Transparent cathode, Micro OLED device and preparation method

Abstract

The invention discloses a transparent cathode, a Micro OLED device and a preparation method, and belongs to the technical field of OLEDs. The invention discloses a preparation method of a transparent cathode. The preparation method comprises the following steps: constructing a nanowire grid on a substrate; depositing a transition layer on the nanowire grid; providing a graphene layer; and transferring the graphene layer to the transition layer. A transparent cathode comprising: a nanowire mesh; a transition layer, wherein the transition layer is arranged on the metal nanowire grid; and the graphene layer is arranged on the transition layer. By constructing the transition layer and the nanowire grid, the problem that the resistance value of a contact resistor between a graphene cathode and a light-emitting layer in an existing OLED device is large is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of OLED, and particularly relates to a transparent cathode, a Micro OLED device and a preparation method thereof. Background Art

[0002] Micro OLED is a micro-display device that combines semiconductor technology and organic light-emitting display technology. It generally includes a driving backplane, an anode structure, an organic layer, a cathode structure, etc., and is applicable to various display fields such as AR / VR.

[0003] The cathode structure of Micro OLED needs to have both high conductivity and transparency. Traditional materials such as Mg / Ag alloy have good conductivity, but their light transmittance is limited.

[0004] For example, Chinese Patent with publication number CN114203930B discloses a cathode, an organic light-emitting diode and a preparation method thereof. The cathode is a graphene stack formed by stacking multiple layers of graphene sheets. The thickness range of each layer of the graphene sheet is any value from 0.332 nm to 0.357 nm, the number of layers stacked by the graphene sheets is any integer from 35 layers to 55 layers, and the work function of the cathode is any value from 2.5 eV to 3 eV. By using graphene as the cathode, it has high light transmittance, water and oxygen corrosion resistance, and high conductivity, etc.

[0005] However, although graphene has high light transmittance and high conductivity as a transparent electrode material, there is a contact resistance of 500 Ω - 2000 Ω between its interface with the organic layer, and the contact resistance value is relatively large, which affects the device efficiency.

[0006] Therefore, it is urgently necessary to develop a transparent cathode, a Micro OLED device and a preparation method to solve the problems in the prior art. Summary of the Invention

[0007] The purpose of the present invention is to provide a transparent cathode, a Micro OLED device and a preparation method thereof, by constructing a transition layer and a nanowire grid on the graphene layer to solve the problem of the relatively large contact resistance between the existing graphene cathode and the light-emitting layer proposed in the above background art.

[0008] To solve the above technical problems, the specific technical solution of the present invention is as follows:

[0009] A preparation method of a transparent cathode, comprising the following steps:

[0010] Construct a nanowire grid on a substrate;

[0011] Deposit a transition layer on the nanowire grid;

[0012] Provide a graphene layer;

[0013] Transfer the graphene layer onto the transition layer.

[0014] Furthermore, the substrate is the organic layer of an OLED.

[0015] Furthermore, fabricating the nanowire grid on the substrate includes the following steps:

[0016] Set a mask on the substrate;

[0017] By thermal evaporation process, thermally evaporate metallic silver at 1300 °C and 0.8 Å / S to construct the nanowire grid;

[0018] Strip the mask.

[0019] Furthermore, depositing the transition layer on the nanowire grid includes the following steps:

[0020] Deposit an IZO nanothin layer on the nanowire grid by magnetron sputtering; wherein, the temperature during deposition is 0 °C - 30 °C, and the coating rate is 1 Å / S - 2 Å / S.

[0021] Furthermore, transferring the graphene layer onto the transition layer includes the following steps:

[0022] Adhere a second substrate to the side of the graphene layer away from the first substrate;

[0023] Remove the first substrate;

[0024] Bond the side of the graphene layer away from the second substrate to the organic layer;

[0025] Remove the second substrate.

[0026] A transparent cathode, comprising:

[0027] A nanowire grid;

[0028] A transition layer, which is disposed on the nanowire grid;

[0029] A graphene layer, which is disposed on the transition layer.

[0030] Furthermore, the transition layer is an IZO nanothin layer, and the thickness of the transition layer is 7 nm - 10 nm.

