Top-emitting OLED (Organic Light Emitting Diode) display panel and preparation method

Abstract

The invention relates to the technical field of display, and specifically provides a top-emitting OLED display panel and a preparation method thereof. The top-emitting OLED display panel of the present invention comprises: a substrate; a top emission OLED light emitting unit formed on the substrate; the covering layer is formed on the light-emitting side of the top-emitting OLED light-emitting unit; the packaging layer is formed on the covering layer and comprises a first inorganic packaging layer, an organic packaging layer and a second inorganic packaging layer which are stacked; the first inorganic packaging layer comprises at least two sub-packaging layers which are arranged in a stacked mode in the light emitting direction of the OLED light emitting unit, and the covering layer and the at least two sub-packaging layers form a first optical structure. Furthermore, the refractive index of the hole transport layer is smaller than the refractive index of the adjacent layer, the front light emitting efficiency of the top-emitting OLED display panel can be improved, the problem of large-viewing-angle brightness attenuation is effectively relieved, and the device is light and thin by limiting the thickness of the covering layer and the sub-packaging layer.

Description

Technical Field

[0001] The present invention relates to the field of display technology, and specifically provides a top emission OLED display panel and a preparation method thereof. Background Art

[0002] In recent years, organic light-emitting diode (OLED) luminous display technology has played an increasingly important role in people's production and life. As a new generation of display technology, OLED is made of organic small molecules or polymers. Due to its advantages such as soft light emission, fast response speed, rich color and wide viewing angle, OLED is gradually regarded by the industry as the most ideal display technology and has broad application prospects.

[0003] Due to the huge advantages of OLED devices in the display and lighting fields, people pay more attention to the research on high-efficiency organic materials and device performance that affect OLED. Usually, high-efficiency and long-life organic electroluminescent devices are obtained by optimizing the combination of different organic materials and device structures. This provides huge opportunities and challenges for the design and development of functional materials and device structures of various structures.

[0004] However, compared with other display devices, OLED top-emitting devices have more obvious brightness attenuation at wide viewing angles. It is necessary to develop a technology that can effectively suppress the brightness attenuation of OLED devices at wide viewing angles, thereby optimizing the viewing angle characteristics. Summary of the invention

[0005] In order to overcome the above defects, the present invention proposes a top-emitting OLED display panel and a preparation method, which can effectively suppress the brightness attenuation of the OLED under a large viewing angle, thereby optimizing the viewing angle characteristics.

[0006] In a first aspect, the present invention provides a top-emitting OLED display panel, comprising:

[0007] substrate;

[0008] A top-emitting OLED light-emitting unit formed on the substrate;

[0009] A covering layer formed on the light-emitting side of the top-emitting OLED light-emitting unit;

[0010] The encapsulation layer is formed on the cover layer, and includes a first inorganic encapsulation layer, an organic encapsulation layer, and a second inorganic encapsulation layer stacked along the light emitting direction of the OLED light emitting unit; wherein,

[0011] The first inorganic encapsulation layer includes at least two sub-encapsulation layers stacked along the light emitting direction of the OLED light emitting unit.

[0012] The cover layer and the at least two sub-packaging layers form a first optical structure with high and low refractive indices arranged alternately.

[0013] Furthermore, the refractive index of the cover layer is greater than the refractive index of other layers in the first optical structure.

[0014] Furthermore, in the first optical structure, the absolute value of the difference in refractive index between adjacent layers is 0.1-0.9.

[0015] Furthermore, the at least two sub-encapsulation layers include 2-4 sub-encapsulation layers.

[0016] Furthermore, the at least two sub-encapsulation layers include a first sub-encapsulation layer, a second sub-encapsulation layer and a third sub-encapsulation layer stacked along the light emitting direction of the OLED light emitting unit.

[0017] Furthermore, at 460 nm, the refractive index difference between the cover layer and the first sub-packaging layer is 0.5-0.9, the refractive index difference between the first sub-packaging layer and the second sub-packaging layer is 0.1-0.4, and the refractive index difference between the second sub-packaging layer and the third sub-packaging layer is 0.2-0.5.

[0018] Furthermore, the total thickness of the cover layer and the three-layer sub-packaging layer is in the range of 2650-2750 angstroms, and the thickness of the cover layer accounts for 2.5%-3% of the total thickness.

[0019] Furthermore, the material of the covering layer is selected to satisfy the following conditions:

[0020] The refractive index at the wavelength of 460nm blue light is ≥2.0;

[0021] The refractive index n at a wavelength of 530nm for green light is ≥ 1.9; and

[0022] The refractive index n≥1.85 at the red light wavelength of 620nm.

[0023] Furthermore, the covering layer is an aromatic amine compound, and the general structural formula is:

[0024]

[0025] Wherein, X1 is any one of CR2, O, N, NR3, and S;

[0026] A1 and Ar2 are any one of a C6 to C60 aryl group, a C10 to C60 condensed aryl group, and a C5 to C60 five-membered or six-membered aromatic heterocycle;

[0027] L is any of a direct bond, a substituted or unsubstituted C6-C50 arylene group, or a substituted or unsubstituted C2-C50 heteroaryl group.

