Patent Publication Number: US-9887364-B2

Title: Organic light-emitting devices

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Korean Patent Application No. 10-2014-0127682, filed on Sep. 24, 2014, in the Korean Intellectual Property Office, and entitled: “Organic Light-Emitting Devices,” is incorporated by reference herein in its entirety. 
     BACKGROUND 
     1. Field 
     Embodiments relate to organic light-emitting devices. 
     2. Description of the Related Art 
     Organic light-emitting devices (OLEDs), which are self-emitting devices, have advantages such as wide viewing angles, excellent contrast, quick response, high brightness, excellent driving voltage characteristics, and can provide multicolored images. 
     An organic light-emitting device may have a structure in which a first electrode, a hole transport region, an emission layer, an electron transport region, and a second electrode are sequentially disposed in this order on a substrate. Holes injected from the first electrode move to the emission layer via the hole transport region, while electrons injected from the second electrode move to the emission layer via the electron transport region. Carriers such as the holes and electrons recombine in the emission layer to generate exitons. When the exitons drop from an excited state to a ground state, light is emitted. 
     SUMMARY 
     Embodiments are directed to an organic light-emitting device including a first electrode, a second electrode, and an organic layer between the first electrode and the second electrode. The organic layer includes an emission layer. The emission layer includes a first host represented by Formula 1 and a second host represented by Formula 2. A volume ratio of the first host to the second host is in a range of about 94:3 to about 77:20: 
     
       
         
         
             
             
         
       
     
     wherein, in Formulae 1 and 2, 
     X 21  is selected from N-[(L 22 ) a22 -(R 22 ) b22 ], an oxygen atom (O), a sulfur atom (S) and C(R 27 )(R 28 ); 
     L 11 , and L 21  to L 23  are each independently selected from a substituted or unsubstituted C 6 -C 60  arylene group, and a substituted or unsubstituted C 1 -C 60  heteroarylene group; 
     a11, and a21 to a23 are each independently selected from 0, 1, 2, and 3; 
     R 11 , R 21 , and R 22  are each independently selected from a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group; 
     b11, b21, and b22 are each independently selected from 1, 2, and 3; 
     R 12  to R 14 , and R 23  to R 28  are each independently selected from a hydrogen, a 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 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl 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 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q 1 )(Q 2 )(Q 3 ); 
     b12 to b14, and b23 to b26 are each independently selected from 1, 2, 3, and 4; 
     n21 is selected from 0, 1, 2, and 3; 
     at least one substituent of the substituted C 6 -C 60  arylene group, the substituted C 1 -C 60  heteroarylene group, the substituted C 1 -C 60  alkyl group, the substituted C 1 -C 60  alkoxy group, the substituted C 3 -C 10  cycloalkyl group, the substituted C 6 -C 60  aryl group, the substituted C 6 -C 60  aryloxy group, the substituted C 1 -C 60  heteroaryl group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group is selected from 
     a 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 of a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q 11 )(Q 12 )(Q 13 ), 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10 heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group, 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group, each substituted with at least one of a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q 21 )(Q 22 )(Q 23 ), and 
     —Si(Q 31 )(Q 32 )(Q 33 ), 
     wherein Q 1  to Q 3 , Q 11  to Q 13 , Q 21  to Q 23  and Q 31  to Q 33  are each independently selected from a C 1 -C 60  alkyl group, a C 6 -C 60  aryl group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Features will become apparent to those of skill in the art by describing in detail exemplary embodiments with reference to the attached drawings in which: 
         FIG. 1  illustrates a schematic view of a structure of an organic light-emitting device according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully hereinafter with reference to the accompanying drawing; however, they may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey exemplary implementations to those skilled in the art. 
     In the drawing figures, the dimensions of layers and regions may be exaggerated for clarity of illustration. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     As used herein, it is to be understood that the terms such as “including” or “having,” etc., are intended to indicate the existence of the features or components disclosed in the specification, and are not intended to preclude the possibility that one or more other features or components may exist or may be added. 
     As used herein, the term “(an emission layer) including a first host represented by Formula 1 may be interpreted as “(the emission layer) including one of the first host falling within the category of Formula 1 or including at least two first hosts falling within the category of Formula 1”. 
     As used herein, the term “organic layer” refers to a single layer and/or a plurality of layers disposed between the first and second electrodes of the organic light-emitting device. A material in the “organic layer” may include other materials besides an organic material. 
       FIG. 1  illustrates a schematic sectional view of an organic light-emitting device  10  according to an embodiment of the present disclosure. 
     Referring to  FIG. 1 , the organic light-emitting device  10  includes a first electrode  110 , an organic layer  150 , and a second electrode  190 . 
     A substrate may be disposed under the first electrode  110  or on the second electrode  190  in  FIG. 1 . The substrate may be a glass or transparent plastic substrate with good mechanical strength, thermal stability, transparency, surface smoothness, ease of handling, and water resistance. 
     For example, the first electrode  110  may be formed by depositing or sputtering a first electrode-forming material on the substrate  11 . When the first electrode  110  is an anode, a material having a high work function may be used as the first electrode-forming material to facilitate hole injection. The first electrode  110  may be a reflective electrode, a semi-transmissive electrode, or a transmissive electrode. Transparent and conductive materials such as ITO, IZO, SnO 2 , and ZnO may be used to form the first electrode. The first electrode  110  as a semi-transmissive electrode or a reflective electrode may be formed of at least one material selected from magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), and magnesium-silver (Mg—Ag). 
     The first electrode  110  may have a single-layer structure or a multi-layer structure including a plurality of layers. For example, the first electrode  110  may have a three-layered structure of ITO/Ag/ITO. 
     The organic layer  150  may be disposed on the first electrode  110 . The organic layer  150  may include an emission layer (EML). The organic layer  150  may further include a hole transport region disposed between the first electrode and the EML, and an electron transport region disposed between the EML and the second electrode. 
     The hole transport region may include at least one of a hole injection layer (HIL), a hole transport layer (HTL), a buffer layer, and an electron blocking layer (EBL). Rhe electron transport layer may include, for example, at least one of a hole blocking layer (HBL), an electron transport layer (ETL), and an electron injection layer (EIL). The hole transport region may have a single-layered structure including a single material, a single-layered structure including a plurality of materials, or a multi-layered structure including a plurality of layers including different materials. 
     In some embodiments, the hole transport region may have a single-layered structure including a plurality of materials, or a multi-layered structure of HIL/HTL, HIL/HTL/buffer layer, HIL/buffer layer, HTL/buffer layer, HIL/HTL/EBL, or HTL/EBL. These layers forming a multi-layered structure may be sequentially disposed on the first electrode  110  in the order stated above. 
     When the hole transport region includes a HIL, the HIL may be formed on the first electrode  110  by using a suitable method, for example, by using vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) deposition, inkjet printing, laser printing, laser induced thermal imaging (LITI), or the like. 
     When the HIL is formed using vacuum deposition, the deposition conditions may vary depending on the material that is used to form the HIL and the structure of the HIL. For example, the deposition conditions may be selected from the following conditions: a deposition temperature of about 100° C. to about 500° C., a degree of vacuum of about 10 −8  to about 10 −3  torr, and a deposition rate of about 0.01 to 100 Å/sec. 
     When the HIL is formed using spin coating, the coating conditions may vary depending on the material that is used to form the HIL and the structure of the HIL. For example, the coating conditions may be selected from the following conditions: a coating rate of about 2,000 rpm to about 5,000 rpm and a heat treatment temperature of about 800° C. to about 200° C. 
     When the hole transport region includes a HTL, the HTL may be formed on the first electrode  110  or the HIL by using a suitable method, for example, by using vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) deposition, inkjet printing, laser printing, laser induced thermal imaging (LITI), or the like. When the HTL is formed using vacuum deposition or spin coating, the conditions for deposition and coating may be similar to the above-described deposition and coating conditions for forming the HIL. 
     In some embodiments, the hole transport region may include at least one of 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/dodecylbenzene sulfonic 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 below, and a compound represented by Formula 202. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 201 and 202, 
     L 201  to L 205  may be each independently selected from a substituted or unsubstituted C 3 -C 10  cycloalkylene group, a substituted or unsubstituted C 1 -C 10  heterocycloalkylene group, a substituted or unsubstituted C 3 -C 10  cycloalkenylene group, a substituted or unsubstituted C 1 -C 10  heterocycloalkenylene group, a substituted or unsubstituted C 6 -C 60  arylene group, a substituted or unsubstituted C 1 -C 60  heteroarylene group, a substituted or unsubstituted divalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted divalent non-aromatic condensed heteropolycyclic group; 
     xa1 to xa4 may be each independently 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 be each independently the same as described herein in conjunction with R 11 . 
     The compound represented by Formula 201 may be a compound represented by Formula 201A. 
     
