A quantum dot light-emitting diode and its fabrication method
By treating the hole transport layer TFB surface of QLED devices with halogen-containing organic materials, the energy level difference and surface roughness are reduced, solving the problems of difficult electron and hole injection and short lifetime in QLED devices, and achieving high efficiency and long lifetime device performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2020-11-30
- Publication Date
- 2026-03-10
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Figure CN114583088B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of quantum dot light-emitting devices, and more particularly to a quantum dot light-emitting diode and its fabrication method. Background Technology
[0002] Quantum dot electroluminescent display technology has become the best candidate for next-generation display technology due to its advantages such as tunable wavelength, high color saturation, high material stability, and low manufacturing cost. After nearly two decades of development, the external quantum efficiency of quantum dot light-emitting diodes (QLEDs) has increased from 0.01% to over 20%, and in terms of device efficiency, QLEDs are now quite close to organic light-emitting diodes (OLEDs). However, despite the aforementioned advantages of quantum dot devices, their performance has not yet fully met the requirements for industrialization, especially for blue QLED devices.
[0003] Currently, the device structure of QLEDs is similar to that of OLEDs, forming a sandwich structure similar to a pin junction through a hole injection layer, a hole transport layer, a light-emitting layer, and an electron transport layer. This achieves efficient light emission by balancing the injection of electrons and holes. However, because the band gap of blue quantum dots is wider than that of red and green quantum dots, it is more difficult to inject electrons and holes, further increasing the start-up voltage and causing more severe interface charge accumulation, which significantly impacts the device's lifetime and efficiency.
[0004] Therefore, existing technologies still need to be improved and developed. Summary of the Invention
[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a quantum dot light-emitting diode and its fabrication method, aiming to solve the problem that the efficiency of existing devices still needs to be improved.
[0006] The technical solution of the present invention is as follows:
[0007] A method for fabricating a quantum dot light-emitting diode, comprising the following steps:
[0008] A hole transport layer is formed on the first electrode, the hole transport layer comprising a TFB;
[0009] A processing liquid is coated onto the hole transport layer and then subjected to heat treatment; wherein the processing liquid includes organic matter containing halogen elements.
[0010] A quantum dot luminescent layer is formed on the processed hole transport layer;
[0011] A second electrode is formed on the quantum dot light-emitting layer to obtain the quantum dot light-emitting diode.
[0012] A quantum dot light-emitting diode (LED) includes: a first electrode, a second electrode, a quantum dot light-emitting layer located between the first electrode and the second electrode, and a hole transport layer located between the first electrode and the quantum dot light-emitting layer. The hole transport layer comprises a TFB (trace element-free polymer), and the surface of the hole transport layer near the quantum dot light-emitting layer has an organic compound containing a halogen element.
[0013] Beneficial effects: This invention uses halogen-containing organic materials to post-process the surface of the hole transport layer of the TFB. Due to the presence of halogen, the HOMO energy level of the TFB can be reduced, thereby reducing the energy level difference at the interface with the quantum dot, reducing the interface barrier between the TFB and the quantum dot, improving the hole transport capability from the TFB to the quantum dot, improving the overall hole transport efficiency of the device, and improving the balance between hole transport and electron transport in the device, thereby improving the luminous efficiency of the device. At the same time, it also reduces damage to the functional layer in the device, thereby improving the device lifetime. Attached Figure Description
[0014] Figure 1 This is a schematic flowchart illustrating a method for fabricating a quantum dot light-emitting diode according to an embodiment of the present invention.
[0015] Figure 2 This is a schematic diagram of the structure of a quantum dot light-emitting diode provided in an embodiment of the present invention. Detailed Implementation
[0016] This invention provides a quantum dot light-emitting diode and its fabrication method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
[0017] The inventors discovered that designing more rational device structures and energy level structures, as well as introducing more stable material systems, are key to further improving device efficiency and lifespan.
