Patent Publication Number: US-2021184119-A1

Title: Organic light-emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 15/183,627, filed Jun. 15, 2016, which claims priority to and the benefit of Korean Patent Application No. 10-2015-0166411, filed Nov. 26, 2015, the entire content of both of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     One or more aspects of example embodiments of the present disclosure are related to an organic light-emitting device. 
     2. Description of the Related Art 
     Organic light-emitting devices are self-emission devices that may have wide viewing angles, high contrast ratios, short response times, and/or excellent brightness, driving voltage, and/or response speed characteristics compared to devices in the related art. 
     An example organic light-emitting device may include a first electrode on a substrate, and a hole transport region, an emission layer, an electron transport region, and a second electrode sequentially positioned 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 holes and electrons) may recombine in the emission layer to produce excitons. These excitons may transition (e.g., radiatively decay) from an excited state to a ground state to thereby generate light. 
     SUMMARY 
     One or more aspects of example embodiments of the present disclosure are directed toward an organic light-emitting device that has a low driving voltage, high efficiency, and/or a long lifespan. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
     One or more example embodiments of the present disclosure provide an organic light-emitting device including: a first electrode; a second electrode facing the first electrode; and an organic layer between the first electrode and the second electrode, the organic layer including an emission layer, wherein: 
     the organic layer includes a first compound, 
     the emission layer includes a second compound and a third compound, 
     the second compound is a fluorescent host and the third compound is a fluorescent dopant, and 
     the first compound, the second compound, and the third compound each independently include at least one selected from moieties represented by Formulae A to D: 
     
       
         
         
             
             
         
       
     
     In Formulae A to D, 
     X 1  and X 11  may each independently be selected from O and S, 
     X 12  may be selected from O, S, N(R 14 ), and C(R 15 )(R 16 ), 
     rings A 1  and A 11  to A 13  may each independently be selected from a C 5 -C 30  carbocyclic group and a C 2 -C 30  heterocyclic group, 
     R 1 , R 2 , and R 11  to R 16  may each independently be selected from a binding site (e.g., to another formula), hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —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 ), and —P(═O)(Q 1 )(Q 2 ), 
     a1 and a11 to a13 may each independently be an integer selected from 0 to 10, 
     a2 may be an integer selected from 0 to 2, and 
     at least one substituent of the substituted C 3 -C 10  cycloalkylene group, the substituted C 1 -C 10  heterocycloalkylene group, the substituted C 3 -C 10  cycloalkenylene group, the substituted C 1 -C 10  heterocycloalkenylene group, the substituted C 6 -C 60  arylene group, the substituted C 1 -C 60  heteroarylene group, the substituted divalent non-aromatic condensed polycyclic group, the substituted divalent non-aromatic condensed heteropolycyclic group, the substituted C 1 -C 60  alkyl group, the substituted C 2 -C 60  alkenyl group, the substituted C 2 -C 60  alkynyl group, the substituted C 1 -C 60  alkoxy group, the substituted C 3 -C 10  cycloalkyl group, the substituted C 1 -C 10  heterocycloalkyl group, the substituted C 3 -C 10  cycloalkenyl group, the substituted C 1 -C 10  heterocycloalkenyl group, the substituted C 6 -C 60  aryl group, the substituted C 6 -C 60  aryloxy group, the substituted C 6 -C 60  arylthio group, the substituted C 1 -C 60  heteroaryl group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group may be selected from the group consisting of: 
     deuterium (-D), —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, and a C 1 -C 60  alkoxy group; 
     a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, and a C 1 -C 60  alkoxy group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 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 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic 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 ), and —P(═O)(Q 11 )(Q 12 ); 
     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 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group; 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 60  alkyl group, 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 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 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic 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 ), and —P(═O)(Q 21 )(Q 22 ); and 
     —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 ), and —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 selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 60  alkyl group, 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 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, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of example embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic diagram of a structure of an organic light-emitting device according to an embodiment of the present disclosure; 
         FIG. 2  is a schematic diagram of a structure of an organic light-emitting device according to an embodiment of the present disclosure; 
         FIG. 3  is a schematic diagram of a structure of an organic light-emitting device according to an embodiment of the present disclosure; and 
         FIG. 4  is a schematic diagram of a structure of an organic light-emitting device according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in more detail to example embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout and duplicative descriptions thereof may not be provided. In this regard, the present example embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the example embodiments are merely described below, by referring to the figures, to explain aspects of the present description. 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. 
     The thicknesses of layers, films, panels, regions, etc., may be exaggerated in the drawings for clarity. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening element(s) may also be present. In contrast, when an element is referred to as being “directly on” another element, no intervening elements are present. 
     An organic 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 organic layer between the first electrode and the second electrode and including an emission layer. 
     The organic layer may include a first compound, and the emission layer may include a second compound and a third compound, wherein the second compound may be a fluorescent host, and the third compound may be a fluorescent dopant. 
     The first electrode may be an anode, the second electrode may be a cathode, and the first electrode and the second electrode may each be the same as described below. 
     The first compound, the second compound, and the third compound may each independently include at least one selected from moieties represented by Formulae A to D: 
     
       
         
         
             
             
         
       
     
     In Formulae A to D, 
     X 1  and X 11  may each independently be selected from O and S, and 
     X 12  may be selected from O, S, N(R 14 ), and C(R 15 )(R 16 ), wherein R 14  to R 16  may each independently be the same as described below. 
     For example, in Formulae C and D, X 11  may be selected from O and S, and X 12  may be selected from N(R 14 ) and C(R 15 )(R 16 ). However, embodiments of X 11  and X 12  are not limited thereto. 
     Rings A 1  and A 11  to A 13  in Formulae A to D may each independently be selected from a C 5 -C 60  carbocyclic group and a C 1 -C 60  heterocyclic group. 
     For example, rings A 1  and A 11  to A 13  in Formulae A to D may each independently be selected from a benzene, a naphthalene, a phenanthrene, a chrysene, a pyridine, a pyrimidine, a quinoline, an isoquinoline, a benzoquinoline, a quinoxaline, a quinazoline, a phenanthroline, a fluorene, a benzofluorene, a spiro-bifluorene, an indole, a carbazole, a benzofuran, a benzothiophene, a dibenzofuran, and a dibenzothiophene. 
     In one or more embodiments, rings A 1 , A 11 , and A 12  in Formulae A to D may each independently be selected from a benzene, a naphthalene, a phenanthrene, a chrysene, a pyridine, a pyrimidine, a quinoline, an isoquinoline, a benzoquinoline, a quinoxaline, a quinazoline, a phenanthroline, a fluorene, a benzofluorene, a spiro-bifluorene, an indole, a carbazole, a benzofuran, a benzothiophene, a dibenzofuran, and a dibenzothiophene, and 
     ring A 13  may be selected from a benzene, a naphthalene, a phenanthrene, a chrysene, a fluorene, a benzofluorene, a benzofuran, a benzothiophene, a dibenzofuran, and a dibenzothiophene. 
     R 1 , R 2 , and R 11  to R 16  in Formulae A to D may each independently be selected from a binding site (e.g., to another formula), hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —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 ), and —P(═O)(Q 1 )(Q 2 ), wherein Q 1  to Q 3  may each independently be the same as described below. 
     For example, R 1 , R 2 , and R 11  to R 16  in Formulae A to D may each independently be selected from the group consisting of: 
     a binding site (e.g., to another formula), hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 20  alkyl group, and a C 1 -C 20  alkoxy group; 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a bertzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group; 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, and —Si(Q 31 )(Q 32 )(Q 33 ); and 
     —Si(Q 1 )(Q 2 )(Q 3 ), 
     wherein Q 1  to Q 3  and Q 31  to Q 33  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group. 
     In one or more embodiments, R 1 , R 2 , and R 11  to R 16  in Formulae A to D may each independently be selected from the group consisting of: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 20  alkyl group, and a C 1 -C 20  alkoxy group; 
     a phenyl group, a biphenyl group, a terphenyl group, a fluorenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a quinazolinyl group, a quinoxalinyl group, and a carbazolyl group; 
     a phenyl group, a biphenyl group, a terphenyl group, a fluorenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a quinazolinyl group, a quinoxalinyl group, and a carbazolyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group; and 
     —Si(Q 1 )(Q 2 )(Q 3 ), 
     wherein Q 1  to Q 3  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group. 
     In Formulae A to D, a1 and a11 to a13 may each independently be an integer selected from 0 to 10, and a2 may be an integer selected from 0 to 2. 
     a1 indicates the number of R 1 (s), and when a1 is two or more, two or more R 1 (s) may be identical to or different from each other. a11 to a13 may each independently be the same as described herein in connection with a1 and Formulae B to D. 
     a2 indicates the number of R 2 (s), and when a2 is two or more, two or more R 2 (s) may be identical to or different from each other. 
     For example, a1 and a11 to a13 in Formulae A to D may each independently be an integer selected from 0 to 8, but embodiments of the present disclosure are not limited thereto. 
     In one or more embodiments, the first compound may be selected from compounds represented by Formulae 1A to 1C and may not have a nitrogen-containing heterocyclic group having *═N—*′ as a ring-forming moiety; the second compound may be a compound represented by Formula 2A; the third compound may be a compound represented by Formula 3A or 3B; and the first compound and the third compound may be different from each other: 
     
