Patent Publication Number: US-2021193939-A1

Title: Organometallic compound and organic light-emitting device including same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2019-0172114, filed on Dec. 20, 2019, in the Korean Intellectual Property Office, the entire content of which is incorporated herein by reference. 
    
    
     BACKGROUND 
     1. Field 
     One or more aspects of embodiments of the present disclosure relate to an organometallic compound and an organic light-emitting device including the same. 
     2. Description of Related Art 
     Organic light-emitting devices (OLEDs) are self-emission devices that, as compared with conventional devices, may have wide viewing angles, high contrast ratios, short response times, and/or excellent characteristics in terms of brightness, driving voltage, and/or response speed, and can produce full-color images. 
     An example OLED includes a first electrode on a substrate, and a hole transport region, an emission layer, an electron transport region, and a second electrode sequentially stacked on the first electrode. Holes provided from the first electrode may move toward the emission layer through the hole transport region, and electrons provided from the second electrode may move toward the emission layer through the electron transport region. Carriers, such as holes and electrons, may recombine in the emission layer to produce excitons. These excitons may transition from an excited state to the ground state to thereby generate light. 
     SUMMARY 
     One or more aspects of embodiments of the present disclosure are directed toward a novel organometallic compound and an organic light-emitting device including the same. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments of the disclosure. 
     One or more example embodiments of the present disclosure provide an organometallic compound represented by Formula 1: 
     
       
         
         
             
             
         
       
     
     wherein, in Formula 1, 
     M 11  may 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), 
     A 10 , A 20 , A 30 , and A 40  may each independently be selected from a C 5 -C 60  carbocyclic group and a C 1 -C 60  heterocyclic group, 
     X 11  may be Si(R 1 )(R 2 ) or Ge(R 1 )(R 2 ), 
     Y 10 , Y 20 , Y 30 , and Y 40  may each independently be N or C, 
     Y 11 , Y 12 , Y 21 , Y 22 , Y 23 , Y 31 , Y 32 , and Y 41  may each independently be N or C, 
     T 11  to T 14  may each independently be or indicate a chemical bond, 
     L 11  and L 12  may each independently be selected from a single bond, *—O—*′, *—S—*′, *—C(R 3 )(R 4 )—*′, *—C(R 3 )═*′, *═C(R 3 )—*′, *—C(R 3 )═C(R 4 )—*′, *—C(═O)—*′, *—C(═S)—*′, *—C≡C—*′, *—B(R 3 )—*′, *—N(R 3 )—*′, *—P(R 3 )—*′, *—Si(R 3 )(R 4 )—*′, *—P(R 3 )(R 4 )—*′, and *—Ge(R 3 )(R 4 )—*′, 
     a 11  and a 12  may each independently be selected from 0, 1, 2, 3, 4, and 5, 
     R 1  to R 4 , R 10 , R 20 , R 30 , and R 40  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 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 C 1 -C 60  heteroaryloxy group, a substituted or unsubstituted C 1 -C 60  heteroarylthio group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 1 )(Q 2 )(Q 3 ), —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 ), 
     R 1  to R 4 , R 10 , R 20 , R 30 , and R 40  may optionally be bound to form a substituted or unsubstituted C 5 -C 60  carbocyclic group or a substituted or unsubstituted C 1 -C 60  heterocyclic group, 
     b10, b20, b30, and b40 may each independently be selected from 1, 2, 3, 4, 5, 6, 7, and 8, 
     * and *′ each indicate a binding site to an adjacent atom, and 
     at least one substituent of the substituted C 5 -C 60  carbocyclic group, the substituted C 1 -C 60  heterocyclic group, the substituted C 1 -C 60  alkyl group, the substituted C 2 -C 60  alkenyl group, the substituted C 2 -C 60  alkynyl group, the substituted C 1 -C 60  alkoxy group, the substituted C 3 -C 10  cycloalkyl group, the substituted C 1 -C 10  heterocycloalkyl group, the substituted C 3 -C 10  cycloalkenyl group, the substituted C 1 -C 10  heterocycloalkenyl group, the substituted C 6 -C 60  aryl group, the substituted C 6 -C 60  aryloxy group, the substituted C 6 -C 60  arylthio group, the substituted C 1 -C 60  heteroaryl group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group, when present, 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 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 11 )(Q 12 )(Q 13 ), —N(Q 11 )(Q 12 ), —B(Q 11 )(Q 12 ), —C(═O)(Q 11 ), —S(═O) 2 (Q 11 ), and —P(═O)(Q 11 )(Q 12 ); 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group; 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 21 )(Q 22 )(Q 23 ), —N(Q 21 )(Q 22 ), —B(Q 21 )(Q 22 ), —C(═O)(Q 21 ), —S(═O) 2 (Q 21 ), and —P(═O)(Q 21 )(Q 22 ); and 
     —Si(Q 31 )(Q 32 )(Q 33 ), —N(Q 31 )(Q 32 ), —B(Q 31 )(Q 32 ), —C(═O)(Q 31 ), —S(═O) 2 (Q 31 ), and —P(═O)(Q 31 )(Q 32), 
     wherein Q 1  to Q 3 , Q 11  to Q 13 , Q 21  to Q 23 , and Q 31  to Q 33  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  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. 
     One or more example embodiments of the present disclosure provide an organic light-emitting device including a first electrode; a second electrode; an organic layer between the first electrode and the second electrode and including an emission layer; and 
     at least one organometallic compound represented by Formula 1. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a schematic cross-sectional view of an embodiment of an organic light-emitting device; 
         FIG. 2  is a schematic cross-sectional view of an embodiment of an organic light-emitting device; 
         FIG. 3  is a schematic cross-sectional view of an embodiment of an organic light-emitting device; and 
         FIG. 4  is a schematic cross-sectional view of an embodiment of an organic light-emitting device. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in more detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout and duplicative descriptions thereof may not be provided. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects of the present description. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Throughout the disclosure, the expression “at least one of a, b, or c” may indicate or include only a, only b, only c, both a and b, both a and c, both b and c, all of a, b, and c, or variations thereof. 
     As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and/or groups thereof. 
     As used herein, expressions such as “at least one of,” “one of,” and “selected from,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. Further, the use of “may” when describing embodiments of the present disclosure refers to “one or more embodiments of the present disclosure”. 
     One or more example embodiments of the present disclosure provide an organometallic compound represented by Formula 1: 
     
       
         
         
             
             
         
       
     
