Patent Publication Number: US-9847491-B2

Title: Organic light-emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and the benefits of Korean Patent Application No. 10-2015-0062021, filed on Apr. 30, 2015, in the Korean Intellectual Property Office, and Korean Patent Application No. 10-2016-0019788, filed on Feb. 19, 2016, in the Korean Intellectual Property Office, the entire content of each of which is incorporated herein by reference. 
     BACKGROUND 
     1. Field 
     One or more aspects of example embodiments of the present disclosure are related to an organic light-emitting device. 
     2. Description of the Related Art 
     Organic light-emitting devices are self-emission devices that have wide viewing angles, high contrast ratios, short response times, and/or excellent brightness, driving voltage, and/or response speed characteristics, and may produce full-color images. 
     An example organic light-emitting device includes a first electrode on a substrate, and a hole transport region, an emission layer, an electron transport region, and a second electrode sequentially positioned on the first electrode. Holes provided from the first electrode may move toward the emission layer through the hole transport region, and electrons provided from the second electrode may move toward the emission layer through the electron transport region. Carriers (such as holes and electrons) may recombine in the emission layer to produce excitons. These excitons may transition from an excited state to a ground state to thereby generate light. 
     SUMMARY 
     One or more aspects of example embodiments of the present disclosure are directed toward an organic light-emitting device having low driving voltage, high efficiency, long lifespan, and improved efficiency. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
     One or more example embodiments of the present disclosure provide an organic light-emitting device including: a first electrode; a second electrode; an emission layer between the first electrode and the second electrode; and a hole transport region between the first electrode and the emission layer, wherein the hole transport region comprises a first compound represented by Formula 1 and a second compound represented by Formula 2: 
     
       
         
         
             
             
         
       
     
     In Formulae 1 and 2, 
     X 1  and X 2  may each independently be selected from nitrogen (N), boron (B), and phosphorus (P), 
     Y 1  may be selected from oxygen (O), sulfur (S), and N[(L 11 ) a11 -R 14 ], and Y 2  may be selected from O, S, and N[(L 12 ) a12 -R 15 ], 
     L 1  to L 4 , L 11 , and L 12  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, wherein L 4  in Formula 2 may not be a substituted or unsubstituted carbazolylene group, 
     a1 to a4, a11, and a12 may each independently be an integer selected from 0 to 3, 
     Ar 1  and Ar 2  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 Ar 2  in Formula 2 may not be a substituted or unsubstituted carbazolyl group, 
     R 1  to R 8  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q 1 )(Q 2 )(Q 3 ), 
     R 11  to R 15  may each independently be selected from a substituted or unsubstituted C 1 -C 60  alkyl 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 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, 
     b1, b4, b5, and b7 may each independently be an integer selected from 1 to 4, 
     b2, b3, b6, and b8 may each independently be an integer selected from 1 to 3, and 
     at least one substituent of 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 1 -C 60  heteroaryl group, the substituted monovalent non-aromatic condensed polycyclic group, the substituted monovalent non-aromatic condensed heteropolycyclic group, the substituted C 1 -C 60  alkyl group, the substituted C 2 -C 60  alkenyl group, the substituted C 2 -C 60  alkynyl group, the substituted C 1 -C 60  alkoxy group, the substituted C 3 -C 10  cycloalkyl group, the substituted C 1 -C 10  heterocycloalkyl group, the substituted C 3 -C 10  cycloalkenyl group, the substituted C 1 -C 10  heterocycloalkenyl group, the substituted C 6 -C 60  aryl group, the substituted C 6 -C 60  aryloxy group, the substituted C 6 -C 60  arylthio group, the substituted C 1 -C 60  heteroaryl group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group may be selected from the group consisting of: 
     deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 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 amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 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, and —Si(Q 11 )(Q 12 )(Q 13 ), 
     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 amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 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, and —Si(Q 21 )(Q 22 )(Q 23 ), and 
     —Si(Q 31 )(Q 32 )(Q 33 ), 
     wherein Q 1  to Q 3 , Q 11  to Q 13 , Q 21  to Q 23 , and Q 31  to Q 33  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 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, and a monovalent non-aromatic condensed heteropolycyclic group. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       These and/or other aspects will become apparent and more readily appreciated from the following description of example embodiments, taken in conjunction with the drawing, which is a schematic cross-sectional view illustrating the structure of an organic light-emitting device according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in more detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout and duplicative descriptions thereof will not be provided. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the drawing, 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. 
     The thicknesses of layers, films, panels, regions, etc., may be exaggerated in the drawings for clarity. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening element(s) may also be present. In contrast, when an element is referred to as being “directly on” another element, no intervening elements are present. 
     The drawing is a schematic cross-sectional view of an organic light-emitting device  10  according to an embodiment of the present disclosure. The organic light-emitting device  10  includes a first electrode  110 , a hole transport region  130 , an emission layer  150 , an electron transport region  170 , and a second electrode  190 . Here, the first electrode  110  may be an anode, and the second electrode  190  may be a cathode. 
     Hereinafter, the structure of an organic light-emitting device  10  according to an embodiment of the present disclosure and a method of manufacturing an organic light-emitting device  10  according to an embodiment of the present disclosure will be described in connection with the drawing. 
     In the drawing, a substrate may be under the first electrode  110  and/or above the second electrode  190 . The substrate may be a glass substrate or a transparent plastic substrate, each having excellent mechanical strength, thermal stability, transparency, surface smoothness, ease of handling, and/or water-resistance. 
     The first electrode  110  may be formed by, for example, depositing and/or sputtering a material for forming the first electrode  110  on the substrate. When the first electrode  110  is an anode, the material for forming the first electrode  110  may be selected from materials with a high work function in order to facilitate hole injection. The first electrode  110  may be a reflective electrode, a semi-transmissive electrode, or a transmissive electrode. The material for forming the first electrode  110  may be a transparent and highly conductive material, and non-limiting examples of such a material may include indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO 2 ), and zinc oxide (ZnO). When the first electrode  110  is a semi-transmissive electrode or a reflective electrode, at least one selected from magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), and magnesium-silver (Mg—Ag) may be used as a material for forming the first electrode  110 . 
     The first electrode  110  may have a single-layer structure, or a multi-layer structure including two or more layers. For example, the first electrode  110  may have a three-layered structure of ITO/Ag/ITO, but embodiments of the structure of the first electrode  110  are not limited thereto. 
     The hole transport region  130 , the emission layer  150 , and the electron transport region  170  may be sequentially stacked on the first electrode  110  in this stated order. 
     The hole transport region  130  may include a first compound represented by Formula 1 and a second compound represented by Formula 2: 
     
       
         
         
             
             
         
       
     