       
         
         
             
             
         
       
     
     In Formulae 1A to 1C, 2A, 3A, and 3B, 
     L 21  to L 25 , L 31 , and L 41  to L 45  may each independently be selected from a divalent group having a moiety represented by any of Formulae A to D, a substituted or unsubstituted C 3 -C 10  cycloalkylene group, a substituted or unsubstituted C 1 -C 10  heterocycloalkylene group, a substituted or unsubstituted C 3 -C 10  cycloalkenylene group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenylene group, a substituted or unsubstituted C 6 -C 60  arylene group, a substituted or unsubstituted C 1 -C 60  heteroarylene group, a substituted or unsubstituted divalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted divalent non-aromatic condensed heteropolycyclic group. 
     For example, L 21  to L 25  may each independently be selected from a divalent group having a moiety represented by any of Formulae A to D, and a group represented by any of Formulae 3-1 to 3-11, 3-27 to 3-29, and 3-33 to 3-44, and 
     L 31  and L 41  to L 45  may each independently be selected from a divalent group having a moiety represented by any of Formulae A to D, and a group represented by any of Formulae 3-1 to 3-44: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 3-1 to 3-44, 
     Y 1  may be selected from O, S, C(Z 3 )(Z 4 ), N(Z 5 ), and Si(Z 6 )(Z 7 ), 
     Z 1  to Z 7  may each independently be selected from 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 phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a dibenzothiophenyl group, a dibenzofuranyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a phenanthrenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a triazinyl group, and —Si(Q 31 )(Q 32 )(Q 33 ), 
     wherein Q 31  to Q 33  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group, 
     d1 may be an integer selected from 1 to 4, d2 may be an integer selected from 1 to 3, d3 may be an integer selected from 1 to 6, d4 may be an integer selected from 1 to 8, d5 may be selected from 1 and 2, and d6 may be an integer selected from 1 to 5, and 
     * and *′ may indicate a binding site to a neighboring atom. 
     In Formulae 1A to 1C, 2A, 3A, and 3B, 
     b1 to b5, x1, and z1 to z5 may each independently be an integer selected from 0 to 3. 
     b1 indicates the number of L 21 (s), and when b1 is zero, *-(L 21 ) b1 -′ may be a single bond, and when b1 is two or more, two or more L 21 (s) may be identical to or different from each other. b2 to b5 may each independently be the same as described herein in connection with b1 and Formulae 1A to 1C. 
     x1 indicates the number of L 31 (s), and when x1 is zero, *-(L 31 ) x1 -*′ may be a single bond, and when x1 is two or more, two or more L 31 (s) may be identical to or different from each other. 
     z1 indicates the number of L 41 (s), and when z1 is zero, *-(L 41 ) z1 -*′ may be a single bond, and when z1 is two or more, two or more L 41 (s) may be identical to or different from each other. z2 to z5 may each independently be the same as described herein in connection with z1 and Formulae 3A and 3B. 
     In Formulae 1A to 1C, 3A, and 3B, 
     Ar 21  to Ar 24  and Ar 41  to Ar 44  may each independently be selected from a monovalent group having a moiety represented by any of Formulae A to D, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group. 
     For example, Ar 21  to Ar 24  may each independently be selected from a monovalent group having a moiety represented by any of Formulae A to D and a group represented by any of Formulae 5-1 to 5-17, and 
     Ar 41  to Ar 44  may each independently be selected from a monovalent group having a moiety represented by any of Formulae A to D and a group represented by any of Formulae 5-1 to 5-61: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 5-1 to 5-61, 
     Y 31  may be selected from O, S, C(Z 35 )(Z 36 ), N(Z 37 ), and Si(Z 38 )(Z 39 ), 
     Z 31  to Z 39  may each independently be selected from the group consisting of: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 20  alkyl group, and a C 1 -C 20  alkoxy group; 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, and a dibenzothiophenyl group; 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, and a dibenzothiophenyl group, each substituted with at least one selected from 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 phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group; and 
     —Si(Q 31 )(Q 32 )(Q 33 ), 
     wherein Q 31  to Q 33  may each independently be selected from a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group, 
     e2 may be selected from 1 and 2, e3 may be an integer selected from 1 to 3, e4 may be an integer selected from 1 to 4, e5 may be an integer selected from 1 to 5, e6 may be an integer selected from 1 to 6, e7 may be an integer selected from 1 to 7, and e9 may be an integer selected from 1 to 9, and 
     * may indicate a binding site to a neighboring atom. 
     In Formula 2A, Ar 31  may be selected from monovalent groups having moieties represented by Formulae A to D. 
     In Formula 1A, i) at least one selected from Ar 21  to Ar 23  may be selected from monovalent groups having moieties represented by Formulae A to D, or ii) at least one selected from L 21  to L 23  may be selected from divalent groups having moieties represented by Formulae A to D, 
     in Formula 1B, i) at least one selected from Ar 21  to Ar 24  may be selected from monovalent groups having moieties represented by Formulae A to D, or ii) L 25  may be selected from groups having moieties represented by Formulae A to D, 
     in Formula 1C, i) at least one selected from Ar 21  and Ar 22  may be selected from monovalent groups having moieties represented by Formulae A to D, or ii) at least one selected from L 21  to L 23  may be selected from divalent groups having moieties represented by Formulae A to D, 
     in Formula 3A, i) at least one selected from Ar 41  to Ar 43  may be selected from monovalent groups having moieties represented by Formulae A to D, or ii) at least one selected from L 41  to L 43  may be selected from divalent groups having moieties represented by Formulae A to D, and 
     in Formula 3B, i) at least one selected from Ar 41  to Ar 44  may be selected from monovalent groups having moieties represented by Formulae A to D, or ii) L 45  may be selected from divalent groups having moieties represented by Formulae A to D. 
     In one or more embodiments, in Formula 1A, i) at least one selected from Ar 21  to Ar 23  may be selected from monovalent groups having moieties represented by Formulae B to D, or ii) at least one selected from L 21  to L 23  may be selected from divalent groups having moieties represented by Formulae B to D, 
     in Formula 1B, i) at least one selected from Ar 21  to Ar 24  may be selected from monovalent groups having moieties represented by Formulae B to D, or ii) L 25  may be selected from divalent groups having moieties represented by Formula B, 
     in Formula 1C, at least one selected from Ar 21  and Ar 22  may be selected from monovalent groups having moieties represented by Formula B, 
     in Formula 3A, i) at least one selected from Ar 41  to Ar 43  may be selected from monovalent groups having moieties represented by Formulae B to D, or ii) at least one selected from L 41  to L 43  may be selected from divalent groups having moieties represented by Formulae B to D, and 
     in Formula 3B, i) at least one selected from Ar 41  to Ar 44  may be selected from monovalent groups having moieties represented by Formulae B to D, or ii) L 45  may be selected from divalent groups having moieties represented by Formulae B to D. 
     In one or more embodiments, in Formula 3B, i) one selected from Ar 18  and Ar 42  may be selected from monovalent groups having moieties represented by Formulae B to D, and one selected from Ar 43  and Ar 44  may be selected from monovalent groups having moieties represented by Formulae B to D, or ii) L 45  may be selected from divalent groups having moieties represented by Formulae B to D. 
     In Formulae 1A to 1C, 2A, 3A, and 3B, R 21  to R 24  and R 31  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q 41 )(Q 42 )(Q 43 ), wherein Q 41  to Q 43  may each independently be the same as described below. 
     For example, in Formulae 1A to 1C, 2A, 3A, and 3B, R 21  to R 24  and R 31  may each independently be selected from the group consisting of: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 20  alkyl group, and a C 1 -C 20  alkoxy group; 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group; 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, and —Si(Q 31 )(Q 32 )(Q 33 ); and 
     —Si(Q 41 )(Q 42 )(Q 43 ). 
     Q 41  to Q 43  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 3 -C 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, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group. 
     For example, Q 41  to Q 43  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group. 
     In Formulae 1A to 1C, 2A, 3A, and 3B, c1 and c4 may each independently be an integer selected from 0 to 4, c2 and c3 may each independently be an integer selected from 0 to 3, and y1 may be an integer selected from 1 to 3. 
     c1 indicates the number of R 21 (s), and when c1 is two or more, two or more R 21 (s) may be identical to or different from each other. c2 to c4 may each independently be the same as described herein in connection with c1 and Formula 1C. 
     y1 indicates the number of R 31 (s), and when y1 is two or more, two or more R 31 (s) may be identical to or different from each other. 
     The organic layer may include a hole transport region between the first electrode and the emission layer, the hole transport region including a hole auxiliary layer, wherein the hole auxiliary layer may include the first compound represented by one selected from Formulae 1A to 1C. 
     In some embodiments, the hole auxiliary layer may directly contact the emission layer. 
     The first compound may be selected from Compounds 1-1 to 1-23, 
     the second compound may be selected from Compounds 2-1 to 2-20, and 
     the third compound may be selected from Compounds 3-1 to 3-23, but embodiments of the first compound, the second compound, and the third compound are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In one or more embodiments, the first compound may be selected from compounds represented by Formulae 4A to 4E and may have a nitrogen-based heterocyclic group having *═N—*′ as a ring-forming moiety, the second compound may be a compound represented by Formula 2A, and the third compound may be a compound represented by Formula 4A or 4B: 
     