[0018] Further research revealed that, from the perspective of quantum dot light-emitting diode (LED) device structure, the excessively high potential barrier at the interface between the hole transport layer (HTL) and the quantum dot (QD), and the resulting charge accumulation, severely impact device efficiency and lifetime. For example, a significant energy level difference exists at the TFB (poly(9,9-dioctylfluorene-CO-N-(4-butylphenyl)diphenylamine) / QD interface, resulting in a large potential barrier. This significantly hinders hole injection into the quantum dot layer, affecting hole injection and consequently impacting device efficiency. Simultaneously, charge accumulation at the interface leads to TFB degradation, ultimately causing device failure. This is because TFB has a high HOMO energy level of approximately 5.5 eV, while other hole transport materials such as PVK have a HOMO energy level of approximately 6.1 eV, and quantum dots have an energy level of approximately 6.2 eV. Therefore, the large energy level difference at the TFB-quantum dot interface results in a high potential barrier, significantly impeding hole transport from the TFB to the quantum dot.
[0019] Based on this, embodiments of the present invention provide a method for fabricating a quantum dot light-emitting diode, comprising the following steps:
[0020] S10. A hole transport layer is formed on the first electrode, wherein the hole transport layer includes a TFB;
[0021] S20. A processing liquid is coated on the hole transport layer and subjected to heat treatment; wherein the processing liquid includes organic matter containing halogen elements.
[0022] S30. Form a quantum dot luminescent layer on the processed hole transport layer;
[0023] S40. A second electrode is formed on the quantum dot light-emitting layer to obtain the quantum dot light-emitting diode.
[0024] In one embodiment, the hole transport layer is composed of TFBs, that is, the hole transport layer is a TFB layer.
[0025] In one embodiment, the halogen-containing organic compound includes at least one of fluorine, chlorine, and bromine, and the halogen is not iodine, because iodine-containing organic compounds have been found to not improve hole transport efficiency in the TFB layer. For example, the organic compound may contain fluorine, chlorine, or bromine, or both chlorine and bromine, or both fluorine and bromine.
[0026] This invention employs halogen-containing organic compounds to post-treat the surface of the TFB layer. The presence of halogens lowers the HOMO level of the TFB. This is because Cl, F, and Br have strong electron-withdrawing capabilities and inherently strong negative dipole moments. Their combination with TFB significantly modulates the electronic structure of the TFB, causing the HOMO level to bend downwards, thus lowering the TFB's HOMO level. Lowering the HOMO level of the TFB reduces the energy level difference at the quantum dot interface, reduces the interfacial barrier between the TFB and the quantum dot, improves the hole transport capability from the TFB to the quantum dot, and ultimately enhances the overall hole transport efficiency of the device. From the perspective of overall charge balance, since QLED devices originally have higher electron transport efficiency than hole transport efficiency, this invention improves the hole transport efficiency, thus enhancing the balance between hole and electron transport in the device. This reduces electron accumulation in the quantum dot emitting layer, decreases the probability of Auger recombination in the quantum dots, suppresses fluorescence quenching, and improves the device's luminous efficiency. It also reduces damage to the functional layers, thereby increasing the device's lifespan. Furthermore, the formed TFB layer typically has some unavoidable protrusions on its surface, resulting in a certain degree of roughness. Post-processing the TFB layer surface with a halogen-containing organic compound covers the protruding TFB layer surface with a layer of halogen-containing organic compound, filling the gaps between the protrusions, reducing the surface roughness of the TFB layer, and making the interface between the TFB layer and the quantum dot emitting layer smoother, thus reducing device leakage.
[0027] In step S10, in one embodiment, before the step of forming a hole transport layer on the first electrode, the method further includes: forming a hole injection layer on the first electrode, and then forming the hole transport layer on the hole injection layer. By providing the hole injection layer, the hole injection capability is improved.
[0028] In step S20, a treatment liquid is applied to the hole transport layer, and the treatment liquid covers the entire surface of the hole transport layer.
[0029] In this embodiment of the invention, the treatment liquid includes an organic compound containing halogen elements and a solvent.
[0030] In one embodiment, the treatment liquid consists of an organic compound containing halogen elements and a solvent.
[0031] In one embodiment, the halogen-containing organic compound includes at least one of trifluoroethylbenzene, trifluorotoluene, trifluoromethylphenol, trichloromethylphenol, trifluoromethylthiophenol, trichloroethylbenzene, and trifluoromethoxybenzene, but is not limited thereto. Compared to chlorine-containing organic compounds, fluorine-containing organic compounds provide better treatment results for the TFB layer.
