Patent Publication Number: US-2023135170-A1

Title: Light-emitting device and electronic apparatus including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority to Korean Patent Application No. 10-2021-0135930 under 35 U.S.C. § 119, filed on Oct. 13, 2021, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     The embodiments relate to a light-emitting device and an electronic apparatus including the same. 
     2. Description of the Related Art 
     Light-emitting devices are self-emissive devices that, have wide viewing angles, high contrast ratios, short response times. The characteristics of light-emitting devices include luminance, driving voltage, and response speed. 
     In a light-emitting device, a first electrode is located on a substrate, and a hole transport region, an emission layer, an electron transport region, and a second electrode are sequentially formed on the first electrode. Holes provided from the first electrode move toward the emission layer through the hole transport region, and electrons provided from the second electrode move toward the emission layer through the electron transport region. Carriers, such as holes and electrons, recombine (or combine) in the emission layer to produce light. 
     It is to be understood that this background of the technology section is, in part, intended to provide useful background for understanding the technology. However, this background of the technology section may also include ideas, concepts, or recognitions that were not part of what was known or appreciated by those skilled in the pertinent art prior to a corresponding effective filing date of the subject matter disclosed herein. 
     SUMMARY 
     The embodiments include a device or the like having improved efficiency and lifespan by preventing deterioration of an electron blocking layer. 
     Other aspects will be set forth in part in the description, which follows and, in part, will be apparent from the description, or may be learned by practice of the embodiments of the disclosure. 
     According to an embodiment, a light-emitting device may include a first electrode, a second electrode facing the first electrode, and an interlayer disposed between the first electrode and the second electrode. The interlayer may include an emission layer. The emission layer may include a first emission layer and a second emission layer. The first emission layer may include a first host and a second host. The second emission layer may include a third host. A triplet energy T 1_H1  of the first host, a triplet energy T 1_H2  of the second host, and a triplet energy T 1_H3  of the third host may satisfy Formulae (1) and (2) as defined below. 
         T   1_H1   −T   1_H3 ≥0.2 eV  (1).
 
         T   1_H2   −T   1_H3 ≥0.2 eV  (2).
 
     In an embodiment, the first electrode may be an anode. The second electrode may be a cathode. The interlayer may include a hole transport region disposed between the first electrode and the emission layer, and an electron transport region disposed between the emission layer and the second electrode. The hole transport region may include at least one of an electron blocking layer, a hole injection a hole transport layer and an emission auxiliary layer. The electron transport region may include at least one of a hole blocking layer, an electron transport layer, and an electron injection layer. 
     In an embodiment, the first emission layer and the second emission layer may each comprise a dopant. The dopant of the first mission layer and the dopant of the second emission layer may include a same compound. 
     In an embodiment, the first emission layer may contact the second emission layer. 
     In an embodiment, the emission layer may emit blue light. 
     In an embodiment, the emission layer may be a fluorescent emission layer. 
     In an embodiment, the interlayer may include a hole transport layer, and an electron blocking layer. The hole transport layer and the electron blocking layer may be disposed between the first electrode and the emission layer. The first emission layer may contact the electron blocking layer 
     In an embodiment, the interlayer may include an electron transport layer, and a hole blocking layer. The electron transport layer and the hole blocking layer may be disposed between the second electrode and the emission layer. The second emission layer may contact the hole blocking layer. 
     In an embodiment, the first electrode may be an anode. The second electrode may be a cathode. The first emission layer may contact the second emission layer. 
     Holes that are injected from the first electrode and electrons that are injected from the second electrode may combine at an interface disposed between the first emission layer and the second emission layer. 
     In an embodiment, a charge transport capacities capacity of the first host and a charge transport capacity of the second host may be different. 
     In an embodiment, a ratio of a thickness of the first emission layer and a thickness of the second emission layer may be in a range of about 4:6 to about 6:4. 
     In an embodiment, a weight ratio of the first host and the second host may be in a range of about 1:9 to about 9:1. 
     In an embodiment, the first host and the second host may each be a pyrene derivative compound. 
     In an embodiment, the pyrene derivative compound may be symmetrical. 
     In an embodiment, the third host may be an anthracene derivative compound. 
     In an embodiment, the interlayer may include m emitting portions, and m−1 charge generation portions disposed between adjacent ones among the m emitting portions. At least one of the m emitting portions may include the first emission layer and the second emission layer. m may be a natural number. 
     According to an embodiment, an electronic apparatus may include the light-emitting device. 
     In an embodiment, the electronic apparatus may further comprise at least one of a color filter, a color conversion layer including quantum dots, a touch screen layer, and a polarizing layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects and features of the disclosure will be more apparent by describing in detail embodiments thereof with reference to the attached drawings, in which: 
         FIG.  1    is a schematic view of a light-emitting device according to an embodiment; 
         FIG.  2    is a schematic cross-sectional view showing a light-emitting apparatus according to an embodiment of the disclosure; and 
         FIG.  3    is a schematic cross-sectional view showing a light-emitting apparatus according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments are shown. This disclosure may, however, 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 the scope of the disclosure to those skilled in the art. 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout the specification. In the drawings, sizes, thicknesses, ratios, and dimensions of the elements may be exaggerated for ease of description and for clarity. 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. For example, “A and/or B” may be understood to mean “A, B, or A and B.” The terms “and” and “or” may be used in the conjunctive or disjunctive sense and may be understood to be equivalent to “and/or.” 
     In the specification and the claims, the phrase “at least one of” is intended to include the meaning of “at least one selected from the group of” for the purpose of its meaning and interpretation. For example, “at least one of A and B” may be understood to mean “A, B, or A and B.” 
     It will be understood that, although the terms first, second, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. 
     For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element without departing from the scope of the disclosure. 
     “About,” “substantially,” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system). For example, “about” may mean within one or more standard deviations, or within ±30%, 20%, 10%, 5% of the stated value. 
     It will be understood that when an element (or a region, a layer, a portion, or the like) is referred to as “being on”, “connected to” or “coupled to” another element in the specification, it can be directly disposed on, connected or coupled to another element mentioned above, or intervening elements may be disposed therebetween. 
     It will be understood that the terms “connected to” or “coupled to” may include a physical or electrical connection or coupling. 
     Unless otherwise defined or implied herein, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     A fluorescent blue emission layer of an organic light-emitting device may include a single host and a single dopant, and such a host has stronger electron transporting characteristics than hole transporting characteristics. For this reason, the holes and electrons recombine (or combine) in an interface between an electron blocking layer and an emission layer, thereby causing triplet-triplet fusion (TTF). As a result, the electron blocking layer is deteriorated and the device lifespan is decreased. 
     According to an embodiment, a light-emitting device may include a first electrode, a second electrode facing the first electrode, and an interlayer between the first electrode and the second electrode. The interlayer may include an emission layer. 
     The emission layer may include a first emission layer including a first host and a second host, and a second emission layer including a third host. 
     A triplet energy T 1_H1  of the first host, a triplet energy T 1_H2  of the second host, and a triplet energy T 1_H3  of the third host may satisfy Formulae (1) and (2): 
         T   1_H1   −T   1_H3 ≥0.2 eV  (1)
 
         T   1_H2   −T   1_H3 ≥0.2 eV  (2)
 
     In the light-emitting device according to an embodiment, a recombination zone of holes and electrons may be moved to an interface between the first emission layer and the second emission layer. Therefore, deterioration of an electron blocking layer due to generated excitons may be prevented. 
     The triplet energy of first host and the second host of the first emission layer may satisfy Formulae (1) and (2) in relation to the triplet energy of the third host of the second emission layer. The triplet energy of the first host may be greater than the triplet energy of the third host by about 0.2 eV or more, and the triplet energy of the second host may be greater than the triplet energy of the third host by about 0.2 eV or more. 
     Because the first emission layer has a relatively greater T1 energy level than that of the second emission layer, TTF may occur at the side of the second emission layer (thus, TTF occurs at an interface between the first emission layer and the second emission layer), and the TTF region may be narrow. Therefore, the emission efficiency may be improved. 
     When the difference between the triplet energy of each of the first and second hosts and the triplet energy of the third host is less than about 0.2 eV, the region where TTF occurs may be relatively wide compared to when the difference is about 0.2 eV or more, and thus, the device efficiency may not be improved. 
     In an embodiment, in the light-emitting device, the first electrode may include an anode. The second electrode may include a cathode. The interlayer may include a hole transport region disposed between the first electrode and the emission layer, and an electron transport region disposed between the emission layer and the second electrode. The hole transport region may include at least one of a hole injection layer, a hole transport layer, a emission auxiliary layer, and an electron blocking layer. The electron transport region may include at least one of a hole blocking layer, an electron transport layer, and an electron injection layer. 
     In an embodiment, in the light-emitting device, the first emission layer and the second emission layer may each include a dopant. The dopant of the first emission layer and the dopant of the second emission layer may include the same compound. 
     In an embodiment, the first emission layer of the light-emitting device may contact the second emission layer of the light-emitting device. For example, the first emission layer may physically contact the second emission layer. 
     In an embodiment, the emission layer of the light-emitting device may emit blue light. 
     In an embodiment, the emission layer of the light-emitting device may include a fluorescent emission layer. 
     In an embodiment, the interlayer of the light-emitting device may include a hole transport layer and an electron blocking layer. The hole transport layer and the electron blocking may be disposed between the first electrode and the emission layer. The first emission layer may contact the electron blocking layer. For example, the interlayer may further include a hole injection layer, and the hole injection layer may contact the first electrode. For example, the hole injection layer may include a charge generation material. For example, the hole injection layer may include a p-dopant compound. 
     In an embodiment, the interlayer of the light-emitting device may include an electron transport layer and a hole blocking layer. The electron transport layer and the hole blocking layer may be disposed between the second electrode and the emission layer. The second emission layer may contact the hole blocking layer. 
     For example, the electron transport layer may include a metal-containing material. The metal-containing material will be described later. 
     In an embodiment, in the light-emitting device, the first electrode may include an anode. The second electrode may include a cathode. The first emission layer may contact the second emission layer. The holes injected from the first electrode and the electrons injected from the second electrode may recombine (or combine) at an interface between the first emission layer and the second emission layer. For example, the first emission layer may be positioned towards the first electrode. 
     The hole and the electron may recombine (or combine), generate TTF, and emit light. Because the region where the hole and the electron recombine (or combine) is the interface between the first emission layer and the second emission layer, deterioration of the electron blocking layer of the light-emitting device may not occur. Therefore, the device lifespan may be improved. 
     When the first emission layer includes only a single type of host satisfying Formula (1) or (2), the triplet energy of the single type of host may be greater than the triplet energy of the third host of the second emission layer. Therefore, the lifespan of the single type of host is shorter than that of the third host. As a result, as time passes, charge in the emission layer becomes out of balance. The thickness of the first emission layer may be increased to maintain charge balance, but as a result, the device lifespan may decrease rapidly. 
     A solution that does not involve changing the thicknesses of the first emission layer and the second emission layer may involve including two types of hosts. The two hosts may not have the same charge transport capacity in the first emission layer. The mixing ratio of the two types of hosts may be adjusted. 
     In an embodiment, the charge transport capacity of the first host and the second host may not be the same. The charge transport capacities of the first host and the second host may be different. The charge transport capacity may include both the hole transport capacity and the electron transport capacity. For example, not having the same charge transport capacity may mean not having the same (having a different) hole transport capacity. Not having the same charge transport capacity may mean not having the same (having a different) electron transport capacity. 
     The charge transport capacity of the first host and the second host may not be the same in case that the first host may be a hole transport host, and the second host may be an electron transport host. 
     The hole transport host may be a compound having strong hole properties. A compound having strong hole properties may refer to a compound that is may easily accept holes, and such properties may be obtained by including a hole-receiving moiety (also, referred to as a HT moiety). 
     A HT moiety may include, for example, a π-electron-rich heteroaromatic compound, for example, a carbazole derivative or an indole derivative, or an aromatic amine compound. 
     The electron transport host may be a compound having strong electron properties. A compound having strong electron properties may refer to a compound that may easily accept electrons, and such properties may be obtained by including an electron-receiving moiety (also, referred to as an ET moiety). 
     An ET moiety may include, for example, a π electron-deficient heteroaromatic compound. For example, the ET moiety may include a nitrogen-containing heteroaromatic compound. 
     When a compound includes only a HT moiety or only an ET moiety, it is clear whether the nature of the compound has HT properties or ET properties. 
     In an embodiment, a compound may include both a HT moiety and an ET moiety. A simple comparison between the total number of the HT moieties and the total number of the ET moieties in a compound may be help predict whether the compound is a HT compound or an ET compound, but cannot be an absolute criterion. One of the reasons why such a simple comparison may not be a sufficient criterion is that each of the HT moieties and the ET moieties do not have exactly the same ability to attract holes and electrons. Therefore, in order to determine whether a compound of a certain structure is a hole transport compound or an electron transport compound, a simulation may be run in advance to make predictions, and the properties of the compound may be reliably confirmed after directly implementing the compound in a device. 
     In an embodiment, the ratio of the thickness of the first emission layer and the thickness of the second emission layer may be in range from about 4:6 to about 6:4. For example, the ratio of the thickness of the first emission layer and the thickness of the second emission layer may be about 5:5. 
     In an embodiment, a weight ratio of the first host and the second host may be in a range from about 1:9 to about 9:1. For example, the weight ratio of the first host and the second host may be in a range from about 2:8 to about 8:2. 
     In the first emission layer of the light-emitting device according to an embodiment, the first host may be a hole transport host and the second host may be an electron transport host, or the first host may be an electron transport host and the second host may be a hole transport host. The triplet energy of the first host and the second first host of the first emission layer may satisfy Formulae (1) and (2) in relation to the triplet energy of the third host of the second emission layer: 
         T   1_H1   −T   1_H3 ≥0.2 eV  (1)
 
         T   1_H2   −T   1_H3 ≥0.2 eV  (2).
 