[0031] Furthermore, the nanowire grid includes a plurality of silver nanowires, the diameter of the silver nanowires is 20 nm - 25 nm, the length is 2 μm - 9 μm, and the grid density is 10 lines / μm - 50 lines / μm.

[0032] A Micro OLED device includes a driving backplane and a light-emitting device structure module, and the light-emitting device structure module is disposed on the driving backplane;

[0033] The light-emitting device structure module includes:

[0034] An anode structure, and the anode structure is disposed on the driving backplane;

[0035] An organic layer, and the organic layer is disposed on the anode structure;

[0036] The transparent cathode, and the transparent cathode is disposed on the organic layer.

[0037] Furthermore, it further includes:

[0038] A packaging layer, and the packaging layer is disposed on the light-emitting device structure module.

[0039] The present invention has the following advantages:

[0040] (1) By constructing a transition layer and a nanowire grid on one side of the graphene layer for connecting with the organic layer, the problem of large contact resistance between the graphene cathode and the light-emitting layer in the existing OLED device is solved. Combining the high light transmittance of graphene and the high conductivity of metal nanowires, the performance bottleneck of a single material is broken through, so that the sheet resistance of the cathode structure is <30 Ω / sq and the light transmittance >95%. At the same time, in terms of cost, the present application reduces the usage amount of precious metals such as Ag, and the large-scale production cost of graphene is also relatively low.

[0041] (2) Through the thermal evaporation process under the conditions of 1300 °C and 0.8 Å / S, the magnetron sputtering process with a temperature of 0 °C - 30 °C and a coating rate of 1 Å / S - 2 Å / S, and the graphene layer transfer process of the present application, the transparent cathode of the present application is directly constructed on the organic layer of the OLED. The steps adopt the mainstream semiconductor process, are compatible with the existing Micro OLED production line, and are easy to implement.

[0042] (3) The packaging layer extends to cover the edge of the light-emitting device structure module, blocking the side water and oxygen penetration path, and the water and oxygen transmittance ≤ 9×10⁻ 4 g / m² / day.

[0043] Other features and advantages of the present invention will be disclosed in detail in the following specific embodiments and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a schematic diagram of the overall structure of the light-emitting device structure module of the present application;

[0045] Figure 2 It is a schematic diagram of the overall structure of the Micro OLED device of the present application.

[0046] Figure 3 This is the flowchart for preparing the transparent cathode of the present application.

[0047] Description of the markings in the figure: 1. Light-emitting device structure module; 11. Graphene layer; 12. Transition layer; 13. Nanowire grid; 14. Organic layer; 15. Anode structure; 2. Driving backplane; 3. Encapsulation layer. Detailed implementation manners

[0048] To better understand the purpose, structure and function of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0049] Example 1

[0050] A transparent cathode, as Figure 1 shown, is applied to a Micro OLED device and includes:

[0051] Nanowire grid 13;

[0052] Transition layer 12, which is disposed on the metal nanowire grid 13;

[0053] Graphene layer 11, which is disposed on the transition layer 12.

[0054] In this embodiment, the nanowire grid 13 includes a plurality of silver nanowires, which are formed by a plurality of silver nanowires. The diameter of the silver nanowires is 20 nm - 25 nm, the length is 2 μm - 9 μm, and the grid density is 10 lines / μm - 50 lines / μm. The nanowire grid 13 is used to provide a high-conductivity network.

[0055] Optionally, the material of the nanowire grid 13 can also be copper, gold, etc.

[0056] The transition layer 12 is an IZO nano-thin layer, and the thickness of the transition layer 12 is 7 nm - 10 nm. The transition layer 12 is used to reduce the contact resistance between the graphene layer 11 and the nanowire grid 13.

[0057] The graphene layer 11 is a single layer or multiple layers, and the graphene layer 11 is used as the main conductive layer.

[0058] Table 1: Test result table of the present application and the prior art.