[0032] In one embodiment, the concentration of the halogen-containing organic compound in the treatment solution is 0.1-5 mg / ml.
[0033] In one embodiment, the solvent in the treatment liquid includes, but is not limited to, one or more of, methanol, ethanol, chlorobenzene, toluene, and butanol. For example, halogen-containing organic compounds can be dissolved in methanol, ethanol, chlorobenzene, toluene, butanol, or in a mixed solvent of methanol and ethanol, or in a mixed solvent of methanol and butanol.
[0034] In this embodiment, after covering the hole transport layer with a processing liquid, the substrate covered with the processing liquid is heated. For example, the substrate can be heated by placing it on a heating plate.
[0035] In one embodiment, the temperature of the heat treatment is 50-300°C.
[0036] In one embodiment, the heat treatment time is 5-30 minutes.
[0037] In one embodiment, in the step of forming a hole transport layer on the first electrode, the thickness of the hole transport layer is 15-100 nm.
[0038] In one embodiment, the thickness of the treatment liquid layer is 1-2 nm, and the surface treatment of the TFB layer can be achieved with an extremely thin layer of treatment liquid.
[0039] In step S40, in one embodiment, before the step of forming the second electrode on the quantum dot light-emitting layer, the step further includes: forming an electron transport layer on the quantum dot light-emitting layer, and forming the second electrode on the electron transport layer.
[0040] This invention provides a quantum dot light-emitting diode, comprising: a first electrode, a second electrode, a quantum dot light-emitting layer located between the first electrode and the second electrode, and a hole transport layer located between the first electrode and the quantum dot light-emitting layer, wherein the hole transport layer comprises a TFB (tungsten-free radical), and the surface of the hole transport layer near the quantum dot light-emitting layer has an organic material containing a halogen element.
[0041] In one embodiment, the hole transport layer is composed of TFB (tungsten-free) material, i.e., the hole transport layer is a TFB layer. In other words, in this embodiment, the surface of the TFB layer near the quantum dot emitting layer is covered with a layer of halogen-containing organic material; the technical effects of this are described above and will not be repeated here.
[0042] In this embodiment of the invention, quantum dot light-emitting diodes come in various forms, and this embodiment will mainly use, for example... Figure 2 The quantum dot light-emitting diode shown is used as an example for a detailed introduction. Specifically, as... Figure 2 As shown, the quantum dot light-emitting diode includes a first electrode 1 (as an anode, disposed on a substrate), a hole injection layer 2, a hole transport layer 3, a quantum dot light-emitting layer 4, an electron transport layer 5, and a second electrode 6 (as a cathode) stacked from bottom to top.
[0043] In one embodiment, the substrate can be a rigid substrate, such as glass, or a flexible substrate, such as polyethylene terephthalate (PET) or polyimide (PI).
[0044] In one embodiment, the first electrode may be selected from one or more of indium-doped tin oxide (ITO), fluorine-doped tin oxide (FTO), antimony-doped tin oxide (ATO), and aluminum-doped zinc oxide (AZO).
[0045] In one embodiment, the material of the hole injection layer may be selected from materials with good hole injection performance, such as including but not limited to one or more of poly(N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)benzidine) (Poly-TPD), 4,4',4”-tris(carbazole-9-yl)triphenylamine (TCTA), poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) (PEDOT:PSS), 4,4'-bis(9-carbazole)biphenyl (CBP), NiO, MoO3, etc.
[0046] In one embodiment, the material of the quantum dot emitting layer can be oil-soluble quantum dots, which include one or more of binary, ternary, and quaternary quantum dots. Binary quantum dots include one or more of CdS, CdSe, CdTe, InP, AgS, PbS, PbSe, and HgS; ternary quantum dots include one or more of ZnCdS, CuInS, ZnCdSe, ZnSeS, ZnCdTe, and PbSeS; and quaternary quantum dots include one or more of ZnCdS / ZnSe, CuInS / ZnS, ZnCdSe / ZnS, CuInSeS, ZnCdTe / ZnS, and PbSeS / ZnS. The material of the quantum dot emitting layer can be any of the three common types of quantum dots (red, green, and blue) or other yellow-light-emitting quantum dots. The quantum dots can be cadmium-containing or cadmium-free. This material's quantum dot emitting layer has a broad and continuously distributed excitation spectrum and high emission spectrum stability. In this embodiment, the thickness of the quantum dot light-emitting layer is approximately 20–60 nm.
