Organic light emitting element

Abstract

Disclosed is an organic light emitting element. The organic light emitting element includes a first electrode, a hole transport region disposed on the first electrode, an emission layer disposed on the hole transport region, an electron transport region disposed on the emission layer and including an electron transport layer, and a second electrode disposed on the electron transport region. The hole transport region can include a first hole transport layer having a first refractive index, a second hole transport layer disposed on the first hole transport layer and having a second refractive index less than the first refractive index, and a third hole transport layer disposed below the first hole transport layer and having a third refractive index less than the first refractive index. The difference between the first refractive index and the second refractive index and the difference between the first refractive index and the third refractive index can each be about 0.1 to about 1.0.

Description

[0001] This application claims priority to and the benefit of Korean Patent Application No. 10-2020-0090885, filed on July 22, 2020, in the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0002] Disclosed relates to an organic light emitting element including a hole transport layer having different refractive indexes. BACKGROUND

[0003] Development of various types of display devices used in multimedia devices such as televisions, mobile phones, tablet computers, navigation systems, and game consoles is in progress. In such display devices, a so-called self-emissive display element implements display by using a light emitting material including an organic compound or a quantum dot in an emission layer disposed between electrodes facing each other to emit light.

[0004] In the application of light emitting elements in display devices, there has been a constant need for light emitting elements having high light emitting efficiency, and there has been a constant need to develop materials and structures capable of stably obtaining these characteristics. SUMMARY

[0005] Disclosed provides an organic light emitting element exhibiting excellent light emitting efficiency.

[0006] Embodiments of the inventive concept provide an organic light emitting element including a first electrode, a hole transport region disposed on the first electrode, an emission layer disposed on the hole transport region, an electron transport region disposed on the emission layer and including an electron transport layer, and a second electrode disposed on the electron transport region. The hole transport region can include a first hole transport layer having a first refractive index, a second hole transport layer disposed above the first hole transport layer and having a second refractive index less than the first refractive index, and a third hole transport layer disposed below the first hole transport layer and having a third refractive index less than the first refractive index. A difference between the first refractive index and the second refractive index can be in a range of about 0.1 to about 1.0, and a difference between the first refractive index and the third refractive index can be in a range of about 0.1 to about 1.0.

[0007] The hole transport region can further include an electron blocking layer disposed between the second hole transport layer and the emission layer, wherein the electron blocking layer can have a refractive index greater than a refractive index of the emission layer and greater than the second refractive index.

[0008] A thickness of the second hole transport layer and a thickness of the third hole transport layer can each be in a range of about 30% to about 40% of a total thickness of the first hole transport layer to the third hole transport layer.

[0009] The thickness ratio of the second hole transport layer, the first hole transport layer, and the third hole transport layer can be in the range of about 3:4:3 to about 4:2:4.

[0010] The thickness of the second hole transport layer and the thickness of the third hole transport layer can each be in the range of about 10 nm to about 100 nm.

[0011] The second refractive index and the third refractive index can each be in the range of about 1.2 to about 1.7.

[0012] The first refractive index can be in the range of about 1.7 to about 2.2.

[0013] The third hole transport layer can be disposed directly on the first electrode, and the third refractive index and the refractive index of the emission layer can be the same.

[0014] The second hole transport layer and the third hole transport layer can each independently include an aromatic compound represented by one of the following Formulae 1 to 4.

[0015] [Formula 1]

[0016]

[0017] [Formula 2]

[0018]

[0019] [Formula 3]

[0020]

[0021] [Formula 4]

[0022]

[0023] In the above Formulae 1 to 4, a, b, and f to j are each independently an integer of 1 to 4, c to e are each independently an integer of 1 to 5, R1 to R3, R 11 to R 13 , R 21 to R 24 , R 31 , and R 32 are each independently a hydrogen atom, a deuterium atom, a halogen atom, a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 30 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 30 ring-forming carbon atoms, and optionally, R1 to R3, R 11 to R 13 , R 21 to R 24 , R 31 , and R32 each independently binds to an adjacent group to form a ring, and at least one of R 11 to R 13 at least one of R 21 to R 24 at least one of R 31 and at least one of R 32 each independently is a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms or a substituted or unsubstituted cycloalkyl group having 3 to 30 carbon atoms.

[0024] at least one of R 11 to R 13 each independently can be a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms or a substituted or unsubstituted cycloalkyl group having 3 to 10 carbon atoms.

[0025] The emission layer and the electron transport layer can each include an aromatic compound represented by one of the above Formulae 1 to 4.

[0026] The refractive index of the emission layer and the refractive index of the electron transport layer can each be less than the first refractive index.

[0027] The electron transport region can further include a hole blocking layer disposed on the emission layer, and the refractive index of the emission layer and the refractive index of the electron transport layer can each be less than the refractive index of the hole blocking layer.

[0028] The difference between the refractive index of the hole blocking layer and the refractive index of the emission layer can be in the range of about 0.1 to about 1.0, and the difference between the refractive index of the hole blocking layer and the refractive index of the electron transport layer can be in the range of about 0.1 to about 1.0.

[0029] The organic light emitting element can further include a hole injection layer disposed between the first electrode and the third hole transport layer, wherein the refractive index of the hole injection layer can be less than the first refractive index.

[0030] The refractive index of the emission layer and the refractive index of the electron transport layer can each be in the range of about 1.2 to about 1.7.

[0031] In embodiments of the inventive concept, an organic light emitting element includes a first electrode, a hole transport layer disposed on the first electrode, an emission layer disposed on the hole transport layer, a hole blocking layer disposed on the emission layer, an electron transport layer disposed on the hole blocking layer, and a second electrode disposed on the electron transport layer. The hole transport layer can include a first hole transport layer having a first refractive index, a second hole transport layer disposed between the emission layer and the first hole transport layer and having a second refractive index less than the first refractive index, and a third hole transport layer disposed between the first hole transport layer and the first electrode and having a third refractive index less than the first refractive index. The second refractive index, the third refractive index, a refractive index of the emission layer, and a refractive index of the electron transport layer can each be in a range of about 1.2 to about 1.7. The first refractive index and a refractive index of the hole blocking layer can each be in a range of about 1.7 to about 2.2. The second refractive index, the third refractive index, the refractive index of the emission layer, and the refractive index of the electron transport layer can each be less than the first refractive index.

[0032] A difference between the first refractive index and the second refractive index can be in a range of about 0.1 to about 1.0, and a difference between the first refractive index and the third refractive index can be in a range of about 0.1 to about 1.0.

[0033] The second refractive index, the third refractive index, the refractive index of the emission layer, and the refractive index of the electron transport layer can be the same.

[0034] The second hole transport layer, the third hole transport layer, the emission layer, and the electron transport layer can each independently include an aromatic compound represented by one of Formulas 1 to 4 above. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings are included to provide a further understanding of the inventive concept, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the inventive concept and, together with the description, serve to explain principles of the inventive concept. In the drawings:

[0036] Figure 1 is a schematic cross-sectional view of an organic light emitting element according to an embodiment;

[0037] Figure 2 is a schematic cross-sectional view of an organic light emitting element according to an embodiment;

[0038] Figure 3 is a schematic cross-sectional view illustrating a portion of an organic light emitting element according to an embodiment;

[0039] Figure 4 is a graph illustrating luminous efficiency according to a position of a layer having a low refractive index; and

[0040] Figure 5 is a graph illustrating luminous efficiency according to a color coordinate. DETAILED DESCRIPTION

[0041] The present disclosure can be modified in a number of alternative forms, and thus embodiments will be shown in the drawings and described in detail. It is to be understood, however, that no limitation of the inventive concept is intended by the particular description and description thereof. Rather, all modifications, equivalents, and alternatives falling within the spirit and scope of the invention are to be included.