[0028] Furthermore, A1 and Ar2 are any one of the following groups:

[0029]

[0030] X1, X2, X3 are any one of CR1, O, N, NR2, S;

[0031] L, L1, L2 are direct bonds, phenyl, biphenyl, naphthyl;

[0032] R1-R9 are hydrogen, deuterium, halogen, nitro, nitrile, alkyl, alkenyl, alkoxy, thioether, aryl, or heteroaryl, or adjacent substituents are fused to form a ring.

[0033] Furthermore, the top-emitting OLED light-emitting unit includes an anode, a hole injection layer, a hole transport layer, an electron blocking layer, an organic light-emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer and a cathode on the substrate, wherein the hole injection layer, the hole transport layer and the electron blocking layer constitute a second optical structure with alternating high and low refractive indices.

[0034] Furthermore, the refractive index of the hole transport layer is smaller than the refractive index of the adjacent layer.

[0035] Further, the hole transport layer material is selected to have a refractive index that satisfies the following conditions:

[0036] The refractive index at 460 nm is not greater than 1.75 and the refractive index at 620 nm is not greater than 1.70.

[0037] In a second aspect, the present invention provides a method for preparing a top-emitting OLED display panel, comprising:

[0038] forming a top-emitting OLED light-emitting unit on a substrate;

[0039] forming a covering layer on the light-emitting side of the top-emitting OLED light-emitting unit;

[0040] A first inorganic encapsulation layer, an organic encapsulation layer, and a second inorganic encapsulation layer are sequentially formed on the cover layer along the light emitting direction of the OLED light emitting unit, wherein the first inorganic encapsulation layer includes at least two sub-encapsulation layers stacked along the light emitting direction of the OLED light emitting unit, and the cover layer and the at least two sub-encapsulation layers constitute a first optical structure with alternating high and low refractive indices.

[0041] Furthermore, forming a top-emitting OLED light-emitting unit on the substrate includes:

[0042] An anode, a hole injection layer, a hole transport layer, an electron blocking layer, an organic light-emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer and a cathode are sequentially formed on the substrate, wherein the hole injection layer, the hole transport layer and the electron blocking layer constitute a second optical structure with high and low refractive indices arranged alternately.

[0043] Furthermore, the refractive index of the hole transport layer is smaller than the refractive index of the adjacent layer.

[0044] The above one or more technical solutions of the present invention have at least one or more of the following beneficial effects:

[0045] The present invention can effectively suppress the brightness attenuation of OLED devices at a large viewing angle by constructing a specific optical structure with periodically overlapping high and low refractive index layers, thereby optimizing the viewing angle characteristics. In addition, the hole transport layer of the present invention adopts a low refractive index material, which significantly improves the brightness in the positive viewing angle direction, and further suppresses the brightness attenuation through the constructed optical structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The disclosure of the present invention will become more easily understood with reference to the accompanying drawings. It is easy for those skilled in the art to understand that these drawings are only for illustrative purposes and are not intended to limit the scope of protection of the present invention. In addition, similar numbers in the figures are used to represent similar components, among which:

[0047] Figure 1 is a schematic diagram of the main structure of a top-emitting OLED display panel according to an embodiment of the present invention;

[0048] Figure 2 is a schematic diagram of the main structure of a top-emitting OLED display panel including anode to cathode functional layers according to an embodiment of the present invention;

[0049] Figure 3 It is a main flow diagram of a preparation method according to the present invention.

[0050] Reference numerals list :

[0051] 1: substrate; 2: top emission OLED light-emitting unit; 2-1: anode; 2-2: hole injection layer HIL; 2-3: hole transport layer HTL; 2-4: electron blocking layer EBL; 2-5: organic light-emitting layer EML; 2-6: hole blocking layer HBL; 2-7: electron transport layer ETL; 2-8: electron injection layer EIL; 2-9: cathode; 3: covering layer; 4: encapsulation layer; 4-1: first inorganic encapsulation layer; 411: first sub-encapsulation layer; 412: second sub-encapsulation layer; 413: third sub-encapsulation layer; 4-2: organic encapsulation layer; 4-3: second inorganic encapsulation layer; 5: flat layer. DETAILED DESCRIPTION

[0052] Some embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the protection scope of the present invention.

[0053] According to the different directions of light emission, OLED devices can be divided into bottom-emitting OLED devices and top-emitting OLED devices. In bottom-emitting devices, light is emitted from the substrate, the reflective electrode is above the organic light-emitting layer, and the transparent electrode is below the organic light-emitting layer. The thin-film transistor part in the bottom-emitting OLED device cannot transmit light, resulting in a smaller light-emitting area. In top-emitting devices, the transparent electrode is on the organic light-emitting layer, and the reflective electrode is below the organic light-emitting layer, so the light is emitted from the opposite direction of the substrate, thereby increasing the light transmission area. Therefore, current OLED devices are mainly top-emitting devices. The present invention provides a top-emitting OLED display panel, and the characteristics of the top-emitting OLED are reflected in that the anode is a fully reflective anode and the cathode is a semi-transparent and semi-reflective cathode.

