Patent Publication Number: US-2021167296-A1

Title: Organic compound containing heterocyclic ring and having low lumo properties, and organic electroluminescent device using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2019-0159363, filed on Dec. 3, 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 a heterocyclic compound and an organic light-emitting device including the same. 
     2. Description of the Related Art 
     Organic light-emitting devices (OLEDs) are self-emitting devices that have advantages such as wide viewing angles, excellent contrast, quick response times, excellent luminance, and/or excellent driving voltage characteristics, and can produce full-color images. 
     An organic light-emitting device may have a structure in which a first electrode, a hole transport region, an emission layer, an electron transport region, and a second electrode are sequentially positioned in this order on a substrate. Holes injected from the first electrode move to the emission layer via the hole transport region, while electrons injected from the second electrode move to the emission layer via the electron transport region. Carriers, such as the holes and electrons, may then recombine in the emission layer to generate excitons. When the excitons transition from an excited state to a ground state, light is emitted. 
     SUMMARY 
     One or more aspects of embodiments of the present disclosure are directed toward a novel heterocyclic 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. 
     According to one or more embodiments, provided is a heterocyclic compound represented by Formula 1: 
     
       
         
         
             
             
         
       
     
     wherein, in Formulae 1 to 3, 
     A 1  to A 3  may each independently be selected from a group represented by Formula 2, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 1 )(Q 2 )(Q 3 ), —N(Q 1 )(Q 2 ), —B(Q 1 )(Q 2 ), —P(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O) 2 (Q 1 ), and —P(═O)(Q 1 )(Q 2 ), 
     at least one of A 1  to A 3  is a group represented by Formula 2, 
     X 1  may be N or C(R 31 ), X 2  may be N or C(R 32 ), X 3  may be N or C(R 33 ), 
     at least one of X 1  to X 3  is N, 
     L 1 , L 2 , L 10 , and L 20  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, 
     a1, a2, a10, and a20 may each independently be an integer selected from 0 to 5, 
     L 3  may be a group represented by Formula 3, 
     a3 may be an integer selected from 0 to 5, 
     Ar 1  and Ar 2  may each independently be selected from deuterium, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 1 )(Q 2 )(Q 3 ), —N(Q 1 )(Q 2 ), —B(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O) 2 (Q 1 ), and —P(═O)(Q 1 )(Q 2 ), 
     R 10 , R 20 , and R 31  to R 33  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 1 )(Q 2 )(Q 3 ), —N(Q 1 )(Q 2 ), —B(Q 1 )(Q 2 ), —P(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O) 2 (Q 1 ), and —P(═O)(Q 1 )(Q 2 ), 
     optionally at least two neighboring groups selected from R 10 , R 20 , and R 31  to 
     R 33  are linked to one another to form a substituted or unsubstituted C 5 -C 60  carbocyclic group or a substituted or unsubstituted C 1 -C 60  heterocyclic group, 
     b10 is an integer selected from 1 to 5, 
     b20 is an integer selected from 1 to 4, 
     *, *′, and *″ are each a binding site to a neighboring atom, 
     at least one substituent of the substituted C 5 -C 60  carbocyclic group, substituted C 1 -C 60  heterocyclic group, substituted C 3 -C 10  cycloalkylene group, substituted C 1 -C 10  heterocycloalkylene group, substituted C 3 -C 10  cycloalkenylene group, a substituted C 1 -C 10  heterocycloalkenylene group, substituted C 6 -C 60  arylene group, substituted C 1 -C 60  heteroarylene group, substituted divalent non-aromatic condensed polycyclic group, substituted divalent non-aromatic condensed heteropolycyclic group, substituted C 1 -C 60  alkyl group, substituted C 2 -C 60  alkenyl group, substituted C 2 -C 60  alkynyl group, substituted C 1 -C 60  alkoxy group, substituted C 3 -C 10  cycloalkyl group, substituted C 1 -C 10  heterocycloalkyl group, substituted C 3 -C 10  cycloalkenyl group, substituted C 1 -C 10  heterocycloalkenyl group, substituted C 6 -C 60  aryl group, substituted C 6 -C 60  aryloxy group, substituted C 6 -C 60  arylthio group, substituted C 1 -C 60  heteroaryl group, substituted monovalent non-aromatic condensed polycyclic group, substituted monovalent non-aromatic condensed heteropolycyclic group, and substituted ring 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 ), —P(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, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group; 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl 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, a biphenyl group, a terphenyl group, —Si(Q 21 )(Q 22 )(Q 23 ), —N(Q 21 )(Q 22 ), —B(Q 21 )(Q 22 ), —P(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 ), —P(Q 31 )(Q 32 ), —C(═O)(Q 31 ), —S(═O) 2 (Q 31 ), and —P(═O)(Q 31 )(Q 32 ), and 
     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  aryl group substituted with a C 1 -C 60  alkyl group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group. 
     According to one or more embodiments, provided is an organic light-emitting device including: a first electrode; a second electrode facing to the first electrode; an organic layer between the first electrode and the second electrode and including an emission layer; and the above-described at least one heterocyclic compound. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings in which: 
         FIGS. 1-4  are schematic views respectively illustrating structures of organic light-emitting devices according to embodiments of the present disclosure. 
     
    
    
     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. 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. 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.” 
     Reference will now be made in more detail to embodiments, examples of which are illustrated in the accompanying drawings. Effects, features, and a method of achieving the present disclosure should become obvious by referring to example embodiments of the present disclosure with reference to the attached drawings. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. 
     Hereinafter, example embodiments of the present disclosure will be described in more detail with reference to the attached drawings. In the following description and drawings, constituent elements which are substantially the same, or correspond constituent elements are assigned the same or like reference numerals, and overlapping descriptions thereof will not be provided. 
     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. 
     As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “have,” and “having” are intended to indicate the presence of features, elements, and/or components stated in the specification, but not to preclude the presence or addition of one or more other features, elements, and/or components. 
     In the following embodiments, when an element such as a layer, a film, a region or a component is referred to as being “on” another layer or region, it can be “directly on” the other layer or region (without any intervening films, regions, or components therebetween), or intervening films, regions, or components may also be present. 
     In the drawings, for convenience of explanation, the size of components or elements may be exaggerated or reduced. In other words, because the size and thickness of components in the drawings are arbitrarily illustrated for convenience of explanation, the present concept is not limited to the following embodiments. 
     According to an embodiment of the present disclosure, provided is a heterocyclic compound represented by Formula 1. 
     
       
         
         
             
             
         
       
     
     In Formula 1, A 1  to A 3  may each independently be selected from a group represented by Formula 2, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 1 )(Q 2 )(Q 3 ), —N(Q 1 )(Q 2 ), —B(Q 1 )(Q 2 ), —P(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O) 2 (Q 1 ), and —P(═O)(Q 1 )(Q 2 ), and 
     at least one of A 1  to A 3  may be a group represented by Formula 2, 
     In one or more embodiments, one of A 1  to A 3  may be a group represented by Formula 2, and 
     the others may each independently be selected from a substituted or unsubstituted C 1 -C 60  alkyl 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. 
     In one or more embodiments, one of A 1  to A 3  may be a group represented by Formula 2, and 
     the others may each independently be selected from: 
     a methyl group, an ethyl group, a propyl group, an isobutyl group, a sec-butyl group, a ter-butyl group, a pentyl group, an iso-amyl group, and a hexyl group; and 
     a methyl group, an ethyl group, a propyl group, an isobutyl group, a sec-butyl group, a ter-butyl group, a pentyl group, an iso-amyl group, and a hexyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, a C 1 -C 60  alkyl group, a C 6 -C 60  aryl group, and a C 2 -C 60  heteroaryl group; 
     a phenyl group, a naphthyl group, a pyridyl group, a pyrimidyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a biphenyl group, and a terphenyl group; and 
     a phenyl group, a naphthyl group, a pyridyl group, a pyrimidyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a biphenyl group, and a terphenyl group, each substituted with at least one selected from deuterium, —F, —CI, — 
     Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, a C 1 -C 60  alkyl group, a C 6 -C 60  aryl group, and a C 2 -C 60  heteroaryl group. 
     In Formula 2, X 1  may be N or C(R 31 ), X 2  may be N or C(R 32 ), X 3  may be N or C(R 33 ), and at least one of X 1  to X 3  may be N. 
     In one or more embodiments, one of X 1  to X 3  may be N. 
     In one or more embodiments, two of X 1  to X 3  may be N. 
     In one or more embodiments, X 1  to X 3  may each be N. 
     In Formulae 1 to 3, L 1 , L 2 , L 10  and L 20  may each independently 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, 
     In one or more embodiments, L 1 , L 2 , L 10  and L 20  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 spiro-fluorene-benzofluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenalenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a naphthacenylene group, a picenylene group, a perylenylene group, a pentaphenylene group, a hexacenylene group, a pentacenylene group, a rubicenylene group, a coronenylene group, an ovalenylene group, a pyrrolylene group, a thiophenylene group, a furanylene group, an imidazolylene group, a pyrazolylene group, a thiazolylene group, an isothiazolylene group, an oxazolylene group, an isoxazolylene group, a pyridinylene group, a pyrazinylene group, a pyrimidinylene group, a pyridazinylene group, an isoindolylene group, an indolylene group, an indazolylene group, a purinylene group, a quinolinylene group, an isoquinolinylene group, a benzoquinolinylene group, a phthalazinylene group, a naphthyridinylene group, a quinoxalinylene group, a quinazolinylene group, a cinnolinylene group, a carbazolylene group, a phenanthridinylene group, an acridinylene group, a phenanthrolinylene group, a phenazinylene group, a benzimidazolylene group, a benzofuranylene group, a benzothiophenylene group, an isobenzothiazolylene group, a benzoxazolylene group, an isobenzoxazolylene group, a triazolylene group, a tetrazolylene group, an oxadiazolylene group, a triazinylene group, a dibenzofuranylene group, a dibenzothiophenylene group, a dibenzosilolylene group, a benzocarbazolylene group, a dibenzocarbazolylene group, a thiadiazolylene group, an imidazopyridinylene group, and an imidazopyrimidinylene 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 spiro-fluorene-benzofluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenalenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a naphthacenylene group, a picenylene group, a perylenylene group, a pentaphenylene group, a hexacenylene group, a pentacenylene group, a rubicenylene group, a coronenylene group, an ovalenylene group, a pyrrolylene group, a thiophenylene group, a furanylene group, an imidazolylene group, a pyrazolylene group, a thiazolylene group, an isothiazolylene group, an oxazolylene group, an isoxazolylene group, a pyridinylene group, a pyrazinylene group, a pyrimidinylene group, a pyridazinylene group, an isoindolylene group, an indolylene group, an indazolylene group, a purinylene group, a quinolinylene group, an isoquinolinylene group, a benzoquinolinylene group, a phthalazinylene group, a naphthyridinylene group, a quinoxalinylene group, a quinazolinylene group, a cinnolinylene group, a carbazolylene group, a phenanthridinylene group, an acridinylene group, a phenanthrolinylene group, a phenazinylene group, a benzimidazolylene group, a benzofuranylene group, a benzothiophenylene group, an isobenzothiazolylene group, a benzoxazolylene group, an isobenzoxazolylene group, a triazolylene group, a tetrazolylene group, an oxadiazolylene group, a triazinylene group, a dibenzofuranylene group, a dibenzothiophenylene group, a dibenzosilolylene group, a benzocarbazolylene group, a dibenzocarbazolylene group, a thiadiazolylene group, an imidazopyridinylene group, and an imidazopyrimidinylene 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 pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolylene group, a benzocarbazolyl group, a dibenzocarbazolyl group, a thiadiazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, —Si(Q 31 )(Q 32 )(Q 33 ), —N(Q 31 )(Q 32 ), —B(Q 31 )(Q 32 ), —C(═O)(Q 31 ), —S(═O) 2 (Q 31 ), and —P(═O)(Q 31 )(Q 32 ), and 
     Q 31  to Q 33  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a phenyl group substituted with a C 1 -C 10  alkyl group, a biphenyl group, a terphenyl group, a naphthyl group, a pyridinyl group, a pyrimidyl group, a quinolinyl group, and an isoquinolinyl group. 
     In one or more embodiments, L 1 , L 2 , L 10  and L 20  may each independently be a group represented by one of Formulae 3-1 to 3-99. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 3-1 to 3-99, 
     Y 1  may be O, S, C(Z 3 )(Z 4 ), N(Z 5 ), or Si(Z 6 )(Z 7 ), 
     Z 1  to Z 7  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, a silolyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an indolyl group, an isoindolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a 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, a benzofuranyl group, a benzothiophenyl group, a benzosilolyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a carbazolyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, a thiadiazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, a benzonaphthyridinyl group, an azafluorenyl group, an azaspiro-bifluorenyl group, an azacarbazolyl group, an azadibenzofuranyl group, an azadibenzothiophenyl group, an azadibenzosilolyl 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 ), 
     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, a naphthyl group, a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, and a quinazolinyl group; and 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, and a quinazolinyl group, each substituted with at least one selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, and a phenyl group, 
     d2 may be an integer selected from 0 to 2, 
     d3 may be an integer selected from 0 to 3, 
     d4 may be an integer selected from 0 to 4, 
     d5 may be an integer selected from 0 to 5, 
     d6 may be an integer selected from 0 to 6, 
     d8 may be an integer selected from 0 to 8, and 
     * and * 1  may each be a binding site to a neighboring atom. 
     In Formulae 1 to 3, a1, a2, a10, and a20 may each independently be an integer selected from 0 to 5. 
     In Formula 2, L 3  may be a group represented by Formula 3. 
     In one or more embodiments, L 3  may be a group represented by one of 
     Formulae 4-1 to 4-3. 
     