     In an embodiment, the first host and the second host may include a pyrene derivative compound. For example, the first host and the second host may include a symmetrical pyrene derivative compound. For example, the first host may be a pyrene derivative compound in which two N-containing heteroaryl groups are substituted into pyrene. 
     In an embodiment, the first host and the second host may include at least one of the following compounds: 
     
       
         
         
             
             
         
       
     
     300. 
     The first host and the second host may satisfy Formulae (1) and (2) in relation to the third host. In an embodiment, whether a compound is a first host, or a second host may not be determined in advance for the reasons described above. 
     The third host may be a general blue host compound used for a blue fluorescent emission layer under a condition in which Formulae (1) and (2) may be satisfied in relation to the first host and the second host included in the first emission layer. 
     In an embodiment, the third host may be an anthracene derivative compound. For example, the third host may be an anthracene derivative compound in which one aryl group and one heteroaryl group are substituted into anthracene. For example, the third host may be an asymmetric compound. 
     In an embodiment, the third host may include at least one of the following compounds: 
     
       
         
         
             
             
         
       
     
     In an embodiment, the interlayer may include emitting portions and charge generation portions. For example, the interlayer may include m emitting portions and m−1 charge generation portion(s) between adjacent emitting portions, where m is a number greater than 1. 
     At least one of the m emitting portions may include an emission layer that includes the first emission layer and the second emission layer. 
     The light-emitting device may include m−1 charge generation portion(s) disposed between adjacent emitting. 
     For example, when m is 2, the first electrode, a first emitting portion, a first charge generation portion, and a second emitting portion may be sequentially disposed. In this state, the first emitting portion may emit first-color light, the second light emitting portion may emit second-color light, and the maximum emission wavelength of first-color light and the maximum emission wavelength of second-color light may be identical to or different from each other. At least first emitting portion and the second emitting portion may include the emission layer (which may include the first emission layer and the second emission layer), a first buffer layer, a second buffer layer, and an electron transport layer. 
     As another example, when m is 3, the first electrode, the first emitting portion, the first charge generation portion, the second emitting portion, a second charge generation portion, and a third emitting portion may be sequentially disposed. The first emitting portion may emit a first-color light, the second emitting portion may emit a second-color light, the third emitting portion may emit a third-color light, and the maximum emission wavelength of first-color light, the maximum emission wavelength of second-color light, and the maximum emission wavelength of third-color light may be identical to or different from each other. At least one of the first emitting portion, the second emitting portion, and the third emitting portion may include the emission layer (which may include the first and second emission layers), a first buffer layer, a second buffer layer, and an electron transport layer. 
     As another example, when m is 4, the first electrode, the first emitting portion, the first charge generation portion, the second emitting portion, the second charge generation portion, the third emitting portion, the third charge generation portion, and fourth emitting portion may be sequentially disposed. The first emitting portion may emit a first-color light, the second emitting portion may emit a second-color light, the third emitting portion may emit a third-color light, the fourth emitting portion may emit a fourth-color light, and the maximum emission wavelengths of the first-color light, the second-color light, the third-color light, and the fourth color light may be identical to or different from each other. 
     In an embodiment, an electronic apparatus may include the light-emitting device. 
     In an embodiment, the electronic apparatus may include a thin-film transistor. The thin-film transistor may include a source electrode and a drain electrode. The first electrode of the light-emitting device may be electrically connected to at least one of the source and drain electrodes of the thin-film transistor. 
     In an embodiment, the electronic apparatus may further include at least one of a color filter, a color conversion layer, a touch screen layer, and a polarizing layer. 
     In an embodiment, the electronic apparatus may include quantum dots. For example, the electronic apparatus may include a color conversion layer, and the color conversion layer may include quantum dots. 
     The term “interlayer” as used herein may refer to a single layer and/or all of the multiple layers located between the first electrode and the second electrode of the light-emitting device. 
     [Description of  FIG.  1   ] 
       FIG.  1    is a schematic cross-sectional view of a light-emitting device  10  according to an embodiment. The light-emitting device  10  includes a first electrode  110 , an interlayer  130 , and a second electrode  150 . 
     Hereinafter, the structure and manufacturing method of the light-emitting device  10  according to an embodiment will be described with reference to  FIG.  1   . 
     [First Electrode  110 ] 
     In  FIG.  1   , a substrate may be located under the first electrode  110  or on the second electrode  150 . A glass substrate or a plastic substrate may be used as the substrate. In the embodiments, the substrate may be a flexible substrate, and may include durable and heat-resistant plastics, such as polyimide, polyethylene terephthalate (PET), polycarbonate, polyethylene napthalate, polyarylate (PAR), polyetherimide, or any combination thereof. 
     The first electrode  110  may be formed by, for example, depositing or sputtering a material for forming the first electrode  110  on the substrate. When the first electrode  110  is an anode, a material for forming the first electrode  110  may be a high-work function material that facilitates the injection of holes. 
     The first electrode  110  may be a reflective electrode, a semi-transmissive electrode, or a transmissive electrode. When the first electrode  110  is a transmissive electrode, a material for forming the first electrode  110  may include indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO 2 ), zinc oxide (ZnO), or any combination thereof. In the embodiments, when the first electrode  110  is a semi-transmissive electrode or a reflective electrode, a material for forming the first electrode  110  may include magnesium (Mg), silver (Ag), aluminum (AI), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), or any combination thereof. 
     The first electrode  110  may have a single-layered structure consisting of a single layer or a multi-layered structure including multiple layers. For example, the first electrode  110  may have a three-layered structure of ITO/Ag/ITO. 
     [Interlayer  130 ] 
     The interlayer  130  may be located on the first electrode  110 . The interlayer  130  may include an emission layer. 
     The interlayer  130  may further include a hole transport region located between the first electrode  110  and the emission layer, and an electron transport region located between the emission layer and the second electrode  150 . 
     The interlayer  130  may further include, in addition to various organic materials, a metal-containing compound such as an organometallic compound, an inorganic material such as quantum dots, or the like. 
     In the embodiments, the interlayer  130  may include, i) two or more emitting portions sequentially stacked between the first electrode  110  and the second electrode  150 , and ii) a charge generation layer located between the two or more emitting portions. When the interlayer  130  includes emitting portions and a charge generation layer as described above, the light-emitting device  10  may be a tandem light-emitting device. 
     [Hole Transport Region in Interlayer  130 ] 
     The hole transport region may have: i) a single-layered structure consisting of a single layer consisting of a single material, ii) a single-layered structure consisting of a single layer consisting of multiple materials, or iii) a multi-layered structure including multiple layers including different materials. 
     The hole transport region may include at least one of a hole injection layer, a hole transport layer, an emission auxiliary layer, and an electron blocking layer. 
     For example, the hole transport region may have a multi-layered structure including a hole injection layer/hole transport layer structure, a hole injection layer/hole transport layer/emission auxiliary layer structure, a hole injection layer/emission auxiliary layer structure, a hole transport layer/emission auxiliary layer structure, or a hole injection layer/hole transport layer/electron blocking layer structure, the layers of each structure being stacked sequentially from the first electrode  110 . 
     The hole transport region may include a compound represented by Formula 201, a compound represented by Formula 202, or any combination thereof. 
     
       
         
         
             
             
         
       
     
     In Formulae 201 and 202, L 201  to L 204  may each independently be a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a  or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a . L 205  may be *—O—*′, *—S—*′, *—N(Q 201 )-*′, a C 1 -C 20  alkylene group unsubstituted or substituted with at least one R 10a , a C 2 -C 20  alkenylene group unsubstituted or substituted with at least one R 10a , a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a , or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a . xa1 to xa4 may each independently be an integer from 0 to 5. xa5 may be an integer from 1 to 10. 
     R 201  to R 204  and Q 201  may each independently be a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a  or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a . R 201  and R 202  may optionally be linked to each other via a single bond, a C 1 -C 5  alkylene group unsubstituted or substituted with at least one R 10a , or a C 2 -C 5  alkenylene group unsubstituted or substituted with at least one R 10a , to form a C 8 -C 60  polycyclic group (for example, a carbazole group or the like) unsubstituted or substituted with at least one R 10a  (for example, compound HT16). R 203  and R 204  may optionally be linked to each other, via a single bond, a C 1 -C 5  alkylene group unsubstituted or substituted with at least one R 10a , or a C 2 -C 5  alkenylene group unsubstituted or substituted with at least one R 10a , to form a C 8 -C 60  polycyclic group unsubstituted or substituted with at least one R 10a . na1 may be an integer from 1 to 4. 
     For example, each of Formulae 201 and 202 may include at least one of groups represented by Formulae CY201 to CY217. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     R 10b  and R 10c  in Formulae CY201 to CY217 are the same as described in connection with R 10a , ring CY 201  to ring CY 204  may each independently be a C 3 -C 20  carbocyclic group or a C 1 -C 20  heterocyclic group, and at least one hydrogen in Formulae CY201 to CY217 may be unsubstituted or substituted with R 10a . 
     In the embodiments, ring CY 201  to ring CY 204  in Formulae CY201 to CY217 may each independently be a benzene group, a naphthalene group, a phenanthrene group, or an anthracene group. 
     In the embodiments, each of Formulae 201 and 202 may include at least one of the groups represented by Formulae CY201 to CY203. 
     In the embodiments, Formula 201 may include at least one of the groups represented by Formulae CY201 to CY203 and at least one of the groups represented by Formulae CY204 to CY217. 
     In the embodiments, in Formula 201, xa1 may be 1, R 201  may be a group represented by one of Formulae CY201 to CY203, xa2 may be 0, and R 202  may be a group represented by one of Formulae CY204 to CY207. 
     In the embodiments, each of Formulae 201 and 202 may not include a group represented by one of Formulae CY201 to CY203. 
     In the embodiments, each of Formulae 201 and 202 may not include a group represented by one of Formulae CY201 to CY203, and may include at least one of the groups represented by Formulae CY204 to CY217. 
     In the embodiments, each of Formulae 201 and 202 may not include a group represented by one of Formulae CY201 to CY217. 
     In an embodiment, the hole transport region may include one of compounds HT1 to HT44, m-MTDATA, TDATA, 2-TNATA, NPB(NPD), β-NPB, TPD, Spiro-TPD, Spiro-NPB, methylated NPB, TAPC, HMTPD, 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA), polyaniline/dodecylbenzenesulfonic acid (PANI/DBSA), poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS), polyaniline/camphor sulfonic acid (PANI/CSA), polyaniline/poly(4-styrenesulfonate) (PANI/PSS), or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A thickness of the hole transport region may be in a range of about 50 Å to about 10,000 Å, for example, about 100 Å to about 4,000 Å. When the hole transport region includes at least one of a hole injection layer, and a hole transport layer, a thickness of the hole injection layer may be in a range of about 100 Å to about 9,000 Å, for example, about 100 Å to about 1,000 Å, and a thickness of the hole transport layer may be in a range of about 50 Å to about 2,000 Å, for example, about 100 Å to about 1,500 Å. When the thicknesses of the hole transport region, the hole injection layer, and the hole transport layer are within these ranges, satisfactory hole transporting characteristics may be obtained without a substantial increase in driving voltage. 
     The emission auxiliary layer may increase light-emission efficiency by compensating for an optical resonance distance according to the wavelength of light emitted by an emission layer, and the electron blocking layer may block the flow of electrons from an electron transport region. The emission auxiliary layer and the electron blocking layer may include the materials as described above. 
     [p-dopant] 
     The hole transport region may include, in addition to these materials, a charge-generation material for the improvement of conductive properties. The charge-generation material may be uniformly or non-uniformly dispersed in the hole transport region (for example, in the form of a single layer consisting of a charge-generation material). 
     The charge-generation material may be, for example, a p-dopant. 
     For example, the lowest unoccupied molecular orbital (LUMO) energy level of the p-dopant may be −3.5 eV or less. 
     In the embodiments, the p-dopant may include a quinone derivative, a cyano group-containing compound, a compound including element EL1 and element EL2, or any combination thereof. 
     Examples of the quinone derivative are TCNQ, F4-TCNQ, and the like. 
     Examples of the cyano group-containing compound are HAT-CN, and a compound represented by Formula 221 below: 
     