[0054] However, compared with other display devices, OLED top-emitting devices have a more obvious brightness attenuation phenomenon at a wide viewing angle. At a wide viewing angle, the JNCD increases significantly, but the brightness attenuates significantly. To address this problem, the improved device of the present invention refers to Figure 1 , which can solve the brightness attenuation and effectively suppress the brightness attenuation of OLED devices under large viewing angles, thereby optimizing the viewing angle characteristics. The device structure specifically includes:

[0055] substrate1;

[0056] A top-emitting OLED light-emitting unit 2 is formed on the substrate 1;

[0057] A covering layer 3 is formed on the light-emitting side of the top-emitting OLED light-emitting unit 2;

[0058] The encapsulation layer 4 is formed on the cover layer 3, and includes a first inorganic encapsulation layer 4-1, an organic encapsulation layer 4-2, and a second inorganic encapsulation layer 4-3 stacked along the light emitting direction of the OLED light emitting unit; wherein,

[0059] The first inorganic encapsulation layer 4 - 1 includes at least two sub-encapsulation layers stacked along the light emitting direction of the OLED light emitting unit.

[0060] The cover layer 3 and the at least two sub-packaging layers constitute a first optical structure in which the refractive indexes are alternately arranged in high and low order.

[0061] In the present invention, the structure of the top-emitting OLED device is optimized and improved. Specifically, the cover layer 3 and at least two sub-encapsulation layers together form a first optical structure. Through this design, the propagation path of light can be effectively controlled.

[0062] Since the anode total reflection electrode and the first optical structure together constitute an optical microcavity, the emitted light is constantly reflected back and forth in the optical microcavity. This repeated reflection process improves the output coupling efficiency of the OLED, thereby enhancing the intensity of light of some wavelength bands. This structure can provide high light reflectivity. This high reflectivity effectively reduces the loss of light during transmission, thereby suppressing the attenuation of brightness. In addition, it is also beneficial to shorten the reflection distance of light, thereby greatly reducing the possibility of light absorption and attenuation.

[0063] In this way, the present invention can effectively improve the brightness attenuation of L-decay at a large viewing angle and further improve the device efficiency.

[0064] In one embodiment, the refractive index of the cover layer 3 is greater than the refractive index of other layers in the first optical structure. This design makes the refractive index of the sub-encapsulation layer directly adjacent to the cover layer 3 lower than the refractive index of the cover layer 3. Furthermore, another sub-encapsulation layer adjacent to the sub-encapsulation layer with a low refractive index has a higher refractive index. In this way, the entire structure forms an alternating refractive index distribution, that is, high refractive index layers and low refractive index layers appear alternately, thereby realizing a high and low refractive index distribution layer structure.

[0065] In one embodiment, in the first optical structure, the absolute value of the difference in refractive index between adjacent layers is 0.1-0.9. This design helps to optimize the propagation and reflection characteristics of light between different layers and suppress brightness attenuation.

[0066] In one embodiment, when designing the packaging structure, it is necessary to control the number of sub-packaging layers to ensure that the packaging effect is optimal. If the number of sub-packaging layers is too small, it may result in poor packaging effect, which in turn makes the sealing during the packaging process not tight enough, thereby affecting the performance and reliability of the device. On the contrary, if the number of sub-packaging layers is too large, the entire device will become too thick and heavy, which is obviously not in line with the current development trend of lightweight devices. Therefore, in order to balance the relationship between the packaging effect and the thickness of the device, the at least two layers of sub-packaging layers should be controlled between 2-4 layers. Such a design can not only ensure the strictness of the package, but also meet the requirements of lightweight, so as to ensure the performance of the device while taking into account its lightweight and portability.

[0067] In one embodiment, referring to Figure 2 The at least two sub-encapsulation layers include a first sub-encapsulation layer 411, a second sub-encapsulation layer 412, and a third sub-encapsulation layer 413 stacked along the light emitting direction of the OLED light emitting unit. In one embodiment, the refractive indexes of the cover layer 3, the first sub-encapsulation layer 411, the second sub-encapsulation layer 412, and the third sub-encapsulation layer 413 are distributed in the order of high, low, high, and low.

[0068] In one embodiment, at 460nm, the refractive index difference between the cover layer 3 and the first sub-packaging layer 411 is 0.5-0.9, and such a refractive index difference helps to achieve effective light wave reflection and refraction. At the same time, the refractive index difference between the first sub-packaging layer 411 and the second sub-packaging layer 412 is 0.1-0.4 to ensure that the light can produce appropriate reflection and refraction effects when propagating between these layers, and the refractive index difference between the second sub-packaging layer 412 and the third sub-packaging layer 413 is 0.2-0.5, which further optimizes the propagation path of the light wave. The present invention can form multiple reflections and refractions by stacking film layers with different refractive indices, and then significantly enhance the light extraction efficiency through the interference phenomenon of light. This design not only improves the utilization rate of light, but also optimizes the overall optical performance.

[0069] In one embodiment, if the thickness of the covering layer 3 is too large or too small, it will affect the device efficiency and brightness decay L-decay. At the same time, the thickness of the packaging layer will also affect L-decay and the thinness of the device. Therefore, the total thickness of the covering layer 3 and the three-layer sub-packaging layer is controlled in the range of 2650-2750 angstroms and the thickness of the covering layer accounts for 2.5%-3% of the total thickness.

[0070] In one embodiment, the cover layer is an organic cover layer.

[0071] In one embodiment, the material of the cover layer is selected to satisfy the following conditions:

[0072] The refractive index at the wavelength of 460nm blue light is ≥2.0;

[0073] The refractive index n at a wavelength of 530nm for green light is ≥ 1.9; and

[0074] The refractive index n≥1.85 at the red light wavelength of 620nm.

