NOVEL COMPOUND FOR CAPPING LAYER AND ORGANIC LIGHT-EMITTING DEVICE COMPRISING THE SAME

Abstract

The present invention provides a novel compound for a capping layer and an organic light-emitting device containing the same.

Description

[Technical field]

[0001] The present invention relates to a compound for a capping layer and an organic light-emitting device including the same. [Background technology]

[0002] Materials used as organic layers in organic light-emitting devices are roughly classified into light-emitting materials, hole-injecting materials, hole-transporting materials, electron-transporting materials, electron-injecting materials, etc., depending on their functions.

[0003] Among them, the light-emitting materials are classified into fluorescent materials derived from a singlet excited state of electrons and phosphorescent materials derived from a triplet excited state of electrons according to the light-emitting mechanism, and are classified into blue light-emitting materials, green light-emitting materials, and red light-emitting materials according to the light-emitting color.

[0004] A typical organic light emitting device may have a structure in which an anode is formed on a substrate, and a hole transport layer, a light emitting layer, an electron transport layer, and a cathode are sequentially formed on the anode, where the hole transport layer, the light emitting layer, and the electron transport layer are organic thin films made of organic compounds. The driving principle of the organic light emitting device having the above-mentioned structure is as follows.

[0005] When a voltage is applied between the anode and the cathode, holes injected from the anode move to the light-emitting layer via the hole transport layer, and electrons injected from the cathode move to the light-emitting layer via the electron transport layer, where the holes and electrons recombine to generate excitons.

[0006] Light is generated as these excitons change from an excited state to a ground state. The efficiency of organic light-emitting devices is usually divided into internal luminous efficiency and external luminous efficiency. The internal luminous efficiency is related to how efficiently excitons are generated and light conversion is carried out in the organic layers between the first and second electrodes, such as the hole transport layer, the light-emitting layer, and the electron transport layer, and is theoretically known to be 25% for fluorescence and 100% for phosphorescence.

[0007] Meanwhile, the external luminance efficiency indicates the efficiency with which light generated in the organic layer is extracted to the outside of the organic light emitting device, and is generally known to be extracted to the outside at a level of about 20% of the internal luminance efficiency. As a method for increasing the light extraction, various organic compounds having a refractive index of 1.7 or more have been used as a capping layer to prevent the light emitted to the outside from being lost due to total reflection. In order to further increase the external luminance efficiency of the organic light emitting device, an organic light emitting device including a composite layer structure of a capping layer having a high refractive index and a capping layer having a low refractive index has been developed. LiF has been commercialized as a low refractive index capping layer material, but such inorganic compounds have been pointed out as having problems such as high deposition temperature and poor eutectic property, and efforts are ongoing to replace it with an organic compound. Boron coordination compounds are known as materials having a low refractive index, but there has been a problem that the boron coordination compounds are insufficient in stability and reduce the life of the organic light emitting device. As a result, efforts are ongoing to develop an organic capping layer material that maintains a low refractive index and has excellent compound stability. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a compound for a capping layer, which has an amine-based structure including a cycloalkyl group or a heterocyclyl group and can form a low refractive index, and in particular can maintain a wide band gap, thereby ensuring a low extinction coefficient even in a short wavelength range and achieving an even lower refractive index, and an organic light-emitting device including the compound.

[0009] Another object of the present invention is to provide a compound for a capping layer, which is very effective in improving the efficiency and color purity of an organic light-emitting device, since a cycloalkyl group or heterocyclyl group having a low polarizability can be introduced to have an even lower refractive index, and an organic light-emitting device including the compound.

[0010] Another object of the present invention is to provide a compound for a capping layer which has high thermal stability due to its structural characteristics and at the same time has excellent thin film thermal distribution properties, thereby improving stability against contamination by external oxygen, air, moisture, etc., and which is very effective in improving the life of an organic light-emitting device when used as a capping layer, and an organic light-emitting device containing the same. The above and additional issues are described in detail below. [Means for solving the problem]

[0011] In order to solve the above problems, in one embodiment, the present invention provides a method for manufacturing a semiconductor device comprising: The compound for the capping layer is represented by the following Chemical Formula 1:

[0012] <Chemical formula 1> JPEG2024524469000002.jpg37137In the above Chemical Formula 1, Cy is a substituted or unsubstituted C3-C20 cycloalkyl group or a substituted or unsubstituted C1-C20 heterocyclyl group; L is a direct bond, a substituted or unsubstituted C1-C50 alkylene group, a substituted or unsubstituted C2-C50 alkenylene group, a substituted or unsubstituted C1-C50 alkyleneoxy group, an ether group, a substituted or unsubstituted C1-C50 ester group, a substituted or unsubstituted C1-C50 sulfide group, a thioether group, a substituted or unsubstituted C1-C50 thioester group, a substituted or unsubstituted C1-C50 carbonyl group, a substituted or unsubstituted -C(X1)NR3-, or a substituted or unsubstituted -NR4C(X2)-, or a combination thereof; L1 and L2 are a direct bond, a substituted or unsubstituted C1-C50 alkylene group, a substituted or unsubstituted C2-C50 alkenylene group, a substituted or unsubstituted C1-C50 alkyleneoxy group, an ether group, a substituted or unsubstituted C1-C50 ester group, a substituted or unsubstituted C1-C50 sulfide group, a thioether group, a substituted or unsubstituted C1-C50 thioester group, a substituted or unsubstituted C1-C50 carbonyl group, a substituted or unsubstituted ?C(X1)NR3?, a substituted or unsubstituted ?NR4C(X2)?, a substituted or unsubstituted ?NR?, a substituted or unsubstituted C3-C50 cycloalkylene group, a substituted or unsubstituted C1-C50 heterocyclylene group, a substituted or unsubstituted C3-C50 arylene group, or a substituted or unsubstituted C2-C50 heteroarylene group, or a combination thereof, with the proviso that a carbazole group is excluded; X1 and X2 are each independently O, S, Se, Te, NR5, or CR6R7; R1 to R7 are each independently hydrogen, deuterium, a halogen, a nitro group, a nitrile group, a hydroxy group, a thiol group, a substituted or unsubstituted amino group, a substituted or unsubstituted C1 to C50 alkyl group, a substituted or unsubstituted C2 to C50 alkenyl group, a substituted or unsubstituted C1 to C50 alkoxy group, a substituted or unsubstituted C1 to C50 sulfide group, a substituted or unsubstituted silyl group, a substituted or unsubstituted C3 to C50 cycloalkyl group, a substituted or unsubstituted C3 to C50 cycloalkenyl group, a substituted or unsubstituted C1 to C50 heterocyclyl group, a substituted or unsubstituted C3 to C50 aryl group, or a substituted or unsubstituted C2 to C50 heteroaryl group, and adjacent pairs of R1 to R7 may or may not be bonded to each other to form a ring, with the exception of a carbazole group.

