FeF 2 , FeCl 2 , FeBr 2 , FeI 2 , etc.), a ruthenium halide (for example, RuF 2 , RuCl 2 , RuBr 2 , RuI 2 , etc.), an osmium halide (for example, OsF 2 , OsCl 2 , OsBr 2 , OsI 2 , etc.), a cobalt halide (for example, CoF 2 , CoCl 2 , CoBr 2 , CoI 2 , etc.), a rhodium halide (for example, RhF 2 , RhCl 2 , RhBr 2 , RhI 2 , etc.), an iridium halide (for example, IrF 2 , IrCl 2 , IrBr 2 , IrI 2 , etc.), a nickel halide (for example, NiF 2 , NiCl 2 , NiBr 2 , NiI 2 , etc.), a palladium halide (for example, PdF 2 , PdCl 2 , PdBr 2 , PdI 2 , etc.), a platinum halide (for example, PtF 2 , PtCl 2 , PtBr 2 , PtI 2 , etc.), a copper halide (for example, CuF, CuCl, CuBr, CuI, etc.), a silver halide (for example, AgF, AgCl, AgBr, AgI, etc.), and a gold halide (for example, AuF, AuCl, AuBr, AuI, etc.). 
     Examples of the post-transition metal halide may include a zinc halide (for example, ZnF 2 , ZnCl 2 , ZnBr 2 , ZnI 2 , etc.), an indium halide (for example, InI 3 , etc.), and a 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 . 
     An example of the metalloid halide may include antimony halide (for example, SbCl 5 , etc.). 
     Examples of the metal telluride may include an alkali metal telluride (for example, Li 2 Te, Na 2 Te, K 2 Te, Rb 2 Te, Cs 2 Te, etc.), an alkaline earth metal telluride (for example, BeTe, MgTe, CaTe, SrTe, BaTe, etc.), a 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.), a post-transition metal telluride (for example, ZnTe, etc.), and a 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   
     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 one or more embodiments, 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 may contact each other or may be separated from each other. In one or more embodiments, the emission layer may include two or more materials of 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 about 0.01 to about 15 parts by weight based on 100 parts by weight of the host. 
     In one or more embodiments, the emission layer may include a quantum dot. 
     In some embodiments, the emission layer may include a delayed fluorescence material. The delayed fluorescence material may act 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 this range, 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: 
     Formula 301 
       [Ar 301 ] xb11 -[(L 301 ) xb1 -R 301 ] xb21 , 
     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 . 
     For example, 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 one or more embodiments, the host may include a compound represented by Formula 301-1, a compound represented by Formula 301-2, or any combination thereof: 
     
       
         
         
             
             
         
       
     