     In Formulae 1 and 2, X 1  and X 2  may each independently be selected from nitrogen (N), boron (B), and phosphorus (P). 
     For example, in Formulae 1 and 2, X 1  and X 2  may each independently be N. 
     In Formula 1, Y 1  may be selected from O, S, and N[(L 11 ) a11 -R 14 ], and Y 2  may be selected from O, S, and N[(L 12 ) a12 -R 15 ]. 
     For example, Y 1  and Y 2  may be identical to or different from each other. 
     In one or more embodiments, Y 1  and Y 2  may be identical to each other. 
     In one or more embodiments, Y 1  and Y 2  may both be O, or Y 1  and Y 2  may both be S. 
     L 11 , L 12 , a11, a12, R 14 , and R 15  may each independently be the same as described below. 
     In Formulae 1 and 2, L 1  to L 4 , L 11 , and L 12  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, wherein L 4  in Formula 2 may not be a substituted or unsubstituted carbazolylene group. 
     In one or more embodiments, in Formula 2, L 1  to L 4  are both not a substituted or unsubstituted carbazolylene group. 
     In one or more embodiments, in Formulae 1 and 2, L 1  to L 4 , L 11 , and L 12  may each independently be selected from the group consisting of: 
     a phenylene group, a pentalenylene group, an indenylene group, a naphthylene group, an azulenylene group, a heptalenylene group, an indacenylene group, an acenaphthylene group, a fluorenylene group, a spiro-fluorenylene 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, a benzofuranylene group, a benzothiophenylene group, a dibenzofuranylene group, a dibenzothiophenylene group, a benzocarbazolylene group, and a dibenzocarbazolylene 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-fluorenylene 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, a benzofuranylene group, a benzothiophenylene group, a dibenzofuranylene group, a dibenzothiophenylene group, a benzocarbazolylene group, and a dibenzocarbazolylene group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a 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 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-fluorenyl 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, a benzofuranyl group, a benzothiophenyl group a dibenzofuranyl group, a dibenzothiophenyl group, a benzocarbazolyl group, and a dibenzocarbazolyl group. 
     In one or more embodiments, in Formulae 1 and 2, L 1  to L 4 , L 11 , and L 12  may each independently be selected from the group consisting of: 
     a phenylene group, a naphthylene group, a fluorenylene group, a spiro-fluorenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a dibenzofuranylene group, and a dibenzothiophenylene group; and 
     a phenylene group, a naphthylene group, a fluorenylene group, a spiro-fluorenylene group, a phenanthrenylene group, an anthracenylene group, a fluoranthenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a dibenzofuranylene group, and a dibenzothiophenylene group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a dibenzofuranyl group, a dibenzothiophenyl group, and —Si(Q 31 )(Q 32 )(Q 33 ), 
     wherein Q 31  to Q 33  may each independently be selected from a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, and a naphthyl group. 
     In one or more embodiments, in Formulae 1 and 2, L 1  to L 4 , L 11 , and L 12  may each independently be selected from groups represented by Formulae 3-1 to 3-11, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 3-1 to 3-11, 
     Y 1  may be selected from O, S, C(Z 3 )(Z 4 ), and N(Z 5 ), 
     Z 1  to Z 5  may each independently be selected from hydrogen, deuterium, —F, —CI, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, and a chrysenyl group, 
     d1 may be an integer selected from 1 to 4, d2 may be an integer selected from 1 to 3, d3 may be an integer selected from 1 to 6, d4 may be an integer selected from 1 to 8, and d5 may be an integer selected from 1 to 5, and 
     * and *′ may each indicate a binding site to a neighboring atom. 
     For example, in Formulae 3-4 and 3-5, Y 1  may be selected from O, S, and C(Z 3 )(Z 4 ), wherein Z 3  and Z 4  may each independently be the same as described above. 
     In one or more embodiments, in Formulae 1 and 2, *-(L 1 ) a1 -*′ to *-(L 4 ) a4 -*′, *-(L 11 ) a11 -*′, and *-(L 12 ) a12 -*′ may each independently be selected from a single bond and a group represented by any of Formulae 3-1 and 3-12: 
     
       
         
         
             
             
         
       
     
     In Formulae 3-1 and 3-12, Z 1 , Z 2 , and d1 may each independently be the same as described herein in connection with Formulae 3-1 to 3-11, and * and *′ may each indicate a binding site to a neighboring atom. 
     For example, in Formulae 3-1 and 3-12, 
     Z 1  and Z 2  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, and a chrysenyl group, and 
     d1 may be an integer selected from 1 to 4. 
     In one or more embodiments, in Formulae 1 and 2, L 1  to L 4 , L 11 , and L 12  may each independently be selected from groups selected from Formulae 4-1 to 4-17: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 4-1 to 4-17, * and *′ may each indicate a binding site to a neighboring atom. 
     In one or more embodiments, in Formulae 1 and 2, *-(L 1 ) a1 -*′ to *-(L 4 ) a4 -*′, *-(L 11 ) a11 -*′, and *-(L 12 ) a12 -*′ may each independently be selected from a single bond and a group represented by any of Formulae 4-1 and 4-18: 
     
       
         
         
             
             
         
       
     