[0013] In one embodiment, the present invention provides an organic light emitting device including the compound for a capping layer described above. Effect of the Invention

[0014] The compound for the capping layer according to one embodiment of the present invention has an amine-based structure including a cycloalkyl group or a heterocyclyl group, and therefore can form a low refractive index. In particular, since it can maintain a wide band gap, it is possible to ensure a low extinction coefficient even in the short wavelength range, and thus realize an even lower refractive index.

[0015] Furthermore, by introducing a cycloalkyl group or a heterocyclyl group having a low polarizability, it is possible to obtain a lower refractive index, which is extremely effective in improving the efficiency and color purity of the organic light-emitting device.

[0016] In addition, due to its structural characteristics, it can have high thermal stability and at the same time has excellent thin film thermal distribution, thereby improving stability against contamination by external oxygen, air, moisture, etc., and when used as a capping layer, it is extremely effective in improving the life of organic light-emitting devices. The above effects and additional effects are described in detail below. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view showing a configuration of an organic light-emitting device according to an embodiment of the present invention. **Explanation of symbols** 100 Substrate 200 Hole injection layer 300 Hole transport layer 400 Light-emitting layer 500 Electron transport layer 600 Electron injection layer 1000 First electrode 2000 Second electrode 3000 Capping layer DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Before describing the present invention in detail below, it should be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention, which is limited only by the appended claims. All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art, unless otherwise defined.

[0019] Throughout this specification and the claims, unless otherwise indicated, the words comprise, comprise, and comprising are used to mean the inclusion of the stated item, step or group of items and steps and are not used to mean the exclusion of any other item, step or group of items or steps.

[0020] Throughout the present specification and claims, the term "aryl" refers to a C5-50 aromatic hydrocarbon ring group, such as phenyl, benzyl, naphthyl, biphenyl, terphenyl, fluorene, phenanthrenyl, triphenylenyl, perylenyl, chrysenyl, fluoranthenyl, benzofluorenyl, benzotriphenylenyl, benzochrysenyl, anthracenyl, stilbenyl, pyrenyl, and the like, and "heteroaryl" refers to a C2-50 aromatic ring containing at least one hetero element, such as pyrrolyl, pyrazinyl, pyridinyl, indolyl, isoindolyl, furyl, benzofuranyl, isobenzofuranyl, dibenzofuranyl, benzothiophene, and the like. It can mean including heterocyclic groups formed from a pyridine ring, a pyrazine ring, a pyrimidine ring, a pyridazine ring, a triazine ring, an indole ring, a quinoline ring, an acridine ring, a pyrrolidine ring, a dioxane ring, a piperidine ring, a morpholine ring, a piperazine ring, a carbazole ring, a furan ring, a thiophene ring, an oxazole ring, an oxadiazole ring, a benzofuran ring, a thiazole ring, a thiadiazole ring, a benzothiophene ring, a triazole ring, an imidazole ring, a benzimidazole ring, a pyran ring, a dibenzofuran ring, or the like.

[0021] In the chemical formulas, Arx (where x is an integer) means, unless otherwise defined, a substituted or unsubstituted C6-C50 aryl group or a substituted or unsubstituted C2-C50 heteroaryl group; Lx (where x is an integer) means, unless otherwise defined, a direct bond, a substituted or unsubstituted C6-C50 arylene group, or a substituted or unsubstituted C2-C50 heteroarylene group; and Rx (where x is an integer) means, unless otherwise defined, hydrogen, deuterium, halogen, a nitro group, a nitrile group, a substituted or unsubstituted C1-C30 alkyl group, a substituted or unsubstituted C2-C30 alkenyl group, a substituted or unsubstituted C1-C30 alkoxy group, a substituted or unsubstituted C1-C30 sulfide group, a substituted or unsubstituted C6-C50 aryl group, or a substituted or unsubstituted C2-C50 heteroaryl group.

[0022] Throughout this specification and the claims, the term "substituted or unsubstituted" means any of deuterium, halogen, amino group, cyano group, nitrile group, nitro group, nitroso group, sulfamoyl group, isothiocyanate group, thiocyanate group, carboxyl group, C1 to C30 alkyl group, C1 to C30 alkylsulfinyl group, C1 to C30 alkylsulfonyl group, C1 to C30 alkylsulfanyl group, C1 to C12 fluoroalkyl group, C2 to C30 alkenyl group, C1 to C30 alkoxy ... It may mean that it is substituted or unsubstituted with one or more groups selected from the group consisting of a C12 N-alkylamino group, a C2-C20 N,N-dialkylamino group, a substituted or unsubstituted C1-C30 sulfide group, a C1-C6 N-alkylsulfamoyl group, a C2-C12 N,N-dialkylsulfamoyl group, a C0-C30 silyl group, a C3-C20 cycloalkyl group, a C3-C20 heterocycloalkyl group, a C6-C50 aryl group, and a C3-C50 heteroaryl group. In addition, the same symbols throughout this specification may have the same meaning unless otherwise specified.

[0023] On the other hand, various embodiments of the present invention may be combined with any other embodiment unless clearly indicated to the contrary. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention and their effects will be described.

[0024] An organic light emitting device according to an embodiment of the present invention may include a capping layer, specifically, an organic light emitting device including a first electrode, a second electrode, one or more organic layers interposed between the first electrode and the second electrode, and a capping layer disposed outside at least one of the first electrode and the second electrode and including the compound for a capping layer of the present invention. A specific example of the compound for the capping layer of the present invention is a compound for the capping layer represented by the following Chemical Formula 1.

