Patent Publication Number: US-10333074-B2

Title: Organic light-emitting device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2015-0129279, filed on Sep. 11, 2015, in the Korean Intellectual Property Office, the entire content 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 wider viewing angles, higher contrast ratios, and shorter response times compared to devices of the related art. In addition, OLEDs may have better brightness, driving voltage, and response speed characteristics, and the ability to produce full-color images. 
     An organic light-emitting device may include a first electrode on a substrate, and a hole transport region, an emission layer, an electron transport region, and a second electrode sequentially positioned on the first electrode. Holes provided from the first electrode may move toward the emission layer through the hole transport region, and electrons provided from the second electrode may move toward the emission layer through the electron transport region. Carriers (such as holes and electrons) may recombine in the emission layer to produce excitons. These excitons change (e.g., decay or 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 a high 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 aspects of example embodiments of the present disclosure provides an organic light-emitting device including a first electrode, a second electrode facing the first electrode, and an organic layer including an emission layer between the first electrode and the second electrode, wherein the organic layer includes a first compound and a second compound, the first compound is selected from compounds represented by Formula 1, and the second compound is selected from compounds represented by Formula 2: 
     
       
         
         
             
             
         
       
     
     In Formulae 1 and 2, 
     ring A 1  may be selected from a C 5 -C 30  carbocyclic group and a C 1 -C 30  heterocyclic group, 
     X 1  may be selected from oxygen (O) and sulfur (S), 
     L 1  to L 4  and L 21  to L 23  may each independently be selected from a substituted or unsubstituted C 3 -C 10  cycloalkylene group, a substituted or unsubstituted C 1 -C 10  heterocycloalkylene group, a substituted or unsubstituted C 3 -C 10  cycloalkenylene group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenylene group, a substituted or unsubstituted C 6 -C 60  arylene group, a substituted or unsubstituted C 1 -C 60  heteroarylene group, a substituted or unsubstituted divalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted divalent non-aromatic condensed heteropolycyclic group, 
     a1 to a4 and a21 to a23 may each independently be selected from 0, 1, 2, and 3, 
     R 1  to R 6 , R 11 , R 12 , and R 21  to R 23  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, —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 4 )(Q 5 ), and —N(Q 6 )(Q 7 ), 
     b1 to b6 and b21 to b23 may each independently be an integer selected from 0 to 10, 
     n21 to n23 may each independently be an integer selected from 0 to 4, and 
     at least one substituent of the substituted C 5 -C 30  carbocyclic group, substituted C 1 -C 30  heterocyclic group, substituted C 1 -C 10  heterocycloalkylene group, substituted C 3 -C 10  cycloalkenylene group, substituted C 1 -C 10  heterocycloalkenylene group, substituted C 6 -C 60  arylene group, substituted C 1 -C 60  heteroarylene group, substituted divalent non-aromatic condensed polycyclic group, substituted divalent non-aromatic condensed heteropolycyclic group, substituted C 1 -C 60  alkyl group, substituted C 2 -C 60  alkenyl group, substituted C 2 -C 60  alkynyl group, substituted C 1 -C 60  alkoxy group, substituted C 3 -C 10  cycloalkyl group, substituted C 1 -C 10  heterocycloalkyl group, substituted C 3 -C 10  cycloalkenyl group, substituted C 1 -C 10  heterocycloalkenyl group, substituted C 6 -C 60  aryl group, substituted C 6 -C 60  aryloxy group, substituted C 6 -C 60  arylthio group, substituted C 1 -C 60  heteroaryl group, substituted monovalent non-aromatic condensed polycyclic group, and substituted monovalent non-aromatic condensed heteropolycyclic group may be selected from the group consisting of: 
     deuterium, —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, —Si(Q 11 )(Q 12 )(Q 13 ), —B(Q 14 )(Q 15 ), and —N(Q 16 )(Q 17 ), 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group; 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an 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, —Si(Q 21 )(Q 22 )(Q 23 ), —B(Q 24 )(Q 25 ), and —N(Q 26 )(Q 27 ); and 
     —Si(Q 31 )(Q 32 )(Q 33 ), —B(Q 34 )(Q 35 ), and —N(Q 36 )(Q 37 ), 
     wherein Q 1  to Q 7 , Q 11  to Q 17 , Q 21  to Q 27 , and Q 31  to Q 37  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, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       These and/or other aspects will become apparent and more readily appreciated from the following description of the example embodiments, taken in conjunction with the drawing, which is a schematic drawing illustrating a structure of an organic light-emitting device according to one or more embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in more detail to example embodiments, examples of which are illustrated in the accompanying drawing, wherein like reference numerals refer to like elements throughout and duplicative descriptions thereof may not be provided. In this regard, the present example embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the example embodiments are merely described below, by referring to the 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 selected from”, “one of”, “at least one selected from”, and “one selected from” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     In the drawing, the thicknesses of layers, films, panels, regions, etc., may be exaggerated for clarity. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening element(s) may also be present. In contrast, when an element is referred to as being “directly on” another element, no intervening elements are present. 
     An organic light-emitting device according to an embodiment of the present disclosure will be described with reference to the drawing. 
     The drawing is a schematic view of an organic light-emitting device  10  according to an embodiment of the present disclosure. The organic light-emitting device  10  includes a first electrode  110 , an organic layer  150 , and a second electrode  190 . 
     Hereinafter, the structure of an organic light-emitting device according to an embodiment of the present disclosure and a method of manufacturing an organic light-emitting device 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  or above the second electrode  190 . The substrate may be a glass substrate or a transparent plastic substrate having excellent mechanical strength, thermal stability, transparency, surface smoothness, ease of handling, and/or water-resistance. 
     The first electrode  110  may be formed by depositing and/or sputtering a material for forming the first electrode  110  on the substrate. When the first electrode  110  is an anode, the material for the first electrode  110  may be selected from materials with a high work function to facilitate hole injection. The first electrode  110  may be a reflective electrode or a transmissive electrode. The material for the first electrode  110  may be a transparent and/or 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. 
     An organic layer  150  may be on the first electrode  110 . The organic layer  150  may include an emission layer. 
     The organic layer  150  may further include a hole transport region between the first electrode and the emission layer, and an electron transport region between the emission layer and the second electrode. 
     The hole transport region may include at least one selected from a hole injection layer (HIL), a hole transport layer (HTL), a buffer layer, and an electron blocking layer (EBL), and the electron transport region may include at least one selected from a hole blocking layer (HBL), an electron transport layer (ETL), and an electron injection layer (EIL), but embodiments of the present disclosure are not limited thereto. 
     The hole transport region may have a single-layered structure formed of a single material, a single-layered structure formed of a plurality of different materials, or a multi-layered structure having a plurality of layers formed of a plurality of different materials. 
     For example, the hole transport region may have a single-layered structure formed of a plurality of different materials, a structure of hole injection layer/hole transport layer, a structure of hole injection layer/hole transport layer/buffer layer, a structure of hole injection layer/buffer layer, a structure of hole transport layer/buffer layer, or a structure of hole injection layer/hole transport layer/electron blocking layer, wherein layers of each structure are sequentially stacked from the first electrode  110  in each stated order, but embodiments of the present disclosure are not limited thereto. 
     When the hole transport region includes a hole injection layer, the hole injection layer may be formed on the first electrode  110  using one or more suitable methods selected from vacuum deposition, spin coating, casting, a Langmuir-Blodgett (LB) method, ink-jet printing, laser-printing, and laser-induced thermal imaging. 
     When a hole injection layer is formed by vacuum deposition, the vacuum deposition may be performed at a deposition temperature of about 100 to about 500° C., at a vacuum degree of about 10 −8  to about 10 −3  torr, and at a deposition rate of about 0.01 to about 100 Å/sec, depending on the compound to be deposited in 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. 
     When the hole transport region includes a hole transport layer, the hole transport layer may be formed on the first electrode  110  or on the hole injection layer using one or more suitable methods selected from vacuum deposition, spin coating, casting, a LB method, ink-jet printing, laser-printing, and laser-induced thermal imaging. When the hole transport layer is formed by vacuum deposition and/or spin coating, the deposition and coating conditions for the hole transport layer may be similar to the deposition and coating conditions used for the hole injection layer. 
     The hole transport region may include the condensed cyclic compound represented by Formula 1. For example, the hole transport region may include the hole transport layer, wherein the hole transport layer includes the condensed cyclic compound represented by Formula 1. 
     In some embodiments, the hole transport region may include 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), (polyaniline)/poly(4-styrenesulfonate) (PANI/PSS), a compound represented by Formula 201, and a compound represented by Formula 202: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 201 and 202, 
     L 201  to L 205  may each be the same as described herein in connection with L 1 , 
     xa1 to xa4 may each independently be selected from 0, 1, 2, and 3, 
     xa5 may be selected from 1, 2, 3, 4, and 5, and 
     R 201  to R 204  may each independently be selected from a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group. 
     For example, in Formulae 201 and 202, 
     L 201  to L 205  may each independently be selected from the group consisting of: 
     a phenylene group, a naphthylene group, a fluorenylene group, a spiro-bifluorenylene group, a benzofluorene group, a dibenzofluorene group, a phenanthrenylene group, an anthracenylene group, a pyrenylene group, a chrysenylene group, a pyridinylene group, a pyrazinylene group, a pyrimidinylene group, a pyridazinylene group, a quinolinylene group, an isoquinolinylene group, a quinoxalinylene group, a quinazolinylene group, a carbazolylene group, and a triazinylene group; and 
     a phenylene group, a naphthylene group, a fluorenylene group, a spiro-bifluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenanthrenylene group, an anthracenylene group, a pyrenylene group, a chrysenylene group, a pyridinylene group, a pyrazinylene group, a pyrimidinylene group, a pyridazinylene group, a quinolinylene group, an isoquinolinylene group, a quinoxalinylene group, a quinazolinylene group, a carbazolylene group, and a triazinylene 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 biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group, 
     xa1 to xa4 may each independently be selected from 0, 1, and 2, 
     xa5 may be selected from 1, 2, and 3, and 
     R 201  to R 204  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-bifluorenyl 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 biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a 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 biphenyl group, a terphenyl group, a naphthyl group, an azulenyl group, a fluorenyl group, a spiro-bifluorenyl 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, but embodiments of the present disclosure are not limited thereto. 
     The compound represented by Formula 201 may be further represented by Formula 201A: 
     
