Patent Publication Number: US-2020283463-A1

Title: Organometallic compound, organic light-emitting device including the organometallic compound, and apparatus including the organic light-emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2019-0025862, filed on Mar. 6, 2019, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     One or more embodiments relate to an organometallic compound, an organic light-emitting device including the organometallic compound, and an apparatus including the organic light-emitting device. 
     2. Description of the Related Art 
     Organic light-emitting devices are self-emission devices that produce full-color images, and also have wide viewing angles, high contrast ratios, short response times, as well as excellent characteristics in terms of brightness, driving voltage, and response speed. 
     The organic light-emitting device may include a first electrode disposed on a substrate, and a hole transport region, an emission layer, an electron transport region, and a second electrode, which are sequentially disposed 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, recombine in the emission layer to produce excitons. These excitons transit from an excited state to a ground state, thereby generating light. 
     SUMMARY 
     Aspects of the present disclosure provide an organometallic compound, an organic light-emitting device including the organometallic compound, and an apparatus including the organic light-emitting device. 
     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. 
     An aspect of the present disclosure provides an organometallic compound represented by Formula 1: 
       M 11 M 12 (L 11 )n 11 (L 12 )n 12 .  &lt;Formula 1&gt;
 
     In Formula 1, 
     M 11  and M 12  may each independently be selected from a Period 1 transition metal, a Period 2 transition metal, and a Period 3 transition metal, 
     L 11  may be a ligand represented by Formula 1-1, 
     L 12  may be selected from a monodentate ligand and a bidentate ligand, 
     n11 may be 1, and 
     n12 may be selected from 0, 1, 2, 3, and 4: 
     
       
         
         
             
             
         
       
     
     In Formula 1-1, 
     Y 12  to Y 18  may each independently be N or C, 
     T 11  to T 18  may each independently be selected from a single bond, *—O—*′, *—S—*′, *—C(B 11 )(B 12 )—*′, *—Si(B 11 )(B 12 )—*′, *—B(B 11 )—*′, *—N(B 11 )—*′, and * P(B 11 )—*′, and 
     L 11  to L 14  may each independently be selected from a group represented by Formula 10, a single bond, *—O—*′, *—S—*′, *—C(R 17 )(R 1 )—*′, *—C(R 17 )═*′, *═C(R 17 )—*′, *—C(R 17 )═C(R 18 )—*′, *—C(═O)—*′, *—C(═S)—*′, *—C≡C—*′, *—B(R 17 )—*′, *—N(R 17 )—*′, *—P(R 17 )—*′, *—Si(R 17 )(R 18 )—*′, *—P(R 17 )(R 18 )—*′, and *—Ge(R 17 )(R 18 )—*′, wherein at least one selected from L 11  to L 14  may be a group represented by Formula 10: 
     
       
         
         
             
             
         
       
     
     In Formula 10, 
     X 101  may be selected from a single bond, *—O—*′, *—S—*′, *—C(R 103 )(R 104 )—*′, *—Si(R 103 )(R 104 )—*′, *—B(R 103 )—*′, *—N(R 103 )—*′, and *—P(R 103 )—*′, 
     ring A 101  and ring A 102  may each independently be selected from a C 5 -C 60  carbocyclic group and a C 1 -C 60  heterocyclic group, 
     R 101  to R 104  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 hydrazine group, a hydrazone 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 7 -C 60  alkylaryl 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 C 2 -C 60  alkyl heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —C(Q 1 )(Q 2 )(Q 3 ), —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 1 )(Q 2 ), —N(Q 1 )(Q 2 ), —P(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O)(Q 1 ), —S(═O) 2 (Q 1 ), —P(═O)(Q 1 )(Q 2 ), and —P(═S)(Q 1 )(Q 2 ), 
     b101 and b102 may each independently be an integer from 1 to 10, 
     a11 to a14 may each independently be selected from 1, 2, and 3, 
     A 11  to A 16  may each independently be selected from a C 5 -C 60  carbocyclic group and a C 1 -C 60  heterocyclic group, 
     B 11 , B 12 , and R 11  to R 18  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 hydrazine group, a hydrazone 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 7 -C 60  alkylaryl 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 C 2 -C 60  alkyl heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —C(Q 1 )(Q 2 )(Q 3 ), —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 1 )(Q 2 ), —N(Q 1 )(Q 2 ), —P(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O)(Q 1 ), —S(═O) 2 (Q 1 ), P(═O)(Q 1 )(Q 2 ), and —P(═S)(Q 1 )(Q 2 ), 
     b11 to b16 may each independently be an integer from 1 to 10, 
     Q 1  to Q 3  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 hydrazine group, a hydrazone 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, a C 1 -C 60  alkyl group substituted with at least one selected from deuterium, —F, a cyano group, a C 1 -C 60  alkyl group, a phenyl group, and a biphenyl group, a C 6 -C 60  aryl group substituted with at least one selected from deuterium, —F, a cyano group, a C 1 -C 10  alkyl group, a phenyl group, and a biphenyl group, and a C 1 -C 60  heteroaryl group substituted with at least one selected from deuterium, —F, a cyano group, a C 1 -C 10  alkyl group, a phenyl group, and a biphenyl group, 
     *1 to *4 each indicate a binding site to M 11 , 
     *5 to *8 each indicate a binding site to M 12 , and 
     * and *′ each indicate a binding site to a neighboring atom. 
     Another aspect of the present disclosure provides an organic light-emitting device including: a first electrode; a second electrode; and an organic layer between the first electrode and the second electrode and including an emission layer, wherein the organic layer includes the organometallic compound. 
     Another aspect of the present disclosure provides an apparatus including: a thin-film transistor including a source electrode, a drain electrode, and an active layer; and the organic light-emitting device, wherein the first electrode of the organic light-emitting device is electrically connected to one of the source electrode and the drain electrode of the thin-film transistor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a schematic cross-sectional view of an organic light-emitting device according to an embodiment; 
         FIG. 2  is a schematic cross-sectional view of an organic light-emitting device according to an embodiment; 
         FIG. 3  is a schematic cross-sectional view of an organic light-emitting device according to an embodiment; and 
         FIG. 4  is a schematic cross-sectional view of an organic light-emitting device according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure will now be described more fully with reference to exemplary embodiments. The disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the disclosure to those skilled in the art. 
     Advantages, features, and how to achieve them of the present invention will become apparent by reference to the embodiment that will be described later in detail, together with the accompanying drawings. This invention may, however, be embodied in many different forms and should not be limited to the exemplary embodiments. 
     Hereinafter, embodiments are described in detail by referring to the attached drawings, and in the drawings, like reference numerals denote like elements, and a redundant explanation thereof will not be provided herein. 
     As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     It will be further understood that the terms “comprises” and/or “comprising” used herein specify the presence of stated features or components, but do not preclude the presence or addition of one or more other features or components. 
     It will be understood that when a layer, region, or component is referred to as being “on” or “onto” another layer, region, or component, it may be directly or indirectly formed on the other layer, region, or component. That is, for example, intervening layers, regions, or components may be present. 
     Sizes of elements in the drawings may be exaggerated for convenience of explanation. In other words, since sizes and thicknesses of components in the drawings are arbitrarily illustrated for convenience of explanation, the following embodiments of the present disclosure are not limited thereto. 
     The term “an organic layer” as used herein refers to a single layer and/or a plurality of layers disposed between the first electrode and the second electrode of the organic light-emitting device. A material included in the “organic layer” is not limited to an organic material. 
     An aspect of the present disclosure provides an organometallic compound represented by Formula 1: 
       M 11 M 12 (L 11 )n 11 (L 12 )n 12 .  &lt;Formula 1&gt;
 
     In Formula 1, 
     M 11  and M 12  may each independently be selected from a Period 1 transition metal, a Period 2 transition metal, and a Period 3 transition metal. 
     For example, in Formula 1, M 11  and M 12  may each independently be selected from platinum (Pt), palladium (Pd), copper (Cu), silver (Ag), gold (Au), rhodium (Rh), iridium (Ir), ruthenium (Ru), osmium (Os), titanium (Ti), zirconium (Zr), hafnium (Hf), europium (Eu), terbium (Tb), and thulium (Tm), but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, in Formula 1, M 11  and M 12  may each independently be selected from Pt, Pd, Cu, Ag, Au, Rh, Ir, Ru, and Os, but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, in Formula 1, M 11  and M 12  may each independently be selected from Pt, Pd, Cu, Ag, Au, Ru, and Os, but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, in Formula 1, M 11  and M 12  may each independently be selected from Pt, Pd, Ru, and Os, but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, in Formula 1, M 11  and M 12  may be identical to each other. 
     In Formula 1, L 11  may be a ligand represented by Formula 1-1: 
     
       
         
         
             
             
         
       
     
     In Formula 1-1, Y 12  to Y 18  may each independently be N or C. 
     In Formula 1-1, T 11  to T 18  may each independently be selected from a single bond, *—O—*′, *—S—*′, *—C(B 11 )(B 12 )—*′, *—Si(B 11 )(B 12 )—*′, *—B(B 11 )—*′, *—N(B 11 )—*′, and *—P(B 11 )—*′. B 11  and B 12  may be understood by referring to the description provided below. 
     For example, in Formula 1-1, T 11  to T 18  may each independently be selected from a single bond, *—O—*′, and *—S—*′, but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, in Formula 1-1, T 11  to T 18  may each independently be a single bond, but embodiments of the present disclosure are not limited thereto. 
     In Formula 1-1, L 11  to L 14  may each independently be selected from a group represented by Formula 10, a single bond, *—O—*′, *—S—*′, *—C(R 17 )(R 18 )—*′, *—C(R 17 )═*′, *═C(R 17 )—*′, *—C(R 17 )═C(R 18 )—*′, *—C(═O)—*′, *—C(═S)—*′, *—C≡C—*′, *—B(R 17 )—*′, *—N(R 17 )—*′, *—P(R 17 )—*′, *—Si(R 17 )(R 18 )—*′, *—P(R 17 )(R 18 )—*′, and *—Ge(R 17 )(R 18 )—*′, wherein at least one selected from L 11  to L 14  may be a group represented by Formula 10: 
     
       
         
         
             
             
         
       
     