[0042] In this specification, when an element (or region, layer, part, etc.) is referred to as being "on" another element, "connected to" or "bonded to" another element, it means that the element can be directly placed on / connected to / bonded to the other element, or one or more elements can be placed therebetween.

[0043] Throughout the specification, like drawing reference numerals refer to like elements throughout the specification. In the drawings, the thickness, ratio, and size of elements can be exaggerated for the sake of efficiency in describing the technical content. Therefore, the size and thickness of components in the drawings can be arbitrarily shown for the sake of explanation, and thus the following embodiments disclosed are not limited thereto.

[0044] As used herein, unless the context clearly indicates otherwise, expressions used in the singular also encompass the plural. For example, "a" or "an" can mean one or more than one.

[0045] 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" can be understood to mean "A, B, or A and B." The terms "and" and "or" can be used in the sense of conjunction or disjunction, and can be understood to be equivalent to "and / or."

[0046] For the purpose of its meaning and explanation, the term "at least one of" is intended to include the meaning of "at least one selected from." For example, "at least one of A and B" can be understood to mean "A, B, or A and B." When the term "at least one of" is placed after a list of elements (elements), it modifies the entire list of elements (elements), not individual elements (elements) in the list.

[0047] It will be understood that, although the terms "first," "second," etc. can 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. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element without departing from the scope of embodiments of the present inventive concept.

[0048] Also, terms such as "below," "under," "above," "on," and the like are used to describe relationships of the components shown in the drawings in terms of their orientation to one another. The terms are used as relative concepts and are described with reference to the directions indicated in the drawings.

[0049] The term "about" or "approximately," as used herein, takes into account the measurements discussed and the errors associated with the measurement of the quantities (i.e., limitations of the measurement system), and includes the stated value, and means within an acceptable range of deviation from the stated value as determined by one of ordinary skill in the art. For example, "about" can mean within one or more standard deviations, or within ±20%, ±10%, or ±5% of the stated value.

[0050] It is to be understood that the terms "including," "comprising," and variations thereof are intended to mean that the disclosed features, integers, steps, operations, elements, components, or combinations thereof are present, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

[0051] Unless otherwise defined or implied herein, all terms used are intended to have the same meaning as commonly understood by one of ordinary skill in the art in the field of the disclosure. It will also be understood that, unless clearly indicated otherwise, the terminology used herein is intended to be interpreted in accordance with its common meaning in the relevant technical field, and is not to be interpreted in an idealized or overly formal sense.

[0052] Hereinafter, an organic light emitting element according to an embodiment of the inventive concept will be described with reference to the accompanying drawings.

[0053] Figure 1 and Figure 2 are schematic cross-sectional views of an organic light emitting element according to an embodiment of the inventive concept. Reference is made to Figure 1 and Figure 2 In the organic light emitting elements 10 and 10a according to the embodiments, a first electrode EL1 and a second electrode EL2 can be disposed to face each other, and a hole transport region HTR, an emission layer EML, and an electron transport region ETR can be disposed between the first electrode EL1 and the second electrode EL2. The organic light emitting element 10a according to the embodiments can further include a cap layer CPL disposed on the second electrode EL2.

[0054] In comparison with Figure 1 , Figure 2 shows a schematic cross-sectional view of the organic light emitting element 10a of the embodiment, in which the hole transport region HTR includes a hole injection layer HIL, a first hole transport layer HTL1, a second hole transport layer HTL2, and a third hole transport layer HTL3, and an electron blocking layer EBL.Figure 2 An organic light emitting element 10a of an embodiment is shown, in which the electron transport region ETR includes a hole blocking layer HBL and an electron transport layer ETL.

[0055] The organic light emitting elements 10 and 10a according to the embodiments can include a first electrode EL1, a hole transport region HTR disposed on the first electrode EL1, an emission layer EML disposed on the hole transport region HTR, an electron transport region ETR disposed on the emission layer EML, and a second electrode EL2 disposed on the electron transport region ETR. The electron transport region ETR can include an electron transport layer ETL. The hole transport region HTR can include a first hole transport layer HTL1, a second hole transport layer HTL2, and a third hole transport layer HTL3.

[0056] According to the embodiments, the first hole transport layer HTL1 can have a first refractive index. The second hole transport layer HTL2 can have a second refractive index that is less than the first refractive index. The third hole transport layer HTL3 can have a third refractive index that is less than the first refractive index. The difference between the first refractive index and the second refractive index can be in the range of about 0.1 to about 1.0, and the difference between the first refractive index and the third refractive index can be in the range of about 0.1 to about 1.0. The first refractive index can be greater than the second refractive index and can be greater than the third refractive index. The hole transport region HTR will be described in more detail later.

[0057] The first electrode EL1 has electrical conductivity. The first electrode EL1 can be formed of a metal alloy or an electrically conductive compound. The first electrode EL1 can be an anode or a cathode. The first electrode EL1 can be a pixel electrode. The first electrode EL1 can be a transmissive electrode, a transreflective electrode, or a reflective electrode. When the first electrode EL1 is a transmissive electrode, the first electrode EL1 can include a transparent metal oxide such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), and indium tin zinc oxide (ITZO). When the first electrode EL1 is a transreflective electrode or a reflective electrode, the first electrode EL1 can include Ag, Mg, Cu, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, LiF, Mo, Ti, a compound thereof, a mixture thereof (e.g., a mixture of Ag and Mg), or a material having a multi-layer structure such as LiF / Ca or LiF / Al. For example, the first electrode EL1 can have a multi-layer structure including a reflective film or a transreflective film formed of the above-described materials and a transparent conductive film formed of indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium tin zinc oxide (ITZO), or the like. For example, the first electrode EL1 can have a three-layer structure of ITO / Ag / ITO, but is not limited thereto. The thickness of the first electrode EL1 can be in the range of about 10 nm to about 1,000 nm, for example. to about For example, the thickness of the first electrode EL1 can be in a range of about 1 nm to about 100 nm. For example, the thickness of the first electrode EL1 can be in a range of about 5 nm to about 50 nm. For example, the thickness of the first electrode EL1 can be in a range of about 1 nm to about 100 nm. For example, the thickness of the first electrode EL1 can be in a range of about 5 nm to about 50 nm. For example, the thickness of the first electrode EL1 can be in a range of about 1 nm to about 100 nm. For example, the thickness of the first electrode EL1 can be in a range of about 5 nm to about 50 nm.

[0058] A hole transport region HTR can be disposed on the first electrode EL1. The hole transport region HTR can include a first hole transport layer HTL1, a second hole transport layer HTL2, and a third hole transport layer HTL3. For example, the third hole transport layer HTL3 can be disposed directly on the first electrode EL1. The hole transport region HTR can further include an electron blocking layer EBL or a hole injection layer HIL. However, embodiments of the inventive concept are not limited thereto. In the organic light emitting elements 10 and 10a according to embodiments, any one of the electron blocking layer EBL and the hole injection layer HIL can be omitted.

[0059] Referring to Figure 2 , the hole transport region HTR can include the third hole transport layer HTL3, the first hole transport layer HTL1, and the second hole transport layer HTL2, which are sequentially stacked. The second hole transport layer HTL2 can be disposed above the first hole transport layer HTL1, and the third hole transport layer HTL3 can be disposed below the first hole transport layer HTL1. A second refractive index of the second hole transport layer HTL2 can be less than a first refractive index of the first hole transport layer HTL1. A third refractive index of the third hole transport layer HTL3 can be less than the first refractive index of the first hole transport layer HTL1. The first refractive index can be in a range of about 1.7 to about 2.2. For example, the first refractive index can be in a range of about 1.8 to about 1.9. The second refractive index and the third refractive index can each be in a range of about 1.2 to about 1.7. For example, the second refractive index and the third refractive index can each be less than or equal to about 1.6.