       
         
         
             
             
         
       
     
     Formula 221. 
     In Formula 221, R 221  to R 223  may each independently be a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a  or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a . At least one of R 221  to R 223  may each independently be any combination of a C 3 -C 60  carbocyclic group or a C 1 -C 60  heterocyclic group, each substituted with a cyano group; —F; —CI; —Br; —I; a C 1 -C 20  alkyl group substituted with a cyano group, —F, —Cl, —Br, —I, or any combination thereof. 
     In the compound including element EL1 and element EL2, element EL1 may be metal, metalloid, or any combination thereof, and element EL2 may be non-metal, metalloid, or any combination thereof. 
     Examples of the metals may include alkali metals (for example, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), etc.), alkaline earth metals (for example, beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), etc.), transition metals (for example, titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), manganese (Mn), technetium (Tc), rhenium (Re), iron (Fe), ruthenium (Ru), osmium (Os), cobalt (Co), rhodium (Rh), iridium (Ir), nickel (Ni), palladium (Pd), platinum (Pt), copper (Cu), silver (Ag), gold (Au), etc.), post-transition metals (for example, zinc (Zn), indium (In), tin (Sn), etc.), and/or lanthanide metals (for example, lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), etc.), or any combination thereof. 
     Examples of the metalloids may include silicon (Si), antimony (Sb), and tellurium (Te), and any combination thereof. 
     Examples of the non-metals may include oxygen (O) and halogen (for example, F, Cl, Br, I, etc.), or any combination thereof. 
     Examples of the compound including element EL1 and element EL2 may include metal oxides, metal halides (for example, metal fluoride, metal chloride, metal bromide, or metal iodide), metalloid halides (for example, metalloid fluoride, metalloid chloride, metalloid bromide, or metalloid iodide), metal telluride, or any combination thereof. 
     Examples of the metal oxides may include tungsten oxides (for example, WO, W 2 O 3 , WO 2 , WO 3 , W 2 O 5 , etc.), vanadium oxides (for example, VO, V 2 O 3 , VO 2 , V 2 O 5 , etc.), molybdenum oxides (MoO, Mo 2 O 3 , MoO 2 , MoO 3 , Mo 2 O 5 , etc.), and/or rhenium oxides (for example, ReO 3 , etc.), or any combination thereof. 
     Examples of the metal halides may include alkali metal halides, alkaline earth metal halides, transition metal halides, post-transition metal halides, and lanthanide metal halides, or any combination thereof. 
     Examples of alkali metal halides may include LiF, NaF, KF, RbF, CsF, LiCI, NaCl, KCl, RbCI, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, KI, RbI, CsI, and the like, or any combination thereof. 
     Examples of the alkaline earth metal halides are BeF 2 , MgF 2 , CaF 2 , SrF 2 , BaF 2 , BeCl 2 , MgCl 2 , CaCl 2 ), SrCl 2 , BaCl 2 , BeBr 2 , MgBr 2 , CaBr 2 , SrBr 2 , BaBr 2 , BeI 2 , MgI 2 , CaI 2 , SrI 2 , and BaI 2 , or any combination thereof. 
     Examples of the transition metal halides may include titanium halides (for example, TiF 4 , TiCl 4 , TiBr 4 , Til 4 , etc.), zirconium halides (for example, ZrF 4 , ZrCl 4 , ZrBr 4 , ZrI 4 , etc.), hafnium halides (for example, HfF 4 , HfCl 4 , HfBr 4 , Hfl 4 , etc.), vanadium halides (for example, VF 3 , VCI 3 , VBr 3 , Vl 3 , etc.), niobium halides (for example, NbF 3 , NbCl 3 , NbBr 3 , NbI 3 , etc.), tantalum halides (for example, TaF 3 , TaCI 3 , TaBr 3 , Tal 3 , etc.), chromium halides (for example, CrF 3 , CrCl 3 , CrBr 3 , CrI 3 , etc.), molybdenum halides (for example, MoF 3 , MoCI 3 , MoBr 3 , Mol 3 , etc.), tungsten halides (for example, WF 3 , WCl 3 , WBr 3 , WI 3 , etc.), manganese halides (for example, MnF 2 , MnCl 2 , MnBr 2 , Mnl 2 , etc.), technetium halides (for example, TcF 2 , TcCl 2 , TcBr 2 , TcI 2 , etc.), rhenium halides (for example, ReF 2 , ReCl 2 , ReBr 2 , ReI 2 , etc.), iron halides (for example, FeF 2 , FeCl 2 , FeBr 2 , FeI 2 , etc.), ruthenium halides (for example, RuF 2 , RuCl 2 , RuBr 2 , Rul 2 , etc.), osmium halides (for example, OsF 2 , OsCl 2 , OsBr 2 , OsI 2 , etc.), cobalt halides (for example, CoF 2 , CoCl 2 , CoBr 2 , CoI 2 , etc.), rhodium halides (for example, RhF 2 , RhCl 2 , RhBr 2 , Rhl 2 , etc.), iridium halides (for example, IrF 2 , IrCl 2 , IrBr 2 , IrI 2 , etc.), nickel halides (for example, NiF 2 , NiCl 2 , NiBr 2 , Nil 2 , etc.), palladium halides (for example, PdF 2 , PdCI 2 , PdBr 2 , PdI 2 , etc.), platinum halides (for example, PtF 2 , PtCl 2 , PtBr 2 , PtI 2 , etc.), copper halides (for example, CuF, CuCl, CuBr, Cul, etc.), silver halides (for example, AgF, AgCI, AgBr, Agl, etc.), and gold halides (for example, AuF, AuCI, AuBr, Aul, etc.), or any combination thereof. 
     Examples of the post-transition metal halides may include zinc halides (for example, ZnF 2 , ZnCl 2 , ZnBr 2 , ZnI 2 , etc.), indium halides (for example, InI 3 , etc.), and tin halides (for example, SnI 2 , etc.), or any combination thereof. 
     Examples of the lanthanide metal halides may include YbF, YbF 2 , YbF 3 , SmF 3 , YbCI, YbCl 2 , YbCl 3  SmCl 3 , YbBr, YbBr 2 , YbBr 3  SmBr 3 , Ybl, Ybl 2 , Ybl 3 , and SmI 3 , or any combination thereof. 
     An example of the metalloid halide may include antimony halide (for example, SbCI 5 , etc.). 
     Examples of the metal telluride may include alkali metal telluride (for example, Li 2 Te, a na 2 Te, K 2 Te, Rb 2 Te, Cs 2 Te, etc.), alkaline earth metal telluride (for example, BeTe, MgTe, CaTe, SrTe, BaTe, etc.), transition metal telluride (for example, TiTe 2 , ZrTe 2 , HfTe 2 , V 2 Te 3 , Nb 2 Te 3 , Ta 2 Te 3 , Cr 2 Te 3 , Mo 2 Te 3 , W 2 Te 3 , MnTe, TcTe, ReTe, FeTe, RuTe, OsTe, CoTe, RhTe, IrTe, NiTe, PdTe, PtTe, Cu 2 Te, CuTe, Ag 2 Te, AgTe, Au 2 Te, etc.), post-transition metal telluride (for example, ZnTe, etc.), and lanthanide metal telluride (for example, LaTe, CeTe, PrTe, NdTe, PmTe, EuTe, GdTe, TbTe, DyTe, HoTe, ErTe, TmTe, YbTe, LuTe, etc.), or any combination thereof. 
     [Emission Layer in Interlayer  130 ] 
     When the light-emitting device  10  is a full-color light-emitting device, the emission layer may be patterned into a red emission layer, a green emission layer, and/or a blue emission layer, according to a sub-pixel. In the embodiments, the emission layer may have a stacked structure of two or more layers of a red emission layer, a green emission layer, and a blue emission layer, in which the two or more layers contact each other or are separated from each other to emit white light. In the embodiments, the emission layer may include two or more materials of a red light-emitting material, a green light-emitting material, and a blue light-emitting material, in which the two or more materials are mixed with each other in a single layer to emit white light. 
     The emission layer may include a host and a dopant. The dopant may include a phosphorescent dopant, a fluorescent dopant, or any combination thereof. 
     The amount of the dopant in the emission layer may be from about 0.01 to about 15 parts by weight based on 100 parts by weight of the host. 
     The emission layer may include a delayed fluorescence material. The delayed fluorescence material may act as a host or a dopant in the emission layer. 
     A thickness of the emission layer may be in a range of about 100 Å to about 1,000 Å, for example, about 200 Å to about 600 Å. When the thickness of the emission layer is within these ranges, suitable light-emission characteristics may be obtained without substantially increasing the driving voltage. 
     [Hosts in the Emission Layer] 
     The triplet energy T 1_H1  of the first host included in the first emission layer and the second emission layer, the triplet energy T 1_H2  of the second host, and the triplet energy T 1_H3  of the third host may satisfy Formulae (1) and (2): 
         T   1_H1   −T   1_H3 ≥0.2 eV  (1)
 
         T   1_H2   −T   1_H3 ≥0.2 eV  (2).
 
     In the light-emitting device according to an embodiment, the relation of the triplet energy of the first host, the second host, and the third host only needs to satisfy Formulae (1) and (2). Thus, any first host, second host, and third host satisfying Formulae (1) and (2) may be used. 
     The first host and the second host may be a pyrene derivative compound. For example, the first host and the second host may be a symmetrical pyrene derivative compound. For example, the first host may be a hole transport pyrene derivative compound, and the second host may be an electron transport pyrene derivative compound. 
     The third host may be a general blue host compound used in a blue fluorescent emission layer under a condition in which Formulae (1) and (2) must be satisfied in relation to the first host and the second host included in the first emission layer. 
     For example, the third host may be an anthracene derivative compound. For example, the third host may be an anthracene derivative compound in which one aryl group and one heteroaryl group are substituted into anthracene. For example, the third host may be an asymmetric compound. 
     Detailed examples of the first host, the second host, and the third host are as described above. Other examples of the first host, the second host, and the third host are as below: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     [Fluorescent Dopant] 
     The fluorescent dopant may include an amine group-containing compound, a styryl group-containing compound, or any combination thereof. 
     For example, the fluorescent dopant may include a compound represented by Formula 501. 
     