     In Formulae 4-1 and 4-18, * and *′ may each indicate a binding site to a neighboring atom. 
     In Formulae 1 and 2, a1 to a4, a11, and a12 may each independently be an integer selected from 0 to 3. 
     In Formula 1, a1 indicates the number of L 1 (s) and may be an integer selected from 0 to 3. For example, in Formula 1, when a1 is 0, *-(L 1 ) a1 -*′ is a single bond, and when a1 is 2 or more, 2 or more L 1 (s) may be identical to or different from each other. 
     a2 to a4, a11, and a12 may each independently be the same as described herein in connection with a1 and the structures of Formulae 1 and 2. 
     For example, in Formula 1, the sum of a1, a2, and a3 may be 1 or more. 
     In one or more embodiments, in Formula 1, the sum of a1, a2, and a3 may be 1. 
     In one or more embodiments, in Formula 1, 
     a1, a2, and a3 may all be 0, 
     a1 may be 0, a2 may be 1, and a3 may be 0, or 
     a1 and a2 may be 0, and a3 may be 1. 
     For example, in Formula 2, 
     a4 may be an integer selected from 0 to 2, and a11 and a12 may each independently be selected from 0 and 1. 
     In one or more embodiments, a4, a11, and a12 may each independently be an integer selected from 0 and 1. 
     In Formulae 1 and 2, Ar 1  and Ar 2  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 Ar 2  in Formula 2 may not be a substituted or unsubstituted carbazolyl group. 
     In one or more embodiments, in Formula 2, Ar 1  and Ar 2  are both not a substituted or unsubstituted carbazolyl group. 
     For example, in Formulae 1 and 2, Ar 1  and Ar 2  may each independently be selected from the group consisting of: 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group; and 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, and —Si(Q 31 )(Q 32 )(Q 33 ), 
     wherein Q 31  to Q 33  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, and a naphthyl group, and wherein Ar 2  in Formula 2 may not be a carbazolyl group or substituted carbazolyl group. 
     In one or more embodiments, in Formulae 1 and 2, Ar 1  and Ar 2  may each independently be selected from the group consisting of: 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, an anthracenyl group, a phenanthrenyl group, a pyridinyl group, a pyrimidinyl group, a triazinyl group, a dibenzofuranyl group, and a dibenzothiophenyl group; and 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, an anthracenyl group, a phenanthrenyl group, a pyridinyl group, a pyrimidinyl group, a triazinyl group, a dibenzofuranyl group, and a dibenzothiophenyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, an anthracenyl group, a phenanthrenyl group, a pyridinyl group, a pyrimidinyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, and —Si(Q 31 )(Q 32 )(Q 33 ), 
     wherein Q 31  to Q 33  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, and a naphthyl group. 
     In Formulae 1 and 2, R 1  to R 8  may each independently be selected from the group consisting of: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q 1 )(Q 2 )(Q 3 ), wherein Q 1  to Q 3  may each independently be the same as described above. 
     In Formulae 1 and 2, R 11  to R 15  may each independently be selected from a substituted or unsubstituted C 1 -C 60  alkyl 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 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group. 
     For example, in Formulae 1 and 2, 
     R 1  to R 5  may each independently be selected from the group consisting of: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, and a C 1 -C 20  alkoxy group; 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group; 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, and —Si(Q 31 )(Q 32 )(Q 33 ); and 
     —Si(Q 1 )(Q 2 )(Q 3 ), and 
     R 11  to R 15  may each independently be selected from the group consisting of: 
     a C 1 -C 20  alkyl group and a C 1 -C 20  alkoxy group; 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group; 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, and —Si(Q 31 )(Q 32 )(Q 33 ); and 
     —Si(Q 1 )(Q 2 )(Q 3 ), 
     wherein Q 1  to Q 3  and Q 31  to Q 33  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, and a naphthyl group. 
     In one or more embodiments, in Formulae 1 and 2, R 1  to R 8  may each independently be selected from the group consisting of: 
     hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, and a C 1 -C 10  alkoxy group; 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a carbazolyl group, a dibenzofuranyl group, and a dibenzothiophenyl group; 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl 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 amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a naphthyl group, and —Si(Q 31 )(Q 32 )(Q 33 ); and 
     —Si(Q 1 )(Q 2 )(Q 3 ), and 
     R 11  to R 15  may each independently be selected from the group consisting of: 
     a C 1 -C 10  alkyl group and a C 1 -C 10  alkoxy group; 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a carbazolyl group, a dibenzofuranyl group, and a dibenzothiophenyl group; 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl 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 amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, a naphthyl group, and —Si(Q 31 )(Q 32 )(Q 33 ); and 
     —Si(Q 1 )(Q 2 )(Q 3 ), 
     wherein Q 1  to Q 3  and Q 31  to Q 33  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, a phenyl group, and a naphthyl group. 
     In one or more embodiments, in Formulae 1 and 2, 
     Ar 1  and Ar 2  may each independently be selected from groups represented by Formulae 5-1 to 5-20, 
     R 1  to R 5  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, and a group represented by any of Formulae 5-1 to 5-12, 
     R 11  to R 15  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, and a group represented by any of Formulae 5-1 to 5-12: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 5-1 to 5-20, 
     Y 31  may be selected from O, S, C(Z 35 )(Z 36 ), N(Z 37 ), and Si(Z 38 )(Z 39 ), 
     Z 31  to Z 39  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group, 
     e1 may be an integer selected from 1 to 5, e2 may be an integer selected from 1 to 7, 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 and 2, e6 may be an integer selected from 1 to 6, and e7 may be an integer selected from 1 to 9, and 
     * may indicate a binding site to a neighboring atom. 
     For example, in Formulae 5-4 and 5-5, Y 31  may be selected from O, S, C(Z 35 )(Z 36 ), and Si(Z 38 )(Z 39 ). 
     In one or more embodiments, in Formulae 1 and 2, Ar 1  and Ar 2  may each independently be selected from groups represented by Formulae 6-1 to 6-33, R 1  to R 8  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, and a group represented by any of Formulae 6-1 to 6-29, 
     R 11  to R 15  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, and a group represented by any of Formulae 6-1 to 6-33: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 6-1 to 6-33, * may indicate a binding site to a neighboring atom. 
     In one or more embodiments, in Formulae 1 and 2, Ar 1  and Ar 2  may each independently be selected from groups represented by Formulae 6-1 to 6-14, Formulae 6-16 to 6-18, and Formulae 6-20 to 6-33, 
     R 1  to R 8  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, and a group represented by any of Formulae 6-1 to 6-14, Formulae 6-16 to 6-18, and Formulae 6-20 to 6-29, and 
     R 11  to R 15  may each independently be selected from a C 1 -C 10  alkyl group, a C 1 -C 10  alkoxy group, and a group represented by any of Formulae 6-1 to 6-14, Formulae 6-16 to 6-18, and Formulae 6-20 to 6-29. 
     In Formulae 1 and 2, b1, b4, b5, and b7 may each independently be an integer selected from 1 to 4, and 
     b2, b3, b6, and b8 may each independently be an integer selected from 1 to 3. 
     In Formulae 1 and 2, b1 indicates the number of R 1 (s), and when b1 is 2 or more, 2 or more R 1 (s) may be identical to or different from each other. b2 to b8 may each independently be the same as described herein in connection with b1 and the structures of Formulae 1 and 2. 
     In one or more embodiments, the first compound represented by Formula 1 may be represented by one selected from Formulae 1-1 to 1-4: 
     
       
         
         
             
             
         
       
     
     In Formulae 1-1 to 1-4, X 1 , L 1  to L 3 , a1 to a3, Ar 1 , R 11  to R 13 , R 1  to R 4 , and b1 to b4 may each independently be the same as described herein in connection with Formula 1. 
     For example, in Formulae 1-1 to 1-4, a1 to a3 may each independently be selected from 0 and 1. 
     In one or more embodiments, in Formulae 1-1 to 1-4, a1 and a3 may each independently be 0, and a2 may be 1. 
     In one or more embodiments, the first compound represented by Formula 1 may be represented by one selected from Formulae 1-1(1) and 1-1(2): 
     
       
         
         
             
             
         
       
     
     In Formulae 1-1(1) and 1-1(2), X 1 , L 1 , L 3 , a1, a3, Ar 1 , R 1  to R 4 , R 13 , and b1 to b4 may each independently be the same as described herein in connection with Formula 1, 
     R 31  to R 33  may each independently be the same as described herein in connection with R 1 , and 
     b31 may be an integer selected from 1 to 4, and b32 and b33 may each independently be an integer selected from 1 to 5. 
     In one or more embodiments, the second compound represented by Formula 2 may be represented by one selected from Formulae 2-1 to 2-3: 
     
       
         
         
             
             
         
       
     