       
         
         
             
             
         
       
     
     The compound represented by Formula 201 may be a compound represented by Formula 201A-1: 
     
       
         
         
             
             
         
       
     
     For example, the compound represented by Formula 201 may be a compound represented by Formula 202A: 
     
       
         
         
             
             
         
       
     
     In Formulae 201A, 201A-1, and 202A, 
     L 201  to L 203 , xa1 to xa3, xa5, and R 202  to R 204  may be the same as those described herein; 
     R 211  and R 212  may be defined as described above herein in conjunction with R 203 ; and 
     R 213  to R 216  may be each independently selected from a hydrogen, a 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. 
     For example, in Formulae 201A, 201A-1, and 202A, 
     L 201  to L 203  may be each independently selected from a phenylene group, a naphthylene group, a fluorenylene group, a spiro-fluorenylene group, a benzofluorenylene group, a dibenzofluorenylene group, a phenanthrenylene group, an anthracenylene group, a pyrenylene group, 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-fluorenylene 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 a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group; 
     xa1 to xa3 may be each independently 0 or 1; 
     R 203 , R 204 , R 211 , and R 212  may be each independently selected from 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group, and 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a 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 a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group; 
     R 213  and R 214  may be each independently selected from 
     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 a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group, 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group, and 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group, each substituted with at least one selected from a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group; 
     R 215  and R 216  may be each independently selected from 
     a 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 a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group, 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, and a triazinyl group, and 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group, each substituted with at least one selected from a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group; and 
     xa5 may be 1 or 2. 
     In Formulae 201A and 201A-1, R 213  and R 214  may be linked to each other to form a saturated or unsaturated ring. 
     The compound represented by Formula 201 and the compound represented by Formula 202 may include Compounds HT1 to HT20. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A thickness of the hole transport region may be from about 100 Å to about 10,000 Å, and in some embodiments, from about 100 Å to about 2,000 Å. When the hole transport region includes both a HIL and a HTL, a thickness of the HIL may be in a range from about 100 Å to about 10,000 Å, and in some embodiments, from about 100 Å to about 1,000 Å, and a thickness of the HTL may be in a range of from about 50 Å to about 2,000 Å, and in some embodiments, from about 100 Å to about 1,500 Å. When the thicknesses of the hole transport region, the HIL, and the HTL are within these ranges, satisfactory hole transport characteristics may be obtained without a substantial increase in driving voltage. 
     The hole transport region may further include a charge-generating material to improve conductivity, in addition to the materials as described above. The charge-generating material may be homogeneously or inhomogeneously dispersed in the hole transport region. 
     The charge-generating material may be, for example, a p-dopant. The p-dopant may be one of quinine derivatives, metal oxides, and compounds with a cyano group. Examples of the p-dopant are quinone derivatives such as tetracyanoquinonedimethane (TCNQ), 2,3,5,6-tetrafluoro-tetracyano-1,4-benzoquinonedimethane (F4-TCNQ), or the like; metal oxides such as tungsten oxide, molybdenum oxide, or the like; and Compound HT-D1. 
     
       
         
         
             
             
         
       
     
     The hole transport region may further include at least one of a buffer layer and an EBL, in addition to the HIL and HTL described above. The buffer layer may compensate for an optical resonance distance of light according to a wavelength of the light emitted from the EML, and thus may improve light-emission efficiency. A material in the buffer layer may be a suitable material used in the hole transport region. The EBL may block migration of electrons from the emission layer into the hole transport region. 
     An example of the EBL is mCP. 
     
       
         
         
             
             
         
       
     
     The EML may be formed on the first electrode  110  or the hole transport region by using a suitable methods, for example, by using vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) deposition, inkjet printing, laser printing, laser induced thermal imaging (LITI), or the like. When the EML is formed using vacuum deposition or spin coating, the deposition and coating conditions for forming the EML may be similar to the above-described deposition and coating conditions for forming the HIL. 
     When the organic light-emitting device  10  is a full color organic light-emitting device, the EML may be patterned into a red emission layer, a green emission layer, and a blue emission layer to correspond to individual subpixels, respectively. In some implementations, the EML may have a structure in which a red emission layer, a green emission layer and a blue emission layer are stacked upon one another, or a structure including a mixture of a red light-emitting material, a green light-emitting material, and a blue light-emitting material without separation of layers for the different colors, and thus may emit white light. In some implementations, the EML may be a white EML, and may further include a cover converting layer or a color filter to convert white light into light of a desired color. 
     For example, the EML of the organic layer  150  may include a first host represented by Formula 1 and a second host represented by Formula 2. A volume ratio of the first host to the second host may be in a range of about 94:3 to about 77:20. 
     
       
         
         
             
             
         
       
     