     wherein, in Formulae 301-1 and 301-2, 
     ring A301 to ring A304 may each independently be a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a  or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a , 
     X 301  may be O, S, N-[(L 304 ) xb4 -R 304 ], C(R 304 )(R 305 ), or Si(R 304 )(R 305 ), 
     xb22 and xb23 may each independently be 0, 1, or 2, 
     L 301 , xb1, and R 301  may each independently be the same as 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 one or more embodiments, the host may include an alkaline earth metal complex, a post-transition metal complex, or any combination thereof. In one or more embodiments, the host may include a Be complex (for example, Compound H55), an Mg complex, a Zn complex, or any combination thereof. 
     In an embodiment, the host may include one of Compounds H1 to 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), PH2, 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. 
     For example, 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 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, and when xc2 is 2 or more, two or more 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(Q 411 )=*′, 
     X 403  and X 404  may each independently be a chemical bond (for example, a covalent bond or a coordination 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 *′ in Formula 402 each indicate a binding site to M in Formula 401. 
     For example, in Formula 402, i) X 401  may be nitrogen, and X 402  may be carbon, or ii) each of X 401  and X 402  may be nitrogen (e.g., simultaneously). 
     In one or more embodiments, when xc1 in Formula 402 is 2 or more, two ring A401 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. For example, L 402  may include a halogen group, a diketone group (for example, an acetylacetonate group), a carboxylic acid group (for example, a picolinate group), —C(═O), an isonitrile group, —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 one or more embodiments, 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 one or more embodiments, 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 one or more embodiments, xd4 in Formula 501 may be 2. 
     In one or more embodiments, the fluorescent dopant may include: one of Compounds FD1 to FD36; DPVBi; DPAVBi; or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Delayed Fluorescence Material 
     The emission layer may include a delayed fluorescence material. 
     In the present specification, the delayed fluorescence material may be selected from compounds capable of emitting delayed fluorescence based on a delayed fluorescence emission mechanism. 
     The delayed fluorescence material included in the emission layer may act as a host or a dopant depending on the type or function of other materials included in the emission layer. 
     In one or more embodiments, the difference between the triplet energy level (eV) of the delayed fluorescence material and the singlet energy level (eV) of the delayed fluorescence material 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 material and the singlet energy level (eV) of the delayed fluorescence material satisfies the above-described range, up-conversion of the triplet state (e.g., triplet state excitons) to the singlet state of the delayed fluorescence materials (e.g., singlet state excitons) may effectively occur, and thus, the emission efficiency of the light-emitting device  10  may be improved. 
     In one or more embodiments, the delayed fluorescence material 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). 
     In one or more embodiments, the delayed fluorescence material 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” refers to a crystal of a semiconductor compound, and may include any 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 chemical vapor deposition process, a molecular beam epitaxy process, or any suitable process similar thereto. 
     According to 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 as a dispersant coordinated on the surface of the quantum dot crystal and controls the growth of the crystal, such that the growth of quantum dot particles can be controlled or selected through a process that is more easily performed than vapor deposition methods (such as metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE)) and which requires low costs. 
     The quantum dot may include Group II-VI semiconductor compounds, Group III-V semiconductor compounds, Group III-VI semiconductor compounds, Group I-III-VI semiconductor compounds, Group IV-VI semiconductor compounds, Group IV elements or compounds, 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); and/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, InSb, and/or the like); a ternary compound (such as GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InGaP, InNP, InAlP, InNAs, InNSb, InPAs, InPSb, GaAlNP, and/or the like); a quaternary compound (such as GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, and/or the like); and/or any combination thereof. In some embodiments, the Group III-V semiconductor compound may further include a Group II element. Examples of the Group III-V semiconductor compound further including a Group II element may include InZnP, InGaZnP, InAlZnP, etc. 
     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 ); and 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 ); and 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); and any combination thereof. 
     The Group IV element or compound may include a single element compound (e.g., an elemental material, such as Si and/or Ge); a binary compound (such as SiC and/or SiGe); and any combination thereof. 
     Each element included in a multi-element compound (such as the binary compound, ternary compound and/or quaternary compound), may exist in a particle with a substantially uniform concentration or may exist with a non-uniform concentration (for example, with a concentration or compositional gradient). 
     In some embodiments, 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 one or more embodiments, 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 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 interface between the core and the shell may have a concentration gradient that decreases toward the center of the element present in the shell. 
     Examples of the shell of the quantum dot may include an oxide of a metal, a metalloid, or a non-metal, a semiconductor compound, and any combination thereof. Examples of the oxide of metal, metalloid, 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 ); and any combination thereof. Examples of the semiconductor compound may include, as described herein, Group II-VI semiconductor compounds; Group III-V semiconductor compounds; Group III-VI semiconductor compounds; Group I-III-VI semiconductor compounds; Group IV-VI semiconductor compounds; and 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 and/or color gamut may be increased. In some embodiments, because light emitted through the quantum dot is emitted in all directions, a wide viewing angle can be improved. 
     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 or selected by controlling or selecting the size of the quantum dot, light having one or more suitable wavelength bands can be obtained from the quantum dot emission layer. Therefore, by utilizing quantum dots of different sizes, a light-emitting device that is to emit light of one or more suitable wavelengths may be implemented. In one or more embodiments, the size of the quantum dot may be selected to emit red, green and/or blue light. In some embodiments, the device may be configured to emit white light by combining quantum dots of one or more suitable sizes to emit light of one or more suitable colors. 
     Electron Transport Region in Interlayer  130   
     The electron transport region may include an electron transport layer as described herein. The detailed description of the electron transport layer may be the same as described in the present specification. 
     The electron transport region may include, in addition to the electron transport layer, a buffer layer, a hole blocking layer, an electron control layer, an electron injection layer, or any combination thereof. 
     In an embodiment, 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, wherein the constituting layers of each structure are sequentially stacked from an emission layer. 
     The electron transport layer may include a first material and a second material as described herein. 
     In one or more embodiments, in addition to the first material and the second material described herein, the electron transport region (for example, the buffer layer, the hole blocking layer, the electron control layer, and/or the electron transport layer in the electron transport region) may further 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 further include a compound represented by Formula 601: 
     Formula 601 
       [Ar 601 ] xe11 -[(L 601 ) xe1 -R 601 ] xe21 , 