       
         
         
             
             
         
       
     
     In Formula 501, Ar 501 , L 501  to L 503 , R 501 , and R 502  may each independently be a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a  or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a . xd1 to xd3 may each independently be 0, 1, 2, or 3. xd4 may be 1, 2, 3, 4, 5, or 6. 
     For example, Ar 501  in Formula 501 may be a condensed cyclic group (for example, an anthracene group, a chrysene group, or a pyrene group) in which three or more monocyclic groups are condensed together. In the embodiments, xd4 in Formula 501 may be 2. 
     For example, the fluorescent dopant may include one of the compounds FD1 to FD36, DPVBi, DPAVBi, or any combination thereof. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     [Delayed Fluorescence Material] 
     The emission layer may include a delayed fluorescence material. 
     In the specification, the delayed fluorescence material may be selected from compounds capable of emitting delayed fluorescent light based on a delayed fluorescence emission mechanism. 
     The delayed fluorescence material included in the emission layer may act as a host or a dopant depending on the type of other materials included in the emission layer. 
     In the embodiments, the difference between the triplet energy level (eV) of the delayed fluorescence material and the singlet energy level (eV) of the delayed fluorescence material may be greater than or equal to about 0 eV and less than or equal to about 0.5 eV. When the difference between the triplet energy level (eV) of the delayed fluorescence material and the singlet energy level (eV) of the delayed fluorescence material satisfies the above-described range, up-conversion from the triplet state to the singlet state of the delayed fluorescence materials may effectively occur, and thus, the luminescence efficiency of the light-emitting device  10  may be improved. 
     For example, the delayed fluorescence material may include i) a material including at least one electron donor (for example, a π electron-rich C 3 -C 60  cyclic group, such as a carbazole group) and at least one electron acceptor (for example, a sulfoxide group, a cyano group, or a π electron-deficient nitrogen-containing C 1 -C 60  cyclic group), and ii) a material including a C 8 -C 60  polycyclic group in which two or more cyclic groups are condensed while sharing boron (B). 
     Examples of the delayed fluorescence material may include at least one of the following compounds DF1 to DF9. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     [Quantum Dots] 
     The term “quantum dots” as used herein refers to crystals of a semiconductor compound, and may include any material capable of emitting light of various emission wavelengths according to the size of the crystals. 
     A diameter of the quantum dot may be, for example, in a range of about 1 nm to about 10 nm. 
     The quantum dot may be synthesized by a wet chemical process, a metal organic chemical vapor deposition process, a molecular beam epitaxy process, or any process similar thereto. 
     The wet chemical process is a method including mixing a precursor material with an organic solvent and then growing a quantum dot particle crystal. When the crystal grows, the organic solvent naturally acts as a dispersant coordinated on the surface of the quantum dot crystal and controls the growth of the crystal so that the growth of quantum dot particles can be controlled through a process which costs lower, and is easier than vapor deposition methods, such as metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE), 
     The quantum dot may include Group II-VI semiconductor compounds, Group III-V semiconductor compounds, Group III-VI semiconductor compounds, Group I-III-VI semiconductor compounds, Group IV-VI semiconductor compounds, a Group IV element or compound, or any combination thereof. 
     Examples of a Group II-VI semiconductor compound are a binary compound, such as CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, or MgS, a ternary compound, such as CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, or MgZnS, a quaternary compound, such as CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, or HgZnSTe, or any combination thereof. 
     Examples of a Group III-V semiconductor compound may include a binary compound such as GaN, GaP, GaAs, GaSb, AlN, AIP, AIAs, AISb, InN, InP, InAs, or InSb, a ternary compound such as GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AINP, AINAs, AINSb, AIPAs, AIPSb, InGaP, InNP, InAIP, InNAs, InNSb, InPAs, or InPSb, a quaternary compound such as GaAINP, GaAINAs, GaAINSb, GaAIPAs, GaAIPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAINP, InAINAs, InAINSb, InAIPAs, or InAIPSb, or any combination thereof. Group III-V semiconductor compounds may include a Group II element. Examples of the Groups III-V semiconductor compounds including a Group II element are InZnP, InGaZnP, InAlZnP, etc. 
     Examples of a Group III-VI semiconductor compound may include a binary compound, such as GaS, GaSe, Ga 2 Se 3 , GaTe, InS, InSe, In 2 S 3 , In 2 Se 3 , or InTe, a ternary compound, such as InGaS 3 , or InGaSe 3 , and any combination thereof. 
     Examples of a Group I-III-VI semiconductor compound may include a ternary compound, such as AgInS, AgInS 2 , CulnS, CuInS 2 , CuGaO 2 , AgGaO 2 , or AgAIO 2 , or any combination thereof. 
     Examples of a Group IV-VI semiconductor compound may include a binary compound, such as SnS, SnSe, SnTe, PbS, PbSe, or PbTe, a ternary compound, such as SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, or SnPbTe, a quaternary compound, such as SnPbSSe, SnPbSeTe, or SnPbSTe, or any combination thereof. 
     The Group IV element or compound may include a single element compound, such as Si or Ge, a binary compound, such as SiC or SiGe, or any combination thereof. 
     Each element included in a multi-element compound such as the binary compound, the ternary compound, and the quaternary compound may be present at a uniform concentration or non-uniform concentration in a particle. 
     The quantum dot may have a single structure in which the concentration of each element in the quantum dot is uniform, or a core-shell dual structure. For example, the core and the shell may include materials that are different from each other. 
     The shell of the quantum dot may act as a protective layer that prevents chemical degradation of the core to maintain semiconductor characteristics, and/or as a charging layer that imparts electrophoretic characteristics to the quantum dot. The shell may be a single layer or a multi-layer. The interface between the core and the shell may have a concentration gradient in which the concentration of an element existing in the shell decreases toward the center of the core. 
     Examples of the shell of the quantum dot may include an oxide of metal, metalloid, or non-metal, a semiconductor compound, and any combination thereof. 
     Examples of the oxide of metal, metalloid, or non-metal may include a binary compound, such as SiO 2 , Al 2 O 3 , TiO 2 , ZnO, MnO, Mn 2 O 3 , Mn 3 O 4 , CuO, FeO, Fe 2 O 3 , Fe 3 O 4 , CoO, CO 3 O 4 , or NiO, a ternary compound, such as MgAl 2 O 4 , CoFe 2 O 4 , NiFe 2 O 4 , or CoMn 2 O 4 , and any combination thereof. Examples of the semiconductor compound are, as described herein, Group II-VI semiconductor compounds, Group III-V semiconductor compounds, Group III-VI semiconductor compounds, Group I-III-VI semiconductor compounds, Group IV-VI semiconductor compounds, and any combination thereof. For example, the semiconductor compound may include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnSeS, ZnTeS, GaAs, GaP, GaSb, HgS, HgSe, HgTe, InAs, InP, InGaP, InSb, AIAs, AIP, AISb, or any combination thereof. 
     A full width at half maximum (FWHM) of the emission wavelength spectrum of the quantum dot may be about 45 nm or less, for example, about 40 nm or less, for example, about 30 nm or less, and within these ranges, color purity or color reproducibility may be increased. Since the light emitted through the quantum dot is emitted in all directions, the width of the viewing angle may be increased. 
     The quantum dot may be a spherical particle, a pyramidal particle, a multi-arm particle, a cubic nanoparticle, a nanotube particle, a nanowire particle, a nanofiber particle, or a nanoplate particle. 
     Since the energy band gap may be adjusted by controlling the size of the quantum dot, light having various wavelength bands may be obtained from the quantum dot emission layer. Accordingly, by using quantum dots of different sizes, a light-emitting device that emits light of various wavelengths may be implemented. In the embodiments, the size of the quantum dot may be selected to emit red, green and/or blue light. In other examples, the size of the quantum dot may be configured to emit white light by combining of light of various colors. 
     [Electron Transport Region in Interlayer  130 ] 
     The electron transport region may have i) a single-layered structure consisting of a single layer consisting of a single material, ii) a single-layered structure consisting of a single layer consisting of multiple different materials, or iii) a multi-layered structure including multiple layers including different materials. 
     The electron transport region may include at least one of a hole blocking layer, an electron transport layer, and an electron injection layer. 
     In an embodiment, the electron transport region may have an electron transport layer/electron injection layer structure or a hole blocking layer/electron transport layer/electron injection layer structure. In each structure, constituting layers may be sequentially stacked from the emission layer. 
     In an embodiment, the electron transport region (for example, the hole blocking layer, or the electron transport layer in the electron transport region) may include a metal-free compound including at least one π electron-deficient nitrogen-containing C 1 -C 60  cyclic group. 
     For example, the electron transport region may include a compound represented by Formula 601 below. 
       [Ar 601 ] x611 -[(L 601 ) xe1 -R 601 ] xe21   Formula 601
 
     In Formula 601, Ar 601  and L 601  may each independently be a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a  or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a . xe11 may be 1, 2, or 3. xe1 may be 0, 1, 2, 3, 4, or 5. 
     R 601  may be a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a , —Si(Q 601 )(Q 602 )(Q 603 ), —C(═O)(Q 601 ), —S(═O) 2 (Q 601 ), or —P(═O)(Q 601 )(Q 602 ). Q 601  to Q 603  may each be substantially the same as described herein with respect to Q 1 . xe21 may be 1, 2, 3, 4, or 5. At least one of Ar 601 , L 601 , and R 601  may each independently be a π electron-deficient nitrogen-containing C 1 -C 60  cyclic group unsubstituted or substituted with at least one R 10a . For example, when xe11 in Formula 601 is 2 or more, two or more of Ar 601  (s) may be linked to each other via a single bond. In other examples, Ar 601  in Formula 601 may be a substituted or unsubstituted anthracene group. In other embodiments, the electron transport region may include a compound represented by Formula 601-1. 
     
       
         
         
             
             
         
       
     
     In Formula 601-1, X 614  may be N or C(R 614 ), X 615  may be N or C(R 615 ), X 616  may be N or C(R 616 ), and at least one of X 614  to X 616  may be N. L 611  to L 613  may each be substantially similar to L 601 . xe611 to xe613 may each be the substantially similar to xe1. R 611  to R 613  may each be substantially similar to R 601 . R 614  to R 616  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 20  alkyl group, a C 1 -C 20  alkoxy group, a C 3 -C 60  carbocyclic group unsubstituted or substituted with at least one R 10a , or a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a . For example, xe1 and xe611 to xe613 in Formulae 601 and 601-1 may each independently be 0, 1, or 2. 
     The electron transport region may include one of the compounds ET1 to ET45, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), 4,7-diphenyl-1,10-phenanthroline (Bphen), Alq3, BAlq, TAZ, NTAZ, or any combination thereof. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A thickness of the electron transport region may be from about 100 Å to about 5,000 Å, for example, about 160 Å to about 4,000 Å. When the electron transport region includes the hole blocking layer, the electron transport layer, or any combination thereof, a thickness of the hole blocking layer or electron transport layer may each independently be from about 20 Å to about 1,000 Å, for example, about 30 Å to about 300 Å, and the thickness of the electron transport layer may be from about 100 Å to about 1,000 Å, for example, about 150 Å to about 500 Å. When the thicknesses of the hole blocking layer and/or the electron transport layer are within these ranges, satisfactory electron transporting characteristics may be obtained without substantially increasing the driving voltage. 
     The electron transport region (for example, the electron transport layer in the electron transport region) may include, in addition to the materials described above, a metal-containing material. 
     The metal-containing material may include an alkali metal complex, an alkaline earth metal complex, or any combination thereof. The metal ion of an alkali metal complex may be a Li ion, a Na ion, a K ion, a Rb ion, or a Cs ion, and the metal ion of an alkaline earth metal complex may be a Be ion, a Mg ion, a Ca ion, a Sr ion, or a Ba ion. A ligand coordinated with the metal ion of the alkali metal complex or the alkaline earth-metal complex may include a hydroxyquinoline, a hydroxyisoquinoline, a hydroxybenzoquinoline, a hydroxyacridine, a hydroxyphenanthridine, a hydroxyphenyloxazole, a hydroxyphenylthiazole, a hydroxydiphenyloxadiazole, a hydroxydiphenylthiadiazole, a hydroxyphenylpyridine, a hydroxyphenylbenzimidazole, a hydroxyphenylbenzothiazole, a bipyridine, a phenanthroline, a cyclopentadiene, or any combination thereof. 
     For example, the metal-containing material may include a Li complex. The Li complex may include, for example, compound ET-D1 (LiQ) or ET-D2. 
     