     In Formula 10, 
     X 101  may be selected from a single bond, *—O—*′, *—S—*′, *—C(R 103 )(R 104 )—*′, *—Si(R 103 )(R 104 )—*′, *—B(R 103 )—*′, *—N(R 103 )—*′, and *—P(R 103 )—*′ 
     ring A 101  and ring A 102  may each independently be selected from a C 5 -C 60  carbocyclic group and a C 1 -C 60  heterocyclic group, 
     R 101  to R 104  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 hydrazine group, a hydrazone 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 7 -C 60  alkylaryl 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 C 2 -C 60  alkyl heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —C(Q 1 )(Q 2 )(Q 3 ), —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 1 )(Q 2 ), —N(Q 1 )(Q 2 ), —P(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O)(Q 1 ), —S(═O) 2 (Q 1 ), P(═O)(Q 1 )(Q 2 ), and —P(═S)(Q 1 )(Q 2 ), and 
     b101 and b102 may each independently be an integer from 1 to 10. 
     For example, X 101  in Formula 10 may be selected from a single bond, *—O—*′, *—S—*′, *—C(R 103 )(R 104 )—*′, and *—N(R 103 )—*′, but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, X 101  in Formula 10 may be a single bond. 
     For example, ring Aioi and ring A 102  in Formula 10 may each independently be i) a first ring, ii) a second ring, iii) a condensed ring in which two or more first rings are condensed with each other, iv) a condensed ring in which two or more second rings are condensed with each other, or v) a condensed ring in which one or more first rings and one or more second rings are condensed with each other, 
     the first ring may be selected from a cyclopentane group, a cyclopentene group, a cyclopentadiene group, a furan group, a thiophene group, a pyrrole group, a borole group, a phosphorole group, a silole group, a germole group, a selenophene group, an oxazole group, a dihydrooxazole group, an isoxazole group, a dihydroisoxazole group, an oxadiazole group, a dihydrooxadiazole group, an isoxadiazole group, a dihydroisoxadiazole group, an oxatriazole group, a dihydroxatriazole group, an isoxatriazole group, a dihydroisoxatriazole group, a thiazole group, a dihydrothiazole group, an isothiazole group, a dihydroisothiazole group, a thiadiazole group, a dihydrothiadiazole group, an isothiadiazole group, a dihydroisothiadiazole group, a thiatriazole group, a dihydrothiatriazole group, an isothiatriazole group, a dihydroisothiatriazole group, a pyrazole group, a dihydropyrazole group, an imidazole group, a dihydroimidazole group, a triazole group, a dihydrotriazole group, a tetrazole group, a dihydrotetrazole group, an azasilole group, a diazasilole group, and a triazasilole group, and 
     the second ring may be selected from a cyclohexane group, a cyclohexene group, a cyclohexadiene group, an adamantane group, a norbornane group, a norbornene group, a benzene group, a pyridine group, a dihydropyridine group, a tetrahydropyridine group, a pyrimidine group, a dihydropyrimidine group, a tetrahydropyrimidine group, a pyrazine group, a dihydropyrazine group, a tetrahydropyrazine group, a pyridazine group, a dihydropyridazine group, a tetrahydropyridazine group, and a triazine group, 
     but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, A 101  and A 102  in Formula 10 may be selected from a benzene group, a naphthalene group, an anthracene group, a phenanthrene group, a triphenylene group, a pyrene group, a chrysene group, a furan group, a thiophene group, a silole group, an indene group, a fluorene group, a benzofuran group, a dibenzofuran group, a benzothiophene group, a dibenzothiophene group, a benzosilole group, a dibenzosilole group, an indole group, a carbazole group, an indeno pyridine group, an indolopyridine group, a benzofuropyridine group, a benzothienopyridine group, a benzosilolopyridine group, an indeno pyrimidine group, an indolopyrimidine group, a benzofuropyrimidine group, a benzothienopyrimidine group, a benzosilolopyrimidine group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a quinoxaline group, a quinazoline group, a cinnoline group, a phthalazine group, a phenanthroline group, a pyrrole group, a pyrazole group, an imidazole group, a dihydroimidazole group, a triazole group, a dihydrotriazole group, an oxazole group, a dihydrooxazole group, an isoxazole group, a thiazole group, a dihydrothiazole group, an isothiazole group, an oxadiazole group, a dihydrooxadiazole group, a thiadiazole group, a dihydrothiadiazole group, a benzopyrazole group, a benzimidazole group, a dihydrobenzimidazole group, an imidazopyridine group, an imidazopyrimidine group, an imidazopyrazine group, a benzoxazole group, a dihydrobenzoxazole group, a benzothiazole group, a dihydrobenzothiazole group, a benzoxadiazole group, a dihydrobenzoxadiazole group, a benzothiadiazole group, and a dihydrobenzothiadiazole group, but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, A 101  and A 102  in Formula 10 may each independently be selected from a benzene group, a naphthalene group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, and an isoquinoline group, but embodiments of the present disclosure are not limited thereto. 
     For example, R 101  to R 104  in Formula 10 may each independently be selected from: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a cyano group, a C 1 -C 20  alkyl group, and a C 1 -C 20  alkoxy group; 
     a C 1 -C 20  alkyl group and a C 1 -C 20  alkoxy group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a cyano group, a phenyl group, a biphenyl group, and a terphenyl group; 
     a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, 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 perylenyl group, a pentacenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, a silolyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an indolyl group, an isoindolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a benzoisoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a benzoquinoxalinyl group, a quinazolinyl group, a benzoquinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzosilolyl group, a benzothiazolyl group, a benzoisothiazolyl group, a benzoxazolyl group, a benzoisoxazolyl group, a triazolyl group, a tetrazolyl group, a thiadiazolyl group, an oxadiazolyl group, a triazinyl group, a carbazolyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a naphthobenzofuranyl group, a naphthobenzothiophenyl group, a naphthobenzosilolyl group, a dibenzocarbazolyl group, a dinaphthofuranyl group, a dinaphthothiophenyl group, a dinaphtho silolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, an oxazolopyridinyl group, a thiazolopyridinyl group, a benzonaphthyridinyl group, an azafluorenyl group, an azaspiro-bifluorenyl group, an azacarbazolyl group, an azadibenzofuranyl group, an azadibenzothiophenyl group, an azadibenzosilolyl group, an indenopyrrolyl group, an indolopyrrolyl group, an indeno carbazolyl group, and an indolocarbazolyl group; 
     a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, 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 perylenyl group, a pentacenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, a silolyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an indolyl group, an isoindolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a benzoisoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a benzoquinoxalinyl group, a quinazolinyl group, a benzoquinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzosilolyl group, a benzothiazolyl group, a benzoisothiazolyl group, a benzoxazolyl group, a benzoisoxazolyl group, a triazolyl group, a tetrazolyl group, a thiadiazolyl group, an oxadiazolyl group, a triazinyl group, a carbazolyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a naphthobenzofuranyl group, a naphthobenzothiophenyl group, a naphthobenzosilolyl group, a dibenzocarbazolyl group, a dinaphthofuranyl group, a dinaphthothiophenyl group, a dinaphtho silolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, an oxazolopyridinyl group, a thiazolopyridinyl group, a benzonaphthyridinyl group, an azafluorenyl group, an azaspiro-bifluorenyl group, an azacarbazolyl group, an azadibenzofuranyl group, an azadibenzothiophenyl group, an azadibenzosilolyl group, an indenopyrrolyl group, an indolopyrrolyl group, an indeno carbazolyl group, and an indolocarbazolyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a cyano group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, 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 perylenyl group, a pentacenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, a silolyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an indolyl group, an isoindolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a benzoisoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a benzoquinoxalinyl group, a quinazolinyl group, a benzoquinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzosilolyl group, a benzothiazolyl group, a benzoisothiazolyl group, a benzoxazolyl group, a benzoisoxazolyl group, a triazolyl group, a tetrazolyl group, a thiadiazolyl group, an oxadiazolyl group, a triazinyl group, a carbazolyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a naphthobenzofuranyl group, a naphthobenzothiophenyl group, a naphthobenzosilolyl group, a dibenzocarbazolyl group, a dinaphthofuranyl group, a dinaphthothiophenyl group, a dinaphtho silolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, an oxazolopyridinyl group, a thiazolopyridinyl group, a benzonaphthyridinyl group, an azafluorenyl group, an azaspiro-bifluorenyl group, an azacarbazolyl group, an azadibenzofuranyl group, an azadibenzothiophenyl group, an azadibenzosilolyl group, an indenopyrrolyl group, an indolopyrrolyl group, an indeno carbazolyl group, an indolocarbazolyl group, —C(Q 31 )(Q 32 )(Q 33 ), —Si(Q 31 )(Q 32 )(Q 33 ), —B(Q 31 )(Q 32 ), —N(Q 31 )(Q 32 ), —P(Q 31 )(Q 32 ), —C(═O)(Q 31 ), —S(═O)(Q 31 ), —S(═O) 2 (Q 31 ), —P(═O)(Q 31 )(Q 32 ), and —P(═S)(Q 31 )(Q 32 ); and 
     —C(Q 1 )(Q 2 )(Q 3 ), —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 1 )(Q 2 ), —N(Q 1 )(Q 2 ), —P(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O)(Q 1 ), —S(═O) 2 (Q 1 ), —P(═O)(Q 1 )(Q 2 ), and —P(═S)(Q 1 )(Q 2 ), 
     Q 1  to Q 3  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 hydrazine group, a hydrazone 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, a C 1 -C 60  alkyl group substituted with at least one selected from deuterium, —F, a cyano group, a C 1 -C 60  alkyl group, a phenyl group, and a biphenyl group, a C 6 -C 60  aryl group substituted with at least one selected from deuterium, —F, a cyano group, a C 1 -C 10  alkyl group, a phenyl group, and a biphenyl group, and a C 1 -C 60  heteroaryl group substituted with at least one selected from deuterium, —F, a cyano group, a C 1 -C 10  alkyl group, a phenyl group, and a biphenyl group, but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, R 101  to R 104  in Formula 10 may each independently be selected from: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a cyano group, and a C 1 -C 20  alkyl group; 
     a C 1 -C 20  alkyl group substituted with one selected from deuterium, —F, —Cl, —Br, —I, and a cyano group; 
     groups represented by one selected from Formulae 5-1 to 5-138; and 
     —C(Q 1 )(Q 2 )(Q 3 ), —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 1 )(Q 2 ), —N(Q 1 )(Q 2 ), —P(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O)(Q 1 ), —S(═O) 2 (Q 1 ), —P(═O)(Q 1 )(Q 2 ), and —P(═S)(Q 1 )(Q 2 ), but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 5-1 to 5-138, 
     X 51  may be selected from O, S, N(R 51 ), and C(R 51 )(R 60 ); 
     X 52  may be N or C(R 52 ), X 53  may be N or C(R 53 ), X 54  may be N or C(R 54 ), X 55  may be N or C(R 55 ), X 56  may be N or C(R 56 ), X 57  may be N or C(R 57 ), Xs may be N or C(R 58 ), and X 59  may be N or C(R 59 ); 
     R 51  to R 60  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 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a perylenyl group, a thiophenyl group, a furanyl group, a silolyl group, a carbazolyl group, an indolyl group, an isoindolyl group, a benzofuranyl group, a benzothiophenyl group, a benzosilolyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, a dibenzosilolyl group, —C(Q 31 )(Q 32 )(Q 33 ), —Si(Q 31 )(Q 32 )(Q 33 ), —B(Q 31 )(Q 32 ), —N(Q 31 )(Q 32 ), —P(Q 31 )(Q 32 ), —C(═O)(Q 31 ), —S(═O)(Q 31 ), —S(═O) 2 (Q 31 ), —P(═O)(Q 31 )(Q 32 ), and —P(═S)(Q 31 )(Q 32 ), 
     Q 1  to Q 3  and Q 31  to Q 33  may each independently be selected from: 
     a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a 2-methylbutyl group, a sec-pentyl group, a tert-pentyl group, a neo-pentyl group, a 3-pentyl group, a 3-methyl-2-butyl group, a phenyl group, a biphenyl group, a C 1 -C 20  alkyl phenyl group, and a naphthyl group; and 