[0075] In one embodiment, the covering layer is an aromatic amine compound with the general structural formula:

[0076]

[0077] Wherein, X1 is any one of CR2, O, N, NR3, and S;

[0078] A1 and Ar2 are any one of a C6 to C60 aryl group, a C10 to C60 condensed aryl group, and a C5 to C60 five-membered or six-membered aromatic heterocycle;

[0079] L is any of a direct bond, a substituted or unsubstituted C6-C50 arylene group, or a substituted or unsubstituted C2-C50 heteroaryl group.

[0080] In one embodiment, A1 and Ar2 are any one of the following groups:

[0081]

[0082] X1, X2, X3 are any one of CR1, O, N, NR2, S;

[0083] L, L1, L2 are direct bonds, phenyl, biphenyl, naphthyl;

[0084] R1-R9 are hydrogen, deuterium, halogen, nitro, nitrile, alkyl, alkenyl, alkoxy, thioether, aryl, or heteroaryl, or adjacent substituents are fused to form a ring.

[0085] Possible structures shown in Formula 1 include but are not limited to the following structures:

[0086]

[0087]

[0088]

[0089]

[0090] In the above compounds 1-12, L is a direct bond; in compounds 13-20, L is a phenyl group.

[0091] The aromatic amine compounds provided in the embodiments of the present invention have very high polarizability and refractive index, which can effectively improve the light extraction efficiency of the electroluminescent device, while improving the stability of the light extraction layer itself, increasing the thermal stability of the electroluminescent device, and improving the service life of the electroluminescent device.

[0092] In one embodiment, still referring to Figure 2 The top-emitting OLED light-emitting unit 2 includes an anode 2-1, a hole injection layer HIL2-2, a hole transport layer HTL2-3, an electron blocking layer EBL2-4, an organic light-emitting layer EML2-5, a hole blocking layer HBL2-6, an electron transport layer ETL2-7, an electron injection layer EIL2-8 and a cathode 2-9 on the substrate 1, wherein the hole injection layer 2-2, the hole transport layer 2-3 and the electron blocking layer 2-4 constitute a second optical structure with alternating high and low refractive indices.

[0093] In the top-emitting OLED display panel, optical structures are constructed at both ends of the OLED to further optimize the light reflection path and phase, which can effectively reduce the loss of light during the propagation process and suppress the brightness attenuation.

[0094] Referring to the description of the above optical structure, the hole injection layer 2-2, the hole transport layer 2-3 and the electron blocking layer 2-4 constitute adjacent layers whose refractive indices are alternately distributed in the order of high and low or low and high.

[0095] In one embodiment, the refractive index of the hole transport layer 2-3 is less than the refractive index of the adjacent layer. In this way, the refractive index of the hole injection layer 2-2 and the electron blocking layer 2-4 adjacent to the hole transport layer 2-3 are both higher than that of the hole transport layer 2-3, and a high-low refractive index alternating distribution is formed between the three layers.

[0096] In one embodiment, the hole transport layer 2-3 material is selected to have a refractive index that satisfies the following conditions:

[0097] The refractive index at 460 nm is not greater than 1.75 and the refractive index at 620 nm is not greater than 1.70.

[0098] Due to the principle of light reflection and refraction, when the hole transport layer 2-3 in the OLED device uses a low refractive index material, a significant increase in brightness in the normal viewing angle direction will be observed. However, this will also cause the brightness attenuation in the wide viewing angle direction to become more serious. The present invention forms a first optical structure by using a covering layer based on a high refractive index material. This structure can effectively alleviate the brightness attenuation problem in the wide viewing angle direction, thereby further improving the overall efficiency of the OLED device. The OLED device can maintain high brightness and uniformity in all viewing angle directions, thereby significantly improving the display effect and user experience.

[0099] The present invention can improve the L-decay attenuation at a large viewing angle and further improve the efficiency of the device by optimizing the parameters such as the refractive index and thickness of the cover layer and the packaging layer.

[0100] In one embodiment, still referring to Figure 2 The top-emitting OLED display panel further includes a planarization layer 5 formed on the encapsulation layer 4 .

[0101] The materials of the main functional layers in the top-emitting OLED display panel are described below.

[0102] The substrate 1 can be a glass substrate.

[0103] The anode 2-1 can be formed of a high work function electrode material, such as transparent oxide ITO, IZO, or a composite electrode formed of ITO / Ag / ITO, Ag / IZO, CNT / ITO, CNT / IZO, GO / ITO, GO / IZO, etc.

[0104] The hole injection layer HIL2-2 can be an inorganic oxide, such as but not limited to molybdenum oxide, titanium oxide, vanadium oxide, rhenium oxide, ruthenium oxide, chromium oxide, zirconium oxide, hafnium oxide, tantalum oxide, silver oxide, tungsten oxide, manganese oxide, etc. It can also be a dopant of a strong electron-withdrawing system, such as F4TCNQ, HATCN, etc. It is also possible to use p-dopant in the hole transport material for P-type doping to form a hole injection layer material. The specific thickness of the hole injection layer is not particularly limited, for example, the thickness can be 5 to 20 nm, and can be formed by co-evaporation.