       
         
         
             
             
         
       
     
     The electron transport region may include an electron injection layer that facilitates the injection of electrons from the second electrode  150 . The electron injection layer may contact (for example, directly contact) the second electrode  150 . 
     The electron injection layer may have i) a single-layered structure consisting of a single layer consisting of a single material, ii) a single-layered structure consisting of a single layer consisting of multiple different materials, or iii) a multi-layered structure including multiple layers including different materials. 
     The electron injection layer may include an alkali metal, alkaline earth metal, a rare earth metal, an alkali metal-containing compound, alkaline earth metal-containing compound, a rare earth metal-containing compound, an alkali metal complex, an alkaline earth metal complex, a rare earth metal complex, or any combination thereof. 
     The alkali metal may include Li, a Na, K, Rb, Cs, or any combination thereof. The alkaline earth metal may include Mg, Ca, Sr, Ba, or any combination thereof. The rare earth metal may include Sc, Y, Ce, Tb, Yb, Gd, or any combination thereof. 
     The alkali metal-containing compound, the alkaline earth metal-containing compound, and the rare earth metal-containing compound may be oxides, halides (for example, fluorides, chlorides, bromides, or iodides), or tellurides of the alkali metal, the alkaline earth metal, and the rare earth metal, or any combination thereof. 
     The alkali metal-containing compound may include alkali metal oxides, such as Li 2 O, Cs 2 O, or K 2 O, alkali metal halides, such as LiF, NaF, CsF, KF, LiI, NaI, CsI, or KI, or any combination thereof. The alkaline earth metal-containing compound may include an alkaline earth metal compound, such as BaO, SrO, CaO, Ba x Sr 1-x O (where x is a real number, and 0&lt;x&lt;1), Ba x Ca 1-x O (wherein x is a real number, and 0&lt;x&lt;1), or the like. The rare earth metal-containing compound may include YbF 3 , ScF 3 , Sc 2 O 3 , Y 2 O 3 , Ce 2 O 3 , GdF 3 , TbF 3 , Ybl 3 , ScI 3 , Tbl 3 , or any combination thereof. In the embodiments, the rare earth metal-containing compound may include lanthanide metal telluride. Examples of the lanthanide metal telluride are LaTe, CeTe, PrTe, NdTe, PmTe, SmTe, EuTe, GdTe, TbTe, DyTe, HoTe, ErTe, TmTe, YbTe, LuTe, La 2 Te 3 , Ce 2 Te 3 , Pr 2 Te 3 , Nd 2 Te 3 , Pm 2 Te 3 , Sm 2 Te 3 , Eu 2 Te 3 , Gd 2 Te 3 , Tb 2 Te 3 , Dy 2 Te 3 , Ho 2 Te 3 , Er 2 Te 3 , Tm 2 Te 3 , Yb 2 Te 3 , and Lu 2 Te 3 . 
     The alkali metal complex, the alkaline earth-metal complex, and the rare earth metal complex may include i) ions of the alkali metal, the alkaline earth metal, and the rare earth metal and ii), as a ligand bonded to the metal ion, for example, a hydroxyquinoline, a hydroxyisoquinoline, a hydroxybenzoquinoline, a hydroxyacridine, a hydroxyphenanthridine, a hydroxyphenyloxazole, a hydroxyphenylthiazole, a hydroxydiphenyloxadiazole, a hydroxydiphenylthiadiazole, a hydroxyphenylpyridine, a hydroxyphenyl benzimidazole, a hydroxyphenylbenzothiazole, a bipyridine, phenanthroline, a cyclopentadiene, or any combination thereof. 
     The electron injection layer may consist of an alkali metal, an alkaline earth metal, a rare earth metal, an alkali metal-containing compound, an alkaline earth metal-containing compound, a rare earth metal-containing compound, an alkali metal complex, an alkaline earth metal complex, a rare earth metal complex, or any combination thereof, as described above. In the embodiments, the electron injection layer may include an organic material (for example, a compound represented by Formula 601). 
     In the embodiments, the electron injection layer may consist of i) an alkali metal-containing compound (for example, an alkali metal halide), or ii) (a) an alkali metal-containing compound (for example, an alkali metal halide), and (b) an alkali metal, an alkaline earth metal, a rare earth metal, or any combination thereof. For example, the electron injection layer may be a KI:Yb co-deposited layer, an RbI:Yb co-deposited layer, or the like. 
     When the electron injection layer further an organic material, the alkali metal, alkaline earth metal, rare earth metal, alkali metal-containing compound, alkaline earth metal-containing compound, rare earth metal-containing compound, alkali metal complex, alkaline earth-metal complex, rare earth metal complex, or any combination thereof may be uniformly or non-uniformly dispersed in a matrix including the organic material. 
     A thickness of the electron injection layer may be in a range of about 1 Å to about 100 Å, and, for example, about 3 Å to about 90 Å. When the thickness of the electron injection layer is within the ranges described above, satisfactory electron injection characteristics may be obtained without substantially increasing the driving voltage. 
     [Second Electrode  150 ] 
     The second electrode  150  may be located on the interlayer  130  having a structure as described above. The second electrode  150  may be a cathode, which is an electron injection electrode, and as the material for the second electrode  150 , a metal, an alloy, an electrically conductive compound, or any combination thereof, each having a low-work function, may be used. 
     The second electrode  150  may include lithium (Li), silver (Ag), magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), ytterbium (Yb), silver-ytterbium (Ag—Yb), ITO, IZO, or any combination thereof. The second electrode  150  may be a transmissive electrode, a semi-transmissive electrode, or a reflective electrode. 
     The second electrode  150  may have a single-layered structure or a multi-layered structure including multiple layers. 
     [Capping Layer] 
     A first capping layer may be located outside the first electrode  110 , and/or a second capping layer may be located outside the second electrode  150 . The light-emitting device  10  may have a structure in which the first capping layer, the first electrode  110 , the interlayer  130 , and the second electrode  150  are sequentially stacked in the stated order, a structure in which the first electrode  110 , the interlayer  130 , the second electrode  150 , and the second capping layer are sequentially stacked in the stated order, or a structure in which the first capping layer, the first electrode  110 , the interlayer  130 , the second electrode  150 , and the second capping layer are sequentially stacked in the stated order. 
     Light generated in an emission layer of the interlayer  130  of the light-emitting device  10  may be extracted toward the outside through the first electrode  110  which is a semi-transmissive electrode or a transmissive electrode, and the first capping layer. Light generated in an emission layer of the interlayer  130  of the light-emitting device  10  may be extracted toward the outside through the second electrode  150  which is a semi-transmissive electrode or a transmissive electrode, and the second capping layer. 
     The constructive interference from the first capping layer and the second capping layer may increase external emission efficiency. Accordingly, the light extraction efficiency of the light-emitting device  10  is increased, so that the luminescence efficiency of the light-emitting device  10  may be improved. 
     Each of the first capping layer and the second capping layer may include a material having a refractive index of about 1.6 or more (at about 589 nm). 
     The first capping layer and the second capping layer may each independently be an organic capping layer including an organic material, an inorganic capping layer including an inorganic material, or a composite capping layer including an organic material and an inorganic material. 
     At least one of the first capping layer and the second capping layer may each independently include carbocyclic compounds, heterocyclic compounds, amine group-containing compounds, porphyrin derivatives, phthalocyanine derivatives, a naphthalocyanine derivatives, alkali metal complexes, alkaline earth metal complexes, or any combination thereof. Optionally, the carbocyclic compound, the heterocyclic compound, and the amine group-containing compound may be substituted with a substituent including O, N, S, Se, Si, F, Cl, Br, I, or any combination thereof. In the embodiments, at least one of the first capping layer and the second capping layer may each independently include an amine group-containing compound. 
     For example, at least one of the first capping layer and the second capping layer may each independently include a compound represented by Formula 201, a compound represented by Formula 202, or any combination thereof. 
     In the embodiments, at least one of the first capping layer and the second capping layer may each independently include one of compounds HT28 to HT33, one of compounds CP1 to CP6, β-NPB, or any combination thereof. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     [Electronic Apparatus] 
     The light-emitting device may be included in various electronic apparatuses. 
     For example, the electronic apparatus including the light-emitting device may be a light-emitting apparatus, an authentication apparatus, or the like. 
     The electronic apparatus (for example, a light-emitting apparatus) may further include, in addition to the light-emitting device, i) a color filter, ii) a color conversion layer, or iii) a color filter and a color conversion layer. The color filter and/or the color conversion layer may be located in at least one traveling direction of light emitted from the light-emitting device. For example, the light emitted from the light-emitting device may be blue light or white light. Details on the light-emitting device have been described above. In the embodiments, the color conversion layer may include a quantum dot. The quantum dot may be, for example, a quantum dot as described herein. 
     The electronic apparatus may include a first substrate. The first substrate may include multiple subpixels, the color filter may include multiple color filter areas respectively corresponding to the subpixels, and the color conversion layer may include multiple color conversion areas respectively corresponding to the subpixels. 
     A pixel-defining film may be located among the subpixels to define each of the subpixels. 
     The color filter may further include multiple color filter areas and light-shielding patterns located among the color filter areas, and the color conversion layer may further include multiple color conversion areas and light-shielding patterns located among the color conversion areas. 
     The color filter areas (or the color conversion areas) may include a first area emitting a first-color light, a second area emitting a second-color light, and/or a third area emitting third-color light, wherein the first-color light, the second-color light, and/or the third-color light may have different maximum emission wavelengths from one another. For example, the first-color light may be red light, the second-color light may be green light, and the third-color light may be blue light. For example, the color filter areas (or the color conversion areas) may include quantum dots. The first area may include a red quantum dot, the second area may include a green quantum dot, and the third area may not include a quantum dot. Details on the quantum dot have been described above. The first area, the second area, and/or the third area may each include a scatterer. 
     For example, the light-emitting device may emit first light, the first area may absorb the first light to emit first-first-color light, the second area may absorb the first light to emit second-first-color light, and the third area may absorb the first light to emit third-first-color light. In this regard, the first-first-color light, the second-first-color light, and the third-first-color light may have different maximum emission wavelengths. The first light may be blue light, the first-first-color light may be red light, the second-first-color light may be green light, and the third-first-color light may be blue light. 
     The electronic apparatus may include a thin-film transistor, in addition to the light-emitting device as described above. The thin-film transistor may include a source electrode, a drain electrode, and an activation layer. Any one of the source electrode and the drain electrode may be electrically connected to any one of the first electrode and the second electrode of the light-emitting device. 
     The thin-film transistor may further include a gate electrode, a gate insulating film, or the like. 
     The activation layer may include crystalline silicon, amorphous silicon, an organic semiconductor, an oxide semiconductor, or the like. 
     The electronic apparatus may further include a sealing portion for sealing the light-emitting device. The sealing portion may be located between the color conversion layer and/or color filter and the light-emitting device. The sealing portion allows light from the light-emitting device to be extracted to the outside, and simultaneously prevents ambient air and moisture from penetrating into the light-emitting device. The sealing portion may be a sealing substrate including a transparent glass substrate or a plastic substrate. The sealing portion may be a thin-film encapsulation layer including at least one layer of an organic layer and/or an inorganic layer. When the sealing portion is a thin film encapsulation layer, the electronic apparatus may be flexible. 
     Various functional layers may be located on the sealing portion, in addition to the color filter and/or the color conversion layer, according to the use of the electronic apparatus. Examples of the functional layers may include a touch screen layer, a polarizing layer, and the like. The touch screen layer may be a pressure-sensitive touch screen layer, a capacitive touch screen layer, or an infrared touch screen layer. The authentication apparatus may be, for example, a biometric authentication apparatus that authenticates an individual by using biometric information (for example, fingerprints, retinas, etc.). 
     The authentication apparatus may further include, in addition to the light-emitting device as described above, a biometric information collector. 