     a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an isopentyl group, a 2-methylbutyl group, a sec-pentyl group, a tert-pentyl group, a neo-pentyl group, a 3-pentyl group, a 3-methyl-2-butyl group, a phenyl group, and a naphthyl group, each substituted with at least one selected from deuterium and a phenyl group, 
     b51 may be selected from 1, 2, 3, 4, and 5, 
     b52 may be selected from 1, 2, 3, 4, 5, 6, and 7, 
     b53 may be selected from 1, 2, 3, 4, 5, 6, 7, 8, and 9, 
     b54 may be selected from 1, 2, 3, and 4, 
     b55 may be selected from 1, 2, and 3, 
     b56 may be selected from 1 and 2, 
     b57 may be selected from 1, 2, 3, 4, 5, and 6, and 
     * indicates a binding site to a neighboring atom. 
     In one embodiment, in Formula 10, R 101  to R 104  may each independently be selected from: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a cyano group, and groups represented by Formulae 9-1 to 9-16; 
     groups represented by Formulae 9-1 to 9-16, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, and a cyano group; and 
     groups represented by Formulae 6-1 to 6-257, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formula 6-1 to 6-257, 
     i-Pr indicates an isopropyl group, 
     t-Bu indicates a tert-butyl group, 
     Ph indicates a phenyl group, 
     1-Naph indicates a 1-naphthyl group, 
     2-Naph indicates a 2-naphthyl group, and 
     * indicates a binding site to a neighboring atom. 
     In one embodiment, the group represented by Formula 10 may be a group represented by one selected from Formulae 10-1 to 10-15: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 10-1 to 10-15, 
     * and *′ each indicate a binding site to a neighboring atom, and 
     R 101 , R 102 , b101, and b102 may each independently be the same as defined in Formula 10. 
     For example, in Formulae 10-1 to 10-15, R 101  and R 102  may each independently be selected from: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a cyano group, and groups represented by Formulae 9-1 to 9-16; and 
     groups represented by Formulae 9-1 to 9-16, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, and a cyano group, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     For example, in Formula 1-1, L 11  may be a group represented by Formula 10, and L 12  to L 14  may each independently be selected from a single bond, *—O—*′, *—S—*′, *—C(R 17 )(R 18 )—*′, *—C(R 17 )=*′, *═C(R 17 )*′, *—C(R 17 )═C(R 18 )—*′, *—C(═O)—*′, *—C(═S)—*′, *—C≡C—*′, *—B(R 17 )—*′, *—N(R 17 )—*′, *—P(R 17 )—*′, *—Si(R 17 )(R 18 )—*′, *—P(R 17 )(R 18 )—*′, and *—Ge(R 17 )(R 18 )—*′; 
     L 12  may be a group represented by Formula 10, and L 11 , L 13 , and L 14  may each independently be selected from a single bond, *—O—*′, *—S—*′, *—C(R 17 )(R 18 )—*′, *—C(R 17 )=*′, *═C(R 17 )—*′, *—C(R 17 )═C(R 18 )—*′, *—C(═O)—*′, *—C(═S)—*′, *—C≡C—*′, *—B(R 17 )—*′, *—N(R 17 )—*′, *—P(R 17 )—*′, *—Si(R 17 )(R 18 )—*′, *—P(R 17 )(R 18 )—*′, and *—Ge(R 17 )(R 18 )—*′; 
     L 11  and L 12  may each independently be a group represented by Formula 10, and L 13  and L 14  may each independently be selected from a single bond, *—O—*′, *—S—*′, *—C(R 17 )(R 18 )—*′, *—C(R 17 )═*′, *═C(R 17 )—*′, *—C(R 17 )═C(R 18 )—*′, *—C(═O)—*′, *—C(═S)—*′, *—C≡C—*′, *—B(R 17 )—*′, *—N(R 17 )—*′, *—P(R 17 )—*′, *—Si(R 17 )(R 18 )—*′, *—P(R 17 )(R 18 )—*′, and *—Ge(R 17 )(R 18 )—*′; 
     L 11  and L 13  may each independently be a group represented by Formula 10, and L 12  and L 14  may each independently be selected from a single bond, *—O—*′, *—S—*′, *—C(R 17 )(R 18 )—*′, *—C(R 17 )=*′, *═C(R 17 )—*′, *—C(R 17 )═C(R 18 )— *, *—C(═)—*′, *—C(═S)— *, *—C≡C—, *—B(R 17 )— *, *—N(R 17 )—, *—P(R 17 )—*′, *—Si(R 17 )(R 18 )—*′, *—P(R 17 )(R 18 )—*′, and *—Ge(R 17 )(R 18 )—*′; 
     L 11  and L 14  may each independently be a group represented by Formula 10, and L 12  and L 13  may each independently be selected from a single bond, *—O—*′, *—S—*′, *—C(R 17 )(R 18 )—*′, *—C(R 17 )═*′, *═C(R 17 )—*′, *—C(R 17 )═C(R 18 )—*′, *—C(═O)—*′, *—C(═S)—*′, *—C≡C—*′, *—B(R 17 )—*′, *—N(R 17 )—*′, *—P(R 17 )—*′, *—Si(R 17 )(R 18 )—*′, *—P(R 17 )(R 18 )—*′, and *—Ge(R 17 )(R 18 )—*′; 
     L 12  and L 13  may each independently be a group represented by Formula 10, and L 11  and L 14  may each independently be selected from a single bond, *—O—*′, *—S—*′, *—C(R 17 )(R 18 )—*′, *—C(R 17 )═*′, *═C(R 17 )—*′, *—C(R 17 )═C(R 18 )—*′, *—C(═O)—*′, *—C(═S)—*′, *—C≡C—*′, *—B(R 17 )—*′, *—N(R 17 )—*′, *—P(R 17 )—*′, *—Si(R 17 )(R 18 )—*′, *—P(R 17 )(R 18 )—*′, and *—Ge(R 17 )(R 18 )—*′; 
     L 12  to L 14  may each independently be a group represented by Formula 10, and L 11  may be selected from a single bond, *—O—*′, *—S—*′, *—C(R 17 )(R 18 )—*′, *—C(R 17 )═*′, *═C(R 17 )—*′, *—C(R 17 )═C(R 18 )—*′, *—C(═O)—*′, *—C(═S)—*′, *—C≡C—*′, *—B(R 17 )—*′, *—N(R 17 )—*′, *—P(R 17 )—*′, *—Si(R 17 )(R 18 )—*′, *—P(R 17 )(R 18 )—*′, and *—Ge(R 17 )(R 18 )—*′; 
     L 11 , L 13 , and L 14  may each independently be a group represented by Formula 10, and L 12  may be selected from a single bond, *—O—*′, *—S—*′, *—C(R 17 )(R 18 )—*′, *—C(R 17 )=*′, *═C(R 17 )—*′, *—C(R 17 )═C(R 18 )—*′, *—C(═O)—*′, *—C(═S)—*′, *—C≡C—*′, *—B(R 17 )—*′, *—N(R 17 )—*′, *—P(R 17 )—*′, *—Si(R 17 )(R 18 )—*′, *—P(R 17 )(R 18 )—*′, and *—Ge(R 17 )(R 18 )—*′; or 
     L 11  to L 14  may each independently be a group represented by Formula 10, but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, in Formula 1-1, L 11  to L 14  may each independently be selected from a group represented by Formula 10, a single bond, *—O—*′, *—S—*′, *—C(R 17 )(R 18 )—*′, *—C(R 17 )=*′, *═C(R 17 )—*′, *—B(R 17 )—*′, *—N(R 17 )—*′, *—Si(R 17 )(R 18 )—*′, and *—Ge(R 17 )(R 18 )—*′, wherein at least one selected from L 11  to L 14  may be a group represented by Formula 10, but embodiments of the present disclosure are not limited thereto. 
     In Formula 1-1, a11 to a14 may each independently be selected from 1, 2, and 3. 
     For example, in Formula 1-1, a11 to a14 may each independently be 1, but embodiments of the present disclosure are not limited thereto. 
     In Formula 1-1, A 11  to A 16  may each independently be selected from a C 5 -C 60  carbocyclic group and a C 1 -C 60  heterocyclic group. 
     For example, A 11  to A 16  in Formula 1-1 may each independently be i) a first ring, ii) a second ring, iii) a condensed ring in which two or more first rings are condensed with each other, iv) a condensed ring in which two or more second rings are condensed with each other, or v) a condensed ring in which one or more first rings and one or more second rings are condensed with each other, 
     the first ring may be selected from a cyclopentane group, a cyclopentene group, a cyclopentadiene group, a furan group, a thiophene group, a pyrrole group, a borole group, a phosphorole group, a silole group, a germole group, a selenophene group, an oxazole group, a dihydrooxazole group, an isoxazole group, a dihydroisoxazole group, an oxadiazole group, a dihydrooxadiazole group, an isoxadiazole group, a dihydroisoxadiazole group, an oxatriazole group, a dihydroxatriazole group, an isoxatriazole group, a dihydroisoxatriazole group, a thiazole group, a dihydrothiazole group, an isothiazole group, a dihydroisothiazole group, a thiadiazole group, a dihydrothiadiazole group, an isothiadiazole group, a dihydroisothiadiazole group, a thiatriazole group, a dihydrothiatriazole group, an isothiatriazole group, a dihydroisothiatriazole group, a pyrazole group, a dihydropyrazole group, an imidazole group, a dihydroimidazole group, a triazole group, a dihydrotriazole group, a tetrazole group, a dihydrotetrazole group, an azasilole group, a diazasilole group, and a triazasilole group, and 
     the second ring may be selected from a cyclohexane group, a cyclohexene group, a cyclohexadiene group, an adamantane group, a norbornane group, a norbornene group, a benzene group, a pyridine group, a dihydropyridine group, a tetrahydropyridine group, a pyrimidine group, a dihydropyrimidine group, a tetrahydropyrimidine group, a pyrazine group, a dihydropyrazine group, a tetrahydropyrazine group, a pyridazine group, a dihydropyridazine group, a tetrahydropyridazine group, and a triazine group, but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, A 11  to A 16  in Formula 1-1 may each independently be selected from a benzene group, a naphthalene group, an anthracene group, a phenanthrene group, a triphenylene group, a pyrene group, a chrysene group, a furan group, a thiophene group, a silole group, an indene group, a fluorene group, a benzofuran group, a dibenzofuran group, a benzothiophene group, a dibenzothiophene group, a benzosilole group, a dibenzosilole group, an indole group, a carbazole group, an indeno pyridine group, an indolopyridine group, a benzofuropyridine group, a benzothienopyridine group, a benzosilolopyridine group, an indeno pyrimidine group, an indolopyrimidine group, a benzofuropyrimidine group, a benzothienopyrimidine group, a benzosilolopyrimidine group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a quinoxaline group, a quinazoline group, a cinnoline group, a phthalazine group, a phenanthroline group, a pyrrole group, a pyrazole group, an imidazole group, a dihydroimidazole group, a triazole group, a dihydrotriazole group, an oxazole group, a dihydrooxazole group, an isoxazole group, a thiazole group, a dihydrothiazole group, an isothiazole group, an oxadiazole group, a dihydrooxadiazole group, a thiadiazole group, a dihydrothiadiazole group, a benzopyrazole group, a benzimidazole group, a dihydrobenzimidazole group, an imidazopyridine group, an imidazopyrimidine group, an imidazopyrazine group, a benzoxazole group, a dihydrobenzoxazole group, a benzothiazole group, a dihydrobenzothiazole group, a benzoxadiazole group, a dihydrobenzoxadiazole group, a benzothiadiazole group, and a dihydrobenzothiadiazole group, but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, A 11  to A 16  in Formula 1-1 may each independently be selected from a benzene group, a naphthalene group, an indene group, a fluorene group, a benzofuran group, a dibenzofuran group, a benzothiophene group, a dibenzothiophene group, an indole group, a carbazole group, an indeno pyridine group, an indolopyridine group, a benzofuropyridine group, a benzothienopyridine group, an indeno pyrimidine group, an indolopyrimidine group, a benzofuropyrimidine group, a benzothienopyrimidine group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a quinoxaline group, a quinazoline group, a cinnoline group, a phthalazine group, a phenanthroline group, a pyrrole group, a pyrazole group, an imidazole group, a dihydroimidazole group, a triazole group, a dihydrotriazole group, an oxazole group, a dihydrooxazole group, an isoxazole group, a thiazole group, a dihydrothiazole group, an isothiazole group, an oxadiazole group, a dihydrooxadiazole group, a thiadiazole group, a dihydrothiadiazole group, a benzopyrazole group, a benzimidazole group, a dihydrobenzimidazole group, an imidazopyridine group, an imidazopyrimidine group, an imidazopyrazine group, a benzoxazole group, a dihydrobenzoxazole group, a benzothiazole group, a dihydrobenzothiazole group, a benzoxadiazole group, a dihydrobenzoxadiazole group, a benzothiadiazole group, and a dihydrobenzothiadiazole group, but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, A 11  to A 16  in Formula 1-1 may each independently be represented by one selected from Formulae 2-1 to 2-43, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 2-1 to 2-43, 
     X 21  to X 23  may each independently be selected from C(R 24 ) and C—*, wherein at least two selected from X 21  to X 23  may be C—*, 
     X 24  may be N—*, and X 25  and X 26  may each independently be selected from C(R 24 ) and C—*, wherein at least one selected from X 25  and X 26  may be C—*, 
     X 27  and X 28  may each independently be selected from O, S, C(R 24 ), N, N(R 25 ), and N—*, wherein X 29  may be selected from O, S, C(R 24 ), and C—*, wherein i) at least one selected from X 27  and X 28  may be N—*, and X 29  may be C—*, or ii) X 27  and X 28  may each independently be N—*, and X 29  may be selected from O, S, and C(R 24 ), 
     R 21  to R 24  may each independently be the same as defined in connection with R 11  in Formula 1, 
     b21 may be selected from 1, 2, and 3, 
     b22 may be selected from 1, 2, 3, 4, and 5, 
     b23 may be selected from 1, 2, 3, and 4, 
     b24 may be selected from 1 and 2, and 
     * indicates a binding site to a neighboring atom. 
     In one embodiment, in Formula 1, a group represented by 
     