     In Formula 1, M 11  may 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). 
     In some embodiments, M 11  may be selected from Pt, Pd, Cu, Ag, Au, Rh, Ir, Ru, and Os. In some embodiments, M 11  may be Pt. 
     In Formula 1, A 10 , A 20 , A 30 , and A 40  may each independently be selected from a C 5 -C 60  carbocyclic group and a C 1 -C 60  heterocyclic group. 
     In some embodiments, A 10 , A 20 , A 30 , and A 40  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 cyclopentadiene group, a 1,2,3,4-tetrahydronaphthalene group, a furan group, a thiophene group, a silole group, an indene group, a fluorene group, an indole group, a carbazole group, a benzofuran group, a dibenzofuran group, a benzothiophene group, a dibenzothiophene group, a benzosilole group, a dibenzosilole group, an indenopyridine group, an indolopyridine group, a benzofuropyridine group, a benzothienopyridine group, a benzosilolopyridine group, an indenopyrimidine group, an indolopyrimidine group, a benzofuropyrimidine group, a benzothienopyrimidine group, a benzosilolopyrimidine group, a dihydropyridine 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 phenanthroline group, a pyrrole group, a pyrazole group, an imidazole group, a 2,3-dihydroimidazole group, a triazole group, a 2,3-dihydrotriazole group, an oxazole group, an iso-oxazole group, a thiazole group, an isothiazole group, an oxadiazole group, a thiadiazole group, a benzopyrazole group, a benzimidazole group, a 2,3-dihydrobenzimidazole group, an imidazopyridine group, a 2,3-dihydroimidazopyridine group, an imidazopyrimidine group, a 2,3-dihydroimidazopyrimidine group, an imidazopyrazine group, a 2,3-dihydroimidazopyrazine group, a benzoxazole group, a benzothiazole group, a benzoxadiazole group, a benzothiadiazole group, a 5,6,7,8-tetrahydroisoquinoline group, and a 5,6,7,8-tetrahydroquinoline group. 
     In some embodiments, A 10 , A 20 , and A 30  may each independently be a group represented by one of Formulae 2-1 to 2-43: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae 2-1 to 2-43, 
     X 21  to X 23  may each independently be selected from C(Z 24 ) and C—*, provided that at least two selected from X 21  to X 23  may each be C—*, 
     X 24  may be N—*, and X 25  and X 26  may each independently be selected from C(Z 24 ) and C—*, provided that at least one selected from X 25  and X 26  may be C—*, 
     X 27  and X 28  may each independently be selected from N, N(Z 25 ), and N—*, and X 29  may be selected from C(Z 24 ) and C—*, provided that i) at least one selected from X 27  and X 28  is N—*, and X 29  is C—*, or ii) X 27  and X 28  may each be N—*, and X 29  is C(Z 24 ), 
     Z 21  to Z 25  may each independently 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 20  alkyl group, a C 1 -C 20  alkenyl group, a C 1 -C 20  alkynyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyridinyl group, a pyrimidinyl group, a carbazolyl group, and a triazinyl group, 
     c21 may be selected from 1, 2, and 3, 
     c22 may be selected from 1, 2, 3, 4, and 5, 
     c23 may be selected from 1, 2, 3, and 4, 
     c24 may be selected from 1 and 2, and 
     * indicates a binding site to an adjacent atom. 
     In some embodiments, A 10 , A 20 , and A 30  may each independently be selected from a benzene group, a pyridine group, a pyrimidine group, and a triazine group. 
     In some embodiments, A 40  may be a 5-membered C 1 -C 60  heterocyclic group. 
     In some embodiments, A 40  may be a group selected from Formulae 4-1 to 4-115: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae 4-1 to 4-115, 
     Z 41  to Z 43  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  alkenyl group, a C 1 -C 20  alkynyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyridinyl group, a pyrimidinyl group, a carbazolyl group, and a triazinyl group; and 
     a C 1 -C 20  alkyl group, a C 1 -C 20  alkenyl group, a C 1 -C 20  alkynyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a phenanthrenyl group, an anthracenyl group, a triperylenyl group, a pyridinyl group, a pyrimidinyl group, a carbazolyl group, and a triazinyl 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  alkenyl group, a C 1 -C 20  alkynyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a phenanthrenyl group, an anthracenyl group, a triperylenyl group, a pyridinyl group, a pyrimidinyl group, a carbazolyl group, and a triazinyl group, and 
     * and *′ each indicate a binding site to an adjacent atom. 
     In Formula 1, Y 10 , Y 20 , Y 30 , and Y 40  may each independently be N or C. 
     In some embodiments, in Formula 1, Y 10 , Y 20 , and Y 30  may each be C, and Y 40  may be N, 
     Y 10 , Y 20 , and Y 40  may each be C, and Y 30  may be N, 
     Y 10 , Y 30 , and Y 40  may each be C, and Y 20  may be N, 
     Y 20 , Y 30 , and Y 40  may each be C, and Y 10  may be N, 
     Y 10  and Y 40  may each be C, and Y 20  and Y 30  may each be N, 
     Y 10  and Y 40  may each be N, and Y 20  and Y 30  may each be C, 
     Y 10  and Y 20  may each be C, and Y 30  and Y 40  may each be N, 
     Y 10  and Y 20  may each be N, and Y 30  and Y 40  may each be C, 
     Y 10  and Y 30  may each be C, and Y 20  and Y 40  may each be N, or 
     Y 10  and Y 30  may each be N, and Y 20  and Y 40  may each be C. 
     In Formula 1, Y 11 , Y 12 , Y 21 , Y 22 , Y 23 , Y 31 , Y 32 , and Y 41  may each independently be N or C. 
     In Formula 1, T 11  to T 14  may each be or indicate a chemical bond (e.g., a bonding interaction between an atom on one of A 10  to A 40  and the central metal atom M 11 ). 
     In some embodiments, T 11  may be a coordinate (dative) bond or a covalent bond. In some embodiments, T 12  may be a coordinate bond or a covalent bond. In some embodiments, T 13  may be a coordinate bond or a covalent bond. In some embodiments, T 14  may be a chemical bond, and T 14  may be a coordinate bond or a covalent bond. In some embodiments, for example when the corresponding Y atom is a N atom in an amine or aromatic heterocycle, the bond may be a coordinate bond; and when the corresponding Y atom is a C atom in an aryl group, the bond may be a covalent bond. In some embodiments, for example when the corresponding Y atom is a C atom in a carbene, the bond may be a coordinate bond. 
     In some embodiments, the metal M 11  may be in or have a +2 oxidation state, two selected from T 11  to T 14  may each be a coordinate bond, and the other two of T 11  to T 14  may each be a covalent bond. Accordingly, the organometallic compound may not have a form of a salt including a cation and an anion, and may instead be electrically neutral (e.g., may have an overall charge of 0). 
     In some embodiments, T 11  and T 14  may each be a coordinate bond, and T 12  and T 13  may each be a covalent bond. 
     In some embodiments, T 11  and T 13  may each be a covalent bond, and T 12  and T 14  may each be a coordinate bond. 
     In Formula 1, L 11  and L 12  may each independently be selected from a single bond, *—O—*′, *—S—*′, *—C(R 1 )(R 2 )—*′, *—C(R 1 )═*′, *═C(R 1 )—*′, *—C(R 1 )═C(R 2 )—*′, *—C(═O)—*′, *—C(═S)—*′, *—C≡C—*′, *—B(R 1 )—*′, *—N(R 1 )—*′, *—P(R 1 )—*′, *—Si(R 1 )(R 2 )—*′, *—P(R 1 )(R 2 )—*′, and *—Ge(R 1 )(R 2 )—*′. 
     In some embodiments, L 11  and L 12  may each independently be selected from a single bond, *—O—*′, *—S—*′, *—N(R 1 )—*′, *—C(R 1 )(R 2 )—*′, *—Si(R 1 )(R 2 )—*′, and *—B(Ri)—*′. 
     In some embodiments, L 11  may be selected from *—O—*′ and *—S—*′. In some embodiments, L 11  may be *—O—*′. In some embodiments, L 11  may be *—S—*′. 
     In some embodiments, L 12  may be selected from a single bond and *—N(Ri)—*′. In some embodiments, L 12  may be a single bond. 
     In Formula 1, a 11  and a 12  may each independently be selected from 0, 1, 2, 3, 4, and 5. 
     In some embodiments, a 11  and a 12  may each be 1. 
     In Formula 1, R 1  to R 4 , R 10 , R 20 , R 30 , and R 40  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 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 C 1 -C 60  heteroaryloxy group, a substituted or unsubstituted C 1 -C 60  heteroarylthio group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 1 )(Q 2 )(Q 3 ), —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 ). 
     In some embodiments, R 1  to R 4 , R 10 , R 20 , R 30 , and R 40  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, and a biphenyl 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, an isoquinolinyl 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 dinaphthosilolyl 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 indenocarbazolyl 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, an isoquinolinyl 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 dinaphthosilolyl 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 indenocarbazolyl 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, an isoquinolinyl 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 dinaphthosilolyl 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 indenocarbazolyl group, an indolocarbazolyl group, —Si(Q 31 )(Q 32 )(Q 33 ), —N(Q 31 )(Q 32 ), —B(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 
     —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 ), 
     wherein 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 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 2 -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 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 1 -C 60  aryl group substituted with at least one selected from deuterium, —F, and a cyano group, a biphenyl group, and a terphenyl group. 
     In some embodiments, R 1 , R 2 , R 10 , R 20 , R 30 , R 40 , and R 50  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, and a biphenyl group; and 
     a group represented by one of Formulae 5-1 to 5-26 and Formulae 6-1 to 6-55: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, in Formulae 5-1 to 5-26 and 6-1 to 6-55, 
     Y 31  and Y 32  may each independently be O, S, C(Z 33 )(Z 34 ), N(Z 33 ), or Si(Z 33 )(Z 34 ), 
     Z 31  to Z 34  may each independently be 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  alkenyl group, a C 1 -C 20  alkynyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyridinyl group, a pyrimidinyl group, a carbazolyl group, and a triazinyl group, 
     e2 may be 1 or 2, 
     e3 may be an integer from 1 to 3, 
     e4 may be an integer from 1 to 4, 
     e5 may be an integer from 1 to 5, 
     e6 may be an integer from 1 to 6, 
     e7 may be an integer from 1 to 7, 
     e9 may be an integer from 1 to 9, and 
     * indicates a binding site to an adjacent atom. 
     In some embodiments, R 1  to R 4  may each independently be represented by one of Formulae 5-1 to 5-26 and 6-1 to 6-55. 
     In some embodiments, R 10 , R 20 , R 30 , and R 40  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, and a biphenyl 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 carbazolyl group, an acridinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, and a dibenzocarbazolyl group; and 
     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 carbazolyl group, an acridinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, and a dibenzocarbazolyl 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 phenyl group, and a biphenyl group. 
     In Formula 1, at least two adjacent groups selected from R 1 , R 2 , R 10 , R 20 , R 30 , and R 40  may optionally be bound to form a substituted or unsubstituted C 5 -C 60  carbocyclic group or a substituted or unsubstituted C 1 -C 60  heterocyclic group. 
     In some embodiments, at least two adjacent groups selected from R 1 , R 2 , R 10 , R 20 , R 30 , and R 40  may optionally be bound to form any one group selected from: a cyclopentane group, a cyclohexane group, a benzene group, a naphthylene group, a fluorene group, and a carbazole group; and 
     a cyclopentane group, a cyclohexane group, a benzene group, a naphthylene group, a fluorene group, and a carbazole group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a cyano group, a C 1 -C 20  alkyl group, and a C 1 -C 20  alkoxy group, a phenyl group, and a biphenyl group. 
     In some embodiments, at least two adjacent groups selected from R 1 , R 2 , R 10 , R 20 , R 30 , and R 40  may optionally be bound to form a cyclopentane group, a cyclohexane group, a benzene group, a naphthylene group, a fluorene group, or a carbazole group. 
     In some embodiments, R 1 , R 2 , R 10 , R 20 , R 30 , and R 40  may optionally be bound to form a cyclopentane group, a cyclohexane group, a fluorene group, or a carbazole group. 
     In some embodiments, at least one selected from R 1  and R 10 ; R 1  and R 20 , R 1  and R 30 , and R 1  and R 40  may be bound to each other to form a carbazole group. 
     In Formula 1, b10, b20, b30, and b40 may each independently be selected from 1, 2, 3, 4, 5, 6, 7, and 8. 
     In some embodiments, the organometallic compound represented by Formula 1 may be selected from Compounds A1 to A24 and B1 to B24, but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In the organometallic compound represented by Formula 1, ring A 10  and ring A 20  are linked to each other via a single bond, and a binding energy between the ligand and metal M 11  may be increased due to the presence of the —Si(R 1 )(R 2 )— or —Ge(R 1 )(R 2 )— linking group, resulting in excellent stability of the organometallic compound. Accordingly, when the organometallic compound is applied to an organic light-emitting device, energy transfer may be facilitated, luminescence efficiency may be excellent, high colorimetric purity may be achieved, and/or lifespan characteristics may be improved. 
     The organometallic compound may be to emit blue light. In some embodiments, the organometallic compound may be to emit blue light having a maximum emission wavelength of about 400 nanometers (nm) to about 500 nm, e.g. about 410 nm to about 490 nm (bottom emission CIE x,y  color-coordinate X=0.15, Y=0.16 to 0.20), but embodiments are not limited thereto. Accordingly, the organometallic compound represented by Formula 1 may be used effectively in manufacture of an organic light-emitting device that emits blue light. 
     Methods of synthesizing the organometallic compound represented by Formula 1 should be readily apparent to those of ordinary skill in the art by referring to Examples described herein. 
     At least one organometallic compound represented by Formula 1 may be included between a pair of electrodes in an organic light-emitting device. In some embodiments, the organometallic compound may be included in an emission layer. In the emission layer, the organometallic compound may serve as a dopant. In some embodiments, the organometallic compound represented by Formula 1 may be used as a material for forming a capping layer disposed on either or both of the outer sides of the pair of electrodes in an organic light-emitting device. 
     One or more example embodiments of the present disclosure provide an organic light-emitting device including a first electrode; a second electrode facing the first electrode; and an organic layer between the first electrode and the second electrode, wherein the organic layer may include an emission layer and at least one organometallic compound represented by Formula 1. 
     As used herein, “(for example, the organic layer) including at least one organometallic compound” refers to “(the organic layer) including an organometallic compound of Formula 1, or at least two different organometallic compounds of Formula 1”. 
     For example, Compound 1 (a first compound) may be included in the organic layer as an organometallic compound (e.g., as the only compound of its type (kind) and/or function). In this embodiment, Compound 1 may be included in the emission layer of the organic light-emitting device. In some embodiments, Compounds 1 and 2 (a first compound and a second compound) may be included in the organic layer as organometallic compounds. In this embodiment, Compounds 1 and 2 may be included in the same layer (for example, both Compounds 1 and 2 may be included in the emission layer) or in different layers (for example, Compound 1 may be included in the emission layer, and Compound 2 may be included in an electron transport region). 
     In some embodiments, 
     a first electrode of an organic light-emitting device may be an anode, 
     a second electrode of an organic light-emitting device may be a cathode, 
     the organic layer may include a hole transport region between the first electrode and the emission layer and an electron transport region between the emission layer and the second electrode, 
     the hole transport region may include a hole injection layer, a hole transport layer, an emission auxiliary layer, an electron blocking layer, or a combination thereof, and 
     the electron transport region may include a hole blocking layer, an electron transport layer, an electron injection layer, or a combination thereof. 
     The term “organic layer” as used herein refers to a single and/or a plurality of layers between the first electrode and the second electrode in an organic light-emitting device. The materials included in the “organic layer” are not limited to being organic materials. 
     In one or more embodiments, the emission layer may include the organometallic compound represented by Formula 1, the emission layer may further include a host, and the host may be greater in content (amount) than the organometallic compound in the emission layer. 
     In some embodiments, the hole transport region may include an electron blocking layer, and the electron blocking layer may include the organometallic compound; or 
     the electron transport region may include a hole blocking layer, and the hole blocking layer may include the organometallic compound. 
     In an embodiment, a p-dopant in the hole transport region may have a LUMO energy level of about −3.5 eV or less. 
     In some embodiments, the electron transport region may include the electron transport layer and the electron injection layer, and 
     at least one of the electron transport layer and the electron injection layer may further 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 a combination thereof. 
     Description of FIG.  1   
       FIG. 1  illustrates a schematic cross-sectional view of an organic light-emitting device  10  according to an embodiment. The organic light-emitting device  10  may include 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 an organic light-emitting device according to an embodiment will be described in connection with  FIG. 1 . 
     First Electrode  110   
     In  FIG. 1 , a substrate may be additionally located under the first electrode  110  or above the second electrode  190 . The substrate may be a glass substrate and/or a plastic substrate, each having excellent mechanical strength, thermal stability, transparency, surface smoothness, ease of handling, and/or water resistance. 
     The first electrode  110  may be formed by depositing or sputtering a material for forming the first electrode  110  onto 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, the material for forming the first electrode  110  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 are not limited thereto. In some embodiments, when the first electrode  110  is a semi-transmissive electrode or a reflective electrode, at least one of magnesium (Mg), silver (Ag), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), and any combination thereof may be used as a material for forming the first electrode  110 , but embodiments are not limited thereto. 
     The first electrode  110  may have a single-layered structure, or a multi-layered structure including two or more layers. In some embodiments, for example, the first electrode  110  may have a triple-layered structure of ITO/Ag/ITO, but embodiments are not limited thereto. 
     Organic Layer  150   
     The organic layer  150  may be 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 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 (e.g., consisting of) a single layer including (e.g., consisting of) a single material, ii) a single-layered structure including (e.g., consisting of) a single layer including 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 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 (e.g., 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 layers of each structure are sequentially stacked on the first electrode  110  in each stated order, but embodiments are not limited thereto. 
     The hole transport region may include at least one selected from m-MTDATA, TDATA, 2-TNATA, NPB (NPD), β-NPB, TPD, a spiro-TPD, a spiro-NPB, methylated-NPB, TAPC, HMTPD, 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA), polyaniline/dodecylbenzenesulfonic acid (PANI/DBSA), poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS), polyaniline/camphor sulfonic acid (PANI/CSA), polyaniline/poly(4-styrenesulfonate) (PANI/PSS), a compound represented by Formula 201, and a compound represented by Formula 202: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     wherein, 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—*′, *—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. 
     In some embodiments, in Formula 202, R 201  and R 202  may optionally be bound via a single bond, a dimethyl-methylene group, or a diphenyl-methylene group, and R 203  and R 204  may optionally be bound via a single bond, a dimethyl-methylene group, or a diphenyl-methylene group. 
     In an 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 ), 
     wherein Q 31  to Q 33  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group. 
     In one or more embodiments, xa1 to xa4 may each independently be 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 ), 
     wherein Q 31  to Q 33  may each independently be the same as described above. 
     In one or more embodiments, in Formula 201, at least one of R 201  to R 203  may 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 are not limited thereto. 
     In one or more embodiments, in Formula 202, i) R 201  and R 202  may be bound via a single bond, and/or ii) R 203  and R 204  may be bound via a single bond. 
     In one or more embodiments, in Formula 202, at least one of R 201  to R 204  may 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 are not limited thereto. 
     The compound represented by Formula 201 may be represented by Formula 201A: 
     