       
         
         
             
             
         
       
     
     In Formula 2A, 3A, 3B, and 4A to 4E, 
     L 31 , L 41  to L 45 , and L 51  to L 54  may each independently be selected from a divalent group having a moiety represented by any of Formulae A to D, a substituted or unsubstituted C 3 -C 10  cycloalkylene group, a substituted or unsubstituted C 1 -C 10  heterocycloalkylene group, a substituted or unsubstituted C 3 -C 10  cycloalkenylene group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenylene group, a substituted or unsubstituted C 6 -C 60  arylene group, a substituted or unsubstituted C 1 -C 60  heteroarylene group, a substituted or unsubstituted divalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted divalent non-aromatic condensed heteropolycyclic group. 
     For example, L 31 , L 41  to L 45 , and L 51  to L 54  may each independently be selected from a divalent group having a moiety represented by any of Formulae A to D and a group represented by any of Formulae 3-1 to 3-44. 
     x1 and z1 to z4 may each independently be the same as described herein. 
     In Formulae 4A to 4E, 
     v1 to v4 may each independently be an integer selected from 0 to 3. 
     v1 indicates the number of L 51 (s), and when v1 is zero, *-(L 51 ) v1 -′ may be a single bond, and when v1 is two or more, two or more L 51 (s) may be identical to or different from each other. v2 to v4 may each independently be the same as described herein in connection with v1 and Formulae 4A to 4E. 
     In Formulae 2A, 3A, 3B, and 4A to 4E, 
     Ar 41  to Ar 44  and Ar 51  to Ar 54  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a monovalent group having a moiety represented by any of Formulae A to D, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group. 
     For example, in Formulae 2A, 3A, 3B, and 4A to 4E, 
     Ar 41  to Ar 44  and Ar 51  to Ar 54  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a monovalent group having a moiety represented by any of Formulae A to D, and a group represented by any of Formulae 5-1 to 5-61. 
     Ar 31  may be selected from monovalent groups having moieties represented by Formulae A to D. 
     In Formula 3A, i) at least one selected from Ar 41  to Ar 43  may be selected from monovalent groups having moieties represented by Formulae A to D, or ii) at least one selected from L 41  to L 43  may be selected from divalent groups having moieties represented by Formulae A to D, 
     in Formula 3B, i) at least one selected from Ar 41  to Ar 44  may be selected from monovalent groups having moieties represented by Formulae A to D, or ii) L 45  may be selected from divalent groups having moieties represented by Formulae A to D, 
     in Formula 4A, i) at least one selected from Ar 51  to Ar 53  may be selected from monovalent groups having moieties represented by Formulae A to D, or ii) at least one selected from L 51  to L 53  may be selected from divalent groups having moieties represented by Formulae A to D, 
     in Formula 4B, i) at least one selected from Ar 51  to Ar 54  may be selected from monovalent groups having moieties represented by Formulae A to D, or ii) at least one selected from L 51  to L 54  may be selected from divalent groups having moieties represented by Formulae A to D, 
     in Formula 4C, i) at least one selected from Ar 51  and Ar 52  may be selected from monovalent groups having moieties represented by Formulae A to D, or ii) at least one selected from L 51  and L 52  may be selected from divalent groups having moieties represented by Formulae A to D, 
     in Formula 4D, i) at least one selected from Ar 51  to Ar 53  may be selected from monovalent groups having moieties represented by Formulae A to D, or ii) at least one selected from L 51  to L 53  may be selected from divalent groups having moieties represented by Formulae A to D, and 
     in Formula 4E, i) at least one selected from Ar 51  and Ar 52  may be selected from monovalent groups having moieties represented by Formulae A to D, or ii) at least one selected from L 51  and L 52  may be selected from divalent groups having moieties represented by Formulae A to D. 
     For example, in Formula 3A, i) at least one selected from Ar 41  to Ar 43  may be selected from monovalent groups having moieties represented by Formulae B to D, or ii) at least one selected from L 41  to L 43  may be selected from divalent groups having moieties represented by Formulae B to D, 
     in Formula 3B, i) at least one selected from Ar 41  to Ar 44  may be selected from monovalent groups having moieties represented by Formulae B to D, or ii) L 45  may be selected from divalent groups having moieties represented by Formulae B to D, 
     in Formula 4A, i) at least one selected from Ar 51  to Ar 53  may be selected from monovalent groups having moieties represented by Formulae A to D, or ii) at least one selected from L 51  to L 53  may be selected from divalent groups having moieties represented by Formula B, 
     in Formula 4B, at least one selected from Ar 51  to Ar 54  may be selected from monovalent groups having moieties represented by Formula B, 
     in Formula 4C, at least one selected from Ar 51  and Ar 52  may be selected from monovalent groups having moieties represented by Formula B, 
     in Formula 4D, at least one selected from Ar 51  to Ar 53  may be selected from monovalent groups having moieties represented by Formula B, 
     in Formula 4E, i) at least one selected from Ar 51  and Ar 52  may be selected from monovalent groups having moieties represented by Formula B, or ii) at least one selected from L 51  and L 52  may be selected from divalent groups having moieties represented by Formula B. 
     In one or more embodiments, in Formula 3B, i) one selected from Ar 18  and 
     Ar 42  may be selected from monovalent groups having moieties represented by Formulae B to D, and one selected from Ar 43  and Ar 44  may be selected from monovalent groups having moieties represented by Formulae B to D, or ii) L 45  may be selected from divalent groups having moieties represented by Formulae B to D. 
     In Formula 4A, X 51  may be selected from C(R 54 ) and N, X 52  may be selected from C(R 55 ) and N, and X 53  may be selected from C(R 56 ) and N. 
     In Formulae 2A, 3A, 3B, and 4A to 4E, R 31  and R 51  to R 56  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q 41 )(Q 42 )(Q 43 ), wherein Q 41  to Q 43  may each independently be the same as described herein. 
     In Formulae 2A, 3A, 3B, and 4A to 4E, R 31  and R 51  to R 56  may each independently be selected from the group consisting of: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 20  alkyl group, and a C 1 -C 20  alkoxy group; 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group; 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, and —Si(Q 31 )(Q 32 )(Q 33 ); and 
     —Si(Q 41 )(Q 42 )(Q 43 ). 
     In Formulae 2A, 3A, 3B, and 4A to 4E, y1 may be an integer selected from 1 to 3, w1 may be an integer selected from 0 to 4, w2 may be an integer selected from 0 to 2, and w3 may be an integer selected from 0 to 3. 
     w1 indicates the number of R 51 (s), and when w1 is two or more, two or more R 51 (s) may be identical to or different from each other. w2 and w3 may each independently be the same as described herein in connection with w1 and the structures of Formulae 4C and 4E. 
     The organic layer may include an electron transport region between the second electrode and the emission layer, the electron transport region including an electron auxiliary layer, wherein the electron auxiliary layer may include the first compound represented by one selected from Formulae 4A to 4E. 
     In some embodiments, the electron auxiliary layer may directly contact the emission layer. 
     In some embodiments, the first compound may be selected from Compounds 4-1 to 4-20, 
     the second compound may be selected from Compounds 2-1 to 2-20, and 
     the third compound may be selected from Compounds 3-1 to 3-23, but embodiments of the first compound, the second compound, and the third compound are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The compounds represented by Formulae 1A to 1C may each have a relatively high hole transport capability and/or a relatively large energy gap. Thus, when these compounds are introduced into the hole transport region, it may be possible to effectively block or reduce electron leakage from the emission layer. Also, due to their a relatively high glass transition temperatures, these compounds may have excellent thermal stability and may prevent or reduce intermolecular aggregation. Thus, when these compounds are used in an organic light-emitting device, the organic light-emitting device may have a long lifespan. 
     Since the compounds represented by Formulae 4A to 4E each include a nitrogen-containing heterocyclic group having *═N—*′ as a ring-forming moiety (e.g., an electron withdrawing group), the compounds may exhibit bipolar carrier transport characteristics. When these compounds are introduced into the electron transport region, it may be possible to easily adjust the injection and mobility characteristics of electrons. 
     Also, in the organic light-emitting device, when a plurality of layers include compounds represented by Formulae A to D, which have a structural similarity (e.g., the first compound, the second compound, and the third compound are structurally similar), charges may move smoothly and interface characteristics may be improved, thereby further improving or increasing the stability and lifespan of the organic light-emitting device. 
     The minimum triplet energies of two or more compounds selected from the first compound, the second compound, and the third compound may each be 2.0 eV or more, and in some embodiments, 2.1 eV or more. When the minimum triplet energies each satisfy these ranges, the emission efficiency may be improved due to triplet-triplet fusion (TTF), for example, in a fluorescent organic light-emitting device. 
     In some embodiments, two or more compounds selected from the first compound, the second compound, and the third compound may each have an asymmetrical structure. When two or more compounds selected from the first to third compounds have an asymmetrical structure, the degree of stacking and aggregation of molecules in the organic layer may be reduced. 
       FIG. 1  is a schematic view of an organic light-emitting device  10  according to an embodiment of the present disclosure. The organic light-emitting device  10  includes a first electrode  110 , an organic layer  150 , and a second electrode  190 . 
     Hereinafter, the structure of the organic light-emitting device  10  according to an embodiment of the present disclosure and a method of manufacturing the organic light-emitting device  10  will be described in connection with  FIG. 1 . 
     First Electrode  110   
     In  FIG. 1 , a substrate may be under the first electrode  110  and/or above the second electrode  190 . The substrate may be a glass substrate or a plastic substrate, each having excellent mechanical strength, thermal stability, transparency, surface smoothness, ease of handling, and/or water-resistance. 
     The first electrode  110  may be formed by depositing and/or sputtering a material for forming the first electrode  110  on the substrate. When the first electrode  110  is an anode, the material for forming the first electrode  13  may be selected from materials with a high work function to facilitate hole injection. 