     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 6  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 , and R 601  may each independently be a π electron-deficient nitrogen-containing C 1 -C 60  cyclic group unsubstituted or substituted with at least one R 10a . 
     In an embodiment, when xe11 in Formula 601 is 2 or more, two or more Ar 601 (s) may be linked via a single bond. 
     In one or more embodiments, Ar 601  in Formula 601 may be a substituted or unsubstituted anthracene group. 
     In one or more embodiments, the electron transport region may further 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 ), 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 . 
     For example, xe1 and xe611 to xe613 in Formulae 601 and 601-1 may each independently be 0, 1, or 2. 
     The electron transport region may further include one of Compounds ET1 to ET45, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), 4,7-diphenyl-1,10-phenanthroline (Bphen), Alq 3 , BAlq, TAZ, NTAZ, or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A thickness of the electron transport region may be about 100 Å to about 5,000 Å, for example, 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 thicknesses of the buffer layer, the hole blocking layer, or the electron control layer may each independently be about 20 Å to about 1,000 Å, for example, about 30 Å to about 300 Å, and a thickness of the electron transport layer may be about 100 Å to about 1,000 Å, for example, about 150 Å to about 500 Å. When the thicknesses of the buffer layer, the hole blocking layer, the electron control layer, the electron transport layer and/or the electron transport layer are within these ranges, satisfactory electron transporting characteristics may be obtained without a substantial increase in driving voltage. 
     The electron transport region may include an electron injection layer that facilitates injection of electrons from the second electrode  150 . The electron injection layer may directly contact the second electrode  150 . 
     The electron injection layer may have: i) a single-layered structure including (e.g., consisting of) a single layer including (e.g., consisting of) a single material, ii) a single-layered structure including (e.g., 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 each independently be 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 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 one or more embodiments, 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, hydroxyquinoline, hydroxyisoquinoline, hydroxybenzoquinoline, hydroxyacridine, hydroxyphenanthridine, hydroxyphenyloxazole, hydroxyphenylthiazole, hydroxyphenyloxadiazole, hydroxyphenylthiadiazole, hydroxyphenylpyridine, hydroxyphenyl benzimidazole, hydroxyphenylbenzothiazole, bipyridine, phenanthroline, 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 one or more embodiments, the electron injection layer may further include an organic material (for example, a compound represented by Formula 601). 
     In one or more embodiments, the electron injection layer may include (e.g., consist of) i) an alkali metal-containing compound (for example, an alkali metal halide), ii) a) an alkali metal-containing compound (for example, an alkali metal halide); and/or b) an alkali metal, an alkaline earth metal, a rare earth metal, or any combination thereof. In one or more embodiments, the electron injection layer may be a KI:Yb co-deposited layer, an RbI:Yb co-deposited layer, and/or the like. 
     When the electron injection layer further includes an organic material, the alkali metal, alkaline earth metal, rare earth metal, alkali metal-containing compound, alkaline earth metal-containing compound, rare earth metal-containing compound, alkali metal complex, alkaline earth-metal complex, rare earth metal complex, or combination thereof may be substantially 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 range described above, the electron injection layer may have satisfactory electron injection characteristics without a substantial increase in driving voltage. 
     Second Electrode  150   
     The second electrode  150  may be located on the interlayer  130  having such a structure. The second electrode  150  may be a cathode (which is an electron injection electrode), and a metal, an alloy, an electrically conductive compound, or any combination thereof, each having a low work function, may be utilized as the material for the second electrode  150 . 
     In one or more embodiments, the second electrode  150  may include lithium (Li), silver (Ag), magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), ytterbium (Yb), silver-ytterbium (Ag—Yb), ITO, IZO, or 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  (e.g., on the side of either electrode that is opposite the emission layer). 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. 
     Light generated in an emission layer of the interlayer  130  of the light-emitting device  10  may be extracted toward the outside through the first electrode  110  (which may be a semi-transmissive electrode or a transmissive electrode) and the first capping layer, or light generated in an emission layer of the interlayer  130  of the light-emitting device  10  may be extracted toward the outside through the second electrode  150  (which is a semi-transmissive electrode or a transmissive electrode) and the second capping layer. 
     The first capping layer and the second capping layer may increase the external emission efficiency of the device according to the principle of constructive interference. Accordingly, the light extraction efficiency of the light-emitting device  10  may be increased, so that the emission efficiency of the light-emitting device  10  may be improved. 
     Each of the first capping layer and 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 selected from the first capping layer and the second capping layer may each independently include carbocyclic compounds, heterocyclic compounds, amine group-containing compounds, porphyrin derivatives, phthalocyanine derivatives, naphthalocyanine derivatives, alkali metal complexes, 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 one or more embodiments, at least one of the first capping layer and the second capping layer may each independently include an amine group-containing compound. 
     In one or more embodiments, at least one of the first capping layer and the second capping layer may each independently include a compound represented by Formula 201, a compound represented by Formula 202, or any combination thereof. 
     In one or more embodiments, at least one of the first capping layer and the second capping layer may each independently include one of Compounds HT28 to HT33 one of Compounds CP1 to CP6, β-NPB, or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Electronic Apparatus 
     The light-emitting device may be included in various suitable electronic apparatuses. In one or more embodiments, 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, 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 (e.g., to cross or intercept) at least one traveling direction of light emitted from the light-emitting device. In one or more 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 one or more embodiments, 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 areas, the color filter may include a plurality of color filter areas respectively corresponding to the subpixel areas, and the color conversion layer may include a plurality of color conversion areas respectively corresponding to the subpixel areas. 
     A pixel-defining film may be located among (e.g., between) the subpixel areas to define each of the subpixel areas. 
     The color filter may further include a plurality of color filter areas and light-shielding patterns located among the color filter areas, and the color conversion layer may include a plurality of color conversion areas and light-shielding patterns located among the color conversion areas. 
     The color filter areas (and/or the color conversion areas) may include a first area to emit first color light, a second area to emit second color light, and/or a third area to emit 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 one or more embodiments, 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 one or more embodiments, the color filter areas (and/or the color conversion areas) may include quantum dots. In more detail, the first area may include a red quantum dot, the second area may include a green quantum dot, and the third area may not include a quantum dot. The quantum dot may be the same as described in the present specification. The first area, the second area, and/or the third area may each independently include a scatterer. 
