Patent Publication Number: US-2022223814-A1

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

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority to and benefits of Korean Patent Application No. 10-2021-0001059 under 35 U.S.C. § 119, filed on Jan. 5, 2021, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     Embodiments relate to a light-emitting device and an electronic apparatus including the same. 
     2. Description of the Related Art 
     Organic light-emitting devices (OLEDs) are self-emissive devices that, as compared with devices of the related art, have wide viewing angles, high contrast ratios, short response times, and excellent characteristics in terms of luminance, driving voltage, response speed, and the production of full-color images. 
     OLEDs may include a first electrode located on a substrate, and a hole transport region, an emission layer, an electron transport region, and a second electrode sequentially stacked on the first electrode. Holes provided from the first electrode may move toward the emission layer through the hole transport region, and electrons provided from the second electrode may move toward the emission layer through the electron transport region. Carriers, such as holes and electrons, recombine in the emission layer to produce excitons. These excitons transit from an excited state to a ground state, thereby generating 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 
     Embodiments provide a light-emitting device including a spacing layer to prevent deterioration of an emission layer material and having improved lifespan characteristics, and an electronic apparatus including the light-emitting device. 
     Additional aspects will be set forth in part in the description, which follows and, in part, will be apparent from the description, or may be learned by practice of the embodiments of the disclosure. 
     According to embodiments, 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 and at least one of an emission auxiliary layer and a buffer layer, the emission layer may include a host and a dopant, and the dopant may include a first emissive compound and a second emissive compound, the at least one of the emission auxiliary layer and the buffer layer may include a third emissive compound. 
     In an embodiment, an onset emission wavelength of the first emissive compound may be shorter than an onset emission wavelength of the third emissive compound. 
     In an embodiment, the first emissive compound may be a phosphorescent emissive compound. 
     In an embodiment, the first emissive compound may be represented by Formula 411, which is described below. 
     In an embodiment, the first emissive compound may be one selected from Compounds S-1 to S-36, which are described below. 
     In an embodiment, the second emissive compound and the third emissive compound may each independently be a delayed fluorescence-emitting compound. 
     In an embodiment, the second emissive compound and the third emissive compound may each independently be represented by Formula 511, which is described below. 
     In an embodiment, the second emissive compound and the third emissive compound may each independently be selected from Compounds D-01 to D-22, which are described below. 
     In an embodiment, the second emissive compound and the third emissive compound may be identical to each other. 
     In an embodiment, a maximum emission wavelength of the host may be shorter than a maximum emission wavelength of the first emissive compound, and a maximum emission wavelength of the host may be shorter than a maximum emission wavelength of the second emissive compound or a maximum emission wavelength of the third emissive compound. 
     In an embodiment, the host may include a first host compound and a second host compound, the first host compound may be a hole transport host, and the second host compound may be an electron transport host or a bipolar host. 
     In an embodiment, the first host compound and the second host compound may form an exciplex. 
     In an embodiment, the first host compound may be represented by one of Formulae 311-1 to 311-5, which are described below, and the second host compound may be represented by one of Formulae 312-1, 312-2, and 313, which are described below. 
     In an embodiment, the first host compound may be one selected from Compounds H-01 to H-17, which are described below, and the second host compound may be one selected from Compounds E-01 to E-15, which are described below. 
     In an embodiment, the first electrode may be an anode, the second electrode may be a cathode, and the interlayer may further include a hole transport region between the first electrode and the emission layer, and an electron transport region between the emission layer and the second electrode. The hole transport region may include the emission auxiliary layer, or the electron transport region may include the buffer layer. 
     In an embodiment, the emission auxiliary layer may directly contact the emission layer, or the buffer layer may directly contact the emission layer. 
     In an embodiment, the hole transport region may further include a hole injection layer, a hole transport layer, an electron blocking layer, or any combination thereof, and the electron transport region may further include a hole blocking layer, an electron control layer, an electron transport layer, an electron injection layer, or any combination thereof. 
     In an embodiment, the light-emitting device may emit blue light having a maximum emission wavelength in a range of about 400 nm to about 490 nm. 
     According to embodiments, an electronic apparatus may include the light-emitting device. 
     In an embodiment, the electronic apparatus may further include a thin-film transistor. The thin-film transistor may include a source electrode and a drain electrode, and the first electrode of the light-emitting device may be electrically connected to the source electrode or the drain electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects and features of the disclosure will become more apparent by describing in detail embodiments thereof with reference to the accompanying drawings, in which: 
         FIG. 1  is a schematic cross-sectional view of a light-emitting device according to an embodiment; and 
         FIGS. 2 and 3  are each schematic cross-sectional views of an electronic apparatus according to an embodiment. 
     
    
    
     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. 
     In the drawings, the sizes, thicknesses, ratios, and dimensions of the elements may be exaggerated for ease of description and for clarity. Like numbers refer to like elements throughout. 
     In the description, it will be understood that when an element (or region, layer, part, etc.) is referred to as being “on”, “connected to”, or “coupled to” another element, it can be directly on, connected to, or coupled to the other element, or one or more intervening elements may be present therebetween. In a similar sense, when an element (or region, layer, part, etc.) is described as “covering” another element, it can directly cover the other element, or one or more intervening elements may be present therebetween. 
     In the description, when an element is “directly on,” “directly connected to,” or “directly coupled to” another element, there are no intervening elements present. For example, “directly on” may mean that two layers or two elements are disposed without an additional element such as an adhesion element therebetween. 
     As used herein, the expressions used in the singular such as “a,” “an,” and “the,” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     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”. 
     The term “at least one of” is intended to include the meaning of “at least one selected from” 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.” When preceding a list of elements, the term, “at least one of,” modifies the entire list of elements and does not modify the individual elements of the list. 
     When some embodiments can be implemented differently, the specific processing order may be performed differently from the order described. For example, two processes described in succession may be practically performed at the same time, or in the opposite order of the described order. 
     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. Thus, a first element could be termed a second element without departing from the teachings of the disclosure. Similarly, a second element could be termed a first element, without departing from the scope of the disclosure. 
     The spatially relative terms “below”, “beneath”, “lower”, “above”, “upper”, or the like, may be used herein for ease of description to describe the relations between one element or component and another element or component as illustrated in the drawings. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation depicted in the drawings. For example, in the case where a device illustrated in the drawing is turned over, the device positioned “below” or “beneath” another device may be placed “above” another device. Accordingly, the illustrative term “below” may include both the lower and upper positions. The device may also be oriented in other directions and thus the spatially relative terms may be interpreted differently depending on the orientations. 
     The terms “about” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the recited value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the recited quantity (i.e., the limitations of the measurement system). For example, “about” may mean within one or more standard deviations, or within ±20%, 10%, or 5% of the stated value. 
     It should be understood that the terms “comprises,” “comprising,” “includes,” “including,” “have,” “having,” “contains,” “containing,” and the like are intended to specify the presence of stated features, integers, steps, operations, elements, components, or combinations thereof in the disclosure, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. 
     In the disclosure, the term “interlayer” as used herein refers to a single layer and/or all layers between a first electrode and a second electrode of a light-emitting device. 
     Unless otherwise defined or implied herein, all terms (including technical and scientific terms) used have the same meaning as commonly understood by those skilled in the art to which this 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 should not be interpreted in an ideal or excessively formal sense unless clearly defined in the specification. 
     A light-emitting device according to an embodiment 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 and at least one of an emission auxiliary layer and a buffer layer. 
     The emission layer may include a host and a dopant. 
     The dopant may include a first emissive compound and a second emissive compound. 
     The at least one of the emission auxiliary layer and the buffer layer may include a third emissive compound. 
     In the light-emitting device, because energy emitted from the emission layer is transferred to a third emissive compound included in the at least one of the emission auxiliary layer and the buffer layer, emission may not only occur in the emission layer but also supplementarily in an emission auxiliary layer and/or a buffer layer, resulting in the improvement of emission efficiency, and high energy of the emission layer may be dispersed in the emission auxiliary layer and/or the buffer layer, thereby resulting in an improvement of lifespan characteristics. 
     In an embodiment, an onset emission wavelength of the first emissive compound may be a shorter than the onset emission wavelength of the third emissive compound. 
     In the description, the term “onset emission wavelength” may be a wavelength at a point where the tangent line at half the height of the first peak (the peak having the shortest wavelength) of the emission spectrum of the compound meets the wavelength axis. 
     When the onset emission wavelength of the first emissive compound included in the emission layer and the onset emission wavelength of each of the third emissive compound included in the emission auxiliary layer and/or the buffer layer satisfy the aforementioned relationship, the energy of the first emissive compound may be effectively transferred to the third emissive compound, thereby resulting in improvement of emission efficiency and lifespan characteristics of a light-emitting device. 
     In an embodiment, the emission spectrum of the first emissive compound and the absorption spectrum of the third emissive compound may overlap. Thus, the third emissive compound may absorb emitted energy from the first emissive compound, and the third emissive compound may emit light. 
     In an embodiment, the first emissive compound may be a phosphorescent emissive compound. 
     In an embodiment, the first emissive compound may be represented by Formula 411: 
     
       
         
         
             
             
         
       
     