     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, the material for forming the first electrode may be selected from indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO 2 ), zinc oxide (ZnO), and combinations thereof, but embodiments of the present disclosure are not limited thereto. When the first electrode  110  is a semi-transmissive electrode or a reflective electrode, the material for forming the first electrode  110  may be selected from magnesium (Mg), aluminum(Al), aluminum-lithium(Al—Li), calcium (Ca), magnesium-indium(Mg—In), magnesium-silver (Mg—Ag), and combinations thereof. However, embodiments of the material for forming the first electrode  110  are not limited thereto. As used herein, the terms “combination”, “combination thereof” and “combinations thereof” may refer to a chemical combination (e.g., an alloy or chemical compound), a mixture, or a laminated structure of components. 
     The first electrode  110  may have a single-layered structure, or a multi-layered structure including two or more layers. For example, the first electrode  110  may have a three-layered structure of ITO/Ag/ITO, but embodiments of the structure of the first electrode  110  are not limited thereto. 
     Organic Layer  150   
     The organic layer  150  is on the first electrode  110 . The organic layer  150  may include an emission layer. 
     The organic layer  150  may include a first compound, and the emission layer may include a second compound and a third compound. The first compound, the second compound, and the third compound may each be the same as already described herein. 
     The organic layer  150  may further include a hole transport region between the first electrode  110  and the emission layer, and an electron transport region between the emission layer and the second electrode  190 . 
     Hole Transport Region in Organic Layer  150   
     The hole transport region may have i) a single-layered structure including a single layer including a single material, ii) a single-layered structure including a single layer including a plurality of different materials, or iii) a multi-layered structure having a plurality of layers including a plurality of different materials. 
     The hole transport region may include at least one layer selected from a hole injection layer (HIL), a hole transport layer (HTL), a hole auxiliary layer, and an electron blocking layer (EBL). 
     For example, the hole transport region may have a single-layered structure including a single layer including a plurality of different materials, or a multi-layered structure having a structure of hole injection layer/hole transport layer, hole injection layer/hole transport layer/hole auxiliary layer, hole injection layer/hole auxiliary layer, hole transport layer/hole auxiliary layer, or hole injection layer/hole transport layer/electron blocking layer, wherein layers of each structure are sequentially stacked on the first electrode  110  in each stated order, but embodiments of the structure of the hole transport region are not limited thereto. 
     For example, the organic layer  150  may include a hole transport region between the first electrode and the emission layer, the hole transport region including a hole auxiliary layer, wherein the hole auxiliary layer may include the first compound; for example, the first compound represented by one selected from Formulae 1A to 1C. 
     For example, the hole transport region may further include a hole transport layer between the hole auxiliary layer and the first electrode, and the hole auxiliary layer may directly contact the emission layer, but embodiments of the structure of the hole transport region are not limited thereto. 
     In one or more embodiments, the hole transport region may include, in addition to the first compound, at least one selected from m-MTDATA, TDATA, 2-TNATA, NPB(NPD), β-NPB, TPD, Spiro-TPD, Spiro-NPB, methylated NPB, TAPC, HMTPD, TCTA(4,4′,4″-tris(N-carbazolyl)triphenylamine), PANI/DBSA (polyaniline/dodecylbenzenesulfonic acid), PEDOT/PSS (poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate)), PANI/CSA (polyaniline/camphor sulfonic acid), PANI/PSS (polyaniline/poly(4-styrenesulfonate)), a compound represented by Formula 201, and a compound represented by Formula 202: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 201 and 202, 
     L 201  to L 204  may each independently be selected from a substituted or unsubstituted C 3 -C 10  cycloalkylene group, a substituted or unsubstituted C 1 -C 10  heterocycloalkylene group, a substituted or unsubstituted C 3 -C 10  cycloalkenylene group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenylene group, a substituted or unsubstituted C 6 -C 60  arylene group, a substituted or unsubstituted C 1 -C 60  heteroarylene group, a substituted or unsubstituted divalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted divalent non-aromatic condensed heteropolycyclic group, 
     L 205  may be selected from *—O—*′, *—S—*′, *—N(Q 201 )-*′, a substituted or unsubstituted C 1 -C 20  alkylene group, a substituted or unsubstituted C 2 -C 20  alkenylene group, a substituted or unsubstituted C 3 -C 10  cycloalkylene group, a substituted or unsubstituted C 1 -C 10  heterocycloalkylene group, a substituted or unsubstituted C 3 -C 10  cycloalkenylene group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenylene group, a substituted or unsubstituted C 6 -C 60  arylene group, a substituted or unsubstituted C 1 -C 60  heteroarylene group, a substituted or unsubstituted divalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted divalent non-aromatic condensed heteropolycyclic group, 
     xa1 to xa4 may each independently be an integer selected from 0 to 3, 
     xa5 may be an integer selected from 1 to 10, and 
     R 201  to R 204  and Q 201  may each independently be selected from a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group. 
     For example, in Formula 202, R 201  and R 202  may be optionally connected (e.g., coupled) via a single bond, a dimethyl-methylene group, or a diphenyl-methylene group, and R 203  and R 204  may be optionally connected (e.g., coupled) via a single bond, a dimethyl-methylene group, or a diphenyl-methylene group. 
     In one or more embodiments, in Formulae 201 and 202, 
     L 201  to L 205  may each independently be selected from the group consisting of: 
     a phenylene group, a pentalenylene group, an indenylene group, a naphthylene group, an azulenylene group, a heptalenylene group, an indacenylene group, an acenaphthylene group, a fluorenylene group, a spiro-bifluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenalenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a naphthacenylene group, a picenylene group, a perylenylene group, a pentaphenylene group, a hexacenylene group, a pentacenylene group, a rubicenylene group, a coronenylene group, an ovalenylene group, a thiophenylene group, a furanylene group, a carbazolylene group, an indolylene group, an isoindolylene group, a benzofuranylene group, a benzothiophenylene group, a dibenzofuranylene group, a dibenzothiophenylene group, a benzocarbazolylene group, a dibenzocarbazolylene group, a dibenzosilolylene group, and a pyridinylene group; and 
     a phenylene group, a pentalenylene group, an indenylene group, a naphthylene group, an azulenylene group, a heptalenylene group, an indacenylene group, an acenaphthylene group, a fluorenylene group, a spiro-bifluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenalenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a naphthacenylene group, a picenylene group, a perylenylene group, a pentaphenylene group, a hexacenylene group, a pentacenylene group, a rubicenylene group, a coronenylene group, an ovalenylene group, a thiophenylene group, a furanylene group, a carbazolylene group, an indolylene group, an isoindolylene group, a benzofuranylene group, a benzothiophenylene group, a dibenzofuranylene group, a dibenzothiophenylene group, a benzocarbazolylene group, a dibenzocarbazolylene group, a dibenzosilolylene group, and a pyridinylene group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an am idino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a phenyl group substituted with a C 1 -C 10  alkyl group, a phenyl group substituted with —F, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a thiophenyl group, a furanyl group, a carbazolyl group, an indolyl group, an isoindolyl group, a benzofuranyl group, a benzothiophenyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, a dibenzosilolyl group, a pyridinyl group, —Si(Q 31 )(Q 32 )(Q 33 ), and —N(Q 31 )(Q 32 ), 
     wherein Q 31  to Q 33  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group. 
     In one or more embodiments, xa1 to xa4 may each independently be selected from 0, 1, and 2. 
     In one or more embodiments, xa5 may be selected from 1, 2, 3, and 4. 
     In one or more embodiments, R 201  to R 204  and Q 201  may each independently be selected from the group consisting of: 
     a phenyl group, a biphenyl group, a terphenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a thiophenyl group, a furanyl group, a carbazolyl group, an indolyl group, an isoindolyl group, a benzofuranyl group, a benzothiophenyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, a dibenzosilolyl group, and a pyridinyl group; and 
     a phenyl group, a biphenyl group, a terphenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a thiophenyl group, a furanyl group, a carbazolyl group, an indolyl group, an isoindolyl group, a benzofuranyl group, a benzothiophenyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, a dibenzosilolyl group, and a pyridinyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a phenyl group substituted with a C 1 -C 10  alkyl group, a phenyl group substituted with —F, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a thiophenyl group, a furanyl group, a carbazolyl group, an indolyl group, an isoindolyl group, a benzofuranyl group, a benzothiophenyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, a dibenzosilolyl group, a pyridinyl group, —Si(Q 31 )(Q 32 )(Q 33 ), and —N(Q 31 )(Q 32 ), 
     wherein Q 31  to Q 33  may each independently be the same as described herein. 
     In one or more embodiments, at least one selected from R 201  to R 203  in Formula 201 may be selected from the group consisting of: 
     a fluorenyl group, a spiro-bifluorenyl group, a carbazolyl group, a dibenzofuranyl group, and a dibenzothiophenyl group; and 
     a fluorenyl group, a spiro-bifluorenyl group, a carbazolyl group, a dibenzofuranyl group, and a dibenzothiophenyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a phenyl group substituted with a C 1 -C 10  alkyl group, a phenyl group substituted with —F, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a carbazolyl group, a dibenzofuranyl group, and a dibenzothiophenyl group, 
     but embodiments of the present disclosure are not limited thereto. 
     In one or more embodiments, in Formula 202, i) R 201  and R 202  may be connected (e.g., coupled) via a single bond, and/or ii) R 203  and R 204  may be connected (e.g., coupled) via a single bond. 
     In one or more embodiments, at least one selected from R 201  to R 204  in Formula 202 may be selected from the group consisting of: 
     a carbazolyl group; and 
     a carbazolyl group substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a phenyl group substituted with a C 1 -C 10  alkyl group, a phenyl group substituted with —F, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a carbazolyl group, a dibenzofuranyl group, and a dibenzothiophenyl group, 
     but embodiments of the present disclosure are not limited thereto. 
     The compound represented by Formula 201 may be represented by Formula 201A: 
     