       
         
         
             
             
         
       
     
     In some embodiments, the compound represented by Formula 201 may be further represented by Formula 201A-1, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     In some embodiments, the compound represented by Formula 202 may be further represented by Formula 202A, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     In Formulae 201A, 201A-1, and 202A, L 201  to L 203 , xa1 to xa3, xa5, and R 202  to R 204  may each be the same as described herein in connection with Formulae 201 and 202, R 211  and R 212  may each be the same as described herein in connection with R 203 , and R 213  to R 217  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an 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, and a monovalent non-aromatic condensed heteropolycyclic group. 
     The compound represented by Formula 201 and the compound represented by Formula 202 may include Compounds HT1 to HT20, but embodiments of the present disclosure are not limited thereto. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The thickness of the hole transport region may be about 100 Å to about 10,000 Å, and in some embodiments, about 100 Å to about 1,000 Å. When the hole transport region includes at least one selected from a hole injection layer and a hole transport layer, the thickness of the hole injection layer may be about 100 Å to about 10,000 Å, and in some embodiments, about 100 Å to about 1,000 Å. The thickness of the hole transport layer may be about 50 Å to about 2,000 Å, and in some embodiments, about 100 Å to about 1,500 Å. When the thicknesses of the hole transport region, the hole injection layer, and the hole transport layer are each within these ranges, satisfactory hole transporting characteristics may be obtained without a substantial increase in driving voltage. 
     The hole transport region may further include, in addition to these materials, a charge-generation material for the improvement of conductive properties. The charge-generation material may be homogeneously or non-homogeneously dispersed in the hole transport region. 
     The charge-generation material may be, for example, a p-dopant. The p-dopant may be one selected from a quinone derivative, a metal oxide, and a cyano group-containing compound, but embodiments of the present disclosure are not limited thereto. Non-limiting examples of the p-dopant may include a quinone derivative (such as tetracyanoquinonedimethane (TCNQ) and/or 2,3,5,6-tetrafluoro-tetracyano-1,4-benzoquinonedimethane (F4-TCNQ)); a metal oxide (such as a tungsten oxide and/or a molybdenum oxide), and Compound HT-D1 (illustrated below), but embodiments of the present disclosure are not limited thereto. 
     
       
         
         
             
             
         
       
     
     The hole transport region may further include, in addition to the hole injection layer and the hole transport layer, at least one selected from a buffer layer and an electron blocking layer. Since 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), the light-emission efficiency of a formed organic light-emitting device may be improved. Materials that are included in the hole transport region may be used in the buffer layer. The electron blocking layer may prevent or reduce injection of electrons from the electron transport region. 
     An emission layer may be formed on the hole transport region using one or more suitable methods selected from vacuum deposition, spin coating, casting, a LB method, ink-jet printing, laser-printing, and laser-induced thermal imaging. When the emission layer is formed by vacuum deposition or spin coating, the deposition and coating conditions for the emission layer may be similar to the deposition and coating conditions used for the hole injection layer. 
     When the organic light-emitting device  10  is a full color organic light-emitting device, the emission layer may be patterned into a red emission layer, a green emission layer, and/or a blue emission layer, according to a sub pixel. In some embodiments, the emission layer may have a stacked structure of a red emission layer, a green emission layer, and a blue emission layer, or may include a red-light emission material, a green-light emission material, and a blue-light emission material, which are mixed with each other in a single layer to thereby emit white light. 
     The emission layer may include a first compound and a second compound, the first compound may be selected from compounds represented by Formula 1, and the second compound may be selected from compounds represented by Formula 2: 
     