       
         
         
             
             
         
       
     
     In Formulae 4-1 to 4-3, 
     L 20 , a20, R 20 , and b20 may be as defined herein in the specification, and 
     *′ and *″ may each be a binding site to a neighboring atom. 
     In Formula 2, a3 may be an integer selected from 0 to 5. 
     In Formula 2, Ar 1  and Ar 2  may each independently be selected from deuterium, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 1 )(Q 2 )(Q 3 ), —N(Q 1 )(Q 2 ), —B(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O) 2 (Q 1 ), and —P(═O)(Q 1 )(Q 2 ). 
     In one or more embodiments, Ari and Ar 2  may each independently be selected from deuterium, 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, and a substituted or unsubstituted C 1 -C 60  heteroaryl group. 
     In one or more embodiments, Ar 1  and Ar 2  may each independently be selected from deuterium, and a group represented by one selected from Formulae 5-1 to 5-26 and Formulae 6-1 to 6-55: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 5-1 to 5-26 and Formulae 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 triperylenyl 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 selected from 1 to 3, 
     e4 may be an integer selected from 1 to 4, 
     e5 may be an integer selected from 1 to 5, 
     e6 may be an integer selected from 1 to 6, 
     e7 may be an integer selected from 1 to 7, 
     e9 may be an integer selected from 1 to 9, and 
     * may be a binding site to a neighboring atom. 
     In one or more embodiments, Ar 1  and Ar 2  may each independently be selected from: 
     a phenyl group, a naphthyl group, a pyridyl group, a pyrimidyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a biphenyl group, and a terphenyl group; and 
     a phenyl group, a naphthyl group, a pyridyl group, a pyrimidyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a biphenyl group, and a terphenyl group, each substituted with at least one selected from deuterium, —F, —CI, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, a C 1 -C 60  alkyl group, a C 6 -C 60  aryl group, and a C 2 -C 60  heteroaryl group. 
     In Formulae 1 to 3, Rio, R 20 , and R 31  to R 33  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 1 )(Q 2 )(Q 3 ), —N(Q 1 )(Q 2 ), —B(Q 1 )(Q 2 ), —P(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O) 2 (Q 1 ), and —P(═O)(Q 1 )(Q 2 ), where Q 1  to Q 3  are as defined herein. 
     In one or more embodiments, R 10 , R 20 , and R 31  to R 33  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, 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, 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, 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 ), and 
     Q 1  to Q 3 , and Q 31  to Q 33  are each independently 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, a naphthyl group, a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, and a quinazolinyl group; and 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, and a quinazolinyl group, each substituted with at least one selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, and a phenyl group. 
     In one or more embodiments, R 10  and R 20  may each independently be selected from: 
     a methyl group, an ethyl group, a propyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an iso-amyl group, and a hexyl group; and 
     a methyl group, an ethyl group, a propyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an iso-amyl group, and a hexyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, a C 1 -C 60  alkyl group, a C 6 -C 60  aryl group, and a C 2 -C 60  heteroaryl group; 
     a phenyl group, a naphthyl group, a pyridyl group, a pyrimidyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a biphenyl group, and a terphenyl group; and 
     a phenyl group, a naphthyl group, a pyridyl group, a pyrimidyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, a biphenyl group, and a terphenyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, a C 1 -C 60  alkyl group, a C 6 -C 60  aryl group, and a C 2 -C 60  heteroaryl group. 
     In Formulae 1 to 3, optionally at least two neighboring groups selected from R 10 , R 20 , and R 31  to R 33  may be linked to one another to form a substituted or unsubstituted C 5 -C 60  carbocyclic group, or a substituted or unsubstituted C 1 -C 60  heterocyclic group, 
     In one or more embodiments, optionally at least two neighboring groups among R 10 , R 20 , and R 31  to R 33  may be linked to one another to form a benzene, a naphthalene, a fluorene, a spiro-fluorene, an indene, a pyrrole, a thiophene, a furan, an imidazole, a pyrazole, a thiazole, an isothiazole, an oxazole, an isoxazole, a pyridine, a pyrazine, a pyrimidine, a pyridazine, a quinoline, an isoquinoline, a benzoquinoline, a quinoxaline, a quinazoline, a carbazole, a benzimidazole, a benzofuran, a benzothiophene, an isobenzothiophene, a benzoxazole, an isobenzoxazole, a triazole, an oxadiazole, a triazine, a dibenzofuran or a dibenzothiophene; or 
     a benzene, a naphthalene, a fluorene, a spiro-fluorene, an indene, a pyrrole, a thiophene, a furan, an imidazole, a pyrazole, a thiazole, an isothiazole, an oxazole, an isoxazole, a pyridine, a pyrazine, a pyrimidine, a pyridazine, a quinoline, an isoquinoline, a benzoquinoline, a quinoxaline, a quinazoline, a carbazole, a benzimidazole, a benzofuran, a benzothiophene, an isobenzothiophene, a benzoxazole, an isobenzoxazole, a triazole, an oxadiazole, a triazine, a dibenzofuran, or a dibenzothiophene, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a cyano group, and a C 1 -C 60  alkyl group. 
     In Formulae 1 to 3, b10 may be an integer selected from 1 to 5. 
     In Formulae 1 to 3, b20 may bean integer selected from 1 to 4. 
     In one or more embodiments, a10 may be 0, and R 10  may be hydrogen. For example, -[(L 10 ) a10 -R 10 ] b10  may represent hydrogen. 
     In one or more embodiments, a20 may be 0, and R 20  may be hydrogen. For example, -[(L 20 ) a20 -R 20 ] b20  may represent hydrogen. 
     In one or more embodiments, a10 and a20 may each be 0, and R 10  and R 20  may each be hydrogen. For example, -[(L 10 ) a10 -R 10 ] b10  and -[(L 20 ) a20 -R 20 ] b20  may each represent hydrogen. 
     In Formulae 1 to 3, *, *′ and *″ may each be a binding site to a neighboring atom. 
     At least one of the substituents of the substituted C 5 -C 60  carbocyclic group, substituted C 1 -C 60  heterocyclic group, substituted C 3 -C 10  cycloalkylene group, substituted C 1 -C 10  heterocycloalkylene group, substituted C 3 -C 10  cycloalkenylene group, substituted C 1 -C 10  heterocycloalkenylene group, substituted C 6 -C 60  arylene group, substituted C 1 -C 60  heteroarylene group, substituted divalent non-aromatic condensed polycyclic group, substituted divalent non-aromatic condensed heteropolycyclic group, substituted C 1 -C 60  alkyl group, substituted C 2 -C 60  alkenyl group, substituted C 2 -C 60  alkynyl group, substituted C 1 -C 60  alkoxy group, substituted 
     C 3 -C 10  cycloalkyl group, substituted C 1 -C 10  heterocycloalkyl group, substituted C 3 -C 10  cycloalkenyl group, substituted C 1 -C 10  heterocycloalkenyl group, substituted C 6 -C 60  aryl group, substituted C 6 -C 60  aryloxy group, substituted C 6 -C 60  arylthio group, substituted C 1 -C 60  heteroaryl group, substituted monovalent non-aromatic condensed polycyclic group, substituted monovalent non-aromatic condensed heteropolycyclic group; and substituted ring is 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, —C 1 , —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 ), —P(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, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group; 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl 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, a biphenyl group, a terphenyl group, —Si(Q 21 )(Q 22 )(Q 23 ), —N(Q 21 )(Q 22 ), —B(Q 21 )(Q 22 ), —P(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 ), —P(Q 31 )(Q 32 ), —C(═O)(Q 31 ), —S(═O) 2 (Q 31 ), and —P(═O)(Q 31 )(Q 32 ), and 
     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  aryl group substituted with a C 1 -C 60  alkyl group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group. 
     In one or more embodiments, the heterocyclic compound may be a compound represented by one of Formulae 11-1 to 11-3. 
     