     In one or more embodiments, the light-emitting device may be to emit first light, the first area may be to absorb the first light to emit first first-color light, the second area may be to absorb the first light to emit second first-color light, and the third area may be to absorb the first light to emit 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. In more detail, the first light may be blue light, the first first-color light may be red light, the second first-color light may be green light, and the third first-color light may be blue light. 
     The electronic apparatus may further include a thin-film transistor in addition to the light-emitting device as described above. The thin-film transistor may include a source electrode, a drain electrode, and an activation layer, wherein any one of the source electrode and the drain electrode may be electrically connected to any one of the first electrode and the second electrode of the light-emitting device. 
     The thin-film transistor may further include a gate electrode, a gate insulating film, etc. 
     The activation layer may include crystalline silicon, amorphous silicon, organic semiconductor, 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 placed between the color filter and the light-emitting device. The sealing portion may allow light from the light-emitting device to be extracted 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 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 intended use 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, 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, a biometric information collector. 
     The electronic apparatus may be applied to various displays, light sources, lighting, personal computers (for example, a mobile personal computer), mobile phones, digital cameras, electronic organizers, electronic dictionaries, electronic game machines, medical instruments (for example, electronic thermometers, sphygmomanometers, blood glucose meters, pulse measurement devices, pulse wave measurement devices, electrocardiogram displays, ultrasonic diagnostic devices, and/or endoscope displays), fish finders, various measuring instruments, meters (for example, meters for a vehicle, an aircraft, and a vessel), projectors, and/or the like. 
     Description of FIGS.  2  and  3   
       FIG. 2  is a cross-sectional view of a light-emitting apparatus according to an embodiment of the present disclosure. 
     The light-emitting apparatus of  FIG. 2  includes a substrate  100 , a thin-film transistor (TFT), a light-emitting device, and an encapsulation portion  300  that seals the light-emitting device. 
     The substrate  100  may be a flexible substrate, a glass substrate, or a metal substrate. A buffer layer  210  may be formed 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 or polysilicon), an organic semiconductor, or an oxide semiconductor, and may include a source region, a drain region, and a channel region. 
     A gate insulating film  230  for 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 a 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 formed 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 or polyacrylic organic film. In some embodiments, at least some layers of the interlayer  130  may extend beyond the upper portion of the pixel defining layer  290  to be 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 (SiN x ), silicon oxide (SiO x ), 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. 3  is a cross-sectional view of a light-emitting apparatus according to an embodiment of the present disclosure. 
     The light-emitting apparatus of  FIG. 3  is substantially the same as the light-emitting apparatus of  FIG. 2 , 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 a combination of i) a color filter area, ii) a color conversion area, or iii) a combination of the color filter area and the color conversion area. In one or more embodiments, the light-emitting device included in the light-emitting apparatus of  FIG. 3  may be a tandem light-emitting device. 
     Manufacture 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 set or predetermined 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 the layers constituting the hole transport region, the emission layer, and the layers constituting 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 and the structure of the layer to be formed. 
     Definition of Terms 
     The term “C 3 -C 60  carbocyclic group” as utilized herein refers to a cyclic group consisting of carbon only as a ring-forming atom and having three to sixty carbon atoms, and the term “C 1 -C 60  heterocyclic group” as utilized herein refers to a cyclic group that has one to sixty carbon atoms and further has, in addition to carbon, a heteroatom as a ring-forming atom. The C 3 -C 60  carbocyclic group and the C 1 -C 60  heterocyclic group may each be a monocyclic group including (e.g., consisting of) one ring or a polycyclic group in which two or more rings are condensed with each other. For example, the C 1 -C 60  heterocyclic group may have 3 to 61 ring-forming atoms. 
     The term “cyclic group” as utilized 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 utilized 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 utilized herein refers to a heterocyclic group that has one to sixty carbon atoms and includes *—N=*′ as a ring-forming moiety. 
     For example, 
     the C 3 -C 60  carbocyclic group may be i) a group T1 (defined below) or ii) a condensed cyclic group in which two or more groups T1 are condensed with each other (for example, a cyclopentadiene group, an adamantane group, a norbornane group, a benzene group, a pentalene group, a naphthalene group, an azulene group, an indacene group, an acenaphthylene group, a phenalene group, a phenanthrene group, an anthracene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, a perylene group, a pentaphene group, a heptalene group, a naphthacene group, a picene group, a hexacene group, a pentacene group, a rubicene group, a coronene group, an ovalene group, an indene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, an indenophenanthrene group, or an indenoanthracene group), 
     the C 1 -C 60  heterocyclic group may be i) a group T2 (defined below), 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, 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) a group T1, ii) a condensed cyclic group in which two or more groups T1 are condensed with each other, iii) a group T3 (defined below), 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 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) a group T4 (defined below), 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, 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.), 
     where the 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, 
     the 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, 
     the group T3 may be a furan group, a thiophene group, a 1H-pyrrole group, a silole group, or a borole group, and 
     the 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. 
     Terms such as “the cyclic group”, “the C 3 -C 60  carbocyclic group”, “the C 1 -C 60  heterocyclic group”, “the π electron-rich C 3 -C 60  cyclic group”, and/or “the π electron-deficient nitrogen-containing C 1 -C 60  cyclic group” as utilized herein refer to a group condensed to any cyclic 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 utilized. In one or more embodiments, “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 6  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 monovalent C 1 -C 60  heterocyclic group are 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 substituted or unsubstituted divalent non-aromatic condensed heteropolycyclic group. 
     The term “C 1 -C 60  alkyl group” as utilized 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 utilized herein refers to a divalent group having substantially the same structure as the C 1 -C 60  alkyl group. 
     The term “C 2 -C 60  alkenyl group” as utilized herein refers to a monovalent hydrocarbon group having at least one carbon-carbon double bond in the middle or at 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 utilized herein refers to a divalent group having substantially the same structure as the C 2 -C 60  alkenyl group. 
     The term “C 2 -C 60  alkynyl group” as utilized herein refers to a monovalent hydrocarbon group having at least one carbon-carbon triple bond in the middle or at 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 6  alkynylene group” as utilized herein refers to a divalent group having substantially the same structure as the C 2 -C 60  alkynyl group. 
     The term “C 1 -C 60  alkoxy group” as utilized herein refers to a monovalent group represented by —OA 101  (wherein A 101  is a 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 utilized 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 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 utilized herein refers to a divalent group having substantially the same structure as the C 3 -C 10  cycloalkyl group. 