[0059]

[0060] As shown in Table 1 above, it is a specific test result table of the transparent cathode of the present application and the conventional cathode in the prior art. Among them, when the magnesium-silver alloy MgAg is used as the cathode, the film thickness of the magnesium-silver alloy MgAg is generally 110 Å, its sheet resistance is 20.6 Ω / sq, and the transmittance under 450 nm light is 65.7%; when only IZO is used as the cathode, the film thickness of IZO is generally 1500 Å, its sheet resistance is 74 Ω / sq, and the transmittance is 85.6%; while in the present application, an Ag nanowire grid 13, an IZO transition layer 12, and a graphene layer 11 are sequentially arranged on the organic layer 14 away from the anode. Under the conditions that the film thickness of the Ag nanowire grid 13 is 30 Å, the film thickness of the IZO transition layer 12 is 100 Å, and the film thickness of the graphene layer 11 is 10 Å, the sheet resistance is 23.9 Ω / sq, and the transmittance is 95.6%. Compared with using only graphene as the cathode, the contact resistance decreases greatly, and the transmittance decreases less. The figure of merit FoM = σ / τ ≥ 150, which is better than the figure of merit of about 100 of the traditional IZO cathode. And it is applicable to flexible substrates such as PET and PI. When the bending radius ≤ 2 mm, the resistance change rate < 5%.

[0061] A method for preparing a transparent cathode, as Figure 3 shown, includes the following steps:

[0062] S1: Construct a nanowire grid 13 on a substrate;

[0063] S2: Deposit a transition layer 12 on the nanowire grid 13;

[0064] S3: Provide a graphene layer 11;

[0065] S4: Transfer the graphene layer 11 onto the transition layer 12.

[0066] In this embodiment, the substrate is the organic layer 14 of the OLED device. Specifically, the organic layer 14 may include a hole transport layer, a light-emitting layer, an electron transport layer, etc. In this embodiment, the cathode is prepared directly on the organic layer 14 after the organic layer 14 of the OLED device is prepared.

[0067] In this embodiment, the construction of the nanowire grid 13 on the substrate in S1 is achieved by thermal evaporation, and includes the following steps:

[0068] S101: Set an OPEN MASK mask on the substrate; preferably, the OPEN MASK mask is a high-precision OPENMASK mask with an error within 10 nm;

[0069] S102: Through the thermal evaporation process, thermally evaporate metal Ag under the conditions of 1300 °C and 0.8 Å / S;

[0070] S103: Physically peel off the OPEN MASK mask.

[0071] Optionally, the OPEN MASK in S101 can also be other mask plates that can construct the aforementioned nanowire grid 13. Preferably, the aforementioned mask plate can be physically peeled off.

[0072] Depositing the transition layer 12 on the nanowire grid 13 in S2 includes the following steps:

[0073] Depositing an IZO nanothin layer on the nanowire grid 13 by magnetron sputtering; wherein, the temperature during deposition is 0°C - 30°C, and the coating rate is 1 Å / S - 2 Å / S.

[0074] In this embodiment, the graphene layer 11 provided in S3 is grown on one side of the first substrate by CVD method, and the first substrate is a rigid substrate. Optionally, the graphene layer 11 can also be grown on one side of the first substrate by other existing technologies. The

[0075] Transferring the graphene layer 11 to the transition layer 12 in S4 includes the following steps:

[0076] S41: Bond a second substrate to the side of the graphene layer 11 away from the first substrate;

[0077] S42: Remove the first substrate;

[0078] S43: Bond the side of the graphene layer 11 away from the second substrate to the organic layer 14;

[0079] S44: Remove the second substrate.

[0080] In this embodiment, bonding the second substrate to the side of the graphene layer 11 away from the first substrate in S41 includes the following steps in sequence:

[0081] Evaporate a sacrificial layer on the side of the graphene layer 11 away from the first substrate;

[0082] Spin-coat a bonding adhesive on the side of the sacrificial layer away from the first substrate to construct a bonding adhesive layer;

[0083] Bond the second substrate to the side of the bonding adhesive layer away from the first substrate. In this embodiment, the second substrate is a rigid support substrate. In this embodiment, the warpage of the rigid support substrate is less than 20 nm, and the material can be PMMA, etc.

[0084] The method of removing the first substrate in S42 is to peel off the first substrate.

[0085] When bonding the side of the graphene layer 11 away from the second substrate to the side of the organic layer 14 away from the anode in S43, the bonding temperature is 50°C - 100°C and the pressure is 0.1 MPa - 5 MPa;

[0086] In this embodiment, after removing the second substrate in S44, the following steps are further included:

[0087] Removing the bonding glue layer;

[0088] Removing the sacrificial layer.