       
         
         
             
             
         
       
     
     Ring A 1  in Formula 1 may be selected from a C 5 -C 30  carbocyclic group and C 1 -C 30  heterocyclic group. 
     For example, ring A 1  in Formula 1 may be selected from a benzene, a naphthalene, a fluorene, a spiro-fluorene, a phenanthrene, an anthracene, a pyrrole, a thiophene, a furan, an imidazole, a pyrazole, a thiazole, an isothiazole, an oxazole, an isoxazole, a pyridine, a pyrazine, a pyrimidine, a pyridazine, an iso-indole, an indole, an indazole, a quinoline, an isoquinoline, a benzoquinoline, a quinoxaline, a quinazoline, a phthalazinine, a naphthylidine, a phenanthroline, a benzimidazole, a benzofuran, a benzothiophene, a benzothiazole, a benzoxazole, an isobenzoxazole, and a triazine, but embodiments of the present disclosure are not limited thereto. 
     In some embodiments, ring A 1  in Formula 1 may be selected from a benzene, a naphthalene, an anthracene, a pyridine, a pyrimidine, a quinoline, an isoquinoline, a benzoquinoline, a quinoxaline, a quinazoline, and a phenanthroline, but embodiments of the present disclosure are not limited thereto. 
     In some embodiments, ring A1 may be selected from a benzene and a naphthalene. 
     X 1  in Formula 1 may be selected from oxygen (O) and sulfur (S). In some embodiments, X 1  in Formula 1 may be 0. 
     L 1  to L 4  and L 21  to L 23  in Formulae 1 and 2 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. 
     For example, L 1  to L 4  and L 21  to L 23  in Formulae 1 and 2 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 pyrrolylene group, a thiophenylene group, a furanylene group, an imidazolylene group, a pyrazolylene group, a thiazolylene group, an isothiazolylene group, an oxazolylene group, an isoxazolylene group, a pyridinylene group, a pyrazinylene group, a pyrimidinylene group, a pyridazinylene group, an isoindolylene group, an indolylene group, an indazolylene group, a purinylene group, a quinolinylene group, an isoquinolinylene group, a benzoquinolinylene group, a phthalazinylene group, a naphthyridinylene group, a quinoxalinylene group, a quinazolinylene group, a cinnolinylene group, a carbazolylene group, a phenanthridinylene group, an acridinylene group, a phenanthrolinylene group, a phenazinylene group, a benzimidazolylene group, a benzofuranylene group, a benzothiophenylene group, an isobenzothiazolylene group, a benzoxazolylene group, an isobenzoxazolylene group, a triazolylene group, a tetrazolylene group, an oxadiazolylene group, a triazinylene group, a dibenzofuranylene group, a dibenzothiophenylene group, a benzocarbazolylene group, a dibenzocarbazolylene group, a thiadiazolylene group, an imidazopyridinylene group, and an imidazopyrimidinylene group; and 
     a phenylene group, a pentalenylene group, an indenylene group, a naphthylene group, an azulenylene group, a heptalenylene group, an indacenylene group, an acenaphthylene group, a fluorenylene group, a spiro-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 pyrrolylene group, a thiophenylene group, a furanylene group, an imidazolylene group, a pyrazolylene group, a thiazolylene group, an isothiazolylene group, an oxazolylene group, an isoxazolylene group, a pyridinylene group, a pyrazinylene group, a pyrimidinylene group, a pyridazinylene group, an isoindolylene group, an indolylene group, an indazolylene group, a purinylene group, a quinolinylene group, an isoquinolinylene group, a benzoquinolinylene group, a phthalazinylene group, a naphthyridinylene group, a quinoxalinylene group, a quinazolinylene group, a cinnolinylene group, a carbazolylene group, a phenanthridinylene group, an acridinylene group, a phenanthrolinylene group, a phenazinylene group, a benzimidazolylene group, a benzofuranylene group, a benzothiophenylene group, an isobenzothiazolylene group, a benzoxazolylene group, an isobenzoxazolylene group, a triazolylene group, a tetrazolylene group, an oxadiazolylene group, a triazinylene group, a dibenzofuranylene group, a dibenzothiophenylene group, a benzocarbazolylene group, a dibenzocarbazolylene group, a thiadiazolylene group, an imidazopyridinylene group, and an imidazopyrimidinylene group, each substituted with at least one selected from deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an 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 biphenyl group, a terphenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-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, a thiadiazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, —Si(Q 31 )(Q 32 )(Q 33 ), —B(Q 34 )(Q 35 ), and —N(Q 36 )(Q 37 ), 
     wherein Q 31  to Q 37  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, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group, but embodiments of the present disclosure are not limited thereto. 
     For example, L 1  to L 4  and L 21  to L 23  in Formulae 1 and 2 may each independently be selected from groups represented by Formulae 3-1 to 3-18, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 3-1 to 3-18, 
     Z 1  may 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 C 2 -C 20  alkynyl group, a C 1 -C 20  alkoxy group, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a triphenylenyl 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 benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a carbazolyl group, a triazinyl group, —Si(Q 31 )(Q 32 )(Q 33 ), —B(Q 34 )(Q 35 ), and —N(Q 36 )(Q 37 ), 
     wherein Q 31  to Q 37  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, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl 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, d5 may be selected from 1 and 2, d6 may be an integer selected from 1 to 5, and * and *′ may each indicate a binding site to a neighboring atom. 
     For example, L 1  to L 4  and L 21  to L 23  in Formulae 1 and 2 may each independently be selected from groups represented by Formulae 4-1 to 4-26, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     and * and *′ in Formulae 4-1 to 4-26 may each indicate a binding site to a neighboring atom. 
     a1 to a4 and a21 to a23 in Formulae 1 and 2 may each independently be selected from 0, 1, 2, and 3. a1 indicates the number of L 1  in Formula 1, and when a1 is 2 or more, each L 1  group may be identical to or different from each other. When a1 is 0, *-(L 1 ) a1 -*′ may be a single bond. In some embodiments, a1 may be selected from 0, 1, and 2. In some embodiments, a1 may be selected from 0 and 1. a2 to a4 and a21 to a23 may each be the same as described herein in connection with a1 in Formulae 1 and 2. 
     In some embodiments, in Formula 1, a1 may be 0, a2 may be 0, a3 may be 0, and a4 may be 0; a1 may be 0, a2 may be 1, a3 may be 0, and a4 may be 0; a1 may be 0, a2 may be 0, a3 may be 1, and a4 may be 0; or a1 may be 0, a2 may be 1, a3 may be 1, and a4 may be 0, and in some embodiments, in Formula 2, a21 may be 1, a22 may be 0, and a23 may be 0, but embodiments of the present disclosure are not limited thereto. 
     In some embodiments, R 1  to R 6 , R 11 , R 12 , and R 21  to R 23  in Formulae 1 and 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 substituted or unsubstituted C 1 -C 60  alkyl group, a substituted or unsubstituted C 2 -C 60  alkenyl group, a substituted or unsubstituted C 2 -C 60  alkynyl group, a substituted or unsubstituted C 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkyl group, a substituted or unsubstituted C 3 -C 10  cycloalkenyl group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenyl group, a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 6 -C 60  aryloxy group, a substituted or unsubstituted C 6 -C 60  arylthio group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 4 )(Q 5 ), and —N(Q 6 )(Q 7 ). 
     For example, R 1  to R 6 , R 11 , R 12 , and R 21  to R 23  in Formulae 1 and 2 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 C 1 -C 20  alkyl group, and a C 1 -C 20  alkoxy group; 
     a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-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 benzocarbazolyl group, and a dibenzocarbazolyl 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 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 benzocarbazolyl group, and a dibenzocarbazolyl 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 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, a triazinyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, —Si(Q 31 )(Q 32 )(Q 33 ), —B(Q 34 )(Q 35 ), and —N(Q 36 )(Q 37 ); and 
     —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 4 )(Q 5 ), and —N(Q 6 )(Q 7 ), 
     wherein Q 1  to Q 7  and Q 31  to Q 37  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, but embodiments of the present disclosure are not limited thereto. 