     In Formulae 2-1 to 2-3, X 2 , Y 1 , Y 2 , L 4 , L 11 , L 12 , a4, Ar 2 , R 5  to R 8 , and b5 to b8 may each independently be the same as described herein in connection with Formula 2. 
     For example, in Formulae 2-1 to 2-3, Ar 2  may be selected from groups represented by Formulae 6-1 to 6-14, Formulae 6-16 to 6-18, and Formulae 6-20 to 6-33. 
     In one or more embodiments, the first compound represented by Formula 1 may be one selected from Compounds 101 to 109, and the second compound represented by Formula 2 may be one selected from Compounds 1 to 36, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The hole transport region  130  may include a hole transport layer and a hole auxiliary layer. When the hole transport layer includes the first compound represented by Formula 1 and the hole auxiliary layer includes the second compound represented by Formula 2, holes and electrons may have an optimal or suitable recombination balance therebetween, thereby contributing to an improvement in efficiency and lifespan of the organic light-emitting device  10 . 
     In one or more embodiments, the hole transport layer may include the first compound represented by one selected from Formulae 1-1 and 1-4, and the hole auxiliary layer may include the second compound represented by one selected from Formulae 2-1 to 2-3. 
     In one or more embodiments, the hole transport layer may include the first compound represented by one selected from Formulae 1-1(1) and 1-1(2), and the hole auxiliary layer may include the second compound represented by one selected from Formulae 2-1 to 2-3. 
     In one or more embodiments, the hole transport layer may include one compound selected from Compounds 101 to 109, and the hole auxiliary layer may include one compound selected from Compounds 1 to 27. 
     In one or more embodiments, the hole auxiliary layer may be between the emission layer  150  and the first electrode  110 , and the hole transport layer may be between the hole auxiliary layer and the first electrode  110 , wherein the hole transport layer may include the first compound represented by Formula 1 and the hole auxiliary layer may include the second compound represented by Formula 2. 
     The hole auxiliary layer may directly contact the emission layer  150 . 
     The hole transport region  130  may include, in addition to the hole transport layer and the hole auxiliary layer, at least one layer selected from a hole injection layer, a buffer layer, and an electron blocking layer. 
     For example, the hole transport region  130  may have a structure of hole injection layer/hole transport layer/hole auxiliary layer, a structure of hole injection layer/hole transport layer/buffer layer/hole auxiliary layer, a structure of hole transport layer/hole auxiliary layer, and a structure of hole transport layer/buffer layer/hole auxiliary layer, wherein layers of each structure are sequentially stacked on the first electrode  110  in these stated orders, but embodiments of the structure of the hole transport region  130  are not limited thereto. 
     When the hole transport region  130  includes a hole injection layer, the hole injection layer may be formed on the first electrode  110  using one or more suitable methods, such as vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) deposition, an ink-jet printing, a laser-printing, and/or a laser-induced thermal imaging (LITI) method. 
     When a hole injection layer is formed by vacuum deposition, the vacuum deposition may be, for example, performed at a deposition temperature of about 100° C. to about 500° C., at a vacuum degree of about 10 −8  to about 10 −3  torr, and at a deposition rate of about 0.01 to about 100 Å/sec, depending on the compound to be deposited in the hole injection layer and the structure of the hole injection layer to be formed. 
     When a hole injection layer is formed by spin coating, the spin coating may be performed at a coating rate of about 2,000 rpm to about 5,000 rpm, and at a temperature of about 80° C. to 200° C., depending on the compound to be deposited in the hole injection layer and the structure of the hole injection layer to be formed. 
     The hole transport layer, the hole auxiliary layer, the buffer layer, and the electron blocking layer may each be formed using substantially the same method used to form the hole injection layer. 
     The thickness of the hole transport region  130  may be about 100 Å to about 10,000 Å, and in some embodiments, about 100 Å to about 1,000 Å. When the hole transport region  130  includes both a hole transport layer and a hole auxiliary layer, the thickness of the hole transport layer may be about 50 Å to about 2,000 Å, and in some embodiments, about 100 Å to about 1,500 Å; the thickness of the hole auxiliary layer may be about 20 Å to about 2,000 Å. When the thicknesses of the hole transport region  130 , the hole transport layer, and the hole auxiliary layer are within these ranges, satisfactory hole transporting characteristics may be obtained without a substantial increase in driving voltage. 
     The hole transport region  130  may further include, in addition to the first compound represented by Formula 1 and the second compound represented by Formula 2, at least one selected from m-MTDATA, TDATA, 2-TNATA, NPB, β-NPB, TPD, Spiro-TPD, 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), and polyaniline/poly(4-styrenesulfonate) (PANI/PSS): 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The hole transport region  130  may further include, in addition to these materials, a charge-generation material for the improvement of conductive properties. The charge-generation material may be homogeneously or non-homogeneously dispersed in the hole transport region  130 . 
     The charge-generation material may be, for example, a p-dopant. The p-dopant may be selected from a quinone derivative, a metal oxide, and a cyano group-containing compound, but embodiments of the present disclosure are not limited thereto. Non-limiting examples of the p-dopant may include quinone derivatives (such as tetracyanoquinonedimethane (TCNQ) and/or 2,3,5,6-tetrafluoro-tetracyano-1,4-benzoquinonedimethane (F4-TCNQ)); metal oxides (such as tungsten oxide and/or molybdenum oxide); and Compound HT-D1, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     The hole transport region  130  may further include, in addition to the hole transport layer and the hole auxiliary layer, at least one selected from a buffer layer and an electron blocking layer. The buffer layer may compensate for an optical resonance distance according to a wavelength of light emitted from the emission layer (e.g., be used to adjust the optical resonance distance to match the wavelength of light emitted from the emission layer), and the light-emission efficiency of the formed organic light-emitting device may thus be improved. Materials that are included in the hole transport region may also be used in the buffer layer. The electron blocking layer may prevent or reduce injection of electrons from the electron transport region. 
     The emission layer  150  may be formed on the hole transport region  130  using one or more suitable methods, such as vacuum deposition, spin coating, casting, LB deposition, an ink-jet printing, a laser-printing, and/or an LITI method. When the emission layer  150  is formed by vacuum deposition and/or spin coating, the deposition and coating conditions for forming the emission layer  150  may be similar to the deposition and coating conditions used for forming the hole injection layer. 
     The emission layer  150  may include a host and a dopant. 
     The host may include at least one selected from TPBi, TBADN, ADN (also referred to as “DNA”), CBP, CDBP, and TCP: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In one or more embodiments, the host may include a compound represented by Formula 301:
 
Ar 301 —[(L 301 ) xb1 -R 301 ] xb2 .  Formula 301
 
     In Formula 301, 
     Ar 301  may be selected from the group consisting of: 
     a naphthalene group, a heptalene group, a fluorene group, a spiro-fluorene 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, and an indenoanthracene group; 
     a naphthalene group, a heptalene group, a fluorene group, a spiro-fluorene 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, and an indenoanthracene group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a 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, and —Si(Q 301 )(Q 302 )(Q 303 ) (wherein Q 301  to Q 303  may each independently be selected from hydrogen, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 6 -C 60  aryl group, and a C 1 -C 60  heteroaryl group), 
     L 301  may be the same as described herein in connection with L 1 , 
     R 301  may be selected from the group consisting of: 
     a C 1 -C 20  alkyl group and a C 1 -C 20  alkoxy group; 
     a C 1 -C 20  alkyl group and a C 1 -C 20  alkoxy group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group; 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazole group, and a triazinyl group; and 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazole group, and a triazinyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group; 
     xb1 may be selected from 0, 1, 2, and 3, and 
     xb2 may be selected from 1, 2, 3, and 4. 
     For example, in Formula 301, 
     L 301  may be selected from the group consisting of: 
     a phenylene group, a naphthylene group, a fluorenylene group, a spiro-fluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenanthrenylene group, an anthracenylene group, a pyrenylene group, and a chrysenylene group; and 
     a phenylene group, a naphthylene group, a fluorenylene group, a spiro-fluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenanthrenylene group, an anthracenylene group, a pyrenylene group, and a chrysenylene group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, and a chrysenyl group, 
     R 301  may be selected from the group consisting of: 
     a C 1 -C 20  alkyl group and a C 1 -C 20  alkoxy group; 
     a C 1 -C 20  alkyl group and a C 1 -C 20  alkoxy group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, and a chrysenyl group; 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, and a chrysenyl group; and 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, and a chrysenyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, and a chrysenyl group, but embodiments of the present disclosure are not limited thereto. 
     For example, the host may include a compound represented by Formula 301A: 
     
       
         
         
             
             
         
       
     