       
         
         
             
             
         
       
     
     In Formulae 11-1 to 11-3, 
     X 1  to X 3 , L 1  to L 3 , a1 to a3, A 1  to A 3 , Ari, and Are may be as defined herein in the specification, 
     R 11  to R 15  may each be defined the same as R 10  is defined in the specification. 
     In one or more embodiments, the heterocyclic compound may be a compound represented by one of Formulae 12-1 to 12-12. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 12-1 to 12-12, 
     X 1  to X 3 , Li, L 2 , A 1  to A 3 , Ar 1 , and Ar 2  may be as defined herein in the specification 
     L 31  to L 33  may each be defined the same as L 3  herein in the specification, 
     Ru to R 15  may each be defined the same as R 10  herein in the specification. 
     In one or more embodiments, the heterocyclic compound may be selected from Compounds 1 to 1272 as follows. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The heterocyclic compound represented by Formula 1 may have a structure in which A 1 , A 2 , and A 3  positions of a phenanthroline core are substituted. The A 1 , A 2 , and A 3  positions correspond to 2-, 4-, and 9-positions of phenanthroline. 
     
       
         
         
             
             
         
       
     
     The A 1 , A 2 , and A 3  positions are electrophilic sites among nine substitutable positions of phenanthroline. Accordingly, when the A 1 , A 2 , and A 3  positions of the heterocyclic compound according to one or more embodiments are substituted with an alkyl group, an aryl group, a heteroaryl group, and/or the like, electrical stability and thermal stability may be increased. Accordingly, when manufacturing a device, the stability of materials may be increased, and a reduction in lifetime characteristics caused due to the deterioration of materials, such as thermal denaturation, may be prevented or reduced. Accordingly, it is expected that the heterocyclic compound represented by Formula 1 has a long lifespan. 
     In addition, in the heterocyclic compound represented by Formula 1, at least one of A 1 , A 2 , and A 3 , which is a group represented by Formula 2, may include a π electron-depleted nitrogen-containing group. The group represented by Formula 2 may be electrochemically stable and have excellent (or suitable) electron transport characteristics, due to the linkage of phenanthroline (having excellent characteristics as an electron withdrawing group (EWG)) and a nitrogen-containing hetero-ring by a linking group. The phenanthroline has a low lowest unoccupied molecular orbital (LUMO) energy level, and may lower an electron barrier in an organic light-emitting device to facilitate the flow of electrons. Due to the additional bonding of a nitrogen-containing hetero-ring (for example, a triazine) to the phenanthroline, electron mobility may be increased, thus improving electron transport characteristics. Accordingly, due to such structure, the heterocyclic compound represented by Formula 1 may have excellent (or suitable) electron transport capability, and may increase the mobility of electrons, thus preventing or reducing a reduction in efficiency under low current conditions and controlling the charge balance to be suitable under high-current conditions, so that lifetime and efficiency may be increased. 
     Therefore, an electronic device, for example, an organic light-emitting device, using the heterocyclic compound represented by Formula 1, may have a low driving voltage and excellent emission efficiency and lifetime characteristics. 
     A synthesis method of the heterocyclic compound represented by Formula 1 may be understood by a person of ordinary skill in the art with reference to the examples to be described below. 
     At least one heterocyclic compound represented by Formula 1 may be used between a pair of electrodes in an organic light-emitting device. For example, the heterocyclic compound may be included in an electron transport region. In other embodiments, the heterocyclic compound represented by Formula 1 may be used as a material of a capping layer on the outside of a pair of electrodes of an organic light-emitting device. 
     According to one or more embodiments, there is provided an organic light-emitting device including: a first electrode; a second electrode facing to the first electrode; an organic layer between the first electrode and the second electrode and including an emission layer; and at least one heterocyclic compound represented by Formula 1 as described above. 
     In one or more embodiments, the at least one heterocyclic compound may be included in the organic layer. 
     As used herein, the expression that the “(organic layer) may include at least one heterocyclic compound” may be construed as meaning that the “(organic layer) may include one heterocyclic compound corresponding to Formula 1, or at least two different heterocyclic compounds corresponding to Formula 1.” 
     For example, the organic layer may include only Compound 1 as the heterocyclic compound. In this embodiment, Compound 1 may be in the emission layer of the organic light-emitting device. In some embodiments, the organic layer may include Compound 1 and Compound 2 as heterocyclic compounds. In this embodiment, Compound 1 and Compound 2 may be in the same layer (for example, Compound 1 and Compound 2 may both be in the emission layer) or in different layers (for example, Compound 1 may be in the emission layer, and Compound 2 may be in the electron transport layer). 
     In one or more embodiments, the first electrode of the organic light-emitting device may be an anode, 
     the second electrode of the organic light-emitting device may be a cathode, 
     the organic layer of the organic light-emitting device may further include a hole transport region between the first electrode and the emission layer, and an electron transport region between the emission layer and the second electrode, 
     the hole transport region may include at least one selected from a hole injection layer, a hole transport layer, a buffer layer, an emission auxiliary layer, and an electron blocking layer, 
     the electron transport region may include at least one selected from a hole blocking layer, an electron transport layer, and an electron injection layer. 
     In one or more embodiments, the electron transport region may include the heterocyclic compound. 
     For example, the electron transport region may include the electron transport layer and the electron injection layer, and at least one selected from the electron transport layer and the electron injection layer may include the heterocyclic compound. 
     In one or more embodiments, at least one layer selected from 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 any combination thereof. 
     In one or more embodiments, the emission layer may include a host and a dopant. 
     In one or more embodiments, the hole transport region may include a p-dopant, and a LUMO level of the p-dopant may be −3.5 eV or less. 
     Electronic Apparatus 
     According to one or more embodiments, there is provided an electronic apparatus including: a substrate; and an organic light-emitting device on the substrate. The organic light-emitting device is as described above herein. 
     In one or more embodiments, the electric apparatus may include a color conversion layer located in at least one traveling direction of light emitted from the organic light-emitting device including quantum dots. 
     Quantum Dots 
     The emission layer included in the organic light-emitting device according to one or more embodiment may include a quantum dot material. 
     In some embodiments, the color conversion layer included in the electronic apparatus according to one or more embodiments may include a quantum dot material. 
     The quantum dots, which are particles having a crystalline structure of several to tens of nanometers in size, may include (e.g., may consist of) several hundreds or several thousands of atoms. 
     Due to having a very small size, the quantum dots may have a quantum confinement effect, which refers to the phenomenon that a band gap of an object is increased when the object has a small size of nanometers. Accordingly, when the quantum dots are irradiated with light of a wavelength having an energy level greater than the bandgap of the quantum dots, the quantum dots may absorb the light to transit to an excited state. The quantum dots may fall to a ground state while emitting light of a specific wavelength. At this time, the wavelength of the emitted light may have a value corresponding to the bandgap. 
     The core of the quantum dots may include a Group II-VI compound, a Group III-VI compound, a Group III-V compound, a Group IV-VI compound, a Group IV element or compound, a Group compound, or a combination thereof. 
     The Group II-VI compound may be selected from the group consisting of: binary compounds selected from the group consisting of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, and mixtures thereof; a ternary compound selected from the group consisting of CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, and mixtures thereof; and quaternary compounds selected from the group consisting of CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, and mixtures thereof. 
     The Group III-VI compound may include: a binary compound such as In 2 S 3  and/or In 2 Se 3 ; a ternary compound such as InGaS 3  and/or InGaSe 3 ; or any combination thereof. 
     The Group III-V compound may include: a binary compound selected from the group consisting of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, and mixtures thereof; a ternary compound selected from the group consisting of GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AINP, AINAs, AINSb, AIPAs, AIPSb, InGaP, InAIP, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, and mixtures thereof; and a quaternary compound selected from the group consisting of GaAlNAs, GaAlNSb, GaAIPAs, GaAIPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAINP, InAINAs, InAINSb, InAIPAs, InAIPSb, and mixtures thereof. The Group III-V compound may further include a Group II element (for example, InZnP). 
     The Group IV-VI compound may be selected from the group consisting of: binary compounds selected from the group consisting of SnS, SnSe, SnTe, PbS, PbSe, PbTe, and mixtures thereof; ternary compounds selected from the group consisting of SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, and mixtures thereof; and quaternary compounds selected from the group consisting of SnPbSSe, SnPbSeTe, SnPbSTe, and mixtures thereof. The Group IV element may be selected from the group consisting of Si, Ge, and a mixture thereof. The Group IV compound may be a binary compound selected from the group consisting of SiC, SiGe, and a mixture thereof. 