[0089] Among them, the second substrate can be removed by physical peeling, and the bonding glue layer and the sacrificial layer can be removed by wet etching using a non-corrosive solution.

[0090] Embodiment 2

[0091] A Micro OLED device, as Figure 1 and Figure 2 shown, includes a driving backplane 2 and a light-emitting device structure module 1, and the light-emitting device structure module 1 is disposed on the driving backplane 2;

[0092] The driving backplane 2 includes:

[0093] An anode structure 15, and the anode structure 15 is disposed on the driving backplane 2;

[0094] An organic layer 14, and the organic layer 14 is disposed on the anode structure 15;

[0095] A transparent cathode, and the transparent cathode is disposed on the organic layer 14. The transparent cathode includes:

[0096] A nanowire grid 13, and the nanowire grid 13 includes a plurality of silver nanowires and is formed by the plurality of silver nanowires. The diameter of the silver nanowires is 20 nm - 25 nm, the length is 2 μm - 9 μm, and the grid density is 10 lines / μm - 50 lines / μm;

[0097] A transition layer 12, and the transition layer 12 is disposed on the metal nanowire grid 13. The transition layer 12 is an IZO nano-thin layer, and the thickness of the transition layer 12 is 7 nm - 10 nm;

[0098] A graphene layer 11, and the graphene layer 11 is disposed on the transition layer 12. The graphene layer 11 is single-layer or multi-layer.

[0099] In this embodiment, the driving backplane 2 is made based on a silicon substrate, and a plurality of light-emitting device structure modules 1 are disposed on the driving backplane 2.

[0100] Further included is: a packaging layer 3, which is disposed on the light-emitting device structure module 1, and the packaging layer 3 covers the surface of the light-emitting device structure module 1.

[0101] In this embodiment, the material of the packaging layer 3 is Al2O3. The packaging layer 3 is used to cover the top surface and the side surface of the light-emitting device structure module 1. The thickness of the packaging layer 3 on the top surface and the side surface of the light-emitting device structure module 1 is 200 Å - 2000 Å, so as to block water and oxygen, and make the water and oxygen transmittance ≤ 9×10⁻ 4 g / m² / day, and also make the Micro OLED device have better stability. After 1000 hours of aging test at 85°C / 85%RH, the brightness attenuation is < 5%, which is significantly better than the traditional packaging structure.

[0102] A preparation method of a Micro OLED device includes the following steps:

[0103] Prepare a driving circuit on a silicon substrate to form a driving backplane 2;

[0104] Prepare an anode structure 15, a pixel definition layer, and an organic layer 14 on the driving backplane 2;

[0105] Construct a nanowire grid 13 on the organic layer 14;

[0106] Deposit a transition layer 12 on the nanowire grid 13;

[0107] Provide a graphene layer 11; transfer the graphene layer 11 onto the transition layer 12.

[0108] The constructing of the nanowire grid 13 on the substrate includes the following steps:

[0109] Set a mask plate on the substrate;

[0110] By thermal evaporation process, evaporate metallic silver at 1300°C and 0.8 Å / S to construct the nanowire grid 13;

[0111] Strip the mask plate.

[0112] The depositing of the transition layer 12 on the nanowire grid 13 includes the following steps:

[0113] Deposit an IZO nano-thin layer on the nanowire grid 13 by magnetron sputtering method; wherein, the deposition temperature is 0°C - 30°C, and the coating rate is 1 Å / S - 2 Å / S.

[0114] The transferring of the graphene layer 11 onto the transition layer 12 includes the following steps:

[0115] Bond a second substrate to the side of the graphene layer 11 away from the first substrate;

[0116] Remove the first substrate;

[0117] Bond the side of the graphene layer 11 away from the second substrate to the organic layer 14;

[0118] Remove the second substrate.

[0119] The method for preparing the Micro OLED device further includes:

[0120] Construct an encapsulation layer 3 on the graphene layer 11.

[0121] Among them, the preparation of the driving circuit on the silicon substrate to form the driving backplane 2 and the preparation of the anode structure 15, the pixel definition layer and the organic layer 14 on the driving backplane 2 can all refer to the prior art, and will not be elaborated in this application.