       
         
         
             
             
         
       
     
     may be a group represented by one selected from Formulae 3-11 and 3-12, a group represented by 
     
       
         
         
             
             
         
       
     
     may be a group represented by Formula 3-21, a group represented by 
     
       
         
         
             
             
         
       
     
     may be a group represented by Formula 3-31, a group represented by 
     
       
         
         
             
             
         
       
     
     may be a group represented by Formula 3-41, a group represented by 
     
       
         
         
             
             
         
       
     
     may be a group represented by Formula 3-51, and a group represented by 
     
       
         
         
             
             
         
       
     
     may be a group represented by one selected from Formulae 3-61 and 3-62, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     In Formulae 3-11, 3-12, 3-21, 3-31, 3-41, 3-51, 3-61, and 3-62, 
     *, *′, and *″ each indicate a binding site to a neighboring atom, 
     X 31  may be N or C(R 11d ), X 32  may be N or C(R 11e ), X 33  may be N or C(R 11f ), and X 34  may be N or C(R 11g ), 
     X 35  may be N or C(R 16d ), X 36  may be N or C(R 16e ), X 37  may be N or C(R 16f ), and X 38  may be N or C(R 16g ), 
     R 11a , R 11b , R 11c , R 11d , R 11e , R 11f , and R 11g  may each independently be the same as defined in connection with R 11  in Formula 1-1, 
     R 12a , R 12b , and R 12c  may each independently be the same as defined in connection with R 12  in Formula 1-1, 
     R 13a  and R 13b  may each independently be the same as defined in connection with R 13  in Formula 1-1, 
     R 14a  and R 14b  may each independently be the same as defined in connection with R 14  in Formula 1-1, 
     R 15a , R 15b , and R 15c  may each independently be the same as defined in connection with R 15  in Formula 1-1, and 
     R 16a , R 16b , R 16c , R 16d , R 16e , R 16f , and R 16g  may each independently be the same as defined in connection with R 16  in Formula 1-1. 
     In Formula 1-1, B 11 , B 12 , and R 11  to R 18  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 hydrazine group, a hydrazone 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 7 -C 60  alkylaryl 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 C 2 -C 60  alkyl heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —C(Q 1 )(Q 2 )(Q 3 ), —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 1 )(Q 2 ), —N(Q 1 )(Q 2 ), —P(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O)(Q 1 ), —S(═O) 2 (Q 1 ), —P(═O)(Q 1 )(Q 2 ), and —P(═S)(Q 1 )(Q 2 ), and 
     Q 1  to Q 3  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 hydrazine group, a hydrazone 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, a C 1 -C 60  alkyl group substituted with at least one selected from deuterium, —F, a cyano group, a C 1 -C 60  alkyl group, a phenyl group, and a biphenyl group, a C 6 -C 60  aryl group substituted with at least one selected from deuterium, —F, a cyano group, a C 1 -C 10  alkyl group, a phenyl group, and a biphenyl group, and a C 1 -C 60  heteroaryl group substituted with at least one selected from deuterium, —F, a cyano group, a C 1 -C 10  alkyl group, a phenyl group, and a biphenyl group. 
     For example, B 11 , B 12 , and R 11  to R 18  in Formula 1-1 may each independently be selected from: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a cyano group, a C 1 -C 20  alkyl group, and a C 1 -C 20  alkoxy group; 
     a C 1 -C 20  alkyl group and a C 1 -C 20  alkoxy group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a cyano group, a phenyl group, a biphenyl group, and a terphenyl group; 
     a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, 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 perylenyl group, a pentacenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, a silolyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an indolyl group, an isoindolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a benzoisoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a benzoquinoxalinyl group, a quinazolinyl group, a benzoquinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzosilolyl group, a benzothiazolyl group, a benzoisothiazolyl group, a benzoxazolyl group, a benzoisoxazolyl group, a triazolyl group, a tetrazolyl group, a thiadiazolyl group, an oxadiazolyl group, a triazinyl group, a carbazolyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a naphthobenzofuranyl group, a naphthobenzothiophenyl group, a naphthobenzosilolyl group, a dibenzocarbazolyl group, a dinaphthofuranyl group, a dinaphthothiophenyl group, a dinaphtho silolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, an oxazolopyridinyl group, a thiazolopyridinyl group, a benzonaphthyridinyl group, an azafluorenyl group, an azaspiro-bifluorenyl group, an azacarbazolyl group, an azadibenzofuranyl group, an azadibenzothiophenyl group, an azadibenzosilolyl group, an indenopyrrolyl group, an indolopyrrolyl group, an indeno carbazolyl group, and an indolocarbazolyl group; 
     a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, 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 perylenyl group, a pentacenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, a silolyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an indolyl group, an isoindolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a benzoisoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a benzoquinoxalinyl group, a quinazolinyl group, a benzoquinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzosilolyl group, a benzothiazolyl group, a benzoisothiazolyl group, a benzoxazolyl group, a benzoisoxazolyl group, a triazolyl group, a tetrazolyl group, a thiadiazolyl group, an oxadiazolyl group, a triazinyl group, a carbazolyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a naphthobenzofuranyl group, a naphthobenzothiophenyl group, a naphthobenzosilolyl group, a dibenzocarbazolyl group, a dinaphthofuranyl group, a dinaphthothiophenyl group, a dinaphtho silolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, an oxazolopyridinyl group, a thiazolopyridinyl group, a benzonaphthyridinyl group, an azafluorenyl group, an azaspiro-bifluorenyl group, an azacarbazolyl group, an azadibenzofuranyl group, an azadibenzothiophenyl group, an azadibenzosilolyl group, an indenopyrrolyl group, an indolopyrrolyl group, an indeno carbazolyl group, and an indolocarbazolyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a cyano group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, 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 perylenyl group, a pentacenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, a silolyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an indolyl group, an isoindolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a benzoisoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a benzoquinoxalinyl group, a quinazolinyl group, a benzoquinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzosilolyl group, a benzothiazolyl group, a benzoisothiazolyl group, a benzoxazolyl group, a benzoisoxazolyl group, a triazolyl group, a tetrazolyl group, a thiadiazolyl group, an oxadiazolyl group, a triazinyl group, a carbazolyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a naphthobenzofuranyl group, a naphthobenzothiophenyl group, a naphthobenzosilolyl group, a dibenzocarbazolyl group, a dinaphthofuranyl group, a dinaphthothiophenyl group, a dinaphtho silolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, an oxazolopyridinyl group, a thiazolopyridinyl group, a benzonaphthyridinyl group, an azafluorenyl group, an azaspiro-bifluorenyl group, an azacarbazolyl group, an azadibenzofuranyl group, an azadibenzothiophenyl group, an azadibenzosilolyl group, an indenopyrrolyl group, an indolopyrrolyl group, an indeno carbazolyl group, an indolocarbazolyl group, —C(Q 31 )(Q 32 )(Q 33 ), —Si(Q 31 )(Q 32 )(Q 33 ), —B(Q 31 )(Q 32 ), —N(Q 31 )(Q 32 ), —P(Q 31 )(Q 32 ), —C(═O)(Q 31 ), —S(═O)(Q 31 ), —S(═O) 2 (Q 31 ), —P(═O)(Q 31 )(Q 32 ), and —P(═S)(Q 31 )(Q 32 ); and 
     —C(Q 1 )(Q 2 )(Q 3 ), —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 1 )(Q 2 ), —N(Q 1 )(Q 2 ), —P(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O)(Q 1 ), —S(═O) 2 (Q 1 ), —P(═O)(Q 1 )(Q 2 ), and —P(═S)(Q 1 )(Q 2 ), and 
     Q 1  to Q 3  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 hydrazine group, a hydrazone 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, a C 1 -C 60  alkyl group substituted with at least one selected from deuterium, —F, a cyano group, a C 1 -C 60  alkyl group, a phenyl group, and a biphenyl group, a C 6 -C 60  aryl group substituted with at least one selected from deuterium, —F, a cyano group, a C 1 -C 10  alkyl group, a phenyl group, and a biphenyl group, and a C 1 -C 60  heteroaryl group substituted with at least one selected from deuterium, —F, a cyano group, a C 1 -C 10  alkyl group, a phenyl group, and a biphenyl group, but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, B 11 , B 12 , and R 11  to R 18  in Formula 1-1 may each independently be selected from: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a cyano group, and a C 1 -C 20  alkyl group; 
     a C 1 -C 20  alkyl group substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, and a cyano group; 
     groups represented by Formulae 5-1 to 5-138, and 
     —C(Q 1 )(Q 2 )(Q 3 ), —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 1 )(Q 2 ), —N(Q 1 )(Q 2 ), —P(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O)(Q 1 ), —S(═O) 2 (Q 1 ), —P(═O)(Q 1 )(Q 2 ), and —P(═S)(Q 1 )(Q 2 ), but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, B 11 , B 12 , and R 11  to R 18  in Formula 1-1 may each independently be selected from: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a cyano group, and groups represented by Formulae 9-1 to 9-16; 
     groups represented by Formulae 9-1 to 9-16 each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, and a cyano group; and 
     groups represented by Formulae 6-1 to 6-257, 
     but embodiments of the present disclosure are not limited thereto. 
     In Formula 1-1, b11 to b16 may each independently be an integer from 1 to 10. 
     In Formula 1-1, *1 to *4 each indicate a binding site to M 11 . 
     In Formula 1-1, *5 to *8 each indicate a binding site to M 12 . 
     In Formula 1-1, * and *′ each indicate a binding site to a neighboring atom. 
     In one embodiment, in Formula 1, L 11  may be a ligand represented by Formula 1-11, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     In Formula 1-11, 
     Y 12  to Y 18 , T 1  to T 18 , L 1  to L 14 , a11 to a14, A 11  to A 16 , R 11  to R 18 , b 11  to b16, and *1 to *8 may each independently be the same as defined in Formula 1-1, and 
     a bond between Y 11  and Z 11 , a bond between Y 12  and Z 12 , a bond between Y 12  and Z 13 , a bond between Y 13  and Z 14 , a bond between Y 13  and Y 16 , a bond between Y 14  and Y 15 , a bond between Y 15  and Z 15 , a bond between Z 16  and Y 18 , a bond between Y 18  and Z 17 , and a bond between Y 17  and Z 18  may each independently be a single bond or a double bond. 
     In one embodiment, in Formula 1-11, Z 11  to Z 18  may each independently be N or C, and 
     T 11  to T 18  may each independently be a single bond. 
     In one embodiment, L 12  and L 13  may each independently be a group represented by Formula 10, and L 11  and L 14  may each independently be selected from a single bond, *—O—*′, *—S—*′, *—C(R 17 )(R 18 )—*′, *—C(R 17 )═*′, *═C(R 17 )—*′, *—B(R 17 )—*′, *—N(R 17 )—*′, *—Si(R 17 )(R 18 )—*′, and *—Ge(R 17 )(R 18 )—*′; or 
     L 11  to L 14  may each independently be a group represented by Formula 10, and 
     R 17  and R 18  may each independently be the same as defined in Formula 1-1. 
     In Formula 1, L 12  may be selected from a monodentate ligand and a bidentate ligand. 
     For example, in Formula 1, L 12  may be a ligand represented by one selected from Formulae 7-1 to 7-11, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 7-1 to 7-11, 
     A 71  and A 72  may each independently be selected from a C 5 -C 20  carbocyclic group and a C 1 -C 20  heterocyclic group, 
     X 71  and X 72  may each independently be selected from C and N, 
     X 73  may be N or C(Q 73 ), X 24  may be N or C(Q 74 ), X 75  may be N or C(Q 75 ), X 76  may be N or C(Q 76 , and X 27  may be N or C(Q 77 ), 
     X 78  may be O, S, or N(Q 78 ), and X 29  may be O, S, or N(Q 79 ), 
     Y 71  and Y 72  may each independently be selected from a single bond, a double bond, a substituted or unsubstituted C 1 -C 5  alkylene group, a substituted or unsubstituted C 2 -C 5  alkenylene group, and a substituted or unsubstituted C 6 -C 10  arylene group, 
     Z 71  and Z 72  may each independently be selected from N, O, N(R 75 ), P(R 75 )(R 76 ), and As(R 75 )(R 76 ), 
     Z 73  may be selected from P and As, 
     Z 74  may be selected from CO and CH 2 , 
     R 71  to R 80  and Q 73  to Q 79  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, 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, and a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, wherein R 71  and R 72  may optionally be linked to form a ring, R 77  and R 78  may optionally be linked to form a ring, R 78  and R 79  may optionally be linked to form a ring, and R 79  and R 80  may optionally be linked to form a ring, 
     b71 and b72 may each independently be selected from 1, 2, and 3, and 
     * and *′ each independently indicate a binding site to a neighboring atom. 
     For example, ring A 71  and ring A 72  in Formula 7-1 may each independently be selected from a benzene group, a naphthalene group, an imidazole group, a benzimidazole group, a pyridine group, a pyrimidine group, a triazine group, a quinoline group, and an isoquinoline group, but embodiments of the present disclosure are not limited thereto. 
     For example, X 72  and X 79  in Formula 7-1 may each independently be N, but embodiments of the present disclosure are not limited thereto. 
     For example, in Formula 7-7, X 73  may be C(Q 73 ), X 74  may be C(Q 74 ), X 75  may be C(Q 75 ), X 76  may be C(Q 76 ), and X 77  may be C(Q 77 ), but embodiments of the present disclosure are not limited thereto. 
     For example, in Formula 7-8, X 78  may be N(Q 78 ), and X 79  may be N(Q 79 ), but embodiments of the present disclosure are not limited thereto. 
     For example, Y 71  and Y 72  in Formulae 7-2, 7-3, and 7-8 may each independently be selected from a substituted or unsubstituted methylene group and a substituted or unsubstituted phenylene group, but embodiments of the present disclosure are not limited thereto. 
     For example, Z 71  and Z 72  in Formulae 7-1 and 7-2 may each independently be 0, but embodiments of the present disclosure are not limited thereto. 
     For example, Z 73  in Formula 7—may be P, but embodiments of the present disclosure are not limited thereto. 
     For example, R 71  to R 80  and Q 73  to Q 79  in Formulae 7-1 to 7-8 may each independently be selected from: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, and a C 1 -C 20  alkoxy group; 
     a C 1 -C 20  alkyl group and a C 1 -C 20  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 amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a phenyl group, a naphthyl group, a pyridinyl group, and a pyrimidinyl group; 
     a phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl 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, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, and an imidazopyridinyl group; and 
     a phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl 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, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, and an imidazopyridinyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, —CD 3 , —CD 2 H, —CDH 2 , —CF 3 , —CF 2 H, —CFH 2 , a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl 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, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthrolinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, and an imidazopyridinyl group, 
     but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, L 12  in Formula 1 may be represented by one selected from Formulae 8-1 to 8-11, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     * indicates a binding site to a neighboring atom. 
     In Formula 1, n11 indicates the number of L 11 (s), wherein n11 may be 1. 
     In Formula 1, n12 indicates the number of L 12 (S), wherein n12 may be selected from 0, 1, 2, 3, and 4. When n12 is two or more, a plurality of L 12 (S) may be identical to or different from each other. 
     In one embodiment, in Formula 1, n11 may be 1, and n12 may be 0. 
     In one or more embodiments, in Formula 1, n11 may be 1, and n12 may be 4. 
     In one or more embodiments, in Formula 1, M 11  and M 12  may each independently be selected from Pt and Pd, n11 may be 1, and n12 may be 0. 
     In one embodiment, the organometallic compound represented by Formula 1 may be selected from groups I and II, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In the organometallic compound, since at least one selected from L 11  to L 14  is a group represented by Formula 10, the formation of exciplex with a host may be reduced. In addition, since the organometallic compound essentially includes the group represented by Formula 10, the robustness of the organometallic compound may be improved. Therefore, the stability of the organometallic compound may be improved. Consequently, the efficiency of an electronic device (for example, an organic light-emitting device) including the organometallic compound may be improved. 
     In addition, since the organometallic compound simultaneously includes a ring composed of A 11 , L 11 , A 12 , L 12 , and A 13  and a ring composed of A 14 , L 13 , A 15 , L 14 , and A 16  as a dinuclear complex including M 11  and M 12 , the formation of exciplex with a host may be reduced. Therefore, an organic light-emitting device including the organometallic compound may be improved. 
     The organometallic compound may emit blue light having a maximum emission wavelength of about 430 nm or more to about 470 nm or less. 
     A synthesis method for the organometallic compound represented by Formula 1 would be apparent to those of ordinary skill in the art by referring to the following examples. 
     At least one of the organometallic compound of Formula 1 may be used between a pair of electrodes of an organic light-emitting device. Accordingly, provided is 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 at least one organometallic cyclic compound represented by Formula 1. 
     The expression “(an organic layer) includes at least one organometallic compound” as used herein may include a case in which “(an organic layer) includes the same organometallic compound selected from organometallic compounds represented by Formula 1 and a case in which “(an organic layer) includes two or more different organometallic compounds represented by Formula 1. 
     For example, the organic layer may include, as the organometallic compound, only Compound 1. In this regard, Compound 1 may exist only in the emission layer of the organic light-emitting device. In one or more embodiments, the organic layer may include, as the organometallic compound, Compound 1 and Compound 2. In one or more embodiments, Compound 1 and Compound 2 may both exist in an identical layer (for example, Compound 1 and Compound 2 may both exist in an emission layer), or may exist in different layers (for example, Compound 1 may exist in an emission layer and Compound 2 may exist in an electron transport layer). 
     The organic layer includes i) a hole transport region that is disposed between the first electrode (anode) and the emission layer and includes at least one of a hole injection layer, a hole transport layer, a buffer layer, and an electron blocking layer, and/or ii) an electron transport region that is disposed between the emission layer and the second electrode (cathode) and includes at least one selected from a hole blocking layer, an electron transport layer, and an electron injection layer. The emission layer may include at least one of organometallic compounds represented by Formula 1. 
     In one or more embodiment, at least one selected from the hole transport region and the emission layer may include at least one selected from an arylamine-containing compound, an acridine-containing compound, and a carbazole-containing compound; and/or 
     at least one selected from the emission layer and the electron transport region may include at least one selected from a silicon-containing compound, a phoshine oxide-containing compound, a sulfur oxide-containing compound, a phosphorus oxide-containing compound, a triazine-containing compound, a pyrimidine-containing compound, a pyridine-containing compound, a dibenzofuran-containing compound, and a dibenzothiophene-containing compound. 
     [Description of FIG.  1 ] 
       FIG. 1  is a schematic view of an organic light-emitting device  10  according to an embodiment. 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 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 additionally disposed under the first electrode  110  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 water resistance. 
     The first electrode  110  may be formed by, for example, depositing or sputtering a material for forming the first electrode  110  on the substrate. When the first electrode  110  is an anode, the material for forming the first electrode  110  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, a material for forming a first electrode may be selected from indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO 2 ), zinc oxide (ZnO), and any combinations thereof, but embodiments of the present disclosure are not limited thereto. In one or more embodiments, when the first electrode  110  is a semi-transmissive electrode or a reflective electrode, a material for forming the first electrode  110  may be selected from magnesium (Mg), silver (Ag), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), and any combinations thereof, but embodiments of the present disclosure are not limited thereto. 
     The first electrode  110  may have a single-layered structure including a single layer, 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 the structure of the first electrode  110  is not limited thereto. 
     [Organic Layer  150 ] 
     The organic layer  150  is disposed on the first electrode  110 . The organic layer  150  may include an emission layer. 
     The organic layer  150  may further include a hole transport region between the first electrode  110  and the emission layer, and/or 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, a hole transport layer, an emission auxiliary layer, and an electron blocking layer. 
     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 hole injection layer/hole transport layer structure, a hole injection layer/hole transport layer/emission auxiliary layer structure, a hole injection layer/emission auxiliary layer structure, a hole transport layer/emission auxiliary layer structure, or a hole injection layer/hole transport layer/electron blocking layer structure, wherein for each structure, constituting layers are sequentially stacked from the first electrode  110  in this stated order, but the structure of the hole transport region is not limited thereto. 
     The hole transport region may include at least one selected from m-MTDATA, TDATA, 2-TNATA, NPB (NPD), ρ-NPB, TPD, spiro-TPD, spiro-NPB, methylted-NPB, TAPC, HMTPD, 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA), polyaniline/dodecylbenzenesulfonic acid (PANI/DBSA), poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS), polyaniline/camphor sulfonic acid (PANI/CSA), polyaniline/poly(4-styrenesulfonate) (PANI/PSS), a group represented by Formula 201, and a group 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 from 0 to 3, 
     xa5 may be an integer 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 optionally be linked via a single bond, a dimethyl-methylene group, or a diphenyl-methylene group, and R 203  and R 204  may optionally be linked via a single bond, a dimethyl-methylene group, or a diphenyl-methylene group. 
     In one embodiment, in Formulae 201 and 202, 
     L 201  to L 205  may each independently be selected from: 
     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 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 ), 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, xa1 to xa4 may each independently be 0, 1, or 2. 
     In one or more embodiments, xa5 may be 1, 2, 3, or 4. 
     In one or more embodiments, R 201  to R 204  and Q 201  may each independently be selected from 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 ), and 
     Q 31  to Q 33  are the same as described above. 
     In one or more embodiments, at least one selected from R 201  to R 203  in Formula 201 may each independently be selected from: 
     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 linked via a single bond, and/or ii) R 203  and R 204  may be linked via a single bond. 
     In one or more embodiments, at least one selected from R 201  to R 204  in Formula 202 may each independently be selected from: 
     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 one embodiment, 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 embodiment, 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 embodiment, the compound represented by Formula 202 may be represented by Formula 202A: 
     