[0025] <Chemical formula 1> JPEG2024524469000003.jpg38137

[0026] During the ceremony, Cy is a substituted or unsubstituted C3-C20 cycloalkyl group or a substituted or unsubstituted C1-C20 heterocyclyl group; L is a direct bond, a substituted or unsubstituted C1-C50 alkylene group, a substituted or unsubstituted C2-C50 alkenylene group, a substituted or unsubstituted C1-C50 alkyleneoxy group, an ether group, a substituted or unsubstituted C1-C50 ester group, a substituted or unsubstituted C1-C50 sulfide group, a thioether group, a substituted or unsubstituted C1-C50 thioester group, a substituted or unsubstituted C1-C50 carbonyl group, a substituted or unsubstituted -C(X1)NR3-, a substituted or unsubstituted -NR4C(X2)-, or a combination thereof, and specifically may be a combination of three or less of these; L1 and L2 are each a direct bond, a substituted or unsubstituted C1-C50 alkylene group, a substituted or unsubstituted C2-C50 alkenylene group, a substituted or unsubstituted C1-C50 alkyleneoxy group, an ether group, a substituted or unsubstituted C1-C50 ester group, a substituted or unsubstituted C1-C50 sulfide group, a thioether group, a substituted or unsubstituted C1-C50 thioester group, a substituted or unsubstituted C1-C50 carbonyl group, a substituted or unsubstituted ?C(X1) NR3?, substituted or unsubstituted ?NR4C(X2)?, substituted or unsubstituted ?NR?, a substituted or unsubstituted C3-C50 cycloalkylene group, a substituted or unsubstituted C1-C50 heterocyclylene group, a substituted or unsubstituted C3-C50 arylene group, or a substituted or unsubstituted C2-C50 heteroarylene group, or a combination thereof, specifically a combination of up to three of these, except that a carbazole group is excluded; X1 and X2 are each independently O, S, Se, Te, NR5, or CR6R7; R1 to R7 are each independently hydrogen, deuterium, a halogen, a nitro group, a nitrile group, a hydroxy group, a thiol group, a substituted or unsubstituted amino group, a substituted or unsubstituted C1 to C50 alkyl group, a substituted or unsubstituted C2 to C50 alkenyl group, a substituted or unsubstituted C1 to C50 alkoxy group, a substituted or unsubstituted C1 to C50 sulfide group, a substituted or unsubstituted silyl group, a substituted or unsubstituted C3 to C50 cycloalkyl group, a substituted or unsubstituted C3 to C50 cycloalkenyl group, a substituted or unsubstituted C1 to C50 heterocyclyl group, a substituted or unsubstituted C3 to C50 aryl group, or a substituted or unsubstituted C2 to C50 heteroaryl group, and adjacent pairs of R1 to R7 may or may not be bonded to each other to form a ring, with the exception of a carbazole group.

[0027] In the above, Cy can specifically be a substituted or unsubstituted C3 to C10 cycloalkyl group. Also specifically, L2 may be a direct bond and R2 may be hydrogen. Specifically, L may be a direct bond, a carbonyl group, -CH2CO-, an ester group, a thioester group, an ether group, or a thioether group, or a combination of up to three of these.

[0028] Specific examples of the compound for a capping layer of the present invention include compounds for a capping layer in which the above Chemical Formula 1 is represented by the following Chemical Formulas 2 to 5.

[0029] <Chemical formula 2> JPEG2024524469000004.jpg38137 <Chemical formula 3> JPEG2024524469000005.jpg44137 <Chemical formula 4> JPEG2024524469000006.jpg36137 <Chemical formula 5> JPEG2024524469000007.jpg49137

[0030] In the formulas 2 and 3, The same symbols as those in Chemical Formula 1 are defined as in Chemical Formula 1.

[0031] The compounds for capping layers of the present invention represented by Chemical Formulae 2 to 5 maintain a low refractive index due to the introduction of an amide group, and at the same time, are excellent in chemical stability and thermal stability.

[0032] In the above Chemical Formula 1, at least one of R1 and R2 may be a substituted or unsubstituted C3 to C50 cycloalkyl group or a substituted or unsubstituted C1 to C50 heterocyclyl group, which can reduce the polarizability and form a low refractive index.

[0033] Specifically, R1 and R2 may each be a substituted or unsubstituted C3 to C50 cycloalkyl group, or a substituted or unsubstituted C1 to C50 heterocyclyl group, which can increase the molecular weight, improve the thermal stability, and is effective in improving the life span.

[0034] Meanwhile, in the above formula 1, L1 is a direct bond, R1 is hydrogen, and R2 can be a substituted or unsubstituted C3-C50 cycloalkyl group or a substituted or unsubstituted C1-C50 heterocyclyl group, in which case the bulk properties of the molecule are minimized and the polarizability is lower, thereby further improving the efficiency.

[0035] In the above Chemical Formulas 1 to 5, Cy can be a substituted C3 to C20 cycloalkyl group or a substituted C1 to C20 heterocyclyl group, which can further improve the thermal stability and simultaneously reduce the polarizability to form a low refractive index.

[0036] The substituents of Cy are not limited, and each may be independently selected from the group consisting of a hydroxyl group, a thiol group, an amino group, an alkyl group having 1 to 30 carbon atoms, an alkoxy group having 1 to 30 carbon atoms, a sulfide group having 1 to 30 carbon atoms, a silyl group having 0 to 30 carbon atoms, a halogen group, a cycloalkyl group having 3 to 30 carbon atoms, a heterocyclyl group having 1 to 30 carbon atoms, and combinations thereof. By having such a substituent, it is possible to maintain a low refractive index and at the same time have high thermal stability. In addition, in the above Chemical Formulae 1 to 5, the above Cy can be selected from the following Chemical Structural Formulae A-1 to A-21.

[0037] JPEG2024524469000008.jpg117137JPEG2024524469000009.jpg100137

[0038] In the chemical structural formulas A-1 to A-21, W1 is each independently a methyl group, an ethyl group, a t-butyl group, a cyclohexyl group, an adamantane group, a dihydroamine group, a dimethylamine group, a hydroxyl group, a methoxy group, a mercaptan group, a methylthio group, a fluoro group, a trifluoromethyl group, or a trimethylsilyl group; n is independently an integer of 0 to 10, specifically an integer of 0 to 4, * indicates the bond position. In addition, in the above Chemical Formula 1, at least one of -L1-R1 and -L2-R2 can be independently selected from the following Chemical Structural Formulas B-1 to B-47.