[0105] The hole transport layer HTL2-3 may be formed of an organic material having good hole transport properties, for example, an aromatic amine or carbazole material, such as NPB, TPD, BAFLP, DFLDPBi, and the like.

[0106] The organic light-emitting layer EML2-5 can be formed by selecting different materials according to different luminescent colors. For example, a phosphorescent host and a red phosphorescent dopant can be selected to form a red light-emitting layer, a phosphorescent host and a green phosphorescent dopant can be selected to form a green light-emitting layer, or a fluorescent host and a fluorescent dopant can be selected to form a blue light-emitting layer. In addition, each light-emitting layer host can be composed of one material or a mixed material of more than two materials. More specifically, the main material of the blue light-emitting layer can be selected from anthracene derivatives, such as ADN, MADN, etc.; the guest material can be a pyrene derivative, a fluorene derivative, a perylene derivative, a styrylamine derivative, a metal complex, etc., such as TBPe, BDAVBi, DPAVBi, FIrpic, etc. The main material of the green light-emitting layer can be selected from coumarin dyes, quinacrine copper derivatives, polycyclic aromatic hydrocarbons, diamine anthracene derivatives, carbazole derivatives, such as DMQA, BA-NPB, Alq3, etc. The guest material can be a metal complex, such as Ir(ppy)3, Ir(ppy)2(acac), etc. The red light-emitting host material can be selected from DCM series materials, such as DCM, DCJTB, DCJTI, etc., and the guest material can be a metal complex, such as Ir(piq)2(acac), PtOEP, Ir(btp)2(acac), etc.

[0107] The constitution of the blue, green and red light emitting regions of the organic light emitting layer is briefly shown below.

[0108] ITO: Indium Tin Oxide Glass; HIL: Hole Injection Layer; HTL: Hole Transport Layer; B′: Blue Electron Blocking Layer; G': Green Electron Blocking Layer; R': Red Electron Blocking Layer; EML: Organic Light Emitting Layer; HBL: Hole Blocking Layer. ETL: Electron Transport Layer; CPL: Covering Layer; P-Dopant: p-type dopant (hole dopant); CVD1-1: First Sub-Encapsulation Layer; CVD1: Second Sub-Encapsulation Layer; CVD1-2: Third Sub-Encapsulation Layer;

[0109] B Host: main material of blue light-emitting layer; G Host: main material of green light-emitting layer; RHost: main material of red light-emitting layer;

[0110] B Dopant: doping material for blue light-emitting layer; G Dopant: doping material for green light-emitting layer; R Dopant: doping material for red light-emitting layer;

[0111] LiQ: A type of N-type dopant.

[0112] Blue light emitting area structure:

[0113] ITO / HIL(HTL+2%P-Dopant)10nm / HTL 100nm / B'5nm / Thickness ratio B Host:BDopant=0.1:0.9,20nm / HBL 5nm / Thickness ratio ETL:LiQ=1:1,40nm / Yb 1nm / Mg:Ag 13nm / CPL 70nm / CVD1-11μm / CVD11.5μm / CVD1-20.1μm.

[0114] Green light emitting area structure:

[0115] ITO / HIL(HTL+2%P-Dopant)10nm / HTL 100nm / G'40nm / film thickness ratio G Host:GDopant=0.1:0.9,35nm / HBL 5nm / film thickness ratio ETL:LiQ=1:1,40nm / Yb 1nm / Mg:Ag 13nm / CPL 70nm / CVD1-11μm / CVD11.5μm / CVD1-20.1μm.

[0116] Red light emitting area structure:

[0117] ITO / HIL(HTL+2%P-Dopant)10nm / HTL 100nm / R'80nm / Thickness ratio R Host:RDopant=0.1:0.9,45nm / HBL 5nm / Thickness ratio ETL:LiQ=1:1,40nm / Yb 1nm / Mg:Ag 13nm / CPL 70nm / CVD1-11μm / CVD11.5μm / CVD1-20.1μm.

[0118] The electron injection layer EIL2-8 can be made of a material having the ability to transport electrons and a compound having the effect of injecting electrons from the cathode. For example, a material having excellent film forming ability can be selected, such as an alkali metal or metal, such as LiF, Yb, Mg, Ca or their compounds.

[0119] The electron transport layer ETL2-7 may be formed of an organic material having good electron transport properties, for example, an imidazole material such as BPhen, 1,3,4-oxadiazole, and the like.

[0120] The cathode 2-9 material can be selected from materials with low work function so that electrons can be easily injected into the organic layer, and have good light transmittance and conductivity. Specific examples of cathode materials that can be used in the present invention include: metals, metal oxides, and metal alloys, such as aluminum (Al), silver (Ag), gold (Au), magnesium (Mg), calcium (Ca), ytterbium (Yb), indium (In), lithium (Li), potassium (K), sodium (Na), tin (Sn), titanium (Ti), lead (Pb), samarium (Sm), yttrium (Y), indium tin oxide (ITO), magnesium silver alloy (Mg:Ag), ytterbium gold alloy (Yb:Au), Ytterbium silver alloy (Yb:Ag), lithium aluminum alloy (Li:Al), lithium calcium magnesium alloy (Li:Ca:Al), etc.; and laminated materials, such as magnesium / aluminum (Mg / Al), magnesium / silver (Mg / Ag), aluminum / silver (Al / Ag), aluminum / gold (Al / Au), ytterbium / gold (Yb / Au), ytterbium / silver (Yb / Ag), calcium / magnesium (Ca / Mg), calcium / silver (Ca / Ag), barium / silver (Ba / Ag), etc., but not limited to these.