     wherein X 21  in Formula 2 may be selected from N-[(L 22 ) a22 -(R 22 ) b22 ], an oxygen atom (O), a sulfur atom (S), and C(R 27 )(R 28 ); 
     L 11 , and L 21  to L 23  in Formulae 1 and 2 may be each independently selected from a substituted or unsubstituted C 6 -C 60  arylene group, and a substituted or unsubstituted C 1 -C 60  heteroarylene group; 
     at least one substituent of the substituted C 6 -C 60  arylene group and the substituted C 1 -C 60  heteroarylene group may be selected from 
     a 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 of a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q 11 )(Q 12 )(Q 13 ), 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10 heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group, 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group, each substituted with at least one of a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10 heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q 21 )(Q 22 )(Q 23 ), and 
     —Si(Q 31 )(Q 32 )(Q 33 ), 
     wherein Q 1  to Q 3 , Q 11  to Q 13 , Q 21  to Q 23  and Q 31  to Q 33  may be each independently selected from a C 1 -C 60  alkyl group, a C 6 -C 60  aryl group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group. 
     For example, in Formulae 1 and 2, L 11 , and L 21  to L 23  may be each independently selected from 
     a phenylene group, a naphthylene group, a phenanthrenylene group, an anthracenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a pyrrolylene group, a thiophenylene group, a furanylene group, an imidazolylene group, a pyridinylene group, a pyrazinylene group, a pyrimidinylene group, a pyridazinylene group, an indolylene group, a quinolinylene group, an isoquinolinylene group, a benzoquinolinylene group, a phenanthridinylene group, an acridinylene group, a phenanthrolinylene group, a benzofuranylene group, a benzothiophenylene group, a triazolylene group, a tetrazolylene group, a triazinylene group, a dibenzofuranylene group, and a dibenzothiophenylene group, and 
     a phenylene group, a naphthylene group, a phenanthrenylene group, an anthracenylene group, a triphenylenylene group, a pyrenylene group, a chrysenylene group, a pyrrolylene group, a thiophenylene group, a furanylene group, an imidazolylene group, a pyridinylene group, a pyrazinylene group, a pyrimidinylene group, a pyridazinylene group, an indolylene group, a quinolinylene group, an isoquinolinylene group, a benzoquinolinylene group, a phenanthridinylene group, an acridinylene group, a phenanthrolinylene group, a benzofuranylene group, a benzothiophenylene group, a triazolylene group, a tetrazolylene group, a triazinylene group, a dibenzofuranylene group, and a dibenzothiophenylene group, each substituted with at least one of a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclopentenyl group, a cyclohexenyl group, a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a 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 benzoimidazolyl 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, and an imidazopyridinyl group. 
     In some embodiments, in Formulae 1 and 2, L 11  and L 21  to L 23  may be each independently selected from 
     a phenylene group, a naphthylene group, a pyridinylene group, a quinolinylene group, and an isoquinolinylene group, and 
     a phenylene group, a naphthylene group, a pyridinylene group, a quinolinylene group, and an isoquinolinylene group, each substituted with at least one of a deuterium, —F, —Cl, —Br, —I, a cyano group, a nitro group, a C 1 -C 20  alkyl group, a phenyl group, and a naphthyl group. 
     In some embodiments, in Formulae 1 and 2, L 11 , and L 21  to L 23  may be each independently selected from groups represented by Formulae 3-1 to 3-10. 
     
       
         
         
             
             
         
       
     
     In Formulae 3-1 to 3-10, 
     R 31  may be selected from a hydrogen, a deuterium, —F, —Cl, —Br, —I, a cyano group, a nitro group, a C 1 -C 20  alkyl group, a phenyl group, and a naphthyl group; 
     b31 may be selected from 1, 2, 3, and 4; 
     b32 may be selected from 1, 2, 3, 4, 5, and 6; 
     b33 may be selected from 1, 2, and 3; and 
     * and *′ indicate binding sites with adjacent atoms. 
     In some embodiments, in Formulae 1 and 2, L 11 , and L 21  to L 23  may be each independently selected from groups represented by Formulae 4-1 to 4-6. 
     In Formulae 4-1 to 4-6, * and *′ indicate binding sites with adjacent atoms. 
     
       
         
         
             
             
         
       
     
     In Formula 1, a11, which indicates the number of L 11 s, may be selected from 0, 1, 2, and 3. For example, a11 in Formula 1 may be 1. When a11 is 0, (L 11 ) a11  may be a single bond. When a11 is selected from 2 and 3, the plurality of L 11 s may be the same or different. a21 to a23 may be understood based on the above-described definition of a11 and the structures of Formulae 1 and 2 as described above. 
     In Formula 2, a21 to a23 may be each independently selected from 0, 1, 2, and 3. For example, in Formulae 2-1 to 2-3, a21 to a23 may be each independently selected from 0 and 1. 
     In Formulae 1 and 2, R 11 , R 21 , and R 22  may be each independently selected from a substituted or unsubstituted C 6 -C 60  aryl group, a substituted or unsubstituted C 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, 
     wherein at least one substituent of the substituted C 6 -C 60  aryl group, the substituted C 1 -C 60  heteroaryl group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group may be selected from 
     a 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 of a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 3 -C 10  cycloalkyl group, a C 1 -C 10 heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10 heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q 11 )(Q 12 )(Q 13 ), 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group, 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group, each substituted with at least one of a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q 21 )(Q 22 )(Q 23 ), and 
     —Si(Q 31 )(Q 32 )(Q 33 ), 
     wherein Q 11  to Q 13 , Q 21  to Q 23 , and Q 31  to Q 33  may be each independently selected from a C 1 -C 60  alkyl group, a C 6 -C 60  aryl group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group. 
     For example, in Formulae 1 and 2, R 11 , R 21 , and R 22  may be each independently selected from 
     a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a carbazolyl group, a benzoquinolinyl group, phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzothiazoly group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, and a dibenzocarbazolyl group, and 
     a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a carbazolyl group, a benzoquinolinyl group, phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzothiazoly group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, and a dibenzocarbazolyl group, each substituted with at least one of a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a carbazolyl 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, a benzothiazolyl 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, and a dibenzocarbazolyl group. 
     In some embodiments, in Formulae 1 and 2, R 11 , R 21 , and R 22  may be each independently selected from 
     a phenyl group, a naphthyl group, a fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a 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 quinolinyl group, an isoquinolinyl group, a carbazolyl group, a benzoquinolinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzothiazolyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, and a dibenzocarbazolyl group, and 
     a phenyl group, a naphthyl group, a fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a 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 quinolinyl group, an isoquinolinyl group, a carbazolyl group, a benzoquinolinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, a benzothiazolyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, and a dibenzocarbazolyl group, each substituted with at least one of a deuterium, —F, —Cl, —Br, —I, a cyano group, a nitro group, a C 1 -C 20  alkyl group, a phenyl group, and a naphthyl group. 
     In some embodiments, in Formula 1, R 11  may be selected from 
     a phenyl group, a naphthyl group, a fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a furanyl group, a thiophenyl group, a carbazolyl group, a benzofuranyl group, a benzothiophenyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, and a dibenzocarbazolyl group, and 
     a phenyl group, a naphthyl group, a fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a furanyl group, a thiophenyl group, a carbazolyl group, a benzofuranyl group, a benzothiophenyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, and a dibenzocarbazolyl group, each substituted with at least one of a deuterium, —F, —Cl, —Br, —I, a cyano group, a nitro group, a C 1 -C 20  alkyl group, a phenyl group, and a naphthyl group. 
     In some other embodiments, in Formula 1, R 11  may be selected from groups represented by Formulae 5-1 to 5-7. 
     