[0060] A difference between the first refractive index and the second refractive index can be in a range of about 0.1 to about 1.0. The first refractive index can be greater than the second refractive index by about 0.1 to about 1.0. A difference between the first refractive index and the third refractive index can be in a range of about 0.1 to about 1.0. The third refractive index can be less than the first refractive index by about 0.1 to about 1.0. The second refractive index and the third refractive index can be identical to each other. The second refractive index and the third refractive index can be different from each other. The difference between the first refractive index and the second refractive index and the difference between the first refractive index and the third refractive index can be identical. The difference between the first refractive index and the second refractive index and the difference between the first refractive index and the third refractive index can be different.

[0061] For example, the difference between the first refractive index and the second refractive index can be in the range of about 0.2 to about 1.0. The first refractive index can be greater than the second refractive index by about 0.2 to about 1.0. The third refractive index can be less than the first refractive index by about 0.2 to about 1.0. However, this is presented as an example, and embodiments of the inventive concept are not limited thereto.

[0062] The hole transport region HTR of the embodiments can include the first hole transport layer HTL1, the second hole transport layer HTL2, and the third hole transport layer HTL3, and can have enhanced interface reflection due to the difference in refractive index between the hole transport layers HTL1, HTL2, and HTL3. The enhanced interface reflection can cause the direction of light incident from the emission layer EML (to be described later) to the hole transport region HTR to be upwardly shifted, thereby emitting light upwardly. Accordingly, the organic light emitting element 10 and 10a including the hole transport region HTR according to the embodiments can exhibit improved light emitting efficiency.

[0063] The thickness T2 of the second hole transport layer HTL2 and the thickness T3 of the third hole transport layer HTL3 can each be in a range of about 10 nm to about 100 nm. The thickness T1 of the first hole transport layer HTL1 can be in a range of about 10 nm to about 100 nm. The thickness T2 of the second hole transport layer HTL2 and the thickness T3 of the third hole transport layer HTL3 can each be in a range of about 30% to about 40% of a total thickness of the first hole transport layer HTL1, the second hole transport layer HTL2, and the third hole transport layer HTL3. For example, the thickness T2 of the second hole transport layer HTL2 and the thickness T3 of the third hole transport layer HTL3 can each be in a range of about 30% to about 40% relative to the total thickness of the first hole transport layer HTL1, the second hole transport layer HTL2, and the third hole transport layer HTL3. The thickness T2 of the second hole transport layer HTL2 can be in a range of about 30% to about 40% relative to the total thickness of the first hole transport layer HTL1, the second hole transport layer HTL2, and the third hole transport layer HTL3. The thickness T3 of the third hole transport layer HTL3 can be in a range of about 30% to about 40% relative to the total thickness of the first hole transport layer HTL1, the second hole transport layer HTL2, and the third hole transport layer HTL3. For example, the thickness T2 of the second hole transport layer HTL2 can be about 33% of the total thickness of the first hole transport layer HTL1, the second hole transport layer HTL2, and the third hole transport layer HTL3. The thickness T3 of the third hole transport layer HTL3 can be about 33% of the total thickness of the first hole transport layer HTL1, the second hole transport layer HTL2, and the third hole transport layer HTL3. The total thickness of the first hole transport layer HTL1, the second hole transport layer HTL2, and the third hole transport layer HTL3 can be about 300 nm, and the thickness T2 of the second hole transport layer HTL2 and the thickness T3 of the third hole transport layer HTL3 can each be about 100 nm. However, this is presented by way of example, and embodiments of the inventive concept are not limited thereto.

[0064] According to embodiments, a ratio of the thickness T2 of the second hole transport layer HTL2, the thickness T1 of the first hole transport layer HTL1, and the thickness T3 of the third hole transport layer HTL3 can be in a range of about 3:4:3 to about 4:2:4. The thickness T1 of the first hole transport layer HTL1 can be greater than the thickness T2 of the second hole transport layer HTL2, and can be greater than the thickness T3 of the third hole transport layer HTL3. The thickness T2 of the second hole transport layer HTL2 and the thickness T3 of the third hole transport layer HTL3 can each be less than the thickness T1 of the first hole transport layer HTL1.

[0065] The thickness T1 of the first hole transport layer HTL1 can be less than the thickness T2 of the second hole transport layer HTL2, and can be less than the thickness T3 of the third hole transport layer HTL3. The thickness T2 of the second hole transport layer HTL2 and the thickness T3 of the third hole transport layer HTL3 can each be greater than the thickness T1 of the first hole transport layer HTL1.

[0066] The thickness T2 of the second hole transport layer HTL2 and the thickness T3 of the third hole transport layer HTL3 can be the same. The thickness T2 of the second hole transport layer HTL2 and the thickness T3 of the third hole transport layer HTL3 can be different. For example, the ratio of the thickness T2 of the second hole transport layer HTL2, the thickness T1 of the first hole transport layer HTL1, and the thickness T3 of the third hole transport layer HTL3 can be about 3:4:3. However, this is presented as an example, and embodiments of the inventive concept are not limited thereto.

[0067] In the specification, the term "substituted or unsubstituted" can mean that a group or a substance is not substituted or substituted with at least one substituent selected from the group consisting of a deuterium atom, a halogen atom, a cyano group, a nitro group, an amine group, a silyl group, an oxy group, a thio group, a sulfinyl group, a sulfonyl group, a carbonyl group, a boron group, a phosphine oxide group, a phosphine sulfide group, an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, a hydrocarbon ring group, an aryl group, and a heterocyclic group. Each of the above-mentioned substituents can be substituted or unsubstituted. For example, a biphenyl group can be interpreted as an aryl group or a phenyl group substituted with a phenyl group.

[0068] In the specification, the term "combined with an adjacent group to form a ring" can mean that a group is combined with an adjacent group to form a substituted or unsubstituted hydrocarbon ring or a substituted or unsubstituted heterocyclic ring. The hydrocarbon ring includes an aliphatic hydrocarbon ring and an aromatic hydrocarbon ring. The heterocyclic ring includes an aliphatic heterocyclic ring and an aromatic heterocyclic ring. The hydrocarbon ring and the heterocyclic ring can be a single ring or a multiple ring. The ring formed by being combined with each other can be connected to another ring to form a spiro structure.

[0069] In the specification, examples of the halogen atom can include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0070] In the specification, the number of carbon atoms in the alkyl group is 1 to 30, 1 to 20, 1 to 10, or 1 to 6. Examples of the alkyl group can include methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, t-butyl, isobutyl, 2-ethylbutyl, 3,3-dimethylbutyl, n-pentyl, isopentyl, neopentyl, t-pentyl, 1-methylpentyl, 3-methylpentyl, 2-ethylpentyl, 4-methyl-2-pentyl, n-hexyl, 1-methylhexyl, 2-ethylhexyl, 2-butylhexyl, n-heptyl, 1-methylheptyl, 2,2-dimethylheptyl, 2-ethylheptyl, 2-butylheptyl, n-octyl, t-octyl, 2-ethyloctyl, 2-butyloctyl, 2-hexyloctyl, 3,7-dimethyloctyl, n-nonyl, n-decyl, and the like, but are not limited thereto.

[0071] In the specification, the number of carbon atoms in the cycloalkyl group is 3 to 30, 3 to 20, 3 to 10, or 3 to 6. Examples of the cycloalkyl group can include cyclopentyl, cyclohexyl, 4-methylcyclohexyl, 4-t-butylcyclohexyl, cyclooctyl, and the like, but are not limited thereto.