       
         
         
             
             
         
       
     
     In some embodiments, the compound represented by Formula 201 may be represented by Formula 201A(1), but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
     
     In some embodiments, the compound represented by Formula 201 may be represented by Formula 201A-1, but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
     
     In some embodiments, the compound represented by Formula 202 may be represented by Formula 202A: 
     
       
         
         
             
             
         
       
     
     In some embodiments, the compound represented by Formula 202 may be represented by Formula 202A-1: 
     
       
         
         
             
             
         
       
     
     In Formulae 201A, 201A(1), 201A-1, 202A, and 202A-1, 
     L 201  to L 203,  xa1 to xa3, xa5, and R 202  to R 204  may each independently be the same as described above, 
     R 211  and R 212  may each independently be each independently be the same as described 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 HT 1  to HT 39,  but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The thickness of the hole transport region may be about 100 (Angstroms) Å to about 10,000 Å, and in some embodiments, about 100 Å to about 1,000 Å. When the hole transport region includes at least one selected from a hole injection layer and a hole transport layer, the thickness of the hole injection layer may be about 100 Å to about 9,000 Å, and in some embodiments, about 100 Å to about 1,000 Å, and the thickness of the hole transport layer may be about 50 Å to about 2,000 Å, and in some embodiments, about 100 Å to about 1,500 Å. When the thicknesses of the hole transport region, the hole injection layer, and the hole transport layer are within any of these ranges, excellent hole transport 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. The electron blocking layer may reduce or eliminate the flow of electrons from an electron transport region. The emission auxiliary layer and the electron blocking layer may include the aforementioned materials. 
     p-Dopant 
     The hole transport region may include a charge generating material in addition to the aforementioned materials, to improve conductive properties of the hole transport region. The charge generating material may be substantially homogeneously or non-homogeneously dispersed in the hole transport region. 
     The charge generating material may include, for example, a p-dopant. 
     In some embodiments, the LUMO of the p-dopant may be −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 are not limited thereto. 
     In some embodiments, the p-dopant may include at least one selected from: 
     a quinone derivative (such as tetracyanoquinodimethane (TCNQ) and/or 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ)); 
     a metal oxide (such as tungsten oxide and/or molybdenum oxide); 
     1,4,5,8,9,12-hexaazatriphenylene-hexacarbonitrile (HAT-CN); and 
     a compound represented by Formula 221, 
     but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
     
     wherein, 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 include 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. The stacked structure may include two or more layers selected from a red emission layer, a green emission layer, and a blue emission layer. In some embodiments, the two or more layers may be in direct contact with each other. In some embodiments, the two or more layers may be separated from each other. In one or more embodiments, the emission layer may include two or more materials. The two or more materials may include a red light-emitting material, a green light-emitting material, and/or a blue light-emitting material. The two or more materials may be mixed with each other in a single layer. The two or more materials mixed with each other in the single layer may be to emit white light. 
     The emission layer may include a host and a dopant. The dopant may include at least one of a fluorescent dopant and a phosphorescent dopant. The phosphorescent dopant may include the organometallic compound represented by Formula 1. 
     The amount of the dopant in the emission layer may be, in general, about 0.01 parts to about 15 parts by weight based on 100 parts by weight of the host, but embodiments are not limited thereto. 
     The thickness of the emission layer may be about 100 Å to about 1,000 Å, and in some embodiments, about 200 Å to about 600 Å. When the thickness of the emission layer is within any of these ranges, improved luminescence characteristics may be obtained without a substantial increase in driving voltage. 
     Host in Emission Layer 
     The host may include a compound represented by Formula 301: 
       [Ar 301 ] xb11 -[(L 301 ) xb1 -R 301 ] xb21 ,    Formula 301
 
     wherein, in Formula 301, 
     Ar 301  may be selected from a substituted or unsubstituted C 5 -C 60  carbocyclic group and 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 ), and 
     xb21 may be an integer from 1 to 5, 
     wherein 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 are not limited thereto. 
     In some embodiments, in Formula 301, Ar 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 ), 
     wherein Q 31  to Q 33  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group, but embodiments are not limited thereto. 
     When xb11 in Formula 301 is 2 or greater, at least two Ar 301 (s) may be bound 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: 
     
       
         
         
             
             
         
       
     
     wherein, in Formulae 301-1 to 301-2, 
     A 301  to 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  may each independently be the same as described above, 
     L 302  to L 304  may each independently be the same as described in connection with L 301 , 
     xb2 to xb4 may each independently be the same as described in connection with xb1, and 
     R 302  to R 304  may each independently be the same as described in connection with R 301 . 
     In some embodiments, in Formulae 301, 301-1, and 301-2, L 301  to L 304  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 ), 
     wherein Q 31  to Q 33  may each independently be the same as described above. 
     In some embodiments, in Formulae 301, 301-1, and 301-2, R 301  to R 304  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 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 ), 
     wherein Q 31  to Q 33  may each independently be the same as described above. 
     In some embodiments, the host may include an alkaline earth metal complex. For example, the host may include a beryllium (Be) complex, e.g., Compound H55, and/or a magnesium (Mg) complex. In some embodiments, the host may include a zinc (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), and Compounds H1 to H55, but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, the host may include at least one selected from a silicon-containing compound (e.g., BCPDS and/or the like, as used in the Examples) and a phosphine oxide-containing compound (e.g., POPCPA and/or the like, as used in the Examples). 
     The host may include one type (kind) of compounds only, or two or more different types (kinds) of compounds (for example, the constituent hosts in Examples were BCPDS and POPCPA). As such, embodiments may be modified in various suitable ways. 
     Phosphorescent Dopant Included in Emission Layer of Organic Layer  150   
     The phosphorescent dopant may include the organometallic compound represented by Formula 1. 
     Further, the phosphorescent dopant may include an organometallic complex represented by Formula 401: 
     