     In Formula 301A, L 301 , R 301 , xb1, and xb2 may each independently be the same as described herein in connection with Formula 301. 
     The compound represented by Formula 301 may include at least one selected from Compounds H1 to H42, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In one or more embodiments, the host may include at least one selected from Compounds H43 to H49, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The dopant included in the emission layer may include at least one selected from a fluorescent dopant and a phosphorescent dopant. 
     The phosphorescent dopant may include an organometallic complex represented by Formula 401: 
     
       
         
         
             
             
         
       
     
     In Formula 401, 
     M may be selected from iridium (Ir), platinum (Pt), osmium (Os), titanium (Ti), zirconium (Zr), hafnium (Hf), europium (Eu), terbium (Tb), and thulium (Tm), 
     X 401  to X 404  may each independently be selected from nitrogen and carbon, 
     rings A 401  and A 402  may each independently be selected from a substituted or unsubstituted benzene, a substituted or unsubstituted naphthalene, a substituted or unsubstituted fluorene, a substituted or unsubstituted spiro-fluorene, a substituted or unsubstituted indene, a substituted or unsubstituted pyrrole, a substituted or unsubstituted thiophene, a substituted or unsubstituted furan, a substituted or unsubstituted imidazole, a substituted or unsubstituted pyrazole, a substituted or unsubstituted thiazole, a substituted or unsubstituted isothiazole, a substituted or unsubstituted oxazole, a substituted or unsubstituted isoxazole, a substituted or unsubstituted pyridine, a substituted or unsubstituted pyrazine, a substituted or unsubstituted pyrimidine, a substituted or unsubstituted pyridazine, a substituted or unsubstituted quinoline, a substituted or unsubstituted isoquinoline, a substituted or unsubstituted benzoquinoline, a substituted or unsubstituted quinoxaline, a substituted or unsubstituted quinazoline, a substituted or unsubstituted carbazole, a substituted or unsubstituted benzimidazole, a substituted or unsubstituted benzofuran, a substituted or unsubstituted benzothiophene, a substituted or unsubstituted isobenzothiophene, a substituted or unsubstituted benzoxazole, a substituted or unsubstituted isobenzoxazole, a substituted or unsubstituted triazole, a substituted or unsubstituted oxadiazole, a substituted or unsubstituted triazine, a substituted or unsubstituted dibenzofuran, and a substituted or unsubstituted dibenzothiophene, 
     at least one substituent of the substituted benzene, the substituted naphthalene, the substituted fluorene, the substituted spiro-fluorene, the substituted indene, the substituted pyrrole, the substituted thiophene, the substituted furan, the substituted imidazole, the substituted pyrazole, the substituted thiazole, the substituted isothiazole, the substituted oxazole, the substituted isoxazole, the substituted pyridine, the substituted pyrazine, the substituted pyrimidine, the substituted pyridazine, the substituted quinoline, the substituted isoquinoline, the substituted benzoquinoline, the substituted quinoxaline, the substituted quinazoline, the substituted carbazole, the substituted benzimidazole, the substituted benzofuran, the substituted benzothiophene, the substituted isobenzothiophene, the substituted benzoxazole, the substituted isobenzoxazole, the substituted triazole, the substituted oxadiazole, the substituted triazine, the substituted dibenzofuran, and the substituted dibenzothiophene may be selected from the group consisting of: 
     deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 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, —CI, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 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(non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, —N(Q 401 )(Q 402 ), —Si(Q 403 )(Q 404 )(Q 405 ), and —B(Q 406 )(Q 407 ), 
     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 amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 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, —N(Q 411 )(Q 412 ), —Si(Q 413 )(Q 414 )(Q 415 ), and —B(Q 416 )(Q 417 ); and 
     —N(Q 421 )(Q 412 ), —Si(Q 423 )(Q 424 )(Q 425 ), and —B(Q 426 )(Q 427 ), 
     L 401  may be an organic ligand, 
     xc1 may be selected from 1, 2, and 3, and 
     xc2 may be selected from 0, 1, 2, and 3. 
     L 401  in Formula 401 may be a monovalent organic ligand, a divalent organic ligand, or a trivalent organic ligand. For example, L 401  in Formula 401 may be selected from a halogen ligand (for example, CI and/or F), a diketone ligand (for example, acetylacetonate, 1,3-diphenyl-1,3-propanedionate, 2,2,6,6-tetramethyl-3,5-heptanedionate, and/or hexafluoroacetonate), a carboxylic acid ligand (for example, picolinate, dimethyl-3-pyrazolecarboxylate, and/or benzoate), a carbon monoxide ligand, an isonitrile ligand, a cyano group ligand, and a phosphorus-based ligand (for example, phosphine and/or phosphite), but embodiments of the present disclosure are not limited thereto. 
     In one or more embodiments, Q 401  to Q 407 , Q 411  to Q 417 , and Q 421  to Q 427  in Formula 4-1 may each independently be selected from hydrogen, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 6 -C 60  aryl group, and a C 1 -C 60  heteroaryl group. 
     When ring A 401  in Formula 401 has two or more substituents, the two or more substituents of ring A 401  may bind (e.g., couple) to form a saturated or unsaturated ring. 
     When ring A 402  in Formula 401 has two or more substituents, the two or more substituents of ring A 402  may bind (e.g., couple) to form a saturated or unsaturated ring. 
     When xc1 in Formula 401 is 2 or more, a plurality of ligands denoted as 
                         
may be identical to or different from each other. When xc1 in Formula 401 is 2 or more, rings A 401  and A 402  may each independently be directly connected (e.g., by a bond) or connected via a linking group (for example, a C 1 -C 5  alkylene group, —N(R′)— (wherein R′ may be a C 1 -C 10  alkyl group or a C 6 -C 20  aryl group), and/or —C(═O)—) to rings A 401  and A 402 , respectively, of other neighboring ligands.
 
     The phosphorescent dopant may include at least one selected from Compounds PD1 to PD74, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In one or more embodiments, the phosphorescent dopant may include PtOEP: 
     
       
         
         
             
             
         
       
     
     The fluorescent dopant may include at least one selected from DPVBi, DPAVBi, TBPe, DCM, DCJTB, Coumarin 6, and C545T: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In one or more embodiments, the fluorescent dopant may include a compound represented by Formula 501: 
     
       
         
         
             
             
         
       
     