[0039] JPEG2024524469000010.jpg112137JPEG2024524469000011.jpg126130 JPEG2024524469000012.jpg118130 JPEG2024524469000013.jpg84137

[0040] In the above chemical structural formula, each W1 is independently a methyl group, an ethyl group, a t-butyl group, a cyclohexyl group, an adamantane group, a dihydroamine group, a dimethylamine group, a hydroxyl group, a methoxy group, a mercaptan group, a methylthio group, a nitrile group, a nitro group, a fluoro group, a trifluoromethyl group, or a trimethylsilyl group; n is independently an integer of 0 to 10, specifically an integer of 0 to 4, * indicates the bond position.

[0041] In addition, one or more of -L1-R1 and -L2-R2 may each independently have a chemical structural formula in which the -CO* structure in the chemical structural formulas B-1 to B-47 is changed to -Z-* or *-Z-, and Z may be selected from -O-, -S-, -CH2CO-, -CH2-NH-CO-, -O-NH-CO-, -S-NH-CO-, -CO-NH-CO-, -NH-C(=NMe)-, -NHC(=CHMe)-, -NHCOO-, -NH-, -CO-NH-, -OCONH-, -SCONH-, -CO-CO-NH-, -CS-, -C(=NH)-, -C(=NMe)-, -C(=CHMe)-, -SCO-, -OCO-, -COCO-, -CH2-, or "-".

[0042] In addition, the compound for a capping layer represented by Chemical Formula 1 may have a low refractive index of 1.55 or less at a wavelength of 450 nm when the refractive index is measured in a thickness range of 20 nm to 100 nm, specifically, a refractive index of 1.50 or less, more specifically, a refractive index of 1.47 or less at a wavelength of 450 nm.

[0043] In addition, the compound represented by Chemical Formula 1 may be a compound for a capping layer represented by any of the following compounds: The following compounds are merely examples for explaining the present invention, and the present invention is not limited thereto.

[0044] JPEG2024524469000014.jpg132137JPEG2024524469000015.jpg177163JPEG20245244690 00016.jpg177163JPEG2024524469000017.jpg177163JPEG2024524469000018.jpg177163 JPEG2024524469000019.jpg176163JPEG2024524469000020.jpg177163JPEG20245244690 00021.jpg177163JPEG2024524469000022.jpg176163JPEG2024524469000023.jpg177163 JPEG2024524469000024.jpg177163JPEG2024524469000025.jpg177163JPEG20245244690 00026.jpg177163JPEG2024524469000027.jpg177163JPEG2024524469000028.jpg177163 JPEG2024524469000029.jpg177163JPEG2024524469000030.jpg176163JPEG20245244690 00031.jpg176163JPEG2024524469000032.jpg177163JPEG2024524469000033.jpg132137

[0045] One embodiment of the compounds of the present invention can be synthesized according to the general scheme below.

[0046] <Scheme 1> JPEG2024524469000034.jpg39137(h is a halogen element)

[0047] As another embodiment, the present invention provides an organic light-emitting device including a capping layer, the capping layer containing the compound for the capping layer described above. Next, an organic light emitting device according to an embodiment of the present invention will be described in detail.

[0048] According to an embodiment of the present invention, an organic light emitting device may include a first electrode, a second electrode, one or more organic layers interposed between the first electrode and the second electrode, and a capping layer. The capping layer may be disposed on the outer side of at least one of the first electrode and the second electrode.

[0049] Specifically, of the two sides of the first electrode or the second electrode, the side adjacent to the organic layer interposed between the first electrode and the second electrode is referred to as the inside, and the side not adjacent to the organic layer is referred to as the outside. In other words, when a capping layer is disposed on the outside of the first electrode, the first electrode is disposed between the capping layer and the organic layer, and when a capping layer is disposed on the outside of the second electrode, the second electrode is disposed between the capping layer and the organic layer.

[0050] According to an embodiment of the present invention, the organic light emitting device may have one or more organic layers interposed between the first electrode and the second electrode, and may have a capping layer formed on the outside of at least one of the first electrode and the second electrode. That is, the capping layer may be formed on both the outside of the first electrode and the outside of the second electrode, or may be formed only on the outside of the first electrode or the outside of the second electrode.

[0051] In this case, the capping layer may include a compound for a capping layer according to the present invention, and may include a compound for a capping layer according to the present invention alone or in combination with a known compound. The capping layer may have a thickness of 100 Å to 3000 Å.

[0052] Meanwhile, the capping layer may have a composite capping layer structure in which a first capping layer having a relatively low refractive index and a second capping layer having a higher refractive index than the first capping layer are stacked, and in this case, the compound for the capping layer according to the present invention may be included in the first capping layer. The stacking order of the first capping layer and the second capping layer is not limited, and the first capping layer may be disposed outside the second capping layer, or conversely, the second capping layer may be disposed outside the first capping layer. As a specific example, the second capping layer may be interposed between the first capping layer and the first electrode or the second electrode, and specifically, the second capping layer may be in contact with the first capping layer and the first electrode, or the first capping layer and the second electrode.

[0053] Alternatively, the capping layer may have a multi-layer structure in which a number of first capping layers and a number of second capping layers are stacked. In this case, the first capping layers and the second capping layers may be stacked alternately, and the stacking order is not limited to the above, and the first capping layer may be arranged outside the second capping layer, or conversely, the second capping layer may be arranged outside the first capping layer.

[0054] In addition, the first capping layer may have a refractive index of 1.55 or less, specifically 1.50 or less, more specifically 1.47 or less, at a wavelength of 450 nm. The second capping layer may have a refractive index of 2.10 or more, specifically 2.25 or more, more specifically 2.30 or more, at a wavelength of 450 nm, and the difference between the refractive index of the first capping layer and the refractive index of the second capping layer at a wavelength of 450 nm may be in the range of 0.2 to 1.2, more specifically 0.4 to 1.2. If the difference in refractive index is less than 0.2 or exceeds 1.2, there is a problem in that the light extraction efficiency is poor. The first capping layer may have a total thickness in the range of 50 Å to 2000 Å, and the second capping layer may have a total thickness in the range of 50 Å to 2000 Å.

[0055] Meanwhile, the capping layer may have a refractive index gradient. The refractive index gradient may be such that the refractive index gradually decreases toward the outside, or may be such that the refractive index gradually increases toward the outside. For this reason, the capping layer may be formed by gradually varying the concentration of the compound for the capping layer according to the present invention, thereby realizing a refractive index gradient in the capping layer. Meanwhile, the organic layer may generally include a hole transport layer, a light emitting layer, and an electron transport layer that constitute a light emitting portion, but is not limited thereto.