       
         
         
             
             
         
       
     
     wherein, in Formulae 401 and 402, 
     M may be selected from iridium (Ir), platinum (Pt), palladium (Pd), osmium (Os), titanium (Ti), zirconium (Zr), hafnium (Hf), europium (Eu), terbium (Tb), rhodium (Rh), and thulium (Tm), 
     L 401  may be selected from ligands represented by Formula 402, and xc1 may be 1, 2, or 3; when xc1 is 2 or greater, at least two L 401 (s) may be identical to or different from each other, 
     L 402  may be an organic ligand, and xc2 may be an integer selected from 0 to 4; when xc2 is 2 or greater, at least two L 402 (s) may be identical to or different from each other, 
     X 401  to X 404  may each independently be nitrogen or carbon, 
     X 401  and X 403  may be bound to each other via a single bond or a double bond, X 402  and X 404  may be bound to each other via a single bond or a double bond, 
     A 401  and A 402  may each independently be a C 5 -C 60  carbocyclic group or a C 1 -C 60  heterocyclic group, 
     X 405  may be a single bond, *—O—*′, *—S—*′, *—C(═O)—*′, *—N(Q 411 )—*′, *—C(Q 411 )(Q 412 )—*′, *—C(Q 411 )═C(Q 412 )—*′, *—C(Q 411 )═*′, or *═C═*′, wherein Q 411  and Q 412  may each independently be hydrogen, deuterium, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, or a naphthyl group, 
     X 406  may be a single bond, O, or S, 
     R 401  and R 402  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 substituted or unsubstituted C 1 -C 20  alkyl group, a substituted or unsubstituted C 1 -C 20  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 401 )(Q 402 )(Q 403 ), —N(Q 401 )(Q 402 ), —B(Q 401 )(Q 402 ), —C(═O)(Q401), —S(═O) 2 (Q 401 ), and —P(═O)(Q 401 )(Q 402 ), wherein Q 401  to Q 403  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a C 6 -C 20  aryl group, and a C 1 -C 20  heteroaryl group, 
     xc11 and xc12 may each independently be an integer from 0 to 10, and 
     * and *′ in Formula 402 each indicate a binding site to M in Formula 401. 
     In some embodiments, in Formula 402, A 401  and A 402  may each independently be selected from a benzene group, a naphthalene group, a fluorene group, a spiro-bifluorene group, an indene group, a pyrrole group, a thiophene group, a furan 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, a quinoline group, an isoquinoline group, a benzoquinoline group, a quinoxaline group, a quinazoline group, a carbazole group, a benzimidazole group, a benzofuran group, a benzothiophene group, an isobenzothiophene group, a benzoxazole group, an isobenzoxazole group, a triazole group, a tetrazole group, an oxadiazole group, a triazine group, a dibenzofuran group, and a dibenzothiophene group. 
     In one or more embodiments, in Formula 402, i) X 401  may be nitrogen, and X 402  may be carbon, or ii) X 401  and X 402  may each be nitrogen. 
     In an embodiment, in Formula 402, R 401  and R 402  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, 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 amidino group, a hydrazino group, a hydrazono group, a phenyl group, a naphthyl group, a cyclopentyl group, a cyclohexyl group, an adamantyl group, a norbornanyl group, and a norbornenyl group; 
     a cyclopentyl group, a cyclohexyl group, an adamantyl group, a norbornanyl group, a norbornenyl group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a dibenzofuranyl group, and a dibenzothiophenyl group; 
     a cyclopentyl group, a cyclohexyl group, an adamantyl group, a norbornanyl group, a norbornenyl group a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl 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, an adamantyl group, a norbornanyl group, a norbornenyl group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a dibenzofuranyl group, and a dibenzothiophenyl group; and 
     —Si(Q 401 )(Q 402 )(Q 403 ), —N(Q 401 )(Q 402 ), —B(Q 401 )(Q 402 ), —C(═O)(Q 401 ), —S(═O) 2 (Q 401 ), and —P(═O)(Q 401 )(Q 402 ), 
     wherein Q 401  to Q 403  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, and a naphthyl group, but embodiments are not limited thereto. 
     In one or more embodiments, when xc1 in Formula 401 is 2 or greater, two A 401 (s) of at least two L 401 (s) may optionally be linked via X 407  as a linking group; or two A 402 (s) may optionally be linked via X 408  as a linking group (see Compounds PD1 to PD4 and PD7). X 407  and X 408  may each independently be selected from a single bond, *—O—*′, *—S—*′, *—C(═O)—*′, *—N(Q 413 )—*′, *—C(Q 413 )(Q 414 )—*′, and *—C(Q 413 )═C(Q 414 )—*′, wherein Q 413  and Q 414  may each independently be hydrogen, deuterium, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, or a naphthyl group, but embodiments are not limited thereto. 
     L 402  in Formula 401 may be any suitable monovalent, divalent, or trivalent organic ligand. For example, L 402  may be selected from halogen, diketone (e.g., acetylacetonate), a carboxylic acid (e.g., picolinate), —C(═O), isonitrile, —CN, and phosphorus (e.g., phosphine or phosphite), but embodiments are not limited thereto. 
     In some embodiments, the phosphorescent dopant may include, for example, at least one selected from Compounds PD1 to PD25, but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Fluorescent Dopant in Emission Layer 
     The fluorescent dopant may include an arylamine compound or a styrylamine compound. 
     In some embodiments, the fluorescent dopant may include a compound represented by Formula 501: 
     
       
         
         
             
             
         
       
     
     wherein, in Formula 501, 
     Ar 501  may be selected from a substituted or unsubstituted C 5 -C 60  carbocyclic group and a substituted or unsubstituted C 1 -C 60  heterocyclic group, 
     L 501  to L 503  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, 
     xd1 to xd3 may each independently be an integer from 0 to 3, 
     R 501  and R 502  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, and 
     xd4 may be an integer from 1 to 6. 
     In some embodiments, in Formula 501, Ar 501  may be selected from: 
     a naphthalene group, a heptalene 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, and an indenophenanthrene group; and 
     a naphthalene group, a heptalene 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, and an indenophenanthrene 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, and a naphthyl group. 
     In an embodiment, in Formula 501, L 501  and L 503  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, and a pyridinylene 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, 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 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, and a pyridinyl group. 
     In an embodiment, in Formula 501, R 501  and R 502  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, and a pyridinyl 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, 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 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, and —Si(Q 31 )(Q 32 )(Q 33 ), 
     wherein Q 31  to Q 33  may 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, xd4 in Formula 501 may be 2, but embodiments are not limited thereto. 
     In some embodiments, the fluorescent dopant may be selected from Compounds FD1 to FD22: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, the fluorescent dopant may be selected from the following compounds, but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
     
     Electron Transport Region in Organic Layer  150   
     The electron transport region may have i) a single-layered structure including (e.g., consisting of) a single layer including (e.g., consisting of) a single material, ii) a single-layered structure including (e.g., consisting of) a single layer including a plurality of different materials, or iii) a multi-layered structure each having a plurality of layers, each having 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 are not limited thereto. 
     In some embodiments, 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 layers of each structure are sequentially stacked on the emission layer in each stated order, but embodiments are not limited thereto. 
     The electron transport region (for example, the buffer layer, the hole blocking layer, the electron control layer, and/or the electron transport layer in the electron transport region) may include a metal-free compound including at least one π electron-depleted nitrogen-containing ring. 
     The term “π electron-depleted nitrogen-containing ring” as used herein refers to 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 at least two 5-membered to 7-membered heteromonocyclic groups, each having at least one *—N═*′ moiety, are condensed, or iii) a heteropolycyclic group in which at least one of a 5-membered to 7-membered heteromonocyclic group, each having at least one *—N═*′ moiety, is condensed with at least one C 5 -C 60  carbocyclic group. 
     Non-limiting examples of the π electron-depleted nitrogen-containing ring include imidazole, pyrazole, thiazole, isothiazole, oxazole, isoxazole, pyridine, pyrazine, pyrimidine, pyridazine, indazole, purine, quinoline, isoquinoline, benzoquinoline, phthalazine, naphthyridine, quinoxaline, quinazoline, cinnoline, phenanthridine, acridine, phenanthroline, phenazine, benzimidazole, isobenzothiazole, benzoxazole, isobenzoxazole, triazole, tetrazole, oxadiazole, triazine, thiadiazole, imidazopyridine, imidazopyrimidine, and azacarbazole, but embodiments are not limited thereto. 
     In some embodiments, the electron transport region may include a compound represented by Formula 601: 
       [Ar 601 ] xe11 -[(L 601 ) xe1 -R 601 ] xe 21,   Formula 601
 
     wherein, in Formula 601, 
     Ar 601  may be selected from a substituted or unsubstituted C 5 -C 60  carbocyclic group and 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 ), 
     wherein 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 some embodiments, at least one selected from Ar 601 (s) in the number of xe11 and R 601 (s) in the number of xe21 may include the 7 electron-depleted nitrogen-containing ring. 
     In some embodiments, in Formula 601, ring Ar 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 ), 
     wherein Q 31  to Q 33  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group. 
     When xe11 in Formula 601 is 2 or greater, at least two Ar 601 (s) may be bound via a single bond. 
     In one or more embodiments, Ar 601  in Formula 601 may be an anthracene group. 
     In some embodiments, the compound represented by Formula 601 may be represented by Formula 601-1: 
     
       
         
         
             
             
         