     In Formula 411, 
     M 41  may be platinum (Pt), palladium (Pd), copper (Cu), silver (Ag), gold (Au), rhodium (Rh), iridium (Ir), ruthenium (Ru), osmium (Os), titanium (Ti), zirconium (Zr), hafnium (Hf), europium (Eu), terbium (Tb), or thulium (Tm), 
     Y 41  to Y 44  may each independently be N or C, 
     A 41  to A 44  may each independently be a C 3 -C 60  carbocyclic group or a C 1 -C 60  heterocyclic group, 
     T 41  to T 44  may each independently be a single bond, *—O—*′, or *—S—*′, 
     L 41  to L 44  may each independently be a single bond, *—O—*′, *—S—*′, *—C(R 45 )(R 46 )—*′, *—C(R 45 )═*′, *═C(R 45 )—*′, *—C(R 45 )═C(R 46 )—*′, *—C(═O)—*′, *—C(═S)—*′, *—C≡C—*′, *—B(R 45 )—*′, *—N(R 45 )—*′, *—P(R 45 )—*′, *—Si(R 45 )(R 46 )—*′, *—P(═O)(R 45 )—*′, or *—Ge(R 45 )(R 46 )—*′, 
     m41 to m44 may each independently be 0, 1, 2, or 3, 
     R 41  to R 46  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 20  alkoxy group, unsubstituted or substituted with at least one R 10a , a C 3 -C 10  cycloalkyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 10  heterocycloalkyl group unsubstituted or substituted with at least one R 10a , a C 3 -C 10  cycloalkenyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 10  heterocycloalkenyl group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  aryl group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  aryloxy group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  arylthio group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroaryl group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroaryloxy group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroarylthio group unsubstituted or substituted with at least one R 10a , a monovalent non-aromatic condensed polycyclic group unsubstituted or substituted with at least one R 10a , a monovalent non-aromatic condensed heteropolycyclic group unsubstituted or substituted with at least one R 10a , —Si(Q 41 )(Q 42 )(Q 43 ), —N(Q 41 )(Q 42 ), —B(Q 41 )(Q 42 ), —C(═O)(Q 41 ), —S(═O) 2 (Q 41 ), or —P(═O)(Q 41 )(Q 42 ), 
     R 45  and R 41 ; R 45  and R 42 ; R 45  and R 43 ; or R 45  and R 44  may optionally be linked to form 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 , 
     b41 to b44 may each independently be 1, 2, 3, 4, 5, 6, 7, or 8, 
     * and *′ each indicate a binding site to a neighboring atom, 
     R 10a  may be: 
     deuterium (-D), —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, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio 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, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryloxy group, or a C 1 -C 60  heteroarylthio group, each unsubstituted or substituted with deuterium, —F, —Cl, —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, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio 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 ), 
     wherein Q 11  to Q 13 , Q 21  to Q 23 , Q 31  to Q 33 , and Q 41  to Q 43  may each independently be: hydrogen; deuterium; —F; —Cl; —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; 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. 
     For example, in an embodiment, the first emissive compound may be one selected from Compounds S-1 to S-36: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In an embodiment, the maximum emission wavelength of the first emissive compound may be less than or equal to about 470 nm. 
     In an embodiment, the onset T 1  energy of the first emissive compound may be greater than or equal to about 2.6 eV. 
     In the description, “T 1  energy” of a compound may be the lowest excitation triplet energy level of the compound. For example, from a sample having a thickness of 1,000 Å, wherein a compound is deposited on a quartz substrate of the compound, an emission spectrum of the sample may be obtained at a temperature of 77K, the first peak (the peak with the shortest wavelength) of the photoluminescence spectrum may be analyzed, and the T 1  energy may be calculated therefrom. In the description, “onset T 1  energy” of a compound may be the T 1  energy level of a compound in an onset wavelength. 
     In an embodiment, the second emissive compound and the third emissive compound may each independently be a delayed fluorescence-emitting compound. 
     In an embodiment, a difference between the lowest excitation triplet energy level and the lowest excitation singlet energy level of the delayed fluorescence-emitting compound may be in a range of about 0 eV to about 0.5 eV. When the difference between the lowest excitation triplet energy level and the lowest excitation singlet energy level of the delayed fluorescence-emitting compound is within the range described above, reverse intersystem crossing of the delayed fluorescence-emitting compound from a triplet state to a singlet state may occur efficiently. 
     In an embodiment, the second emissive compound and the third emissive compound may each independently be represented by Formula 511: 
     
       
         
         
             
             
         
       
     
     In Formula 511, 
     Y 51  and Y 52  may each independently be a single bond, —O—, —S—, —C(R 54 )(R 55 )—, —N(R 54 )—, —Si(R 54 )(R 55 )—, —C(═O)—, —S(═O) 2 —, —B(R 54 )—, —P(R 54 )—, or —P(═O)(R 54 )—, 
     Y 53  may be N, B, P, P(═O), or P(═S), 
     A 51  to A 53  may each independently be a C 3 -C 60  carbocyclic group or a C 1 -C 60  heterocyclic group, 
     R 51  to R 55  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 20  alkyl group, unsubstituted or substituted with at least one R 10a , a C 1 -C 20  alkoxy group, unsubstituted or substituted with at least one R 10a , a C 3 -C 10  cycloalkyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 10  heterocycloalkyl group unsubstituted or substituted with at least one R 10a , a C 3 -C 10  cycloalkenyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 10  heterocycloalkenyl group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  aryl group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  aryloxy group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  arylthio group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroaryl group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroaryloxy group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroarylthio group unsubstituted or substituted with at least one R 10a , a monovalent non-aromatic condensed polycyclic group unsubstituted or substituted with at least one R 10a , a monovalent non-aromatic condensed heteropolycyclic group unsubstituted or substituted with at least one R 10a , —Si(Q 41 )(Q 42 )(Q 43 ), —N(Q 41 )(Q 42 ), —B(Q 41 )(Q 42 ), —C(═O)(Q 41 ), —S(═O) 2 (Q 41 ), or —P(═O)(Q 41 )(Q 42 ), 
     b51 to b53 may each independently be 1, 2, 3, 4, 5, 6, 7, or 8, 
     R 10a  may be: 
     deuterium (-D), —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, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio 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, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryloxy group, or a C 1 -C 60  heteroarylthio group, each unsubstituted or substituted with deuterium, —F, —Cl, —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, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio 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 ), 
     wherein Q 11  to Q 13 , Q 21  to Q 23 , Q 31  to Q 33 , and Q 41  to Q 43  may each independently be: hydrogen; deuterium; —F; —Cl; —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; 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. 
     For example, in an embodiment, the second emissive compound and the third emissive compound may each independently be selected from Compounds D-01 to D-22: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In an embodiment, the second emissive compound and the third emissive compound may each independently have a maximum emission wavelength of less than or equal to about 475 nm. 
     In an embodiment, the second emissive compound and the third emissive compound may each independently have an onset S 1  energy of greater than or equal to about 2.6 eV, and an onset T 1  energy of greater than or equal to about 2.0 eV. 
     In the description, “S 1  energy” of a compound may be the lowest excitation singlet energy level of the compound. For example, by preparing, on a quartz substrate of the compound, a sample having a thickness of 1,000 Å and analyzing the obtained absorption spectrum from the sample at room temperature, S 1  energy may be calculated. In the description, “onset S 1  energy” of a compound may be the S 1  energy level of a compound in an onset wavelength. 
     When the above energy ranges are satisfied, the second emissive compound and the third emissive compound may each effectively receive energy from the first emissive compound, thereby resulting in improvement of emission efficiency and lifespan characteristics of a light-emitting device. 
     In an embodiment, the second emissive compound and the third emissive compound may be identical to each other. Thus, in the light-emitting device, a compound identical to the second emissive compound included in the emission layer may be doped into the emission auxiliary layer and/or the buffer layer. 
     In an embodiment, a maximum emission wavelength of the host may be shorter than a maximum emission wavelength of the first emissive compound, and a maximum emission wavelength of the host may be shorter than a maximum emission wavelength of the second emissive compound or a maximum emission wavelength of the third emissive compound. 
     In an embodiment, an onset emission wavelength of the host may be shorter than an onset emission wavelength of the first emissive compound, or an onset emission wavelength of the host may be shorter than an onset emission wavelength of the second emissive compound or an onset emission wavelength of the third emissive compound. 
     In the light-emitting device according to an embodiment, when the host, the first emissive compound, the second emissive compound, and the third emissive compound are compared based on at least one of the maximum emission wavelength and the onset emission wavelength, the wavelength of the host may be the shortest, followed by the wavelength of the first emissive compound, and the wavelength of the second emissive compound or the third emissive compound (thus, the host may have the shortest wavelength, and the second emissive compound and/or the third emissive compound may have the longest wavelength). Accordingly, energy may be effectively transferred from the host to the first emissive compound, and from the first emissive compound to the second emissive compound and/or the third emissive compound, thereby resulting in improvement of emission efficiency and lifespan characteristics of a light-emitting device. 
     In an embodiment, the host may include two or more host compounds, for example, a first host compound and a second host compound. 
     In an embodiment, the first host compound may be a hole transport host, and the second host compound may be an electron transport host or a bipolar host. 
     In an embodiment, the first host compound and the second host compound may form an exciplex. 
     In an embodiment, the first host compound may be represented by one of Formulae 311-1 to 311-5, and 
     the second host compound may be represented by one of Formulae 312-1, 312-2, and 313: 
     
       
         
         
             
             
         
       
     