     For example, R 1  to R 6 , R 11 , R 12 , and R 21  to R 23  in Formulae 1 and 2 may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a methyl group, an ethyl group, a propyl group, an iso-propyl group, a butyl group, an iso-butyl group, a sec-butyl group, a tert-butyl group, a methoxy group, an ethoxy group, an iso-propoxy group, a butoxy group, an iso-butoxy group, a sec-butoxy group, a tert-butoxy group, and a group represented by any of Formulae 6-1 to 6-69, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 6-1 to 6-69, 
     Y 11  may be selected from O, S, S(═O), S(═O) 2 , C(Z 14 )(Z 15 ), N(Z 16 ), and Si(Z 17 )(Z 18 ), 
     Z 11  to Z 18  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 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, and a phosphoric acid group or a salt thereof; 
     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; 
     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 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, an imidazopyrimidinyl group, —Si(Q 21 )(Q 22 )(Q 23 ), —B(Q 24 )(Q 25 ), and —N(Q 26 )(Q 27 ); and 
     —Si(Q 31 )(Q 32 )(Q 33 ), —B(Q 34 )(Q 35 ), and —N(Q 36 )(Q 37 ), 
     wherein Q 1  to Q 3 , Q 6 , Q 7 , Q 21  to Q 27  and Q 31  to Q 37  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, and a carbazolyl group, 
     e1 may be an integer selected from 1 to 5, e2 may be 1 or 2, e3 may be an integer selected from 1 to 3, e4 may be an integer selected from 1 to 4, e5 may be an integer selected from 1 to 5, e6 may be an integer selected from 1 to 6, e7 may be an integer selected from 1 to 7, and * may indicate a binding site to a neighboring atom. 
     In some embodiments, R 1  to R 6 , R 11 , R 12 , and R 21  to R 23  in Formulae 1 and 2 may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a methyl group, an ethyl group, a propyl group, an iso-propyl group, a butyl group, an iso-butyl group, a sec-butyl group, a tert-butyl group, a methoxy group, an ethoxy group, an iso-propoxy group, a butoxy group, an iso-butoxy group, a sec-butoxy group, a tert-butoxy group, and a group represented by any of Formulae 7-1 to 7-83, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     * in Formulae 7-1 to 7-83 may indicate a binding site to a neighboring atom. 
     In some embodiments, in Formulae 1 and 2, R 1 , R 2 , and R 21  may each independently be selected from groups represented by Formulae 7-1 to 7-83, and R 3  to R 6 , R 11 , R 12 , R 22 , and R 23  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a methyl group, an ethyl group, a propyl group, an iso-propyl group, a butyl group, an iso-butyl group, a sec-butyl group, a tert-butyl group, a methoxy group, an ethoxy group, an iso-propoxy group, a butoxy group, an iso-butoxy group, a sec-butoxy group, and a tert-butoxy group, but embodiments of the present disclosure are not limited thereto. 
     In some embodiments, R 1  may be a group represented by Formula 7-1, R 2  and R 21  may each independently be selected from groups represented by Formulae 7-1 to 7-83, and R 3  to R 6 , R 11 , R 12 , R 22 , and R 23  may each independently be selected from hydrogen, deuterium, —F, —Cl, —Br, —I, a methyl group, an ethyl group, a propyl group, an iso-propyl group, a butyl group, an iso-butyl group, a sec-butyl group, a tert-butyl group, a methoxy group, an ethoxy group, an iso-propoxy group, a butoxy group, an iso-butoxy group, a sec-butoxy group, and a tert-butoxy group, but embodiments of the present disclosure are not limited thereto. 
     b1 to b6 and b21 to b23 in Formulae 1 and 2 may each independently be an integer selected from 0 to 10. b1 indicates the number of R 1  in Formula 1, and when b1 is 2 or more, each R 1  group may be identical to or different from each other. In some embodiments, b1 in Formula 1 may be selected from 0, 1, and 2. In some embodiments, b1 may be selected from 0 and 1. b2 to b6 and b21 to b23 may each be the same as described herein in connection with b1 and Formulae 1 and 2. 
     n21 to n23 in Formula 2 may each independently be an integer selected from 0 to 4. n21 indicates the number of *-(L 21 ) a21 -(R 21 ) b21 -*′ in Formula 2, and when n21 is 2 or more, each *-(L 21 ) a21 -(R 21 ) b21 -*′ moiety may be identical to or different from each other. In some embodiments, n21 may be selected from 0 and 1. n22 and n23 each may be the same as described herein in connection with n21 and Formula 2. 
     For example, n21 may be 1, n22 may be 0, and n23 may be 0, but embodiments of the present disclosure are not limited thereto. 
     In some embodiments, the sum of n21, n22, and n23 is not 0. 
     In some embodiments, the first compound may be selected from compounds represented by Formulae 1-1 to 1-4, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     Ring A 1 , X 1 , L 1  to L 4 , a1 to a4, R 1  to R 6 , R 11 , R 12 , and b1 to b6 in Formulae 1-1 to 1-4 may each be the same as described herein in connection with Formula 1. 
     In some embodiments, the first compound may be selected from compounds represented by Formulae 1-1-1 to 1-1-4, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 1-1-1 to 1-1-4, 
     X 1 , L 2 , L 3 , a2, a3, R 2  to R 6 , R 11 , R 12 , b2, and b4 to b6 may each be the same as described herein in connection with Formula 1, 
     Z 11  may 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 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 carbazolyl group, a benzocarbazolyl group, and a dibenzocarbazolyl group, 
     b3a may be an integer selected from 0 to 4, b3b may be an integer selected from 0 to 6, and e1 may be an integer selected from 0 to 5. 
     In some embodiments, the second compound may be selected from compounds represented by Formulae 2-1 and 2-2, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     In Formulae 2-1 and 2-2, 
     L 21 , a21, and b21 may each be the same as described herein in connection with Formula 2, 
     R 21a  to R 21d  may each be the same as described herein in connection with R 21 , R 22a  to R 22d  may each be the same as described herein in connection with R 22 , and R 23a  to R 23d  may each be the same as described herein in connection with R 23 . 
     For example, the first compound may be selected from Compounds 1-1 to 1-54, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, the second compound may be selected from Compounds 2-1 to 2-24, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The emission layer may further include a third compound. 
     In some embodiments, the third compound may be selected from organometallic complexes represented by Formula 401, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     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 (N) and carbon (C), 
     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, and when A 401  has two or more substituents, the two or more substituents of A 401  may bind (e.g., couple) to each other to form a saturated or unsaturated ring; when A 402  has two or more substituents, the two or more substituents of A 402  may bind (e.g., couple) to each other to form a saturated or unsaturated ring, 
     at least one substituent of the substituted benzene, substituted naphthalene, substituted fluorene, substituted spiro-fluorene, substituted indene, substituted pyrrole, substituted thiophene, substituted furan, substituted imidazole, substituted pyrazole, substituted thiazole, substituted isothiazole, substituted oxazole, substituted isoxazole, substituted pyridine, substituted pyrazine, substituted pyrimidine, substituted pyridazine, substituted quinoline, substituted isoquinoline, substituted benzoquinoline, substituted quinoxaline, substituted quinazoline, substituted carbazole, substituted benzimidazole, substituted benzofuran, substituted benzothiophene, substituted isobenzothiophene, substituted benzoxazole, substituted isobenzoxazole, substituted triazole, substituted oxadiazole, substituted triazine, substituted dibenzofuran, and 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, —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 (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 422 ), —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  may be a monovalent, divalent, or trivalent organic ligand. For example, 
     L 401  may be selected from a halogen ligand (for example, chloride (Cl) and/or fluoride (F)), a diketone ligand (for example, acetylacetonate, 1,3-diphenyl-1,3-propandionate, 2,2,6,6-tetramethyl-3,5-heptandionate, 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 ligand, and/or a phosphorus-based ligand (for example, phosphine and/or phosphite), but embodiments of the present disclosure are not limited thereto. 
     Q 401  to Q 407 , Q 411  to Q 417 , and Q 421  to Q 427  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 A 401  in Formula 401 has two or more substituents, the substituents of A 402  may bind (e.g., couple) to each other to form a saturated or unsaturated ring. 
     When A 402  in Formula 401 has two or more substituents, the substituents of A 402  may bind (e.g., couple) to each other to form a saturated or unsaturated ring. 
     When xc1 in Formula 401 is two or more, a plurality of ligands 
                         