       
     
     wherein, in Formula 601-1, 
     X 614  may be N or C(R 614 ), X 615  may be N or C(R 615 ), X 616  may be N or C(R 616 ), at least one selected from X 614  to X 616  may be N, 
     L 611  to L 613  may each independently be the same as described in connection with L 601 , 
     xe611 to xe613 may each independently be the same as described in connection with xe1, 
     R 611  to R 613  may each independently be the same as described in connection with R 601,  and 
     R 614  to R 616  may each independently be 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 some embodiments, in Formulae 601 and 601-1, L 601  and L 611  to L 613  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 are not limited thereto. 
     In one or more embodiments, in Formulae 601 and 601-1, xe1 and xe611 to xe613 may each independently be 0, 1, or 2. 
     In one or more embodiments, in Formulae 601 and 601-1, R 601  and R 611  to R 613  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 ), 
     wherein Q 601  and Q 602  may each independently be the same as described above. 
     The electron transport region may include at least one compound selected from Compounds ET 1  to ET 36,  but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, the electron transport region may include at least one compound selected from 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), 4,7-diphenyl-1,10-phenanthroline (Bphen), Alq 3 , BAlq, 3-(biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole (TAZ), and NTAZ: 
     
       
         
         
             
             
         
       
     
     In some embodiments, the electron transport region may include a phosphine oxide-containing compound, but embodiments are not limited thereto. In some embodiments, the phosphine oxide-containing compound may be used in a hole blocking layer in the electron transport region, but embodiments are not limited thereto. 
     The thicknesses of the buffer layer, the hole blocking layer, or the electron control layer may each independently be about 20 Å to about 1,000 Å, and in some embodiments, about 30 Å to about 300 Å. When the thicknesses of the buffer layer, the hole blocking layer, and/or the electron control layer are within any of these ranges, excellent hole blocking characteristics and/or excellent electron controlling characteristics may be obtained without a substantial increase in driving voltage. 
     The thickness of the electron transport layer may be about 100 Å to about 1,000 Å, and in some embodiments, about 150 Å to about 500 Å. When the thickness of the electron transport layer is within any of these ranges, excellent 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 an alkali metal complex and an alkaline earth metal complex. The alkali metal complex may include a metal ion selected from a lithium (Li) ion, a sodium (Na) ion, a potassium (K) ion, a rubidium (Rb) ion, and a cesium (Cs) ion. The alkaline earth metal complex may include a metal ion selected from a beryllium (Be) ion, a magnesium (Mg) ion, a calcium (Ca) ion, a strontium (Sr) ion, and a barium (Ba) ion. Each ligand coordinated with the metal ion of the alkali metal complex and/or the alkaline earth metal complex may independently be selected from hydroxyquinoline, hydroxyisoquinoline, hydroxybenzoquinoline, hydroxyacridine, hydroxyphenanthridine, hydroxyphenyloxazole, hydroxyphenylthiazole, hydroxyphenyloxadiazole, hydroxyphenylthiadiazole, hydroxyphenylpyridine, hydroxyphenylbenzimidazole, hydroxyphenylbenzothiazole, bipyridine, phenanthroline, and cyclopentadiene, but embodiments are not limited thereto. 
     For example, the metal-containing material may include a Li complex. The Li complex may include, e.g., Compound ET-D1 (LiQ) and/or Compound ET-D2: 
     
       
         
         
             
             
         
       
     
     The electron transport region may include an electron injection layer that facilitates injection of electrons from the second electrode  190 . The electron injection layer may be in direct contact with the second electrode  190 . 
     The electron injection layer may have i) a single-layered structure including (e.g., consisting of) a single layer including (e.g., consisting of) a single material, ii) a single-layered structure including (e.g., consisting of) a single layer including a plurality of different materials, or iii) a multi-layered structure having a plurality of layers, each 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 combination thereof. 
     The alkali metal may be selected from Li, Na, K, Rb, and Cs. In some embodiments, the alkali metal may be Li, Na, or Cs. In one or more embodiments, the alkali metal may be Li or Cs, but embodiments 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 each independently be selected from oxides and halides (e.g., fluorides, chlorides, bromides, and/or iodines) of the alkali metal, the alkaline earth metal, and the rare earth metal, respectively. 
     The alkali metal compound may be selected from alkali metal oxides (such as Li 2 O, Cs 2 O, and/or K 2 O), and alkali metal halides (such as LiF, NaF, CsF, KF, LiI, NaI, CsI, and/or KI). In some embodiments, the alkali metal compound may be selected from LiF, Li 2 O, NaF, LiI, NaI, CsI, and KI, but embodiments are not limited thereto. 
     The alkaline earth-metal compound may be selected from alkaline earth-metal compounds (such as BaO, SrO, CaO, Ba x Sr 1-x O (wherein 0&lt;x&lt;1), and/or Ba x Ca 1-x O (wherein 0&lt;x&lt;1)). In some embodiments, the alkaline earth metal compound may be selected from BaO, SrO, and CaO, but embodiments are not limited thereto. 
     The rare earth metal compound may be selected from YbF 3 , ScF 3 , Sc 2 O 3 , Y 2 O 3 , Ce 2 O 3 , GdF 3 , and TbF 3 . In some embodiments, the rare earth metal compound may be selected from YbF 3 , ScF 3 , TbF 3 , Ybi 3 , ScI 3 , and Tbi 3 , but embodiments are not limited thereto. 
     The alkali metal complex, the alkaline earth metal complex, and the rare earth metal complex may each include ions of the above-described alkali metal, alkaline earth metal, and rare earth metal. Each ligand coordinated with the metal ion of the alkali metal complex, the alkaline earth metal complex, and/or the rare earth metal complex may independently be selected from hydroxyquinoline, hydroxyisoquinoline, hydroxybenzoquinoline, hydroxyacridine, hydroxyphenanthridine, hydroxyphenyloxazole, hydroxyphenylthiazole, hydroxyphenyloxadiazole, hydroxyphenylthiadiazole, hydroxyphenylpyridine, hydroxyphenylbenzimidazole, hydroxyphenylbenzothiazole, bipyridine, phenanthroline, and cyclopentadiene, but embodiments are not limited thereto. 
     The electron injection layer may include (e.g., 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 combination thereof, as described above. In some embodiments, the electron injection layer may further include an organic material. When the electron injection layer further includes an organic material, the alkali metal, the alkaline earth metal, the rare earth metal, the alkali metal compound, the alkaline earth metal compound, the rare earth metal compound, the alkali metal complex, the alkaline earth metal complex, the rare earth metal complex, or any combination thereof may be homogeneously or non-homogeneously dispersed in a matrix including the organic material. 
     The thickness of the electron injection layer may be about 1 Å to about 100 Å, and in some embodiments, about 3 Å to about 90 Å. When the thickness of the electron injection layer is within any of these ranges, excellent electron injection characteristics may be obtained without a substantial increase in driving voltage. 
     Second Electrode  190   
     The second electrode  190  may be on the organic layer  150 . In an embodiment, the second electrode  190  may be a cathode that is an electron injection electrode. In this embodiment, a material for forming the second electrode  190  may be a material having a low work function, for example, a metal, an alloy, an electrically conductive compound, or any combination thereof. 
     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 are not limited thereto. The second electrode  190  may be a transmissive electrode, a semi-transmissive electrode, or a reflective electrode. 
     The second electrode  190  may have a single-layered structure, or a multi-layered structure including two or more layers. 
     Description of FIGS.  2  to  4   
     Referring to  FIG. 2 , an organic light-emitting device  20  has a structure including a first capping layer  210 , the first electrode  110 , the organic layer  150 , and the second electrode  190 , wherein the layers are sequentially stacked in this stated order. Referring to  FIG. 3 , an organic light-emitting device  30  has a structure including the first electrode  110 , the organic layer  150 , the second electrode  190 , and a second capping layer  220 , wherein the layers are sequentially stacked in this stated order. Referring to  FIG. 4 , an organic light-emitting device  40  has a structure including the first capping layer  210 , the first electrode  110 , the organic layer  150 , the second electrode  190 , and the second capping layer  220 , wherein the layers are stacked in this stated order. 
     The first electrode  110 , the organic layer  150 , and the second electrode  190  illustrated in  FIGS. 2 to 4  may be substantially the same as those illustrated in  FIG. 1 . 
     In the organic light-emitting devices  20  and  40 , light emitted from the emission layer in the organic layer  150  may pass through the first electrode  110  (which may be a semi-transmissive electrode or a transmissive electrode) and through the first capping layer  210  to the outside. In the organic light-emitting devices  30  and  40 , light emitted from the emission layer in the organic layer  150  may pass through the second electrode  190  (which may be a semi-transmissive electrode or a transmissive electrode) and through the second capping layer  220  to the outside. 
     The first capping layer  210  and the second capping layer  220  may improve the external luminescence efficiency based on the principle of constructive interference. 
     The first capping layer  210  and the second capping layer  220  may each independently be a capping layer including an organic material, an inorganic capping layer including an inorganic material, or a composite capping layer including an organic material and an inorganic material. 
     At least one of 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, porphyrin derivatives, phthalocyanine derivatives, naphthalocyanine derivatives, alkali metal complexes, and alkaline earth metal complexes. The carbocyclic compound, the heterocyclic compound, and the amine group-containing compound may optionally be substituted with a substituent containing at least one element selected from O, N, S, Se, Si, F, Cl, Br, and I. In some embodiments, at least one of the first capping layer  210  and the second capping layer  220  may each independently include an amine-based compound. 
     In one or more embodiments, at least one of the first capping layer  210  and the second capping layer  220  may each independently include a compound represented by Formula 201 or a compound represented by  202 . 
     In one or more embodiments, at least one of the first capping layer  210  and the second capping layer  220  may each independently include a compound selected from Compounds HT 28  to HT 33  and Compound CP1 to CP5, but embodiments are not limited thereto: 
     
       
         
         
             
             
         
       
     