     The term “C 1 -C 10  heterocycloalkyl group” as utilized herein refers to a monovalent cyclic group that further includes, in addition to a carbon atom, at least one heteroatom as a ring-forming atom and has 1 to 10 carbon atoms, 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 utilized herein refers to a divalent group having substantially the same structure as the C 1 -C 10  heterocycloalkyl group. 
     The term C 3 -C 10  cycloalkenyl group utilized herein refers to a monovalent cyclic group that has three to ten carbon atoms, 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 utilized herein refers to a divalent group having substantially the same structure as the C 3 -C 10  cycloalkenyl group. 
     The term “C 1 -C 10  heterocycloalkenyl group” as utilized herein refers to a monovalent cyclic group that has, in addition to a carbon atom, at least one heteroatom as a ring-forming atom, 1 to 10 carbon atoms, and at least one 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 utilized herein refers to a divalent group having substantially the same structure as the C 1 -C 10  heterocycloalkenyl group. 
     The term “C 6 -C 60  aryl group” as utilized 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 utilized 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 include two or more rings, the rings may be condensed with each other. 
     The term “C 1 -C 60  heteroaryl group” as utilized herein refers to a monovalent group having a heterocyclic aromatic system that has, in addition to a carbon atom, at least one heteroatom as a ring-forming atom, and 1 to 60 carbon atoms. The term “C 1 -C 60  heteroarylene group” as utilized herein refers to a divalent group having a heterocyclic aromatic system that has, in addition to a carbon atom, at least one heteroatom as a ring-forming atom, and 1 to 60 carbon atoms. 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, and a naphthyridinyl group. When the C 1 -C 6  heteroaryl group and the C 1 -C 60  heteroarylene group each include two or more rings, the rings may be condensed with each other. 
     The term “monovalent non-aromatic condensed polycyclic group” as utilized herein refers to a monovalent group (for example, having 8 to 60 carbon atoms) having two or more rings condensed to each other, only carbon atoms as ring-forming atoms, and no aromaticity in its entire molecular structure. 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, and an indeno anthracenyl group. The term “divalent non-aromatic condensed polycyclic group” as utilized herein refers to a divalent group having substantially the same structure as a monovalent non-aromatic condensed polycyclic group. 
     The term “monovalent non-aromatic condensed heteropolycyclic group” as utilized herein refers to a monovalent group (for example, having 1 to 60 carbon atoms) having two or more rings condensed to each other, at least one heteroatom other than carbon atoms, as a ring-forming atom, and non-aromaticity in its entire molecular structure. Examples of the monovalent non-aromatic condensed heteropolycyclic group may include a pyrrolyl group, a thiophenyl group, a furanyl group, an indolyl group, a benzoindolyl group, a naphtho indolyl 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 indenocarbazolyl group, an indolocarbazolyl group, a benzofurocarbazolyl group, a benzothienocarbazolyl group, a benzosilolocarbazolyl group, a benzoindolocarbazolyl group, a benzocarbazolyl group, a benzonaphthofuranyl group, a benzonaphthothiophenyl group, a benzonaphthosilolyl group, a benzofurodibenzofuranyl group, a benzofurodibenzothiophenyl group, and a benzothienodibenzothiophenyl group. The term “divalent non-aromatic heterocondensed polycyclic group” as utilized herein refers to a divalent group having substantially the same structure as a monovalent non-aromatic heterocondensed polycyclic group. 
     The term “C 6 -C 60  aryloxy group” as utilized herein indicates —OA 102  (wherein A 102  is a C 6 -C 60  aryl group), and the term “C 6 -C 60  arylthio group” as utilized herein indicates —SA 103  (wherein A 103  is a C 6 -C 60  aryl group). 
     The term “C 7 -C 60  aryl alkyl group” utilized herein refers to -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  heteroaryl alkyl group” utilized herein refers to -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 utilized 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  aryl alkyl group, a C 2 -C 60  heteroaryl alkyl 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 6  heterocyclic group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 7 -C 60  aryl alkyl group, or a C 2 -C 60  heteroaryl alkyl 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  aryl alkyl group, a C 2 -C 60  heteroaryl alkyl 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  utilized herein may each independently be: hydrogen; deuterium; —F; —Cl; —Br; —I; a hydroxyl group; a cyano group; a nitro group; a C 7 -C 60  aryl alkyl group; or a C 2 -C 60  heteroaryl alkyl group, or a C 1 -C 6  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 6  alkoxy group, a phenyl group, a biphenyl group, or any combination thereof. 
     The term “hetero atom” as utilized herein refers to any atom other than a carbon atom. Examples of the heteroatom may include O, S, N, P, Si, B, Ge, Se, and any combination thereof. 
     The term “the third-row transition metal” utilized herein includes hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), etc. 
     The term “Group 3 transition metal” utilized herein includes scandium (Sc), Yttrium (Y), etc. 
     The term “Ph” as utilized herein refers to a phenyl group, the term “Me” as utilized herein refers to a methyl group, the term “Et” as utilized herein refers to an ethyl group, the term “ter-Bu” or “Bu t ” as utilized herein refers to a tert-butyl group, and the term “OMe” as utilized herein refers to a methoxy group. 
     The term “biphenyl group” as utilized 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 utilized 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 utilized herein, unless defined otherwise, each refer to a binding site to a neighboring atom in a corresponding formula or moiety. 
     Hereinafter, a light-emitting device according to embodiments will be described in more detail with reference to Examples. 
     EXAMPLES 
     Compounds Used in the Comparative Examples and Examples 
     The compounds utilized in the Comparative Examples and Examples are as follows: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Comparative Example (R)-1 
     A glass substrate (product of Corning Inc.) including a 15 Ω/cm 2  (120 nm) ITO electrode (anode) was cut to a size of 50 mm×50 mm×0.7 mm, sonicated with isopropyl alcohol and pure water each for 5 minutes, and then cleaned by exposure to ultraviolet rays and ozone for 30 minutes. Then, the ITO glass substrate was provided to a vacuum deposition apparatus. 
     HTM1 was deposited on the ITO electrode to form a hole transport layer having a thickness of 110 nm, and HTM2 was deposited on the hole transport layer to form an emission auxiliary layer having a thickness of 10 nm. 
     Then, a host (a first host (PH1) and a second host (PH2) were included at a weight ratio of 5:5) and a dopant (RD1) were co-deposited at a weight ratio of 90:10 on the emission auxiliary layer to form an emission layer having a thickness of 30 nm. 
     Thereafter, ETM1 was deposited on the emission layer to form a buffer layer having a thickness of 10 nm, a first material and a second material shown in Table 1 were co-deposited at a weight ratio shown in Table 1 on the buffer layer to form an electron transport layer having a thickness of 20 nm, LiF was deposited on the electron transport layer to form an electron injection layer having a thickness of 1 nm, and A1 was deposited on the electron injection layer to form a cathode having a thickness of 30 nm, thereby completing the manufacture of an organic light-emitting device having a structure of ITO (120 nm)/HTM1 (110 nm)/HTM2 (10 nm)/PH1+PH2 (5:5): RD1 (10 wt %) (30 nm)/ETM1 (10 nm)/ETM3:LiQ (5:5) (20 nm)/LiF (1 nm)/Al (30 nm). 
     Comparative Examples (R)-2 and (R)-3 and Examples (R)-1 to (R)-24 
     Additional organic light-emitting devices were manufactured in substantially the same manner as in Comparative Example (R)-1, except that in an electron transport layer, a first material, a second material, and a weight ratio of the first material to the second material were changed as shown in Table 1. 
     Evaluation Example 1 
     The driving voltage (V) at 1,000 cd/m 2 , luminescence efficiency (Cd/A), and lifespan (T 97 ) of the organic light-emitting devices manufactured according to Comparative Examples (R)-1 to (R)-3 and Examples (R)-1 to (R)-24 were measured by utilizing a Keithley MU 236 and a luminance meter PR650, and the results thereof are shown in Table 1. In Table 1, lifespan (T 97 ) was evaluated as the time (hr) taken for luminance to reach 97% of the initial luminance, and is represented as a relative value (%). 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Electron transport layer 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 Weight 
                   