[0122] In this embodiment, the encapsulation layer 3 is realized by atomic layer deposition (ALD). By depositing Al2O3 on the graphene layer 11, an encapsulation layer 3 with a thickness of 800 Å - 2000 Å is constructed on the side and top surface of the light-emitting device structure module 1.

[0123] Through the thermal evaporation process under the conditions of 1300 °C and 0.8 Å / S, the magnetron sputtering process with a temperature of 0 °C - 30 °C and a coating rate of 1 Å / S - 2 Å / S, and the graphene layer transfer process of this application, the transparent cathode of this application is directly constructed on the organic layer of the OLED. The steps adopt the mainstream semiconductor process, are compatible with the existing Micro OLED production line, and are easy to implement.

[0124] Embodiment III

[0125] The difference between this embodiment and Embodiment I and Embodiment II lies in:

[0126] The transfer of the graphene layer 11 to the transition layer 12 includes the following steps:

[0127] Spin-coat a PMMA glue layer on the side of the graphene layer 11 away from the first substrate to construct a PMMA glue layer on the graphene layer 11, so as to directly bond the second substrate to the graphene layer 11;

[0128] Peel off the first substrate;

[0129] Bond the side of the graphene layer 11 away from the second substrate to the organic layer 14;

[0130] Dry-etch to remove the second substrate, wherein a non-corrosive gas is used during the dry-etching.

[0131] It will be understood that the present invention is described by way of some embodiments, and those skilled in the art will appreciate that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the present invention. Additionally, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the scope protected by the present invention.

[0132] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment contains only one independent technical solution. This narrative style of the specification is only for clarity, and those skilled in the art should regard the specification as a whole. The technical solutions in the various embodiments can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a transparent cathode, characterized in that, It includes the following steps: Construct a nanowire grid on a substrate; Deposit a transition layer on the nanowire grid; Provide a graphene layer; Transfer the graphene layer onto the transition layer.

2. The method for preparing the transparent cathode according to claim 1, wherein, The substrate is an organic layer of an OLED.

3. The preparation method of the transparent cathode according to claim 2, characterized in that, The step of constructing a nanowire grid on the substrate includes the following steps: Set a mask on the substrate; Through a thermal evaporation process, thermally evaporate metallic silver at 1300 °C and 0.8 Å / S to construct a nanowire grid; Remove the mask.

4. The method for preparing a transparent cathode according to claim 2, wherein, The step of depositing a transition layer on the nanowire grid includes the following steps: Deposit an IZO nano-thin layer on the nanowire grid by magnetron sputtering; wherein, the temperature during deposition is 0 °C - 30 °C, and the coating rate is 1 Å / S - 2 Å / S.

5. The method for preparing the transparent cathode according to claim 2, characterized in that, The step of transferring the graphene layer onto the transition layer includes the following steps: Adhere a second substrate to the side of the graphene layer away from the first substrate; Remove the first substrate; Bond the side of the graphene layer away from the second substrate to the organic layer; Remove the second substrate.

6. A transparent cathode, characterized in that, It includes: A nanowire grid; A transition layer, which is disposed on the nanowire grid; A graphene layer, which is disposed on the transition layer.

7. The transparent cathode according to claim 6, characterized in that, The transition layer is an IZO nano-thin layer, and the thickness of the transition layer is 7 nm - 10 nm.

8. The transparent cathode according to claim 7, wherein The nanowire grid includes a plurality of silver nanowires, the diameter of the silver nanowires is 20 nm - 25 nm, the length is 2 μm - 9 μm, and the grid density is 10 lines / μm - 50 lines / μm.

9. A Micro OLED device, characterized in that, It includes a driving backplane and a light-emitting device structure module, and the light-emitting device structure module is disposed on the driving backplane; The light-emitting device structure module includes: An anode structure, which is disposed on the driving backplane; An organic layer, which is disposed on the anode structure; The transparent cathode according to any one of claims 6 - 8, and the transparent cathode is disposed on the organic layer.

10. The Micro OLED device according to claim 9, characterized in that, It further includes: A packaging layer, which is disposed on the light-emitting device structure module.

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