       
         
         
             
             
         
       
     
     In some embodiments, the compound represented by Formula 201 may be represented by Formula 201A(1), but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     In one or more embodiments, the compound represented by Formula 201 may be represented by Formula 201A-1, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     In some embodiments, the compound represented by Formula 202 may be represented by Formula 202A: 
     
       
         
         
             
             
         
       
     
     In one or more embodiments, the compound represented by Formula 202 may be represented by Formula 202A-1: 
     
       
         
         
             
             
         
       
     
     In Formulae 201A, 201A(1), 201A-1, 202A, and 202A-1, 
     L 201  to L 203 , xa1 to xa3, xa5, and R 202  to R 204  may each independently be the same as described herein. 
     R 211  and R 212  may each independently be the same as described herein in connection with R 203 , and 
     R 213  to R 217  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an am idino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a phenyl group substituted with a C 1 -C 10  alkyl group, a phenyl group substituted with —F, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a thiophenyl group, a furanyl group, a carbazolyl group, an indolyl group, an isoindolyl group, a benzofuranyl group, a benzothiophenyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, a dibenzosilolyl group, and a pyridinyl group. 
     The hole transport region may include at least one selected from Compounds HT1 to HT39, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The thickness of the hole transport region may be about 100 Å to about 10,000 Å, and in some embodiments, about 100 Å to about 1,000 Å. When the hole transport region includes at least one selected from a hole injection layer and a hole transport layer, the thickness of the hole injection layer may be about 100 Å to about 9,000 Å, and in some embodiments, about 100 Å to about 1,000 Å; the thickness of the hole transport layer may be about 50 Å to about 2,000 Å, and in some embodiments, 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 hole auxiliary layer may increase light-emission efficiency by compensating for an optical resonance distance according to the wavelength of light emitted by an emission layer (e.g., by adjusting the optical resonance distance to match the wavelength of light emitted from the emission layer), and the electron blocking layer may block or reduce the flow of electrons from an electron transport region. The hole auxiliary layer and the electron blocking layer may include those materials as described above. 
     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 homogeneously or non-homogeneously dispersed in the hole transport region. 
     The charge-generation material may be, for example, a p-dopant. 
     The p-dopant may include at least one selected from a quinone derivative, a metal oxide, and a cyano group-containing compound, but embodiments of the present disclosure are not limited thereto. 
     For example, the p-dopant may include at least one selected from the group consisting of: 
     a quinone derivative (such as TCNQ (tetracyanoquinodimethane) and/or F4-TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane)); 
     a metal oxide (such as tungsten oxide and/or molybdenum oxide); 
     HAT-CN (1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile); and 
     a compound represented by Formula 221, 
     but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     In Formula 221, 
     R 221  to R 223  may each independently be selected from a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, provided that at least one selected from R 221  to R 223  has at least one substituent selected from a cyano group, —F, —Cl, —Br, —I, a C 1 -C 20  alkyl group substituted with —F, a C 1 -C 20  alkyl group substituted with —Cl, a C 1 -C 20  alkyl group substituted with Br, and a C 1 -C 20  alkyl group substituted with —I. 
     Emission Layer in Organic Layer  150   
     When the organic light-emitting device  10  is a full color organic 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 selected from 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 selected from a red-light emission material, a green-light emission material, and a blue-light emission material, in which the two or more materials may be mixed with each other in a single layer to thereby emit white light. 
     The emission layer may include a host and a dopant. The host may include at least one selected from a phosphorescent host and a fluorescent host. The dopant may be at least one selected from a phosphorescent dopant and a fluorescent dopant. 
     For example, a fluorescent host in the emission layer may be the second compound and a fluorescent dopant in the emission layer may be the third compound. 
     The 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, but embodiments of the present disclosure are not limited thereto. 
     The thickness of the emission layer may be about 100 Å to about 1,000 Å, and in some embodiments, about 200 Å to about 600 Å. When the thickness of the emission layer is within these ranges, excellent light-emission characteristics may be obtained without a substantial increase in driving voltage. 
     Electron Transport Region in Organic Layer  150   
     The electron transport region may have i) a single-layered structure including a single layer including a single material, ii) a single-layered structure including a single layer including a plurality of different materials, or iii) a multi-layered structure having a plurality of layers including a plurality of different materials. 
     The electron transport region may include at least one selected from an electron auxiliary layer, a hole blocking layer, an electron control layer, an electron transport layer (ETL), and an electron injection layer, but embodiments of the present disclosure are not limited thereto. 
     For example, the electron transport region may have a structure of electron transport layer/electron injection layer, a structure of hole blocking layer/electron transport layer/electron injection layer, a structure of electron control layer/electron transport layer/electron injection layer, or a structure of electron auxiliary layer/electron transport layer/electron injection layer, wherein layers of each structure are sequentially stacked on an emission layer in each stated order. However, embodiments of the structure of the electron transport layer are not limited thereto. 
     The electron transport region may include the first compound, for example, the compound represented by one selected from Formulae 4A to 4E. 
     The electron transport region may include at least one selected from an electron auxiliary layer, a hole blocking layer, an electron transport layer (ETL), and an electron injection layer, but embodiments of the present disclosure are not limited thereto. 
     In one or more embodiments, the organic layer  150  may include an electron transport region between the second electrode and the emission layer, the electron transport region including an electron auxiliary layer, wherein the electron auxiliary layer may include the first compound (for example, a first compound represented by one selected from Formulae 4A to 4E). 
     For example, the electron transport region may include an electron transport layer between the electron auxiliary layer and the second electrode, wherein the electron auxiliary layer directly contacts the emission layer. However, embodiments of the structure of the electron transport region are not limited thereto. 
     The electron transport region may include at least one compound selected from BCP(2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), Bphen(4,7-diphenyl-1,10-phenanthroline), Alq 3 , Balq, TAZ (3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole), and NTAZ. 
     
       
         
         
             
             
         
       
     
     The thicknesses of the electron auxiliary layer, the hole blocking layer, and/or the electron controlling layer may each independently be about 20 Å to about 1,000 Å, and in some embodiments, about 30 Å to about 300 Å. When the thicknesses of the electron auxiliary layer, the hole blocking layer, and the electron control layer are each within these ranges, the electron blocking layer may have excellent electron blocking and/or control characteristics without a substantial increase in driving voltage. 
     The thickness of the electron transport layer may be about 100 Å to about 1,000 Å, and in some embodiments, about 150 Å to about 500 Å. When the thickness of the electron transport layer is within these ranges, the electron transport layer may have satisfactory electron transport characteristics without a substantial increase in driving voltage. 
     The electron transport region (for example, the electron transport layer in the electron transport region) may further include, in addition to the materials described above, a metal-containing material. 
     The metal-containing material may include at least one selected from an alkali metal complex and an alkaline earth metal complex. The alkali metal complex may include a metal ion selected from a lithium (Li) ion, a sodium (Na) ion, a potassium (K) ion, a rubidium (Rb) ion, and a cesium (Cs) ion, and the alkaline earth metal complex may include a metal ion selected from a beryllium (Be) ion, a magnesium (Mg) ion, a calcium (Ca) ion, a strontium (Sr) ion, and a barium (Ba) ion. Each ligand coordinated with the metal ion of the alkali metal complex or the alkaline earth metal complex may independently be selected from a hydroxy quinoline, a hydroxy isoquinoline, a hydroxy benzoquinoline, a hydroxy acridine, a hydroxy phenanthridine, a hydroxyphenyl oxazole, a hydroxyphenyl thiazole, a hydroxydiphenyl oxadiazole, a hydroxydiphenyl thiadiazole, a hydroxyphenyl pyridine, a hydroxyphenyl benzimidazole, a hydroxyphenyl benzothiazole, a bipyridine, a phenanthroline, and a cyclopentadiene, but embodiments of the present disclosure are not limited thereto. 
     For example, the metal-containing material may include a Li complex. The Li complex may include, for example, Compound ET-D1 (lithium quinolate, LiQ) and/or ET-D2. 
     