                   
                   
               
               
                   
                   
                   
                 ratio of first 
               
               
                   
                   
                   
                 material 
                 Driving 
                 Luminescence 
                 Lifespan 
               
               
                   
                 First 
                 Second 
                 to second 
                 voltage 
                 efficiency 
                 (T 97 ) 
               
               
                   
                 material 
                 material 
                 material 
                 (V) 
                 (Cd/A) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Comparative 
                 ETM3 
                 LiQ 
                 5:5 
                 5.2 
                 19.5 
                 98 
               
               
                 Example (R)-1 
               
               
                 Comparative 
                 ETM4 
                 LiQ 
                 5:5 
                 5.4 
                 18.1 
                 89 
               
               
                 Example (R)-2 
               
               
                 Comparative 
                 ETM5 
                 LiQ 
                 5:5 
                 5.3 
                 17.8 
                 81 
               
               
                 Example (R)-3 
               
               
                 Example (R)-1 
                 ETM6 
                 LiQ 
                 5:5 
                 5.1 
                 19.5 
                 103 
               
               
                 Example (R)-2 
                 ETM6 
                 Li 
                 9:1 
                 4.8 
                 19.7 
                 107 
               
               
                 Example (R)-3 
                 ETM6 
                 Yb 
                 9:1 
                 4.9 
                 20.1 
                 107 
               
               
                 Example (R)-4 
                 ETM7 
                 LiQ 
                 5:5 
                 5.1 
                 19.5 
                 103 
               
               
                 Example (R)-5 
                 ETM7 
                 Li 
                 9:1 
                 4.9 
                 19.7 
                 107 
               
               
                 Example (R)-6 
                 ETM7 
                 Yb 
                 9:1 
                 5.0 
                 19.6 
                 107 
               
               
                 Example (R)-7 
                 ETM8 
                 LiQ 
                 5:5 
                 5.0 
                 18.9 
                 104 
               
               
                 Example (R)-8 
                 ETM8 
                 Li 
                 9:1 
                 4.8 
                 19.1 
                 110 
               
               
                 Example (R)-9 
                 ETM8 
                 Yb 
                 9:1 
                 4.9 
                 19.1 
                 111 
               
               
                 Example (R)-10 
                 ETM9 
                 LiQ 
                 5:5 
                 5.1 
                 19.5 
                 105 
               
               
                 Example (R)-11 
                 ETM9 
                 Li 
                 9:1 
                 4.9 
                 19.6 
                 110 
               
               
                 Example (R)-12 
                 ETM9 
                 Yb 
                 9:1 
                 4.9 
                 19.7 
                 111 
               
               
                 Example (R)-13 
                 ETM10 
                 LiQ 
                 5:5 
                 5.0 
                 19.2 
                 109 
               
               
                 Example (R)-14 
                 ETM10 
                 Li 
                 9:1 
                 4.8 
                 19.7 
                 114 
               
               
                 Example (R)-15 
                 ETM10 
                 Yb 
                 9:1 
                 4.8 
                 19.9 
                 114 
               
               
                 Example (R)-16 
                 ETM11 
                 LiQ 
                 5:5 
                 5.0 
                 19.2 
                 110 
               
               
                 Example (R)-17 
                 ETM11 
                 Li 
                 9:1 
                 4.7 
                 19.3 
                 116 
               
               
                 Example (R)-18 
                 ETM11 
                 Yb 
                 9:1 
                 4.8 
                 19.5 
                 116 
               
               
                 Example (R)-19 
                 ETM12 
                 LiQ 
                 5:5 
                 5.0 
                 19.1 
                 105 
               
               
                 Example (R)-20 
                 ETM12 
                 Li 
                 9:1 
                 4.8 
                 19.3 
                 113 
               
               
                 Example (R)-21 
                 ETM12 
                 Yb 
                 9:1 
                 4.9 
                 19.2 
                 115 
               
               
                 Example (R)-22 
                 ETM13 
                 LiQ 
                 5:5 
                 5.1 
                 19.1 
                 108 
               
               
                 Example (R)-23 
                 ETM13 
                 Li 
                 9:1 
                 4.8 
                 19.3 
                 113 
               
               
                 Example (R)-24 
                 ETM13 
                 Yb 
                 9:1 
                 4.8 
                 19.2 
                 116 
               
               
                   
               
            
           
         
       
     
     From Table 1, it is confirmed that the organic light-emitting devices of Examples (R)-1 to (R)-24 have excellent or suitable characteristics in terms of driving voltage, luminescence efficiency, and/or lifespan, compared to the organic light-emitting devices of Comparative Examples (R)-1 to (R)-3. 
     Comparative Example (G)-1 
     An organic light-emitting device having a structure of ITO (120 nm)/HTM1 (110 nm)/HTM2 (10 nm)/PH1+PH2 (5:5):GD1 (8 wt %) (30 nm)/ETM1 (10 nm)/ETM3:LiQ (5:5) (20 nm)/LiF (1 nm)/Al (30 nm) was manufactured in substantially the same manner as in Comparative Example (R)-1, except that in an emission layer, GD1 was utilized as a dopant instead of RD1, and a weight ratio of a host and a dopant was changed to a weight ratio of 92:8. 
     Comparative Examples (G)-2 and (G)-3 and Examples (G)-1 to (G)-24 
     Organic light-emitting devices were manufactured in substantially the same manner as in Comparative Example (G)-1, except that in an electron transport layer, a first material, a second material, and a weight ratio of the first material to the second material were changed as shown in Table 2. 
     Evaluation Example 2 
     The driving voltage (V) at 1,000 cd/m 2 , luminescence efficiency (Gd/A), and lifespan (T 97 ) of the organic light-emitting devices manufactured according to Comparative Examples (G)-1 to (G)-3 and Examples (G)-1 to (G)-24 were measured in substantially the same manner as in Evaluation Example 1, and the results thereof are shown in Table 2. In Table 2, lifespan (T 97 ) was evaluated as the time (hr) taken for luminance to reach 97% of the initial luminance, and was represented as a relative value (%). 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 2 
               