[0121] The covering layer 3 may be made of a material that can improve the luminous efficiency of the device and increase the service life of the device, and may be a hole-type material, such as aromatic amines, or an electronic-type material.

[0122] The materials of the first inorganic encapsulation layer 4 - 1 and the second inorganic encapsulation layer 4 - 3 on the cover layer 3 are generally SiN, SiO, or SiOxNy.

[0123] The commonly used commercial materials for each functional layer in OLED devices are shown in Table 1.

[0124] Table 1 Commonly used commercial materials for each functional layer

[0125]

[0126]

[0127] The present invention also provides a method for preparing a top-emitting OLED display panel, referring to Figure 3 ,

[0128] include:

[0129] S1, forming a top-emitting OLED light-emitting unit 2 on a substrate 1;

[0130] S2, forming a covering layer 3 on the light emitting side of the top-emitting OLED light-emitting unit 2;

[0131] S3, a first inorganic encapsulation layer 4-1, an organic encapsulation layer 4-2 and a second inorganic encapsulation layer 4-3 are sequentially formed on the covering layer 3 along the light emitting direction of the OLED light emitting unit 2, wherein the first inorganic encapsulation layer 4-1 includes at least two sub-encapsulation layers stacked along the light emitting direction of the OLED light emitting unit, and the covering layer 3 and the at least two sub-encapsulation layers constitute a first optical structure.

[0132] In one embodiment, the forming of the top-emitting OLED light-emitting unit 2 on the substrate 1 includes:

[0133] An anode 2-1, a hole injection layer HIL2-2, a hole transport layer HTL2-3, an electron blocking layer EBL2-4, an organic light-emitting layer EML2-5, a hole blocking layer HBL2-6, an electron transport layer ETL2-7, an electron injection layer EIL2-8 and a cathode 2-9 are sequentially formed on the substrate 1, wherein the hole injection layer 2-2, the hole transport layer 2-3 and the electron blocking layer 2-4 constitute a second optical structure.

[0134] In one embodiment, the total thickness of the cover layer and the three-layer sub-encapsulation layer is in the range of 2650-2750 angstroms and the thickness of the cover layer accounts for 2.5%-3% of the total thickness. By limiting the thickness of the cover layer, the brightness attenuation suppression effect is optimized and the device is made thinner and lighter.

[0135] In one embodiment, the refractive index of the hole transport layer 2-3 is smaller than the refractive index of the adjacent layer.

[0136] The hole transport layer of the present invention adopts a material with a low refractive index, so that the brightness in the positive viewing angle direction is significantly improved, and at the same time, the brightness attenuation is suppressed by the constructed optical structure.

[0137] The present invention can further improve the L-decay attenuation at a large viewing angle by optimizing the refractive index and thickness of the cover layer and the encapsulation layer, while further improving the efficiency of the device and increasing the lightness and thinness of the L-decay and the device.

[0138] According to the following preparation method, the top emission OLED display panels of Examples 1-5 were prepared, and the performance of the devices was tested.

[0139] Device structure reference Figure 2 , the OLED devices in Examples 1-5 all satisfy the following characteristics:

[0140] The cover layer and the three-layer sub-packaging layer constitute a first optical structure, and the hole injection layer, the hole transport layer and the electron blocking layer constitute a second optical structure.

[0141] The hole transport layer material is selected to have a refractive index satisfying the following conditions:

[0142] The refractive index at 460nm is not greater than 1.75 and the refractive index at 620nm is not greater than 1.70. At 460nm, the refractive index difference between the cover layer and the first sub-encapsulation layer is 0.5-0.9, the refractive index difference between the first sub-encapsulation layer and the second sub-encapsulation layer is 0.1-0.4, and the refractive index difference between the second sub-encapsulation layer and the third sub-encapsulation layer is 0.2-0.5.

[0143] The total thickness of the cover layer and the three-layer sub-encapsulation layer is in the range of 2650-2750 angstroms, and the thickness of the cover layer accounts for 2.5%-3% of the total thickness.

[0144] The preparation process is as follows:

[0145] (1) ultrasonically treating the glass plate with ITO in a cleaning agent, rinsing in deionized water, ultrasonically degreasing in an acetone-ethanol mixed solvent, and baking in a clean environment until the water is completely removed;

[0146] (2) The glass substrate with the anode is placed in a vacuum chamber and the vacuum is evacuated to 1×10-5 to 1×10-6. A P-type doping compound and a hole transport (HTL) material are vacuum co-evaporated on the anode layer to form a hole injection layer HIL.

[0147] (3) A hole transport compound is deposited on the HIL to function as a hole transport layer (HTL).

[0148] (4) On the HTL, EBL material is evaporated to form an electron blocking layer.

[0149] (5) A host material and a dopant material are co-evaporated on the electron blocking layer to form a light-emitting layer. The concentration of the host material in the light-emitting layer is 97%, and the concentration of the dopant material is 3%.

[0150] (6) A hole blocking layer material is deposited on the light emitting layer to a thickness of 5 nm to function as a hole blocking layer HBL.