     In Formulae 311-1 to 311-5, 312-1, 312-2, 313, and 313A, 
     Ar 301  may 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 , 
     xb11 may be 1, 2, or 3, 
     A 301  to A 304  may each independently be a benzene group, a naphthalene group, a phenanthrene group, a fluoranthene group, a triphenylene group, a pyrene group, a chrysene group, an indene group, a fluorene group, a spiro-bifluorene group, a benzofluorene group, a dibenzofluorene group, an indole group, a pyridine group, a pyrimidine group, a carbazole group, a benzocarbazole group, a dibenzocarbazole group, a furan group, a benzofuran group, a dibenzofuran group, a naphthofuran group, a benzonaphthofuran group, a dinaphthofuran group, a thiophene group, a benzothiophene group, a dibenzothiophene group, a naphthothiophene group, a benzonaphthothiophene group, or a dinaphthothiophene group, 
     X 301  may be O, S, N-[(L 304 ) xb4 -R 304 ], C[(L 304 ) xb4 -R 304 ][(L 305 ) xb5 -R 305 ], or Si[(L 304 ) xb4 -R 304 ][(L 305 ) xb5 -R 305 ], 
     X 302 , Y 301 , and Y 302  may each independently be a single bond, O, S, N-[(L 305 ) xb5 -R 305 ], C[(L 304 ) xb4 -R 304 ][(L 305 ) xb5 -R 305 ], Si[(L 304 ) xb4 -R 304 ][(L 305 ) xb5 -R 305 ], or S(═O) 2 , 
     xb1 to xb5 may each independently be 0, 1, 2, 3, 4, or 5, 
     xb6 may be 1, 2, 3, 4, or 5, 
     X 321  to X 327  may each independently be N or C[(L 324 ) xb24 -R 324 ], 
     xb21 to xb24 may each independently be 0, 1, 2, 3, 4, or 5, 
     A 31 , A 32 , and A 34  may each independently be a C 3 -C 60  carbocyclic group or a C 1 -C 30  heterocyclic group, 
     A 33  may be a group represented by Formula 313A, 
     X 31  may be N[(L 335 ) xb35 -(R 335 )], O, S, Se, C[(L 335 ) xb35 -(R 335 )][(L 336 ) xb36 -(R 336 )], or Si[(L 335 ) xb35 -(R 335 )][(L 336 ) xb36 -(R 336 )], 
     xb31 to xb36 may each independently be 0, 1, 2, 3, 4, or 5, 
     xb42 to xb44 may each independently be 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, 
     L 301  to L 306 , L 321  to L 324 , and L 331  to L 336  may each independently be a single bond, 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 2 -C 20  alkynylene group unsubstituted or substituted with at least one R 10a , a C 3 -C 10  cycloalkylene group unsubstituted or substituted with at least one R 10a , a C 1 -C 10  heterocycloalkylene group unsubstituted or substituted with at least one R 10a , C 3 -C 10  cycloalkenylene group unsubstituted or substituted with at least one R 10a , a C 1 -C 10  heterocycloalkenylene group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  arylene group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroarylene group unsubstituted or substituted with at least one R 10a , a divalent non-aromatic condensed polycyclic group unsubstituted or substituted with at least one R 10a , or a divalent non-aromatic condensed heteropolycyclic group unsubstituted or substituted with at least one R 10a , 
     R 301  to R 305 , R 311  to R 314 , R 321  to R 324 , and R 331  to R 336  may each independently be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazino group, a hydrazono group, a C 1 -C 60  alkyl group unsubstituted or substituted with at least one R 10a , a C 2 -C 60  alkenyl group unsubstituted or substituted with at least one R 10a , a C 2 -C 60  alkynyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  alkoxy group unsubstituted or substituted with at least one R 10a , a C 3 -C 10  cycloalkyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 10  heterocycloalkyl group unsubstituted or substituted with at least one R 10a , a C 3 -C 10  cycloalkenyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 10  heterocycloalkenyl group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  aryl group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  aryloxy group unsubstituted or substituted with at least one R 10a , a C 6 -C 60  arylthio group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroaryl group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroaryloxy group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  heteroarylthio group unsubstituted or substituted with at least one R 10a , a monovalent non-aromatic condensed polycyclic group unsubstituted or substituted with at least one R 10a , a monovalent non-aromatic condensed heteropolycyclic group unsubstituted or substituted with at least one R 10a , —Si(Q 1 )(Q 2 )(Q 3 ), —B(Q 1 )(Q 2 ), —N(Q 1 )(Q 2 ), —P(Q 1 )(Q 2 ), —C(═O)(Q 1 ), —S(═O)(Q 1 ), —S(═O) 2 (Q 1 ), —P(═O)(Q 1 )(Q 2 ), or —P(═S)(Q 1 )(Q 2 ), 
     at least two of R 321  to R 324  may optionally be linked to form 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 10a  may be: 
     deuterium (-D), —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, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio 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, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryloxy group, or a C 1 -C 60  heteroarylthio group, each unsubstituted or substituted with deuterium, —F, —Cl, —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, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio 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 ), 
     wherein Q 1  to Q 3 , Q 11  to Q 13 , Q 21  to Q 23 , Q 31  to Q 33 , Q 301 , and Q 302  may each independently be: hydrogen; deuterium; —F; —Cl; —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; 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. 
     In an embodiment, the hole transport host may be represented by one of Formulae 311-1 to 311-5, and 313, or a combination thereof. 
     In an embodiment, the electron transport host may be a compound represented by one of Formulae 312-1, 312-2, and 313 or a combination thereof. 
     In an embodiment, the bipolar host may be a compound represented by one of Formulae 311-1 to 311-5, 312-1, 312-2, and 313 or a combination thereof. 
     For example, in an embodiment, the first host compound may be one selected from Compounds H-01 to H-17, and 
     the second host compound may be one selected from Compounds E-01 to E-15: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In an embodiment, an amount of the host included in the emission layer may be in a range of about 0.1 parts by weight to about 99 parts by weight, based on 100 parts by weight of the emission layer. For example, an amount of the host included in the emission layer may be in a range of about 0.1 parts by weight to about 95 parts by weight, based on 100 parts by weight of the emission layer. For example, an amount of the host included in the emission layer may be in a range of about 0.5 parts by weight to about 90 parts by weight, based on 100 parts by weight of the emission layer. 
     In an embodiment, when the host includes a first host compound and a second host compound, an amount of the first host compound may be in a range of about 0.1 parts by weight to about 99 parts by weight, based on 100 parts by weight of the host, and the second host compound may be in a range of about 0.1 parts by weight to about 99 parts by weight, based on 100 parts by weight of the host. For example, an amount of the first host compound may be in a range of about 0.1 parts by weight to about 95 parts by weight. For example, an amount of the first host compound may be in a range of about 0.5 parts by weight to about 90 parts by weight. For example, an amount of the second host compound may be in a range of about 0.1 parts by weight to about 95 parts by weight. For example, an amount of the second host compound may be in a range of about 0.5 parts by weight to about 90 parts by weight. 
     In an embodiment, when the host includes a hole transport host and an electron transport host, on a weight basis, an amount of the hole transport host and an amount of the electron transport host may be substantially the same. In another embodiment, when the host includes a hole transport host and an electron transport host, on a weight basis, an amount of the hole transport host may be greater than an amount of the electron transport host, or an amount of the electron transport host may be greater than an amount of the hole transport host. 
     In an embodiment, an amount of the first emissive compound included in the emission layer may be in a range of about 0.1 parts by weight to about 40 parts by weight, based on 100 parts by weight of the emission layer. For example, an amount of the first emissive compound included in the emission layer may be in a range of about 0.1 parts by weight to about 30 parts by weight, based on 100 parts by weight of the emission layer. For example, an amount of the first emissive compound included in the emission layer may be in a range of about 0.5 parts by weight to about 20 parts by weight, based on 100 parts by weight of the emission layer. 
     In an embodiment, an amount of the second emissive compound included in the emission layer may be in a range of about 0.01 parts by weight to about 10 parts by weight, based on 100 parts by weight of the emission layer. For example, an amount of the second emissive compound included in the emission layer may be in a range of about 0.05 parts by weight to about 5 parts by weight, based on 100 parts by weight of the emission layer. For example, an amount of the second emissive compound included in the emission layer may be in a range of about 0.1 parts by weight to about 2 parts by weight, based on 100 parts by weight of the emission layer. 
     In an embodiment, the first electrode of the light-emitting device may be an anode, the second electrode of the light-emitting device may be a cathode, and the interlayer may further include a hole transport region between the first electrode and the emission layer, and an electron transport region between the emission layer and the second electrode. 
     The hole transport region may include an emission auxiliary layer, or the electron transport region may include a buffer layer. 
     In an embodiment, the emission auxiliary layer may include the third emissive compound, and may be directly contact the emission layer. 
     In an embodiment, the buffer layer may include the third emissive compound, and may be directly contact the emission layer. 
     Thus, the light-emitting device may have an emission auxiliary layer/emission layer stacked structure, an emission layer/buffer layer stacked structure, or an emission auxiliary layer/emission layer/buffer layer stacked structure, wherein for each structure, constituting layers are stacked from the first electrode in this stated order, and at least one of the emission auxiliary layer and the buffer layer may include the third emissive compound. 
     In an embodiment, the onset emission wavelength of the host may be in a range of about 380 nm to about 430 nm. 
     In an embodiment, the onset emission wavelength of the first emissive compound may be in a range of about 400 nm to about 450 nm. 
     In an embodiment, the onset emission wavelength of the second emissive compound may be in a range of about 410 nm to about 460 nm. 
     In an embodiment, the onset emission wavelength of the third emissive compound may be in a range of about 410 nm to about 460 nm. 
     In an embodiment, the energy of the onset emission wavelength of the host may be greater than the energy of the onset emission wavelength of the first emissive compound. 
     In an embodiment, the energy of the onset emission wavelength of the first emissive compound may be greater than the energy of the onset emission wavelength of the second emissive compound, and the energy of the onset emission wavelength of the first emissive compound may be greater than the energy of the onset emission wavelength of the third emissive compound. 
     In an embodiment, the light-emitting device may emit blue light having a maximum emission wavelength in a range of about 400 nm to about 490 nm. In an embodiment, the light-emitting device may emit blue light having a maximum emission wavelength in range of about 430 nm to about 480 nm. 
     Another aspect of the disclosure provides an electronic apparatus that may include the light-emitting device. The electronic apparatus may further include a thin-film transistor. In embodiments, the electronic apparatus may further include a thin-film transistor including a source electrode and a drain electrode, and the first electrode of the light-emitting device may be electrically connected to the source electrode or the drain electrode. In an embodiment, the electronic apparatus may further include a color filter, a color conversion layer, a touch screen layer, a polarizing layer, or any combination thereof. Details on the electronic apparatus are the same as described in the specification. 
     [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 of the light-emitting device  10  according to an embodiment and a method of manufacturing the light-emitting device  10  will be described in connection with  FIG. 1 . 
     [First Electrode  110 ] 
     In  FIG. 1 , a substrate may be further included under the first electrode  110  or above the second electrode  150 . The substrate may be a glass substrate or a plastic substrate. In embodiments, the substrate may be a flexible substrate, and may include plastics with excellent heat resistance and durability, 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 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 combinations thereof. In embodiments, when the first electrode  110  is a semi-transmissive electrode or a reflective electrode, magnesium (Mg), silver (Ag), aluminum (AI), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), or any combinations thereof may be used as a material for forming the first electrode  110 . 
     The first electrode  110  may have a single layer consisting of a single-layered structure or a multilayer 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 placed between the first electrode  110  and the emission layer and an electron transport region placed between the emission layer and the second electrode  150 . 
     The interlayer  130  may further include metal element-containing compounds such as organometallic compounds, inorganic materials such as quantum dots, and the like, in addition to various organic materials. 
     In embodiments, the interlayer  130  may include two or more emitting units sequentially stacked between the first electrode  110  and the second electrode  150 , and at least one charge generation layer located between the two or more emitting units. When the interlayer  130  includes the at least two emitting units and the at least one 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 a single-layered structure consisting of a single layer consisting of a single material, a single-layered structure consisting of a single layer consisting of different materials, or a multi-layered structure including multiple layers including different materials. 
     The hole transport region may include a hole injection layer, a hole transport layer, an emission auxiliary layer, an electron-blocking layer, or any combination thereof. 
     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, wherein, in each structure, layers are 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 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 , and 
     na1 may be an integer from 1 to 4. 
     In embodiments, each of Formulae 201 and 202 may include at least one group represented by Formulae CY201 to CY217. 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     In Formulae CY201 to CY217, R 10b  and R 10c  may be the same as described in connection with R 10a , ring CY 201  to ring CY 2 O 4  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 an embodiment, ring CY 201  to ring CY 2 O 4  in Formulae CY201 to CY217 may each independently be a benzene group, a naphthalene group, a phenanthrene group, or an anthracene group. 
     In embodiments, each of Formulae 201 and 202 may include at least one group represented by Formulae CY201 to CY203. 
     In embodiments, Formula 201 may include at least one group represented by Formulae CY201 to CY203 and at least one group represented by Formulae CY204 to CY217. 
     In embodiments, xa1 in Formula 201 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 embodiments, each of Formulae 201 and 202 may not include a group represented by one of Formulae CY201 to CY203. 
     In 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 group represented by Formulae CY204 to CY217. 
     In 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 HT46, 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, the thickness of the hole transport region may be in a range of about 100 Å to about 4,000 Å. When the hole-transporting region includes a hole injection layer, a hole transport layer, or any combination thereof, a thickness of the hole injection layer may be in a range of about 100 Å to about 9,000 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, the thickness of the hole injection layer may be in a range of about 100 Å to about 1,000 Å. For example, the thickness of the hole transport layer may be in a range of 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 a wavelength of light emitted by an emission layer, and the electron-blocking layer may block the leakage of electrons from an emission layer to a hole transport region. Materials that may be included in the hole transport region may be included in the emission auxiliary layer and the electron-blocking layer. 
     [p-Dopant] 
     The hole transport region may further include, in addition to these materials, a charge-generation material for the improvement of conductive properties. The charge-generation material may be 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. 
     In embodiments, a lowest unoccupied molecular orbital (LUMO) energy level of the p-dopant may be less than or equal to about −3.5 eV. 
     In embodiments, the p-dopant may include a quinone derivative, a cyano group-containing compound, a compound containing element EL1 and element EL2, or any combination thereof. 
     Examples of the quinone derivative may include TCNQ, F4-TCNQ, etc. 
     Examples of the cyano group-containing compound may include HAT-CN, and a compound represented by Formula 221 below. 
     