     The Group compound may include: a ternary compound such as AgInS, AgInS 2 , CuInS, CuInS 2 , CuGaO 2 , AgGaO 2 , and/or AgAlO 2 ; or any combination thereof. 
     The binary compound, ternary compound, and/or quaternary compound may be present in a particle at a uniform concentration, or may be present in the same particle in different states with partially different concentration distributions. The quantum dots may have a core/shell structure in which one quantum dot surrounds another quantum dot. The interface between the core and shell may have a concentration gradient in which the concentration of atoms present in the shell gradually decreases toward the core. 
     In some embodiments, the quantum dots may have a core-shell structure having a core including nanocrystals as described above, and a shell surrounding the core. The shell of the quantum dots may serve as a protective layer for preventing or reducing chemical denaturation of the core to maintain semiconductor characteristics, and/or a charging layer for imparting electrophoretic properties to the quantum dots. The shell may be a single layer or a multilayer. The interface between the core and shell may have a concentration gradient in which the concentration of atoms present in the shell gradually decreases toward the core. The shell of the quantum dots may include, for example, an oxide of a metal, an oxide of a non-metal, a semiconductor compound, or a combination thereof. 
     For example, the oxide of a metal or the oxide of a non-metal may be a binary compound such as SiO 2 , Al 2 O 3 , TiO 2 , ZnO, MnO, Mn 2 O 3 , Mn 3 O 4 , CuO, FeO, Fe 2 O 3 , Fe 3 O 4 , CoO, Co 3 O 4 , and/or NiO; or a ternary compound such as MgAl 2 O 4 , CoFe 2 O 4 , NiFe 2 O 4 , and/or CoMn 2 O 4 . However, embodiments are not limited thereto. 
     The semiconductor compound may be, for example, CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnSeS, ZnTeS, GaAs, GaP, GaSb, HgS, HgSe, HgTe, InAs, InP, InGaP, InSb, AlAs, AlP, or AlSb. However, embodiments are not limited thereto. 
     The quantum dot may have a full width of half maximum (FWHM) of emission wavelength spectrum of about 45 nm or less, for example, about 40 nm or less, for example, about 30 nm or less. When the FWHM is within these ranges, color purity and color reproducibility may be improved. In addition, light emitted through such quantum dots may move in a forward direction, thus increasing a light viewing angle. 
     The shape of the quantum dots is not specifically limited and may be any suitable shape used in the art. For example, the quantum dots as spherical, pyramidal multi-arm, and/or cubic nanoparticles, and/or as nanotubes, nanowires, nanofibers, and/or nanoplate particles may be used. 
     According to the particle size of the quantum dots, color of emitted light may be controlled. Accordingly, the quantum dots may emit light of a variety of colors, for example, blue, red, and green. 
     The term “organic layer” used herein may refer to a single layer and/or a plurality of layers between the first electrode and the second electrode of the organic light-emitting device. The material included in the “organic layer” is not limited to an organic material. 
     Description of FIG.  1   
       FIG. 1  is a schematic cross-sectional view of an organic light-emitting device  10  according to an example embodiment. The organic light-emitting device  10  may include a first electrode  110 , an organic layer  150 , and a second electrode  190 . 
     Hereinafter, a structure of the organic light-emitting device  10  according to an embodiment and a method of manufacturing the organic light-emitting device according to an embodiment will be described with reference to  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 (or suitable) mechanical strength, thermal stability, transparency, surface smoothness, ease of handling, and/or water resistance. 
     The first electrode  110  may be formed by providing, onto the substrate, a material for forming the first electrode  110 , for example, by deposition or sputtering. When the first electrode  110  is an anode, the material for forming the first electrode  110  may be selected from materials having a high-work function to facilitate hole injection. 
     The first electrode  110  may be a reflective electrode, a semi-transmissive electrode, or a transmissive electrode. When the first electrode  110  is a transmissive electrode, a material for forming 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, a material for forming the first electrode  110  may be selected from magnesium (Mg), silver (Ag), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), and any combinations thereof, but embodiments 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, the first electrode  110  may have a triple-layered structure of ITO/Ag/ITO. However, embodiments are not limited thereto. 
     Organic Layer  150   
     The organic layer  150  may be located 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 of Organic Layer  150   
     The hole transport region may have i) a single-layered structure consisting of a single layer consisting of a single material, ii) a single-layered structure consisting of a single layer including 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 consisting of a single layer including a plurality of different materials, or a multi-layered structure of, for example, a hole injection layer/hole transport layer, a hole injection layer/hole transport layer/emission auxiliary layer, a hole injection layer/emission auxiliary layer, a hole transport layer/emission auxiliary layer, or a hole injection layer/hole transport layer/electron blocking layer, wherein the layers of each structure are sequentially stacked on the first electrode  110  in the 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. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     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 selected from 0 to 3, 
     xa5 may be an integer selected from 1 to 10, 
     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 linked via a single bond, a dimethyl-methylene group, and/or a diphenyl-methylene group, and R 203  and R 204  may optionally be linked via a single bond, a dimethyl-methylene group, and/or a diphenyl-methylene group. 
     In one or more embodiments, in Formulae 201 and 202, 
     L 201  to L 205  may each independently be selected from: 
     a phenylene group, a pentalenylene group, an indenylene group, a naphthylene group, an azulenylene group, a heptalenylene group, an indacenylene group, an acenaphthylene group, a fluorenylene group, a spiro-bifluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenalenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a naphthacenylene group, a picenylene group, a perylenylene group, a pentaphenylene group, a hexacenylene group, a pentacenylene group, a rubicenylene group, a coronenylene group, an ovalenylene group, a thiophenylene group, a furanylene group, a carbazolylene group, an indolylene group, an isoindolylene group, a benzofuranylene group, a benzothiophenylene group, a dibenzofuranylene group, a dibenzothiophenylene group, a benzocarbazolylene group, a dibenzocarbazolylene group, a dibenzosilolylene group, and a pyridinylene group; and 
     a phenylene group, a pentalenylene group, an indenylene group, a naphthylene group, an azulenylene group, a heptalenylene group, an indacenylene group, an acenaphthylene group, a fluorenylene group, a spiro-bifluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenalenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a naphthacenylene group, a picenylene group, a perylenylene group, a pentaphenylene group, a hexacenylene group, a pentacenylene group, a rubicenylene group, a coronenylene group, an ovalenylene group, a thiophenylene group, a furanylene group, a carbazolylene group, an indolylene group, an isoindolylene group, a benzofuranylene group, a benzothiophenylene group, a dibenzofuranylene group, a dibenzothiophenylene group, a benzocarbazolylene group, a dibenzocarbazolylene group, a dibenzosilolylene group, and a pyridinylene group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a phenyl group substituted with a C 1 -C 10  alkyl group, a phenyl group substituted with —F, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a thiophenyl group, a furanyl group, a carbazolyl group, an indolyl group, an isoindolyl group, a benzofuranyl group, a benzothiophenyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, a dibenzosilolyl group, a pyridinyl group, —Si(Q 31 )(Q 32 )(Q 33 ), and —N(Q 31 )(Q 32 ), and 
     Q 31  to Q 33  are each independently selected from a C 1 -C 10  alkyl group, a C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group. 
     In some embodiments, xa1 to xa4 may each independently be 0, 1, or 2. 
     In some embodiments, xa5 may be 1, 2, 3, or 4. 
     In some 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 substitute with a C 1 -C 10  alkyl group, a phenyl group substituted with —F, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a thiophenyl group, a furanyl group, a carbazolyl group, an indolyl group, an isoindolyl group, a benzofuranyl group, a benzothiophenyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, a dibenzosilolyl group, a pyridinyl group, —Si(Q 31 )(Q 32 )(Q 33 ), and —N(Q 31 )(Q 32 ), and 
     Q 31  to Q 33  may be as defined herein in the specification. 
     In some embodiments, in Formula 201, at least one of R 201  to R 203  may each independently be selected from: 
     a fluorenyl group, a spiro-bifluorenyl group, a carbazolyl group, a dibenzofuranyl group, and a dibenzothiophenyl group; and 
     a fluorenyl group, a spiro-bifluorenyl group, a carbazolyl group, a dibenzofuranyl group, and a dibenzothiophenyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a phenyl group substituted with a C 1 -C 10  alkyl group, a phenyl group substituted with —F, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a carbazolyl group, a dibenzofuranyl group, and a dibenzothiophenyl group. However, embodiments are not limited thereto. 
     In some embodiments, in Formula 202, i) R 201  and R 202  may be linked via a single bond, and/or ii) R 203  and R 204  may be linked via a single bond. 
     In some 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. However, embodiments are not limited thereto. 
     The compound represented by Formula 201 may be represented by Formula 201A. 
     