     Hereinbefore, the organic light-emitting device has been described with reference to  FIGS. 1 to 4 , but embodiments are not limited thereto. 
     The layers constituting the hole transport region, the emission layer, and the layers constituting the electron transport region may each be formed in a specific or predetermined region by using one or more suitable methods (such as vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) deposition, ink-jet printing, laser printing, and/or laser-induced thermal imaging). 
     When the layers constituting the hole transport region, the emission layer, and the layers constituting the electron transport region are each formed by vacuum deposition, the vacuum deposition may be performed at a deposition temperature of about 100° C. to about 500° C. at a vacuum degree of about 10 −8  torr to about 10 −3  torr, and at a deposition rate of about 0.01 Angstroms per second (Å/sec) to about 100 Å/sec, depending on the material to be included in each layer and the structure of each layer to be formed. 
     When the layers constituting the hole transport region, the emission layer, and the layers constituting the electron transport region are each formed by spin coating, the spin coating may be performed at a coating rate of about 2,000 revolutions per minute (rpm) to about 5,000 rpm and at a heat treatment temperature of about 80° C. to about 200° C., depending on the material to be included in each layer and the structure of each layer to be formed. 
     General Definitions of Substituents 
     The term “C 1 -C 60  alkyl group” as used herein refers to a linear or branched aliphatic hydrocarbon monovalent group having 1 to 60 carbon atoms. Non-limiting examples thereof include a methyl group, an ethyl group, a propyl group, an iso-butyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an iso-amyl group, and a hexyl group. The term “C 1 -C 60  alkylene group” as used herein refers to a divalent group having substantially the same structure as the C 1 -C 60  alkyl group. 
     The term “C 2 -C 60  alkenyl group” as used herein refers to a hydrocarbon group having at least one carbon-carbon double bond in the middle or at the terminus of the C 2 -C 60  alkyl group. Non-limiting 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 substantially the same structure as the C 2 -C 60  alkenyl group. 
     The term “C 2 -C 60  alkynyl group” as used herein refers to a 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. Non-limiting 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 substantially the same structure as the C 2 -C 60  alkynyl group. 
     The term “C 1 -C 60  alkoxy group” as used herein refers to a monovalent group represented by -OA 101  (wherein A 101  is a C 1 -C 60  alkyl group). Non-limiting examples thereof include a methoxy group, an ethoxy group, and an isopropoxy group. 
     The term “C 3 -C 10  cycloalkyl group” as used herein refers to a monovalent saturated hydrocarbon monocyclic group including 3 to 10 carbon atoms. Non-limiting 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 substantially the same structure as the C 3 -C 10  cycloalkyl group. 
     The term “C 1 -C 10  heterocycloalkyl group” as used herein refers to a monovalent monocyclic group including at least one heteroatom selected from N, O, Si, P, and S as a ring-forming atom and 1 to 10 carbon atoms. Non-limiting 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 substantially the same structure as the C 1 -C 10  heterocycloalkyl group. 
     The term “C 3 -C 10  cycloalkenyl group” as used herein refers to a monovalent monocyclic group that has 3 to 10 carbon atoms and at least one double bond in its ring, and is not aromatic. Non-limiting 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 substantially the same structure as the C 3 -C 10  cycloalkenyl group. 
     The term “C 1 -C 10  heterocycloalkenyl group” as used herein refers to a monovalent monocyclic group including at least one heteroatom selected from N, O, Si, P, and S as a ring-forming atom, 1 to 10 carbon atoms, and at least one double bond in its ring. Non-limiting examples of the C 1 -C 10  heterocycloalkenyl group include a 4,5-dihydro-1,2,3,4-oxatriazolylgroup, a 2,3-dihydrofuranyl group, and a 2,3-dihydrothiophenyl group. The term “C 1 -C 10  heterocycloalkylene group” as used herein refers to a divalent group having substantially the same structure as the C 1 -C 10  heterocycloalkyl group. 
     The term “C 6 -C 60  aryl group” as used herein refers to a monovalent group having a carbocyclic aromatic system having 6 to 6 carbon atoms. The term “C 6 -C 60  arylene group” as used herein refers to a divalent group having a carbocyclic aromatic system having 6 to 60 carbon atoms. Non-limiting examples of the C 6 -C 60  aryl group 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 independently include two or more rings, the respective rings may be fused. 
     The term “C 1 -C 60  heteroaryl group” as used herein refers to a monovalent group having a heterocyclic aromatic system having at least one heteroatom selected from N, O, Si, P, and S as a ring-forming atom and 1 to 60 carbon atoms. The term “C 1 -C 60  heteroarylene group” as used herein refers to a divalent group having a heterocyclic aromatic system having at least one heteroatom selected from N, O, Si, P, and S as a ring-forming atom and 1 to 60 carbon atoms. Non-limiting examples of the C 1 -C 60  heteroaryl group 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 independently include two or more rings, the respective rings may be fused. 
     The term “C 6 -C 60  aryloxy group” as used herein refers to a monovalent group represented by -OA 102  (wherein A 102  is a C 6 -C 60  aryl group). The term “C 6 -C 60  arylthio group” as used herein refers to a monovalent group represented by -SA 103  (wherein 
     A 103  is a C 6 -C 60  aryl group). 
     The term “monovalent non-aromatic condensed polycyclic group” as used herein refers to a monovalent group that has two or more rings condensed and only carbon atoms as ring forming atoms (e.g., 8 to 60 carbon atoms), wherein the entire molecular structure is non-aromatic. Non-limiting examples of the monovalent non-aromatic condensed polycyclic group include a fluorenyl group. The term “divalent non-aromatic condensed polycyclic group” as used herein refers to a divalent group having substantially the same structure as the monovalent non-aromatic condensed polycyclic group. 
     The term “monovalent non-aromatic condensed heteropolycyclic group” as used herein refers to a monovalent group that has two or more condensed rings and at least one heteroatom selected from N, O, Si, P, and S, in addition to carbon atoms (e.g., 1 to 60 carbon atoms), as a ring-forming atom, wherein the entire molecular structure is non-aromatic. Non-limiting examples of the monovalent non-aromatic condensed heteropolycyclic group include a carbazolyl group. The term “divalent non-aromatic condensed heteropolycyclic group” as used herein refers to a divalent group having substantially the same structure as the monovalent non-aromatic condensed heteropolycyclic group. 
     The term “C 5 -C 60  carbocyclic group” as used herein refers to a monocyclic or polycyclic group having 5 to 60 carbon atoms only as ring-forming atoms. The C 5 -C 60  carbocyclic group may be an aromatic carbocyclic group or a non-aromatic carbocyclic group. The term “C 5 -C 60  carbocyclic group” as used herein refers to a ring (e.g., a benzene group), a monovalent group (e.g., a phenyl group), or a divalent group (e.g., a phenylene group). Also, depending on the number of substituents connected to the C 5 -C 60  carbocyclic group, the C 5 -C 60  carbocyclic group may be a trivalent group or a quadrivalent group. 
     The term “C 1 -C 60  heterocyclic group” as used herein refers to a group having substantially the same structure as the C 5 -C 60  carbocyclic group, except that at least one heteroatom selected from N, O, Si, P, and S is used as a ring-forming atom, in addition to carbon atoms (e.g., 1 to 60 carbon atoms). 
     In the present specification, the substituents 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 6 -C 60  aryloxy group, the substituted C 6 -C 60  arylthio group, the substituted C 1 -C 60  heteroaryl group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group may each independently be selected from: 
     deuterium (-D), —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, and a C 1 -C 60  alkoxy group; a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, and a 
     C 1 -C 60  alkoxy group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 11 )(Q 12 )(Q 13 ), —N(Q 11 )(Q 12 ), —B(Q 11 )(Q 12 ), —C(═O)(Q 11 ), —S(═O) 2 (Q 11 ), and —P(═O)(Q 11 )(Q 12 ); 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group; 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 21 )(Q 22 )(Q 23 ), —N(Q 21 )(Q 22 ), —B(Q 21 )(Q 22 ), —C(═O)(Q 21 ), —S(═O) 2 (Q 21 ), and —P(═O)(Q 21 )(Q 22 ); and 
     —Si(Q 31 )(Q 32 )(Q 33 ), —N(Q 31 )(Q 32 ), —B(Q 31 )(Q 32 ), —C(═O)(Q 31 ), —S(═O) 2 (Q 31 ), and —P(═O)(Q 31 )(Q 32 ), 
     wherein Q 11  to Q 13,  Q 21  to Q 23,  and Q 31  to Q 33  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group; a 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. 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. The “biphenyl group” may be envisioned as 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. The “terphenyl group” may be envisioned as a substituted phenyl group having a C 6 -C 60  aryl group substituted with a C 6 -C 60  aryl group as a substituent. 
     The symbols * and *′ as used herein, unless defined otherwise, refer to a binding site to an adjacent atom in a corresponding formula. 
     Hereinafter, compounds and an organic light-emitting device according to one or more embodiments will be described in more detail with reference to Synthesis Examples and Examples. The wording “B was used instead of A” used in describing Synthesis Examples refers to an identical number of molar equivalents of B being used in place of A. 
     SYNTHESIS EXAMPLES 
     Synthesis Example 1: Synthesis of Compound A1 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     1) Synthesis of Intermediate C2 