in Formula 401 may be identical or different. When xc1 in Formula 401 is two or more, A 401  and A 402  may be respectively connected (e.g., coupled) to A 401  and A 402  of other neighboring ligands via a linker (for example, a C 1 -C 5  alkylene, —N(R′)— (wherein R′ may be a C 1 -C 10  alkyl group or a C 6 -C 20  aryl group) or C(═O)— therebetween), or directly (via a bond).
 
     The phosphorescent dopant may be selected from Compounds PD1 to PD76, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, the third compound may be selected from organometallic complexes represented by Formula 501, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     In Formula 501, 
     Ar 501  may be selected from the group consisting of: 
     a naphthalene, a heptalene, a fluorene, a spiro-fluorene, a benzofluorene, a dibenzofluorene, a phenalene, a phenanthrene, an anthracene, a fluoranthene, a triphenylene, a pyrene, a chrysene, a naphthacene, a picene, a perylene, a pentaphene, and an indenoanthracene; and 
     a naphthalene, a heptalene, a fluorene, a spiro-fluorene, a benzofluorene, a dibenzofluorene, a phenalene, a phenanthrene, an anthracene, a fluoranthene, a triphenylene, a pyrene, a chrysene, a naphthacene, a picene, a perylene, a pentaphene, and an indenoanthracene, 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 be the same as described herein in connection with L 1 , 
     R 501  and R 502  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 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 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, 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 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, 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 third compound may include at least one selected from Compounds FD1 to FD9; 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The organic light-emitting device may concurrently (e.g., simultaneously) include the compound represented by Formula 1 (which is the first compound) and the compound represented by Formula 2 (which is the second compound) in the emission layer. The compound represented by Formula 1 may include an xanthenyl group (in which X 1  in Formula 1 is O) or a thioxanthenyl group (in which X 1  in Formula 1 is S). Due to the inclusion of the xanthenyl group or thioxanthenyl group, the compound represented by Formula 1 may have a high glass transition temperature and/or a high melting point. The compound represented by Formula 2 has a triphenylenyl group, and due to the inclusion of the triphenylenyl group, the compound represented by Formula 2 may have a high T1 (triplet) energy level (e.g., about 2.6 to 2.7 eV). Accordingly, an organic light-emitting device concurrently (e.g., simultaneously) including the compound represented by Formula 1 and the compound represented by Formula 2 may exhibit high heat resistance and high durability, thereby having a long lifespan, and due to the increased balance between electrons and holes, the organic light-emitting device may show high efficiency. 
     In some embodiments, the first compound and the second compound included in the emission layer may act as a host, and the third compound included in the emission layer may act as a dopant. 
     In some embodiments, the emission layer includes a host and a dopant, and the host may include the first compound and the second compound, and the dopant may include the third compound. 
     An organic light-emitting device including the first compound, the second compound, and the third compound may be a phosphorescent device. The organic light-emitting device may have a long wavelength in the red emission region, and accordingly, its color region may be wide, thereby providing a wide color gamut. 
     In some embodiments, the weight ratio of the first compound to the second compound in the emission layer may be 1:9 to 9:1. 
     In some embodiments, the weight ratio of the host and the dopant in the emission layer may be 7:3 to 9.5:0.5. In some embodiments, the weight ratio of the host and the dopant in the emission layer may be 8:2 to 9:1. However, the weight ratio thereof is not limited to these ranges. 
     The term “organic layer” used herein may refer to a single layer and/or a plurality of layers between the first electrode and the second electrode of an organic light-emitting device. The material included in the “organic layer” is not limited to being an organic material. 
     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 this range, excellent light-emission characteristics may be obtained without a substantial increase in driving voltage. 
     An electron transport region may be on the emission layer. 
     The electron transport region may include at least one selected from a hole blocking layer, an electron transport layer (ETL), and an electron injection layer, but embodiments of the present disclosure are not limited thereto. 
     For example, the electron transport region may have a structure of electron transport layer/electron injection layer 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 in each stated order, but the structures of embodiments of the present disclosure are not limited thereto. 
     According to an embodiment of the present disclosure, the organic layer  150  of the organic light-emitting device may include an electron transport region between the emission layer and the second electrode  190 . 
     When the electron transport region includes a hole blocking layer, the hole blocking layer may be formed on the emission layer using one or more suitable methods selected from vacuum deposition, spin coating, casting, a LB method, ink-jet printing, laser-printing, and laser-induced thermal imaging. When a hole blocking layer is formed by vacuum deposition and/or spin coating, the deposition and coating conditions for the electron transport layer may be similar to the deposition and coating conditions used for the hole injection layer. 
     The hole blocking layer may include, for example, at least one selected from BCP and Bphen, but embodiments of the present disclosure are not limited thereto: 
     