       
         
         
             
             
         
       
     
     The electron transport region may include an electron injection layer that facilitates injection of electrons from the second electrode  190 . The electron injection layer may directly contact the second electrode  190 . 
     The electron injection layer may have i) a single-layered structure including a single layer including a single material, ii) a single-layered structure including a single layer including a plurality of different materials, or iii) a multi-layered structure having a plurality of layers including a plurality of different materials. 
     The electron injection layer may include a reducing dopant. 
     The reducing dopant may include at least one selected from an alkali metal, an alkaline earth metal, a rare earth based metal, an alkali metal compound, an alkaline earth metal compound, a rare earth based metal compound, an alkali metal complex, an alkaline earth metal complex, and a rare earth based metal complex. 
     The alkali metal may be selected from Na, K, Rb, and Cs. In one embodiment, the alkali metal may be selected from K, Rb, and Cs. In one or more embodiments, the alkaline metal may be selected from Rb and Cs, but embodiments of the present disclosure are not limited thereto. 
     The alkaline earth metal may be selected from Ca, Sr, and Ba. 
     The rare earth metal may be selected from scandium (Sc), yttrium (Y), cerium (Ce), yttrium (Yb), gadolinium (Gd), and terbium (Tb). 
     The alkali metal compound, the alkaline earth metal compound, and the rare earth metal compound may be selected from oxides and halides (for example, fluorides, chlorides, bromides, and/or iodines) of the alkali metal, the alkaline earth metal, and the rare earth metal, respectively. 
     The alkali metal compound may be selected from alkali metal oxides (such as Li 2 O, Cs 2 O, and/or K 2 O), and alkali metal halides (such as LiF, NaF, CsF, KF, LiI, NaI, CsI, and/or KI). In one embodiment, the alkali metal compound may be selected from LiF, Li 2 O, NaF, LiI, NaI, CsI, and KI, but embodiments of the present disclosure are not limited thereto. 
     The alkaline earth metal compound may be selected from alkaline earth metal compounds (such as BaO, SrO, CaO, Ba x Sr 1-x O(0&lt;x&lt;1), and/or Ba x Ca 1-x O(0&lt;x&lt;1)). In one embodiment, the alkaline earth metal compound may be selected from BaO, SrO, and CaO, but embodiments of the present disclosure are not limited thereto. 
     The rare earth metal compound may be selected from YbF 3 , ScF 3 , ScO 3 , Y 2 O 3 , Ce 2 O 3 , GdF 3 , and TbF 3 . In one embodiment, the rare earth metal compound may be selected from YbF 3 , ScF 3 , TbF 3 , Ybi 3 , Sci 3 , and Tbi 3 , but embodiments of the present disclosure are not limited thereto. 
     The alkali metal complex, the alkaline earth metal complex, and the rare earth metal complex may each include an alkali metal ion, an alkaline earth metal ion, and a rare earth metal ion as described above, respectively, and each ligand coordinated with the metal ion of the alkali metal complex, the alkaline earth metal complex, and the rare earth metal complex may independently be selected from hydroxyquinoline, hydroxyisoquinoline, hydroxybenzoquinoline, hydroxyacridine, hydroxyphenanthridine, hydroxyphenyl oxazole, hydroxyphenyl thiazole, hydroxydiphenyl oxadiazole, hydroxydiphenyl thiadiazole, hydroxyphenyl pyridine, hydroxyphenyl benzim idazole, hydroxyphenyl benzothiazole, bipyridine, phenanthroline, and cyclopentadiene, but embodiments of the present disclosure are not limited thereto. 
     The electron injection layer may include (e.g., consist of) the reducing dopant described above, or may include the reducing dopant and an organic material. When the electron injection layer includes the reducing dopant and an organic material, the reducing dopant may be homogeneously or non-homogeneously dispersed in a matrix of the organic material. 
     The thickness of the electron injection layer may be about 1 Å to about 100 Å, and in some embodiments, about 3 Å to about 90 Å. When the thickness of the electron injection layer is within these ranges, the electron injection layer may have satisfactory electron injection characteristics without a substantial increase in driving voltage. 
     Second Electrode  190   
     The second electrode  190  may be on the organic layer  150 . The second electrode  190  may be a cathode that is an electron injection electrode, and in this regard, the material for forming the second electrode  190  may be a material having a low work function, and may be selected from a metal, an alloy, an electrically conductive compound, and combinations thereof. 
     The second electrode  190  may include at least one selected from lithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), ITO, and IZO, but embodiments of the present disclosure are not limited thereto. The second electrode  190  may be a transmissive electrode, a semi-transmissive electrode, or a reflective electrode. 
     The second electrode  190  may have a single-layered structure, or a multi-layered structure including two or more layers. 
     Description of FIGS.  2  to  4   
     The organic light-emitting device  20  of  FIG. 2  includes a first capping layer  210 , a first electrode  110 , an organic layer  150 , and a second electrode  190  sequentially stacked in this stated order. The organic light-emitting device  30  of  FIG. 3  includes a first electrode  110 , an organic layer  150 , a second electrode  190 , and a second capping layer  220  sequentially stacked in this stated order. The organic light-emitting device  40  of  FIG. 4  includes a first capping layer  210 , a first electrode  110 , an organic layer  150 , a second electrode  190 , and a second capping layer  220  sequentially stacked in this stated order. 
     In  FIGS. 2 to 4 , the first electrode  110 , the organic layer  150 , and the second electrode  190  may each be the same as described herein in connection with  FIG. 1 . 
     In the organic layer  150  of each of the organic light-emitting devices  20  and  40 , light generated in an emission layer may pass through the first electrode  110 , (which may be a semi-transmissive electrode or a transmissive electrode) and the first capping layer  210  toward the outside. In the organic layer  150  of each of the organic light-emitting devices  30  and  40 , light generated in an emission layer may pass through the second electrode  190  (which is a semi-transmissive electrode or a transmissive electrode) and the second capping layer  220  toward the outside. 
     The first capping layer  210  and the second capping layer  220  may increase the external luminescent efficiency according to the principle of constructive interference. 
     The first capping layer  210  and the second capping layer  220  may each independently be a capping layer including an organic material, an inorganic capping layer including an inorganic material, or a composite capping layer including an organic material and an inorganic material. 
     At least one selected from the first capping layer  210  and the second capping layer  220  may include at least one material selected from carbocyclic compounds, heterocyclic compounds, amine-based compounds, porphyrin derivatives, phthalocyanine derivatives, naphthalocyanine derivatives, alkali metal complexes, and alkaline earth metal complexes. The carbocyclic compound, the heterocyclic compound, and the amine-based compound may each independently be optionally substituted with a substituent containing at least one element selected from oxygen (O), nitrogen (N), sulfur (S), selenium (Se), silicon (Si), fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). In one embodiment, at least one selected from the first capping layer  210  and the second capping layer  220  may include an amine-based compound. 
     In one embodiment, at least one selected from the first capping layer  210  and the second capping layer  220  may include the compound represented by Formula 201 and/or the compound represented by Formula 202. 
     In one or more embodiments, at least one selected from the first capping layer  210  and the second capping layer  220  may include a compound selected from Compounds HT28 to HT33 and Compounds CP1 to CP5, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Hereinbefore, the organic light-emitting device according to an embodiment of the present disclosure has been described in connection with  FIGS. 1-4 . However, embodiments of the present disclosure are not limited thereto. 
     The layers constituting the hole transport region, the emission layer, and the layers constituting the electron transport region may be formed in a specific region using one or more suitable methods selected from vacuum deposition, spin coating, casting, a Langmuir-Blodgett (LB) method, ink-jet printing, laser-printing, and laser-induced thermal imaging. 
     When the respective layers of the hole transport region, the emission layer, and the respective layers of the electron transport region are formed by deposition, the deposition may be performed at a deposition temperature of about 100 to about 500° C., at a vacuum degree of about 10 −8  to about 10 −3  torr, and at a deposition rate of about 0.01 to about 100 Å/sec, depending on the compound to be deposited in each layer, and the structure of each layer to be formed. 
     When the layers constituting the hole transport region, an emission layer, and the layers constituting the electron transport region are formed by spin coating, the spin coating may be performed at a coating speed of about 2,000 rpm to about 5,000 rpm and at a heat treatment temperature of about 80° C. to 200° C., depending on the compound to be included in each layer, and the structure of each layer to be formed. 
     General Definition of Substituents 
     The term “C 1 -C 60  alkyl group”, as used herein, refers to a linear or branched aliphatic hydrocarbon monovalent group having 1 to 60 carbon atoms, and non-limiting examples thereof may include a methyl group, an ethyl group, a propyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an iso-amyl group, and a hexyl group. The term “C 1 -C 60  alkylene group”, as used herein, refers to a divalent group having substantially the same structure as the C 1 -C 60  alkyl group. 
     The term “C 2 -C 60  alkenyl group”, as used herein, refers to a hydrocarbon group formed by substituting at least one carbon-carbon double bond in the body (e.g., middle) or at the terminus of the C 2 -C 60  alkyl group, and non-limiting examples thereof may include an ethenyl group, a propenyl group, and a butenyl group. The term “C 2 -C 60  alkylene group”, as used herein, refers to a divalent group having substantially the same structure as the C 2 -C 60  alkyl group. 
     The term “C 2 -C 60  alkynyl group”, as used herein, refers to a hydrocarbon group formed by substituting at least one carbon-carbon triple bond in the body (e.g., middle) or at the terminus of the C 2 -C 60  alkyl group, and non-limiting examples thereof may include an ethynyl group and a propynyl group. The term “C 2 -C 60  alkylene group”, as used herein, refers to a divalent group having substantially the same structure as the C 2 -C 60  alkyl group. 
     The term “C 1 -C 60  alkoxy group”, as used herein, refers to a monovalent group represented by —O-A 101  (wherein Ani is a C 1 -C 60  alkyl group), and non-limiting examples thereof may include a methoxy group, an ethoxy group, and an isopropyloxy group. 
     The term “C 3 -C 10  cycloalkyl group”, as used herein, refers to a monovalent hydrocarbon monocyclic group having 3 to 10 carbon atoms, and non-limiting examples thereof may include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, and a cycloheptyl group. The term “C 3 -C 10  cycloalkylene group”, as used herein, refers to a divalent group having substantially the same structure as the C 3 -C 10  cycloalkyl group. 