     Compound Cl (1 eq.) as a starting material was dissolved in tetrahydrofuran (THF) and cooled to a temperature of −78° C. Then, n-BuLi (2.5 M in hexane) (2.2 eq.) was slowly added thereto. After stirring for 4 hours, SiCl 4  (2 eq.) was added thereto, followed by raising the temperature and stirring for 12 hours. The reaction mixture was subjected to extraction using dichloromethane and distilled water. The organic layer was washed three times using distilled water, dried using magnesium sulfate, filtered, and concentrated under reduced pressure. The concentrate was purified through column chromatography to obtain Intermediate C2 at a yield of 70%. 
     2) Synthesis of Intermediate C3 
     Bromobenzene (2.2 eq.) was dissolved in THF and cooled to a temperature of −78° C. Then, n-BuLi (2.5 M in hexane) was added thereto, followed by stirring for 4 hours. Intermediate C2 (1 eq.) was dissolved in THF, and the solution was added to the reaction mixture, followed by stirring at room temperature for 12 hours. The reaction mixture was subjected to extraction using dichloromethane and distilled water. The organic layer was washed three times using distilled water, dried using magnesium sulfate, filtered, and concentrated under reduced pressure. The concentrate was purified through column chromatography to obtain Intermediate C3 at a yield of 60%. 
     3) Synthesis of Intermediate C4 
     Intermediate C3 (1 eq.) was suspended in HBr (0.5 M) and acetic acid (0.5 M), followed by stirring at a temperature of 120° C. for 6 hours. The reaction mixture was neutralized using 0.3 M NaOH aqueous solution, then the resulting solid was filtered. The filtered solid was subjected to extraction using dichloromethane and distilled water. The organic layer was washed three times using distilled water, dried using magnesium sulfate, filtered, and concentrated under reduced pressure. The concentrate was purified through column chromatography to obtain Intermediate C4 at a yield of 75%. 
     4) Synthesis of Intermediate C5 
     Intermediate C4 (1 eq.), 1-(3-bromophenyl)-1H-imidazole (1.0 eq.), copper iodide (0.1 eq.), potassium phosphate (2.0 eq.), and L-proline (0.1 eq.) were suspended in 100 milliliters (mL) of a dimethyl formamide solvent, followed by raising the temperature to 120° C. and stirring for 12 hours. The reaction mixture was subjected to extraction using dichloromethane and distilled water. The organic layer was washed three times using distilled water, dried using magnesium sulfate, filtered, and concentrated under reduced pressure. The concentrate was purified through column chromatography to obtain Intermediate C5 at a yield of 70%. 
     5) Synthesis of Intermediate C6 
     Intermediate C5 was dissolved in acetone, and iodomethane (2 eq.) was added thereto, followed by stirring at room temperature for 24 hours. Once the reaction was complete, the solvent was removed therefrom under reduced pressure. Then, the concentrate was purified through column chromatography to obtain Intermediate C6 at a yield of 80%. 
     6) Synthesis of Intermediate C7 
     Intermediate C6 (1 eq.) was dissolved in acetone, and NH4PF6 (1 eq.) was added thereto, followed by stirring at room temperature for 24 hours. Once the reaction was complete, the solvent was removed therefrom under a reduced pressure. Then, the concentrate was purified through column chromatography to obtain Intermediate C7 ata yield of 80%. 
     7) Synthesis of Compound A1 
     Intermediate C7 (1 eq.), sodium acetate (3.0 eq), and dichloro(1,5-cyclooctadiene)platinum (II) (1.1 eq.) were suspended in a 1,4-dioxane solvent. The temperature of the reaction mixture was raised to 120° C., followed by stirring for 12 hours. Once the reaction was complete, the solvent was removed therefrom under reduced pressure. Through column purification, Compound A1 was obtained at a yield of 40%. 
     Synthesis Example 2: Synthesis of Compound A2 
     Compound A2 was obtained in substantially the same manner as in Synthesis Example 1, except that 1-(3-bromophenyl)-1H-benzo[d]imidazole was used instead of 1-(3-bromophenyl)-1H-imidazole. 
     Synthesis Example 3: Synthesis of Compound A3 
     Compound A3 was obtained in substantially the same manner as in Synthesis Example 1, except that iodomethane-d3 was used instead of iodomethane. 
     Synthesis Example 4: Synthesis of Compound A4 
     Compound A4 was obtained in substantially the same manner as in Synthesis Example 1, except that 1-(3-bromophenyl)-1H-benzo[d]imidazole was used instead of 1-(3-bromophenyl)-1H-imidazole, and iodomethane-d3 was used instead of iodomethane. 
     Synthesis Example 5: Synthesis of Compound A5 
     Compound A5 was obtained in substantially the same manner as in Synthesis Example 1, except that iodobenzene was used instead of iodomethane. 
     Synthesis Example 6: Synthesis of Compound A6 
     Compound A6 was obtained in substantially the same manner as in Synthesis Example 1, except that 1-(3-bromophenyl)-1H-benzo[d]imidazole was used instead of 1-(3-bromophenyl)-1H-imidazole, and iodobenzene was used instead of iodomethane. 
     Synthesis Example 7: Synthesis of Compound A7 
     Compound A7 was obtained in substantially the same manner as in Synthesis Example 1, except that 1-iodo-4-methylbenzene was used instead of iodomethane. 
     Synthesis Example 8: Synthesis of Compound A8 
     Compound A8 was obtained in substantially the same manner as in Synthesis Example 1, except that 1-(3-bromophenyl)-1H-benzo[d]imidazole was used instead of 1-(3-bromophenyl)-1H-imidazole, and 1-iodo-4-methylbenzene was used instead of iodomethane. 
     Synthesis Example 9: Synthesis of Compound A9 
     Compound A9 was obtained in substantially the same manner as in Synthesis Example 2, except that 2-iodo-1,3,5-trimethylbenzene was used instead of iodomethane. 
     Synthesis Example 10: Synthesis of Compound A10 
     Compound A10 was obtained in substantially the same manner as in Synthesis Example 1, except that 1-(3-bromophenyl)-1H-benzo[d]imidazole was used instead of 1-(3-bromophenyl)-1H-imidazole, and 2-iodo-1,3,5-trimethylbenzene was used instead of iodomethane. 
     Synthesis Example 11: Synthesis of Compound 11 
     Compound A11 was obtained in substantially the same manner as in Synthesis Example 2, except that 2-iodo-1,1′-biphenyl was used instead of iodomethane. 
     Synthesis Example 12: Synthesis of Compound A12 
     Compound A12 was obtained in substantially the same manner as in Synthesis Example 1, except that 1-(3-bromophenyl)-1H-benzo[d]imidazole was used instead of 1-(3-bromophenyl)-1H-imidazole, and 2-iodo-1,1′-biphenyl was used instead of iodomethane. 
     Synthesis Example 13: Synthesis of Compound A13 
     Compound A13 was obtained in substantially the same manner as in Synthesis Example 2, except that 2-iodo-4′-methyl-1,1′-biphenyl was used instead of iodomethane. 
     Synthesis Example 14: Synthesis of Compound A14 
     Compound A14 was obtained in substantially the same manner as in Synthesis Example 1, except that 1-(3-bromophenyl)-1H-benzo[d]imidazole was used instead of 1-(3-bromophenyl)-1H-imidazole, and 2-iodo-4′-methyl-1,1′-biphenyl was used instead of iodomethane. 
     Synthesis Example 15: Synthesis of Compound A15 
     Compound A15 was obtained in substantially the same manner as in Synthesis Example 1, except that 4′-(tert-butyl)-2-iodo-1,1′-biphenyl was used instead of iodomethane. 
     Synthesis Example 16: Synthesis of Compound A16 
     Compound A16 was obtained in substantially the same manner as in Synthesis Example 1, except that 1-(3-bromophenyl)-1H-benzo[d]imidazole was used instead of 1-(3-bromophenyl)-1H-imidazole, and 4′-(tert-butyl)-2-iodo-1,1′-biphenyl was used instead of iodomethane. 
     Synthesis Example 17: Synthesis of Compound A17 
     Compound A17 was obtained in substantially the same manner as in Synthesis Example 2, except that 2′-iodo-1,1′:3′,1″-terphenyl was used instead of iodomethane. 
     Synthesis Example 18: Synthesis of Compound A18 
     Compound A18 was obtained in substantially the same manner as in Synthesis Example 1, except that 1-(3-bromophenyl)-1H-benzo[d]imidazole was used instead of 1-(3-bromophenyl)-1H-imidazole, and 2′-iodo-1,1′:3′,1″-terphenyl was used instead of iodomethane. 
     Synthesis Example 19: Synthesis of Compound A19 
     Compound A19 was obtained in substantially the same manner as in Synthesis Example 4,4, except that 4,4″-di-tert-butyl-2′-iodo-1,1′:3′,1″-terphenyl was used instead of iodomethane. 
     Synthesis Example 20: Synthesis of Compound A20 
     Compound A20 was obtained in substantially the same manner as in Synthesis Example 1, except that 1-(3-bromophenyl)-1H-benzo[d]imidazole was used instead of 1-(3-bromophenyl)-1H-imidazole, and 4,4″-di-tert-butyl-2′-iodo-1,1′:3′,1″-terphenyl was used instead of iodomethane. 
     Synthesis Example 21: Synthesis of Compound A21 
     Compound A21 was obtained in substantially the same manner as in 
     Synthesis Example 2, except that 2′-iodo-1,1′:3′,1″-terphenyl-2,2″,3,3″,4,4″,5,5″,6,6″-d10 was used instead of iodomethane. 
     Synthesis Example 22: Synthesis of Compound A22 
     Compound A22 was obtained in substantially the same manner as in Synthesis Example 1, except that 1-(3-bromophenyl)-1H-benzo[d]imidazole was used instead of 1-(3-bromophenyl)-1H-imidazole, and 2′-iodo-1,1′:3′,1″-terphenyl-2,2″,3,3″,4,4″,5,5″,6,6″-d10 was used instead of iodomethane. 
     Synthesis Example 23: Synthesis of Compound A23 
     Compound A23 was obtained in substantially the same manner as in Synthesis Example 2, except that 2′-iodo-4,4″-bis(methyl-d3)-1,1′:3′,1″-terphenyl-2,2″,3,3″,5,5″,6,6″-d8 was used instead of iodomethane. 
     Synthesis Example 24: Synthesis of Compound A24 
     Compound A24 was obtained in substantially the same manner as in Synthesis Example 1, except that 1-(3-bromophenyl)-1H-benzo[d]imidazole was used instead of 1-(3-bromophenyl)-1H-imidazole, and 2′-iodo-4,4″-bis(methyl-d3)-1,1′:3′,1″-terphenyl-2,2″,3,3″,5,5″,6,6″-d8 was used instead of iodomethane. 
     Synthesis Examples 25 to 48: Synthesis of Compounds B1 to B24 
     Compounds B1 to B24 were respectively obtained in substantially the same manner as in Synthesis Examples 1 to 24, except that germanium (IV) chloride was used instead of silicon tetrachloride. 
     The compounds synthesized in the Synthesis Examples were identified by  1 H nuclear magnetic resonance (NMR) and mass spectroscopy/fast atom bombardment (MS/FAB). The results thereof are shown in Table 1. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Compound 
                   