[0151] (7) The electron transport layer (ETL) material and Liq are co-evaporated on the HBL, and the two materials are vaporized at the same rate to form the electron transport layer (ETL) to function.

[0152] (8) Metal Yb and metal cathode Mg:Ag are evaporated on the ETL layer.

[0153] (9) A cover layer is evaporated on the cathode to form a light extraction layer.

[0154] (10) A three-layer sub-encapsulation layer is formed on the light extraction layer by sputtering.

[0155] According to the materials and parameters in Table 2, the top emission OLED display panels of Examples 1-5 were prepared according to the above preparation method.

[0156] In order to reflect the effect of the parameters of Examples 1-5 on the performance of the OLED device, the parameter values ​​in Examples 1-5 are changed or the cover layer materials are changed to form Comparative Examples 1-5. Although named as comparative examples, it does not mean that each comparative example is not within the scope of protection of the present invention. The comparative examples are only used as data performance comparisons. According to the materials and parameters in Table 2, the top-emitting OLED display panels of Comparative Examples 1-5 were prepared using the above-mentioned preparation method.

[0157] The top emission OLED display panels of Examples 1-5 and Comparative Examples 1-5 were tested respectively, and the test results are shown in Table 2.

[0158] Table 2 Test results of OLED display panels of Examples 1-5 and Comparative Examples 1-5

[0159]

[0160] Explanation of the parameters in Table 2

[0161] n(HTL) is the refractive index of the hole transport layer at 460 nm.

[0162] CPL is an organic compound selected for the covering layer.

[0163] It is the total thickness of the cover layer and the three-layer sub-encapsulation layer.

[0164] The CPL thickness ratio is the ratio of the cover layer thickness to the total thickness.

[0165] L-decay is the luminance decay of the device, which is based on the luminance of the display panel at a viewing angle of 0°. When the viewing angle is 45° and 60°, the brightness decay range of white light is measured.

[0166] EQE (%) is the external quantum efficiency (EQE), which is one of the key parameters of OLED display devices.

[0167] Explanation of the materials in Table 2

[0168] The compounds selected for the covering layers of Examples 1-5 are all different aromatic amine compounds corresponding to the above general formula 1.

[0169] The other functional layers of Examples 1-5 are all made of commercial materials listed in Table 1.

[0170] The CPL1 in the comparative example is a commercial organic cover layer having the structural formula Other functional layer materials used in the comparative example are:

[0171]

[0172]

[0173] Explanation of the refractive index of the cover layer in Table 2

[0174] The refractive index is an important physical parameter of light extraction materials, and the size of the refractive index directly reflects the light coupling efficiency of electroluminescent devices.

[0175] The CPL shown in the general formula 1 used in the present invention and the compound CPL1 (commercial organic cover layer CPL) are used as examples and comparative examples. The refractive index is tested by an ellipsometer; the instrument scanning range is 245nm to 1000nm; a thin film of aromatic amine compound is formed by silicon wafer evaporation, and the film thickness is 50nm, and then the refractive index is tested, and the refractive index values ​​of the two are given respectively. The test results are shown in Table 3.

[0176] Table 3 Refractive index of different cover layer compounds

[0177]

[0178] Analyze the test data in Table 2

[0179] In Examples 1-5, the aromatic amine compounds of the general formula 1 are used as the material of the covering layer and a low refractive index HTL is used in combination with the property regulation of the covering layer CPL and the first inorganic encapsulation layer. The low refractive index hole transport layer will improve the front light extraction efficiency, but will aggravate the brightness attenuation at a large viewing angle. By improving and regulating the properties of the covering layer and the first inorganic encapsulation layer, the problem of brightness attenuation at a large viewing angle can be effectively alleviated. Compared with the comparative example using the conventional commercial covering layer CPL1, the present invention uses a high refractive index covering layer CPL to further improve the efficiency and achieve the acquisition of high-performance OLED devices.

[0180] In the embodiment of the present invention, when the viewing angle is 45° and 60°, the brightness attenuation range of the white light is 53%-57% and 70%-75% respectively, which effectively alleviates the viewing angle attenuation.

[0181] Comparative Example 1 is used as a reference example. In the example, a hole transport layer with a low refractive index and a cover layer with a high refractive index of Formula 1 of the present invention are not used. The performance of the OLED device formed in this way is relatively the worst.

[0182] In Comparative Example 2, although the first optical structure can be formed by using the high refractive index covering layer of the present invention, the refractive index of the hole transport layer exceeds the limited range and the second optical structure is not formed. The optimization effect is not as good as that of Examples 1-5.

[0183] Comparative Example 3 does not use a high refractive index cover layer and does not form a first optical structure, so the improvement effect is not as good as that of Examples 1-5.

[0184] In comparative example 4, the thickness X exceeds the range, and in comparative example 5, the CPL thickness ratio exceeds the limited range, both of which affect the overall effect of the device to a certain extent.

[0185] In summary, Example 1 is the most preferred result according to the present invention, Comparative Example 1 is the device data under the conventional structure, and Comparative Examples 2-5 are the device data after changing different parameters. The method of the present invention can improve the brightness attenuation at a large viewing angle and improve the front light extraction efficiency, thereby greatly improving the performance of OLED devices.