       
         
         
             
             
         
       
     
     The thickness of the hole blocking layer may be about 20 Å to about 1,000 Å, and in some embodiments, about 30 Å to about 300 Å. When the thickness of the hole blocking layer is within these ranges, the hole blocking layer may have improved hole blocking ability without a substantial increase in driving voltage. 
     The electron transport region may include an electron transport layer. The electron transport layer may be formed on the emission layer or on the hole blocking layer using one or more suitable methods selected from vacuum deposition, spin coating, casting, a LB method, ink-jet printing, laser-printing, and laser-induced thermal imaging. When an electron transport layer is formed by vacuum deposition and/or spin coating, the deposition and coating conditions for the electron transport layer may be similar to the deposition and coating conditions used for the hole injection layer. 
     In some embodiments, the electron transport layer may include at least one compound selected from a compound represented by Formula 601 and a compound represented by Formula 602 illustrated below:
 
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, a heptalene, a fluorene, a spiro-bifluorene, a benzofluorene, a dibenzofluorene, a phenalene, a phenanthrene, an anthracene, a fluoranthene, a triphenylene, a pyrene, a chrysene, a naphthacene, a picene, a perylene, a pentaphene, and an indenoanthracene; and 
     a naphthalene, a heptalene, a fluorene, a spiro-bifluorene, a benzofluorene, a dibenzofluorene, a phenalene, a phenanthrene, an anthracene, a fluoranthene, a triphenylene, a pyrene, a chrysene, a naphthacene, a picene, a perylene, a pentaphene, and an indenoanthracene, 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, or a C 1 -C 60  heteroaryl group), 
     L 601  may be the same as described herein in connection with L 201 , 
     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 biphenyl group, a terphenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a 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 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 , X 613  may be selected from N and C-(L 613 ) xe613 -R 613 , and at least one selected from X 611  to X 613  may be N, 
     L 611  to L 616  may each be the same as described herein in connection with L 1 , 
     R 611  to R 616  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-bifluorenyl 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 biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a 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 biphenyl group, a terphenyl group, a naphthyl group, an azulenyl group, a fluorenyl group, a spiro-bifluorenyl 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 some embodiments, the electron transport layer may include at least one selected from BCP, Bphen, Alq 3 , Balq, 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 the range described above, the electron transport layer may have satisfactory electron transport characteristics 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, ET-D1 (lithium quinolate, LiQ) or ET-D2. 
     
       
         
         
             
             
         
       
     