                 MS/FAB 
               
            
           
           
               
               
               
               
            
               
                 No. 
                   1 H NMR (CDCl 3 , 400 MHz) 
                 found 
                 calc. 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 A1 
                 8.66 (d, 1H), 7.61 (d, 1H),  
                 700.1258 
                 700.7360 
               
               
                   
                 7.00~7.60 (m, 16H), 6.49 (d, 1H),  
                   
                   
               
               
                   
                 6.46 (d, 1H), 3.67 (s, 3H) 
                   
                   
               
               
                 A2 
                 8.66 (d, 1H), 7.75 (d, 1H), 7.61  
                 750.1415 
                 750.7960 
               
               
                   
                 (d, 1H), 7.00~7.60 (m, 16H), 6.90  
                   
                   
               
               
                   
                 (d, 1H), 6.71 (m, 1H), 6.66 (d, 1H),  
                   
                   
               
               
                   
                 3.36 (s, 3H) 
                   
                   
               
               
                 A4 
                 8.66 (d, 1H), 7.75 (d, 1H), 7.61  
                 753.1603 
                 753.8143 
               
               
                   
                 (d, 1H), 7.00~7.60 (m, 16H), 6.90  
                   
                   
               
               
                   
                 (d, 1H), 6.64~6.72 (m, 2H) 
                   
                   
               
               
                 A22 
                 8.66 (d, 1H), 8.20 (d, 2H), 7.75  
                 974.2825 
                 975.1240 
               
               
                   
                 (d, 1H), 7.61 (d, 1H), 7.0~7.60  
                   
                   
               
               
                   
                 (m, 16H), 6.85~7.00 (m, 3H),  
                   
                   
               
               
                   
                 6.66 (d, 1H) 
                   
                   
               
               
                 B4 
                 8.33 (d, 1H), 7.25~7.05 (m, 14H),  
                 799.1045 
                 798.3593 
               
               
                   
                 7.00~7.25 (m, 3H), 6.80~7.00  
                   
                   
               
               
                   
                 (m, 2H), 6.60~6.80(m, 2H) 
                   
                   
               
               
                 B22 
                 8.33 (d, 1H), 8.20 (d, 2H), 7.48  
                 1020.2267 
                 1019.6690 
               
               
                   
                 (d, 1H), 7.00~7.40 (m, 16H),  
                   
                   
               
               
                   
                 6.85~7.00 (m, 4H), 6.66 (d, 1H) 
               
               
                   
               
            
           
         
       
     
     Methods of synthesizing compounds other than compounds shown in Table 1 may be easily understood to those skilled in the art by referring to the synthesis pathways and raw materials described above. 
     Evaluation Example 1 
     i) A percentage of a triplet metal-to-ligand charge transfer state ( 3 MLCT), ii) a maximum emission wavelength (λ max   sim ), iii) an energy level of a triplet metal-centered state ( 3 MC), and iv) a bond dissociation energy between an N atom in a pyridine ligand moiety and a Pt metal center of the compounds synthesized in Synthesis Examples were measured using quantum simulation according to density functional theory (DFT) at a degree of B3LYP. The results thereof are shown in Table 2. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                   
                   
                 Bond  
               
               
                   
                   3 MLCT 
                 λ max   sim   
                 λ max   exp   
                   3 MC 
                 dissociation 
               
               
                   
                 (%) 
                 (nm) 
                 (nm) 
                 (eV) 
                 energy (eV) 
               
               
                   
               
             
            
               
                 Compound A1 
                 13.0 
                 455.13 
                 453 
                 0.82 
                 3.00 
               
               
                 Compound A2 
                 15.1 
                 457.25 
                 455 
                 0.85 
                 3.01 
               
               
                 Compound A4 
                 15.3 
                 453.23 
                 455 
                 0.82 
                 3.50 
               
               
                 Compound A22 
                 18.2 
                 454.25 
                 452 
                 0.98 
                 3.50 
               
               
                 Compound B4 
                 15.0 
                 459.35 
                 457 
                 0.82 
                 3.01 
               
               
                 Compound B22 
                 17.5 
                 456.56 
                 454 
                 0.90 
                 3.50 
               
               
                 Compound A 
                 10.3 
                 460.68 
                 458 
                 0.83 
                 3.00 
               
               
                 Compound B 
                 11.0 
                 465.61 
                 463 
                 0.70 
                 2.90 
               
               
                 Compound C 
                  9.8 
                 467.24 
                 465 
                 0.67 
                 2.88 
               
               
                 Compound D 
                  11.34 
                 465.39 
                 452 
                 0.78 
                 3.03 
               
               
                   
               
               
                 
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                   
                     
                     
                         
                         
                     
                   
                 
               
            
           
         
       
     
     Referring to the results of Table 2, it was found that each of organometallic compound had a high  3 MC energy value and a short maximum emission wavelength compared to Compounds A to D. That is, the organometallic compound according to embodiments of the present disclosure is suitable for blue light emission, may have a decreased probability of transition from a  3 MCLT state to a  3 MC state (a non-luminescent state), and thus, stability in an excited state may be excellent. Accordingly, the organic light-emitting device including the organometallic compound may have improved efficiency and lifespan. 
     EXAMPLES 
     Example 1 
     As for a substrate and an anode, a Corning 15 Ω/cm 2  (1,200 Å) ITO glass substrate was cut to a size of 50 mm×50 mm×0.7 mm, sonicated using isopropyl alcohol and deionized water for 5 minutes each, and cleaned by exposure to ultraviolet rays with ozone. Then, the glass substrate was mounted on a vacuum deposition device. 
     2-TNATA was vacuum-deposited on the ITO anode formed on the glass substrate to form a hole injection layer having a thickness of about 600 Å, and NPB was then deposited on the hole injection layer to form a hole transport layer having a thickness of about 300 Å. 
     Bis(4-(9H-carbazol-9-yl)phenyl)diphenylsilane (BCPDS) and (4-(1-(4-(diphenylamino)phenyl)cyclohexyl)phenyl)diphenyl-phosphine oxide (POPCPA) (as co-hosts at a weight ratio of 1:1) and a dopant, Compound A1, were co-deposited on the hole transport layer at a host:dopant weight ratio of 90:10 to form an emission layer having a thickness of 300 Å. 
     Diphenyl(4-(triphenylsilyl)phenyl)-phosphine oxide (TSPO1) was deposited on the emission layer to form a hole blocking layer having a thickness of 50 Å, Alq 3  was deposited on the hole blocking layer to form an electron transport layer having a thickness of 300 Å, LiF was deposited on the electron transport layer to form an electron injection layer having a thickness of 10 Å, and Al was vacuum-deposited on the electron injection layer having a thickness of 3,000 Å, thereby completing the manufacture of an organic light-emitting device. 
     
       
         
         
             
             
         
       
     
     Examples 2 to 6 and Comparative Examples 1 and 4 
     Organic light-emitting devices were manufactured in substantially the same manner as in Example 1, except that the compounds shown in Table 1 were used instead of Compound Al as a dopant in the formation of an emission layer. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Evaluation Example 2 
     The driving voltage, current density, luminance, luminescence efficiency, emission color, and maximum emission wavelength of the organic light-emitting devices manufactured according to Examples 1 to 6 and Comparative Examples 1 to 4 were measured by using Keithley SMU 236 and a luminance meter PR 650.  The results thereof are shown in Table 3. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Dopant  
                   
                   
                   
                   
                   
                   
               
               
                   
                 in the 
                 Driving 
                 Current 
                   
                   
                   
                 Emission 
               
               
                   
                 emission 
                 voltage 
                 density 
                 Luminance 
                 Efficiency 
                 Emission  
                 wavelength 
               
               
                   
                 layer 
                 (V) 
                 (mA/cm 2 ) 
                 (cd/m 2 ) 
                 (cd/A) 
                 color 
                 (nm) 
               
               
                   
               
             
            
               
                 Example 1 
                 Compound 
                 5.20 
                 50 
                 5.20 
                 20.50 
                 Blue 
                 453 
               
               
                   
                 A1 
                   
                   
                   
                   
                   
                   
               
               
                 Example 2 
                 Compound 
                 4.88 
                 50 
                 4.88 
                 21.20 
                 Blue 
                 455 
               
               
                   
                 A2 
                   
                   
                   
                   
                   
                   
               
               
                 Example 3 
                 Compound 
                 4.85 
                 50 
                 4.87 
                 23.00 
                 Blue 
                 455 
               
               
                   
                 A4 
                   
                   
                   
                   
                   
                   
               
               
                 Example 4 
                 Compound 
                 4.52 
                 50 
                 4.52 
                 25.01 
                 Blue 
                 452 
               
               
                   
                 A22 
                   
                   
                   
                   
                   
                   
               
               
                 Example 5 
                 Compound 
                 4.90 
                 50 
                 4.90 
                 18.99 
                 Blue 
                 457 
               
               
                   
                 B4 
                   
                   
                   
                   
                   
                   
               
               
                 Example 6 
                 Compound 
                 4.60 
                 50 
                 4.85 
                 18.50 
                 Blue 
                 454 
               
               
                   
                 B22 
                   
                   
                   
                   
                   
                   
               
               
                 Comparative 
                 Compound A 
                 5.42 
                 50 
                 5.42 
                 15.50 
                 Blue 
                 458 
               
               
                 Example 1 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Comparative 
                 Compound B 
                 5.50 
                 50 
                 5.50 
                 13.20 
                 Blue 
                 463 
               
               
                 Example 2 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Comparative 
                 Compound C 
                 5.80 
                 50 
                 5.50 
                 13.00 
                 Blue 
                 465 
               
               
                 Example 3 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Comparative 
                 Compound D 
                 5.30 
                 50 
                 5.30 
                 18.00 
                 Blue 
                 452 
               
               
                 Example 4 
               
               
                   
               
            
           
         
       
     
     Referring to the results of Table 3, it was found that each of the organic light-emitting devices of Examples 1 to 4 had a low driving voltage, excellent luminance, and excellent luminescence efficiency. In addition, each of the organic light-emitting device of Examples 1 to 4 were found to have a low driving voltage and excellent luminescence efficiency, as compared with the organic light-emitting device of Comparative Examples 1 to 4. 
     As apparent from the foregoing description, an organic light-emitting device including the organometallic compound may have a low driving voltage, excellent luminance, excellent efficiency, high colorimetric purity, and/or long lifespan. 
     As used herein, the terms “substantially,” “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by those of ordinary skill in the art. 
     Any numerical range recited herein is intended to include all sub-ranges of the same numerical precision subsumed within the recited range. For example, a range of “1.0 to 10.0” is intended to include all subranges between (and including) the recited minimum value of 1.0 and the recited maximum value of 10.0, that is, having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as, for example, 2.4 to 7.6. Any maximum numerical limitation recited herein is intended to include all lower numerical limitations subsumed therein and any minimum numerical limitation recited in this specification is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicant reserves the right to amend this specification, including the claims, to expressly recite any sub-range subsumed within the ranges expressly recited herein. 
     It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. While one or more embodiments have been described with reference to the 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 and equivalents thereof.