       
         
         
             
             
         
       
     
     For example, 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 be as defined herein in the specification, 
     R 211  and R 212  may be defined the same as R 203  herein in the specification, 
     R 213  to R 217  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a biphenyl group, a terphenyl group, a phenyl group substituted with a C 1 -C 10  alkyl group, a phenyl group substituted with —F, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a thiophenyl group, a furanyl group, a carbazolyl group, an indolyl group, an isoindolyl group, a benzofuranyl group, a benzothiophenyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, a dibenzosilolyl group, and a pyridinyl group. 
     The hole transport region may include at least one compound selected from Compounds HT1 to HT39, but embodiments are not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The thickness of the hole transport region may be in a range of 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 of a hole injection layer or a hole transport layer, the thickness of the hole injection layer may be in a range of 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 in a range of 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 (or suitable) 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 from the emission layer. The electron blocking layer may reduce or eliminate the flow of electrons from the electron transport region. The emission auxiliary layer and the electron blocking layer may each independently include any of the suitable materials mentioned above. 
     p-Dopant 
     The hole transport region may include a charge generating material as well as 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 be, for example, a p-dopant. 
     In one or more embodiments, a lowest unoccupied molecular orbital (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. 
     For example, the p-dopant may be 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. 
     
       
         
         
             
             
         
       
     
     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 of 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 —CI, a C 1 -C 20  alkyl group substituted with —Br, and a C 1 -C 20  alkyl group substituted with —I. 
     Emission Layer in the 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 in which two or more layers selected from a red emission layer, a green emission layer, and a blue emission layer are stacked on one another in direct contact with or separated from each other. In one or more embodiments, the emission layer may have a structure in which two or more materials selected from a red light-emitting material, a green light-emitting material, and a blue light-emitting material may be mixed in a single layer, and thus emit white light. 
     The emission layer may include a host and a dopant. The dopant may include at least one of a phosphorescent dopant or a fluorescent dopant. 
     The amount of the dopant in the emission layer may be, for example, in a range of about 0.01 parts to about 15 parts by weight with respect to 100 parts by weight of the host, but embodiments are not limited thereto. 
     The thickness of the emission layer may be in a range of 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
 
     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 selected from 0 to 5, 
     R 301  may be selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 301 )(Q 302 )(Q 303 ), —N(Q 301 )(Q 302 ), —B(Q 301 )(Q 302 ), —C(═O)(Q 301 ), —S(═O) 2 (Q 301 ), and —P(═O)(Q 301 )(Q 302 ), 
     xb21 may be an integer selected from 1 to 5, and 
     Q 301  to Q 303  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group, but embodiments 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 ), and 
     Q 31  to Q 33  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group, but embodiments are not limited thereto. 
     When xb11 in Formula 301 is 2 or greater, at least two Ar 301 (s) may be linked to one another via a single bond. 
     In one or more embodiments, the compound represented by Formula 301 may be represented by Formula 301-1 or Formula 301-2: 
     
       
         
         
             
             
         
       
     
     In Formulae 301-1 and 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 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 be as defined herein, 
     L 302  to L 304  may be defined the same as L 301  is defined herein, 
     xb2 to xb4 may each be defined the same as xb1 is defined herein, and 
     R 302  to R 304  may each independently defined the same as R 301  is defined herein. 
     For example, 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 ), and 
     Q 31  to Q 33  may be as defined herein. 
     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 ), and 
     Q 31  to Q 33  may be as defined herein. 
     In some embodiments, the host may include an alkaline earth metal complex. For example, the host may be selected from a beryllium (Be) complex (for example, Compound H55), a magnesium (Mg) complex, and 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. However, embodiments are not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Phosphorescent Dopant Included in Emission Layer of the Organic Layer  150   
     The phosphorescent dopant may include an organometallic complex represented by Formula 401. 
     
       
         
         
             
             
         
       
     
     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 the ligands represented by Formula 402, xc1 may be 1, 2, or 3, and when xc1 is 2 or greater, two or more L 401 (s) may be the same or different, 
     L 402  may be an organic ligand, xc2 may be an integer selected from 0 to 4, and when xc2 is 2 or greater, two or more L 402 (s) may be the same or different, 
     X 401  to X 404  may each independently be nitrogen or carbon, 
     X 401  and X 403  may be linked to each other via a single bond or a double bond, and X 402  and X 404  may be linked 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(Q 411 )=*′, wherein Q 411  and Q 412  may each independently be hydrogen, deuterium, 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, 0, 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 heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, and 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)(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 C 6 -C 20  aryl group, and a C 1 -C 20  heteroaryl group, 
     xc11 and xc12 may each independently be an integer selected from 0 to 10, 
     In Formula 402, * and *′ are each a binding site to M in Formula 401. 
     In one or more 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 some embodiments, in Formula 402, i) X 401  may be nitrogen, and X 402  may be carbon, or ii) X 401  and X 402  may both be nitrogen. 
     In some embodiments, 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 adamantanyl group, a norbornanyl group, and a norbornenyl group; 
     a cyclopentyl group, a cyclohexyl group, an adamantanyl 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 adamantanyl 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 adamantanyl 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 ), and 
     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. 
     However, embodiments are not limited thereto. 
     In some embodiments, in Formula 401, when xc1 is 2 or greater, two A 401 (s) of two or more L 401 (s) may optionally be linked via X 407 , which is a linking group, or two A 402  (s) may optionally be linked via X 408 , which is a linking group (see e.g., Compounds PD1 to PD4 and PD7). X 407  and X 408  may each independently be a single bond, *—O—*′, *—S—*′, *—C(═O)—*′, *—N(Q 413 )—*′, *—C(Q 413 )(Q 414 )—′ or *—C(Q 413 )═C(Q 414 )—*′ (wherein Q 413  and Q 414  may each independently be hydrogen, deuterium, 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). However, embodiments are not limited thereto. 
     In Formula 401, L 402  may be any suitable monovalent, divalent, or trivalent organic ligand. For example, L 402  may be selected from a halogen, a diketone (for example, acetylacetonate), carboxylic acid (for example, picolinate), —C(═O), isonitrile, —CN, and phosphorus (for example, phosphine and/or phosphate). However, embodiments are not limited thereto. 
     In other embodiments, the phosphorescent dopant may be selected from Compounds PD1 to PD25. However, embodiments are not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Fluorescent Dopant in Emission Layer 
     The fluorescent dopant may include an arylamine compound or a styrylamine compound. 
     The fluorescent dopant may include a compound represented by Formula 501. 
     
       
         
         
             
             
         
       
     
     In Formula 501, 
     Ar 501  may be a substituted or unsubstituted C 5 -C 60  carbocyclic group, or 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 selected 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 selected from 1 to 6. 
     In one or more embodiments, in Formula 501, Ar 501  may be selected from: 
     a naphthalene group, a heptalene group, a fluorene group, 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, 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, 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, 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 some embodiments, in Formula 501, L 501  to 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, 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, 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 some embodiments, 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 ), and 
     Q 31  to Q 33  may each independently be selected from a C 1 -C 10  alkyl group, a alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl. 
     In some embodiments, in Formula 501, xd4 may be 2. However, embodiments are not limited thereto. 
     For example, the fluorescent dopant may be selected from Compounds FD1 to FD22. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, the fluorescent dopant may be selected from the following compounds (shown below). However, embodiments are not limited thereto. 
     
       
         
         
             
             
         
       
     
     Electron Transport Region of the Organic Layer ( 150 ) 
     The electron transport region may have i) a single-layered structure consisting of a single layer consisting of a single material, ii) a single-layered structure consisting of a single layer including 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. 
     For example, the electron transport region may have an electron transport layer/electron injection layer structure, a hole blocking layer/electron transport layer/electron injection layer structure, an electron control layer/electron transport layer/electron injection layer structure, or a buffer layer/electron transport layer/electron injection layer structure, wherein layers of each structure are sequentially stacked on the emission layer in the 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. 
     Examples of the π electron-depleted nitrogen-containing ring may 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 ] xe21 .  Formula 601
 
     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 an embodiment, 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 it electron-depleted nitrogen-containing ring. 
     In some embodiments, in Formula 601, 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 ), and 
     Q 31  to Q 33  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, and a naphthyl group. 
     When xe11 in Formula 601 is 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 one or more embodiments, a compound represented by Formula 601 may be represented by Formula 601-1. 
     
       
         
         
             
             
         
       
     
     In Formula 601-1, 
     X 614  may be N or C(R 614 ), X 615  may be N or C(R 615 ), 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 understood by referring to the descriptions for L 601  provided herein, 
     xe611 to xe613 may each independently be understood by referring to the descriptions for xe1 provided herein, 
     R 611  to R 613  may each independently be understood by referring to the descriptions for R 601  provided herein, 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 an embodiment, 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, xe1 and xe611 to xe613 in Formulae 601 and 601-1 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 be understood by referring to the descriptions thereof provided herein. 
     The electron transport region may include at least one compound selected from Compounds ET1 to ET36, 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. 
     
       
         
         
             
             
         
       
     