             
            
               
                   
                   
               
               
                   
                 Electron transport layer 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 Weight 
                   
                   
                   
               
               
                   
                   
                   
                 ratio of first 
               
               
                   
                   
                   
                 material 
                 Driving 
                 Luminescence 
                 Lifespan 
               
               
                   
                 First 
                 Second 
                 to second 
                 voltage 
                 efficiency 
                 (T 97 ) 
               
               
                   
                 material 
                 material 
                 material 
                 (V) 
                 (Cd/A) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Comparative 
                 ETM3 
                 LiQ 
                 5:5 
                 5.1 
                 43.0 
                 97 
               
               
                 Example (G)-1 
               
               
                 Comparative 
                 ETM4 
                 LiQ 
                 5:5 
                 5.1 
                 40.0 
                 90 
               
               
                 Example (G)-2 
               
               
                 Comparative 
                 ETM5 
                 LiQ 
                 5:5 
                 5.2 
                 39.7 
                 88 
               
               
                 Example (G)-3 
               
               
                 Example (G)-1 
                 ETM6 
                 LiQ 
                 5:5 
                 4.9 
                 41.8 
                 102 
               
               
                 Example (G)-2 
                 ETM6 
                 Li 
                 9:1 
                 4.9 
                 41.9 
                 107 
               
               
                 Example (G)-3 
                 ETM6 
                 Yb 
                 9:1 
                 4.8 
                 41.9 
                 107 
               
               
                 Example (G)-4 
                 ETM7 
                 LiQ 
                 5:5 
                 4.9 
                 43.0 
                 102 
               
               
                 Example (G)-5 
                 ETM7 
                 Li 
                 9:1 
                 4.9 
                 43.1 
                 105 
               
               
                 Example (G)-6 
                 ETM7 
                 Yb 
                 9:1 
                 4.8 
                 43.1 
                 106 
               
               
                 Example (G)-7 
                 ETM8 
                 LiQ 
                 5:5 
                 4.8 
                 39.9 
                 108 
               
               
                 Example (G)-8 
                 ETM8 
                 Li 
                 9:1 
                 4.6 
                 40.7 
                 111 
               
               
                 Example (G)-9 
                 ETM8 
                 Yb 
                 9:1 
                 4.7 
                 41.1 
                 111 
               
               
                 Example (G)-10 
                 ETM9 
                 LiQ 
                 5:5 
                 4.8 
                 41.9 
                 110 
               
               
                 Example (G)-11 
                 ETM9 
                 Li 
                 9:1 
                 4.8 
                 41.9 
                 116 
               
               
                 Example (G)-12 
                 ETM9 
                 Yb 
                 9:1 
                 4.8 
                 42.0 
                 115 
               
               
                 Example (G)-13 
                 ETM10 
                 LiQ 
                 5:5 
                 4.9 
                 41.5 
                 105 
               
               
                 Example (G)-14 
                 ETM10 
                 Li 
                 9:1 
                 4.8 
                 41.6 
                 108 
               
               
                 Example (G)-15 
                 ETM10 
                 Yb 
                 9:1 
                 4.7 
                 41.7 
                 108 
               
               
                 Example (G)-16 
                 ETM11 
                 LiQ 
                 5:5 
                 4.7 
                 41.9 
                 105 
               
               
                 Example (G)-17 
                 ETM11 
                 Li 
                 9:1 
                 4.5 
                 41.8 
                 111 
               
               
                 Example (G)-18 
                 ETM11 
                 Yb 
                 9:1 
                 4.5 
                 41.9 
                 113 
               
               
                 Example (G)-19 
                 ETM12 
                 LiQ 
                 5:5 
                 4.9 
                 42.0 
                 102 
               
               
                 Example (G)-20 
                 ETM12 
                 Li 
                 9:1 
                 4.8 
                 42.3 
                 108 
               
               
                 Example (G)-21 
                 ETM12 
                 Yb 
                 9:1 
                 4.7 
                 42.3 
                 107 
               
               
                 Example (G)-22 
                 ETM13 
                 LiQ 
                 5:5 
                 5.0 
                 41.8 
                 110 
               
               
                 Example (G)-23 
                 ETM13 
                 Li 
                 9:1 
                 4.9 
                 42.1 
                 116 
               
               
                 Example (G)-24 
                 ETM13 
                 Yb 
                 9:1 
                 4.8 
                 42.2 
                 115 
               
               
                   
               
            
           
         
       
     
     From Table 2, it is confirmed that the organic light-emitting devices of Examples (G)-1 to (G)-24 have excellent or suitable characteristics in terms of driving voltage, luminescence efficiency, and/or lifespan, compared to the organic light-emitting devices of Comparative Examples (G)-1 to (G)-3. 
     Comparative Example (B)-1 
     An organic light-emitting device having a structure of ITO (120 nm)/HTM1 (110 nm)/HTM2 (10 nm)/BH1:BD1 (2 wt %) (30 nm)/ETM1 (10 nm)/ETM3:LiQ (5:5) (20 nm)/LiF (1 nm)/Al (30 nm) was manufactured in substantially the same manner as in Comparative Example (R)-1, except that in an emission layer, a host and a dopant were changed to BH1 and BD1 respectively, and a weight ratio of the host and the dopant was changed to a weight ratio of 98:2. 
     Comparative Examples (B)-2 and (B)-3 and Examples (B)-1 to (B)-24 
     Organic light-emitting devices were manufactured in substantially the same manner as in Comparative Example (B)-1, except that in an electron transport layer, a first material, a second material, and a weight ratio of the first material to the second material were changed as shown in Table 3. 
     Evaluation Example 3 
     The driving voltage (V) at 1,000 cd/m 2 , luminescence efficiency (Cd/A), and lifespan (T 97 ) of the organic light-emitting devices manufactured according to Comparative Examples (B)-1 to (B)-3 and Examples (B)-1 to (B)-24 were measured in substantially the same manner as in Evaluation Example 1, and the results thereof are shown in Table 3. In Table 3, lifespan (T 97 ) was evaluated as the time (hr) taken for luminance to reach 97% of the initial luminance, and was represented as a relative value (%). 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 3 
               