       
         
         
             
             
         
       
     
     In one or 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  are the same as described above, 
     R 211  and R 212  may each independently be the same as defined 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 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, and a pyridinyl group. 
     The hole transport region may include at least one compound selected from Compounds HT1 to HT39, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A thickness of the hole transport region may be from about 100 Å to about 10,000 Å, for example, about 100 Å to about 3,000 Å. When the hole transport region includes at least one selected from a hole injection layer and a hole transport layer, a thickness of the hole injection layer may be in a range of about 100 Å to about 9,000 Å, for example, about 100 Å to about 1,000 Å, and a thickness of the hole transport layer may be in a range of about 50 Å to about 2,000 Å, for example about 100 Å to about 1,500 Å. When the thicknesses of the hole transport region, the hole injection layer, and the hole transport layer are within these ranges, satisfactory hole transporting characteristics may be obtained without a substantial increase in driving voltage. 
     The emission auxiliary layer may increase light-emission efficiency by compensating for an optical resonance distance according to the wavelength of light emitted by an emission layer, and the electron blocking layer may block the flow of electrons from an electron transport region. 
     The emission auxiliary layer and the electron blocking layer may include the 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. 
     In one embodiment, the hole transport region may further include a p-dopant having a lowest unoccupied molecular orbital (LUMO) energy level of about −3.5 eV or less. 
     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; 
     a quinone derivative, such as tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ); 
     a metal oxide, such as tungsten oxide or molybdenum oxide; 
     1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN); 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, wherein at least one selected from R 221  to R 223  may have 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, 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 contact each other or are separated from each other. In one or more embodiments, the emission layer may include two or more materials selected from a red light-emitting material, a green light-emitting material, and a blue light-emitting material, in which the two or more materials are mixed with each other in a single layer to emit white light. 
     The emission layer may include a host and a dopant. The dopant may include the organometallic compound represented by Formula 1. In one or more embodiments, the dopant may further include, in addition to the organometallic compound represented by Formula 1, at least one of a phosphorescent dopant and a fluorescent dopant: 
     In the emission layer, an amount of the dopant may be in a range of about 0.01 parts by weight 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. 
     A thickness of the emission layer may be in a range of about 100 A to about 1,000 Å, for example, about 200 Å to about 600 Å. When the thickness of the emission layer is within this range, excellent light-emission characteristics may be obtained without a substantial increase in driving voltage. 
     [Host in Emission Layer] 
     In one or more embodiments, the host may include a compound represented by Formula 301: 
       [Ar 301 ] xb11 -[(L 301 ) xb1 -R 301 ] xb21 .  &lt;Formula 301&gt;
 
     In Formula 301, 
     Ar 301  may be a substituted or unsubstituted C 5 -C 60  carbocyclic group or a substituted or unsubstituted C 1 -C 60  heterocyclic group, 
     xb11 may be 1, 2, or 3, 
     L 301  may 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, 
     xb1 may be an integer from 0 to 5, 
     R 301  may be 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 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 301 )(Q 302 )(Q 303 ), —N(Q 301 )(Q 302 ), —B(Q 301 )(Q 302 ), —C(═O)(Q 301 ), —S(═O) 2 (Q 301 ), and —P(═O)(Q 301 )(Q 302 ), 
     xb21 may be an integer from 1 to 5, and 
     Q 301  to Q 303  may each independently be 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, 
     but embodiments of the present disclosure are not limited thereto. 
     In one embodiment, Ar 301  in Formula 301 may be selected from: 
     a naphthalene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, a dibenzofluorene group, a phenalene group, a phenanthrene group, an anthracene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, a naphthacene group, a picene group, a perylene group, a pentaphene group, an indenoanthracene group, a dibenzofuran group, and a dibenzothiophene group; and 
     a naphthalene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, a dibenzofluorene group, a phenalene group, a phenanthrene group, an anthracene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, a naphthacene group, a picene group, a perylene group, a pentaphene group, an indenoanthracene group, a dibenzofuran group, and a dibenzothiophene 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 phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, —Si(Q 31 )(Q 32 )(Q 33 ), —N(Q 31 )(Q 32 ), —B(Q 31 )(Q 32 ), —C(═O)(Q 31 ), —S(═O) 2 (Q 31 ), and —P(═O)(Q 31 )(Q 32 ), 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, 
     but embodiments of the present disclosure are not limited thereto. 
     When xb11 in Formula 301 is two or more, two or more Ar 301 (s) may be linked via a single bond. 
     In one or more embodiments, the compound represented by Formula 301 may be represented by Formula 301-1 or 301-2: 
     
       
         
         
             
             
         
       
     