       
         
         
             
             
         
       
     
     In Formulae 5-1 to 5-7, 
     X 51  may be selected from O, S, and C(R 53 )(R 54 ); 
     R 51  to R 54  may be each independently selected from a hydrogen, a deuterium, —F, —Cl, —Br, —I, a cyano group, a nitro group, a C 1 -C 20  alkyl group, a phenyl group, and a naphthyl group; 
     b51 may be selected from 1, 2, 3, 4, and 5; 
     b52 may be selected from 1, 2, 3, 4, 5, 6, and 7; 
     b53 may be selected from 1, 2, and 3; 
     b54 may be selected from 1, 2, 3, and 4; and 
     * indicates a binding site with an adjacent atom. 
     In some other embodiments, in Formula 1, R 11  may be selected from groups represented by Formulae 6-1 to 6-13. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 6-1 to 6-13, * indicates a binding site with an adjacent atom. 
     In some embodiments, in Formula 2, R 21  and R 22  may be each independently selected from 
     a phenyl group, a naphthyl group, a fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a furanyl group, a thiophenyl group, a carbazolyl group, a benzofuranyl group, a benzothiophenyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, a pyridyl group, a pyrimidinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, and a benzimidazolyl group, and 
     a phenyl group, a naphthyl group, a fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a furanyl group, a thiophenyl group, a carbazolyl group, a benzofuranyl group, a benzothiophenyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, a pyridyl group, a pyrimidinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, an isoquinolinyl group, and a benzimidazolyl group, each substituted with at least one of a deuterium, —F, —Cl, —Br, —I, a cyano group, a nitro group, a C 1 -C 20  alkyl group, a phenyl group, and a naphthyl group. 
     In some other embodiments, in Formula 2, R 21  and R 22  may be each independently selected from groups represented by Formulae 5-1 to 5-32. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 5-1 to 5-32, 
     X 51  may be selected from O, S, and C(R 53 )(R 54 ); 
     R 51  to R 54  may be each independently selected from a hydrogen, a deuterium, —F, —Cl, —Br, —I, a cyano group, a nitro group, a C 1 -C 20  alkyl group, a phenyl group, and a naphthyl group; 
     b51 may be selected from 1, 2, 3, 4, and 5; 
     b52 may be selected from 1, 2, 3, 4, 5, 6, and 7; 
     b53 may be selected from 1, 2, and 3; 
     b54 may be selected from 1, 2, 3, and 4; 
     b55 may be selected from 1, 2, 3, 4, 5, and 6; 
     * indicates a binding site with an adjacent atom. 
     In some other embodiments, in Formula 2, R 21  and R 22  may be each independently selected from groups represented by Formulae 7-1 to 7-107. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 7-1 to 7-107, Ph indicates a phenyl group; and * indicates a binding site with an adjacent atom. 
     In Formula 1, b11, which indicates the number of R 11 s, may be selected from 1, 2, and 3. For example, in Formula 1, b11 may be 1. When b11 is 2 or more, the plurality of R 11 s may be the same or different. b21 and b22 may be understood based on the above-described definition of b11 and the structures of Formulae 1 and 2 described above. 
     In Formula 2, b21 and b22 may be each independently selected from 1, 2, and 3. For example, in Formula 2, b21 and b22 may be both  1 . 
     In Formulae 1 and 2, R 12  to R 14 , and R 23  to R 28  may be each independently selected from a hydrogen, a 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 1 -C 60  alkoxy group, a substituted or unsubstituted C 3 -C 10  cycloalkyl 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 1 -C 60  heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, a substituted or unsubstituted monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q 1 )(Q 2 )(Q 3 ), 
     wherein at least one substituent of the substituted C 1 -C 60  alkyl group, the substituted C 1 -C 60  alkoxy group, the substituted C 3 -C 10  cycloalkyl group, the substituted C 6 -C 60  aryl group, the substituted C 6 -C 60  aryloxy group, the substituted C 1 -C 60  heteroaryl group, the substituted monovalent non-aromatic condensed polycyclic group, and the substituted monovalent non-aromatic condensed heteropolycyclic group may be selected from 
     a 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 of a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q 11 )(Q 12 )(Q 13 ), 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group, 
     a C 3 -C 10  cycloalkyl group, a C 1 -C 10 heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group, each substituted with at least one of a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 3 -C 10  cycloalkyl group, a C 1 -C 10 heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, a monovalent non-aromatic condensed heteropolycyclic group, and —Si(Q 21 )(Q 22 )(Q 23 ), and 
     —Si(Q 31 )(Q 32 )(Q 33 ), 
     wherein Q 1  to Q 3 , Q 11  to Q 13 , Q 21  to Q 23 , and Q 31  to Q 33  may be each independently selected from a C 1 -C 60  alkyl group, a C 6 -C 60  aryl group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group. 
     For example, in Formulae 1 and 2, R 12  to R 14 , and R 23  to R 28  may be each independently selected from a hydrogen, a deuterium, —F, —Cl, —Br, —I, a cyano group, a nitro group, a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, a sec-butyl group, an iso-butyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a carbazolyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzimidazolyl group, a benzofuranyl group, a benzothiophenyl group, an isobenzothiazolyl group, a benzoxazolyl group, an isobenzoxazolyl group, a triazolyl group, a tetrazolyl group, an oxadiazolyl group, a triazinyl group, a dibenzofuranyl group, a dibenzothiophenyl group, a dibenzosilolyl group, a benzocarbazolyl group, a dibenzocarbazolyl group, and —Si(Q 1 )(Q 2 )(Q 3 ), 
     wherein Q 1  to Q 3  may be each independently selected from a C 1 -C 60  alkyl group and a C 6 -C 60  aryl group. In some other embodiments, in Formulae 1 and 2, R 12  to R 14 , and R 23  to R 28  may be each independently selected from a hydrogen, a deuterium, —F, —Cl, —Br, —I, a cyano group, a nitro group, a methyl group, an ethyl group, an n-propyl group, an iso-propyl group, an n-butyl group, a sec-butyl group, an iso-butyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, a phenyl group, a naphthyl group, and —Si(CH 3 ) 3 . 
     In Formula 1, b12, which indicates the number of R 12 s, may be selected from 1, 2, 3, and 4. When b12 is 2 or more, the plurality of R 12 s may be the same or differ. b13, b14, and b23 to b26 may be understood based on the above-described definition of b12 and the structures of Formulae 1 and 2 described above. 
     In Formula 1, b13 and b14 may be each independently selected from 1, 2, 3, and 4. For example, in Formula 1, b13 may be 1. 
     In Formula 2, b23 to b26 may be each independently selected from 1, 2, 3, and 4. 
     In Formula 2, n21 may be selected from 1, 2, and 3. For example, in Formula 2, n21 may be 1. 
     In some embodiments, the first host may be represented by one of Formulae 1-1 and 1-2, and the second host may be represented by Formulae 2-1 to 2-8. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 1-1, 1-2, and 2-1 to 2-8, R 11  to R 14 , b11 to b14, X 21 , L 21 , L 23 , a21, a23, R 21 , R 23  to R 26 , b21, and b23 to b26 may be the same as those described above. 
     In some embodiments, the first host may be represented by one of Formulae 1-11 and 1-12, and the second host may be represented by one of Formulae 2-11 to 2-14. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae 1-1, 1-2, and 2-21 to 2-14, R 11 , b11, X 21 , L 21 , L 23 , a21, a23, R 21 , and b21 may be the same as those described above. 
     In some embodiments, the first host may be selected from the following compounds. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, the second host may be selected from the following compounds. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In some embodiments, the first host may be selected from Compounds H-1a to H-9a, and the second host may be selected from Compounds H-1b to H-8b. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     The first host includes a phenyl group substituted to the No. 9 carbon of an anthracene core thereof. The first host may lower a mobility of electrons. The second host includes a carbazole core having a large band gap and a low lowest unoccupied molecular orbital (LUMO) energy level. An organic light-emitting device including the first and second hosts may have a high efficiency and long lifespan characteristics. 
     A volume ratio of the first host to the second host may be in a range of about 94:3 to about 77:20, or, for example, about 94:3 to about 87:10. When the volume ratio of the first host to the second host is within these ranges, an organic light-emitting device with a high efficiency and improved lifetime may be obtained. 
     The EML of any of the organic light-emitting devices according to the above-described embodiments may further include a dopant, in addition to the first and second hosts. 
     The amount of the dopant in the EML may be in a range of, for example, about 0.01 to about 15 parts by weight based on 100 parts by weight of the host (by weight of the first host and the second host). 
     The dopant may be a fluorescent dopant. 
     For example, the fluorescent dopant may include at least one of DPAVBi, BDAVBi, TBPe, DCM, DCJTB, Coumarin 6, and C545T. 
     