[0056] More specifically, an organic light emitting device according to an embodiment of the present invention may include at least one organic layer constituting a light emitting part, such as a hole injection layer (HIL), a hole transport layer (HTL), an emission layer (EML), an electron transport layer (ETL), an electron injection layer (EIL), etc., between a first electrode (anode) and a second electrode (cathode). Optionally, a hole blocking layer (HBL, not shown) or an electron transport auxiliary layer may be further included between the emission layer (EML) and the electron transport layer (ETL), and an electron blocking layer (EBL, not shown) or an emission auxiliary layer may be further included between the hole transport layer HTL and the emission layer EML.

[0057] 1 is a cross-sectional view illustrating a schematic configuration of an organic light emitting device according to an embodiment of the present invention. The organic light emitting device according to an embodiment of the present invention can be manufactured according to the structure illustrated in FIG.

[0058] As shown in FIG. 1, the organic light emitting device may have a structure in which a substrate 100, a first electrode 1000, a hole injection layer 200, a hole transport layer 300, an emission layer 400, an electron transport layer 500, an electron injection layer 600, a second electrode 2000, and a capping layer 3000 are sequentially stacked from the bottom. Here, although not shown, the capping layer 3000 may have a structure in which a first capping layer and a second capping layer are stacked as described above. In addition, the capping layer may have a structure in which a third capping layer having a refractive index different from that of the first capping layer and the second capping layer is further added and stacked, and is not limited thereto. In addition, the capping layer may have a refractive index gradient. The refractive index gradient may be such that the refractive index gradually decreases toward the outside, or may be such that the refractive index gradually increases toward the outside.

[0059] Here, the substrate 100 may be a substrate commonly used in organic light-emitting devices, and may be a transparent glass substrate or a flexible plastic substrate having excellent mechanical strength, thermal stability, transparency, surface smoothness, ease of handling, and water resistance.

[0060] In addition, the first electrode 1000 is used as a hole injection electrode for injecting holes into the organic light emitting device. The first electrode 1000 is manufactured using a material having a low work function so that holes can be injected, and may be formed of a transparent material such as indium tin oxide (ITO), indium zinc oxide (IZO), graphene, etc.

[0061] The hole injection layer 200 may be formed by depositing a hole injection layer material on the first electrode 1000 by a method such as vacuum deposition, spin coating, casting, or LB (Langmuir-Blodgett) method. When the hole injection layer 200 is formed by the vacuum deposition method, the deposition conditions vary depending on the compound used as the material of the hole injection layer 200, the structure and thermal properties of the target hole injection layer 200, and the like, but generally can be appropriately selected from the ranges of a deposition temperature of 50 to 500°C, a vacuum degree of 10-8 to 10-3 torr, a deposition rate of 0.01 to 100 Å / sec, and a layer thickness of 10 Å to 5 μm. Meanwhile, a charge generation layer may be further deposited on the surface of the hole injection layer 200 as necessary. As the charge generation layer material, a conventional material may be used, and HATCN may be given as an example.

[0062] The hole transport layer 300 may be formed by depositing a hole transport layer material on the hole injection layer 200 by a method such as vacuum deposition, spin coating, casting, or LB method. When the hole transport layer 300 is formed by the vacuum deposition method, the deposition conditions vary depending on the compound used, but generally, the deposition conditions may be selected from the same range as the hole injection layer 200. The hole transport layer 300 may be formed using a known compound. The hole transport layer 300 may be one or more layers, and although not shown in FIG. 1, a light emitting auxiliary layer may be further formed on the hole transport layer 300.

[0063] The light-emitting layer 400 may be formed by depositing a light-emitting layer material on the hole transport layer 300 or the light-emitting auxiliary layer by a method such as vacuum deposition, spin coating, casting, or LB method. When the light-emitting layer 400 is formed by the vacuum deposition method, the deposition conditions vary depending on the compound used, but generally, they may be selected from the same range of conditions as those for forming the hole injection layer 200. The light-emitting layer material may use a known compound as a host or dopant. The dopant is not limited, but may be used together with a phosphorescent or fluorescent dopant to form the light-emitting layer. As an example, BD142 (N6,N12-bis(3,4-dimethylphenyl)-N6,N12-dimesitylchrysene-6,12-diamine) can be used as a fluorescent dopant, and green phosphorescent dopant Ir(ppy)3 (tris(2-phenylpyridine)iridium), blue phosphorescent dopant F2Irpic (iridium(III)bis[4,6-difluorophenyl)-pyridinato-N,C2']picolinate), red phosphorescent dopant RD61 manufactured by UDC, and the like can be co-evaporated (doped) by vacuum deposition. The doping concentration of the dopant is not particularly limited, but it is preferable that the dopant is doped at 0.01 to 15 parts by weight per 100 parts by weight of the host. If the content of the dopant is less than 0.01 parts by weight, there is a problem that the color is not properly developed due to the insufficient amount of dopant, and if it exceeds 15 parts by weight, there is a problem that the efficiency is rapidly reduced due to the concentration quenching phenomenon.

[0064] Here, when a phosphorescent dopant is used together with the light-emitting layer material, a hole-blocking material (HBL) can be further laminated on the upper part of the light-emitting layer 400 by a vacuum deposition method or a spin coating method in order to prevent the phenomenon that triplet excitons or holes diffuse into the electron transport layer 500. The hole-blocking material that can be used is not particularly limited, and any known material can be selected and used. For example, oxadiazole derivatives, triazole derivatives, phenanthroline derivatives, or hole-blocking materials described in JP-A-11-329734(A1) can be mentioned, and representative examples include Balq (bis(8-hydroxy-2-methylquinolinonate)-aluminum biphenoxide), phenanthrolines-based compounds (for example, BCP (bathocuproine) manufactured by UDC), and the like. Such a light-emitting layer 400 of the present invention can include one or more blue light-emitting layers.

[0065] The electron transport layer 500 is formed on the light emitting layer 400 and may be formed by a method such as vacuum deposition, spin coating, or casting. The deposition conditions for the electron transport layer 500 vary depending on the compound used, but may generally be selected from the same range of conditions as those for forming the hole injection layer 200. As a commonly known material, for example, a quinoline derivative, particularly tris(8-quinolinolato)aluminum (Alq3), or ET4 (6,6'-(3,4-dimesityl-1,1-dimethyl-1H-thiol-2,5-diyl)di-2,2'-bipyridine) may be used.