     The thicknesses of the buffer layer, the hole blocking layer, and the electron control layer may each independently be in a range of 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 (or improved) hole blocking characteristics and/or excellent (or improved) electron controlling characteristics may be obtained without a substantial increase in driving voltage. 
     The thickness of the electron transport layer may be in a range of 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 (or improved) 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 the alkaline earth metal complex may independently be selected from a hydroxy quinoline, a hydroxy isoquinoline, a hydroxy benzoquinoline, a hydroxy acridine, a hydroxy phenanthridine, a hydroxy phenyloxazole, a hydroxy phenylthiazole, a hydroxy phenyloxadiazole, a hydroxy phenylthiadiazole, a hydroxy phenylpyridine, a hydroxy phenylbenzimidazole, a hydroxy phenylbenzothiazole, a bipyridine, a phenanthroline, and a 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 consisting of a single layer consisting of a single material, ii) a single-layered structure 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 a combination thereof. 
     The alkali metal may be selected from Li, Na, K, Rb, and Cs. In an embodiment, the alkali metal may be Li, Na, or Cs. In one or more embodiments, the alkali metal may be Li or Cs, but is 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 an alkali metal, an alkaline earth metal, and a 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, KI, and/or RbI). In an embodiment, the alkali metal compound may be selected from LiF, Li 2 O, NaF, LiI, NaI, CsI, KI, and RbI, 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 BaxCa 1-x O (wherein 0&lt;x&lt;1). In an embodiment, 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 an embodiment, the rare earth metal compound may be selected from YbF3, ScF3, TbF3, 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 respectively include ions of the above-described alkali metal, alkaline earth metal, and rare earth metal. The ligands coordinated with the metal ion of the alkali metal complex, the alkaline earth metal complex, and the rare earth metal complex may each independently be selected from a hydroxy quinoline, a hydroxy isoquinoline, a hydroxy benzoquinoline, a hydroxy acridine, a hydroxy phenanthridine, a hydroxy phenyloxazole, a hydroxy phenylthiazole, a hydroxy phenyloxadiazole, a hydroxy phenylthiadiazole, a hydroxy phenylpyridine, a hydroxy phenylbenzimidazole, a hydroxy phenylbenzothiazole, a bipyridine, a phenanthroline, and a cyclopentadiene, but embodiments are not limited thereto. 
     In one or more embodiments, the electron injection layer may include a combination of an alkali metal compound and a rare earth metal compound. For example, the electron injection layer may be formed by co-deposition of Rbl and Yb. For example, the electron injection layer may be formed by co-deposition of KI and Yb. 
     The electron injection layer may include (e.g., may consist of) an alkali metal, an alkaline earth metal, a rare earth metal, an alkali metal compound, an alkaline earth metal compound, a rare earth metal compound, an alkali metal complex, an alkaline earth metal complex, a rare earth metal complex, or a 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 the combination thereof may be homogeneously or non-homogeneously dispersed in a matrix with (e.g., including) the organic material. 
     The thickness of the electron injection layer may be in a range of 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 (or improved) 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 a 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), silver-magnesium (Ag—Mg), ytterbium (Yb), silver-ytterbium (Ag—Yb), 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 first capping layer  210 , the first electrode  110 , the organic layer  150 , and the second electrode  190  structure, wherein the layers are sequentially stacked in this stated order. Referring to  FIG. 3 , an organic light-emitting device  30  has the first electrode  110 , the organic layer  150 , the second electrode  190 , and a second capping layer  220  structure, wherein the layers are sequentially stacked in this stated order. Referring to  FIG. 4 , an organic light-emitting device  40  has the first capping layer  210 , the first electrode  110 , the organic layer  150 , the second electrode  190 , and the second capping layer  220  structure, 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  or the second capping layer  220  may each independently include at least one material selected from carbocyclic compounds, heterocyclic compounds, amine-based compounds, porphine derivatives, phthalocyanine derivatives, naphthalocyanine derivatives, alkali metal complexes, and alkaline earth metal complexes. The carbocyclic compound, the heterocyclic compound, and the amine-based compound may each independently be optionally be substituted with a substituent containing at least one element selected from O, N, S, Se, Si, F, Cl, Br, and I. In an embodiment, 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  or the second capping layer  220  may each independently include a compound represented by Formula 201 or a compound represented by Formula 202. 
     In one or more embodiments, at least one of the first capping layer  210  or the second capping layer  220  may each independently include a compound selected from Compounds HT28 to HT33 and Compounds 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 be formed in a specific 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 formed by vacuum deposition, the vacuum deposition may be performed at a deposition temperature in a range of about 100° C. to about 500° C., at a vacuum degree in a range of about 10 −8  torr to about 10 −3  torr, and at a deposition rate in a range 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 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 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 and/or at either 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 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 and/or at either 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 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 Ani is a C 1 -C 1  alkyl group). Non-limiting examples thereof include a methoxy group, an ethoxy group, and an isopropyloxy group. 
     The term “C 3 -C 10  cycloalkyl group” as used herein refers to a monovalent saturated hydrocarbon monocyclic group 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 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 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 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-oxatriazolyl group, 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 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. 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. The term “C 6 -C 60  arylene group” as used herein refers to a divalent group having the same structure as the C 6 -C 60  aryl 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. 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. The term “C 1 -C 60  heteroarylene group” as used herein refers to a divalent group having a heterocyclic aromatic system having the same structure as the C 1 -C 60  heteroaryl 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 group represented by —OA 102  (wherein A 102  is the C 6 -C 60  aryl group). The term “C 6 -C 60  arylthio group” as used herein refers to a group represented by —SA 103  (wherein A 103  is the 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 to each other 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 may include a 1,2,3,4-tetrahydronaphthalenyl 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 may include a 1,2,3,4-tetrahydroquinolinyl 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 may refer to a benzene ring, a monovalent group (e.g., a phenyl group), or a divalent group (e.g., a phenylene group). In addition, the C 5 -C 60  carbocyclic group may be varied, for example, as a trivalent group or a tetravalent group, according to the number of substituents connected to the C 5 -C 60  carbocyclic group. For example, the “benzene group” may represent a benzene ring, a phenyl group, a phenylene group, or a trivalent or tetravalent group corresponding to these groups. 
     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). 
     As used herein, at least one substituent of the substituted C 5 -C 60  carbocyclic group, the substituted C 1 -C 60  heterocyclic group, the substituted C 3 -C 10  cycloalkylene group, the substituted C 1 -C 10  heterocycloalkylene group, the substituted C 3 -C 10  cycloalkenylene group, the substituted C 1 -C 10  heterocycloalkenylene group, the substituted C 6 -C 60  arylene group, the substituted C 1 -C 60  heteroarylene group, the substituted divalent non-aromatic condensed polycyclic group, the substituted divalent non-aromatic condensed heteropolycyclic group, the substituted C 1 -C 60  alkyl group, the substituted C 2 -C 60  alkenyl group, the substituted C 2 -C 60  alkynyl group, the substituted C 1 -C 60  alkoxy group, the substituted C 3 -C 10  cycloalkyl group, the substituted C 1 -C 10  heterocycloalkyl group, the substituted C 3 -C 10  cycloalkenyl group, the substituted C 1 -C 10  heterocycloalkenyl group, the substituted C 6 -C 60  aryl group, the substituted C 6 -C 60  aryloxy group, the substituted C 6 -C 60  arylthio group, the substituted C 1 -C 60  heteroaryl group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group may be selected from: 
     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 ), and 
     Q 11  to Q 13 , Q 21  to Q 23 , and Q 31  to Q 33  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group. 
     “Ph” used herein represents a phenyl group, “Me” used herein represents a methyl group, “Et” used herein represents an ethyl group, “ter-Bu” or “But” used herein represents a tert-butyl group, “OMe” used herein represents a methoxy group, and “D” may refer to deuterium. 
     The term “biphenyl group” as used herein may refer to a phenyl group substituted with at least one phenyl group. The “biphenyl group” may be described as “a substituted phenyl group” having a “C 6 -C 60  aryl group” as a substituent. 
     The term “terphenyl group” as used herein may refer to a phenyl group substituted with at least two phenyl groups. The “terphenyl group” may be described 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 a neighboring atom in a corresponding formula. 
     Hereinafter, compounds and organic light-emitting devices according to one or more embodiments will be described in more detail with reference to Synthesis Examples and Examples. However, these examples are only for illustrative purposes and are not intended to limit the scope of the one or more embodiments of the present disclosure. The wording “B was used instead of A” used in describing Synthesis Examples may refer to an amount of B used that was identical to an amount of A used in terms of molar equivalents. 
     Synthesis Example 1. Synthesis of Compound 12 
     
       
         
         
             
             
         
       
     
     4-chloro-2,9-dimethyl-1,10-phenanthroline (12.1 g, 50 mmol), (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid (21.2 g, 60 mmol), Cs 2 CO 3  (32.6 g, 100 mmol), X-phos (4.8 g, 10 mmol), Pd(OAc) 2 (0.6 g, 5 mol %), and 1,4-dioxane/H 2 O (400 ml/100 ml) were mixed under nitrogen atmosphere and stirred at 120° C. for 12 hours. 
     After termination of the reaction, extraction was carried out with methylene chloride, and magnesium sulfate (MgSO 4 ) was added thereto and then filtered to obtain an organic layer. After removing the solvent from the obtained organic layer, the resulting product was purified by column chromatography to obtain Compound 12 (17.5 g, Yield: 68%). 
     Mass: [(M+H) + ]: 516 
     Synthesis Example 2. Synthesis of Compound 18 
     
       
         
         
             
             
         
       
     
     Compound 18 (23.3 g, Yield: 72%) was obtained through substantially the same process as in Synthesis Example 1, except that 4-chloro-2,9-diisopropyl-1,10-phenanthroline (14.9 g, 50 mmol) and (3′-(2,6-diphenylpyrimidin-4-yl)-[1,1′-biphenyl]-3-yl)boronic acid (25.7 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 647 
     Synthesis Example 3. Synthesis of Compound 90 
     
       
         
         
             
             
         
       
     
     Compound 90 (21.2 g, Yield: 66%) was obtained through substantially the same process as in Synthesis Example 1, except that (3-(4-phenyl-6-(3-(quinolin-8-yl)phenyl)-1,3,5-triazin-2-yl)phenyl)boronic acid (28.8 g, 60 mmol) was used instead of (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid. 
     Mass: [(M+H) + ]: 643 
     Synthesis Example 4. Synthesis of Compound 126 
     
       
         
         
             
             
         
       
     
     Compound 126 (26.4 g, Yield: 75%) was obtained through substantially the same process as in Synthesis Example 1, except that 4-chloro-9-methyl-2-(naphthalen-1-yl)-1,10-phenanthroline (17.7 g, 50 mmol) and (4′-(4,6-diphenyl-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-4-yl)boronic acid (25.8 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 704 
     Synthesis Example 5. Synthesis of Compound 160 
     
       
         
         
             
             
         
       
     
     Compound 160 (26.8 g, Yield: 70%) was obtained through substantially the same process as in Synthesis Example 1, except that 4-chloro-9-isopropyl-2-phenyl-1,10-phenanthroline (16.6 g, 50 mmol) and (4′-(6-([1,1′-biphenyl]-4-yl)-2-phenylpyrimidin-4-yl)-[1,1′-biphenyl]-3-yl)boronic acid (30.3 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 757 
     Synthesis Example 6. Synthesis of Compound 190 
     
       
         
         
             
             
         
       
     
     Compound 190 (22.9 g, Yield: 65%) was obtained through substantially the same process as in Synthesis Example 1, except that 4-chloro-9-methyl-2-phenyl-1,10-phenanthroline (15.2 g, 50 mmol) and (3-(2-phenyl-6-(3-(quinolin-8-yl)phenyl)pyrimidin-4-yl)phenyl)boronic acid (28.8 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 704 
     Synthesis Example 7. Synthesis of Compound 209 
     
       
         
         
             
             
         
       
     
     Compound 209 (20.4 g, Yield: 66%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-(4-chloro-9-phenyl-1,10-phenanthrolin-2-yl)-2-methylpropan-1-ylium (17.3 g, 50 mmol) and (4-(4,6-diphenylpyridin-2-yl)phenyl)boronic acid (21.1 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 618 
     Synthesis Example 8. Synthesis of Compound 236 
     
       
         
         
             
             
         
       
     
     Compound 236 (22.2 g, Yield: 68%) was obtained through substantially the same process as in Synthesis Example 1, except that 4-chloro-2-methyl-9-phenyl-1,10-phenanthroline (15.2 g, 50 mmol) and (4′-(4,6-diphenyl-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-3-yl)boronic acid (25.8 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 654 
     Synthesis Example 9. Synthesis of Compound 275 
     
       
         
         
             
             
         
       
     
     Compound 275 (20.3 g, Yield: 62%) was obtained through substantially the same process as in Synthesis Example 1, except that 4-chloro-2-methyl-9-phenyl-1,10-phenanthroline (15.2 g, 50 mmol) and (3′-(4-phenyl-6-(pyridin-3-yl)pyrimidin-2-yl)-[1,1′-biphenyl]-3-yl)boronic acid (25.8 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 654 
     Synthesis Example 10. Synthesis of Compound 313 
     
       
         
         
             
             
         
       
     
     Compound 313 (27.5 g, Yield: 77%) was obtained through substantially the same process as in Synthesis Example 1, except that 9-([1,1′-biphenyl]-3-yl)-4-chloro-2-phenyl-1,10-phenanthroline (22.2 g, 50 mmol) and (4-(4,6-diphenylpyrimidin-2-yl)phenyl)boronic acid (21.2 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 715 
     Synthesis Example 11. Synthesis of Compound 318 
     
       
         
         
             
             
         
       
     