     The term “C 10 -C 10  heterocycloalkyl group”, as used herein, refers to a monovalent monocyclic group having at least one heteroatom selected from N, O, Si, phosphorus (P), and S as a ring-forming atom and 1 to 10 carbon atoms, and non-limiting examples thereof may include a 1,2,3,4-oxatriazolidinyl group, a tetrahydrofuranyl group, and a tetrahydrothiophenyl group. The term “C 1 -C 10  heterocycloalkylene group”, as used herein, refers to a divalent group having substantially the same structure as the C 1 -C 10  heterocycloalkyl group. 
     The term “C 3 -C 10  cycloalkenyl group”, as used herein, refers to a monovalent monocyclic group that has 3 to 10 carbon atoms and at least one double bond in the ring thereof and does not have aromaticity, and non-limiting examples thereof may include a cyclopentenyl group, a cyclohexenyl group, and a cycloheptenyl group. The term “C 3 -C 10  cycloalkenylene group”, as used herein, refers to a divalent group having substantially the same structure as the C 3 -C 10  cycloalkenyl group. 
     The term “C 1 -C 10  heterocycloalkenyl group”, as used herein, refers to a monovalent monocyclic group that has at least one heteroatom selected from N, O, Si, P, and S as a ring-forming atom, 1 to 10 carbon atoms, and at least one double bond in its ring. Non-limiting examples of the C 1 -C 10  heterocycloalkenyl group may include a 4,5-dihydro-1,2,3,4-oxatriazolyl group, a 2,3-hydrofuranyl group, and a 2,3-hydrothiophenyl group. The term “C 1 -C 10  heterocycloalkenylene group”, as used herein, refers to a divalent group having substantially the same structure as the C 1 -C 10  heterocycloalkenyl group. 
     The term “C 6 -C 60  aryl group”, as used herein, refers to a monovalent group having a carbocyclic aromatic system having 6 to 60 carbon atoms, and the term “C 6 -C 60  arylene group”, as used herein, refers to a divalent group having a carbocyclic aromatic system having 6 to 60 carbon atoms. Non-limiting examples of the C 6 -C 60  aryl group may include a phenyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, a pyrenyl group, and a chrysenyl 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 fused (e.g., condensed). 
     The term “C 1 -C 60  heteroaryl group”, as used herein, refers to a monovalent group having a carbocyclic aromatic system that has at least one heteroatom selected from N, O, Si, P, and S as a ring-forming atom, and 1 to 60 carbon atoms. The term “C 1 -C 60  heteroarylene group”, as used herein, refers to a divalent group having a carbocyclic aromatic system that has at least one heteroatom selected from N, O, Si, P, and S as a ring-forming atom, and 1 to 60 carbon atoms. Non-limiting 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, and an isoquinolinyl group. When the C 1 -C 60  heteroaryl group and the C 1 -C 60  heteroarylene group each include two or more rings, the rings may be fused (e.g., condensed). 
     The term “C 6 -C 60  aryloxy group”, as used herein, refers to —O-A 102  (wherein A 102  is a C 6 -C 60  aryl group), and the term “C 6 -C 60  arylthio group”, as used herein, refers to —S-A 103  (wherein A 103  is a C 6 -C 60  aryl group). 
     The term “monovalent non-aromatic condensed polycyclic group”, as used herein, refers to a monovalent group that has two or more rings condensed (e.g., fused), only carbon atoms (for example, 8 to 60 carbon atoms) as ring forming atoms, and non-aromaticity in the entire molecular structure. The term “divalent non-aromatic condensed polycyclic group”, as used herein, refers to a divalent group having substantially the same structure as the monovalent non-aromatic condensed polycyclic group. 
     The term “monovalent non-aromatic condensed heteropolycyclic group”, as used herein, refers to a monovalent group that has two or more rings condensed (e.g., fused), at least one heteroatom selected from N, O, Si, P, and S in addition to carbon atoms (for example, 1 to 60 carbon atoms) as ring forming atoms, and non-aromaticity in the entire molecular structure. The term “divalent non-aromatic condensed heteropolycyclic group”, as used herein, refers to a divalent group having substantially the same structure as the monovalent non-aromatic condensed heteropolycyclic group. 
     The term “C 5 -C 60  carbocyclic group”, as used herein, refers to a monocyclic or polycyclic group having 5 to 60 carbon atoms in which a ring-forming atom is a carbon atom only (e.g., only carbon atoms are ring-forming atoms). The term “C 5 -C 60  carbocyclic group”, as used herein, refers to an aromatic carbocyclic group or a non-aromatic carbocyclic group. The term “C 5 -C 60  carbocyclic group,” as used herein, may refer to a ring (such as a benzene), a monovalent group (such as a phenyl group), or a divalent group (such as a phenylene group). In one or more embodiments, depending on the number of substituents connected to the C 5 -C 60  carbocyclic group, the C 5 -C 60  carbocyclic group may be a trivalent group or a quadrivalent group. 
     The term “C 1 -C 60  heterocyclic group”, as used herein, refers to a group having substantially the same structure as the C 1 -C 60  carbocyclic group, except that as a ring-forming atom, at least one heteroatom selected from N, O, Si, P, and S is used in addition to carbon (the number of carbon atoms may be 1 to 60). 
     At least one substituent of the substituted C 5 -C 60  carbocyclic group, substituted C 1 -C 60  heterocyclic group, substituted C 3 -C 10  cycloalkylene group, substituted C 1 -C 10  heterocycloalkylene group, substituted C 3 -C 10  cycloalkenylene group, substituted C 1 -C 10  heterocycloalkenylene group, substituted C 6 -C 60  arylene group, substituted C 1 -C 60  heteroarylene group, substituted divalent non-aromatic condensed polycyclic group, substituted divalent non-aromatic condensed heteropolycyclic group, substituted C 1 -C 60  alkyl group, substituted C 2 -C 60  alkenyl group, substituted C 2 -C 60  alkynyl group, substituted C 1 -C 60  alkoxy group, substituted C 3 -C 10  cycloalkyl group, substituted C 1 -C 10  heterocycloalkyl group, substituted C 3 -C 10  cycloalkenyl group, substituted C 1 -C 10  heterocycloalkenyl group, substituted C 6 -C 60  aryl group, substituted C 6 -C 60  aryloxy group, substituted C 6 -C 60  arylthio group, substituted C 1 -C 60  heteroaryl group, substituted monovalent non-aromatic condensed polycyclic group, and substituted monovalent non-aromatic condensed heteropolycyclic group may be selected from the group consisting of: 
     deuterium (-D), —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, and a C 1 -C 60  alkoxy group; 
     a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, and a C 1 -C 60  alkoxy group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 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 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic 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 ), and —P(═O)(Q 11 )(Q 12 ); 
     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 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group; 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 60  alkyl group, 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 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 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic 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 ), and —P(═O)(Q 21 )(Q 22 ); and 
     —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 ), and —P(═O)(Q 31 )(Q 32 ), 
     wherein Q 11  to Q 13 , Q 21  to Q 23 , and Q 31  to Q 33  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 60  alkyl group, 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 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, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group. 
     The term “Ph”, as used herein, may refer to a phenyl group; the term “Me”, as used herein, may refer to a methyl group; the term “Et”, as used herein, may refer to an ethyl group; the terms “ter-Bu” or “But”, as used herein, may refer to a tert-butyl group; and the term “OMe”, as used herein, may refer to a methoxy group. 
     The term “biphenyl group”, as used herein, refers to “a phenyl group substituted with a phenyl group”. In other words, a biphenyl group is a substituted phenyl group having a C 6 -C 60  aryl group as a substituent. 
     The term “terphenyl group”, as used herein, refers to “a phenyl group substituted with a biphenyl group”. In other words, a “terphenyl group” is a substituted phenyl group having a C 6 -C 60  aryl group substituted with a C 6 -C 60  aryl group as a substituent. 
     Symbols * and *′ used herein, unless defined otherwise, refer to a binding site to a neighboring atom in a corresponding formula. 
     Hereinafter, a compound according to embodiments of the present disclosure and an organic light-emitting device according to embodiments of the present disclosure will be described in more detail with reference to Examples. 
     EXAMPLE 
     Example 1 
     An ITO glass substrate (a product of Corning Co., Ltd.) with an ITO layer having a thickness of 15 Ω/cm 2  (1,200 Å) thereon was cut to a size of 50 mm×50 mm×0.5 mm, sonicated using isopropyl alcohol and pure water for 15 minutes each, cleaned by exposure to ultraviolet rays for 30 minutes, and cleaned by exposure to ozone. The ITO glass substrate (anode) was then mounted on a vacuum deposition apparatus. 
     Compound NPB was vacuum deposited on the ITO anode to form a hole transport layer having a thickness of 600 Å. Compound 1-1 was vacuum deposited on the hole transport layer to form a hole auxiliary layer having a thickness of 100 Å. Compound 2-1 (fluorescent host) and Compound 3-1 (fluorescent dopant) were co-deposited on the hole auxiliary layer at a weight ratio of 95:5 to form an emission layer having a thickness of 300 Å. 
     Alq 3  was vacuum deposited on the emission layer to form an electron transport layer having a thickness of 300 Å. LiF was deposited on the electron transport layer to form an electron injection layer having a thickness of 10 Å, and Al was deposited on the electron injection layer to form a cathode having a thickness of 2,000 Å, thereby completing the manufacture of an organic light-emitting device. 
     Example 2 to 8 and Comparative Example 1 
     Additional organic light-emitting devices were manufactured in substantially the same manner as in Example 1, except that the compounds shown in Table 1 were used in forming each hole transport layer, hole auxiliary layer, and emission layer. 
     Comparative Example 2 
     An organic light-emitting device was manufactured in substantially the same manner as in Example 1, except that the hole transport layer was formed to a thickness of 700 Å and the hole auxiliary layer was not formed. 
     Example 9 
     An ITO glass substrate (a product of Corning Co., Ltd.) with an ITO layer having a thickness of 15 Ω/cm 2  (1,200 Å) thereon was cut to a size of 50 mm×50 mm×0.5 mm, sonicated using isopropyl alcohol and pure water for 15 minutes each, cleaned by exposure to ultraviolet rays for 30 minutes, and cleaned by exposure to ozone. The ITO glass substrate (anode) was then mounted on a vacuum deposition apparatus. 
     Compound HT3 was vacuum deposited on the ITO anode to form a hole transport layer having a thickness of 700 Å. Compound 2-1 (fluorescent host) and Compound 3-1 (fluorescent dopant) were co-deposited on the hole transport layer at a weight ratio of 95:5 to form an emission layer having a thickness of 300 Å. 
     Compound 4-1 was vacuum deposited on the emission layer to form an electron auxiliary layer having a thickness of 100 Å. Alq 3  was vacuum deposited on the electron auxiliary layer to form an electron transport layer having a thickness of 200 Å. LiF was deposited on the electron transport layer to form an electron injection layer having a thickness of 10 Å, and Al was deposited on the electron injection layer to form a cathode having a thickness of 2,000 Å, thereby completing the manufacture of an organic light-emitting device. 
     Example 10 to 16 and Comparative Example 3 
     Additional organic light-emitting devices were manufactured in substantially the same manner as in Example 9, except that the compounds shown in Table 1 were used in forming the hole transport layer, the emission layer, and the electron auxiliary layer: 
     