     The electron transport region may include an electron injection layer that facilitates the injection of electrons from the second electrode  190 . 
     The electron injection layer may be formed on the electron transport layer using one or more suitable methods selected from vacuum deposition, spin coating, casting, a LB method, ink-jet printing, laser-printing, and laser-induced thermal imaging. When an electron injection layer is formed by vacuum deposition and/or spin coating, the deposition and coating conditions for the electron injection layer may be similar to the deposition and coating conditions used for 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 the ranges described above, the electron injection layer may have satisfactory electron injection characteristics without a substantial increase in driving voltage. 
     The second electrode  190  may be on the organic layer  150 . The second electrode  190  may be a cathode that is an electron injection electrode, and in this regard, a material for forming the second electrode  190  may be a material having a low work function, and non-limiting examples of such a material may include metal, an alloy, an electrically conductive compound, or mixtures thereof. Non-limiting examples of suitable material for the second electrode  190  may include lithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), and magnesium-silver (Mg—Ag). In some embodiments, the material for forming the second electrode  190  may be ITO or IZO. The second electrode  190  may be a semi-transmissive electrode or a transmissive electrode. 
     Hereinbefore, the organic light-emitting device has been described with reference to the drawing, but embodiments of the present disclosure are not limited thereto. 
     Another aspect of embodiments of the present disclosure provides an organic light-emitting apparatus including the organic light-emitting device and a thin film transistor, wherein the first electrode of the organic light-emitting device is electrically connected to the thin film transistor. 
     The term “C 1 -C 60  alkyl group” as used herein refers to a linear or branched aliphatic hydrocarbon monovalent group having 1 to 60 carbon atoms, and non-limiting examples thereof may include a methyl group, an ethyl group, a propyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an iso-amyl group, and a hexyl group. The term “C 1 -C 60  alkylene group” as used herein refers to a divalent group having substantially the same structure as the C 1 -C 60  alkyl group. 
     The term “C 1 -C 60  alkoxy group” as used herein refers 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 refers to a hydrocarbon group formed by substituting at least one carbon-carbon double bond in the body (e.g., middle) or at the terminus of the C 2 -C 60  alkyl group, and non-limiting examples thereof may include an ethenyl group, a propenyl group, and a butenyl group. The term “C 2 -C 60  alkylene group” as used herein refers to a divalent group having substantially the same structure as the C 2 -C 60  alkyl group. 
     The term “C 2 -C 60  alkynyl group” as used herein refers to a hydrocarbon group formed by substituting at least one carbon-carbon triple bond in the body (e.g., middle) or at the terminus of the C 2 -C 60  alkyl group, and non-limiting examples thereof may include an ethynyl group and a propynyl group. The term “C 2 -C 60  alkylene group” as used herein refers to a divalent group having substantially the same structure as the C 2 -C 60  alkyl group. 
     The term “C 3 -C 10  cycloalkyl group” as used herein refers to a monovalent hydrocarbon monocyclic group having 3 to 10 carbon atoms, and non-limiting examples thereof may include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, and a cycloheptyl group. The term “C 3 -C 10  cycloalkylene group” as used herein refers to a divalent group having substantially the same structure as the C 3 -C 10  cycloalkyl group. 
     The term “C 1 -C 10  heterocycloalkyl group” as used herein refers to a monovalent monocyclic group having at least one heteroatom selected from N, O, silicon (Si), phosphorus (P), and sulfur (S) as a ring-forming atom in addition to 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 refers to a divalent group having substantially the same structure as the C 1 -C 10  heterocycloalkyl group. 
     The term “C 3 -C 10  cycloalkenyl group” as used herein refers to a monovalent monocyclic group that has 3 to 10 carbon atoms and at least one double bond in the ring thereof and does not have aromaticity, and non-limiting examples thereof may include a cyclopentenyl group, a cyclohexenyl group, and a cycloheptenyl group. The term “C 3 -C 10  cycloalkenylene group” as used herein refers to a divalent group having substantially the same structure as the C 3 -C 10  cycloalkenyl group. 
     The term “C 1 -C 10  heterocycloalkenyl group” as used herein refers to a monovalent monocyclic group that has at least one heteroatom selected from N, O, Si, P, and S as a ring-forming atom, 1 to 10 carbon atoms, and at least one double bond in its ring. Non-limiting examples of the C 1 -C 10  heterocycloalkenyl group may include a 2,3-hydrofuranyl group and a 2,3-hydrothiophenyl group. The term “C 1 -C 10  heterocycloalkenylene group” as used herein refers to a divalent group having substantially the same structure as the C 1 -C 10  heterocycloalkenyl group. 
     The term “C 6 -C 60  aryl group” as used herein refers to a monovalent group having a carbocyclic aromatic system having 6 to 60 carbon atoms, and the term “C 6 -C 60  arylene group” as used herein refers to a divalent group having a carbocyclic aromatic system having 6 to 60 carbon atoms. Non-limiting examples of the C 6 -C 60  aryl group may include a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, a pyrenyl group, and a chrysenyl group. When the C 6 -C 60  aryl group and the C 6 -C 60  arylene group each include two or more rings, the rings may be fused to each other. 
     The term “C 1 -C 60  heteroaryl group” as used herein refers to a monovalent group having a carbocyclic aromatic system that has at least one heteroatom selected from N, O, Si, P, and S as a ring-forming atom, and 1 to 60 carbon atoms. The term “C 1 -C 60  heteroarylene group” as used herein refers to a divalent group having a carbocyclic aromatic system that has at least one heteroatom selected from N, O, P, and S as a ring-forming atom, and 1 to 60 carbon atoms. Non-limiting examples of the C 1 -C 60  heteroaryl group may include a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, and an isoquinolinyl group. When the C 1 -C 60  heteroaryl group and the C 1 -C 60  heteroarylene group each include two or more rings, the rings may be fused to each other. 
     The term “C 6 -C 60  aryloxy group” as used herein indicates —O-A 102  (wherein A 102  is the C 6 -C 60  aryl group), and the term “C 6 -C 60  arylthio group” as used herein indicates —S-A 103  (wherein A 103  is the C 6 -C 60  aryl group). 
     The term “monovalent non-aromatic condensed polycyclic group” as used herein refers to a monovalent group that has two or more rings condensed to each other, only carbon atoms as ring forming atoms (for example, 8 to 60 carbon atoms), and non-aromaticity in the entire molecular structure. A non-limiting example of the monovalent non-aromatic condensed polycyclic group may include a fluorenyl group. The term “divalent non-aromatic condensed polycyclic group” as used herein refers to a divalent group having substantially the same structure as the monovalent non-aromatic condensed polycyclic group. 
     The term “monovalent non-aromatic condensed heteropolycyclic group” as used herein refers to a monovalent group having two or more rings condensed to each other, a heteroatom selected from N, O, Si, P, and S as a ring forming atom in addition to carbon atoms (for example, 1 to 60 carbon atoms), and has non-aromaticity in the entire molecular structure. A non-limiting example of the monovalent non-aromatic condensed heteropolycyclic group may include a carbazolyl group. The term “divalent non-aromatic condensed heteropolycyclic group” as used herein refers to a divalent group having substantially the same structure as the monovalent non-aromatic condensed heteropolycyclic group. 
     In the present specification, at least one substituent of the substituted C 5 -C 30  carbocyclic group, substituted C 1 -C 30  heterocyclic group, substituted C 1 -C 5  alkylene group, substituted C 2 -C 5  alkenylene group, substituted C 3 -C 10  cycloalkylene group, substituted C 1 -C 10  heterocycloalkylene group, substituted C 3 -C 10  cycloalkenylene group, substituted C 1 -C 10  heterocycloalkenylene group, substituted C 6 -C 60  arylene group, substituted C 1 -C 60  heteroarylene group, substituted divalent non-aromatic condensed polycyclic group, substituted divalent non-aromatic condensed heteropolycyclic group, substituted C 1 -C 60  alkyl group, substituted C 2 -C 60  alkenyl group, substituted C 2 -C 60  alkynyl group, substituted C 1 -C 60  alkoxy group, substituted C 3 -C 10  cycloalkyl group, substituted C 1 -C 10  heterocycloalkyl group, substituted C 3 -C 10  cycloalkenyl group, substituted C 1 -C 10  heterocycloalkenyl group, substituted C 6 -C 60  aryl group, substituted C 6 -C 60  aryloxy group, substituted C 6 -C 60  arylthio group, substituted C 1 -C 60  heteroaryl group, substituted monovalent non-aromatic condensed polycyclic group, and substituted monovalent non-aromatic condensed heteropolycyclic group may be selected from the group consisting of: 
     deuterium, —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, —Si(Q 11 )(Q 12 )(Q 13 ), and —B(Q 14 )(Q 15 ), 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group; 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group, each substituted with 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, —Si(Q 21 )(Q 22 )(Q 23 ), and —B(Q 24 )(Q 25 ), and 
     —Si(Q 31 )(Q 32 )(Q 33 ) and —B(Q 34 )(Q 35 ), 
     wherein Q 11  to Q 15 , Q 21  to Q 25 , and Q 31  to Q 35  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, a monovalent non-aromatic condensed heteropolycyclic group, a biphenyl group, and a terphenyl group. 
     The term “Ph” as used herein refers to a phenyl group, the term “Me” as used herein refers to a methyl group, the term “Et” as used herein refers to an ethyl group, and the term “ter-Bu” or “Bu t ” as used herein refers to a tert-butyl group. 
     The term “biphenyl group” as used herein refers to a monovalent group having two benzene rings linked to each other via a single bond, and the term “terphenyl group” as used herein refers to a monovalent group having three benzene rings linked to each other via two single bonds. 
     Hereinafter, an organic light-emitting device according to an embodiment of the present disclosure will be described in more detail with reference to Synthesis Examples and Examples. The wording “B was used instead of A” used in describing Synthesis Examples below indicates that an identical amount (e.g., molar equivalent) of B was used in place of A. 
     EXAMPLE 
     Example 1 
     A 15 Ohms per square centimeter (Q/cm 2 ) 1200 Å (Angstroms) ITO glass substrate (available from Corning Co., Ltd) was cut to a size of 50 millimeters (mm)×50 mm×0.5 mm, sonicated in isopropyl alcohol and pure water for 10 minutes in each solvent, cleaned with ultraviolet rays for 10 minutes, cleaned with ozone, and then mounted on a vacuum deposition apparatus. 
     2-TNATA was vacuum-deposited on the ITO anode of the glass substrate to form a hole injection layer having a thickness of about 600 Å. NPB was then vacuum-deposited on the hole injection layer to form a hole transport layer having a thickness of about 300 Å. 
     Compounds 1-1 and 2-2 (host) and Compound PD1 (dopant) were co-deposited on the hole transport layer at a weight ratio of about 20:70:10 to form an emission layer having a thickness of about 400 Å. 
     Alq 3  was vacuum-deposited on the emission layer to form an electron transport layer having a thickness of about 300 Å, and Al was vacuum-deposited on the electron transport layer to form a cathode having a thickness of about 2,000 Å, thereby completing the manufacture of an organic light-emitting device. 
     