     Compound 318 (23.7 g, Yield: 74%) was obtained through substantially the same process as in Synthesis Example 1, except that 4-chloro-2,9-diphenyl-1,10-phenanthroline (18.3 g, 50 mmol) was used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline. 
     Mass: [(M+H) + ]: 640 
     Synthesis Example 12. Synthesis of Compound 387 
     
       
         
         
             
             
         
       
     
     Compound 387 (25.8 g, Yield: 72%) was obtained through substantially the same process as in Synthesis Example 1, except that 4-chloro-2,9-diphenyl-1,10-phenanthroline (18.3 g, 50 mmol) and (4′-(4-phenyl-6-(pyridin-3-yl)-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-3-yl)boronic acid (25.8 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 717 
     Synthesis Example 13. Synthesis of Compound 420 
     
       
         
         
             
             
         
       
     
     Compound 420 (18.5 g, Yield: 68%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-chloro-9-isopropyl-4-methyl-1,10-phenanthroline (13.5 g, 50 mmol) was used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline. 
     Mass: [(M+H) + ]: 544 
     Synthesis Example 14. Synthesis of Compound 449 
     
       
         
         
             
             
         
       
     
     Compound 449 (21.3 g, Yield: 72%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-chloro-4,9-dimethyl-1,10-phenanthroline (12.1 g, 50 mmol) and (3-(2-([1,1′-biphenyl]-4-yl)-6-phenylpyrimidin-4-yl)phenyl)boronic acid (25.7 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 591 
     Synthesis Example 15. Synthesis of Compound 473 
     
       
         
         
             
             
         
       
     
     Compound 473 (18.8 g, Yield: 73%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-chloro-4,9-dimethyl-1,10-phenanthroline (12.1 g, 50 mmol) and (4-(4-phenyl-6-(pyridin-2-yl)pyrimidin-2-yl)phenyl)boronic acid (21.2 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 516 
     Synthesis Example 16. Synthesis of Compound 516 
     
       
         
         
             
             
         
       
     
     Compound 516 (19.6 g, Yield: 68%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-chloro-9-methyl-4-phenyl-1,10-phenanthroline (15.2 g, 50 mmol) and (4-(2,6-diphenylpyrimidin-4-yl)phenyl)boronic acid (21.1 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 577 
     Synthesis Example 17. Synthesis of Compound 536 
     
       
         
         
             
             
         
       
     
     Compound 536 (22.9 g, Yield: 66%) was obtained through substantially the same process as in Synthesis Example 1, except that 9-(tert-butyl)-2-chloro-4-phenyl-1,10-phenanthroline (17.3 g, 50 mmol) and (3′-(2,6-diphenylpyrimidin-4-yl)-[1,1′-biphenyl]-4-yl)boronic acid (25.7 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 695 
     Synthesis Example 18. Synthesis of Compound 597 
     
       
         
         
             
             
         
       
     
     Compound 597 (24.7 g, Yield: 70%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-chloro-9-methyl-4-phenyl-1,10-phenanthroline (15.2 g, 50 mmol) and (4-(4-phenyl-6-(3-(quinolin-8-yl)phenyl)-1,3,5-triazin-2-yl)phenyl)boronic acid (28.8 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 705 
     Synthesis Example 19. Synthesis of Compound 637 
     
       
         
         
             
             
         
       
     
     Compound 637 (24.5 g, Yield: 72%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-chloro-4-isopropyl-9-phenyl-1,10-phenanthroline (16.6 g, 50 mmol) and (3′-(4,6-diphenylpyridin-2-yl)-[1,1′-biphenyl]-4-yl)boronic acid (25.6 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 680 
     Synthesis Example 20. Synthesis of Compound 658 
     
       
         
         
             
             
         
       
     
     Compound 658 (22.6 g, Yield: 62%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-chloro-4-methyl-9-phenyl-1,10-phenanthroline (15.2 g, 50 mmol) and (3′-(6-([1,1′-biphenyl]-4-yl)-2-phenylpyrimidin-4-yl)-[1,1′-biphenyl]-3-yl)boronic acid (30.3 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 729 
     Synthesis Example 21. Synthesis of Compound 693 
     
       
         
         
             
             
         
       
     
     Compound 693 (21.4 g, Yield: 64%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-chloro-4-ethyl-9-phenyl-1,10-phenanthroline (15.9 g, 50 mmol) and (4′-(4-phenyl-6-(pyridin-4-yl)-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-3-yl)boronic acid (25.8 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 669 
     Synthesis Example 22. Synthesis of Compound 724 
     
       
         
         
             
             
         
       
     
     Compound 724 (21.1 g, Yield: 66%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-chloro-4,9-diphenyl-1,10-phenanthroline (18.3 g, 50 mmol) and (3-(2,6-diphenylpyrimidin-4-yl)phenyl)boronic acid (21.1 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 639 
     Synthesis Example 23. Synthesis of Compound 758 
     
       
         
         
             
             
         
       
     
     Compound 758 (26.0 g, Yield: 68%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-chloro-4-(naphthalen-1-yl)-9-phenyl-1,10-phenanthroline (20.9 g, 50 mmol) and (3-(4-([1,1′-biphenyl]-4-yl)-6-phenyl-1,3,5-triazin-2-yl)phenyl)boronic acid (25.8 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 766 
     Synthesis Example 24. Synthesis of Compound 802 
     
       
         
         
             
             
         
       
     
     Compound 802 (26.8 g, Yield: 70%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-chloro-4,9-diphenyl-1,10-phenanthroline (18.3 g, 50 mmol) and (3-(2-phenyl-6-(3-(quinolin-8-yl)phenyl)pyrimidin-4-yl)phenyl)boronic acid (28.8 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 766 
     Synthesis Example 25. Synthesis of Compound 833 
     
       
         
         
             
             
         
       
     
     Compound 833 (20.4 g, Yield: 66%) was obtained through substantially the same process as in Synthesis Example 1, except that 9-chloro-4-isopropyl-2-methyl-1,10-phenanthroline (13.5 g, 50 mmol) and (3′-(4,6-diphenylpyridin-2-yl)-[1,1′-biphenyl]-3-yl)boronic acid (25.6 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 618 
     Synthesis Example 26. Synthesis of Compound 846 
     
       
         
         
             
             
         
       
     
     Compound 846 (18.9 g, Yield: 64%) was obtained through substantially the same process as in Synthesis Example 1, except that 9-chloro-4-isopropyl-2-methyl-1,10-phenanthroline (12.1 g, 50 mmol) and (4′-(2,6-diphenylpyrimidin-4-yl)-[1,1′-biphenyl]-3-yl)boronic acid (25.7 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 619 
     Synthesis Example 27. Synthesis of Compound 872 
     
       
         
         
             
             
         
       
     
     Compound 872 (22.6 g, Yield: 65%) was obtained through substantially the same process as in Synthesis Example 1, except that 9-chloro-4-isopropyl-2-methyl-1,10-phenanthroline (13.5 g, 50 mmol) and (3′-(4-([1,1′-biphenyl]-4-yl)-6-phenyl-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-4-yl)boronic acid (30.3 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 696 
     Synthesis Example 28. Synthesis of Compound 932 
     
       
         
         
             
             
         
       
     
     Compound 932 (21.6 g, Yield: 75%) was obtained through substantially the same process as in Synthesis Example 1, except that 9-chloro-2-methyl-4-phenyl-1,10-phenanthroline (15.2 g, 50 mmol) and (2-(2,6-diphenylpyrimidin-4-yl)phenyl)boronic acid (21.1 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 577 
     Synthesis Example 29. Synthesis of Compound 948 
     
       
         
         
             
             
         
       
     
     Compound 948 (25.0 g, Yield: 72%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-(9-chloro-4-phenyl-1,10-phenanthrolin-2-yl)-2-methylpropan-1-ylium (17.3 g, 50 mmol) and (4′-(2,6-diphenylpyrimidin-4-yl)-[1,1′-biphenyl]-3-yl)boronic acid (25.7 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 695 
     Synthesis Example 30. Synthesis of Compound 987 
     
       
         
         
             
             
         
       
     
     Compound 987 (23.9 g, Yield: 73%) was obtained through substantially the same process as in Synthesis Example 1, except that 4-([1,1′-biphenyl]-3-yl)-9-chloro-2-methyl-1,10-phenanthroline (19.0 g, 50 mmol) and (3-(4-phenyl-6-(pyridin-2-yl)-1,3,5-triazin-2-yl)phenyl)boronic acid (21.3 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 655 
     Synthesis Example 31. Synthesis of Compound 1026 
     
       
         
         
             
             
         
       
     
     Compound 1026 (20.7 g, Yield: 70%) was obtained through substantially the same process as in Synthesis Example 1, except that 9-chloro-4-ethyl-2-phenyl-1,10-phenanthroline (15.9 g, 50 mmol) and (4-(2,6-diphenylpyrimidin-4-yl)phenyl)boronic acid (21.1 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 591 
     Synthesis Example 32. Synthesis of Compound 1072 
     
       
         
         
             
             
         
       
     
     Compound 1072 (24.8 g, Yield: 68%) was obtained through substantially the same process as in Synthesis Example 1, except that 9-chloro-4-methyl-2-phenyl-1,10-phenanthroline (15.2 g, 50 mmol) and (4′-(4-([1,1′-biphenyl]-4-yl)-6-phenyl-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-4-yl)boronic acid (30.32 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 730 
     Synthesis Example 33. Synthesis of Compound 1097 
     
       
         
         
             
             
         
       
     
     Compound 1097 (23.7 g, Yield: 71%) was obtained through substantially the same process as in Synthesis Example 1, except that 9-chloro-4-ethyl-2-phenyl-1,10-phenanthroline (15.9 g, 50 mmol) and (3′-(4-phenyl-6-(pyridin-2-yl)pyrimidin-2-yl)-[1,1′-biphenyl]-4-yl)boronic acid (25.8 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 669 
     Synthesis Example 34. Synthesis of Compound 1131 
     
       
         
         
             
             
         
       
     
     Compound 1131 (22.4 g, Yield: 65%) was obtained through substantially the same process as in Synthesis Example 1, except that 9-chloro-4-(naphthalen-1-yl)-2-phenyl-1,10-phenanthroline (20.9 g, 50 mmol) and (3-(4,6-diphenylpyridin-2-yl)phenyl)boronic acid (21.1 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 688 
     Synthesis Example 35. Synthesis of Compound 1133 
     