[0047] In one embodiment, the material of the electron transport layer can be selected from materials with good electron transport performance, such as, but not limited to, one or more of the following: n-type ZnO, TiO2, Fe2O3, SnO2, Ta2O3, AlZnO, ZnSnO, InSnO, etc.
[0048] In one embodiment, the second electrode can be selected from aluminum (Al) electrodes, silver (Ag) electrodes, and gold (Au) electrodes, or from aluminum nanowires, silver nanowires, and gold nanowires. These materials have low resistance, allowing for smooth carrier injection. In this embodiment, the thickness of the second electrode is approximately 15–30 nm.
[0049] The present invention will be further described in detail below through specific embodiments.
[0050] Example 1
[0051] ITO was deposited on the substrate as the first electrode with a thickness of 40 nm. Then, UVO (ultraviolet ozone) cleaning was performed for 15 min to clean the surface, improve surface wettability and increase the work function of ITO.
[0052] A layer of PEDOT:PSS was spin-coated onto ITO to create a hole injection layer. The spin-coating speed was 4000 rpm and the spin-coating time was 40 seconds. After that, the coating was annealed at 150°C for 15 minutes. The entire process was carried out in air.
[0053] A layer of TFB was spin-coated onto the hole injection layer to form a hole transport layer. The TFB was dissolved in chlorobenzene at a concentration of 8 mg / ml. The spin-coating speed was 3000 rpm and the spin-coating time was 30 seconds. After that, the spin-coating was annealed at 150°C for 20 minutes. The entire process was carried out in a glove box.
[0054] The surface of the TFB layer was treated by adding an ethanol solution of trifluoromethoxybenzene with a concentration of 1 mg / ml to the surface of the TFB layer, and then heating at 120°C for 10 min.
[0055] A quantum dot luminescent layer was spin-coated onto the hole transport layer. The quantum dots were dissolved in n-octane at a concentration of 20 mg / ml. The spin-coating speed was 3000 rpm for 30 seconds, followed by heating at 100°C for 20 minutes. This step was performed in a glove box.
[0056] A zinc oxide layer was spin-coated onto the quantum dot luminescent layer as an electron transport layer. The zinc oxide was dissolved in ethanol at a concentration of 30 mg / ml. The spin-coating speed was 3000 rpm for 30 seconds, followed by heating at 100°C for 30 minutes. This step was carried out in a glove box.
[0057] A layer of Ag is deposited on the zinc oxide layer to serve as the second electrode, with a thickness of 100 nm.
[0058] Example 2
[0059] ITO was deposited on the substrate as the first electrode with a thickness of 40 nm. Then, UVO (ultraviolet ozone) cleaning was performed for 15 min to clean the surface, improve surface wettability and increase the work function of ITO.
[0060] A layer of PEDOT:PSS was spin-coated onto ITO to create a hole injection layer. The spin-coating speed was 4000 rpm and the spin-coating time was 40 seconds. After that, the coating was annealed at 150°C for 15 minutes. The entire process was carried out in air.
[0061] A layer of TFB was spin-coated onto the hole injection layer to form a hole transport layer. The TFB was dissolved in chlorobenzene at a concentration of 8 mg / ml. The spin-coating speed was 3000 rpm and the spin-coating time was 30 seconds. After that, the spin-coating was annealed at 150°C for 20 minutes. The entire process was carried out in a glove box.
[0062] The surface of the TFB layer was treated by adding a 0.5 mg / ml solution of trichloromethylphenol in ethanol to the surface of the TFB layer, followed by heating at 100 °C for 20 min.
[0063] A quantum dot luminescent layer was spin-coated onto the hole transport layer. The quantum dots were dissolved in n-octane at a concentration of 20 mg / ml. The spin-coating speed was 3000 rpm for 30 seconds, followed by heating at 100°C for 20 minutes. This step was performed in a glove box.