     In Formula 501, 
     Ar 501  may be selected from the group consisting of: 
     a naphthalene group, a heptalene group, a fluorene group, a spiro-fluorene 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, and an indenoanthracene group; and 
     a naphthalene group, a heptalene group, a fluorene group, a spiro-fluorene 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, and an indenoanthracene group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a 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, and —Si(Q 501 )(Q 502 )(Q 503 ) (wherein Q 501  to Q 503  may each independently be selected from hydrogen, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 6 -C 60  aryl group, and a C 1 -C 60  heteroaryl group), 
     L 501  to L 503  may each independently be the same as described herein in connection with L 301 , 
     R 501  and R 502  may each independently be selected from the group consisting of: 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazole group, a triazinyl group, a dibenzofuranyl group, and a dibenzothiophenyl group; and 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a triazinyl group, 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 amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a triazinyl group, a dibenzofuranyl group, and a dibenzothiophenyl group, 
     xd1 to xd3 may each independently be selected from 0, 1, 2 and 3, and 
     xd4 may be selected from 1, 2, 3, and 4. 
     The fluorescent dopant may include at least one selected from Compounds FD1 to FD9: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The amount of dopant included in the emission layer may be about 0.01 parts by weight to about 15 parts by weight based on 100 parts by weight of the host, but embodiments of the amount of dopant are not limited thereto. 
     The thickness of the emission layer may be about 100 Å to about 1,000 Å, and in some embodiments, about 200 Å to about 600 Å. When the thickness of the emission layer is within any of these ranges, the emission layer may have excellent light-emitting characteristics without a substantial increase in driving voltage. 
     When the organic light-emitting device  10  is a full-color organic light-emitting device, the emission layer  150  may be patterned into a red emission layer, a green emission layer, and/or a blue emission layer according to each individual sub-pixel. In one or more embodiments, the emission layer  150  may have a multi-layer structure in which a red emission layer, a green emission layer, and a blue emission layer are stacked on each other, or a single-layer structure including a red-light emitting material, a green-light emitting material, and a blue-light emitting material mixed in a single layer to thereby emit white light. 
     The electron transport region  170  may be on the emission layer  150 . 
     The electron transport region  170  may include at least one selected from a hole blocking layer, an electron transport layer, and an electron injection layer. The hole blocking layer, the electron transport layer, and the electron injection layer may each be formed using substantially the same method used to form the hole injection layer. 
     For example, the electron transport region  170  may have a structure of electron transport layer/electron injection layer or a structure of hole blocking layer/electron transport layer/electron injection layer, wherein layers of each structure are sequentially stacked on the emission layer  150 . 
     The electron transport layer may include at least one selected from a compound represented by Formula 601 and a compound represented by Formula 602:
 
Ar 601 -[(L 601 ) xe1 -E 601 ] xe2 .  Formula 601
 
     In Formula 601, 
     Ar 601  may be selected from the group consisting of: 
     a naphthalene group, a heptalene group, a fluorene group, a spiro-fluorene 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, and an indenoanthracene group; and 
     a naphthalene group, a heptalene group, a fluorene group, a spiro-fluorene 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, and an indenoanthracene group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a 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, and —Si(Q 301 )(Q 302 )(Q 303 ) (wherein Q 301  to Q 303  may each independently be selected from hydrogen, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 6 -C 60  aryl group, and a C 1 -C 60  heteroaryl group), 
     L 601  may be the same as described herein in connection with L 301 , 
     E 601  may be selected from the group consisting of: 
     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 benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group; and 
     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 benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a 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-fluorenyl 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 benzocarbazolyl group, a dibenzocarbazolyl group, an imidazopyridinyl group, and an imidazopyrimidinyl group, 
     xe1 may be selected from 0, 1, 2, and 3, and 
     xe2 may be selected from 1, 2, 3, and 4. 
     In one or more embodiments, the electron transport layer may include at least one selected from compounds represented by Formula 602: 
     
       
         
         
             
             
         
       
     
     In Formula 602, 
     X 611  may be selected from N and C-(L 611 ) xe611 -R 611 , X 612  may be selected from N and C-(L 612 ) xe612 -R 612 , and X 613  may be selected from N and C-(L 613 ) xe613 -R 613 , wherein at least one selected from X 611  to X 613  is N, 
     L 611  to L 616  may each independently be the same as described herein in connection with L 301 , 
     R 611  to R 616  may each independently be selected from the group consisting of: 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group; and 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, an azulenyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group, and 
     xe611 to xe616 may each independently be selected from 0, 1, 2, and 3. 
     The compound represented by Formula 601 and the compound represented by Formula 602 may each independently be selected from Compounds ET1 to ET15: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In one or more embodiments, the electron transport layer may include at least one selected from BCP, Bphen, Alq 3 , BAIq, TAZ, and NTAZ: 
     
       
         
         
             
             
         
       
     
     The thickness of the electron transport layer may be about 100 Å to about 1,000 Å, and in some embodiments, about 150 Å to about 500 Å. When the thickness of the electron transport layer is within these ranges, satisfactory electron transporting characteristics may be obtained without a substantial increase in driving voltage. 
     The electron transport layer may further include, in addition to the materials described above, a metal-containing material. 
     The metal-containing material may include a Li complex. The Li complex may include, for example, Compound ET-D1 (lithium quinolate, LiQ) and/or Compound ET-D2: 
     
       
         
         
             
             
         
       
     