     In Formulae 301-1 to 301-2, 
     ring A 301  to ring A 304  may each independently be selected from a benzene group, a naphthalene group, a phenanthrene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, a pyridine group, a pyrimidine group, an indene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, a dibenzofluorene group, an indole group, a carbazole group, a benzocarbazole group, a dibenzocarbazole group, a furan group, a benzofuran group, a dibenzofuran group, a naphthofuran group, a benzonaphthofuran group, a dinaphthofuran group, a thiophene group, a benzothiophene group, a dibenzothiophene group, a naphthothiophene group, a benzonaphthothiophene group, and a dinaphthothiophene group, 
     X 301  may be O, S, or N-[(L 304 ) xb4 -R 304 ], 
     R 311  to R 314  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 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group —Si(Q 31 )(Q 32 )(Q 33 ), —N(Q 31 )(Q 32 ), —B(Q 31 )(Q 32 ), —C(═O)(Q 31 ), —S(═O) 2 (Q 31 ), and —P(═O)(Q 31 )(Q 32 ), 
     xb22 and xb23 may each independently be 0, 1, or 2, 
     L 301 , xb1, R 301 , and Q 31  to Q 33  are the same as described above, 
     L 302  to L 304  may each independently be the same as defined in connection with L 301 , 
     xb2 to xb4 may each independently be the same as defined in connection with xb1, and 
     R 302  to R 304  may each independently be the same as defined in connection with R 301 . 
     For example, L 3o01  to L 304  in Formulae 301, 301-1, and 301-2 may each independently be selected from: 
     a phenylene group, a naphthylene group, a fluorenylene group, a spiro-bifluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a perylenylene group, a pentaphenylene group, a hexacenylene group, a pentacenylene 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, a pyridinylene group, an imidazolylene group, a pyrazolylene group, a thiazolylene group, an isothiazolylene group, an oxazolylene group, an isoxazolylene group, a thiadiazolylene group, an oxadiazolylene group, a pyrazinylene group, a pyrimidinylene group, a pyridazinylene group, a triazinylene group, a quinolinylene group, an isoquinolinylene group, a benzoquinolinylene group, a phthalazinylene group, a naphthyridinylene group, a quinoxalinylene group, a quinazolinylene group, a cinnolinylene group, a phenanthridinylene group, an acridinylene group, a phenanthrolinylene group, a phenazinylene group, a benzimidazolylene group, an isobenzothiazolylene group, a benzoxazolylene group, an isobenzoxazolylene group, a triazolylene group, a tetrazolylene group, an imidazopyridinylene group, an imidazopyrimidinylene group, and an azacarbazolylene group; and 
     a phenylene group, a naphthylene group, a fluorenylene group, a spiro-bifluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a perylenylene group, a pentaphenylene group, a hexacenylene group, a pentacenylene 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, a pyridinylene group, an imidazolylene group, a pyrazolylene group, a thiazolylene group, an isothiazolylene group, an oxazolylene group, an isoxazolylene group, a thiadiazolylene group, an oxadiazolylene group, a pyrazinylene group, a pyrimidinylene group, a pyridazinylene group, a triazinylene group, a quinolinylene group, an isoquinolinylene group, a benzoquinolinylene group, a phthalazinylene group, a naphthyridinylene group, a quinoxalinylene group, a quinazolinylene group, a cinnolinylene group, a phenanthridinylene group, an acridinylene group, a phenanthrolinylene group, a phenazinylene group, a benzimidazolylene group, an isobenzothiazolylene group, a benzoxazolylene group, an isobenzoxazolylene group, a triazolylene group, a tetrazolylene group, an imidazopyridinylene group, an imidazopyrimidinylene group, and an azacarbazolylene 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 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 fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl 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, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a thiadiazolyl group, an oxadiazolyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, an azacarbazolyl group, —Si(Q 31 )(Q 32 )(Q 33 ), —N(Q 31 )(Q 32 ), —B(Q 31 )(Q 32 ), —C(═O)(Q 31 ), —S(═O) 2 (Q 31 ), and —P(═O)(Q 31 )(Q 32 ), and 
     Q 31  to Q 33  are the same as described above. 
     In one embodiment, R 301  to R 304  in Formulae 301, 301-1, and 301-2 may each independently be selected from: 
     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 fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl 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, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a thiadiazolyl group, an oxadiazolyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, and an azacarbazolyl group; and 
     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 fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl 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, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a thiadiazolyl group, an oxadiazolyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, and an azacarbazolyl group, each substituted with at least one selected 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 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 fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl 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, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a thiadiazolyl group, an oxadiazolyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, an azacarbazolyl group, —Si(Q 31 )(Q 32 )(Q 33 ), —N(Q 31 )(Q 32 ), —B(Q 31 )(Q 32 ), —C(═O)(Q 31 ), —S(═O) 2 (Q 31 ), and —P(═O)(Q 31 )(Q 32 ), and 
     Q 31  to Q 33  are the same as described above. 
     In one or more embodiments, the host may include an alkaline earth metal complex. For example, the host may be selected from a Be complex (for example, Compound H55), a Mg complex, and a Zn complex. 
     The host may include at least one selected from 9,10-di(2-naphthyl)anthracene) (ADN), 2-methyl-9,10-bis(naphthalen-2-yl)anthracene (MADN), 9,10-di-(2-naphthyl)-2-t-butyl-anthracene (TBADN), 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP), 1,3-di-9-carbazolylbenzene (mCP), 1,3,5-tri(carbazol-9-yl)benzene (TCP), bis(4-(9H-carbazol-9-yl)phenyl)diphenylsilane (BCPDS), (4-(1-(4-(diphenylamino)phenyl)cyclohexyl)phenyl)diphenyl-phosphine oxide (POPCPA), and Compounds H1 to H55, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In one embodiment, the host may include at least one selected from a silicon-containing compound (for example, BCPDS used in the following examples or the like) and a phosphine oxide-containing compound (for example, POPCPA used in the following examples or the like). 
     However, embodiments of the present disclosure are not limited thereto. In one embodiment, the host may include only one compound, or two or more different compounds (for example, a host used in the following examples includes BCPDS and POPCPA). 
     [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 a buffer layer, a hole blocking layer, an electron control layer, an electron transport layer, and an electron injection layer, but embodiments of the present disclosure are not limited thereto. 
     For example, the electron transport region may have an electron transport layer/electron injection layer structure, a hole blocking layer/electron transport layer/electron injection layer structure, an electron control layer/electron transport layer/electron injection layer structure, or a buffer layer/electron transport layer/electron injection layer structure, wherein for each structure, constituting layers are sequentially stacked from an emission layer. However, embodiments of the structure of the electron transport region are not limited thereto. 
     The hole transport region may include the second compound as described above. 
     In one embodiment, the hole transport region may include a buffer layer. The buffer layer may directly contact the emission layer, and may include the second compound. 
     In one or more embodiments, the electron transport region may include a buffer layer, an electron transport layer, and an electron injection layer, which are stacked in this stated order on the emission layer, and the buffer layer may include the second compound as described above. 
     The electron transport region (for example, a buffer layer, a hole blocking layer, an electron control layer, or an electron transport layer in the electron transport region) may include a metal-free compound containing at least one π electron-depleted nitrogen-containing ring. 
     The “π electron-depleted nitrogen-containing ring” indicates a C 1 -C 60  heterocyclic group having at least one *—N═*′ moiety as a ring-forming moiety. 
     For example, the “π electron-depleted nitrogen-containing ring” may be i) a 5-membered to 7-membered heteromonocyclic group having at least one *—N=*′ moiety, ii) a heteropolycyclic group in which two or more 5-membered to 7-membered heteromonocyclic groups each having at least one *—N=*′ moiety are condensed with each other, or iii) a heteropolycyclic group in which at least one of 5-membered to 7-membered heteromonocyclic groups, each having at least one *—N=*′ moiety, is condensed with at least one C 5 -C 60  carbocyclic group. 
     Examples of the π electron-depleted nitrogen-containing ring include an imidazole, a pyrazole, a thiazole, an isothiazole, an oxazole, an isoxazole, a pyridine, a pyrazine, a pyrimidine, a pyridazine, an indazole, a purine, a quinoline, an isoquinoline, a benzoquinoline, a phthalazine, a naphthyridine, a quinoxaline, a quinazoline, a cinnoline, a phenanthridine, an acridine, a phenanthroline, a phenazine, a benzimidazole, an isobenzothiazole, a benzoxazole, an isobenzoxazole, a triazole, a tetrazole, an oxadiazole, a triazine, a thiadiazol, an imidazopyridine, an imidazopyrimidine, and an azacarbazole, but are not limited thereto. 
     For example, the electron transport region may include a compound represented by Formula 601: 
       [Ar 601 ] xe11 -[(L 601 ) xe1 -R 601 ] xe21    
     In Formula 601, 
     Ar 601  may be a substituted or unsubstituted C 5 -C 60  carbocyclic group or a substituted or unsubstituted C 1 -C 60  heterocyclic group, 
     xe11 may be 1, 2, or 3, 
     L 601  may 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, 
     xe1 may be an integer from 0 to 5, 
     R 601  may 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, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 601 )(Q 602 )(Q 603 ), —C(═O)(Q 601 ), —S(═O) 2 (Q 601 ), and —P(═O)(Q 601 )(Q 602 ), 
     Q 601  to Q 603  may each independently be a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, or a naphthyl group, and 
     xe21 may be an integer from 1 to 5. 
     In one embodiment, at least one of Ar 601 (s) in the number of xe11 and R 601 (s) in the number of xe21 may include the π electron-depleted nitrogen-containing ring. 
     In one embodiment, Ar 601  in Formula 601 may be selected from: 
     a benzene group, a naphthalene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, a dibenzofluorene group, a phenalene group, a phenanthrene group, an anthracene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, a naphthacene group, a picene group, a perylene group, a pentaphene group, an indenoanthracene group, a dibenzofuran group, a dibenzothiophene group, a carbazole group, an imidazole group, a pyrazole group, a thiazole group, an isothiazole group, an oxazole group, an isoxazole group, a pyridine group, a pyrazine group, a pyrimidine group, a pyridazine group, an indazole group, a purine group, a quinoline group, an isoquinoline group, a benzoquinoline group, a phthalazine group, a naphthyridine group, a quinoxaline group, a quinazoline group, a cinnoline group, a phenanthridine group, an acridine group, a phenanthroline group, a phenazine group, a benzimidazole group, an isobenzothiazole group, a benzoxazole group, an isobenzoxazole group, a triazole group, a tetrazole group, an oxadiazole group, a triazine group, a thiadiazole group, an imidazopyridine group, an imidazopyrimidine group, and an azacarbazole group; and 
     a benzene group, a naphthalene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, a dibenzofluorene group, a phenalene group, a phenanthrene group, an anthracene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, a naphthacene group, a picene group, a perylene group, a pentaphene group, an indenoanthracene group, a dibenzofuran group, a dibenzothiophene group, a carbazole group, an imidazole group, a pyrazole group, a thiazole group, an isothiazole group, an oxazole group, an isoxazole group, a pyridine group, a pyrazine group, a pyrimidine group, a pyridazine group, an indazole group, a purine group, a quinoline group, an isoquinoline group, a benzoquinoline group, a phthalazine group, a naphthyridine group, a quinoxaline group, a quinazoline group, a cinnoline group, a phenanthridine group, an acridine group, a phenanthroline group, a phenazine group, a benzimidazole group, an isobenzothiazole group, a benzoxazole group, an isobenzoxazole group, a triazole group, a tetrazole group, an oxadiazole group, a triazine group, a thiadiazole group, an imidazopyridine group, an imidazopyrimidine group, and an azacarbazole 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 phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, —Si(Q 31 )(Q 32 )(Q 33 ), —S(═O) 2 (Q 31 ), and —P(═O)(Q 31 )(Q 32 ), 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. 
     When xe11 in Formula 601 is two or more, two or more Ar 601 (s) may be linked via a single bond. 
     In one or more embodiments, Ar 601  in Formula 601 may be an anthracene group. 
     In one or more embodiments, the compound represented by Formula 601 may be represented by Formula 601-1: 
     
       
         
         
             
             
         
       
     
     In Formula 601-1, 
     X 614  may be N or C(R 614 ), X 615  may be N or C(R 615 ), and X 616  may be N or C(R 616 ), wherein at least one selected from X 614  to X 616  may each independently be N, 
     L 611  to L 613  may each independently be the same as defined in connection with L 601 , 
     xe611 to xe613 may each independently be the same as defined in connection with xe1, 
     R 611  to R 613  may each independently be the same as defined in connection with R 601 , and 
     R 614  to R 616  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 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group. 
     In one embodiment, L 601  and L 611  to L 613  in Formulae 601 and 601-1 may each independently be selected from: 
     a phenylene group, a naphthylene group, a fluorenylene group, a spiro-bifluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a perylenylene group, a pentaphenylene group, a hexacenylene group, a pentacenylene 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, a pyridinylene group, an imidazolylene group, a pyrazolylene group, a thiazolylene group, an isothiazolylene group, an oxazolylene group, an isoxazolylene group, a thiadiazolylene group, an oxadiazolylene group, a pyrazinylene group, a pyrimidinylene group, a pyridazinylene group, a triazinylene group, a quinolinylene group, an isoquinolinylene group, a benzoquinolinylene group, a phthalazinylene group, a naphthyridinylene group, a quinoxalinylene group, a quinazolinylene group, a cinnolinylene group, a phenanthridinylene group, an acridinylene group, a phenanthrolinylene group, a phenazinylene group, a benzimidazolylene group, an isobenzothiazolylene group, a benzoxazolylene group, an isobenzoxazolylene group, a triazolylene group, a tetrazolylene group, an imidazopyridinylene group, an imidazopyrimidinylene group, and an azacarbazolylene group; and 
     a phenylene group, a naphthylene group, a fluorenylene group, a spiro-bifluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a perylenylene group, a pentaphenylene group, a hexacenylene group, a pentacenylene 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, a pyridinylene group, an imidazolylene group, a pyrazolylene group, a thiazolylene group, an isothiazolylene group, an oxazolylene group, an isoxazolylene group, a thiadiazolylene group, an oxadiazolylene group, a pyrazinylene group, a pyrimidinylene group, a pyridazinylene group, a triazinylene group, a quinolinylene group, an isoquinolinylene group, a benzoquinolinylene group, a phthalazinylene group, a naphthyridinylene group, a quinoxalinylene group, a quinazolinylene group, a cinnolinylene group, a phenanthridinylene group, an acridinylene group, a phenanthrolinylene group, a phenazinylene group, a benzimidazolylene group, an isobenzothiazolylene group, a benzoxazolylene group, an isobenzoxazolylene group, a triazolylene group, a tetrazolylene group, an imidazopyridinylene group, an imidazopyrimidinylene group, and an azacarbazolylene 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 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 fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl 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, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a thiadiazolyl group, an oxadiazolyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, and an azacarbazolyl group, 
     but embodiments of the present disclosure are not limited thereto. 
     In one or more embodiments, xe1 and xe611 to xe613 in Formulae 601 and 601-1 may each independently be 0, 1, or 2. 
     In one or more embodiments, R 601  and R 611  to R 613  in Formulae 601 and 601-1 may each independently be selected from: 
     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 fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl 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, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a thiadiazolyl group, an oxadiazolyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, and an azacarbazolyl 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 fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl 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, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a thiadiazolyl group, an oxadiazolyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, and an azacarbazolyl 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 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 fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl 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, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a thiadiazolyl group, an oxadiazolyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, and an azacarbazolyl group; and 
     —S(═O) 2 (Q 601 ) and —P(═O)(Q 601 )(Q 602 ), and 
     Q 601  and Q 602  are the same as described above. 
     The electron transport region may include at least one compound selected from Compounds ET1 to ET36, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In one or more embodiments, the electron transport region may include at least one selected from 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), 4,7-dphenyl-1,10-phenanthroline (Bphen), Alq 3 , BAlq, 3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole (TAZ), NTAZ, diphenyl(4-(triphenylsilyl)phenyl)-phosphine oxide (TSPO1), and 3P-T 2 T: 
     
       
         
         
             
             
         
       
     
     A thickness of the buffer layer, the hole blocking layer, or the electron control layer may be in a range of about 20 Å to about 1000 Å, for example, about 30 Å to about 300 Å. When the thicknesses of the buffer layer, the hole blocking layer, and the electron control layer are within these ranges, excellent electron blocking characteristics or electron control characteristics may be obtained without a substantial increase in driving voltage. 
     A thickness of the electron transport layer may be from about 100 Å to about 1,000 Å, for example, about 150 Å to about 500 Å. When the thickness of the electron transport layer is within the range described above, satisfactory electron transport characteristics may be obtained without a substantial increase in driving voltage. 
     The electron transport region (for example, the electron transport layer in the electron transport region) may further include, in addition to the materials described above, a metal-containing material. 
     The metal-containing material may include at least one selected from alkali metal complex and alkaline earth-metal complex. The alkali metal complex may include a metal ion selected from a Li ion, a Na ion, a K ion, a Rb ion, and a Cs ion, and the alkaline earth-metal complex may include a metal ion selected from a Be ion, a Mg ion, a Ca ion, a Sr ion, and a Ba ion. A ligand coordinated with the metal ion of the alkali metal complex or the alkaline earth-metal complex may be selected from a hydroxy quinoline, a hydroxy isoquinoline, a hydroxy benzoquinoline, a hydroxy acridine, a hydroxy phenanthridine, a hydroxy phenyloxazole, a hydroxy phenylthiazole, a hydroxy diphenyloxadiazole, a hydroxy diphenylthiadiazol, a hydroxy phenylpyridine, a hydroxy phenylbenzimidazole, a hydroxy phenylbenzothiazole, 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) or ET-D2: 
     
       
         
         
             
             
         
       
     