[0072] In the specification, the aryl group represents any functional group or substituent derived from an aromatic hydrocarbon ring. The aryl group can be a monocyclic aryl group or a polycyclic aryl group. The number of ring-forming carbon atoms in the aryl group can be 6 to 30, 6 to 20, or 6 to 15. Examples of the aryl group can include phenyl, naphthyl, fluorenyl, anthryl, phenanthryl, biphenyl, terphenyl, quaterphenyl, quinquephenyl, sexiphenyl, benzo[9,10]phenanthryl, pyrenyl, benzofluoranthene,

[0073] The second hole transport layer HTL2 and the third hole transport layer HTL3 of the embodiment can each independently include an aromatic compound represented by any one of the following Formulae 1 to 4. The aromatic compound represented by any one of the Formulae 1 to 4 can have a relatively low refractive index. The second refractive index and the third refractive index of the second hole transport layer HTL2 and the third hole transport layer HTL3 including the aromatic compound represented by any one of the Formulae 1 to 4 can each be in the range of about 1.2 to about 1.7.

[0074] [Formula 1]

[0075]

[0076] [Formula 2]

[0077]

[0078] [Formula 3]

[0079] ​

[0080] [Formula 4]

[0081]

[0082] In Formulae 1 to 4, a, b, and f to j can each independently be an integer of 1 to 4, and c to e can each independently be an integer of 1 to 5. When a is an integer of 2 or more, then R2may all be the same or different from each other. When b is an integer of 2 or more, then R3may all be the same or different from each other. When f to i are integers of 2 or more, then R 21 , R 22 , R 23 , and R 24 may each all be the same or different from each other. When j is an integer of 2 or more, then R 32 may all be the same or different from each other. When c to e are integers of 2 or more, then R 11 to R 13 may each all be the same or different from each other. For example, when f is an integer of 2 or more, R 21 may all be the same or different from each other. For example, when c is an integer of 2 or more, R 11 may all be the same or different from each other.

[0083] In Formulae 1 to 4, R1to R3, R 11 to R 13 , R 21 to R 24 , R 31 , and R 32 may each independently be a hydrogen atom, a deuterium atom, a halogen atom, a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 30 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 30 ring-forming carbon atoms, optionally, R1to R3, R 11 to R 13 , R 21 to R 24 , R 31 , and R 32 may each independently be combined with an adjacent group to form a ring. At least one of R1to R3, at least one of R 11 to R 13 , at least one of R 21 to R 24 , and at least one of R 31 and R 32 may each independently be a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms or a substituted or unsubstituted cycloalkyl group having 3 to 30 carbon atoms. However, this is presented by way of example, and embodiments of the inventive concept are not limited thereto.

[0084] According to an embodiment, in Formula 2, R 11 to R 13 Each of at least one of R

[0085]

[0086] The first hole transport layer HTL1 can include a compound represented by the following Formula 5. The first hole transport layer HTL1 including the compound represented by Formula 5 can exhibit a refractive index in the range of about 1.7 to about 2.2.

[0087] [Formula 5]

[0088]

[0089] In Formula 5, Ar1 and Ar2 can each independently be a hydrogen atom, a deuterium atom, a halogen atom, a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group having 2 to 30 ring-forming carbon atoms, and optionally, Ar1 and Ar2 can each independently be combined with adjacent groups to form a ring. Ar3 can be a substituted or unsubstituted aryl group having 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group having 2 to 30 ring-forming carbon atoms.

[0090] In Formula 5, a and b can each independently be 0 or 1, L1 and L2 can each independently be a substituted or unsubstituted cycloalkylene group having 3 to 10 ring-forming carbon atoms, a substituted or unsubstituted heterocycloalkylene group having 2 to 10 ring-forming carbon atoms, a substituted or unsubstituted cycloalkenylene group having 3 to 10 ring-forming carbon atoms, a substituted or unsubstituted arylene group having 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group having 2 to 60 ring-forming carbon atoms. In Formula 5, p and s can each independently be an integer of 0 to 4, q and r can each independently be an integer of 0 to 3, and R1 to R5 can each independently be a hydrogen atom, a deuterium atom, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amino group, a substituted or unsubstituted silyl group, a substituted or unsubstituted oxy group, a substituted or unsubstituted alkyl group having 1 to 60 carbon atoms, a substituted or unsubstituted heterocycloalkyl group having 3 to 60 ring-forming carbon atoms, a substituted or unsubstituted aryl group having 6 to 60 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group having 2 to 60 ring-forming carbon atoms.

[0091] The first hole transport layer HTL1 of the embodiment can include at least one of the compounds in the following Compound Group 1. The first hole transport layer HTL1 including at least one of the compounds in Compound Group 1 can exhibit a refractive index in the range of about 1.7 to about 2.2.

[0092] [Compound Group 1]

[0093]

[0094]

[0095]

[0096] According to the embodiment, the hole transport region HTR can further include a hole injection layer HIL or an electron blocking layer EBL. The hole injection layer HIL can be disposed between the first electrode EL1 and the third hole transport layer HTL3. The hole injection layer HIL can have a refractive index less than the first refractive index of the first hole transport layer HTL1. The hole injection layer HIL can have a refractive index identical to the third refractive index of the third hole transport layer HTL3. The hole injection layer HIL can have a refractive index different from the third refractive index of the third hole transport layer HTL3. The hole injection layer HIL can have a refractive index in the range of about 1.2 to about 1.7. The difference between the first refractive index and the refractive index of the hole injection layer HIL can be in the range of about 0.1 to about 1.0. The hole injection layer HIL can include an aromatic compound represented by any one of the above-mentioned Formulae 1 to 4.

[0097] The electron blocking layer EBL can be disposed between the second hole transport layer HTL2 and the emission layer EML. The electron blocking layer EBL can have a refractive index greater than the second refractive index of the second hole transport layer HTL2. The electron blocking layer EBL can have a refractive index greater than the refractive index of the emission layer EML, which will be described later. For example, the electron blocking layer EBL can have a refractive index greater than the second refractive index and the refractive index of the emission layer EML. The electron blocking layer EBL can have a refractive index in the range of about 1.7 to about 2.2. The difference between the refractive index of the electron blocking layer EBL and the second refractive index and the difference between the refractive index of the electron blocking layer EBL and the refractive index of the emission layer EML can each be in the range of about 0.1 to about 1.0.

[0098] According to an embodiment, the hole transport region HTR can include a first hole transport layer HTL1, a second hole transport layer HTL2, and a third hole transport layer HTL3. The second hole transport layer HTL2 and the third hole transport layer HTL3 among the first hole transport layer HTL1, the second hole transport layer HTL2, and the third hole transport layer HTL3 can be disposed above or below the first hole transport layer HTL1. The second hole transport layer HTL2 and the third hole transport layer HTL3 have a lower refractive index than the first hole transport layer HTL1, and thus a difference between a first refractive index of the first hole transport layer HTL1 and a second refractive index of the second hole transport layer HTL2 and a difference between the first refractive index of the first hole transport layer HTL1 and a third refractive index of the third hole transport layer HTL3 can each be in a range of about 0.1 to about 1.0.

[0099] The hole transport region HTR can be formed using various methods such as a vacuum deposition method, a spin coating method, a casting method, a Langmuir-Blodgett (LB) method, an inkjet printing method, a laser printing method, and a laser-induced thermal imaging (LITI) method.

[0100] The hole injection layer HIL can include an aromatic compound represented by any one of the above-described Formulae 1 to 4. The hole injection layer HIL can include, for example, a phthalocyanine compound (such as copper phthalocyanine), N,N'-diphenyl-N,N'-bis[4-(di-m-tolyl-amino)-phenyl]-biphenyl-4,4'-diamine (DNTPD), 4,4',4"-[tris(3-methylphenyl)phenylamino]triphenylamine (m-MTDATA), 4,4',4"-tris(N,N-diphenylamino)triphenylamine (TDATA), 4,4',4"-tris{N-(2-naphthyl)-N-phenylamino}triphenylamine (2-TNATA), poly(3,4-ethylenedioxythiophene) / poly(4-styrenesulfonate) (PEDOT / PSS), polyaniline / dodecylbenzenesulfonic acid (PANI / DBSA), polyaniline / camphor sulfonic acid (PANI / CSA), polyaniline / poly(4-styrenesulfonate) (PANI / PSS), N,N'-bis(naphthalen-1-yl)-N,N'-diphenyl-benzidine (NPB), triphenylamine-containing polyether ketone (TPAPEK), 4-isopropyl-4'-methyl diphenyl iodonium tetrakis(pentafluorophenyl)borate, dipyrazino[2,3-f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexanitrile (HAT-CN), or the like.