       
         
         
             
             
         
       
     
     The fluorescent dopant may include a compound represented by Formula 501. 
     
       
         
         
             
             
         
       
     
     In Formula 501, 
     Ar 501  may be selected from 
     a naphthalene, a heptalene, a fluorenene, 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, 
     a naphthalene, a heptalene, a fluorenene, 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 a 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 be each independently selected from a 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 the same definitions as described above with respect to L 201 ; 
     R 501  and R 502  may be each independently selected from 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a triazinyl group, a dibenzofuranyl group, and a dibenzothiophenyl group, and 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a triazinyl group, a dibenzofuranyl group, and a dibenzothiophenyl group, each substituted with at least one selected from a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, a triazinyl group, a dibenzofuranyl group, and a dibenzothiophenyl group; 
     xd1 to xd3 may be each independently selected from 0, 1, 2, and 3; and 
     xd4 may be selected from 1, 2, 3, and 4. 
     For example, the fluorescent dopant may include at least one of Compounds FD1 to FD8. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A thickness of the EML may be about 100 Å to about 1,000 Å. In some implementations, the thickness of the EML may be from about 200 Å to about 600 Å. When the thickness of the EML is within these ranges, the EML may have good light emitting ability without a substantial increase in driving voltage. 
     The EML may emit light having a wavelength of about 400 nm to about 530 nm. 
     The electron transport region may include at least one of a HBL, an ETL, and an EIL. 
     In some embodiments, the electron transport region may have a structure including an ETL/EIL or a HBL/ETL/EIL, wherein the layers forming a structure of the electron transport region may be sequentially stacked on the EML in the order stated above. 
     The electron transport region may include a HBL. When the EML includes a phosphorescent dopant, the HBL may prevent diffusion of triplet exitons or holes into the ETL from the EML. 
     When the electron transport region includes a HBL, the HBL may be formed on the EML by a suitable method, for example, by using vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) deposition, inkjet printing, laser printing, laser induced thermal imaging (LITI), or the like. When the HBL is formed using vacuum deposition or spin coating, the deposition and coating conditions for forming the HBL may be similar to the above-described deposition and coating conditions for forming the HIL. 
     For example, the HBL may include at least one of BCP, Bphen, TmPyPB, and E1. 
     
       
         
         
             
             
         
       
     
     A thickness of the HBL may be from about 20 Å to about 1,000 Å. In some embodiments, the thickness of the HBL may be from about 30 Å to about 300 Å. When the thickness of the HBL is within these ranges, the HBL may have improved hole blocking ability without a substantial increase in driving voltage. 
     The electron transport region may include an ETL. The ETL may be formed on the EML or the HBL by a suitable method, for example, by using vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) deposition, inkjet printing, laser printing, laser induced thermal imaging (LITI), or the like. When the ETL is formed using vacuum deposition or spin coating, the deposition and coating conditions for forming the ETL may be similar to the above-described deposition and coating conditions for forming the HIL. 
     The ETL may further include at least one of BCP, Bphen, Alq 3 , Balq, TAZ, and NTAZ. 
     
       
         
         
             
             
         
       
     
     In some embodiments, the ETL may include at least one of compounds represented by Formula 601.
 
Ar 601 -[(L 601 ) xe1 -E 601 ] xe2   &lt;Formula 601&gt;
 
     In Formula 601, 
     Ar 601  may be selected from 
     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, 
     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 a 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 be each independently selected from a hydrogen, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 6 -C 60  aryl group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group); 
     L 601  may be defined as described above herein in conjunction with L 201 ; 
     E 601  may be selected from 
     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 benzoimidazolyl 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, and a dibenzocarbazolyl 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 benzoimidazolyl 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, and a dibenzocarbazolyl group, each substituted with at least one of a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a pentalenyl group, an indenyl group, a naphthyl group, an azulenyl group, a heptalenyl group, an indacenyl group, an acenaphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a naphthacenyl group, a picenyl group, a perylenyl group, a pentaphenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, an ovalenyl group, a pyrrolyl group, a thiophenyl group, a furanyl group, an imidazolyl group, a pyrazolyl group, a thiazolyl group, an isothiazolyl group, an oxazolyl group, an isoxazolyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, an isoindolyl group, an indolyl group, an indazolyl group, a purinyl group, a quinolinyl group, an isoquinolinyl group, a benzoquinolinyl group, a phthalazinyl group, a naphthyridinyl group, a quinoxalinyl group, a quinazolinyl group, a cinnolinyl group, a carbazolyl group, a phenanthridinyl group, an acridinyl group, a phenanthrolinyl group, a phenazinyl group, a benzoimidazolyl 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, and a dibenzocarbazolyl group; 
     xe1 may be selected from 0, 1, 2, and 3, and 
     xe2 may be selected from 1, 2, 3, and 4. 
     In some other embodiments, the ETL may include at least one of Compounds represented by Formula 602. 
     
       
         
         
             
             
         
       
     
     In Formula 602, 
     X 611  may be N or C-(L 611 ) xe611 -R 611 , X 612  may be N or C-(L 612 ) xe612 -R 612 , X 613  may be N or C-(L 613 ) xe613 -R 613 , at least one of X 611  to X 613  may be N; 
     L 611  to L 616  may be defined as described above in conjunction L 201 ; 
     R 611  to R 616  may be each independently selected from 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group, and 
     a phenyl group, a naphthyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group, each substituted with at least one of a deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amino group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a phenyl group, a naphthyl group, an azulenyl group, a fluorenyl group, a spiro-fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthrenyl group, an anthracenyl group, a pyrenyl group, a chrysenyl group, a pyridinyl group, a pyrazinyl group, a pyrimidinyl group, a pyridazinyl group, a quinolinyl group, an isoquinolinyl group, a quinoxalinyl group, a quinazolinyl group, a carbazolyl group, and a triazinyl group; and 
     xe611 to xe616 may be each independently selected from, 0, 1, 2, and 3. 
     The compound of Formula 601 and the compound of Formula 602 may each independently include at least one of Compounds ET1 to ET15. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A thickness of the ETL may be from about 100 Å to about 1,000 Å, and in some embodiments, from about 150 Å to about 500 Å. When the thickness of the ETL is within these ranges, the ETL may have satisfactory electron transporting ability without a substantial increase in driving voltage. 
     In some embodiments the ETL may further include a metal-containing material, in addition to the above-described materials. 
     The metal-containing material may include a lithium (Li) complex. Examples of the Li complex are compound ET-D1 below (lithium quinolate (LiQ)), and compound ET-D2. 
     