     The electron transport region  170  may include an electron injection layer that facilitates electron injection from the second electrode  190 . 
     The electron injection layer may be formed on the electron transport layer using one or more suitable methods, such as vacuum deposition, spin coating, casting, an ink-jet printing, a laser-printing, and/or an LITI method. When the electron transport layer is formed by vacuum deposition and/or spin coating, the deposition and coating conditions used for forming the electron injection layer may be similar to the deposition and coating conditions used for forming the hole injection layer. 
     The electron injection layer may include at least one selected from LiF, NaCl, CsF, Li 2 O, BaO, and LiQ. 
     The thickness of the electron injection layer may be about 1 Å to about 100 Å, and in some embodiments, about 3 Å to about 90 Å. When the thickness of the electron injection layer is within these ranges, satisfactory electron injecting properties may be obtained without a substantial increase in driving voltage. 
     The second electrode  190  may be on the electron transport region  170 . The second electrode  190  may be a cathode that is an electron injection electrode. In this regard, a material for forming the second electrode  190  may be a material having a low work function, and non-limiting examples thereof may include a metal, an alloy, an electrically conductive compound, and a mixture thereof. For example, lithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), and/or magnesium-silver (Mg—Ag) may be used as the material for forming the second electrode  190 . In one or more embodiments, the material for forming the second electrode  190  may be ITO and/or IZO. The second electrode  190  may be a semi-transmissive electrode or a transmissive electrode. 
     The term “C 1 -C 60  alkyl group” as used herein may refer to a linear or branched aliphatic saturated hydrocarbon monovalent group having 1 to 60 carbon atoms, and non-limiting examples thereof may include a methyl group, an ethyl group, a propyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an iso-amyl group, and a hexyl group. The term “C 1 -C 60  alkylene group” as used herein may refer to a divalent group having substantially the same structure as the C 1 -C 60  alkyl group. 
     The term “C 1 -C 60  alkoxy group” as used herein may refer to a monovalent group represented by —O-A 101  (wherein A 101  is a C 1 -C 60  alkyl group), and non-limiting examples thereof may include a methoxy group, an ethoxy group, and an isopropyloxy group. 
     The term “C 2 -C 60  alkenyl group” as used herein may refer to a hydrocarbon group having at least one carbon-carbon double bond in the body (e.g., middle) or at the terminus of the C 2 -C 60  alkyl group, and non-limiting examples thereof may include an ethenyl group, a propenyl group, and a butenyl group. The term “C 2 -C 60  alkenylene group” as used herein may refer to a divalent group having substantially the same structure as the C 2 -C 60  alkenyl group. 
     The term “C 2 -C 60  alkynyl group” as used herein may refer to a hydrocarbon group having at least one carbon-carbon triple bond in the body (e.g., middle) or at the terminus of the C 2 -C 60  alkyl group, and non-limiting examples thereof may include an ethynyl group and a propynyl group. The term “C 2 -C 60  alkynylene group” as used herein may refer to a divalent group having substantially the same structure as the C 2 -C 60  alkynyl group. 
     The term “C 3 -C 10  cycloalkyl group” as used herein may refer to a monovalent saturated hydrocarbon monocyclic saturated group having 3 to 10 carbon atoms, and non-limiting examples thereof may include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, and a cycloheptyl group. The term “C 3 -C 10  cycloalkylene group” as used herein may refer to a divalent group having substantially the same structure as the C 3 -C 10  cycloalkyl group. 
     The term “C 1 -C 10  heterocycloalkyl group” as used herein may refer to a monovalent saturated monocyclic group having at least one heteroatom selected from N, O, phosphorus (P), silicon (Si) and sulfur (S) as a ring-forming atom and 1 to 10 carbon atoms, and non-limiting examples thereof may include a tetrahydrofuranyl group and a tetrahydrothiophenyl group. The term “C 1 -C 10  heterocycloalkylene group” as used herein may refer to a divalent group having substantially the same structure as the C 1 -C 10  heterocycloalkyl group. 
     The term “C 3 -C 10  cycloalkenyl group” as used herein may refer to a monovalent monocyclic group that has 3 to 10 carbon atoms and at least one carbon-carbon double bond in the ring thereof, and does not have aromaticity, and non-limiting examples thereof may include a cyclopentenyl group, a cyclohexenyl group, and a cycloheptenyl group. The term “C 3 -C 10  cycloalkenylene group” as used herein may refer to a divalent group having substantially the same structure as the C 3 -C 10  cycloalkenyl group. 
     The term “C 1 -C 10  heterocycloalkenyl group” as used herein may refer to a monovalent monocyclic group that has at least one heteroatom selected from N, O, P, Si, and S as a ring-forming atom, 1 to 10 carbon atoms, and at least one double bond in the ring. Non-limiting examples of the C 1 -C 10  heterocycloalkenyl group may include a 2,3-dihydrofuranyl group and a 2,3-dihydrothiophenyl group. The term “C 1 -C 10  heterocycloalkenylene group” as used herein may refer to a divalent group having substantially the same structure as the C 1 -C 10  heterocycloalkenyl group. 
     The term “C 6 -C 60  aryl group” as used herein may refer to a monovalent group having an aromatic system having 6 to 60 carbon atoms, and the term “C 6 -C 60  arylene group” as used herein may refer to a divalent group having an aromatic system having 6 to 60 carbon atoms. Non-limiting examples of the C 6 -C 60  aryl group may include a phenyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, a pyrenyl group, and a chrysenyl group. When the C 6 -C 60  aryl group and the C 6 -C 60  arylene group each independently include two or more rings, the respective rings may be fused (e.g., condensed), or may be linked (e.g., coupled) via a single bond. 
     The term “C 1 -C 60  heteroaryl group” as used herein may refer to a monovalent group having a heterocyclic aromatic system that has at least one heteroatom selected from N, O, Si, P, and S as a ring-forming atom, and 1 to 60 carbon atoms. The term “C 1 -C 60  heteroarylene group” as used herein may refer to a divalent group having a heterocyclic aromatic system that has at least one heteroatom selected from N, O, Si, P, and S as a ring-forming atom, and 1 to 60 carbon atoms. Non-limiting examples of the C 1 -C 60  heteroaryl group may include a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, and an isoquinolinyl group. When the C 1 -C 60  heteroaryl group and the C 1 -C 60  heteroarylene group each independently include two or more rings, the respective rings may be fused (e.g., condensed), or may be linked (e.g., coupled) via a single bond. 
     The term “C 6 -C 60  aryloxy group” as used herein may refer to a monovalent group represented by —O-A 102  (wherein A 102  is a C 6 -C 60  aryl group), and the term “C 6 -C 60  arylthio group” as used herein may refer to a monovalent group represented by —S-A 103  (wherein A 103  is a C 6 -C 60  aryl group). 
     The term “monovalent non-aromatic condensed polycyclic group” as used herein may refer to a monovalent group that has two or more rings condensed to each other, has only carbon atoms as ring-forming atoms (e.g., 8 to 60 carbon atoms), and has non-aromaticity in the entire molecular structure. A non-limiting example of the monovalent non-aromatic condensed polycyclic group may include a fluorenyl group. A divalent non-aromatic condensed polycyclic group as used herein may refer 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 may refer to a monovalent group that has two or more rings condensed to each other, has at least one heteroatom selected from N, O, Si, P, and S as a ring-forming atom, in addition to carbon atoms (e.g., 1 to 60 carbon atoms), and has non-aromaticity in the entire molecular structure. An example of the monovalent non-aromatic condensed heteropolycyclic group includes a carbazolyl group. The term “divalent non-aromatic condensed heteropolycyclic group” as used herein may refer to a divalent group having substantially the same structure as the monovalent non-aromatic condensed heteropolycyclic group. 
     In the present specification, at least one substituent of the substituted C 3 -C 10  cycloalkylene group, the substituted C 1 -C 10  heterocycloalkylene group, the substituted C 3 -C 10  cycloalkenylene group, the substituted C 1 -C 10  heterocycloalkenylene group, the substituted C 6 -C 60  arylene group, the substituted C 1 -C 60  heteroarylene group, the substituted divalent non-aromatic condensed polycyclic group, the substituted divalent non-aromatic condensed heteropolycyclic group, the substituted C 1 -C 60  alkyl group, the substituted C 2 -C 60  alkenyl group, the substituted C 2 -C 60  alkynyl group, the substituted C 1 -C 60  alkoxy group, the substituted C 3 -C 10  cycloalkyl group, the substituted C 1 -C 10  heterocycloalkyl group, the substituted C 3 -C 10  cycloalkenyl group, the substituted C 1 -C 10  heterocycloalkenyl group, the substituted C 6 -C 60  aryl group, the substituted C 6 -C 60  aryloxy group, the substituted C 6 -C 60  arylthio group, the substituted C 1 -C 60  heteroaryl group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group may be selected from the group consisting of: 
     deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 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, —CI, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 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, and —Si(Q 11 )(Q 12 )(Q 13 ); 
     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 amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 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, and —Si(Q 21 )(Q 22 )(Q 23 ); and 
     —Si(Q 31 )(Q 32 )(Q 33 ), 
     wherein Q 1  to Q 3 , Q 11  to Q 13 , Q 21  to Q 23 , and Q 31  to Q 33  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 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, and a monovalent non-aromatic condensed heteropolycyclic group. 
     The term “Ph” as used herein may refer to a phenyl group, the term “Me” as used herein may refer to a methyl group, the term “Et” as used herein may refer to an ethyl group, and the term “ter-Bu” or “Bu t ” as used herein may refer to a tert-butyl group. 
     The term “biphenyl group” as used herein may refer to “a phenyl group substituted with a phenyl group”. In other words, a biphenyl group is a phenyl group substituted with a C 6 -C 60  aryl group. 
     The term “terphenyl group” as used herein may refer to “a phenyl group substituted with a biphenyl group”. In other words, a terphenyl group is a phenyl group substituted with a C 6 -C 60  aryl group substituted with a C 6 -C 60  aryl group. 
     Hereinafter, an organic light-emitting device according to one or more embodiments of the present disclosure will be described in more detail with reference to Examples. 
     EXAMPLE 
     Example 1 
     As a substrate and an anode, a 15 Ω/cm 2  (1,200 Å) glass substrate, on which an indium tin oxide (ITO) anode (manufactured by Corning, Inc.) was formed, was cut into a size of 50 mm×50 mm×0.7 mm, and ultrasonically washed with isopropyl alcohol and pure water for 5 minutes each. Afterwards, the ITO glass substrate was irradiated by UV light for 30 minutes, cleaned by exposure to ozone, and mounted on a vacuum depositor. 
     2-TNATA was vacuum-deposited on the ITO anode of the glass substrate to form a hole injection layer having a thickness of 600 Å, and Compound 105 was vacuum-deposited on the hole injection layer to form a hole transport layer having a thickness of 300 Å. 
     Compound 1 was vacuum-deposited on the hole transport layer to form a hole auxiliary layer having a thickness of 60 Å, thereby forming a hole transport region. 
     CBP (as a host) and PD2 (as a dopant) were co-deposited at a weight ratio of 95:5 on the hole auxiliary layer to form an emission layer having a thickness of 20 nm. 
     ET1 was deposited on the emission layer to form an electron transport layer having a thickness of 300 Å, and LiF was deposited on the electron transport layer to form an electron injection layer having a thickness of 10 Å, thereby forming an electron transport region. 
     Al was deposited on the electron injection layer to form a cathode having a thickness of 3,000 Å, thereby manufacturing an organic light-emitting device: 
     