[0101] The first hole transport layer HTL1, the second hole transport layer HTL2, and the third hole transport layer HTL3 can each further include a known hole transport layer material. For example, the first hole transport layer HTL1, the second hole transport layer HTL2, and the third hole transport layer HTL3 can each further include a carbazole derivative such as N-phenylcarbazole and polyvinylcarbazole, a fluorene derivative, N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (TPD), a triphenylamine derivative such as 4,4',4"-tris(N-carbazolyl)triphenylamine (TCTA), N,N'-di(naphthalen-1-yl)-N,N'-diphenyl-benzidine (NPB), 4,4'-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC), 4,4'-bis[N,N'-(3-methylphenyl)amino]-3,3'-dimethylbiphenyl (HMTPD), 1,3-bis(N-carbazolyl)benzene (mCP), or the like.

[0102] The electron blocking layer EBL can include, for example, a carbazole derivative such as N-phenylcarbazole and polyvinylcarbazole, a fluorene derivative, N,N'-bis(3-methylphenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'-diamine (TPD), a triphenylamine derivative such as 4,4',4"-tris(N-carbazolyl)triphenylamine (TCTA), N,N'-di(naphthalen-1-yl)-N,N'-diphenyl-benzidine (NPB), 4,4'-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC), 4,4'-bis[N,N'-(3-methylphenyl)amino]-3,3'-dimethylbiphenyl (HMTPD), 9-(4-tert-butylphenyl)-3,6-bis(triphenylsilyl)-9H-carbazole (CzSi), 9-phenyl-9H-3,9'-dicarbazole (CCP), 1,3-bis(N-carbazolyl)benzene (mCP), 1,3-bis(1,8-dimethyl-9H-carbazol-9-yl)benzene (mDCP), or the like.

[0103] In addition to the above-described materials, the hole transport region HTR can further include a charge generating material to improve conductivity. The charge generating material can be uniformly or non-uniformly dispersed in the hole transport region HTR. The charge generating material can be, for example, a p-dopant. The p-dopant can be one of a quinone derivative, a metal oxide, and a cyano-containing compound, but is not limited thereto. For example, non-limiting examples of the p-dopant can include a quinone derivative such as tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), a metal oxide such as tungsten oxide and molybdenum oxide, or the like, but is not limited thereto.

[0104] The emission layer EML is disposed on the hole transport region HTR. According to an embodiment, the emission layer EML can have a refractive index less than the first refractive index described above. The emission layer EML can have a refractive index in a range of about 1.2 to about 1.7. When the hole transport region HTR includes the electron blocking layer EBL, the emission layer EML can have a refractive index less than the refractive index of the electron blocking layer EBL. The emission layer EML can have a refractive index identical to the second refractive index. The emission layer EML can have a refractive index identical to the third refractive index. The emission layer EML can have a refractive index different from the second refractive index. The emission layer EML can have a refractive index different from the third refractive index. The emission layer EML, the second refractive index, and the third refractive index can all be identical. However, this is presented by way of example, and embodiments of the inventive concept are not limited thereto. A difference between the refractive index of the emission layer EML and the first refractive index can be in a range of about 0.1 to about 1.0. A difference between the refractive index of the emission layer EML and the refractive index of the electron blocking layer EBL can be in a range of about 0.1 to about 1.0.

[0105] The emission layer EML can have a thickness, for example, in a range of about to about The thickness of the emission layer EML can be, for example, in a range of about to about The emission layer EML can have a single layer formed of a single material, a single layer formed of different materials, or a multi-layer structure having a plurality of layers formed of different materials.

[0106] The emission layer EML can include an aromatic compound represented by any one of the above-described Formulae 1 to 4. The emission layer EML can further include an anthracene derivative, a pyrene derivative, a fluoranthene derivative, a dihydrobenzanthracene derivative, or a benzo[9,10]phenanthrene derivative. For example, the emission layer EML can further include an anthracene derivative or a pyrene derivative.

[0107] For example, the emission layer EML can further include an anthracene derivative represented by the following Formula A.

[0108] [Formula A]

[0109]

[0110] In Formula A, R 31 to R 40 may each independently be a hydrogen atom, a deuterium atom, a halogen atom, a substituted or unsubstituted silyl group, a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted aryl group having 6 to 30 ring-forming carbon atoms, or a substituted or unsubstituted heteroaryl group having 2 to 30 ring-forming carbon atoms, optionally, R 31 to R 40may each independently be combined with an adjacent group to form a ring. In Formula A, R 31 to R 40 may be combined with an adjacent group to form a saturated hydrocarbon ring or an unsaturated hydrocarbon ring. For example, in Formula A, R 31 to R 40 may be optionally combined with an adjacent group to form a saturated hydrocarbon ring or an unsaturated hydrocarbon ring. In Formula A, c and d can each independently be an integer of 0 to 5.

[0111] Formula A can be represented by any one of the following compounds 3-1 to compound 3-16.

[0112]

[0113] In the organic light emitting elements 10 and 10a of the embodiments, the emission layer EML can include a host and a dopant, and the emission layer EML can include a compound represented by Formula A described above as a host material.

[0114] The emission layer EML can further include a conventional material known in the art as a host material. For example, the emission layer EML can include at least one of bis[2-(diphenylphosphino)phenyl]ether oxide (DPEPO), 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP), 1,3-bis(carbazol-9-yl)benzene (mCP), 2,8-bis(diphenylphosphoryl)dibenzo-furan (PPF), 4,4',4"-tris(carbazol-9-yl)triphenylamine (TCTA), and 1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene (TPBi) as a host material. However, embodiments of the inventive concept are not limited thereto, and for example, tris(8-hydroxyquinolinato)aluminum (Alq3), poly(N-vinylcarbazole) (PVK), 9,10-di(naphthalen-2-yl)anthracene (ADN), 2-tert-butyl-9,10-di(naphthalen-2-yl)anthracene (TBADN), distyrylarylidene (DSA), 4,4'-bis(9-carbazolyl)-2,2'-dimethyl-chlorophenyl (CDBP), 2-methyl-9,10-bis(naphthalen-2-yl)anthracene (MADN), hexaphenylcyclotriphosphazene (CP1), 1,4-bis(triphenylsilyl)benzene (UGH2), hexaphenylcyclotrisiloxane (DPSiO3), octaphenylcyclotetrasiloxane (DPSiO4), and the like can be used as a host material.

[0115] As a known dopant material, the emission layer EML can include styryl derivatives (e.g., 1,4-bis[2-(3-N-ethylcarbazolyl)vinyl]benzene (BCzVB), 4-(di-p-tolylamino)-4'-[(di-p-tolylamino)styryl]biphenyl (DPAVB), and N-(4-((E)-2-(6-((E)-4-(diphenylamino)styryl)naphthalen-2-yl)vinyl)phenyl)-N-phenylaniline (N-BDAVBi)), perylene and derivatives thereof (e.g., 2,5,8,11-tetra-tert-butylperylene (TBP)), pyrene and derivatives thereof (e.g., 1,1'-dipyrene, 1,4-dipyrenylbenzene, 1,4-bis(N,N-diphenylamino)pyrene), etc.