     The electronic apparatus may be applied to various displays, light sources, lighting, personal computers (for example, a mobile personal computer), mobile phones, digital cameras, electronic organizers, electronic dictionaries, electronic game machines, medical instruments (for example, electronic thermometers, sphygmomanometers, blood glucose meters, pulse measurement devices, pulse wave measurement devices, electrocardiogram displays, ultrasonic diagnostic devices, or endoscope displays), fish finders, various measuring instruments, meters (for example, meters for a vehicle, an aircraft, and a vessel), projectors, and the like. 
     [Description of  FIGS.  2  and  3   ] 
       FIG.  2    is a schematic cross-sectional view of an electronic apparatus according to an embodiment. 
     The electronic apparatus of  FIG.  2    includes a substrate  100 , a thin-film transistor (TFT), a light-emitting device, and an encapsulation portion  300  that seals the light-emitting device. 
     The substrate  100  may be a flexible substrate, a glass substrate, or a metal substrate. A buffer layer  210  may be located on the substrate  100 . The buffer layer  210  may prevent penetration of impurities through the substrate  100  and may provide a flat surface on the substrate  100 . 
     A TFT may be located on the buffer layer  210 . The TFT may include an activation layer  220 , a gate electrode  240 , a source electrode  260 , and a drain electrode  270 . 
     The activation layer  220  may include an inorganic semiconductor such as silicon or polysilicon, an organic semiconductor, or an oxide semiconductor, and may include a source region, a drain region, and a channel region. 
     A gate insulating film  230  for insulating the activation layer  220  from the gate electrode  240  may be located on the activation layer  220 , and the gate electrode  240  may be located on the gate insulating film  230 . 
     An interlayer insulating film  250  may be located on the gate electrode  240 . The interlayer insulating film  250  may be located between the gate electrode  240  and the source electrode  260  and between the gate electrode  240  and the drain electrode  270 , to insulate the components from each other. 
     The source electrode  260  and the drain electrode  270  may be located on the interlayer insulating film  250 . The interlayer insulating film  250  and the gate insulating film  230  may be formed to expose the source region and the drain region of the activation layer  220 , and the source electrode  260  and the drain electrode  270  may contact the exposed portions of the source region and the drain region of the activation layer  220 . 
     The TFT may be electrically connected to a light-emitting device to drive the light-emitting device, and may be covered and protected by a passivation layer  280 . The passivation layer  280  may include an inorganic insulating film, an organic insulating film, or any combination thereof. A light-emitting device is provided on the passivation layer  280 . The light-emitting device may include a first electrode  110 , an interlayer  130 , and a second electrode  150 . 
     The first electrode  110  may be located on the passivation layer  280 . The passivation layer  280  may expose a portion of the drain electrode  270 , not fully covering the drain electrode  270 , and the first electrode  110  may be electrically connected to the exposed portion of the drain electrode  270 . 
     A pixel defining layer  290  including an insulating material may be located on the first electrode  110 . The pixel defining layer  290  may expose a region of the first electrode  110 , and an interlayer  130  may be formed in the exposed region of the first electrode  110 . The pixel defining layer  290  may be a polyimide or polyacrylic organic film. Although not shown in  FIG.  2   , at least some layers of the interlayer  130  may extend beyond the upper portion of the pixel defining layer  290  to be located in a common layer. 
     The second electrode  150  may be located on the interlayer  130 , and a capping layer  170  may be formed on the second electrode  150 . The capping layer  170  may be formed to cover the second electrode  150 . 
     The encapsulation portion  300  may be located on the capping layer  170 . The encapsulation portion  300  may be located on a light-emitting device to protect the light-emitting device from moisture or oxygen. The encapsulation portion  300  may include an inorganic film including silicon nitride (SiNx), silicon oxide (SiOx), indium tin oxide, indium zinc oxide, or any combination thereof, an organic film including polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyimide, polyethylene sulfonate, polyoxymethylene, polyarylate, hexamethyldisiloxane, an acrylic resin (for example, polymethyl methacrylate, polyacrylic acid, or the like), an epoxy-based resin (for example, aliphatic glycidyl ether (AGE), or the like), or any combination thereof, or any combination of the inorganic films and the organic films. 
       FIG.  3    is a cross-sectional view of an electronic apparatus according to another embodiment of the disclosure. 
     The electronic apparatus of  FIG.  3    is substantially the same as the light-emitting apparatus of  FIG.  2   , except that a light-shielding pattern  500  and a functional region  400  are additionally located on the encapsulation portion  300 . The functional region  400  may be i) a color filter area, ii) a color conversion area, or iii) a combination of the color filter area and the color conversion area. In an embodiment, the light-emitting device included in the light-emitting apparatus of  FIG.  3    may be a tandem light-emitting device. The color conversion area refers to an area that may include the color conversion layer. 
     [Manufacturing Method] 
     The layers included in the hole transport region, the emission layer, and the layers included in the electron transport region may be formed in a certain region by using various methods such as vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) deposition, ink-jet printing, laser-printing, laser-induced thermal imaging, and the like. 
     When layers constituting the hole transport region, an emission layer, and layers constituting the electron transport region are formed by vacuum deposition, the deposition may be performed at a deposition temperature of about 100° C. to about 500° C., a vacuum degree of about 10 −8  torr to about 10 −3  torr, and a deposition speed of about 0.01 Å/sec to about 100 Å/sec, depending on a material to be included in a layer to be formed and the structure of a layer to be formed. 
     When layers constituting the hole transport region, an emission layer, and layers constituting the electron transport region are formed by spin coating, the spin coating may be performed at a coating speed of about 2,000 rpm to about 5,000 rpm and at a heat treatment temperature of about 80° C. to about 200° C. by considering the material to be included in a layer to be formed and the structure of a layer to be formed. 
     [General Definition of Substituents] 
     The term “C 3 -C 60  carbocyclic group” as used herein refers to a cyclic group that may consist of carbon only and may have three to sixty carbon atoms. The “C 1 -C 60  heterocyclic group” as used herein refers to a cyclic group that may have one to sixty carbon atoms and a heteroatom. The C 3 -C 60  carbocyclic group and the C 1 -C 60  heterocyclic group may each be a monocyclic group consisting of one ring or a polycyclic group in which two or more rings are condensed with each other. For example, the number of ring-forming atoms of the C 1 -C 60  heterocyclic group may be from 3 to 61. 
     The “cyclic group” as used herein may include the C 3 -C 60  carbocyclic group, and the C 1 -C 60  heterocyclic group. 
     The “π electron-rich C 3 -C 60  cyclic group” as used herein refers to a cyclic group that has three to sixty carbon atoms and does not include *—N═*′ as a ring-forming moiety, and the term “π electron-deficient nitrogen-containing C 1 -C 60  cyclic group” as used herein refers to a heterocyclic group that has one to sixty carbon atoms and includes *—N=*′ as a ring-forming moiety. 
     For example, the C 3 -C 60  carbocyclic group may be i) a group T1 or ii) a condensed cyclic group in which two or more groups T1 are condensed with each other (for example, a cyclopentadiene group, an adamantane group, a norbornane group, a benzene group, a pentalene group, a naphthalene group, an azulene group, an indacene group, an acenaphthylene group, a phenalene group, a phenanthrene group, an anthracene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, a perylene group, a pentaphene group, a heptalene group, a naphthacene group, a picene group, a hexacene group, a pentacene group, a rubicene group, a coronene group, an ovalene group, an indene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, an indenophenanthrene group, or an indenoanthracene group). 
     The C 1 -C 60  heterocyclic group may be i) a group T2, ii) a condensed cyclic group in which two or more groups T2 are condensed with each other, or iii) a condensed cyclic group in which at least one group T2 and at least one group T1 are condensed with each other (for example, a pyrrole group, a thiophene group, a furan group, an indole group, a benzoindole group, a naphthoindole group, an isoindole group, a benzoisoindole group, a naphthoisoindole group, a benzosilole group, a benzothiophene group, a benzofuran group, a carbazole group, a dibenzosilole group, a dibenzothiophene group, a dibenzofuran group, an indenocarbazole group, an indolocarbazole group, a benzofurocarbazole group, a benzothienocarbazole group, a benzosilolocarbazole group, a benzoindolocarbazole group, a benzocarbazole group, a benzonaphthofuran group, a benzonaphthothiophene group, a benzonaphthosilole group, a benzofurodibenzofuran group, a benzofurodibenzothiophene group, a benzothienodibenzothiophene group, a pyrazole group, an imidazole group, a triazole group, an oxazole group, an isoxazole group, an oxadiazole group, a thiazole group, an isothiazole group, a thiadiazole group, a benzopyrazole group, a benzimidazole group, a benzoxazole group, a benzoisoxazole group, a benzothiazole group, a benzoisothiazole group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a benzoquinoline group, a benzoisoquinoline group, a quinoxaline group, a benzoquinoxaline group, a quinazoline group, a benzoquinazoline group, a phenanthroline group, a cinnoline group, a phthalazine group, a naphthyridine group, an imidazopyridine group, an imidazopyrimidine group, an imidazotriazine group, an imidazopyrazine group, an imidazopyridazine group, an azacarbazole group, an azafluorene group, an azadibenzosilole group, an azadibenzothiophene group, an azadibenzofuran group, etc.). 
     The π electron-rich C 3 -C 60  cyclic group may be i) a group T1, ii) a condensed cyclic group in which two or more groups T1 are condensed with each other, iii) a group T3, iv) a condensed cyclic group in which two or more groups T3 are condensed with each other, or v) a condensed cyclic group in which at least one group T3 and at least one group T1 are condensed with each other (for example, the C 3 -C 60  carbocyclic group, a pyrrole group, a thiophene group, a furan group, an indole group, a benzoindole group, a naphthoindole group, an isoindole group, a benzoisoindole group, a naphthoisoindole group, a benzosilole group, a benzothiophene group, a benzofuran group, a carbazole group, a dibenzosilole group, a dibenzothiophene group, a dibenzofuran group, an indenocarbazole group, an indolocarbazole group, a benzofurocarbazole group, a benzothienocarbazole group, a benzosilolocarbazole group, a benzoindolocarbazole group, a benzocarbazole group, a benzonaphthofuran group, a benzonaphthothiophene group, a benzonaphthosilole group, a benzofurodibenzofuran group, a benzofurodibenzothiophene group, a benzothienodibenzothiophene group, etc.), 
     The π electron-deficient nitrogen-containing C 1 -C 60  cyclic group may be i) group T4, ii) a condensed cyclic group in which two or more groups T4 are condensed with each other, iii) a condensed cyclic group in which at least one group T4 and at least one group T1 are condensed with each other, iv) a condensed cyclic group in which at least one group T4 and at least one group T3 are condensed with each other, or v) a condensed cyclic group in which at least one group T4, at least one group T1, and at least one group T3 are condensed with each other (for example, a pyrazole group, an imidazole group, a triazole group, an oxazole group, an isoxazole group, an oxadiazole group, a thiazole group, an isothiazole group, a thiadiazole group, a benzopyrazole group, a benzimidazole group, a benzoxazole group, a benzoisoxazole group, a benzothiazole group, a benzoisothiazole group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, a quinoline group, an isoquinoline group, a benzoquinoline group, a benzoisoquinoline group, a quinoxaline group, a benzoquinoxaline group, a quinazoline group, a benzoquinazoline group, a phenanthroline group, a cinnoline group, a phthalazine group, a naphthyridine group, an imidazopyridine group, an imidazopyrimidine group, an imidazotriazine group, an imidazopyrazine group, an imidazopyridazine group, an azacarbazole group, an azafluorene group, an azadibenzosilole group, an azadibenzothiophene group, an azadibenzofuran group, etc.). 
     Group T1 may be a cyclopropane group, a cyclobutane group, a cyclopentane group, a cyclohexane group, a cycloheptane group, a cyclooctane group, a cyclobutene group, a cyclopentene group, a cyclopentadiene group, a cyclohexene group, a cyclohexadiene group, a cycloheptene group, an adamantane group, a norbornane (or a bicyclo[2.2.1]heptane) group, a norbornene group, a bicyclo[1.1.1]pentane group, a bicyclo[2.1.1]hexane group, a bicyclo[2.2.2]octane group, or a benzene group. 
     Group T2 may be a furan group, a thiophene group, a 1H-pyrrole group, a silole group, a borole group, a 2H-pyrrole group, a 3H-pyrrole group, an imidazole group, a pyrazole group, a triazole group, a tetrazole group, an oxazole group, an isoxazole group, an oxadiazole group, a thiazole group, an isothiazole group, a thiadiazole group, an azasilole group, an azaborole group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, or a tetrazine group. 