       
         
         
             
             
         
       
     
     Examples 2 to 18 and Comparative Examples 1 to 7 
     Organic light-emitting devices according to Examples 2 to 18 and Comparative Examples 1 to 7 were manufactured in substantially the same manner as in Example 1, except that in forming an emission layer, the host was varied as shown in Table 1. 
     Evaluation Example 1 
     The driving voltage, efficiency, and lifespan (T 90 ) of each organic light-emitting device manufactured in Examples 1 to 18 and Comparative Examples 1 to 7 were measured using a Keithley 236 source-measure unit (SMU) and a PR650 luminance meter. The results thereof are shown in Table 1. The lifespan (T 90 ) refers to the period of time required for the initial luminance of the organic light-emitting device to reduce by 90%. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                   
                   
                   
                 Weight ratio (First 
                   
                   
                 Lifespan 
               
               
                   
                 Host 
                 Dopant 
                 compound:second 
                 Current 
                   
                 (T 90 ) (hr) 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                   
                 (First 
                 (Second 
                 (Third 
                 compound:third 
                 density 
                 Efficiency 
                 (@ 3700 
               
               
                   
                 compound) 
                 compound) 
                 compound) 
                 compound) 
                 (mA/cm 2 ) 
                 (cd/A) 
                 cd/m 2 ) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Example 1 
                 Compound 1-1 
                 Compound 2-2 
                 Compound PD1 
                 25:65:10 
                 10 
                 55.8 
                 143 
               
               
                 Example 2 
                 Compound 1-1 
                 Compound 2-2 
                 Compound PD1 
                 15:75:10 
                 10 
                 41.4 
                 190 
               
               
                 Example 3 
                 Compound 1-7 
                 Compound 2-2 
                 Compound PD1 
                 40:50:10 
                 10 
                 48.2 
                 224 
               
               
                 Example 4 
                 Compound 1-7 
                 Compound 2-2 
                 Compound PD1 
                 25:65:10 
                 10 
                 43.8 
                 250 
               
               
                 Example 5 
                 Compound 1-10 
                 Compound 2-2 
                 Compound PD1 
                 30:60:10 
                 10 
                 32.2 
                 130 
               
               
                 Example 6 
                 Compound 1-10 
                 Compound 2-2 
                 Compound PD1 
                 20:70:10 
                 10 
                 35.2 
                 95 
               
               
                 Example 7 
                 Compound 1-1 
                 Compound 2-3 
                 Compound PD1 
                 30:60:10 
                 10 
                 64.4 
                 206 
               
               
                 Example 8 
                 Compound 1-1 
                 Compound 2-3 
                 Compound PD1 
                 20:70:10 
                 10 
                 47.7 
                 277 
               
               
                 Example 9 
                 Compound 1-7 
                 Compound 2-3 
                 Compound PD1 
                 40:50:10 
                 10 
                 55.6 
                 129 
               
               
                 Example 10 
                 Compound 1-7 
                 Compound 2-3 
                 Compound PD1 
                 30:60:10 
                 10 
                 50.5 
                 188 
               
               
                 Example 11 
                 Compound 1-10 
                 Compound 2-3 
                 Compound PD1 
                 35:55:10 
                 10 
                 28.5 
                 100 
               
               
                 Example 12 
                 Compound 1-10 
                 Compound 2-3 
                 Compound PD1 
                 25:65:10 
                 10 
                 40.7 
                 120 
               
               
                 Example 13 
                 Compound 1-1 
                 Compound 2-8 
                 Compound PD1 
                 40:50:10 
                 10 
                 45.0 
                 145 
               
               
                 Example 14 
                 Compound 1-1 
                 Compound 2-8 
                 Compound PD1 
                 25:55:10 
                 10 
                 33.3 
                 166 
               
               
                 Example 15 
                 Compound 1-7 
                 Compound 2-8 
                 Compound PD1 
                 30:60:10 
                 10 
                 39.9 
                 115 
               
               
                 Example 16 
                 Compound 1-7 
                 Compound 2-8 
                 Compound PD1 
                 20:70:10 
                 10 
                 35.3 
                 172 
               
               
                 Example 17 
                 Compound 1-10 
                 Compound 2-8 
                 Compound PD1 
                 60:30:10 
                 10 
                 35.8 
                 88 
               
               
                 Example 18 
                 Compound 1-10 
                 Compound 2-8 
                 Compound PD1 
                 40:50:10 
                 10 
                 28.3 
                 84 
               
               
                 Comparative 
                 Compound 1-1 
                 — 
                 Compound PD1 
                 90:10 
                 10 
                 30.0 
                 25 
               
               
                 Example 1 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Comparative 
                 Compound 1-7 
                 — 
                 Compound PD1 
                 90:10 
                 10 
                 36.0 
                 19 
               
               
                 Example 2 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Comparative 
                 — 
                 Compound 2-3 
                 Compound PD1 
                 90:10 
                 10 
                 4.9 
                 5 
               
               
                 Example 3 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Comparative 
                 — 
                 Compound 2-8 
                 Compound PD1 
                 90:10 
                 10 
                 13.6 
                 9 
               
               
                 Example 4 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Comparative 
                 Compound 1-10 
                 — 
                 Compound PD1 
                 90:10 
                 10 
                 21.7 
                 15 
               
               
                 Example 5 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Comparative 
                 Compound A 
                 Compound 2-8 
                 Compound PD1 
                 40:50:10 
                 10 
                 20.4 
                 68 
               
               
                 Example 6 
                   
                   
                   
                   
                   
                   
                   
               
               
                 Comparative 
                 Compound B 
                 Compound 2-8 
                 Compound PD1 
                 40:50:10 
                 10 
                 23.6 
                 72 
               
               
                 Example 7 
               
               
                   
               
            
           
         
       
     
     
       
         
         
             
             
         
       
     
     Referring to the results shown in Table 1, it was found that each of the organic light-emitting devices manufactured in Examples 1 to 18 exhibited higher efficiencies and longer lifespans than each of the organic light-emitting devices manufactured in Comparative Examples 1 to 7. 
     As described above, according to the one or more example embodiments of the present disclosure, an organic light-emitting device may have a high efficiency and a long lifespan. 
     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 example embodiment should typically be considered as available for other similar features or aspects in other example embodiments. 
     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”. 
     As used herein, the terms “substantially”, “about”, and similar terms are used as terms of approximation and not as terms of degree, and are intended to account for the inherent deviations in measured or calculated values that would be recognized by those of ordinary skill in the art. 
     Also, any numerical range recited herein is intended to include all subranges of the same numerical precision subsumed within the recited range. For example, a range of “1.0 to 10.0” is intended to include all subranges between (and including) the recited minimum value of 1.0 and the recited maximum value of 10.0, that is, having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as, for example, 2.4 to 7.6. Any maximum numerical limitation recited herein is intended to include all lower numerical limitations subsumed therein and any minimum numerical limitation recited in this specification is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicant reserves the right to amend this specification, including the claims, to expressly recite any sub-range subsumed within the ranges expressly recited herein. 
     While one or more example embodiments have been described with reference to the drawing, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims and equivalents thereof.