[0066] Furthermore, the electron injection layer 600 may be formed by depositing an electron injection layer material on the electron transport layer 500 by a method such as vacuum deposition, spin coating, casting, etc. As the electron injection layer material, known materials such as LiF, NaCl, CsF, Li2O, BaO, etc. may be used.

[0067] Also, the second electrode 2000 is used as an electron injection electrode and can be formed on the electron injection layer 600 by a method such as vacuum deposition or sputtering. Various metals can be used as the material of the second electrode 2000. Specific examples include, but are not limited to, lithium (Li), aluminum (Al), gold (Au), silver (Ag), magnesium (Mg), aluminum-lithium (Al-Li), calcium (Ca), magnesium-indium (Mg-In), magnesium-silver (Mg-Ag), and the like. Also, a transparent electron injection electrode using ITO or IZO can be used to obtain a full-surface light emitting device.

[0068] The organic light-emitting device of the present invention is not limited to the organic light-emitting device having a structure including the first electrode 1000, the hole injection layer 200, the hole transport layer 300, the light-emitting layer 400, the electron transport layer 500, the electron injection layer 600, the second electrode 2000 and the capping layer 3000 described above, but may have various structures and may further include one or two intermediate layers as necessary.

[0069] Meanwhile, the thickness of each organic layer formed according to the present invention can be adjusted according to the requirements, specifically, 1 to 1,000 nm, more specifically, 1 to 150 nm.

[0070] As shown in Fig. 1, the capping layer 3000 may be formed on one of both sides of the first electrode 1000, which is not provided with the hole injection layer 200. Also, the capping layer 3000 may be formed on one of both sides of the second electrode 2000, which is not provided with the electron injection layer 600, but is not limited thereto. The capping layer 3000 may be formed by a deposition process, and may have a thickness of 100 to 3,000 Å, more specifically, 300 to 2,000 Å. By controlling the thickness in this way, it is possible to prevent the transmittance of the capping layer 3000 from decreasing.

[0071] 1, according to an embodiment of the present invention, organic layers having various functions may be further formed between the capping layer 3000 and the first electrode 1000, or between the capping layer 3000 and the second electrode 2000. Alternatively, organic layers having various functions may be further formed on the upper portion (outer surface) of the capping layer 3000, and one or more separate functional layers may be inserted between the capping layer 3000, but the present invention is not limited thereto.

[0072] The present invention will be described in more detail below with reference to a synthesis example of a compound according to an embodiment of the present invention and an example of an organic light-emitting device. The following synthesis examples and examples are merely illustrative of the present invention, and the scope of the present invention is not limited to the following examples. Synthesis Example 1: Synthesis of Compound 90

[0073] JPEG2024524469000035.jpg37137

[0074] In a round-bottom flask, 5.0 g of adamantane-1-carbonyl chloride and 13.9 g of triethylamine were dissolved in 100 ml of 1,4-dioxane, and then 5.3 g of 3,5-di-tert-butylcyclohexanamine dissolved in 15 ml of 1,4-dioxane was slowly added dropwise, stirred at 60°C for 5 hours, and then stirred at room temperature for 24 hours. The reaction solution was added dropwise to 400 ml of diluted hydrochloric acid solution to terminate the reaction. The precipitated solid was filtered under reduced pressure and recrystallized to obtain compound 90 (4.6 g, yield 85%). m / z: 373.3345 (100.0%), 374.3378 (27.0%), 375.3412 (3.5%) Synthesis Example 2: Synthesis of Compound 134

[0075] JPEG2024524469000036.jpg38137

[0076] Compound 134 was synthesized (yield 85%) in the same manner as in Synthesis Example 1, except that 3,5-di-tert-butylaniline was used instead of 3,5-di-tert-butylcyclohexanamine. m / z: 367.2875 (100.0%), 368.2909 (27.0%), 369.2942 (3.5%) Synthesis Example 3: Synthesis of Compound 169

[0077] JPEG2024524469000037.jpg23137

[0078] Compound 169 was synthesized (yield 85%) in the same manner as in Synthesis Example 1, except that 1-adamantanamine hydrochloride was used instead of 3,5-di-tert-butylcyclohexanamine. m / z: 313.2406 (100.0%), 314.2439 (22.7%), 315.2473 (2.5%) Synthesis Example 4: Synthesis of Compound 180

[0079] JPEG2024524469000038.jpg25137

[0080] Compound 180 was synthesized (79% yield) in the same manner as in Synthesis Example 1, except that 5-dimethyladamantane-1-carbonyl chloride and memantine were used in place of 3,5-di-tert-butylcyclohexanamine and benzene-1,4-diamine. m / z: 369.3032 (100.0%), 370.3065 (27.0%), 371.3099 (3.5%) Synthesis Example 5: Synthesis of Compound 204

[0081] JPEG2024524469000039.jpg43137m / z: 455.4127 (100.0%), 456.4161 (33.5%), 457.4194 (5.4%)

[0082] Compound 169 was synthesized (yield 80%) in the same manner as in Synthesis Example 1, except that bis(4-tert-butylcyclohexyl)amine was used instead of 3,5-di-tert-butylcyclohexanamine. Synthesis Examples 6-20

[0083] Compounds were synthesized in the same manner as in Synthesis Example 1, except that starting materials 1 and 2 in Tables 1 to 3 below were used in place of 1-adamantane-1-carbonyl chloride and 3,5-di-tert-butylcyclohexanamine.

[0084]

[0085] [Table 1]

[0086] [Table 2]

[0087] [Table 3] Manufacturing of organic light-emitting devices

[0088] Fig. 1 shows the structure of a general organic light emitting device. As an example, the present invention is manufactured to have the structure of an organic light emitting device shown in Fig. 1. Specifically, the manufactured organic light emitting device is laminated in the order of anode (hole injection electrode 1000), hole injection layer 200, hole transport layer 300, light emitting layer 400, electron transport layer 500, electron injection layer 600, cathode (electron injection electrode 2000), and capping layer 3000 from the bottom. As described above, the capping layer 3000 may be a multi-layer structure in which the first capping layer and the second capping layer are combined. In the fabrication of an organic light emitting device, the substrate 10 can be a transparent glass substrate or a flexible plastic substrate.