       
         
         
             
             
         
       
     
     Examples 2 and 3 
     Additional organic light-emitting devices were manufactured in substantially the same manner as in Example 1, except that the compounds listed in Table 1 were used instead of Compound 105 and Compound 1 in forming the hole transport layer and the hole auxiliary layer, respectively. 
     Comparative Example 1 
     An organic light-emitting device was manufactured in substantially the same manner as in Example 1, except that TPD was used instead of Compound 105 in forming the hole transport layer: 
     
       
         
         
             
             
         
       
     
     Comparative Example 2 
     An organic light-emitting device was manufactured in substantially the same manner as in Example 1, except that NPB was used instead of Compound 1 in forming the hole auxiliary layer: 
     
       
         
         
             
             
         
       
     
     Comparative Example 3 
     An organic light-emitting device was manufactured in substantially the same manner as in Example 1, except that TPD was used instead of Compound 105 in forming the hole transport layer and Compound 8 was used instead of Compound 1 in forming the hole auxiliary layer. 
     Comparative Example 4 
     An organic light-emitting device was manufactured in substantially the same manner as in Example 1, except that TPD was used instead of Compound 105 in forming the hole transport layer and NPB was used instead of Compound 1 in forming the hole auxiliary layer. 
     Comparative Example 5 
     An organic light-emitting device was manufactured in substantially the same manner as in Example 1, except that Compound A was used instead of Compound 105 in forming the hole transport layer and Compound B was used instead of Compound 1 in forming the hole auxiliary layer: 
     
       
         
         
             
             
         
       
     
     Comparative Example 6 
     An organic light-emitting device was manufactured in substantially the same manner as in Example 1, except that a hole auxiliary layer was not formed and Compound C was used instead of Compound 105 in forming the hole transport layer. 
     
       
         
         
             
             
         
       
     
     Comparative Example 7 
     An organic light-emitting device was manufactured in substantially the same manner as in Example 1, except that a hole auxiliary layer was not formed. 
     Evaluation Example 1 
     The driving voltage, current density, efficiency, brightness, emission color, and half-lifespan at 1,000 nit of each of the organic light-emitting devices of Examples 1 to 3 and Comparative Examples 1 to 7 were evaluated using a Keithley SMU 236 and a brightness meter PR650. The results are shown in Table 1. Here, the half-lifespan results are reported as the time at which the brightness of the organic light-emitting device became 50% of the initial brightness after being driven. 
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Material 
                 Material 
                   
                   
                   
                   
                   
                   
               
               
                   
                 for hole 
                 for hole 
                 Driving 
                 Current 
                   
                 Bright- 
                   
                 Half- 
               
               
                   
                 transport 
                 auxiliary 
                 voltage 
                 density 
                 Efficiency 
                 ness 
                 Emission 
                 lifespan 
               
               
                   
                 layer 
                 layer 
                 (V) 
                 (mA/cm 2 ) 
                 (cd/A) 
                 (cd/m 2 ) 
                 color 
                 (hr) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Example 1 
                 Compound 
                 Compound 
                 4.1 
                 10.5 
                 6.5 
                 545 
                 blue 
                 200 
               
               
                   
                 105 
                 1 
               
               
                 Example 2 
                 Compound 
                 Compound 
                 4.0 
                 9.9 
                 5.5 
                 550 
                 blue 
                 160 
               
               
                   
                 105 
                 4 
               
               
                 Example 3 
                 Compound 
                 Compound 
                 4.1 
                 10.3 
                 5.4 
                 560 
                 blue 
                 190 
               
               
                   
                 105 
                 7 
               
               
                 Comparative 
                 TPD 
                 Compound 
                 4.9 
                 12.4 
                 4.3 
                 450 
                 blue 
                 45 
               
               
                 Example 1 
                   
                 1 
               
               
                 Comparative 
                 Compound 
                 NPB 
                 4.6 
                 11.0 
                 3.7 
                 393 
                 blue 
                 79 
               
               
                 Example 2 
                 105 
               
               
                 Comparative 
                 TPD 
                 Compound 
                 5.9 
                 10.9 
                 2.9 
                 299 
                 blue 
                 92 
               
               
                 Example 3 
                   
                 8 
               
               
                 Comparative 
                 TPD 
                 NPB 
                 6.5 
                 9.8 
                 3.4 
                 345 
                 blue 
                 74 
               
               
                 Example 4 
               
               
                 Comparative 
                 Compound 
                 Compound 
                 4.3 
                 10.2 
                 5.1 
                 565 
                 blue 
                 140 
               
               
                 Example 5 
                 A 
                 B 
               
               
                 Comparative 
                 Compound 
                 — 
                 5.0 
                 14.0 
                 2.4 
                 254 
                 blue 
                 135 
               
               
                 Example 6 
                 C 
               
               
                 Comparative 
                 Compound 
                 — 
                 3.8 
                 14.0 
                 3.2 
                 324 
                 blue 
                 140 
               
               
                 Example 7 
                 105 
               
               
                   
               
            
           
         
       
     
     Referring to Table 1, it was confirmed that the organic light-emitting devices of Examples 1 to 3 each had a lower driving voltage, higher efficiency, better brightness, and a longer half-lifespan than the organic light-emitting devices of Comparative Examples 1 to 7. 
     It should be understood that the example embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as being available for similar features or aspects in other embodiments. 
     As used herein, the terms “substantially”, “about”, and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by those of ordinary skill in the art. 
     In addition, as used herein, the terms “use”, “using”, and “used” may be considered synonymous with the terms “utilize”, “utilizing”, and “utilized”, respectively. Further, the use of “may” when describing embodiments of the present disclosure refers to “one or more embodiments of the present disclosure”. 
     Also, any numerical range recited herein is intended to include all subranges of the same numerical precision subsumed within the recited range. For example, a range of “1.0 to 10.0” is intended to include all subranges between (and including) the recited minimum value of 1.0 and the recited maximum value of 10.0, that is, having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as, for example, 2.4 to 7.6. Any maximum numerical limitation recited herein is intended to include all lower numerical limitations subsumed therein and any minimum numerical limitation recited in this specification is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicant reserves the right to amend this specification, including the claims, to expressly recite any sub-range subsumed within the ranges expressly recited herein. 
     While one or more embodiments have been described with reference to the drawings, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the following claims and equivalents thereof.