       
         
         
             
             
         
       
     
     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 , and 
     at least one of R 221  to R 223  may each independently be a C 3 -C 60  carbocyclic group or a C 1 -C 60  heterocyclic group, each substituted with a cyano group; —F; —Cl; —Br; —I; a C 1 -C 20  alkyl group substituted with a cyano group, —F, —Cl, —Br, —I, or any combination thereof; or any combination thereof. 
     In the compound containing element EL1 and element EL2, element EL1 may be metal, metalloid, or a combination thereof, and element EL2 may be non-metal, metalloid, or a combination thereof. 
     Examples of the metal may include an alkali metal (for example, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), etc.); an alkaline earth metal (for example, beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), etc.); a transition metal (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.); a post-transition metal (for example, zinc (Zn), indium (In), tin (Sn), etc.); and a lanthanide metal (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.). 
     Examples of the metalloid may include silicon (Si), antimony (Sb), and tellurium (Te). 
     Examples of the non-metal may include oxygen (O) and halogen (for example, F, Cl, Br, I, etc.). 
     In embodiments, examples of the compound containing element EL1 and element EL2 may include metal oxide, metal halide (for example, metal fluoride, metal chloride, metal bromide, or metal iodide), metalloid halide (for example, metalloid fluoride, metalloid chloride, metalloid bromide, or metalloid iodide), metal telluride, or any combination thereof. 
     Examples of the metal oxide may include tungsten oxide (for example, WO, W 2 O 3 , WO 2 , WO 3 , W 2 O 5 , etc.), vanadium oxide (for example, VO, V 2 O 3 , VO 2 , V 2 O 5 , etc.), molybdenum oxide (MoO, Mo 2 O 3 , MoO 2 , MoO 3 , Mo 2 O 5 , etc.), and rhenium oxide (for example, ReO 3 , etc.). 
     Examples of the metal halide may include alkali metal halide, alkaline earth metal halide, transition metal halide, post-transition metal halide, and lanthanide metal halide. 
     Examples of the alkali metal halide may include LiF, NaF, KF, RbF, CsF, LiCl, NaCl, KCl, RbCl, CsCl, LiBr, NaBr, KBr, RbBr, CsBr, LiI, NaI, Kl, RbI, and CsI. 
     Examples of the alkaline earth metal halide may include 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 . 
     Examples of the transition metal halide may include titanium halide (for example, TiF 4 , TiCl 4 , TiBr 4 , TiI 4 , etc.), zirconium halide (for example, ZrF 4 , ZrCl 4 , ZrBr 4 , ZrI 4 , etc.), hafnium halide (for example, HfF 4 , HfCl 4 , HfBr 4 , HfI 4 , etc.), vanadium halide (for example, VF 3 , VCl 3 , VBr 3 , VI 3 , etc.), niobium halide (for example, NbF 3 , NbCl 3 , NbBr 3 , NbI 3 , etc.), tantalum halide (for example, TaF 3 , TaCl 3 , TaBr 3 , TaI 3 , etc.), chromium halide (for example, CrF 3 , CrCl 3 , CrBr 3 , CrI 3 , etc.), molybdenum halide (for example, MoF 3 , MoCl 3 , MoBr 3 , MoI 3 , etc.), tungsten halide (for example, WF 3 , WCl 3 , WBr 3 , WI 3 , etc.), manganese halide (for example, MnF 2 , MnCl 2 , MnBr 2 , MnI 2 , etc.), technetium halide (for example, TcF 2 , TcCl 2 , TcBr 2 , TcI 2 , etc.), rhenium halide (for example, ReF 2 , ReCl 2 , ReBr 2 , ReI 2 , etc.), iron halide (for example, FeF 2 , FeCl 2 , FeBr 2 , FeI 2 , etc.), ruthenium halide (for example, RuF 2 , RuCl 2 , RuBr 2 , RuI 2 , etc.), osmium halide (for example, OsF 2 , OsCl 2 , OsBr 2 , OsI 2 , etc.), cobalt halide (for example, CoF 2 , CoCl 2 , CoBr 2 , CoI 2 , etc.), rhodium halide (for example, RhF 2 , RhCl 2 , RhBr 2 , RhI 2 , etc.), iridium halide (for example, IrF 2 , IrCl 2 , IrBr 2 , IrI 2 , etc.), nickel halide (for example, NiF 2 , NiCl 2 , NiBr 2 , NiI 2 , etc.), palladium halide (for example, PdF 2 , PdCl 2 , PdBr 2 , PdI 2 , etc.), platinum halide (for example, PtF 2 , PtCl 2 , PtBr 2 , PtI 2 , etc.), copper halide (for example, CuF, CuCl, CuBr, CuI, etc.), silver halide (for example, AgF, AgCl, AgBr, AgI, etc.), and gold halide (for example, AuF, AuCl, AuBr, AuI, etc.). 
     Examples of the post-transition metal halide may include zinc halide (for example, ZnF 2 , ZnCl 2 , ZnBr 2 , ZnI 2 , etc.), indium halide (for example, InI 3 , etc.), and tin halide (for example, SnI 2 , etc.). 
     Examples of the lanthanide metal halide may include YbF, YbF 2 , YbF 3 , SmF 3 , YbCl, YbCl 2 , YbCl 3 , SmCl 3 , YbBr, YbBr 2 , YbBr 3 SmBr 3 , YbI, YbI 2 , YbI 3 , and SmI 3 . 
     An example of the metalloid halide may be antimony halide (for example, SbCl 5 , etc.). 
     Examples of the metal telluride may include alkali metal telluride (for example, Li 2 Te, 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.). 
     [Emission Layer in Interlayer  130 ] 
     The light-emitting device according to an embodiment may include an emission layer in an interlayer. The emission layer may be understood by referring to the description above, or to the light-emitting device to be described later. 
     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 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. In 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 at least one host and a dopant. The dopant may include a phosphorescent dopant, a fluorescent dopant, or any combination thereof. 
     An amount of the dopant in the emission layer may be in a range of about 0.01 parts by weight to about 15 parts by weight, based on 100 parts by weight of the host. 
     In embodiments, the emission layer may include a quantum dot. 
     The emission layer may include a delayed fluorescent dopant. 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, the thickness of the emission layer may be in a range of about 200 Å to about 600 Å. When the thickness of the emission layer is within these ranges, excellent light-emission characteristics may be obtained without a substantial increase in driving voltage. 
     [Host] 
     In embodiments, the host may include a compound represented by Formula 301 below: 
       [Ar 301 ] xb11 -[(L 301 ) xb1 -R 301 ] xb21   [Formula 301]
 
     In Formula 301, 
     Ar 301  and L 301  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 , 
     xb11 may be 1, 2, or 3, 
     xb1 may be an integer from 0 to 5, 
     R 301  may be hydrogen, deuterium, —F, —Cl, —Br, —I, a hydroxyl group, a cyano group, a nitro group, a C 1 -C 60  alkyl group unsubstituted or substituted with at least one R 10a , a C 2 -C 60  alkenyl group unsubstituted or substituted with at least one R 10a , a C 2 -C 60  alkynyl group unsubstituted or substituted with at least one R 10a , a C 1 -C 60  alkoxy 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 , a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a , —Si(Q 301 )(Q 302 )(Q 303 ), —N(Q 301 )(Q 302 ), —B(Q 301 )(Q 302 ), —C(═O)(Q 301 ), —S(═O) 2 (Q 301 ), or —P(═O)(Q 301 )(Q 302 ), 
     xb21 may be an integer from 1 to 5, and 
     Q 301  to Q 303  may be the same as described in connection with Q 1 . 
     For example, when xb11 in Formula 301 is 2 or more, two or more of Ar 301 (s) may be linked to each other via a single bond. 
     In embodiments, the host may include a compound represented by Formula 301-1, a compound represented by Formula 301-2, or any combination thereof: 
     
       
         
         
             
             
         
       
     