       
         
         
             
             
         
       
     
     The electron transport region may include an EIL that may facilitate injection of electrons from the second electrode  190 . 
     The EIL may be formed on the ETL by a suitable method, for example, by using vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) deposition, inkjet printing, laser printing, laser induced thermal imaging (LITI), or the like. When the EIL is formed using vacuum deposition or spin coating, the deposition and coating conditions for forming the EIL may be similar to the above-described deposition and coating conditions for forming the HIL. 
     The EIL may include at least one selected from LiF, NaCl, CsF, Li 2 O, BaO, and LiQ. 
     A thickness of the EIL may be from about 1 Å to about 100 Å. In some implementations, the thickness of the EIL may be from about 3 Å to about 90 Å. When the thickness of the EIL is within these ranges, the EIL may have satisfactory electron injection ability without a substantial increase in driving voltage. 
     The second electrode  190  may be disposed on the electron transport region, as described above. The second electrode  190  may be a cathode as an electron injecting electrode. A material for forming the second electrode  190  may be a metal, an alloy, an electrically conductive compound, which have a low-work function, or a mixture thereof. Examples of materials for forming the second electrode  190  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, a material for forming the second electrode  190  may be ITO or IZO. The second electrode  190  may be a reflective electrode, a semi-transmissive electrode, or a transmissive electrode. 
     The organic light-emitting devices according to the above-described embodiments may be used in a flat-panel display device including a thin film transistor. The thin film transistor may include a gate electrode, a source electrode, a drain electrode, a gate insulating layer, and an active layer. One of the source and drain electrodes may be electrically connected to the first electrode of the organic light-emitting device. The active layer may include crystalline silicon, amorphous silicon, an organic semiconductor, an oxide semiconductor, or the like. 
     As used herein, the term “C 1 -C 60  alkyl group” refers to a linear or branched aliphatic hydrocarbon monovalent group having 1 to 60 carbon atoms. Examples of the C 1 -C 60  alkyl group 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” refers to a divalent group having the same structure as the C 1 -C 60  alkyl. 
     As used herein, the term “C 1 -C 60  alkoxy group” refers to a monovalent group represented by —OA 101 , where A 101  is a C 1 -C 60  alkyl group as described above. Examples of the C 1 -C 60  alkoxy group include a methoxy group, an ethoxy group, and an isopropyloxy group. 
     As used herein, the term “C 2 -C 60  alkenyl group” refers to a structure including at least one carbon double bond in the middle or terminal of the C 2 -C 60  alkyl group. Examples of the C 2 -C 60  alkenyl group include an ethenyl group, a prophenyl group, and a butenyl group. The term “C 2 -C 60  alkylene group” refers to a divalent group having the same structure as the C 2 -C 60  alkenyl group. 
     As used herein, the term “C 2 -C 60  alkynyl group” refers to a structure including at least one carbon triple bond in the middle or terminal of the C 2 -C 60  alkyl group. Examples of the C 2 -C 60  alkynyl group include an ethynyl group, and a propynyl group. The term “C 2 -C 60  alkynylene group” used herein refers to a divalent group having the same structure as the C 2 -C 60  alkynyl group. 
     As used herein, the term “C 3 -C 10  cycloalkyl group” refers to a monovalent, monocyclic hydrocarbon group having 3 to 10 carbon atoms. Examples of the C 3 -C 10  cycloalkyl group 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” refers to a divalent group having the same structure as the C 3 -C 10  cycloalkyl group. 
     As used herein, the term “C 1 -C 10  heterocycloalkyl group” refers to a monovalent monocyclic group having 1 to 10 carbon atoms in which at least one hetero atom selected from N, O, P, and S is included as a ring-forming atom. Examples of the C 1 -C 10  heterocycloalkyl group include a tetrahydrofuranyl group, and a tetrahydrothiophenyl group. The term “C 1 -C 10 heterocycloalkylene group” refers to a divalent group having the same structure as the C 1 -C 10  heterocycloalkyl group. 
     As used herein, the term “C 3 -C 10  cycloalkenyl group” refers to a monovalent monocyclic group having 3 to 10 carbon atoms that includes at least one double bond in the ring but does not have aromaticity. Examples of the C 3 -C 10  cycloalkenyl group include a cyclopentenyl group, a cyclohexenyl group, and a cycloheptenyl group. The term “C 3 -C 10  cycloalkenylene group” refers to a divalent group having the same structure as the C 3 -C 10  cycloalkenyl group. 
     As used herein, the term “C 1 -C 10  heterocycloalkenyl group” used herein refers to a monovalent monocyclic group having 1 to 10 carbon atoms that includes at least one double bond in the ring and in which at least one hetero atom selected from N, O, P, and S is included as a ring-forming atom. Examples of the C 1 -C 10  heterocycloalkenyl group include a 2,3-hydrofuranyl group, and a 2,3-hydrothiophenyl group. The term “C 1 -C 10  heterocycloalkenylene group” used herein refers to a divalent group having the same structure as the C 1 -C 10  heterocycloalkenyl group. 
     As used herein, the term “C 6 -C 60  aryl group” refers to a monovalent, aromatic carbocyclic aromatic group having 6 to 60 carbon atoms, and the term “C 6 -C 60  arylene group” refers to a divalent, aromatic carbocyclic group having 6 to 60 carbon atoms. Examples of the C 6 -C 60  aryl group include a phenyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, a pyrenyl group, and a chrysenyl group. When the C 6 -C 60  aryl group, and the C 6 -C 60 arylene group include at least two rings, the rings may be fused to each other. 
     As used herein, the term “C 1 -C 60  heteroaryl group” refers to a monovalent, aromatic carbocyclic aromatic group having 1 to 60 carbon atoms in which at least one hetero atom selected from N, O, P, and S is included as a ring-forming atom. The term “C 1 -C 60  heteroarylene group” refers to a divalent, aromatic carbocyclic group having 1 to 60 carbon atoms in which at least one hetero atom selected from N, O, P, and S is included as a ring-forming atom. Examples of the C 1 -C 60  heteroaryl group include a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, and an isoquinolinyl group. When the C 1 -C 60  heteroaryl and the C 1 -C 60  heteroarylene include at least two rings, the rings may be fused to each other. 
     As used herein, the term “C 6 -C 60  aryloxy group” indicates —OA 102  (where A 102  is a C 6 -C 60  aryl group as described above), and the term “C 6 -C 60  arylthio group” indicates -SA 103  (where A 103  is a C 6 -C 60  aryl group as described above). 
     As used herein, the term “monovalent non-aromatic condensed polycyclic group” refers to a monovalent group that includes at least two rings condensed to each other and includes only carbon atoms (for example, 8 to 60 carbon atoms) as ring-forming atoms and that represents non-aromaticity as a whole. An example of the monovalent non-aromatic condensed polycyclic group is a fluorenyl group. As used herein, the term “divalent non-aromatic condensed polycyclic group” refers to a divalent group with the same structure as the monovalent non-aromatic condensed polycyclic group. 
     As used herein, the term “monovalent non-aromatic condensed heteropolycyclic group” refers to a monovalent group that includes at least two rings condensed to each other and that includes carbon (for example, 1 to 60 carbon atoms) and hetero atoms selected from N, O, P and S as ring-forming atoms and that represents non-aromaticity as a whole. An example of the monovalent non-aromatic condensed heteropolycyclic group is a carbazolyl group. As used herein, the term “divalent non-aromatic condensed heteropolycyclic group” refers to a divalent group with the same structure as the monovalent non-aromatic condensed polycyclic group. 
     The following Examples and Comparative Examples are provided in order to highlight characteristics of one or more embodiments, but it will be understood that the Examples and Comparative Examples are not to be construed as limiting the scope of the embodiments, nor are the Comparative Examples to be construed as being outside the scope of the embodiments. Further, it will be understood that the embodiments are not limited to the particular details described in the Examples and Comparative Examples. 
     EXAMPLES 
     In the Examples, compounds H-1a to H-9a and H-1b to H8b are as depicted below; 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     Example 1-1 
     A glass substrate with an indium tin oxide (ITO) anode having a thickness of about 1,200 Å was cut to a size of 50 mm×50 mm×0.5 mm, washed by sonication in acetone isopropyl alcohol and then in pure water each for 15 minutes, and washed with UV ozone for 30 minutes. 
     Compound HT13 was deposited on the ITO anode to form an HIL having a thickness of about 500 Å, and then Compound HT3 was deposited on the HIL to form a HTL having a thickness of 450 Å, thereby forming a hole transport region. 
     Compounds H-1a, H-1b, and FD1 were co-deposited on the hole transport region in a volume ratio of 94:3:3 to form an EML having a thickness of about 300 Å. 
     Then, Compound E1 was deposited on the EML to form a HBL having a thickness of about 100 Å, and then Bphen and LiQ were co-deposited on the HBL in a volume ratio of 50:50 to form an ETL having a thickness of about 150 Å. Then, LiF was vacuum-deposited on the ETL to form an EIL having a thickness of about. 5 Å, thereby forming an electron transport region. 
     Aluminum (Al) was deposited on the electron transport region to form an Al cathode having a thickness of about 1,500 Å, thereby completing the manufacture of an organic light-emitting device. 
     Example 1-2 
     An organic light-emitting device was manufactured in the same manner as in Example 1-1, except that Compounds H-1a, H-1b, and FD1 were co-deposited in a volume ratio of about 92:5:3 to form the EML. 
     Example 1-3 
     An organic light-emitting device was manufactured in the same manner as in Example 1-1, except that Compounds H-1a, H-1b, and FD1 were co-deposited in a volume ratio of about 87:10:3 to form the EML. 
     Example 1-4 
     An organic light-emitting device was manufactured in the same manner as in Example 1-1, except that Compounds H-1a, H-1b, and FD1 were co-deposited in a volume ratio of about 77:20:3 to form the EML. 
     Comparative Example 1 
     An organic light-emitting device was manufactured in the same manner as in Example 1-1, except that Compounds H-1a, H-1b, and FD1 were co-deposited in a volume ratio of about 47:50:3 to form the EML. 
     Comparative Example 2 
     An organic light-emitting device was manufactured in the same manner as in Example 1-1, except that Compounds H-1a, H-1b, and FD1 were co-deposited in a volume ratio of about 27:70:3 to form the EML. 
     Comparative Example 3 
     An organic light-emitting device was manufactured in the same manner as in Example 1-1, except that Compounds H-1a and FD1 were co-deposited in a volume ratio of about 97:3 to form the EML. 
     Comparative Example 4 
     An organic light-emitting device was manufactured in the same manner as in Example 1-1, except that Compounds H-1b and FD1 were co-deposited in a volume ratio of about 97:3 to form the EML. 
     Comparative Example 5 
     An organic light-emitting device was manufactured in the same manner as in Example 1-1, except that Compound B, instead of Compound H-1a, was used to form the EML, and Compound B, H-1b, and FD1 were co-deposited in a volume ratio of about 47:50:3. 
     