     Group T3 may be a furan group, a thiophene group, a 1H-pyrrole group, a silole group, or a borole group. 
     Group T4 may be a 2H-pyrrole group, a 3H-pyrrole group, an imidazole group, a pyrazole group, a triazole group, a tetrazole group, an oxazole group, an isoxazole group, an oxadiazole group, a thiazole group, an isothiazole group, a thiadiazole group, an azasilole group, an azaborole group, a pyridine group, a pyrimidine group, a pyrazine group, a pyridazine group, a triazine group, or a tetrazine group. 
     The terms “the cyclic group, the C 3 -C 60  carbocyclic group, the C 1 -C 60  heterocyclic group, the π electron-rich C 3 -C 60  cyclic group, or the π electron-deficient nitrogen-containing C 1 -C 60  cyclic group” as used herein refer to a group condensed to any cyclic group, a monovalent group, or a polyvalent group (for example, a divalent group, a trivalent group, a tetravalent group, etc.) according to the structure of a formula for which the corresponding term is used. For example, the “benzene group” may be a benzo group, a phenyl group, a phenylene group, or the like, which may be easily understood by one of ordinary skill in the art according to the structure of a formula including the “benzene group.” 
     Examples of the monovalent C 3 -C 60  carbocyclic group and the monovalent C 1 -C 60  heterocyclic group are a C 3 -C 10  cycloalkyl group, a C 1 -C 10  heterocycloalkyl group, a C 3 -C 10  cycloalkenyl group, a C 1 -C 10  heterocycloalkenyl group, a C 6 -C 60  aryl group, a C 1 -C 60  heteroaryl group, a monovalent non-aromatic condensed polycyclic group, and a monovalent non-aromatic condensed heteropolycyclic group. Examples of the divalent C 3 -C 60  carbocyclic group and the monovalent C 1 -C 60  heterocyclic group are a C 3 -C 10  cycloalkylene group, a C 1 -C 10  heterocycloalkylene group, a C 3 -C 10  cycloalkenylene group, a C 1 -C 10  heterocycloalkenylene group, a C 6 -C 60  arylene group, a C 1 -C 60  heteroarylene group, a divalent non-aromatic condensed polycyclic group, and a substituted or unsubstituted divalent non-aromatic condensed heteropolycyclic group. 
     The term “C 1 -C 60  alkyl group” as used herein refers to a linear or branched aliphatic hydrocarbon monovalent group that has one to sixty carbon atoms, and specific examples thereof are a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a tert-butyl group, an n-pentyl group, a tert-pentyl group, a neopentyl group, an isopentyl group, a sec-pentyl group, a 3-pentyl group, a sec-isopentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, a tert-hexyl group, an n-heptyl group, an isoheptyl group, a sec-heptyl group, a tert-heptyl group, an n-octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, an n-nonyl group, an isononyl group, a sec-nonyl group, a tert-nonyl group, an n-decyl group, an isodecyl group, a sec-decyl group, and a tert-decyl group. The term “C 1 -C 60  alkylene group” as used herein refers to a divalent group having substantially the same structure as the C 1 -C 60  alkyl group. 
     The term “C 2 -C 60  alkenyl group” as used herein refers to a monovalent hydrocarbon group having at least one carbon-carbon double bond in the middle or at the terminus of the C 2 -C 60  alkyl group, and examples thereof are an ethenyl group, a propenyl group, and a butenyl group. The term “C 2 -C 60  alkenylene group” as used herein refers to a divalent group having substantially the same structure as the C 2 -C 60  alkenyl group. 
     The term “C 2 -C 60  alkynyl group” as used herein refers to a monovalent hydrocarbon group having at least one carbon-carbon triple bond in the middle or at the terminus of the C 2 -C 60  alkyl group, and examples thereof include an ethynyl group, and a propynyl group. The term “C 2 -C 60  alkynylene group” as used herein refers to a divalent group having substantially the same structure as the C 2 -C 60  alkynyl group. 
     The term “C 1 -C 60  alkoxy group” as used herein refers to a monovalent group represented by —OA 101  (wherein A 101  is the C 1 -C 60  alkyl group), and examples thereof include a methoxy group, an ethoxy group, and an isopropyloxy group. 
     The term “C 3 -C 10  cycloalkyl group” as used herein refers to a monovalent saturated hydrocarbon cyclic group having 3 to 10 carbon atoms, and examples thereof are a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, an adamantanyl group, a norbornanyl group (or bicyclo[2.2.1]heptyl group), a bicyclo[1.1.1]pentyl group, a bicyclo[2.1.1]hexyl group, and a bicyclo[2.2.2]octyl group. The term “C 3 -C 10  cycloalkylene group” as used herein refers to a divalent group having substantially the same structure as the C 3 -C 10  cycloalkyl group. 
     The term “C 1 -C 10  heterocycloalkyl group” as used herein refers to a monovalent cyclic group of 1 to 10 carbon atoms, and may include at least one heteroatom, as ring-forming atoms. Examples may include a 1,2,3,4-oxatriazolidinyl group, a tetrahydrofuranyl group, and a tetrahydrothiophenyl group. The term “C 1 -C 10  heterocycloalkylene group” as used herein refers to a divalent group having substantially the same structure as the C 1 -C 10  heterocycloalkyl group. 
     The term “C 3 -C 10  cycloalkenyl group” as used herein refers to a monovalent cyclic group that may have three to ten carbon atoms and at least one carbon-carbon double bond in the ring thereof and no aromaticity. Examples may include a cyclopentenyl group, a cyclohexenyl group, and a cycloheptenyl group. The term “C 3 -C 10  cycloalkenylene group” as used herein refers to a divalent group having substantially the same structure as the C 3 -C 10  cycloalkenyl group. 
     The term “C 1 -C 10  heterocycloalkenyl group” as used herein refers to a monovalent cyclic group of 1 to 10 carbon atoms that may include at least one heteroatom, as ring-forming atoms, and having at least one carbon-carbon double bond in the cyclic structure thereof. Examples of the C 1 -C 10  heterocycloalkenyl group include a 4,5-dihydro-1,2,3,4-oxatriazolyl group, a 2,3-dihydrofuranyl group, and a 2,3-dihydrothiophenyl group. The term “C 1 -C 10  heterocycloalkenylene group” as used herein refers to a divalent group having substantially the same structure as the C 1 -C 10  heterocycloalkenyl group. 
     The term “C 6 -C 60  aryl group” as used herein refers to a monovalent group having a carbocyclic aromatic system of 6 to 60 carbon atoms, and the term “C 6 -C 60  arylene group” as used herein refers to a divalent group having a carbocyclic aromatic system of 6 to 60 carbon atoms. Examples of the C 6 -C 60  aryl group may include a phenyl group, a pentalenyl group, a naphthyl group, an azulenyl group, an indacenyl group, an acenaphthyl group, a phenalenyl group, a phenanthrenyl group, an anthracenyl group, a fluoranthenyl group, a triphenylenyl group, a pyrenyl group, a chrysenyl group, a perylenyl group, a pentaphenyl group, a heptalenyl group, a naphthacenyl group, a picenyl group, a hexacenyl group, a pentacenyl group, a rubicenyl group, a coronenyl group, and an ovalenyl group. When the C 6 -C 60  aryl group and the C 6 -C 60  arylene group each include two or more rings, the rings may be condensed with each other. 
     The term “C 1 -C 60  heteroaryl group” as used herein refers to a monovalent group having a heterocyclic aromatic system of 1 to 60 carbon atoms that may include at least one heteroatom as ring-forming atoms. The term “C 1 -C 60  heteroarylene group” as used herein refers to a divalent group having a heterocyclic aromatic system of 1 to 60 carbon atoms that may include at least one heteroatom as ring-forming atoms. Examples of the C 1 -C 60  heteroaryl group are a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a pyridazinyl group, a triazinyl group, a quinolinyl group, a benzoquinolinyl group, an isoquinolinyl group, a benzoisoquinolinyl group, a quinoxalinyl group, a benzoquinoxalinyl group, a quinazolinyl group, a benzoquinazolinyl group, a cinnolinyl group, a phenanthrolinyl group, a phthalazinyl group, and a naphthyridinyl group. When the C 1 -C 60  heteroaryl group and the C 1 -C 60  heteroarylene group each include two or more rings, the rings may be condensed with each other. 
     The term “monovalent non-aromatic condensed polycyclic group” as used herein refers to a monovalent group (for example, having 8 to 60 carbon atoms) having two or more rings condensed to each other, only carbon atoms as ring-forming atoms, and no aromaticity in its entire molecular structure. Examples of the monovalent non-aromatic condensed polycyclic group are an indenyl group, a fluorenyl group, a spiro-bifluorenyl group, a benzofluorenyl group, an indenophenanthrenyl group, and an indeno anthracenyl group. The term “divalent non-aromatic condensed polycyclic group” as used herein refers to a divalent group having substantially the same structure as the monovalent non-aromatic condensed polycyclic group described above. 
     The term “monovalent non-aromatic condensed heteropolycyclic group” as used herein refers to a monovalent group (for example, having 1 to 60 carbon atoms) having two or more rings condensed to each other, that may include at least one heteroatom as ring-forming atoms, and having non-aromaticity in its entire molecular structure. Examples of the monovalent non-aromatic condensed heteropolycyclic group include a pyrrolyl group, a thiophenyl group, a furanyl group, an indolyl group, a benzoindolyl group, a naphthoindolyl group, an isoindolyl group, a benzoisoindolyl group, a naphthoisoindolyl group, a benzosilolyl group, a benzothiophenyl group, a benzofuranyl group, a carbazolyl group, a dibenzosilolyl group, a dibenzothiophenyl group, a dibenzofuranyl group, an azacarbazolyl group, an azafluorenyl group, an azadibenzosilolyl group, an azadibenzothiophenyl group, an azadibenzofuranyl group, a pyrazolyl group, an imidazolyl group, a triazolyl group, a tetrazolyl group, an oxazolyl group, an isoxazolyl group, a thiazolyl group, an isothiazolyl group, an oxadiazolyl group, a thiadiazolyl group, a benzopyrazolyl group, a benzimidazolyl group, a benzoxazolyl group, a benzothiazolyl group, a benzoxadiazolyl group, a benzothiadiazolyl group, an imidazopyridinyl group, an imidazopyrimidinyl group, an imidazotriazinyl group, an imidazopyrazinyl group, an imidazopyridazinyl group, an indenocarbazolyl group, an indolocarbazolyl group, a benzofurocarbazolyl group, a benzothienocarbazolyl group, a benzosilolocarbazolyl group, a benzoindolocarbazolyl group, a benzocarbazolyl group, a benzonaphthofuranyl group, a benzonaphthothiophenyl group, a benzonaphthosilolyl group, a benzofurodibenzofuranyl group, a benzofurodibenzothiophenyl group, and a benzothienodibenzothiophenyl group. The term “divalent non-aromatic condensed heteropolycyclic group” as used herein refers to a divalent group having substantially the same structure as the monovalent non-aromatic condensed heteropolycyclic group described above. 
     The term “C 6 -C 60  aryloxy group” as used herein indicates —OA 102  (wherein A 102  is the C 6 -C 60  aryl group), and the term “C 6 -C 60  arylthio group” as used herein indicates —SA 103  (wherein A 103  is the C 6 -C 60  aryl group). 
     The term “R 10a ” as used herein refers to deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, or a nitro group, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, or a C 1 -C 60  alkoxy group, each unsubstituted or substituted with deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 3 -C 60  carbocyclic group, a C 1 -C 60  heterocyclic group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, —Si(Q 11 )(Q 12 )(Q 13 ), —N(Q 11 )(Q 12 ), —B(Q 11 )(Q 12 ), —C(═O)(Q 11 ), —S(═O) 2 (Q 11 ), —P(═O)(Q 11 )(Q 12 ), or any combination thereof, a C 3 -C 60  carbocyclic group, a C 1 -C 60  heterocyclic group, a C 6 -C 60  aryloxy group, or a C 6 -C 60  arylthio group, each unsubstituted or substituted with deuterium, —F, —CI, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 60  alkyl group, a C 2 -C 60  alkenyl group, a C 2 -C 60  alkynyl group, a C 1 -C 60  alkoxy group, a C 3 -C 60  carbocyclic group, a C 1 -C 60  heterocyclic group, a C 6 -C 60  aryloxy group, a C 6 -C 60  arylthio group, —Si(Q 21 )(Q 22 )(Q 23 ), —N(Q 21 )(Q 22 ), —B(Q 21 )(Q 22 ), —C(═O)(Q 21 ), —S(═O) 2 (Q 21 ), —P(═O)(Q 21 )(Q 22 ), or any combination thereof, or —Si(Q 31 )(Q 32 )(Q 33 ), —N(Q 31 )(Q 32 ), —B(Q 31 )(Q 32 ), —C(═O)(Q 31 ), —S(═O) 2 (Q 31 ), or —P(═O)(Q 31 )(Q 32 ). 
     Q 1  to Q 3 , Q 11  to Q 13 , Q 21  to Q 23  and Q 31  to Q 33  used herein may each independently be hydrogen, deuterium, —F, —CI, —Br, —I, a hydroxyl group, a cyano group, a nitro group, C 1 -C 60  alkyl group, C 2 -C 60  alkenyl group, C 2 -C 60  alkynyl group, C 1 -C 60  alkoxy group, or a C 3 -C 60  carbocyclic group or a C 1 -C 60  heterocyclic group, each unsubstituted or substituted with deuterium, —F, a cyano group, a C 1 -C 60  alkyl group, a C 1 -C 60  alkoxy group, a phenyl group, a biphenyl group, or any combination thereof. 
     The term “heteroatom” as used herein refers to any atom other than a carbon atom. Examples of the heteroatom are O, S, N, P, Si, B, Ge, Se, and any combinations thereof. 
     “Ph” as used herein refers to a phenyl group, “Me” as used herein refers to a methyl group, “Et” as used herein refers to an ethyl group, “ter-Bu” or “Bu t ” as used herein refers to a tert-butyl group, and “OMe” as used herein refers to a methoxy group. 
     The term “biphenyl group” as used herein refers to “a phenyl group substituted with a phenyl group.” The “biphenyl group” is a substituted phenyl group having a C 6 -C 60  aryl group as a substituent. 
     The term “terphenyl group” as used herein refers to “a phenyl group substituted with a biphenyl group.” The “terphenyl group” is a substituted phenyl group having, as a substituent, a C 6 -C 60  aryl group substituted with a C 6 -C 60  aryl group. 
     * and *′ as used herein, unless defined otherwise, each refer to a binding site to a neighboring atom in a corresponding formula. 
     Hereinafter, compounds according to embodiments and light-emitting devices according to embodiments will be described in detail with reference to the following synthesis examples and examples. The wording “B was used instead of A” used in describing Synthesis Examples means that an identical molar equivalent of B was used in place of A. 
     EXAMPLES 
     Preparation of Host 
     Preparation of BH1 
     