[0116] The emission layer EML can include a known phosphorescent dopant material. For example, as a phosphorescent dopant, a metal complex including iridium (Ir), platinum (Pt), osmium (Os), gold (Au), titanium (Ti), zirconium (Zr), hafnium (Hf), europium (Eu), terbium (Tb), or thulium (Tm) can be used. For example, bis(4,6-difluorophenylpyridinato-N,C2)picolinate iridium(III) (FIrpic), bis(2,4-difluorophenylpyridinato)-tetrakis(1-pyrazolyl)borate iridium(III) (FIr6), octaethylporphyrin platinum (PtOEP), etc. can be used. However, embodiments of the inventive concept are not limited thereto. The emission layer EML can further include a known phosphorescent host material, for example, can further include bis(4-(9H-carbazol-9-yl)phenyl)diphenylsilane (BCPDS).

[0117] The emission layer EML can emit blue light. The emission layer EML can further include a fluorescent material including any one selected from the group consisting of, for example, spiro-DPVBi, spiro-6P, distyryl-benzene (DSB), distyryl-arylene (DSA), polyfluorene-based polymer (PFO), and poly(p-phenylenevinylene)-based polymer (PPV). When the emission layer EML emits blue light, a dopant included in the emission layer EML can be selected from, for example, a metal complex such as (4,6-F2ppy)2Irpic or an organometallic complex, perylene and derivatives thereof.

[0118] According to an embodiment, the electron transport region ETR can be disposed on the emission layer EML and can include an electron transport layer ETL. The electron transport region ETR can include a hole blocking layer HBL. The hole blocking layer HBL can be disposed between the emission layer EML and the electron transport layer ETL. For example, the hole blocking layer HBL can be disposed on the emission layer EML. The hole blocking layer HBL can have a refractive index in a range of about 1.7 to about 2.2. The refractive index of the hole blocking layer HBL can be greater than the refractive index of the emission layer EML. The refractive index of the hole blocking layer HBL can be greater than the refractive index of the electron transport layer ETL. The difference between the refractive index of the hole blocking layer HBL and the refractive index of the emission layer EML and the difference between the refractive index of the hole blocking layer HBL and the refractive index of the electron transport layer ETL can be in a range of about 0.1 to about 1.0.

[0119] The refractive index of the electron transport layer ETL can be less than the first refractive index. The electron transport layer ETL can have a refractive index in a range of about 1.2 to about 1.7. The difference between the first refractive index and the refractive index of the electron transport layer ETL can be in a range of about 0.1 to about 1.0. The refractive index of the electron transport layer ETL can be the same as the refractive index of the emission layer EML. The refractive index of the electron transport layer ETL can be different from the refractive index of the emission layer EML. The refractive index of the electron transport layer ETL can be less than the refractive index of the hole blocking layer HBL. As described above, the difference between the refractive index of the hole blocking layer HBL and the refractive index of the electron transport layer ETL can be in a range of about 0.1 to about 1.0. The electron transport layer ETL can include an aromatic compound represented by any one of the above-described Equation 1 to Equation 4.

[0120] The second refractive index of the second hole transport layer HTL2, the third refractive index of the third hole transport layer HTL3, the refractive index of the emission layer EML, and the refractive index of the electron transport layer ETL can be the same. The second refractive index of the second hole transport layer HTL2, the third refractive index of the third hole transport layer HTL3, the refractive index of the emission layer EML, and the refractive index of the electron transport layer ETL can be different from each other. For example, the third refractive index, the refractive index of the emission layer EML, and the refractive index of the electron transport layer ETL can be the same, and the second refractive index can be different from the third refractive index, the refractive index of the emission layer EML, and the refractive index of the electron transport layer ETL. For example, the third refractive index and the refractive index of the electron transport layer ETL can be the same, and the second refractive index and the refractive index of the emission layer EML can be different from the third refractive index and the refractive index of the electron transport layer ETL. The third refractive index and the refractive index of the emission layer EML can be the same, and the second refractive index and the refractive index of the electron transport layer ETL can be different from the third refractive index and the refractive index of the emission layer EML. However, this is presented as an example, and embodiments of the inventive concept are not limited thereto.

[0121] The electron transport region ETR can be formed using various methods such as a vacuum deposition method, a spin coating method, a casting method, a Langmuir-Blodgett (LB) method, an inkjet printing method, a laser printing method, a laser induced thermal imaging (LITI) method, or the like.

[0122] When the electron transport region ETR includes an electron transport layer ETL, the electron transport layer ETL can include an anthracene compound. However, embodiments of the inventive concept are not limited thereto, and the electron transport layer ETL can include, for example, tris(8-hydroxyquinoline)aluminum (Alq3), 1,3,5-tris[(3-pyridyl)-benzene-3-yl]benzene, 2,4,6-tris(3'-(pyridin-3-yl)biphenyl-3-yl)-1,3,5-triazine, 2-(4-(N-phenylbenzoimidazol-1-yl)phenyl)-9,10-dinaphthylanthracene, 1,3,5-tris(1-phenyl-1H-benzo[d]imidazol-2-yl)benzene (TPBi), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), 4,7-diphenyl-1,10-phenanthroline (Bphen), 3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole (TAZ), 4-(naphthalen-1-yl)-3,5-diphenyl-4H-1,2,4-triazole (NTAZ), 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (tBu-PBD), bis(2-methyl-8-hydroxyquinoline-N1,O8)-(1,1'-biphenyl-4-hydroxy)aluminum (BAlq), bis(benzoquinoline-10-hydroxy)beryllium (Bebq2), 9,10-di(naphthalen-2-yl)anthracene (ADN), 1,3-bis[3,5-di(pyridin-3-yl)phenyl]benzene (BmPyPhB), or a mixture thereof. The thickness of the electron transport layer ETL can be in the range of about 1 nm to about 200 nm, for example, about 1 nm to about 100 nm, about 1 nm to about 50 nm, about 1 nm to about 20 nm, about 1 nm to about 10 nm, about 1 nm to about 5 nm, about 1 nm to about 2 nm, about 2 nm to about 200 nm, about 2 nm to about 100 nm, about 2 nm to about 50 nm, about 2 nm to about 20 nm, about 2 nm to about 10 nm, about 2 nm to about 5 nm, about 5 nm to about 200 nm, about 5 nm to about 100 nm, about 5 nm to about 50 nm, about 5 nm to about 20 nm, about 5 nm to about 10 nm, about 10 nm to about 200 nm, about 10 nm to about 100 nm, about 10 nm to about 50 nm, about 10 nm to about 20 nm, about 20 nm to about 200 nm, about 20 nm to about 100 nm, about 20 nm to about 50 nm, about 50 nm to about 200 nm, about 50 nm to about 100 nm, or about 100 nm to about 200 nm. to about 200 nm. For example, the thickness of the electron transport layer ETL can be in the range of about 1 nm to about 100 nm, about 1 nm to about 50 nm, about 1 nm to about 20 nm, about 1 nm to about 10 nm, about 1 nm to about 5 nm, about 1 nm to about 2 nm, about 2 nm to about 100 nm, about 2 nm to about 50 nm, about 2 nm to about 20 nm, about 2 nm to about 10 nm, about 2 nm to about 5 nm, about 5 nm to about 100 nm, about 5 nm to about 50 nm, about 5 nm to about 20 nm, about 5 nm to about 10 nm, about 10 nm to about 100 nm, about 10 nm to about 50 nm, about 10 nm to about 20 nm, about 20 nm to about 100 nm, about 20 nm to about 50 nm, about 50 nm to about 100 nm, or about 100 nm. When the thickness of the electron transport layer ETL satisfies the above range, satisfactory electron transport properties can be obtained without significantly increasing the driving voltage.