       
         
         
             
             
         
       
     
     Compound 1133 (20.4 g, Yield: 64%) was obtained through substantially the same process as in Synthesis Example 1, except that 9-chloro-2,4-diphenyl-1,10-phenanthroline (18.3 g, 50 mmol) and (3-(4,6-diphenylpyrimidin-2-yl)phenyl)boronic acid (21.1 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 639 
     Synthesis Example 36. Synthesis of Compound 1146 
     
       
         
         
             
             
         
       
     
     Compound 1146 (25.3 g, Yield: 66%) was obtained through substantially the same process as in Synthesis Example 1, except that 9-chloro-4-(naphthalen-1-yl)-2-phenyl-1,10-phenanthroline (20.9 g, 50 mmol) and (4′-(4,6-diphenyl-1,3,5-triazin-2-yl)-[1,1′-biphenyl]-4-yl)boronic acid (25.8 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 766 
     Synthesis Example 37. Synthesis of Compound 1239 
     
       
         
         
             
             
         
       
     
     Compound 1239 (23.8 g, Yield: 60%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-chloro-4,9-diphenyl-1,10-phenanthroline (18.3 g, 50 mmol) and ((3″-(4,6-diphenyl-1,3,5-triazin-2-yl)-[1,1′: 4′,1″-terphenyl]-3-yl)boronic acid (30.3 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 792 
     Synthesis Example 38. Synthesis of Compound 1248 
     
       
         
         
             
             
         
       
     
     Compound 1248 (28.9 g, Yield: 63%) was obtained through substantially the same process as in Synthesis Example 1, except that 9-chloro-2,4-diphenyl-1,10-phenanthroline (18.3 g, 50 mmol) and (3″-(4-phenyl-6-(3-(quinolin-8-yl)phenyl)-1,3,5-triazin-2-yl)-[1,1′: 3′,1″-terphenyl]-3-yl)boronic acid (37.9 g, 60 mmol) were used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline and (3-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)boronic acid, respectively. 
     Mass: [(M+H) + ]: 920 
     Synthesis Example 39. Synthesis of Compound 1250 
     
       
         
         
             
             
         
       
     
     Compound 1250 (17.4 g, Yield: 64%) was obtained through substantially the same process as in Synthesis Example 1, except that 4-chloro-9-isopropyl-2-methyl-1,10-phenanthroline (13.5 g, 50 mmol) was used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline. 
     Mass: [(M+H) + ]: 544 
     Synthesis Example 40. Synthesis of Compound 1251 
     
       
         
         
             
             
         
       
     
     Compound 1251 (17.7 g, Yield: 65%) was obtained through substantially the same process as in Synthesis Example 1, except that 4-chloro-2-isopropyl-9-methyl-1,10-phenanthroline (13.5 g, 50 mmol) was used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline. 
     Mass: [(M+H) + ]: 544 
     Synthesis Example 41. Synthesis of Compound 1252 
     
       
         
         
             
             
         
       
     
     Compound 1252 (16.8 g, Yield: 59%) was obtained through substantially the same process as in Synthesis Example 1, except that 4-chloro-2,9-diisopropyl-1,10-phenanthroline (14.9 g, 50 mmol) was used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline. 
     Mass: [(M+H) + ]: 572 
     Synthesis Example 42 Synthesis of Compound 1268 
     
       
         
         
             
             
         
       
     
     Compound 1268 (18.2 g, Yield: 60%) was obtained through substantially the same process as in Synthesis Example 1, except that 2-chloro-9-isopropyl-4-phenyl-1,10-phenanthroline (16.6 g, 50 mmol) was used instead of 4-chloro-2,9-dimethyl-1,10-phenanthroline. 
     Mass: [(M+H) + ]: 606 
     Examples 1 to 26. Manufacture of Blue-Light-Emitting Organic Electroluminescent Devices 
     After high-purity sublimation purification of the compounds synthesized in the above synthesis examples, using any suitable high-purity sublimation purification method, blue-light-emitting organic electroluminescent devices were manufactured as follows. 
     First, a glass substrate coated with a 1500A-thick indium tin oxide (ITO) film was ultrasonically washed with distilled water. After the washing with distilled water, the glass substrate was ultrasonically washed with a solvent such as isopropyl alcohol, acetone, methanol, and/or the like, dried, and then transferred to a UV OZONE cleaner (Powersonic 405, HWASHIN TECHNOLOGY CO.). Then, the substrate was washed with UV for 5 minutes and then transferred to a vacuum deposition apparatus. 
     On the ITO electrode prepared as above, DS-205 (DOOSAN ELECTRONICS, CO., LTD, 80 nm)/NPB (15 nm)/ADN+5% DS-405 (DOOSAN ELECTRONICS, CO., LTD, 30 nm)/compound of the present embodiments (30 nm) as shown in Table 1/LiF (1 nm)/AI (200 nm) were sequentially stacked one another to manufacture an organic electroluminescent device. 
     Comparative Examples 1 to 8. Manufacture of Blue-Light-Emitting Organic Electroluminescent Devices 
     Blue-light-emitting organic electroluminescent devices were manufactured through substantially the same process as in Example 1, except that Alq 3  and Compound A to Compound G were used, respectively, instead of Compound 12, as the material of the electron transport layer. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Evaluation Example 1 
     The driving voltage, current efficiency, and emission wavelength of the blue-light-emitting organic electroluminescent devices manufactured in Examples 1 to 26 and Comparative Examples 1 to 8 were measured at a current density of 10 mA/cd. The results are shown in Table 1. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Electron 
                 Driving 
                 Emission 
                 Current 
               
               
                   
                 transport 
                 voltage 
                 peak 
                 efficiency 
               
               
                 Sample 
                 layer 
                 (V) 
                 (nm) 
                 (cd/A) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Example 1 
                 Compound 12 
                 4.0 
                 457 
                 8.0 
               
               
                 Example 2 
                 Compound 90 
                 4.1 
                 456 
                 7.9 
               
               
                 Example 3 
                 Compound 126 
                 4.0 
                 457 
                 7.3 
               
               
                 Example 4 
                 Compound 160 
                 4.0 
                 456 
                 7.9 
               
               
                 Example 5 
                 Compound 209 
                 4.2 
                 456 
                 7.3 
               
               
                 Example 6 
                 Compound 236 
                 4.0 
                 458 
                 7.5 
               
               
                 Example 7 
                 Compound 318 
                 4.1 
                 458 
                 7.8 
               
               
                 Example 8 
                 Compound 313 
                 4.1 
                 454 
                 7.5 
               
               
                 Example 9 
                 Compound 387 
                 4.0 
                 457 
                 7.5 
               
               
                 Example 10 
                 Compound 473 
                 4.1 
                 458 
                 7.6 
               
               
                 Example 11 
                 Compound 516 
                 4.0 
                 454 
                 7.4 
               
               
                 Example 12 
                 Compound 536 
                 4.0 
                 454 
                 7.4 
               
               
                 Example 13 
                 Compound 597 
                 4.1 
                 455 
                 7.8 
               
               
                 Example 14 
                 Compound 637 
                 4.1 
                 455 
                 7.8 
               
               
                 Example 15 
                 Compound 658 
                 4.1 
                 457 
                 7.5 
               
               
                 Example 16 
                 Compound 693 
                 4.2 
                 457 
                 7.5 
               
               
                 Example 17 
                 Compound 833 
                 4.2 
                 457 
                 7.2 
               
               
                 Example 18 
                 Compound 846 
                 4.0 
                 454 
                 7.7 
               
               
                 Example 19 
                 Compound 872 
                 4.0 
                 454 
                 7.7 
               
               
                 Example 20 
                 Compound 1146 
                 4.0 
                 455 
                 7.6 
               
               
                 Example 21 
                 Compound 1026 
                 4.1 
                 455 
                 7.5 
               
               
                 Example 22 
                 Compound 1072 
                 4.2 
                 455 
                 7.4 
               
               
                 Example 23 
                 Compound 1239 
                 4.2 
                 456 
                 7.6 
               
               
                 Example 24 
                 Compound 1250 
                 4.0 
                 455 
                 7.9 
               
               
                 Example 25 
                 Compound 1251 
                 4.0 
                 456 
                 8.0 
               
               
                 Example 26 
                 Compound 1252 
                 4.0 
                 456 
                 7.9 
               
               
                 Comparative 
                 Alq 3   
                 4.7 
                 458 
                 5.6 
               
               
                 Example 1 
               
               
                 Comparative 
                 Compound A 
                 4.3 
                 460 
                 6.2 
               
               
                 Example 2 
               
               
                 Comparative 
                 Compound B 
                 4.5 
                 459 
                 6.4 
               
               
                 Example 3 
               
               
                 Comparative 
                 Compound C 
                 4.6 
                 457 
                 6.0 
               
               
                 Example 4 
               
               
                 Comparative 
                 Compound D 
                 4.4 
                 458 
                 6.7 
               
               
                 Example 5 
               
               
                 Comparative 
                 Compound E 
                 4.4 
                 456 
                 6.8 
               
               
                 Example 6 
               
               
                 Comparative 
                 Compound F 
                 4.8 
                 459 
                 6.4 
               
               
                 Example 7 
               
               
                 Comparative 
                 Compound G 
                 4.6 
                 458 
                 6.9 
               
               
                 Example 8 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, the blue-light-emitting organic electroluminescent devices (Examples 1 to 26) using the compounds according to embodiments of the present disclosure in the electron transport layer were found to exhibit excellent performance in terms of driving voltage, emission peak, and current efficiency, as compared to the blue-light-emitting organic electroluminescent device (Comparative Example 1) using conventional Alq 3  in the electron transport layer, and the blue-light-emitting organic electroluminescent devices (Comparative Examples 2 to 8) in which the compounds have different binding sites. 
     As described above, according to the one or more embodiments, an organic light-emitting device including at least one heterocyclic compound as represented above may have a low driving voltage, high emission efficiency, and improved lifetime characteristics. 
     As used herein, the terms “use,” “using,” and “used” may be considered synonymous with the terms “utilize,” “utilizing,” and “utilized,” respectively. 
     In addition, the terms “substantially,” “about,” and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by those of ordinary skill in the art. 
     Also, any numerical range recited herein is intended to include all 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 of the present disclosure as defined by the following claims and their equivalents.