             
            
               
                   
                   
               
               
                   
                 Electron transport layer 
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 Weight 
                   
                   
                   
               
               
                   
                   
                   
                 ratio of first 
               
               
                   
                   
                   
                 material 
                 Driving 
                 Luminescence 
                 Lifespan 
               
               
                   
                 First 
                 Second 
                 to second 
                 voltage 
                 efficiency 
                 (T 97 ) 
               
               
                   
                 material 
                 material 
                 material 
                 (V) 
                 (Cd/A) 
                 (%) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Comparative 
                 ETM3 
                 LiQ 
                 5:5 
                 4.2 
                 6.5 
                 95 
               
               
                 Example (B)-1 
               
               
                 Comparative 
                 ETM4 
                 LiQ 
                 5:5 
                 4.4 
                 5.9 
                 88 
               
               
                 Example (B)-2 
               
               
                 Comparative 
                 ETM5 
                 LiQ 
                 5:5 
                 4.3 
                 5.5 
                 85 
               
               
                 Example (B)-3 
               
               
                 Example (B)-1 
                 ETM6 
                 LiQ 
                 5:5 
                 3.9 
                 6.3 
                 110 
               
               
                 Example (B)-2 
                 ETM6 
                 Li 
                 9:1 
                 3.8 
                 6.3 
                 116 
               
               
                 Example (B)-3 
                 ETM6 
                 Yb 
                 9:1 
                 3.7 
                 6.5 
                 115 
               
               
                 Example (B)-4 
                 ETM7 
                 LiQ 
                 5:5 
                 3.8 
                 6.2 
                 109 
               
               
                 Example (B)-5 
                 ETM7 
                 Li 
                 9:1 
                 3.8 
                 6.1 
                 114 
               
               
                 Example (B)-6 
                 ETM7 
                 Yb 
                 9:1 
                 3.7 
                 6.1 
                 116 
               
               
                 Example (B)-7 
                 ETM8 
                 LiQ 
                 5:5 
                 3.6 
                 6.2 
                 115 
               
               
                 Example (B)-8 
                 ETM8 
                 Li 
                 9:1 
                 3.6 
                 6.2 
                 121 
               
               
                 Example (B)-9 
                 ETM8 
                 Yb 
                 9:1 
                 3.5 
                 6.2 
                 123 
               
               
                 Example (B)-10 
                 ETM9 
                 LiQ 
                 5:5 
                 4.0 
                 6.5 
                 109 
               
               
                 Example (B)-11 
                 ETM9 
                 Li 
                 9:1 
                 3.9 
                 6.4 
                 115 
               
               
                 Example (B)-12 
                 ETM9 
                 Yb 
                 9:1 
                 3.9 
                 6.5 
                 117 
               
               
                 Example (B)-13 
                 ETM10 
                 LiQ 
                 5:5 
                 3.8 
                 5.9 
                 110 
               
               
                 Example (B)-14 
                 ETM10 
                 Li 
                 9:1 
                 3.7 
                 5.8 
                 119 
               
               
                 Example (B)-15 
                 ETM10 
                 Yb 
                 9:1 
                 3.7 
                 5.7 
                 118 
               
               
                 Example (B)-16 
                 ETM11 
                 LiQ 
                 5:5 
                 4.0 
                 6.1 
                 110 
               
               
                 Example (B)-17 
                 ETM11 
                 Li 
                 9:1 
                 4.0 
                 6.2 
                 114 
               
               
                 Example (B)-18 
                 ETM11 
                 Yb 
                 9:1 
                 3.9 
                 6.2 
                 114 
               
               
                 Example (B)-19 
                 ETM12 
                 LiQ 
                 5:5 
                 3.8 
                 6.3 
                 104 
               
               
                 Example (B)-20 
                 ETM12 
                 Li 
                 9:1 
                 3.7 
                 6.4 
                 112 
               
               
                 Example (B)-21 
                 ETM12 
                 Yb 
                 9:1 
                 3.7 
                 6.5 
                 114 
               
               
                 Example (B)-22 
                 ETM13 
                 LiQ 
                 5:5 
                 3.6 
                 6.5 
                 116 
               
               
                 Example (B)-23 
                 ETM13 
                 Li 
                 9:1 
                 3.6 
                 6.5 
                 123 
               
               
                 Example (B)-24 
                 ETM13 
                 Yb 
                 9:1 
                 3.5 
                 6.6 
                 123 
               
               
                   
               
            
           
         
       
     
     From Table 3, it is confirmed that the organic light-emitting devices of Examples (B)-1 to (B)-24 have excellent or suitable characteristics in terms of driving voltage, luminescence efficiency, and/or lifespan, compared to the organic light-emitting devices of Comparative Examples (B)-1 to (B)-3. 
     The light-emitting device has a low driving voltage, high luminescence efficiency, and long lifespan, and thus, may be utilized in manufacturing a high-quality electronic apparatus. 
     As used herein, the terms “substantially,” “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by those of ordinary skill in the art. “About” or “approximately,” as used herein, is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” may mean within one or more standard deviations, or within ±30%, 20%, 10%, 5% of the stated value. 
     Any numerical range recited herein is intended to include all sub-ranges of the same numerical precision subsumed within the recited range. For example, a range of “1.0 to 10.0” is intended to include all subranges between (and including) the recited minimum value of 1.0 and the recited maximum value of 10.0, that is, having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as, for example, 2.4 to 7.6. Any maximum numerical limitation recited herein is intended to include all lower numerical limitations subsumed therein and any minimum numerical limitation recited in this specification is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicant reserves the right to amend this specification, including the claims, to expressly recite any sub-range subsumed within the ranges expressly recited herein. 
     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 various 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.