[0123] ​The electron transport region ETR can further include an electron injection layer. When the electron transport region ETR includes the electron injection layer, the electron injection layer can be a metal halide (such as LiF, NaCl, CsF, RbCl, RbI, CuI, and KI), a lanthanide metal (such as Yb), a composite of a metal halide and a lanthanide metal (such as KI:Yb and RbI:Yb), a metal oxide (such as Li2O and BaO), or lithium quinolate (LiQ), but is not limited thereto. The electron injection layer can also be formed of a mixture material of an electron transport material and an insulating organic metal salt. The organic metal salt can be a material having a band gap greater than or equal to about 4 eV. For example, the organic metal salt can include, for example, a metal acetate, a metal benzoate, a metal acetylacetate, a metal acetylacetonate, or a metal stearate. The thickness of the electron injection layer can be in the range of about to about For example, the thickness of the electron injection layer can be in the range of about to about When the thickness of the electron injection layer satisfies the above range, satisfactory electron injection properties can be obtained without significantly increasing the driving voltage.

[0124] As described above, the electron transport region ETR can include a hole blocking layer HBL. The hole blocking layer HBL can include, for example, at least one of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) and 4,7-diphenyl-1,10-phenanthroline (Bphen), but embodiments of the inventive concept are not limited thereto.

[0125] A second electrode EL2 is disposed on the electron transport region ETR. The second electrode EL2 can be a common electrode. The second electrode EL2 can be an anode or a cathode. For example, when the first electrode EL1 is an anode, the second electrode EL2 can be a cathode. For example, when the first electrode EL1 is a cathode, the second electrode EL2 can be an anode. The second electrode EL2 can be a transmissive electrode, a transreflective electrode, or a reflective electrode. When the second electrode EL2 is a transmissive electrode, the second electrode EL2 can be formed of a transparent metal oxide such as indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium tin zinc oxide (ITZO), or the like.

[0126] When the second electrode EL2 is a transflective electrode or a reflective electrode, the second electrode EL2 can include Ag, Mg, Cu, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, LiF, Mo, Ti, Yb, a compound thereof, a mixture thereof (e.g., AgYb, MgAg), or a material having a multi-layer structure such as LiF / Ca or LiF / Al. For example, the second electrode EL2 can have a multi-layer structure including a reflective film or a transflective film formed of the above-described materials and a transparent conductive film formed of indium tin oxide (ITO), indium zinc oxide (IZO), zinc oxide (ZnO), indium tin zinc oxide (ITZO), or the like.

[0127] Although not shown, the second electrode EL2 can be connected with an auxiliary electrode. When the second electrode EL2 is connected with the auxiliary electrode, the resistance of the second electrode EL2 can be reduced.

[0128] A cap layer CPL can be further provided on the second electrode EL2. The cap layer CPL can be a single layer or a multi-layer. The cap layer CPL can be an organic layer or an inorganic layer. For example, when the cap layer CPL includes an inorganic material, the inorganic material can include an alkali metal compound such as LiF, an alkaline earth metal compound such as MgF2, SiON, SiN x , SiO y , etc.

[0129] For example, when the cap layer CPL includes an organic material, the organic material can include α-NPD, NPB, TPD, m-MTDATA, Alq3, CuPc, N4,N4,N4',N4'-Tetrakis(3-methyl-phenyl)-diphenylamine (TPD15), 4,4',4"-Tris(9H-carbazol-9-yl)-triphenylamine (TCTA), etc., or can include an epoxy resin or an acrylate such as methacrylate. However, embodiments of the inventive concept are not limited thereto, and can further include the following compounds P1 to P5.

[0130]

[0131]

[0132] The cap layer CPL can have a refractive index equal to or greater than about 1.6. For example, the cap layer CPL can have a refractive index equal to or greater than about 1.6 in a wavelength range of about 550 nm to about 660 nm.

[0133] An encapsulation layer (not shown) may be further included on the capping layer CPL. The encapsulation layer may be an organic layer, an inorganic layer, or a composite material layer. The encapsulation layer may include at least one organic layer and at least one inorganic layer. The organic layer included in the encapsulation layer may be a compound in which photopolymerization is possible, and may include, for example, acryloyl or epoxy materials. The inorganic layer included in the encapsulation layer may include materials such as SiON and SiO2. x and SiN y Materials.

[0134] Figure 3 yes Figure 2 An enlarged schematic cross-sectional view of region AA is shown, illustrating how reflections are induced at the interface LF between the second hole transport layer HTL2 and the first hole transport layer HTL1, and at the interface EF between the emitter layer EML and the hole blocking layer HBL. Figure 3 The diagram shows that light LX, generated in the emitter layer EML and incident on the second hole transport layer HTL2, is reflected at the interface LF between the second hole transport layer HTL2 and the first hole transport layer HTL1. The greater the difference between the second refractive index of the second hole transport layer HTL2 and the first refractive index of the first hole transport layer HTL1, the larger the angle α between the line LH perpendicular to the interface LF and the incident light LX becomes. As the angle α increases, the downward-facing light LZ can decrease, and the upward-facing light LY can increase.

[0135] Figure 3 The diagram shows that light EX, generated in the emitter layer EML and guided to the hole-blocking layer HBL, is reflected at the interface EF between the emitter layer EML and the hole-blocking layer HBL. The greater the difference between the refractive index of the emitter layer EML and the refractive index of the hole-blocking layer HBL, the larger the angle β between the line EH perpendicular to the interface EF and the incident light EX becomes. As the angle β increases, the upward-facing light EZ can be reduced. The upward-facing light EZ is refracted light, and reducing the amount of refracted light can improve the top emission efficiency of the organic light-emitting element (OLED). The top emission efficiency of the OLED can be considered relative to the efficiency of unrefracted straight light.

[0136] The organic light emitting elements 10 and 10a according to the embodiments can include a second hole transport layer HTL2, a third hole transport layer HTL3, an emission layer EML, and an electron transport layer ETL, each of which has a lower refractive index than the first hole transport layer HTL1 and each of which has a lower refractive index than the hole blocking layer HBL. The second refractive index of the second hole transport layer HTL2, the third refractive index of the third hole transport layer HTL3, the refractive index of the emission layer EML, and the refractive index of the electron transport layer ETL can each be about 0.1 to about 1.0 less than the first refractive index of the first hole transport layer HTL1. An increase in reflection due to the difference in refractive index can cause an increase in the amount of light in the emission layer EML that is directed upward. Thus, the organic light emitting elements 10 and 10a according to the embodiments can exhibit excellent light emitting efficiency.

[0137] Figure 4 FIG. 4 of the drawings shows light emitting efficiency when any one of the functional layers among the first hole transport layer HTL1, the second hole transport layer HTL2, and the third hole transport layer HTL3, the emission layer EML, and the electron transport layer ETL has a refractive index of about 1.62. Figure 4 FIG. 5 of the drawings shows light emitting efficiency of the organic light emitting element 10 or 10a when any one of the functional layers included in the organic light emitting element 10 or 10a, i.e., the first hole transport layer HTL1, the second hole transport layer HTL2, and the third hole transport layer HTL3, the emission layer EML, and the electron transport layer ETL, contains a compound having a relatively low refractive index. The efficiency “100%” represents light emitting efficiency of the organic light emitting element without the compound having a relatively low refractive index, Figure 4 The “efficiency” in FIG. 5 of the drawings represents a relative value given based on 100%. Hereinafter, a compound that exhibits a low refractive index can be referred to as a “low refractive index compound”. In Figure 4 In FIG. 5 of the drawings, the low refractive index compound can be a compound represented by H1 and / or H2 below.