[0089] The hole injection electrode 1000 is used as an anode for injecting holes into the organic light emitting device. It can be made of a transparent material such as indium tin oxide (ITO), indium zinc oxide (IZO), graphene, etc., using a material having a low work function to enable hole injection.

[0090] The materials used for the hole injection layer 200, the hole transport layer 300, the light emitting layer 400, the electron transport layer 500, the electron injection layer 600, and the high refractive capping layer are summarized in Table 4 below.

[0091] In addition, a cathode 2000 for injecting electrons is formed on the electron injection layer 600. Various metals can be used for the cathode. Specific examples include aluminum, gold, silver, magnesium, and magnesium-silver alloy.

[0092] [Table 4] Example 1

[0093] An indium tin oxide (ITO) substrate with a reflective layer containing silver (Ag) was ultrasonically cleaned with distilled water. After the distilled water cleaning, it was ultrasonically cleaned with solvents such as isopropyl alcohol, acetone, and methanol, and then dried. Then, on the top of the ITO substrate, HT01 was doped with 3 wt% NDP9 to form a hole injection layer with a thickness of 100 Å, and HT01 was deposited with a thickness of 1000 Å as a hole transport layer, and then a host BH01 was doped with 3 wt% BD01 to form a light emitting layer with a thickness of 250 Å. Then, a mixture of ET01 and Liq (1:1, wt. / wt.) was deposited with a thickness of 300 Å as an electron transport layer, and LiF was deposited with a thickness of 10 Å to form an electron injection layer. Then, MgAg was deposited to a thickness of 15 nm to form a cathode, and CPM01 was deposited on the cathode to a thickness of 950 Å as a high refractive capping layer, and then the compound prepared in Synthesis Example 1 was deposited to a thickness of 400 Å as a low refractive capping layer. The device was encapsulated in a glove box to prepare an organic light emitting device. Examples 2 to 20 Organic light emitting devices were manufactured in the same manner as in Example 1, except that the compounds manufactured in Synthesis Examples 2 to 25 were used to form low refractive capping layers. Comparative Example 1 to Comparative Example 4

[0094] Organic light-emitting devices were manufactured in the same manner as in Example 1, except that comparative compounds 1 to 4 shown in Table 5 below were used to form low refractive capping layers.

[0095] [Table 5] <Experimental Example 1> Performance evaluation of organic light-emitting device

[0096] Voltage was applied using a Kisley 2400 source measurement unit to inject electrons and holes, and the brightness at the time of light emission was measured using a Konica Minolta spectrophotometer (CS-2000) to measure the current density and brightness relative to the applied voltage under atmospheric pressure conditions in Examples 1 to 5, Examples 14 to 17, Example 20, and Comparative Examples 1 to 4 to evaluate the performance of the organic light-emitting devices. The results are shown in Table 6 below.

[0097] [Table 6]

[0098] In comparison with the examples of the present invention and the comparative examples, the present invention has a lower refractive index due to an amine-based structure containing a cycloalkyl group or a heterocyclyl group and a substituent with low polarizability, and at the same time has excellent thin film formation and thermal stability, thereby making it possible to realize an organic light emitting device with high color purity, high efficiency, and long life.

[0099] Specifically, comparing the examples of the present invention, comparing Example 1 with Example 2, it is found that when a cycloalkyl group is present in addition to Cy, it has a lower refractive index and is therefore effective in improving efficiency, and comparing Example 1 with Examples 3 and 4, it is found that when adamantane with a rigid structure is further present, it is effective in improving life, and when a substituent is further present, it is excellent in thermal stability and is further effective in improving life. Finally, comparing Example 1 with Example 5, it is found that when a cycloalkyl group is further present in addition to Cy, it has a low refractive index and is also excellent in thermal stability, which is effective in improving efficiency and life. <Experimental Example 2> Evaluation of refractive index

[0100] Using the compounds of Synthesis Example 1 to Synthesis Example 5 and Comparative Compound 1 to Comparative Compound 4, respectively, a 30 nm thick deposition film was prepared on a silicon substrate using a vacuum deposition device, and the refractive index at a wavelength of 450 nm was measured using an ellipsometer device (JA Woollam Co. Inc., M-2000X). The results are summarized in Table 7 below.

[0101] [Table 7]

[0102] As shown in Table 7, the compounds according to the present invention exhibit a low refractive index of 1.55 or less at a wavelength of 450 nm. In addition, although not shown in Table 7, other compounds according to the present invention also exhibit a low refractive index of 1.55 or less at a wavelength of 450 nm.

Claims

1. A compound for a capping layer represented by the following formula 1: <Chemical formula 1> (Cy is a substituted or unsubstituted C3-C20 cycloalkyl group or a substituted or unsubstituted C1-C20 heterocyclyl group; L is a direct bond, a substituted or unsubstituted C1-C50 alkylene group, a substituted or unsubstituted C2-C50 alkenylene group, a substituted or unsubstituted C1-C50 alkyleneoxy group, an ether group, a substituted or unsubstituted C1-C50 ester group, a substituted or unsubstituted C1-C50 sulfide group, a thioether group, a substituted or unsubstituted C1-C50 thioester group, a substituted or unsubstituted C1-C50 carbonyl group, a substituted or unsubstituted -C(X1)NR3-, or a substituted or unsubstituted -NR4C(X2)-, or a combination thereof; L1 and L2 are a direct bond, a substituted or unsubstituted C1-C50 alkylene group, a substituted or unsubstituted C2-C50 alkenylene group, a substituted or unsubstituted C1-C50 alkyleneoxy group, an ether group, a substituted or unsubstituted C1-C50 ester group, a substituted or unsubstituted C1-C50 sulfide group, a thioether group, a substituted or unsubstituted C1-C50 thioester group, a substituted or unsubstituted C1-C50 carbonyl group, a substituted or unsubstituted -C(X1)NR3-, a substituted or unsubstituted -NRC(X2)-, a substituted or unsubstituted -NR-, a substituted or unsubstituted C3-C50 cycloalkylene group, a substituted or unsubstituted C1-C50 heterocyclylene group, a substituted or unsubstituted C3-C50 arylene group, or a substituted or unsubstituted C2-C50 heteroarylene group, or a combination thereof; However, carbazole groups are excluded. X1 and X2 are each independently O, S, Se, Te, NR5, or CR6R7; R1 to R7 are each independently hydrogen, deuterium, halogen, a nitro group, a nitrile group, a hydroxy group, a thiol group, a substituted or unsubstituted amino group, a substituted or unsubstituted C1 to C50 alkyl group, a substituted or unsubstituted C2 to C50 alkenyl group, a substituted or unsubstituted C1 to C50 alkoxy group, a substituted or unsubstituted C1 to C50 sulfide group, a substituted or unsubstituted silyl group, a substituted or unsubstituted C3 to C50 cycloalkyl group, a substituted or unsubstituted C3 to C50 cycloalkenyl group, a substituted or unsubstituted C1 to C50 heterocyclyl group, a substituted or unsubstituted C3 to C50 aryl group, or a substituted or unsubstituted C2 to C50 heteroaryl group, and adjacent R1 to R7 may or may not be bonded to each other to form a ring, with the exception of a carbazole group.