       
         
         
             
             
         
       
     
     Evaluation Example 1 
     The efficiency and lifespan (T 90 ) of each of the organic light-emitting devices of Examples 1 to 16 and Comparative Examples 1 to 3 were evaluated using a luminance-based PR650. The results thereof are shown in Table 1. The lifespan (T 90 ) results were obtained by measuring the time at which the luminance was reduced to 90% of the initial luminance, measured under a driving current of 10 mA/cm 2 . 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Hole 
                 Hole 
                   
                 Electron 
                   
                   
               
               
                   
                 transport 
                 auxiliary 
                 Emission layer 
                 auxiliary 
                 Efficiency 
                 Lifespan 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 layer 
                 layer 
                 Host 
                 Dopant 
                 layer 
                 (cd/A) 
                 (T 90 , hr) 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Example 1 
                 NPB 
                 1-1 
                 2-1 
                 3-1 
                 — 
                 5.2 
                 89 
               
               
                 Example 2 
                 NPB 
                 1-1 
                 2-1 
                 3-7 
                 — 
                 5.4 
                 101 
               
               
                 Example 3 
                 NPB 
                 1-3 
                 2-1 
                 3-11 
                 — 
                 5.5 
                 96 
               
               
                 Example 4 
                 NPB 
                 1-3 
                 2-9 
                 3-11 
                 — 
                 5.7 
                 93 
               
               
                 Example 5 
                 NPB 
                 1-10 
                 2-8 
                 3-14 
                 — 
                 5.4 
                 101 
               
               
                 Example 6 
                 NPB 
                 1-10 
                 2-8 
                 3-18 
                 — 
                 5.3 
                 96 
               
               
                 Example 7 
                 NPB 
                 1-17 
                 2-5 
                 3-12 
                 — 
                 5.8 
                 108 
               
               
                 Example 8 
                 NPB 
                 1-17 
                 2-18 
                 3-12 
                 — 
                 5.7 
                 85 
               
               
                 Example 9 
                 HT3 
                 — 
                 2-1 
                 3-1 
                 4-1 
                 5.6 
                 102 
               
               
                 Example 10 
                 HT3 
                 — 
                 2-1 
                 3-1 
                 4-3 
                 5.9 
                 86 
               
               
                 Example 11 
                 HT3 
                 — 
                 2-11 
                 3-22 
                 4-5 
                 5.5 
                 110 
               
               
                 Example 12 
                 HT3 
                 — 
                 2-13 
                 3-22 
                 4-5 
                 5.6 
                 109 
               
               
                 Example 13 
                 HT3 
                 — 
                 2-4 
                 3-3 
                 4-8 
                 5.9 
                 98 
               
               
                 Example 14 
                 HT3 
                 — 
                 2-5 
                 3-3 
                 4-12 
                 5.7 
                 115 
               
               
                 Example 15 
                 HT3 
                 — 
                 2-15 
                 3-23 
                 4-19 
                 5.8 
                 103 
               
               
                 Example 16 
                 HT3 
                 — 
                 2-15 
                 3-14 
                 4-18 
                 5.6 
                 107 
               
               
                 Comparative 
                 NPB 
                 1-1 
                 ADN 
                 3-1 
                 — 
                 4.6 
                 57 
               
               
                 Example 1 
               
               
                 Comparative 
                 NPB 
                 — 
                 2-1 
                 3-1 
                 — 
                 4.5 
                 61 
               
               
                 Example 2 
               
               
                 Comparative 
                 HT3 
                 — 
                 ADN 
                 3-1 
                 4-1 
                 4.9 
                 70 
               
               
                 Example 3 
               
               
                   
               
            
           
         
       
     
     Referring to Table 1, it was confirmed that the organic light-emitting devices of Examples 1 to 8 each had improved efficiency and long lifespan characteristics, compared to each of the organic light-emitting devices of Comparative Example 1 and 2, and the organic light-emitting devices of Example 9 to 16 each had improved efficiency and long lifespan characteristics, compared to the organic light-emitting device of Comparative Example 3. 
     An organic light-emitting device according to an embodiment of the present disclosure may have a low driving voltage, high efficiency, and a long lifespan. 
     It should be understood that the 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 being available for other similar features or aspects in other embodiments. 
     As used herein, the terms “use”, “using”, and “used” may be considered synonymous with the terms “utilize”, “utilizing”, and “utilized”, respectively. The use of “may” when describing embodiments of the present disclosure refers to “one or more embodiments of the present disclosure”. 
     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. 
     Also, any numerical range recited herein is intended to include all subranges 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. 
     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 changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the following claims and equivalents thereof.