     The electron transport region may include an electron injection layer that facilitates electron injection 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 an alkali metal, an alkaline earth metal, a rare earth metal, an alkali metal compound, an alkaline earth-metal compound, a rare earth metal compound, an alkali metal complex, an alkaline earth-metal complex, a rare earth metal complex, or any combinations thereof. 
     The alkali metal may be selected from Li, Na, K, Rb, and Cs. In one embodiment, the alkali metal may be Li, Na, or Cs. In one or more embodiments, the alkali metal may be Li or Cs, but embodiments of the present disclosure are not limited thereto. 
     The alkaline earth metal may be selected from Mg, Ca, Sr, and Ba. 
     The rare earth metal may be selected from Sc, Y, Ce, Tb, Yb, and Gd. 
     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, or iodides) of the alkali metal, the alkaline earth-metal, and the rare earth metal. 
     The alkali metal compound may be selected from alkali metal oxides, such as Li 2 O, Cs 2 O, or K 2 O, and alkali metal halides, such as LiF, NaF, CsF, KF, LiI, NaI, CsI, KI, or RbI. 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 oxides, such as BaO, SrO, CaO, Ba x Sr 1-x O (0&lt;x&lt;1), 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 include an ion of alkali metal, alkaline earth-metal, and rare earth metal as described above, and a ligand coordinated with a metal ion of the alkali metal complex, the alkaline earth-metal complex, or the rare earth metal complex may be selected from hydroxy quinoline, hydroxy isoquinoline, hydroxy benzoquinoline, hydroxy acridine, hydroxy phenanthridine, hydroxy phenyloxazole, hydroxy phenylthiazole, hydroxy diphenyloxadiazole, hydroxy diphenylthiadiazol, hydroxy phenylpyridine, hydroxy phenylbenzimidazole, hydroxy phenylbenzothiazole, bipyridine, phenanthroline, and cyclopentadiene, but embodiments of the present disclosure are not limited thereto. 
     The electron injection layer may consist of an alkali metal, an alkaline earth metal, a rare earth metal, an alkali metal compound, an alkaline earth-metal compound, a rare earth metal compound, an alkali metal complex, an alkaline earth-metal complex, a rare earth metal complex, or any combinations thereof, as described above. In one or more embodiments, the electron injection layer may further include an organic material. When the electron injection layer further includes an organic material, an alkali metal, an alkaline earth metal, a rare earth metal, an alkali metal compound, an alkaline earth-metal compound, a rare earth metal compound, an alkali metal complex, an alkaline earth-metal complex, a rare earth metal complex, or any combinations thereof may be homogeneously or non-homogeneously dispersed in a matrix including the organic material. 
     A thickness of the electron injection layer may be in a range of about 1 Å to about 100 Å, for example, about 3 Å to about 90 Å. When a thickness of the electron injection layer is within these ranges, satisfactory electron injection characteristics may be obtained without substantial increase in driving voltage. 
     [Second Electrode  190 ] 
     The second electrode  190  is disposed on the organic layer  150  having such a structure. The second electrode  190  may be a cathode which is an electron injection electrode, and in this regard, a material for forming the second electrode  190  may be selected from metal, an alloy, an electrically conductive compound, and a combination thereof, which have a relatively low work function. 
     The second electrode  190  may include at least one selected from lithium (Li), silver (Ag), 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 first electrode  190  may be a transmissive electrode, a semi-transmissive electrode, or a reflective electrode. 
     The first electrode  190  may have a single-layered structure including a single layer, or a multi-layered structure including two or more layers. 
     [Description of FIGS.  2  to  4 ] 
       FIG. 2  is a schematic view of an organic light-emitting device  20  according to an embodiment. The organic light-emitting device  20  includes a first capping layer  210 , the first electrode  110 , the organic layer  150 , and the second electrode  190 , which are sequentially stacked in this stated order.  FIG. 3  is a schematic view of an organic light-emitting device  30  according to an embodiment. The organic light-emitting device  30  includes the first electrode  110 , the organic layer  150 , the second electrode  190 , and a second capping layer  220 , which are sequentially stacked in this stated order.  FIG. 4  is a schematic view of an organic light-emitting device  40  according to an embodiment. The organic light-emitting device  40  includes the first capping layer  210 , the first electrode  110 , the organic layer  150 , the second electrode  190 , and the second capping layer  220 , which are sequentially stacked in this stated order. 
     Regarding  FIGS. 2 to 4 , the first electrode  110 , the organic layer  150 , and the second electrode  190  may be understood by referring to the description presented 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  and the first capping layer  210  toward the outside, wherein the first electrode  110  may be a semi-transmissive electrode or a transmissive electrode. 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  and the second capping layer  220  toward the outside, wherein the second electrode  190  may be a semi-transmissive electrode or a transmissive electrode. 
     The first capping layer  210  and the second capping layer  220  may increase 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 an organic 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 each independently include at least one material selected from carbocyclic compounds, heterocyclic compounds, amine-based compounds, porphyrine derivatives, phthalocyanine derivatives, a naphthalocyanine derivatives, alkali metal complexes, and alkaline earth-based complexes. The carbocyclic compound, the heterocyclic compound, and the amine-based compound may be optionally substituted with a substituent containing at least one element selected from O, N, S, Se, Si, F, Cl, Br, and I. In one embodiment, at least one selected from the first capping layer  210  and the second capping layer  220  may each independently 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 each independently include the compound represented by Formula 201 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 each independently 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 has been described in connection with  FIGS. 1 to 4 , but embodiments of the present disclosure are not limited thereto. 
     Layers constituting the hole transport region, an emission layer, and layers constituting the electron transport region may be formed in a certain region by using one or more suitable methods selected from vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) deposition, ink-jet printing, laser-printing, and laser-induced thermal imaging. 
     When layers constituting the hole transport region, an emission layer, and layers constituting the electron transport region are formed by vacuum deposition, the deposition may be performed at a deposition temperature of about 100° C. to about 500° C., a vacuum degree of about 10 −8  torr to about 10 −3  torr, and a deposition speed of about 0.01 Å/sec to about 100 Å/sec by taking into account a material to be included in a layer to be formed, and the structure of a layer to be formed. 
     When layers constituting the hole transport region, an emission layer, and layers constituting the electron transport region are formed by spin coating, the spin coating may be performed at a coating speed of about 2,000 rpm to about 5,000 rpm and at a heat treatment temperature of about 80° C. to 200° C. by taking into account a material to be included in a layer to be formed, and the structure of a layer to be formed. 
     [Apparatus] 
     The organic light-emitting device may be included in various apparatuses. 
     For example, the apparatus may include a thin-film transistor including a source electrode, a drain electrode, and an active layer, and the organic light-emitting device. One of the first electrode and the second electrode of the light-emitting device may be electrically connected to one of the source electrode and the drain electrode of the thin-film transistor. 
     The thin-film transistor may further include a gate electrode, a gate insulation layer, or the like. 
     The active layer may include crystalline silicon, amorphous silicon, organic semiconductor, oxide semiconductor, or the like, but embodiments of the present disclosure are not limited thereto. 
     The apparatus may further include a sealing part that seals the light-emitting device. The sealing part may implement an image from the light-emitting device, and prevent external air and moisture from penetrating into the organic light-emitting device. The sealing part may be a sealing substrate including a transparent glass or a plastic substrate. The sealing part may be a thin-film encapsulation layer including a plurality of organic layers and/or a plurality of inorganic layers. When the sealing part is a thin-film encapsulation layer, the entire apparatus may be made flexible. 
     For example, the apparatus may be a light-emitting apparatus, an authentication apparatus, or an electronic apparatus. 
     The light-emitting apparatus may be used as various displays, light sources, and the like. 
     The authentication apparatus may be, for example, a biometric authentication apparatus for authenticating an individual by using biometric information of a biometric body (for example, a finger tip, a pupil, or the like). The authentication apparatus may further include, in addition to the organic light-emitting device, a biometric information collector. 
     The electronic apparatus may be applied to personal computers (for example, a mobile personal computer), mobile phones, digital cameras, electronic organizers, electronic dictionaries, electronic game machines, medical instruments (for example, electronic thermometers, sphygmomanometers, blood glucose meters, pulse measurement devices, pulse wave measurement devices, electrocardiogram (ECG) displays, ultrasonic diagnostic devices, or endoscope displays), fish finders, various measuring instruments, meters (for example, meters for a vehicle, an aircraft, and a vessel), projectors, and the like, but embodiments of the present disclosure are not limited thereto. 
     [General Definition of Substituents] 
     The term “Period 1 transition metal” as used herein refers to an element which belongs to Period 4 of the Periodic Table of the Elements and is included in the d-block, and examples thereof are scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), and zinc (Zn). 
     The term “Period 2 transition metal” as used herein refers to an element which belongs to Period 5 of the Periodic Table of the Elements and is included in the d-block, and examples thereof are yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), and cadmium (Cd). 
     The term “Period 3 transition metal” as used herein refers to an element which belongs to Period 6 of the Periodic Table of the Elements and is included in the d-block and the f-block, and examples thereof are lanthanum (La), samarium (Sm), europium (Eu), terbium (Tb), thulium (Tm), ytterbium (Yb), lutetium (Lu), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pr), gold (Au), and mercury (Hg). 
     The term “C 1 -C 60  alkyl group” as used herein refers to a linear or branched aliphatic saturated hydrocarbon monovalent group having 1 to 60 carbon atoms, and examples thereof 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 isoamyl group, and a hexyl group. The term “C 1 -C 60  alkylene group” as used herein refers to a divalent group having the same structure as the C 1 -C 60  alkyl group. 
     The term “C 2 -C 60  alkenyl group” as used herein refers to a hydrocarbon group having at least one carbon-carbon double bond in the middle or at the terminus of the C 2 -C 60  alkyl group, and examples thereof include an ethenyl group, a propenyl group, and a butenyl group. The term “C 2 -C 60  alkenylene group” as used herein refers to a divalent group having the same structure as the C 2 -C 60  alkenyl group. 
     The term “C 2 -C 60  alkynyl group” as used herein refers to a hydrocarbon group having at least one carbon-carbon triple bond in the middle or at the terminus of the C 2 -C 60  alkyl group, and examples thereof include an ethynyl group, and a propynyl group. The term “C 2 -C 60  alkynylene group” as used herein refers to a divalent group having the same structure as the C 2 -C 60  alkynyl group. 
     The term “C 1 -C 60  alkoxy group” as used herein refers to a monovalent group represented by —OA 101  (wherein A 101  is the C 1 -C 60  alkyl group), and examples thereof include a methoxy group, an ethoxy group, and an isopropyloxy group. 
     The term “C 3 -C 10  cycloalkyl group” as used herein refers to a monovalent saturated hydrocarbon monocyclic group having 3 to 10 carbon atoms, and examples thereof 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 the same structure as the C 3 -C 10  cycloalkyl group. 
     The term “C 1 -C 10  heterocycloalkyl group” as used herein refers to a monovalent monocyclic group having at least one heteroatom selected from N, O, Si, P, and S as a ring-forming atom and 1 to 10 carbon atoms, and examples thereof include a 1,2,3,4-oxatriazolidinyl group, a tetrahydrofuranyl group, and a tetrahydrothiophenyl group. The term “C 1 -C 10  heterocycloalkylene group” as used herein refers to a divalent group having the same structure as the C 1 -C 10  heterocycloalkyl group. 
     The term C 3 -C 10  cycloalkenyl group used herein refers to a monovalent monocyclic group that has 3 to 10 carbon atoms and at least one carbon-carbon double bond in the ring thereof and no aromaticity, and examples thereof include a cyclopentenyl group, a cyclohexenyl group, and a cycloheptenyl group. The term “C 3 -C 10  cycloalkenylene group” as used herein refers to a divalent group having the same structure as the C 3 -C 10  cycloalkenyl group. 
     The term “C 1 -C 10  heterocycloalkenyl group” as used herein refers to a monovalent 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 carbon-carbon double bond in its ring. Non-limiting examples of the C 1 -C 10  heterocycloalkenyl group include a 4,5-dihydro-1,2,3,4-oxatriazolyl group, a 2,3-dihydrofuranyl group, and a 2,3-dihydrothiophenyl group. The term “C 1 -C 10  heterocycloalkenylene group” as used herein refers to a divalent group having the same structure as the C 1 -C 10  heterocycloalkenyl group. 
     The term “C 6 -C 60  aryl group” as used herein refers to a monovalent group having a carbocyclic aromatic system having 6 to 60 carbon atoms, and a C 6 -C 60  arylene group 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 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 to each other. The term “C 7 -C 60  alkyl heteroaryl group” as used herein refers to a C 1 -C 60  heteroaryl group substituted with at least one C 1 -C 60  alkyl group. 
     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, in addition to 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, in addition to 1 to 60 carbon atoms. Non-limiting examples of the C 1 -C 60  heteroaryl group 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 condensed with each other. The term “C 2 -C 60  alkyl heteroaryl group” as used herein refers to a C 1 -C 60  heteroaryl group substituted with at least one C 1 -C 60  alkyl group. 
     The term “C 6 -C 60  aryloxy group” as used herein refers to —OA 102  (wherein A 102  is the C 6 -C 60  aryl group), and a C 6 -C 60  arylthio group used herein indicates —SA 103  (wherein A 103  is the C 6 -C 60  aryl group). 
     The term “C 1 -C 60  heteroaryloxy group” as used herein refers to —OA 104  (wherein A 104  is the C 1 -C 60  heteroaryl group), and the term “C 1 -C 60  heteroarylthio group” as used herein refers to —SA 105  (wherein A 105  is the C 1 -C 60  heteroaryl group). 
     The term “monovalent non-aromatic condensed polycyclic group” as used herein refers to a monovalent group (for example, having 8 to 60 carbon atoms) having two or more rings condensed with each other, only carbon atoms as ring-forming atoms, and no aromaticity in its entire molecular structure. A detailed example of the monovalent non-aromatic condensed polycyclic group is a fluorenyl group. The term “divalent non-aromatic condensed polycyclic group” as used herein refers to a divalent group having 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 (for example, having 1 to 60 carbon atoms) having two or more rings condensed to each other, at least one heteroatom selected from N, O, Si, P, and S, other than carbon atoms, as a ring-forming atom, and no aromaticity in its entire molecular structure. An example of the monovalent non-aromatic condensed heteropolycyclic group is a carbazolyl group. The term “divalent non-aromatic condensed heteropolycyclic group” as used herein refers to a divalent group having 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. The term “C 5 -C 60  carbocyclic group” as used herein refers to an aromatic carbocyclic group or a non-aromatic carbocyclic group. The C 5 -C 60  carbocyclic group may be a ring, such as 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 the same structure as the C 5 -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 in a range of 1 to 60). 
     In the present specification, at least one substituent of the substituted C 5 -C 60  carbocyclic group, the substituted C 1 -C 60  heterocyclic group, 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 7 -C 60  alkylaryl 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 C 2 -C 60  alkyl heteroaryl group, the substituted C 1 -C 60  heteroaryloxy group, the substituted C 1 -C 60  heteroarylthio group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group may be 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, 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 7 -C 60  alkylaryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio 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 7 -C 60  alkylaryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio 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 7 -C 60  alkylaryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio 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 7 -C 60  alkylaryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio 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 ), and 
     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 7 -C 60  alkylaryl group, a C 1 -C 60  heteroaryl group, a C 2 -C 60  alkyl heteroaryl group, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, a C 1 -C 60  alkyl group substituted with at least one selected from deuterium, —F, and a cyano group, a C 6 -C 60  aryl group substituted with at least one selected from deuterium, —F, and a cyano group, a biphenyl group, and a terphenyl group. 
     The term “Ph” as used herein refers to a phenyl group, the term “Me” as used herein refers to a methyl group, the term “Et” as used herein refers to an ethyl group, the term “ter-Bu” or “Bu t ” as used herein refers to a tert-butyl group, and the term “OMe” as used herein refers to a methoxy group. 
     The term “biphenyl group” as used herein refers to “a phenyl group substituted with a phenyl group.” In other words, the “biphenyl group” is a substituted phenyl group having a C 6 -C 60  aryl group as a substituent. 
     The term “terphenyl group” as used herein refers to “a phenyl group substituted with a biphenyl group.” In other words, the “terphenyl group” is a phenyl group having, as a substituent, a C 6 -C 60  aryl group substituted with a C 6 -C 60  aryl group. 
     * and *′ used herein, unless defined otherwise, each refer to a binding site to a neighboring atom in a corresponding formula. 
     Hereinafter, a compound according to embodiments and an organic light-emitting device according to embodiments will be described in detail with reference to Synthesis Examples and Examples. The wording “B was used instead of A” used in describing Synthesis Examples refers to that an identical molar equivalent of B was used in place of A. 
     EXAMPLE 
     Synthesis Example 1: Synthesis of Compound BD1 
     Compound BD1 was synthesized with reference to the Scheme 1. 
     