[0138]

[0139] Referring to Figure 4It is seen that, when the low refractive index compound is included in the first hole transport layer HTL1, the luminous efficiency is reduced. For example, it is seen that, when the hole transport layer having a low refractive index among the three hole transport layers is disposed at the center and the other two hole transport layers having a high refractive index are disposed on both sides, the luminous efficiency is reduced. For example, it is seen that, when the second hole transport layer HTL2, the third hole transport layer HTL3, the emission layer EML, or the electron transport layer ETL include the low refractive index compound, excellent luminous efficiency is shown. Thus, it is concluded that the organic light emitting elements 10 and 10a of the embodiments in which the second refractive index of the second hole transport layer HTL2, the third refractive index of the third hole transport layer HTL3, the refractive index of the emission layer EML, and the refractive index of the electron transport layer ETL are lower than the first refractive index of the first hole transport layer HTL1 can exhibit excellent luminous efficiency.

[0140] Figure 5 is a graph showing luminous efficiency of organic light emitting elements according to color coordinates CIE(y) of comparative examples and examples. The color coordinates CIE(y) correspond to the "y" value of the color coordinates of light emitted from the organic light emitting elements of the comparative examples and examples. The organic light emitting elements of the comparative examples and examples have the same element configuration except for the hole transport layer, and the organic light emitting elements of the comparative examples each include only one hole transport layer, while the organic light emitting elements of the examples each include the first to third hole transport layers. The organic light emitting elements of the examples are each an organic light emitting element according to the embodiments of the inventive concept. The organic light emitting elements of the comparative examples do not include the low refractive index compound, while the organic light emitting elements of the examples include the low refractive index compound in the second hole transport layer, the third hole transport layer, the emission layer, and the electron transport layer, and the second hole transport layer, the third hole transport layer, the emission layer, and the electron transport layer can all have a refractive index of about 1.4.

[0141] Referring to Figure 5 , it is seen that, in the range of color coordinate values of about 0.045 to about 0.055, the efficiency of the organic light emitting elements of the examples is improved compared to the organic light emitting elements of the comparative examples. The organic light emitting elements of the examples exhibit an improvement of 205% in luminous efficiency compared to the organic light emitting elements of the comparative examples. It is concluded that, unlike the organic light emitting elements of the comparative examples which do not have the low refractive index compound, the organic light emitting elements of the examples include the low refractive index compound in the second hole transport layer, the third hole transport layer, the emission layer, and the electron transport layer, thereby having improved luminous efficiency.

[0142] The organic light emitting element according to an embodiment includes three hole transport layers, and can show that the refractive indices of the two hole transport layers disposed on both sides are lower than the refractive index of the one hole transport layer disposed at the center. The first refractive index of the first hole transport layer disposed at the center can be greater than the second refractive index of the second hole transport layer and the third refractive index of the third hole transport layer, the second hole transport layer and the third hole transport layer being disposed on both sides. The organic light emitting element can include an emission layer and an electron transport layer having a refractive index lower than that of the adjacent functional layer. The organic light emitting element of the embodiment includes a structure in which a layer including a material exhibiting a low refractive property and a layer including a material exhibiting a high refractive property are alternately stacked, and thus light reflection due to a difference in refractive index between the functional layers can be increased, thereby having improved light emitting efficiency.

[0143] The organic light emitting element of the embodiment includes a functional layer having a low refractive index, and thus can exhibit improved light emitting efficiency.

[0144] Although the inventive concept has been described with reference to the embodiments of the inventive concept, it will be appreciated that the inventive concept is not limited to the embodiments, and various changes and modifications can be made by those skilled in the art without departing from the spirit and scope of the inventive concept.

[0145] Therefore, the technical scope of the inventive concept is not intended to be limited to what is set forth in the specific embodiments of the specification, but is intended to be defined by the claims.

Claims

1. An organic light-emitting element comprising: a first electrode; a hole transport region provided over the first electrode; an emission layer provided over the hole transport region; an electron transport region provided over the emission layer, the electron transport region including an electron transport layer; and a second electrode provided over the electron transport region, wherein the hole transport region includes: a first hole transport layer having a first refractive index; a second hole transport layer provided over the first hole transport layer, the second hole transport layer having a second refractive index smaller than the first refractive index; and a third hole transport layer provided below the first hole transport layer, the third hole transport layer having a third refractive index smaller than the first refractive index, a difference between the first refractive index and the second refractive index is in a range of 0.1 to 1.0, and a difference between the first refractive index and the third refractive index is in a range of 0.1 to 1.0, wherein the third hole transport layer includes an aromatic compound represented by one of Formulae 1 to 4: [Formula 1] [Formula 2] [Formula 3] [Formula 4] wherein in Formulae 1 to 4, a, b, and f to j are each independently an integer of 1 to 4, c to e are each independently an integer of 1 to 5, and the substituents in the substituted alkyl group having 1 to 30 carbon atoms, the substituted cycloalkyl group having 3 to 30 carbon atoms, and the substituted aryl group having 6 to 30 ring carbon atoms are at least one selected from a deuterium atom, a halogen atom, an alkyl group having 1 to 6 carbon atoms, and an aryl group having 6 to 15 carbon atoms.

2. The organic light-emitting element according to claim 1, wherein the hole transport region further includes an electron-blocking layer provided between the second hole transport layer and the emission layer, and the electron-blocking layer has a refractive index larger than that of the emission layer and larger than the second refractive index. The thickness of the second hole transport layer and the thickness of the third hole transport layer are each in a range of 30 % to 40 % of the total thickness of the first hole transport layer to the third hole transport layer. The second refractive index and the third refractive index are each in a range of 1.2 to 1.

7. The first refractive index is in a range of 1.7 to 2.

2. The second hole transport layer includes the aromatic compound represented by one of Formulae 1 to 4. The emission layer and the electron transport layer each include the aromatic compound represented by one of Formulae 1 to 4. The refractive index of the emission layer and the refractive index of the electron transport layer are each smaller than the first refractive index.

9. The organic light-emitting element according to claim 1, wherein the electron transport region further includes a hole-blocking layer provided over the emission layer, and the refractive index of the emission layer and the refractive index of the electron transport layer are each smaller than the refractive index of the hole-blocking layer.

10. The organic light-emitting element according to claim 1, further comprising a hole injection layer provided between the first electrode and the third hole transport layer, wherein ​ ​ ​ ​ ​ ​ ​ ​ ， ​ ​ ​ R1to R3, R 11 to R 13 , R 21 to R 24 , R 31 and R 32 are each independently a hydrogen atom, a deuterium atom, a halogen atom, a substituted or unsubstituted alkyl group having 1 to 30 carbon atoms, a substituted or unsubstituted cycloalkyl group having 3 to 30 carbon atoms, or a substituted or unsubstituted aryl group having 6 to 30 ring-forming carbon atoms, and optionally, R1to R3, R 11 to R 13 , R 21 to R 24 , R 31 and R 32 are each independently combined with an adjacent group to form a ring, and at least one of R1to R3, R 11 at least one of R1to R3, R 13 at least one of R1to R3, R 21 at least one of R1to R3, R 24 at least one of R1to R3, R 31 at least one of R1to R3, R 32 each independently is substituted or unsubstituted alkyl having from 1 to 30 carbon atoms or substituted or unsubstituted cycloalkyl having from 3 to 30 carbon atoms, ​ ​ ​ ​ 3. The organic light-emitting element according to claim 1, wherein ​ 4. The organic light-emitting element according to claim 1, wherein ​ 5. The organic light-emitting element according to claim 1, wherein ​ 6. The organic light-emitting element according to claim 1, wherein ​ 7. The organic light-emitting element according to claim 6, wherein ​ 8. The organic light-emitting element according to claim 1, wherein ​ ​ ​ ​ ​ The refractive index of the hole injection layer is less than the first refractive index.

11. The organic light-emitting element according to claim 1, wherein The first hole transport layer includes at least one of the compounds in Compound Group 1: [Compound Group 1] 。 12. The organic light-emitting element according to claim 1, wherein The aromatic compound represented by Formula 2 is Compound 2-1 or Compound 2-2: 。

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