[0186] It should be pointed out that although the various steps in the above embodiments are described in a specific order, those skilled in the art can understand that in order to achieve the effects of the present invention, different steps do not have to be performed in such an order. They can be performed simultaneously (in parallel) or in other orders. These changes are within the scope of protection of the present invention.

[0187] So far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will fall within the protection scope of the present invention.

Claims

1. A top-emitting OLED display panel, characterized in that: include: substrate; A top-emitting OLED light-emitting unit formed on the substrate; A covering layer formed on the light-emitting side of the top-emitting OLED light-emitting unit; The encapsulation layer is formed on the cover layer, and includes a first inorganic encapsulation layer, an organic encapsulation layer, and a second inorganic encapsulation layer stacked along the light emitting direction of the OLED light emitting unit; wherein, The first inorganic encapsulation layer includes at least two sub-encapsulation layers stacked along the light emitting direction of the OLED light emitting unit. The cover layer and the at least two sub-packaging layers form a first optical structure with high and low refractive indices arranged alternately.

2. The display panel according to claim 1, characterized in that: The refractive index of the cover layer is greater than the refractive index of other layers in the first optical structure.

3. The display panel according to claim 1, characterized in that: In the first optical structure, the absolute value of the difference in refractive index between adjacent layers is 0.1-0.

9.

4. The display panel according to any one of claims 1 to 3, characterized in that: The at least two sub-encapsulation layers include 2-4 sub-encapsulation layers.

5. The display panel according to claim 4, characterized in that: The at least two sub-encapsulation layers include a first sub-encapsulation layer, a second sub-encapsulation layer and a third sub-encapsulation layer stacked along the light emitting direction of the OLED light emitting unit.

6. The display panel according to claim 5, characterized in that: At 460nm, the refractive index difference between the cover layer and the first sub-packaging layer is 0.5-0.9, the refractive index difference between the first sub-packaging layer and the second sub-packaging layer is 0.1-0.4, and the refractive index difference between the second sub-packaging layer and the third sub-packaging layer is 0.2-0.

5.

7. The display panel according to claim 6, characterized in that: The total thickness of the cover layer and the three-layer sub-encapsulation layer is in the range of 2650-2750 angstroms, and the thickness of the cover layer accounts for 2.5%-3% of the total thickness.

8. The display panel according to claim 1 or 2, characterized in that: The material of the cover layer is selected to satisfy the following conditions: The refractive index at the wavelength of 460nm blue light is ≥2.0; The refractive index n at a wavelength of 530nm for green light is ≥ 1.9; and The refractive index n≥1.85 at the red light wavelength of 620nm.

9. The display device according to claim 1 or 8, characterized in that: The covering layer is an aromatic amine compound, and the general structural formula is: Wherein, X1 is any one of CR2, O, N, NR3, and S; A1 and Ar2 are any one of a C6 to C60 aryl group, a C10 to C60 condensed aryl group, and a C5 to C60 five-membered or six-membered aromatic heterocycle; L is any of a direct bond, a substituted or unsubstituted C6-C50 arylene group, or a substituted or unsubstituted C2-C50 heteroaryl group.

10. The display device according to claim 9, characterized in that: The A1 and Ar2 are any one of the following groups: X1, X2, X3 are any one of CR1, O, N, NR2, S; L, L1, L2 are direct bonds, phenyl, biphenyl, naphthyl; R1-R9 are hydrogen, deuterium, halogen, nitro, nitrile, alkyl, alkenyl, alkoxy, thioether, aryl, or heteroaryl, or adjacent substituents are fused to form a ring.

11. The display panel according to claim 1, characterized in that: The top-emitting OLED light-emitting unit includes an anode, a hole injection layer, a hole transport layer, an electron blocking layer, an organic light-emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer and a cathode on the substrate, wherein the hole injection layer, the hole transport layer and the electron blocking layer constitute a second optical structure with alternating high and low refractive indices.

12. The display panel according to claim 11, characterized in that: The hole transport layer has a refractive index that is smaller than that of adjacent layers.

13. The display panel according to claim 12, characterized in that: The hole transport layer material is selected to have a refractive index that satisfies the following conditions: The refractive index at 460 nm is not greater than 1.75 and the refractive index at 620 nm is not greater than 1.

70.

14. A method for preparing a top-emitting OLED display panel, characterized in that: include: forming a top-emitting OLED light-emitting unit on a substrate; forming a covering layer on the light-emitting side of the top-emitting OLED light-emitting unit; A first inorganic encapsulation layer, an organic encapsulation layer, and a second inorganic encapsulation layer are sequentially formed on the cover layer along the light emitting direction of the OLED light emitting unit, wherein the first inorganic encapsulation layer includes at least two sub-encapsulation layers stacked along the light emitting direction of the OLED light emitting unit, and the cover layer and the at least two sub-encapsulation layers constitute a first optical structure with alternating high and low refractive indices.

15. The preparation method according to claim 14, characterized in that: The method of forming a top-emitting OLED light-emitting unit on a substrate comprises: An anode, a hole injection layer, a hole transport layer, an electron blocking layer, an organic light-emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer and a cathode are sequentially formed on the substrate, wherein the hole injection layer, the hole transport layer and the electron blocking layer constitute a second optical structure with high and low refractive indices arranged alternately.

16. The preparation method according to claim 15, characterized in that: The hole transport layer has a refractive index that is smaller than that of adjacent layers.

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