     In Formulae 301-1 and 301-2, 
     A 301  to A 304  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 , 
     X 301  may be O, S, N-[(L 304 ) xb4 -R 304 ], C(R 304 )(R 305 ), or Si(R 304 )(R 305 ), 
     xb22 and xb23 may each independently be 0, 1, or 2, 
     L 301 , xb1, and R 301  may each be the same as described in the specification, 
     L 302  to L 304  may each independently be the same as described in connection with L 301 , 
     xb2 to xb4 may each independently be the same as described in connection with xb1, and 
     R 302  to R 305  and R 311  to R 314  may each independently be the same as described in connection with R 301 . 
     In embodiments, the host may include an alkali earth metal complex, a post-transition metal complex, or a combination thereof. In embodiments, the host may include a Be complex (for example, Compound H55), an Mg complex, a Zn complex, or a combination thereof. 
     In an embodiment, the host may include one of Compounds H1 to H124, 9,10-di(2-naphthyl)anthracene (ADN), 2-methyl-9,10-bis(naphthalen-2-yl)anthracene (MADN), 9,10-di(2-naphthyl)-2-t-butyl-anthracene (TBADN), 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP), 1,3-di(9-carbazolyl)benzene (mCP), 1,3,5-tri(carbazol-9-yl)benzene (TCP), or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     [Phosphorescent Dopant] 
     In embodiments, the phosphorescent dopant may include at least one transition metal as a central metal. 
     The phosphorescent dopant may include a monodentate ligand, a bidentate ligand, a tridentate ligand, a tetradentate ligand, a pentadentate ligand, a hexadentate ligand, or any combination thereof. 
     The phosphorescent dopant may be electrically neutral. 
     For example, the phosphorescent dopant may include an organometallic compound represented by Formula 401: 
     
       
         
         
             
             
         
       
     
     In Formulae 401 and 402, 
     M may be transition metal (for example, iridium (Ir), platinum (Pt), palladium (Pd), osmium (Os), titanium (Ti), gold (Au), hafnium (Hf), europium (Eu), terbium (Tb), rhodium (Rh), rhenium (Re), or thulium (Tm)), 
     L 401  may be a ligand represented by Formula 402, and xc1 may be 1, 2, or 3, wherein when xc1 is two or more, two or more of L 401 (s) may be identical to or different from each other, 
     L 402  may be an organic ligand, and xc2 may be 0, 1, 2, 3, or 4, and when xc2 is 2 or more, two or more of L 402 (s) may be identical to or different from each other, 
     X 401  and X 402  may each independently be nitrogen or carbon, 
     ring A 401  and ring A 402  may each independently be a C 3 -C 60  carbocyclic group or a C 1 -C 60  heterocyclic group, 
     T 401  may be a single bond, *—O—*′, *—S—*′, *—C(═O)—*′, *—N(Q 411 )-*′, *—C(Q 411 )(Q 412 )-*′, *—C(Q 411 )═C(Q 412 )-*′, *—C(Q 411 )═*′, or *═C═*′, 
     X 403  and X 404  may each independently be a chemical bond (for example, a covalent bond or a coordination bond), O, S, N(Q 413 ), B(Q 413 ), P(Q 413 ), C(Q 413 )(Q 414 ), or Si(Q 413 )(Q 414 ), 
     Q 411  to Q 414  may be the same as described in connection with Q 1 , 
     R 401  and R 402  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 unsubstituted or substituted with at least one R 10a , a C 1 -C 20  alkoxy 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 , a C 1 -C 60  heterocyclic group unsubstituted or substituted with at least one R 10a , —Si(Q 401 )(Q 402 )(Q 403 ), —N(Q 401 )(Q 402 ), —B(Q 401 )(Q 402 ), —C(═O)(Q 401 ), —S(═O) 2 (Q 401 ), or —P(═O)(Q 401 )(Q 402 ), 
     Q 401  to Q 403  may be the same as described in connection with Q 1 , 
     xc11 and xc12 may each independently be an integer from 0 to 10, and 
     * and *′ in Formula 402 each indicates a binding site to M in Formula 401. 
     For example, in Formula 402, X 401  may be nitrogen and X 402  may be carbon, or each of X 401  and X 402  may be nitrogen. 
     In embodiments, when xc1 in Formula 401 is 2 or more, two ring A 401  in two or more of L 401 (s) may be optionally linked to each other via T 402 , which is a linking group, and two ring A 402  may optionally be linked to each other via T 403 , which is a linking group (see Compounds PD1 to PD4 and PD7). T 402  and T 403  may be the same as described in connection with T 401 . 
     L 402  in Formula 401 may be an organic ligand. For example, L 402  may include a halogen group, a diketone group (for example, an acetylacetonate group), a carboxylic acid group (for example, a picolinate group), —C(═O), an isonitrile group, —CN group, a phosphorus-containing group (for example, a phosphine group, a phosphite group, etc.), or any combination thereof. 
     The phosphorescent dopant may include, for example, one of compounds PD1 to PD25, or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     [Fluorescent Dopant] 
     The fluorescent dopant may include an amine group-containing compound, a styryl group-containing compound, or any combination thereof. 
     In embodiments, 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, and 
     xd4 may be 1, 2, 3, 4, 5, or 6. 
     In embodiments, 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 embodiments, xd4 in Formula 501 may be 2. 
     In embodiments, the fluorescent dopant may include: one of Compounds FD1 to FD36; DPVBi; DPAVBi; or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     [Delayed Fluorescent Dopant] 
     The emission layer may include a delayed fluorescent dopant. 
     The delayed fluorescent dopant described herein may be selected from compounds capable of emitting delayed fluorescence based on a delayed fluorescence emission mechanism. 
     The delayed fluorescent dopant 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 an embodiment, a difference between the triplet energy level (eV) of the delayed fluorescent dopant and the singlet energy level (eV) of the delayed fluorescent material may be in a range of about 0 eV to about 0.5 eV. When the difference between the triplet energy level (eV) of the delayed fluorescent dopant and the singlet energy level (eV) of the delayed fluorescent dopant satisfies the above-described range, up-conversion from the triplet state to the singlet state of the delayed fluorescent dopants may effectively occur, and thus, the emission efficiency of the light-emitting device  10  may be improved. 
     In embodiments, the delayed fluorescent dopant may include 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 a material including a C 8 -C 60  polycyclic group in which two or more cyclic groups are condensed while sharing boron (B). 
     In an embodiment, the delayed fluorescent dopant may include at least one of the following Compounds DF1 to DF9: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     [Quantum Dot] 
     The emission layer may include a quantum dot. 
     In the specification, a quantum dot may be a crystal of a semiconductor compound, and may include any material capable of emitting light of various emission wavelengths according to the size of the crystal. 
     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. 
     According to the wet chemical process, a precursor material may be mixed with an organic solvent to grow 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 is more easily performed than vapor deposition methods, such as metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE), and which requires low costs. 
     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 the Group II-VI semiconductor compound may include 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 the Group III-V semiconductor compound may include a binary compound, such as GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, or the like; a ternary compound, such as GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InGaP, InNP, InAlP, InNAs, InNSb, InPAs, InPSb, or the like; a quaternary compound, such as GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, or the like; or any combination thereof. The Group III-V semiconductor compound may further include Group II elements. Examples of the Group III-V semiconductor compound further including Group II elements are InZnP, InGaZnP, InAlZnP, etc. 
     Examples of the 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 ; or any combination thereof. 
     Examples of the Group I-III-VI semiconductor compound may include a ternary compound, such as AgInS, AgInS 2 , CuInS, CuInS 2 , CuGaO 2 , AgGaO 2 , or AgAlO 2 . 
     Examples of the Group IV-VI semiconductor compound may include a binary compound, such as SnS, SnSe, SnTe, PbS, PbSe, PbTe, or the like; a ternary compound, such as SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, or the like; a quaternary compound, such as SnPbSSe, SnPbSeTe, SnPbSTe, or the like; 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 exist in a particle with a uniform concentration or a non-uniform concentration. 
     The quantum dot may have a single structure or a dual core-shell structure. In case that the quantum dot has a single structure, the concentration of each element included in the corresponding quantum dot may be uniform. In embodiments, the material contained in the core and the material contained in the shell may be different from each other. 
     The shell of the quantum dot may act as a protective layer to prevent chemical degeneration of the core to maintain semiconductor characteristics and/or as a charging layer to impart 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 the element present in the shell decreases toward the center. 
     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 may include, 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. In an embodiment, the semiconductor compound may include CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnSeS, ZnTeS, GaAs, GaP, GaSb, HgS, HgSe, HgTe, InAs, InP, InGaP, InSb, AlAs, AlP, AlSb, or any combination thereof. 
     A full width at half maximum (FWHM) of an emission wavelength spectrum of the quantum dot may be less than or equal to about 45 nm. For example, a FWHM of an emission wavelength spectrum of the quantum dot may be less than or equal to about 40 nm. For example, a FWHM of an emission wavelength spectrum of the quantum dot may be less than or equal to about 30 nm. Within the above ranges, color purity or color gamut may be improved. Light emitted through the quantum dot may be emitted in all directions, and thus, a wide viewing angle can be improved. 
     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 can be adjusted by controlling the size of the quantum dot, light having various wavelength bands can be obtained from a quantum dot emission layer. Therefore, by using quantum dots of different sizes, a light-emitting device that emits light of various wavelengths may be implemented. In embodiments, the size of the quantum dot may be selected to emit red, green, and/or blue light. The size of the quantum dot may be configured to emit white light by combining light of various colors. 
     [Electron Transport Region in Interlayer  130 ] 
     The electron transport region may have a single-layered structure consisting of a single layer consisting of a single material, a single-layered structure consisting of a single layer consisting of different materials, or a multi-layered structure including multiple layers including different materials. 
     The electron transport region may include a buffer layer, a hole-blocking layer, an electron control layer, an electron transport layer, an electron injection layer, or any combination thereof. 
     In an embodiment, the electron transport region may have an electron transport layer/electron injection layer structure, a hole-blocking layer/electron transport layer/electron injection layer structure, an electron control layer/electron transport layer/electron injection layer structure, or a buffer layer/electron transport layer/electron injection layer structure, wherein, for each structure, constituting layers are sequentially stacked from an emission layer. 
     In an embodiment, the electron transport region (for example, the buffer layer, the hole-blocking layer, the electron control 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. 
     In an embodiment, the electron transport region may include a compound represented by Formula 601 below: 
       [Ar 601 ] xe11 -[(L 601 ) xe1 -R 601 ] xe21   [Formula 301]
 