2. The compound for a capping layer according to claim 1, wherein the formula 1 is represented by the following formulas 2 to 5: <Chemical formula 2> <Chemical formula 3> <Chemical formula 4> <Chemical formula 5> (In the above Chemical Formula 2 to Chemical Formula 3, The same symbols as those in Chemical Formula 1 are defined as in Chemical Formula 1.

3. 2. The compound for a capping layer according to claim 1, wherein Cy in Formula 1 is a substituted C3-C20 cycloalkyl group or a substituted C1-C20 heterocyclyl group.

4. The compound for a capping layer according to claim 3, wherein the substituents of Cy are each independently selected from the group consisting of a hydroxyl group, a thiol group, an amino group, a C1-C30 alkyl group, a C1-C30 alkoxy group, a C1-C30 sulfide group, a C0-C30 silyl group, a halogen group, a C3-C30 cycloalkyl group, a C1-C30 heterocyclyl group, and combinations thereof.

5. 2. The compound for a capping layer according to claim 1, wherein L in Formula 1 may be a direct bond, a carbonyl group, -CH2CO-, an ester group, a thioester group, an ether group, or a thioether group, or a combination of up to three of these.

6. 2. The compound for capping layer according to claim 1, wherein in Formula 1, L1 is a direct bond, R1 is hydrogen, and R2 is a substituted or unsubstituted C3-C50 cycloalkyl group or a substituted or unsubstituted C1-C50 heterocyclyl group.

7. 2. The compound for a capping layer according to claim 1, wherein Cy is selected from the group consisting of the following chemical structural formulas A-1 to A-21. (In the chemical structural formulas A-1 to A-21, W1 is each independently a methyl group, an ethyl group, a t-butyl group, a cyclohexyl group, an adamantane group, a dihydroamine group, a dimethylamine group, a hydroxyl group, a methoxy group, a mercaptan group, a methylthio group, a fluoro group, a trifluoromethyl group, or a trimethylsilyl group; Each n is independently an integer from 0 to 10; * indicates the bond position.)

8. 2. The compound for a capping layer of claim 1, wherein L2 is a direct bond and R2 is hydrogen.

9. 2. The compound for a capping layer according to claim 1, wherein in Formula 1, at least one of -L1-R1 and -L2-R2 is independently selected from the following formulae B-1 to B-47: (wherein, each W1 is independently a methyl group, an ethyl group, a t-butyl group, a cyclohexyl group, an adamantane group, a dihydroamine group, a dimethylamine group, a hydroxyl group, a methoxy group, a mercaptan group, a methylthio group, a nitrile group, a nitro group, a fluoro group, a trifluoromethyl group, or a trimethylsilyl group; Each n is independently an integer from 0 to 10; * indicates the bond position.)

10. The compound for a capping layer according to claim 9, wherein at least one of -L1-R1 and -L2-R2 may each independently have a chemical structural formula in which the -CO* structure in the chemical structural formulas B-1 to B-47 is replaced with -Z-* or *-Z-, and Z is selected from -O-, -S-, -CH2CO-, -CH2-NH-CO-, -O-NH-CO-, -S-NH-CO-, -CO-NH-CO-, -NH-C(=NMe)-, -NHC(=CHMe)-, -NHCOO-, -NH-, -CO-NH-, -OCONH-, -SCONH-, -CO-CO-NH-, -CS-, -C(=NH)-, -C(=NMe)-, -C(=CHMe)-, -SCO-, -OCO-, -COCO-, -CH2-, or "-".

11. 2. The compound for the capping layer according to claim 1, wherein the compound for the capping layer is one of the following compounds:

12. The compound for a capping layer according to claim 1 , wherein the compound for a capping layer has a refractive index of 1.55 or less at a wavelength of 450 nm.

13. An organic light-emitting device comprising a capping layer containing the compound for a capping layer according to claim 1 .

14. The organic light-emitting device is A first electrode; A second electrode; one or more organic layers interposed between the first electrode and the second electrode; The organic light emitting device according to claim 13 , wherein the capping layer is disposed on the outer side of at least one of the first electrode and the second electrode.

15. 14. The organic light-emitting device according to claim 13, wherein the capping layer has a thickness in the range of 100 Å to 3000 Å.

16. The organic light-emitting device according to claim 13, wherein the capping layer has a refractive index of 1.55 or less at a wavelength of 450 nm.

17. The organic light-emitting device according to claim 14, wherein the capping layer comprises a first capping layer containing the compound for a capping layer according to claim 1, and a second capping layer having a higher refractive index than the first capping layer.

18. 18. The organic light emitting device according to claim 17, wherein the second capping layer is interposed between the first capping layer and the first electrode, or between the first capping layer and the second electrode.

19. 18. The organic light emitting device of claim 17, wherein the second capping layer is in contact with the first capping layer and the first electrode, or the first capping layer and the second electrode.

20. 18. The organic light emitting device according to claim 17, wherein the first capping layer and the second capping layer have a combined thickness in the range of 100 to 3000 Å.

21. 18. The organic light-emitting device according to claim 17, wherein the first capping layer has a refractive index of 1.55 or less at a wavelength of 450 nm, the second capping layer has a refractive index of 2.10 or more at a wavelength of 450 nm, and a difference between the refractive index of the first capping layer and the refractive index of the second capping layer at a wavelength of 450 nm is within a range of 0.2 to 1.2.

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