       
         
         
             
             
         
       
     
     In the presence of nitrogen, about 5 g of 1,6-dibromopyrene (13.9 mmol) and about 8.3 g of 2-(tert-butyl)-5H-benzo[b]carbazole (30.6 mmol) were added to 3-neck flask (500 ml), and about 5.8 g of CuI (30.6 mmol), about 5.5 g of 1,10-phenanthroline (30.6 mmol), and about 7.7 g of KOH (137.7 mmol) were added thereto. Thereafter, the reaction mixture was added to and dissolved in p-xylene (250 ml), and was stirred at a temperature of about 140° C. for about 48 hours. 
     After completion of the reaction, the temperature of the reaction product was lowered to room temperature and was filtered through celite by using methylene chloride (MC). The filtered organic layer was washed (three times) using water to wash off impurities therefrom, and remaining water was removed therefrom with anhydrous MgSO 4 . 
     After removing the solvent by using vacuum, about 6.7 g of compound BH1 (yield: 65%) was obtained by column chromatography (eluent, n-hexane:MC=9:1). 
     H 1 -NMR (DMSO-d 6 ): 8.95 (1H, d), 8.36 (1H, d), 8.28 (2H, d), 8.13-8.11 (4H, m), 7.94-7.11 (18H, m) 1.43 (18H, s), m/z: 744.35 
     Preparation of BH2 
     
       
         
         
             
             
         
       
     
     BH2 
     In a nitrogen atmosphere, 1,6-dibromopyrene (about 3 g, 8.33 mmol) and (6-(tert-butyl)naphthalen-2-yl)boronic acid (about 4.4 g, 19.2 mmol) were completely dissolved in about 300 ml of toluene in a 500 ml round-bottom flask, 2M aqueous potassium carbonate solution (about 150 ml) was added thereto, tetrakis-(triphenylphosphine)palladium (about 0.38 g, 0.33 mmol) was added thereto, and the reaction mixture was heated while stirring for about 4 hours. 
     The temperature was lowered to room temperature, the water layer was removed, and after drying with MgSO 4 , column chromatography (eluent, ethyl acetate:n-hexane=1:10) was performed on the resultant mixture to thereby obtain about 2.55 g of compound BH2 (yield: 54%). 
     H 1 -NMR (DMSO-d 6 ): 8.40 (2H, d), 8.15 (2H, d), 7.92-7.70 (6H, m), 7.66 (2H, d), 7.50 (2H, d), 7.43 (2H, d), 7.26 (2H, d), 1.49 (18H, s), m/z: 566.30 
     Manufacture of Light-Emitting Device 
     Comparative Example 1 
     ITO 300 Å/Ag 50 Å/ITO 300 Å (anode) was cut to a size of about 50 mm×about 50 mm×about 0.7 mm, cleaned by sonication with isopropyl alcohol and pure water each for about 15 minutes, and cleaned by irradiation of ultraviolet rays and exposure of ozone for about 30 minutes, and then loaded into a vacuum deposition apparatus. 
     HATCN was vacuum-deposited on the substrate to form a hole injection layer having a thickness of about 50 Å. As a hole transport compound, NPB was vacuum-deposited thereon to form a hole transport layer having a thickness of about 600 Å. 
     Compound TCTA was vacuum-deposited on the hole transport layer to form an electron blocking layer having a thickness of about 50 Å. 
     As a host, compound BH3 and, as a dopant, compound 100 were co-deposited on the layer to a weight ratio of about 97:3 to form an emission layer having a thickness of about 200 Å. 
     Subsequently, T2T was deposited thereon to form a hole blocking layer having a thickness of about 50 Å, and then TPM-TAZ and LiQ were deposited thereon to a weight ratio of about 5:5 to form an electron transport layer having a thickness of about 300 Å. 
     Yb was vacuum-deposited on the electron transport layer to a thickness of about 10 Å, and consecutively, Al was vacuum-deposited thereon to a thickness of about 800 Å, thereby forming a cathode, and CPL was deposited thereon to form a capping layer having a thickness of about 600 Å, thereby completing the manufacture of an organic light-emitting device. 
     Comparative Example 2 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 1 except that, as a host, compound BH1 and, as a dopant, compound 100 were co-deposited on the electron blocking layer to a weight ratio of about 97:3 to form a first emission layer having a thickness of about 100 Å, and as a host, BH3 and, as a dopant, compound 100 were co-deposited on the first emission layer to a weight ratio of about 97:3 to form a second emission layer having a thickness of about 100 Å. 
     Comparative Example 3 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 1 except that, as a host, compound BH2 and, as a dopant, compound 100 were co-deposited on the electron blocking layer to a weight ratio of about 97:3 to form a first emission layer having a thickness of about 100 Å, and as a host, BH3 and, as a dopant, compound 100 were co-deposited on the first emission layer to a weight ratio of about 97:3 to form a second emission layer having a thickness of about 100 Å. 
     Example 1 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 1 except that, as hosts, a hole transport compound BH1 and an electron transport compound BH2 (weight ratio of about 2:8), and as a dopant, compound 100 were co-deposited on the electron blocking layer to a weight ratio of about 97:3 to form a first emission layer having a thickness of about 100 Å, and, as a host, BH3 and, as a dopant, compound 100 were co-deposited on the first emission layer to a weight ratio of about 97:3 to form a second emission layer having a thickness of about 100 Å. 
     Example 2 
     A light-emitting device was manufactured in substantially the same manner as Example 1 except that the weight ratio of the hole transport compound BH1 and the electron transport compound BH2 was about 5:5. 
     Example 3 
     A light-emitting device was manufactured in substantially the same manner as Example 1 except that the weight ratio of the hole transport compound BH1 and the electron transport compound BH2 was about 8:2. 
     Manufacture of Tandem Light-Emitting Device 
     Comparative Example 4 
     A glass substrate with a 15 Ω/cm 2  (800 Å) ITO/Ag/ITO anode formed thereon (a product of Corning Inc.) was cut to a size of about 50 mm×about 50 mm×about 0.7 mm, sonicated with isopropyl alcohol and pure water each for about 5 minutes, and then cleaned by exposure to ultraviolet rays and ozone for about 15 minutes. The resultant glass substrate was loaded onto a vacuum deposition apparatus. 
     HAT-CN was deposited on the ITO/Ag/ITO anode of the glass substrate to form a hole injection layer having a thickness of about 50 Å, NPB was deposited on the hole injection layer to form a hole transport layer having a thickness of about 600 Å, BH3 and compound 100 were co-deposited on the hole transport layer to a weight ratio of about 97:3 to form a first emission layer (blue) having a thickness of about 200 Å, and TPM-TAZ and LiQ were co-deposited on the first emission layer to a weight ratio of about 1:1 to form an electron transport layer having a thickness of about 200 Å. 
     Subsequently, BCP and Li were co-deposited to a weight ratio of about 99:1 on the electron transport layer to form an n-type charge generation layer having a thickness of about 150 Å, and HAT-CN was deposited on the n-type charge generation layer to form a p-type charge generation layer having a thickness of about 50 Å. 
     NPB was deposited on the p-type charge generation layer to form a hole transport layer having a thickness of about 500 Å, BH3 and compound 100 were co-deposited on the hole transport layer to a weight ratio of about 97:3 to form a second emission layer (blue) having a thickness of about 200 Å, and TPM-TAZ and LiQ were co-deposited on the second emission layer to a weight ratio of about 1:1 to form an electron transport layer having a thickness of about 200 Å. 
     Subsequently, BCP and Li were co-deposited to a weight ratio of about 99:1 on the electron transport layer to form an n-type charge generation layer having a thickness of about 150 Å, and HAT-CN was deposited on the n-type charge generation layer to form a p-type charge generation layer having a thickness of about 50 Å. 
     Subsequently, NPB was deposited on the p-type charge generation layer to form a hole transport layer having a thickness of about 400 Å, BH3 and compound 100 were co-deposited on the hole transport layer to a weight ratio of about 97:3 to form a third emission layer (blue) having a thickness of about 200 Å, and TPM-TAZ and LiQ were co-deposited on the third emission layer to a weight ratio of about 1:1 to form an electron transport layer having a thickness of about 200 Å. 
     Subsequently, Yb was deposited thereon to form a layer having a thickness of about 10 Å, and Ag and Mg were co-deposited on the layer to a weight ratio of about 9:1 to form a cathode having a thickness of about 100 Å, thereby completing the manufacture of a tandem light-emitting device. 
     Example 4 
     A light-emitting device was manufactured in substantially the same manner as in Comparative Example 4 except that the third emission layer was formed in two layers including emission layer 3-1 having a thickness of about 100 Å and formed by co-depositing a hole transport compound BH1 and an electron transport compound BH2 (weight ratio of 2:8) as hosts and compound 100 as a dopant on the hole transport layer to a weight ratio of about 97:3, and emission layer 3-2 having a thickness of about 100 Å and formed by co-depositing BH3 as a host and compound 100 as a dopant on the emission layer 3-1 to a weight ratio of about 97:3. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     T1 Energy Level Simulation 
     A simulation of the T1 energy of compounds BH1, BH2, and BH3 was performed using Gaussian ([structurally optimized] #B3LYP/6-31G*, [TD DFT]#B3LYP/6-31G* TD=(50-50, Nstates=3)). The results are shown in Table 1. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Compound 
                 T1(eV) 
               
               
                   
                   
               
             
            
               
                   
                 BH1 
                 1.94 
               
               
                   
                 BH2 
                 1.93 
               
               
                   
                 BH3 
                 1.67 
               
               
                   
                   
               
            
           
         
       
     
     To evaluate the characteristics of the light-emitting devices manufactured according to Comparative Examples 1 to 3 and Examples 1 to 3, the driving voltage, efficiency, and lifespan at a current density of about 10 mA/cm 2  were measured, and the results thereof are shown in Table 2. 
     The driving voltage and current density of the light-emitting devices were measured using a source meter (2400 series, Keithley Instruments Inc.), and the efficiency was measured using a measurement system of (C9920-2-12 of Hamamatsu Photonics Inc.). 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                   
                 External 
                   
                   
               
               
                   
                   
                 Driving 
                 quantum 
               
               
                   
                   
                 voltage 
                 efficiency 
                 Lifespan 
                 Luminance 
               
               
                   
                 Emission layer 
                 (V) 
                 (Cd/A) 
                 (T95) 
                 (nit) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Single emission layer 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Comparative 
                 BH3 
                 5.1 
                 8.0 
                 124 
                 800 
               
               
                 Example 1 
               
            
           
           
               
               
               
               
               
            
               
                 Double-layered emission layer 
                   
                   
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 EML1 
                 EML2 
                   
                   
                   
                   
               
               
                 Comparative 
                 BH1 
                 BH3 
                 4.8 
                 8.9 
                 141 
                 800 
               
               
                 Example 2 
               
               
                 Comparative 
                 BH2 
                 BH3 
                 5.1 
                 9.0 
                 138 
                 800 
               
               
                 Example 3 
               
               
                 Example1 
                 BH1:BH2(2:8) 
                 BH3 
                 5.0 
                 9.2 
                 149 
                 800 
               
               
                 Example 2 
                 BH1:BH2(5:5) 
                 BH3 
                 4.9 
                 9.1 
                 164 
                 800 
               
               
                 Example 3 
                 BH1:BH2(8:2) 
                 BH3 
                 4.8 
                 9.0 
                 182 
                 800 
               
               
                   
               
            
           
         
       
     
     To evaluate the characteristics of the tandem light-emitting devices manufactured according to Comparative Example 4 and Example 4, the driving voltage, efficiency, and lifespan at a current density of about 10 mA/cm 2  were measured, and the results thereof are shown in Table 3. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                 Driving 
                 External quantum 
                 Lifespan 
                   
               
               
                   
                 voltage (V) 
                 efficiency (Cd/A) 
                 (LT 95 ) 
                 L (nit) 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Comparative 
                 6.7 
                 8.1 
                 70 
                 1500 
               
               
                 Example 4 
               
               
                 Example 4 
                 4.6 
                 9.0 
                 90 
                 1500 
               
               
                   
               
            
           
         
       
     
     Tables 2 and 3 show that the light-emitting devices of Examples 1 to 4 exhibited higher efficiency and longer lifespan, compared with the light-emitting devices of Comparative Examples 1 to 4. 
     As described above, according to the embodiments, a light-emitting device may exhibit improved efficiency and lifespan, as compared with the related art, by preventing deterioration of an electron blocking layer. 
     Embodiments have been disclosed herein, and although 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 by one of ordinary skill in the art, features, characteristics, and/or elements described in connection with an 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 ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the disclosure as set forth in the following claims.