     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 independently be the same as described in connection with Q 1 , 
     xe21 may be 1, 2, 3, 4, or 5, and 
     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 via a single bond. 
     In embodiments, Ar 601  in Formula 601 may be a substituted or unsubstituted anthracene group. 
     In an embodiment, 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 ), wherein at least one of X 614  to X 6 16 may be N, 
     L 6 11 to L 613  may each independently be the same as described in connection with L 601 , 
     xe611 to xe613 may each independently be the same as described in connection with xe1, 
     R 611  to R 613  may each independently be the same as described in connection with R 601 , and 
     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 Compounds ET1 to ET45, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), 4,7-diphenyl-1,10-phenanthroline (Bphen), Alq 3 , BAlq, TAZ, NTAZ, or any combination thereof: 
     
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
       
         
         
             
             
         
       
     
     A thickness of the electron transport region may be in a range of about 100 Å to about 5,000 Å. For example, the thickness of the electron transport region may be in a range of about 160 Å to about 4,000 Å. When the electron transport region includes a buffer layer, a hole-blocking layer, an electron control layer, an electron transport layer, or any combination thereof, a thickness of the buffer layer, the hole-blocking layer, and the electron control layer may each independently be in a range of about 20 Å to about 1,000 Å, and a thickness of the electron transport layer may be in a range of about 100 Å to about 1,000 Å, for example, about 150 Å to about 500 Å. For example, the thickness of the buffer layer, the hole-blocking layer, and the electron control layer may each independently be in a range of about 30 Å to about 300 Å. For example, the thickness of the electron transport layer may be in a range of about 150 Å to about 500 Å. When the thicknesses of the buffer layer, hole-blocking layer, electron control layer, and/or electron transport layer are within these ranges, satisfactory electron transporting characteristics may be obtained without a substantial increase in driving voltage. 
     The electron transport region (for example, the electron transport layer in the electron transport region) may further include, in addition to the materials described above, a metal-containing material. 
     The metal-containing material may include an alkali metal complex, 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 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 hydroxyphenyloxadiazole, a hydroxyphenylthiadiazole, 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 directly contact the second electrode  150 . 
     The electron injection layer may have a single-layered structure consisting of a single layer consisting of a single material, a single-layered structure consisting of a single layer consisting of different materials, or 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, alkaline earth metal complex, a rare earth metal complex, or any combination thereof. 
     The alkali metal may include Li, 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 oxide, such as BaO, SrO, CaO, Ba x Sr 1-x O (x is a real number satisfying the condition of 0&lt;x&lt;1), Ba x Ca 1-x O (x is a real number satisfying the condition of 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 , YbI 3 , ScI3, TbI 3 , or any combination thereof. In 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 one of ions of the alkali metal, ions of the alkaline earth metal, and ions of the rare earth metal, and as a ligand bonded to the metal ion, for example, hydroxyquinoline, hydroxyisoquinoline, hydroxybenzoquinoline, hydroxyacridine, hydroxyphenanthridine, hydroxyphenyloxazole, hydroxyphenylthiazole, hydroxyphenyloxadiazole, hydroxyphenylthiadiazole, hydroxyphenylpyridine, hydroxyphenyl benzimidazole, hydroxyphenylbenzothiazole, bipyridine, phenanthroline, 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 embodiments, the electron injection layer may further include an organic material (for example, a compound represented by Formula 601). 
     In embodiments, the electron injection layer may consist of an alkali metal-containing compound (for example, an alkali metal halide); or an alkali metal-containing compound (for example, an alkali metal halide), and an alkali metal, an alkaline earth metal, a rare earth metal, or any combination thereof. In embodiments, 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 includes an organic material, alkali metal, alkaline earth metal, rare earth metal, an alkali metal-containing compound, an alkaline earth metal-containing compound, a rare earth metal-containing compound, alkali metal complex, alkaline earth-metal complex, rare earth metal complex, or any combination thereof may be homogeneously or non-homogeneously 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. For example, the thickness of the electron injection layer may be in a range of about 3 Å to about 90 Å. When the thickness of the electron injection layer is within the ranges described above, the electron injection layer may have satisfactory electron injection characteristics without a substantial increase in driving voltage. 
     [Second Electrode  150 ] 
     The second electrode  150  may be located on the interlayer  130  having such a structure. The second electrode  150  may be a cathode, which is an electron injection electrode. Materials for the second electrode  150  may include a metal, an alloy, an electrically conductive compound, or any combination thereof, each having a low work function. 
     In embodiments, the second electrode  150  may include lithium (Li), silver (Ag), magnesium (Mg), aluminum (AI), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), ytterbium (Yb), silver-ytterbium (Ag—Yb), ITO, IZO, or a 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 two or more 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 . In embodiments, 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 stacked in this stated order, a structure in which the first electrode  110 , the interlayer  130 , the second electrode  150 , and the second capping layer are stacked in this 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 stacked in this 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 may be a semi-transmissive electrode or a transmissive electrode, and through the first capping layer; or 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 may be a semi-transmissive electrode or a transmissive electrode, and through the second capping layer. 
     The first capping layer and the second capping layer may each increase external emission efficiency according to the principle of constructive interference. Accordingly, the light extraction efficiency of the light-emitting device  10  may be increased, so that the emission efficiency of the light-emitting device  10  may be improved. 
     The first capping layer and second capping layer may each include a material having a refractive index (at a wavelength of about 589 nm) greater than or equal to about 1.6. 
     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 an organic-inorganic 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, naphthalocyanine derivatives, alkali metal complexes, alkaline earth metal complexes, or any combination thereof. The carbocyclic compound, the heterocyclic compound, and the amine group-containing compound may each be optionally substituted with a substituent containing O, N, S, Se, Si, F, Cl, Br, I, or any combination thereof. 
     In embodiments, at least one of the first capping layer and the second capping layer may each independently include an amine group-containing compound. 
     In embodiments, 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 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. In embodiments, 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, light-emitting apparatus) may further include, in addition to the light-emitting device, a color filter, a color conversion layer, or 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. In embodiments, the light emitted from the light-emitting device may be blue light or white light. The light-emitting device may be the same as described above. In embodiments, the color conversion layer may include quantum dots. 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 subpixels, the color filter may include color filter areas respectively corresponding to the subpixels, and the color conversion layer may include color conversion areas respectively corresponding to the subpixels. 
     A pixel-defining film may be disposed between the subpixels to define each of the subpixels. 
     The color filter may further include color filter areas and light-shielding patterns located among the color filter areas, and the color conversion layer may include 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 first color light, a second area emitting second color light, and/or a third area emitting third color light, and the first color light, the second color light, and/or the third color light may have different maximum emission wavelengths from one another. In embodiments, 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. In embodiments, the color filter areas (or the color conversion areas) may include quantum dots. In embodiments, 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. The quantum dot may be the same as described in the specification. The first area, the second area, and/or the third area may each include a scatterer. 
     In embodiments, 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. In embodiments, 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 further 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 active layer, wherein 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, etc. 
     The active layer may include crystalline silicon, amorphous silicon, organic semiconductor, 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 placed between the color filter and/or the color conversion layer and the light-emitting device. The sealing portion allows light from the light-emitting device to be extracted to the outside, while simultaneously preventing 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 additionally 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. The functional layers may include a touch screen layer, a polarizing layer, an authentication apparatus, 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 of a living body (for example, fingertips, pupils, etc.). 
     The authentication apparatus may further include, in addition to the light-emitting device, a biometric information collector. 
     The electronic apparatus may be applied, for example, 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 showing a light-emitting apparatus according to an embodiment. 
     The light-emitting 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 formed 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 active layer  220 , a gate electrode  240 , a source electrode  260 , and a drain electrode  270 . 
     The active 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 active layer  220  from the gate electrode  240  may be located on the active layer  220 , and the gate electrode  240  may be located on the gate insulating film  230 . 
     An interlayer insulating film  250  is located on the gate electrode  240 . The interlayer insulating film  250  may be placed between the gate electrode  240  and the source electrode  260  to insulate the gate electrode  240  from the source electrode  260  and between the gate electrode  240  and the drain electrode  270  to insulate the gate electrode  240  from the drain electrode  270 . 
     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 active layer  220 , and the source electrode  260  and the drain electrode  270  may be in contact with the exposed portions of the source region and the drain region of the active layer  220 . 
     The TFT is electrically connected to a light-emitting device to drive the light-emitting device, and is covered by a passivation layer  280 . The passivation layer  280  may include an inorganic insulating film, an organic insulating film, or a 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 formed on the passivation layer  280 . The passivation layer  280  does not completely cover the drain electrode  270  and may expose a portion of the drain electrode  270 , and the first electrode  110  is electrically connected to the exposed portion of the drain electrode  270 . 
     A pixel defining layer  290  containing an insulating material may be located on the first electrode  110 . The pixel defining layer  290  exposes 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 include a polyimide or a 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 disposed in the form of a common layer. 
     The second electrode  150  may be located on the interlayer  130 , and a capping layer  170  may be additionally 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 and/or oxygen. The encapsulation portion  300  may include: an inorganic film including silicon nitride (SiN x ), silicon oxide (SiO x ), 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 a combination thereof; or a combination of the inorganic film and the organic film. 
       FIG. 3  shows a schematic cross-sectional view showing a light-emitting apparatus according to an embodiment. 
     The light-emitting apparatus of  FIG. 3  is 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 a combination of a color filter area, a color conversion area, or a combination of the color filter area and the color conversion area. In embodiments, the light-emitting device included in the light-emitting apparatus of  FIG. 3  may be a tandem light-emitting device. 
     [Manufacturing Method] 
     Respective layers included in the hole transport region, the emission layer, and respective layers included in the electron transport region may be formed in a certain region by using one or more suitable methods selected from vacuum deposition, spin coating, casting, Langmuir-Blodgett (LB) deposition, ink-jet printing, laser-printing, and laser-induced thermal imaging. 
     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. 
     Definitions of Terms 
     The term “C 3 -C 60  carbocyclic group” as used herein refers to a cyclic group consisting of carbon only as a ring-forming atom and having three to sixty carbon atoms, and the term “C 1 -C 60  heterocyclic group” as used herein refers to a cyclic group that has one to sixty carbon atoms and further has, in addition to carbon, a heteroatom as a ring-forming atom. 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 C 1 -C 60  heterocyclic group has 3 to 61 ring-forming atoms. 
     The “cyclic group” as used herein may include the C 3 -C 60  carbocyclic group, and the C 1 -C 60  heterocyclic group. 
     The term “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) 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) 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) group T1, ii) a condensed cyclic group in which two or more groups T1 are condensed with each other, iii) 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 1H-pyrrole group, a silole group, a borole group, a 2H-pyrrole group, a 3H-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 group 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 one another (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, a tetrazine group, a pyrrolidine group, an imidazolidine group, a dihydropyrrole group, a piperidine group, a tetrahydropyridine group, a dihydropyridine group, a hexahydropyrimidine group, a tetrahydropyrimidine group, a dihydropyrimidine group, a piperazine group, a tetrahydropyrazine group, a dihydropyrazine group, a tetrahydropyridazine group, or a dihydropyridazine group, 
     group T3 may be a furan group, a thiophene group, a 1H-pyrrole group, a silole group, or a borole group, and 
     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 or a polyvalent group (for example, a divalent group, a trivalent group, a tetravalent group, etc.), depending on the structure of a formula in connection with which the terms are used. In an embodiment, “a benzene group” may be a benzo group, a phenyl group, a phenylene group, or the like, which may be easily understand 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, and examples of the divalent C 3 -C 60  carbocyclic group and the divalent 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 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 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 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 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 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 that further includes, in addition to a carbon atom, at least one heteroatom as a ring-forming atom and has 1 to 10 carbon atoms, and examples thereof are a 1,2,3,4-oxatriazolidinyl group, a tetrahydrofuranyl group, and a tetrahydrothiophenyl group. The term “C 1 -C 10  heterocycloalkylene group” as used herein refers to a divalent group having the same structure as the C 1 -C 10  heterocycloalkyl group. 
     The term C 3 -C 10  cycloalkenyl group used herein refers to a monovalent cyclic group that has three to ten carbon atoms and at least one carbon-carbon double bond in the ring thereof and no aromaticity, and examples thereof are a cyclopentenyl group, a cyclohexenyl group, and a cycloheptenyl group. The term “C 3 -C 10  cycloalkenylene group” as used herein refers to a divalent group having the same structure as the C 3 -C 10  cycloalkenyl group. 
     The term “C 1 -C 10  heterocycloalkenyl group” as used herein refers to a monovalent cyclic group that has, in addition to a carbon atom, at least one heteroatom as a ring-forming atom, 1 to 10 carbon atoms, and 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 the same structure as the C 1 -C 10  heterocycloalkenyl group. 
     The term “C 6 -C 60  aryl group” as used herein refers to a monovalent group having a carbocyclic aromatic system having six to sixty carbon atoms, and the term “C 6 -C 60  arylene group” as used herein refers to a divalent group having a carbocyclic aromatic system having six to sixty carbon atoms. Examples of the C 6 -C 60  aryl group are 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 that has, in addition to a carbon atom, at least one heteroatom as a ring-forming atom, and 1 to 60 carbon atoms. The term “C 1 -C 60  heteroarylene group” as used herein refers to a divalent group having a heterocyclic aromatic system that has, in addition to a carbon atom, at least one heteroatom as a ring-forming atom, and 1 to 60 carbon 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 the same structure as a monovalent non-aromatic condensed polycyclic group. 
     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, at least one heteroatom other than carbon atoms, as a ring-forming atom, and non-aromaticity in its entire molecular structure. Examples of the monovalent non-aromatic condensed heteropolycyclic group are a pyrrolyl group, a thiophenyl group, a furanyl group, an indolyl group, a benzoindolyl group, a naphtho indolyl 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 heterocondensed polycyclic group” as used herein refers to a divalent group having the same structure as a monovalent non-aromatic heterocondensed polycyclic group. 
     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 “C 7 -C 60  aryl alkyl group” used herein refers to -A 104 A 105  (where A 104  may be a C 1 -C 54  alkylene group, and A 105  may be a C 6 -C 59  aryl group), and the term C 2 -C 60  heteroaryl alkyl group” used herein refers to -A 106 A 107  (where A 106  may be a C 1 -C 59  alkylene group, and A 107  may be a C 1 -C 59  heteroaryl group). 
     The term “C 1 -C 60  heteroaryloxy group” used herein indicates —OA 108  (wherein A 108  is a C 1 -C 60  heteroaryl group), and the term C 6 -C 60  heteroarylthio group used herein indicates —SA 109  (wherein A 109  is the C 1 -C 60  heteroaryl group). 
     The term “R 10a ” as used herein refers to: 
     deuterium (-D), —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, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio group, a C 7 -C 60  arylalkyl group, a C 2 -C 60  heteroarylalkyl 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, a C 6 -C 60  arylthio group, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio group, a C 7 -C 60  arylalkyl group, or a C 2 -C 60  heteroarylalkyl group, each unsubstituted or substituted with deuterium, —F, —Cl, —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, a C 1 -C 60  heteroaryloxy group, a C 1 -C 60  heteroarylthio group, a C 7 -C 60  arylalkyl group, a C 2 -C 60  heteroarylalkyl 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 ), 
     wherein 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; —Cl; —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 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; a C 7 -C 60  aryl alkyl group; or a C 2 -C 60  heteroaryl alkyl group. 
     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 combination thereof. 
     The term “the third-row transition metal” used herein includes hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), etc. 
     The term “Ph” as used herein refers to a phenyl group, the term “Me” as used herein refers to a methyl group, the term “Et” as used herein refers to an ethyl group, the term “tert-Bu” or “Bu t ” as used herein refers to a tert-butyl group, and the term “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.” In other words, 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”. In other words, 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. 
     In the description, * and *′ as used herein, unless defined otherwise, each refer to a binding site to a neighboring atom in a corresponding formula or moiety. 
     Hereinafter, a compound according to embodiments and a light-emitting device according to embodiments will be described in detail with reference to Examples. The wording “B was used instead of A” used in describing Examples refers to that an identical molar equivalent of B was used in place of A. 
     EXAMPLES 
     Example 1 
     An ITO glass substrate (50×50 mm) was subjected to ultrasonic cleaning sequentially using distilled water and isopropanol, followed by UV ozone cleaning for 30 minutes. A glass substrate with a transparent electrode line attached thereon after the cleaning was mounted on a substrate holder of a vacuum deposition apparatus, and 1,4,5,8,9,12-hexaazatriphenylene-hexacarbonitrile (HAT-CN) was deposited on an ITO electrode (anode) to form a hole injection layer having a thickness of 10 nm. N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPB) was deposited on the hole injection layer to form a hole transport layer having a thickness of 40 nm. 
     H-01 (a hole transport host (HT host)) and D-02 (a third emissive compound (EM3)) were co-deposited on the hole transport layer to a weight ratio of 99:1 to form an emission auxiliary layer having a thickness of 5 nm. 
     H-01 (HT host), E-02 (an electron transport host (ET host)), S-02 (a first emissive compound (EM1)), and D-02 (a second emissive compound (EM2)) were co-deposited on the emission auxiliary layer to a weight ratio of 62:26:11:1 to form an emission layer having a thickness of 20 nm. 
     E-02 (ET host) and D-02 (EM3) were co-deposited on the emission layer to a weight ratio of 99:1 to form a buffer layer having a thickness of 5 nm. 
     2,7-di(2,2′-bipyridin-5-yl)triphenylene (BByTP) was deposited on the buffer layer to form an electron transport layer having a thickness of 40 nm. 
     Yb was deposited on the electron transport layer to form an electron injection layer having a thickness of 1 nm, Al was deposited on the electron injection layer to form a cathode having a thickness of 100 nm, thereby completing the manufacture of a light-emitting device. 
     