       
         
         
             
             
         
       
     
     Example 2-1 
     A glass substrate with an indium tin oxide (ITO) anode having a thickness of about 1,200 Å was cut to a size of 50 mm×50 mm×0.5 mm, washed by sonication in acetone isopropyl alcohol and then in pure water each for 15 minutes, and washed with UV ozone for 30 minutes. 
     Compound HT13 was deposited on the ITO anode to form an HIL having a thickness of about 500 Å, and then Compound HT3 was deposited on the HIL to form a HTL having a thickness of 450 Å, thereby forming a hole transport region. 
     Compounds H-1a, H-1b, and FD1 were co-deposited on the hole transport region in a volume ratio of 92:5:3 to form an EML having a thickness of about 300 Å. 
     Then, E1 was deposited on the EML to form a HBL having a thickness of about 100 Å, and then Bphen and LiQ were co-deposited on the HBL in a volume ratio of 50:50 to form an ETL having a thickness of about 150 Å. Then, LiF was vacuum-deposited on the ETL to form an EIL having a thickness of about 5 Å, thereby forming an electron transport region. 
     Aluminum (Al) was deposited on the electron transport region to form an Al cathode having a thickness of about 1,500 Å, thereby completing the manufacture of an organic light-emitting device. 
     Example 2-2 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-2b, instead of Compound H-1b, was used to form the EML. 
     Example 2-3 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-3b, instead of Compound H-1b, was used to form the EML. 
     Example 2-4 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-4b, instead of Compound H-1b, was used to form the EML. 
     Example 2-5 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-5b, instead of Compound H-1b, was used to form the EML. 
     Example 2-6 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-6b, instead of Compound H-1b, was used to form the EML. 
     Example 2-7 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-7b, instead of Compound H-1b, was used to form the EML. 
     Example 2-8 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-8b, instead of Compound H-1b, was used to form the EML. 
     Example 2-9 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-2a, instead of Compound H-1a, was used to form the EML. 
     Example 2-10 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-3a, instead of Compound H-1a, was used to form the EML. 
     Example 2-11 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-4a, instead of Compound H-1a, was used to form the EML. 
     Example 2-12 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-5a, instead of Compound H-1a, was used to form the EML. 
     Example 2-13 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-6a, instead of Compound H-1a, was used to form the EML. 
     Example 2-14 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-7a, instead of Compound H-1a, was used to form the EML. 
     Example 2-15 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-8a, instead of Compound H-1a, was used to form the EML. 
     Example 2-16 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound H-9a, instead of Compound H-1a, was used to form the EML. 
     Example 2-17 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compounds H-2a and H-3b, instead of Compounds H-1a and H-1b, respectively, were used to form the EML. 
     Example 2-18 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compounds H-4a and H-3b, instead of Compounds H-1a and H-1b, respectively, were used to form the EML. 
     Example 2-19 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compounds H-5a and H-3b, instead of Compounds H-1a and H-1b, respectively, were used to form the EML. 
     Example 2-20 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compounds H-7a and H-3b, instead of Compounds H-1a and H-1b, respectively, were used to form the EML. 
     Example 2-21 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compounds H-2a and H-4b, instead of Compounds H-1a and H-1b, respectively, were used to form the EML. 
     Example 2-22 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compounds H-4a and H-4b, instead of Compounds H-1a and H-1b, respectively, were used to form the EML. 
     Example 2-23 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compounds H-5a and H-4b, instead of Compounds H-1a and H-1b, respectively, were used to form the EML. 
     Example 2-24 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compounds H-2a and H-6b, instead of Compounds H-1a and H-1b, respectively, were used to form the EML. 
     Example 2-26 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compounds H-4a and H-6b, instead of Compounds H-1a and H-1b, respectively, were used to form the EML. 
     Example 2-27 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compounds H-5a and H-bb, instead of Compounds H-1a and H-1b, respectively, were used to form the EML. 
     Example 2-28 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compounds H-7a and H-6b, instead of Compounds H-1a and H-1b, respectively, were used to form the EML. 
     Comparative Example 6 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that only Compound A, instead of Compounds H-1a and H-1b, was used to form the EML. 
     
       
         
         
             
             
         
       
     
     Comparative Example 7 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that only Compound B, instead of Compounds H-1a and H-1b, was used to form the EML. 
     