       
         
         
             
             
         
       
     
     (1) Synthesis of Intermediate 1-1 
     Compound 1 reacted with nBuLi and then reacted with 3-bromobenzaldehyde to synthesize Intermediate 1-1. Intermediate 1-1 was identified by LC-MS. 
     C 19 H 15 BrO: M+1 340.15. 
     (2) Synthesis of Intermediate 1-2 
     Intermediate 1-1 reacted with pyridinium chlorochromate (cas: 26299-14-9) at room temperature under a dichloromethane solvent to synthesize Intermediate 1-2. Intermediate 1-2 was identified by LC-MS. 
     C 19 H 13 BrO: M+1 337.13. 
     (3) Synthesis of Intermediate 1-3 
     3-bromopyrazole (cas: 14521-80-3) was activated with magnesium under an iodine catalyst and then reacted with Intermediate 1-2 to obtain Intermediate 1-3. Intermediate 1-3 was identified by LC-MS. 
     C 22 H 17 BrN2O: M+1 146.88. 
     (4) Synthesis of Intermediate 1-4 
     Intermediate 1-3 and hydrochloride (cas: 7647-01-0) reacted with each other under an AcOH solvent to obtain Intermediate 1-4. Intermediate 1-4 was identified by LC-MS. 
     C 22 H 15 BrN2: M+1 387.28. 
     (5) Synthesis of Intermediate 1-5 
     CuI, imidazole, K 2 CO 3 , and L-proline reacted with Intermediate 1-4 at a temperature of 160° C. under a DMSO solvent to synthesize Intermediate 1-5. Intermediate 1-5 was identified by LC-MS. 
     C 25 H 18 N 4 : M+1 374.48. 
     (6) Synthesis of Intermediate 1-6 
     Intermediate 1-5 and iodide methane (cas: 74-88-4) reacted with each other under an acetone solvent to synthesize Intermediate 1-6. Intermediate 1-6 was identified by LC-MS. 
     C 26 H 21 N 4 : M+1 389.49. 
     (7) Synthesis of Compound BD1 
     Intermediate 1-6, dichloro(1,5-cyclooctadiene)platinum(II), and sodium acetate reacted with each other at a temperature of 160° C. under a 1,4-dioxane solvent to synthesize Compound BD1. Compound BD1 was identified by LC-MS. 
     C 52 H 36 N 8 Pt 2 : M+1 1163.08. 
     Synthesis Example 2: Synthesis of Compound BD2 
     Compound BD2 was synthesized with reference to the Scheme II and Synthesis Example 1. 
     
       
         
         
             
             
         
       
     
     Compound BD2 was identified by LC-MS. 
     C 56 H 44 N 8 Pt 2 : M+1 1219.08. 
     Synthesis Example 3: Synthesis of Compound BD3 
     Compound BD3 was synthesized with reference to the Scheme III and Synthesis Example 1. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Compound BD3 was identified by LC-MS. 
     C 60 H 40 N 8 Pt 2 : M+1 1263.20. 
     Synthesis Example 4: Synthesis of Compound BD4 
     Compound BD4 was synthesized with reference to the Scheme IV and Synthesis Example 1. 
     
       
         
         
             
             
         
       
     
     Compound BD4 was identified by LC-MS. 
     C 58 H 38 N 10 Pt 2 : M+1 1265.19. 
     Synthesis Example 5: Synthesis of Compound BD5 
     Compound BD5 was synthesized with reference to the Scheme V and Synthesis Example 1. 
     
       
         
         
             
             
         
       
     
     Compound BD5 was identified by LC-MS. 
     C 56 H 36 N 12 Pt 2 : M+1 1267.16. 
     Synthesis Example 6: Synthesis of Compound BD41 
     Compound BD41 was identified with reference to the Scheme VI. 
     
       
         
         
             
             
         
       
     
     (1) Synthesis of Intermediate 41-1 
     Compound 1 reacted with nBuLi and then reacted with isophthalaldehyde to synthesize Intermediate 41-1. Intermediate 41-1 was identified by LC-MS. 
     C 32 H 26 O 2 : M+1 443.18. 
     (2) Synthesis of Intermediate 41-2 
     Intermediate 41-1 and pyridinium chlorochromate (cas: 26299-14-9) reacted with each other at room temperature under a dichloromethane solvent to synthesize Intermediate 41-2. Intermediate 41-2 was identified by LC-MS. 
     C 32 H 22 O 2 : M+1 438.53. 
     (3) Synthesis of Intermediate 41-3 
     3-bromopyrazole (cas: 14521-80-3) was activated with magnesium under an iodine catalyst and then reacted with Intermediate 41-2 to obtain Intermediate 41-3. Intermediate 41-3 was identified by LC-MS. 
     C 35 H 26 N 2 O 2 : M+1 506.61. 
     (4) Synthesis of Intermediate 41-4 
     Intermediate 41-3 and hydrochloride (cas: 7647-01-0) reacted with each other under an AcOH solvent to obtain Intermediate 41-4. Intermediate 41-4 was identified by LC-MS. 
     C 38 H 28 N 4 O: M+1 489.19. 
     (5) Synthesis of Intermediate 41-5 
     Intermediate 41-5, imidazole (cas: 288-32-4), and potassium carbonate reacted with each other to synthesize Intermediate 41-5. Intermediate 41-5 was identified by LC-MS. 
     C 38 H 28 N 4 O: M+1 556.67. 
     (6) Synthesis of Intermediate 41-6 
     Intermediate 41-5 and hydrochloride (cas: 7647-01-0) reacted with each other under an AcOH solvent to obtain Intermediate 41-6. Intermediate 41-6 was identified by LC-MS. 
     C 38 H 26 N 4 : M+1 538.65. 
     (7) Synthesis of Intermediate 41-7 
     Intermediate 41-6 and iodide methane (cas: 74-88-4) reacted with each other under an acetone solvent to synthesize Intermediate 41-7. Intermediate 41-7 was identified by LC-MS. 
     C 39 H 29 N 4 : M+1 553.69. 
     (8) Synthesis of Compound BD41 
     Intermediate 41-7, dichloro(1,5-cyclooctadiene)platinum(II), and sodium acetate reacted with each other at a temperature of 160° C. under a 1,4-dioxane solvent to synthesize Compound BD41. Compound BD41 was identified by LC-MS. 
     C 78 H 52 N 8 Pt 2 : M+1 1491.50. 
     Synthesis Example 7: Synthesis of Compound BD42 
     Compound BD42 was synthesized with reference to the Scheme VII and Synthesis Example 6. 
     
       
         
         
             
             
         
       
     
     Compound BD42 was identified by LC-MS. 
     C 84 H 54 N 10 Pt 2 : M+1 1593.59. 
     Synthesis Example 8: Synthesis of Compound BD43 
     Compound BD43 was synthesized with reference to the Scheme VIII and Synthesis Example 6. 
     
       
         
         
             
             
         
       
     
     Compound BD43 was identified by LC-MS. 
     C 82 H 52 N 12 Pt 2 : M+1 1595.57. 
     Synthesis Example 9: Synthesis of Compound BD44 
     Compound BD44 was synthesized with reference to the Scheme IX and Synthesis Example 6. 
     
       
         
         
             
             
         
       
     
     Compound BD44 was identified by LC-MS. 
     C 82 H 60 N 8 Pt 2 : M+1 1547.61. 
     Example 1 
     As an anode, an ITO substrate, on which ITO/Ag/ITO were deposited, was cut to a size of 50 mm×50 mm×0.7 mm, sonicated with isopropyl alcohol and pure water each for 5 minutes, and then cleaned by exposure to ultraviolet rays and ozone for 30 minutes. Then, the ITO substrate was provided to a vacuum deposition apparatus. 
     Compound 2-TNATA was vacuum-deposited on the ITO substrate to form a hole injection layer having a thickness of 60 nm, and NPB was vacuum-deposited on the hole injection layer to form a hole transport layer having a thickness of 30 nm. 
     Compound H56 (host) and Compound BD1 (dopant) were co-deposited on the hole transport layer at a weight ratio of 10:1 to form an emission layer having a thickness of 25 nm. 
     BAIq was deposited on the emission layer to form a hole blocking layer having a thickness of 5 nm, Alq 3  was deposited on the hole blocking layer to form an electron transport layer having a thickness of 25 nm, LiF was deposited on the electron transport layer to form an electron injection layer having a thickness of 0.5 nm, and Al was deposited on the electron injection layer to form a cathode having a thickness of 150 nm, thereby completing the manufacture of an organic light-emitting device. 
     Comparative Examples 1 and 2 
     Organic light-emitting devices were manufactured in the same manner as in Example 1, except that Compounds shown in Table 1 were each used instead of Compound BD1. 
     Evaluation Example 
     The driving voltage (V), current density (mA/cm 2 ), current efficiency (cd/A), maximum emission wavelength (nm), and lifespan (T 90 ) of the organic light-emitting devices manufactured according to Example 1 and Comparative Examples 1 and 2 were measured at 1,000 cd/m 2  by using Keithley MU 236 and a luminance meter PR650, and results thereof are shown in Table 1. In Table 1, the lifespan (T 90 ) indicates an amount of time that lapsed when luminance was 90% of initial luminance (100%). 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                   
                   
                 Maximum 
                   
               
               
                   
                 Emission 
                   
                 Driving 
                 Current 
                 Current 
                 emission 
                 Lifespan 
               
               
                   
                 layer 
                 Luminance 
                 voltage 
                 density 
                 efficiency 
                 wavelength 
                 (T 90 ) 
               
               
                   
                 dopant 
                 (cd/m 2 ) 
                 (V) 
                 (mA/cm 2 ) 
                 (cd/A) 
                 (nm) 
                 (hr) 
               
               
                   
               
             
            
               
                 Example 1 
                 BD1 
                 1000 
                 4.5 
                 6.5 
                 28.1 
                 456 
                 3.2 
               
               
                 Comparative 
                 Cl 
                 1000 
                 4.6 
                 5.8 
                 21.0 
                 471 
                 0.5 
               
               
                 Example 1 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Comparative 
                 C2 
                 1000 
                 4.5 
                 6.2 
                 25.5 
                 457 
                 3.0 
               
               
                 Example 2 
               
               
                   
               
               
                 
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                 
               
            
           
         
       
     
     From Table 1, it is confirmed that the organic light-emitting device of Example 1 has excellent current efficiency and lifespan, as compared with the organic light-emitting devices of Comparative Examples 1 and 2. 
     The organic light-emitting device may have high efficiency and a long lifespan. 
     It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. 
     While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.