       
         
         
             
             
         
       
     
     Examples 2 to 30 and Comparative Examples 1 to 10 
     An organic light-emitting device was manufactured in the same manner as in Example 1, except that, in forming an emission layer, materials of light-emitting devices as shown in Tables 1 and 2 were used. 
     In the “emission auxiliary layer doping” column of Tables 1 and 2, “O” indicates that the emission auxiliary layer includes the third emissive compound, and “X” indicates that the emission auxiliary layer does not include the third emissive compound. 
     In the “buffer layer doping” column of Tables 1 and 2, “O” indicates that the buffer layer includes the third emissive compound, and “X” indicates that the buffer layer does not include the third emissive compound. 
     Evaluation Example 1 
     The TADF emission ratio, emission efficiency, and lifespan (T 95 ) of the organic light-emitting devices manufactured according to Examples 1 to 30 and Comparative Examples 1 to 10 were measured using a Keithley SMU 236 and luminance meter PR650, and the results are shown in Tables 1 and 2. 
     The TADF emission ratio was calculated in the following method: 
     (i) A phosphorescent light-emitting device including only a first emissive compound as a dopant, (ii) a TADF light-emitting device including only a second emissive compound as a dopant, and (iii) an EF light-emitting device including a first emissive compound and a second emissive compound as dopants were manufactured, and the height of the peak of each emission spectrum were obtained, thereby obtaining the TADF emission ratio according to Equation T. 
     