       
         
         
             
             
         
       
     
     Comparative Example 8 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that only Compound C, instead of Compounds H-1a and H-1b, was used to form the EML. 
     
       
         
         
             
             
         
       
     
     Comparative Example 9 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that only Compound H-1 b, without Compound H-1a was used to form the EML. 
     Comparative Example 10 
     An organic light-emitting device was manufactured in the same manner as in Example 2-1, except that Compound A, instead of Compounds H-1a, was used to form the EML. 
     Evaluation Example 1 
     Efficiency and lifetime (T 90 ) data of the organic light-emitting devices of Examples 1-1 to 1-4, Examples 2-1 to 2-28, and Comparative Examples 1 to 10 were evaluated using an IVL meter (PhotoResearch PR650, Keithley 238). The results are shown in Tables 1 and 2. In Tables 1 and 2, T 90  indicates the time taken until an initial luminance (assumed as 100%) of the organic light-emitting device measured at a current density of about 50 mA/cm 2  was reduced to 90%. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                 Amount of 
                   
                   
               
               
                   
                 First 
                 Second 
                 Second host in 
                 Efficiency 
                 T 90   
               
               
                 Example 
                 host 
                 host 
                 EML (vol %) 
                 (cd/A) 
                 (hr) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Example 1-1 
                 H-1a 
                 H-1b 
                 3 
                 5.3 
                 140 
               
               
                 Example 1-2 
                 H-1a 
                 H-1b 
                 5 
                 5.4 
                 140 
               
               
                 Example 1-3 
                 H-1a 
                 H-1b 
                 10 
                 5.3 
                 150 
               
               
                 Example 1-4 
                 H-1a 
                 H-1b 
                 20 
                 5.1 
                 100 
               
               
                 Comparative 
                 H-1a 
                 H-1b 
                 50 
                 4.5 
                 90 
               
               
                 Example 1 
               
               
                 Comparative 
                 H-1a 
                 H-1b 
                 70 
                 4.3 
                 50 
               
               
                 Example 2 
               
               
                 Comparative 
                 H-1a 
                 — 
                 0 
                 5.0 
                 90 
               
               
                 Example 3 
               
               
                 Comparative 
                 — 
                 H-1b 
                 97 
                 3.5 
                 40 
               
               
                 Example 4 
               
               
                 Comparative 
                 Compound B 
                 H-1b 
                 50 
                 4.4 
                 80 
               
               
                 Example 5 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                 Efficiency 
                   
               
               
                 Example 
                 First host 
                 Second host 
                 (cd/A) 
                 T 90  (hr) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Example 2-1 
                 H-1a 
                 H-1b 
                 5.3 
                 150 
               
               
                 Example 2-2 
                 H-1a 
                 H-2b 
                 5.4 
                 140 
               
               
                 Example 2-3 
                 H-1a 
                 H-3b 
                 5.6 
                 130 
               
               
                 Example 2-4 
                 H-1a 
                 H-4b 
                 5.3 
                 140 
               
               
                 Example 2-5 
                 H-1a 
                 H-5b 
                 5.4 
                 120 
               
               
                 Example 2-6 
                 H-1a 
                 H-6b 
                 5.6 
                 130 
               
               
                 Example 2-7 
                 H-1a 
                 H-7b 
                 5.4 
                 120 
               
               
                 Example 2-8 
                 H-1a 
                 H-8b 
                 5.4 
                 130 
               
               
                 Example 2-9 
                 H-2a 
                 H-1b 
                 5.4 
                 140 
               
               
                 Example 2-10 
                 H-3a 
                 H-1b 
                 5.4 
                 150 
               
               
                 Example 2-11 
                 H-4a 
                 H-1b 
                 5.2 
                 130 
               
               
                 Example 2-12 
                 H-5a 
                 H-1b 
                 5.3 
                 140 
               
               
                 Example 2-13 
                 H-6a 
                 H-1b 
                 5.3 
                 130 
               
               
                 Example 2-14 
                 H-7a 
                 H-1b 
                 5.4 
                 120 
               
               
                 Example 2-15 
                 H-8a 
                 H-1b 
                 5.1 
                 130 
               
               
                 Example 2-16 
                 H-9a 
                 H-1b 
                 5.4 
                 120 
               
               
                 Example 2-17 
                 H-2a 
                 H-3b 
                 5.2 
                 140 
               
               
                 Example 2-18 
                 H-4a 
                 H-3b 
                 5.4 
                 130 
               
               
                 Example 2-19 
                 H-5a 
                 H-3b 
                 5.3 
                 120 
               
               
                 Example 2-20 
                 H-7a 
                 H-3b 
                 5.4 
                 110 
               
               
                 Example 2-21 
                 H-2a 
                 H-4b 
                 5.2 
                 130 
               
               
                 Example 2-22 
                 H-4a 
                 H-4b 
                 5.3 
                 130 
               
               
                 Example 2-23 
                 H-5a 
                 H-4b 
                 5.2 
                 110 
               
               
                 Example 2-24 
                 H-7a 
                 H-4b 
                 5.1 
                 120 
               
               
                 Example 2-25 
                 H-2a 
                 H-6b 
                 5.2 
                 130 
               
               
                 Example 2-26 
                 H-4a 
                 H-6b 
                 5.4 
                 130 
               
               
                 Example 2-27 
                 H-5a 
                 H-6b 
                 5.3 
                 120 
               
               
                 Example 2-28 
                 H-7a 
                 H-6b 
                 5.4 
                 130 
               
               
                 Comparative 
                 Compound A 
                 — 
                 4.5 
                 40 
               
               
                 Example 6 
               
               
                 Comparative 
                 Compound B 
                 — 
                 4.9 
                 90 
               
               
                 Example 7 
               
               
                 Comparative 
                 Compound C 
                 — 
                 4.8 
                 80 
               
               
                 Example 8 
               
               
                 Comparative 
                 — 
                 H-1b 
                 3.5 
                 40 
               
               
                 Example 9 
               
               
                 Comparative 
                 Compound A 
                 H-1b 
                 4.4 
                 90 
               
               
                 Example 10 
               
               
                   
               
            
           
         
       
     
     Referring to Table 1, it can be seen that the organic light-emitting devices of Examples 1-1 to 1-4 showed improved efficiencies and improved lifetime characteristics compared to the organic light-emitting devices of Comparative Examples 1 to 5, and in particular, when the volume ratio of the first host of Formula 1 to the second host of Formula 2 was in a range of about 94:3 to about 77:20. 
     Referring to Table 2, it can be seen that the organic light-emitting devices of Examples 2-1 to 2-28 showed improved efficiencies and improved lifetime characteristics compared to the organic light-emitting devices of Comparative Examples 6 to 10. 
     As described above, according to the one or more of the above embodiments of the present invention, an organic light-emitting device including a first host of Formula 1 and a second host of Formula 2 in an emission layer may exhibit a high efficiency and improved lifespan characteristics. 
     Example embodiments have been disclosed herein, and although specific terms are employed, they are used and are to be interpreted in a generic and descriptive sense only and not for purpose of limitation. In some instances, as would be apparent to one of ordinary skill in the art as of the filing of the present application, features, characteristics, and/or elements described in connection with a particular embodiment may be used singly or in combination with features, characteristics, and/or elements described in connection with other embodiments unless otherwise specifically indicated. Accordingly, it will be understood by those of skill in the art that various changes in form and details may be made without departing from the spirit and scope thereof as set forth in the following claims.