       
         
           
             
               
                 
                   
                     T 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     A 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     D 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     F 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     emission 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     ratio 
                   
                   = 
                   
                     
                        
                       
                         
                           
                             
                               
                                 ( 
                                 
                                   peak 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   height 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   of 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   E 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   F 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   light 
                                   ⁢ 
                                   
                                     - 
                                   
                                   ⁢ 
                                   emitting 
                                   ⁢ 
                                   
                                       
                                   
                                   ⁢ 
                                   device 
                                 
                                 ) 
                               
                               - 
                             
                           
                         
                         
                           
                             
                               ( 
                               
                                 peak 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 height 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 of 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 phosphorescent 
                               
                             
                           
                         
                         
                           
                             
                               
                                 light 
                                 ⁢ 
                                 
                                   - 
                                 
                                 ⁢ 
                                 emitting 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 device 
                               
                               ) 
                             
                           
                         
                       
                        
                     
                     
                       
                         
                           
                             
                               ( 
                               
                                 peak 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 height 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 of 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 phosphorescent 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 light 
                                 ⁢ 
                                 
                                   - 
                                 
                                 ⁢ 
                                 emitting 
                                 ⁢ 
                                 
                                     
                                 
                                 ⁢ 
                                 device 
                               
                               ) 
                             
                             - 
                           
                         
                       
                       
                         
                           
                             ( 
                             
                               peak 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               height 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               of 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               T 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               A 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               D 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               F 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               light 
                               ⁢ 
                               
                                 - 
                               
                               ⁢ 
                               emitting 
                               ⁢ 
                               
                                   
                               
                               ⁢ 
                               device 
                             
                             ) 
                           
                         
                       
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     T 
                   
                   ] 
                 
               
             
           
         
       
     
     The lifespan (T 95 ) is a measure of time taken when the luminance reaches 95% of the initial luminance. 
     Regarding phosphorescent emissive compounds used in Examples 1 to 30 and Comparative Examples 1 to 10, a sample in a solution state was cooled to a temperature of 77K and the emissive spectrum thereof was measured, an onset wavelength was calculated from the emission start wavelength, the T 1  energy level was measured therefrom, and the result thereof is shown in Table 1. In the same manner, the S 1  energy level (S 1 ) and the T 1  energy level (T 1 ) of the delayed fluorescence-emitting compound used in Examples 1 to 30 and Comparative Examples 1 to 10 were measured, and the results thereof are shown in Tables 1 and 2. 
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                 HT 
                   
                   
                   
                 Emission 
                   
                   
                   
                   
               
               
                   
                 host, 
                   
                 EM2 
                 EM3 
                 auxiliary 
                 Buffer 
                 TADF 
                 Emission 
                   
               
               
                   
                 ET 
                 EM1 
                 (S 1 , eV) 
                 (S 1 , eV) 
                 layer 
                 layer 
                 emission 
                 efficiency 
                 T 95   
               
               
                   
                 host 
                 (T 1 , eV) 
                 (T 1 , eV) 
                 (T 1 , eV) 
                 doping 
                 doping 
                 ratio 
                 (cd/A) 
                 (hr) 
               
               
                   
               
             
            
               
                 Example 1 
                 H-01, 
                 S-2 
                 D-02 
                 D-02 
                 ○ 
                 ○ 
                 0.825 
                 25.1 
                 42.1 
               
               
                 Example 2 
                 E-02 
                 (2.77) 
                 (2.74) 
                 (2.74) 
                 ○ 
                 X 
                 0.763 
                 24.3 
                 38.9 
               
               
                 Example 3 
                   
                   
                 (2.67) 
                 (2.67) 
                 X 
                 ○ 
                 0.701 
                 24.1 
                 33.5 
               
               
                 Comparative 
                   
                   
                   
                 — 
                 X 
                 X 
                 0.604 
                 23.6 
                 31.1 
               
               
                 Example 1 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Example 4 
                 H-03, 
                 S-3 
                 D-21 
                 D-21 
                 ○ 
                 ○ 
                 0.869 
                 25.3 
                 44.2 
               
               
                 Example 5 
                 E-11 
                 (2.78) 
                 (2.69) 
                 (2.69) 
                 ○ 
                 X 
                 0.705 
                 24.0 
                 39.1 
               
               
                 Example 6 
                   
                   
                 (2.60) 
                 (2.60) 
                 X 
                 ○ 
                 0.622 
                 23.3 
                 37.2 
               
               
                 Comparative 
                   
                   
                   
                 — 
                 X 
                 X 
                 0.569 
                 22.7 
                 35.8 
               
               
                 Example 2 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Example 7 
                 H-04, 
                 S-35 
                 D-17 
                 D-17 
                 ○ 
                 ○ 
                 0.820 
                 24.9 
                 45.5 
               
               
                 Example 8 
                 E-13 
                 (2.65) 
                 (2.61) 
                 (2.61) 
                 ○ 
                 X 
                 0.629 
                 23.0 
                 41.5 
               
               
                 Example 9 
                   
                   
                 (2.50) 
                 (2.50) 
                 X 
                 ○ 
                 0.689 
                 23.8 
                 35.5 
               
               
                 Comparative 
                   
                   
                   
                 — 
                 X 
                 X 
                 0.555 
                 21.7 
                 32.8 
               
               
                 Example 3 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Example 10 
                 H-08, 
                 S-11 
                 D-04 
                 D-04 
                 ○ 
                 ○ 
                 0.830 
                 25.5 
                 41.2 
               
               
                 Example 11 
                 E-07 
                 (2.76) 
                 (2.70) 
                 (2.70) 
                 ○ 
                 X 
                 0.788 
                 24.2 
                 39.3 
               
               
                 Example 12 
                   
                   
                 (2.62) 
                 (2.62) 
                 X 
                 ○ 
                 0.699 
                 23.5 
                 35.7 
               
               
                 Comparative 
                   
                   
                   
                 — 
                 X 
                 X 
                 0.673 
                 22.9 
                 33.3 
               
               
                 Example 4 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Example 13 
                 H-11, 
                 S-12 
                 D-15 
                 D-15 
                 ○ 
                 ○ 
                 0.851 
                 23.7 
                 43.3 
               
               
                 Example 14 
                 E-05 
                 (2.64) 
                 (2.62) 
                 (2.62) 
                 ○ 
                 X 
                 0.712 
                 22.5 
                 39.5 
               
               
                 Example 15 
                   
                   
                 (2.49) 
                 (2.49) 
                 X 
                 ○ 
                 0.755 
                 22.8 
                 39.2 
               
               
                 Comparative 
                   
                   
                   
                 — 
                 X 
                 X 
                 0.591 
                 21.9 
                 36.6 
               
               
                 Example 5 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 HT 
                   
                   
                   
                 Emission 
                   
                   
                   
                   
               
               
                   
                 host, 
                   
                 EM2 
                 EM3 
                 auxiliary 
                 Buffer 
                 TADF 
                 Emission 
                   
               
               
                   
                 ET 
                 EM1 
                 (S 1 , eV) 
                 (S 1 , eV) 
                 layer 
                 layer 
                 emission 
                 efficiency 
                 T 95   
               
               
                   
                 host 
                 (T 1 , eV) 
                 (T 1 , eV) 
                 (T 1 , eV) 
                 doping 
                 doping 
                 ratio 
                 (cd/A) 
                 (hr) 
               
               
                   
               
             
            
               
                 Example 16 
                 H-12, 
                 S-29 
                 D-22 
                 D-22 
                 ○ 
                 ○ 
                 0.880 
                 25.5 
                 43.5 
               
               
                 Example 17 
                 E-12 
                 (2.66) 
                 (2.63) 
                 (2.63) 
                 ○ 
                 X 
                 0.701 
                 23.7 
                 40.1 
               
               
                 Example 18 
                   
                   
                 (2.43) 
                 (2.43) 
                 X 
                 ○ 
                 0.792 
                 24.9 
                 42.2 
               
               
                 Comparative 
                   
                   
                   
                 — 
                 X 
                 X 
                 0.655 
                 23.3 
                 37.5 
               
               
                 Example 6 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Example 19 
                 H-13, 
                 S-33 
                 D-20 
                 D-20 
                 ○ 
                 ○ 
                 0.801 
                 23.9 
                 42.2 
               
               
                 Example 20 
                 E-09 
                 (2.69) 
                 (2.67) 
                 (2.67) 
                 ○ 
                 X 
                 0.687 
                 22.5 
                 38.9 
               
               
                 Example 21 
                   
                   
                 (2.39) 
                 (2.39) 
                 X 
                 ○ 
                 0.784 
                 23.2 
                 40.5 
               
               
                 Comparative 
                   
                   
                   
                 — 
                 X 
                 X 
                 0.635 
                 22.2 
                 35.9 
               
               
                 Example 7 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Example 22 
                 H-15, 
                 S-4 
                 D-07 
                 D-07 
                 ○ 
                 ○ 
                 0.840 
                 24.4 
                 45.6 
               
               
                 Example 23 
                 E-11 
                 (2.71) 
                 (2.70) 
                 (2.70) 
                 ○ 
                 X 
                 0.722 
                 23.8 
                 42.1 
               
               
                 Example 24 
                   
                   
                 (2.61) 
                 (2.61) 
                 X 
                 ○ 
                 0.601 
                 23.2 
                 40.7 
               
               
                 Comparative 
                   
                   
                   
                 — 
                 X 
                 X 
                 0.546 
                 23.0 
                 32.5 
               
               
                 Example 8 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Example 25 
                 H-16, 
                 S-14 
                 D-03 
                 D-03 
                 ○ 
                 ○ 
                 0.833 
                 25.1 
                 45.2 
               
               
                 Example 26 
                 E-07 
                 (2.69) 
                 (2.67) 
                 (2.67) 
                 ○ 
                 X 
                 0.658 
                 24.2 
                 41.9 
               
               
                 Example 27 
                   
                   
                 (2.54) 
                 (2.54) 
                 X 
                 ○ 
                 0.651 
                 23.8 
                 40.6 
               
               
                 Comparative 
                   
                   
                   
                 — 
                 X 
                 X 
                 0.594 
                 22.7 
                 39.1 
               
               
                 Example 9 
                   
                   
                   
                   
                   
                   
                   
                   
                   
               
               
                 Example 28 
                 H-17, 
                 S-21 
                 D-13 
                 D-13 
                 ○ 
                 ○ 
                 0.819 
                 25.9 
                 44.9 
               
               
                 Example 29 
                 E-01 
                 (2.72) 
                 (2.65) 
                 (2.65) 
                 ○ 
                 X 
                 0.689 
                 23.7 
                 39.3 
               
               
                 Example 30 
                   
                   
                 (2.52) 
                 (2.52) 
                 X 
                 ○ 
                 0.613 
                 22.9 
                 36.6 
               
               
                 Comparative 
                   
                   
                   
                 — 
                 X 
                 X 
                 0.578 
                 22.2 
                 34.8 
               
               
                 Example 10 
               
               
                   
               
            
           
         
       
     
     From Tables 1 and 2, it can be seen that the light-emitting devices according to an embodiment include a third emissive compound in an emission auxiliary layer and/or a buffer layer, and have higher TADF emission ratio, higher emission efficiency, and longer lifespan than the light-emitting devices of Comparative Examples which do not include a third emissive compound. 
     The light-emitting device according to an embodiment has excellent emission efficiency and lifespan characteristics. 
     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.