[0064] A zinc oxide layer was spin-coated onto the quantum dot luminescent layer as an electron transport layer. The zinc oxide was dissolved in ethanol at a concentration of 30 mg / ml. The spin-coating speed was 3000 rpm for 30 seconds, followed by heating at 100°C for 30 minutes. This step was carried out in a glove box.
[0065] A layer of Ag is deposited on the zinc oxide layer to serve as the second electrode, with a thickness of 100 nm.
[0066] Comparative Example
[0067] ITO was deposited on the substrate as the first electrode with a thickness of 40 nm. Then, UVO (ultraviolet ozone) cleaning was performed for 15 min to clean the surface, improve surface wettability and increase the work function of ITO.
[0068] A layer of PEDOT:PSS was spin-coated onto ITO to create a hole injection layer. The spin-coating speed was 4000 rpm and the spin-coating time was 40 seconds. After that, the coating was annealed at 150°C for 15 minutes. The entire process was carried out in air.
[0069] A layer of TFB was spin-coated onto the hole injection layer to form a hole transport layer. The TFB was dissolved in chlorobenzene at a concentration of 8 mg / ml. The spin-coating speed was 3000 rpm and the spin-coating time was 30 seconds. After that, the spin-coating was annealed at 150°C for 20 minutes. The entire process was carried out in a glove box.
[0070] A quantum dot luminescent layer was spin-coated onto the hole transport layer. The quantum dots were dissolved in n-octane at a concentration of 20 mg / ml. The spin-coating speed was 3000 rpm for 30 seconds, followed by heating at 100°C for 20 minutes. This step was performed in a glove box.
[0071] A zinc oxide layer was spin-coated onto the quantum dot light-emitting layer as an electron transport layer. The zinc oxide was dissolved in ethanol at a concentration of 30 mg / ml. The spin-coating speed was 3000 rpm and the spin-coating time was 30 s. After that, it was heated at 100 °C for 30 min. This step was carried out in a glove box.
[0072] A layer of Ag is deposited on the zinc oxide layer to serve as the second electrode, with a thickness of 100 nm.
[0073] The device performance test data of the above Examples 1, 2 and comparative examples are shown in Table 1 below.
[0074] Table 1. Test Data
[0075] Project Group External quantum efficiency (EQE) T95 (1000nit) Example 1 20.3％ 6500h Example 2 19.1％ 5400h Comparative Example 14.8％ 3130h
[0076] Experimental data clearly shows that devices with treated TFB surfaces exhibit efficiency more than 30% higher and lifespan more than double that of untreated devices. The experimental results demonstrate that treating the TFB surface with organic compounds containing F or Cl can significantly improve the efficiency and lifespan of QLED devices.
[0077] In summary, this invention provides a quantum dot light-emitting diode (TFB) and its fabrication method. This invention uses an organic compound containing halogen elements to post-treat the surface of the TFB layer. The presence of halogens lowers the HOMO energy level of the TFB, thereby reducing the energy level difference at the quantum dot interface, decreasing the interfacial barrier between the TFB and the quantum dot, and improving the hole transport capability from the TFB to the quantum dot, thus improving the overall hole transport efficiency of the device. From the perspective of the overall charge balance of the device, since QLED devices originally have higher electron transport efficiency than hole transport efficiency, this invention improves the hole transport efficiency, thus enhancing the balance between hole and electron transport in the device. This reduces the accumulation of electrons in the quantum dot light-emitting layer, reduces the probability of Auger recombination in the quantum dot, suppresses fluorescence quenching of the quantum dot, improves the luminous efficiency of the device, and also reduces damage to the functional layers of the device, thereby increasing the device's lifetime.
[0078] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.
Claims
1. A method for fabricating a quantum dot light-emitting diode, characterized in that, The method comprises the steps of: forming a hole transport layer on the first electrode, the hole transport layer being composed of TFB; covering a treatment liquid on the hole transport layer, and performing a heating treatment; wherein the treatment liquid is composed of an organic substance containing halogen element and a solvent; forming a quantum dot light-emitting layer on the treated hole transport layer; forming a second electrode on the quantum dot light-emitting layer to obtain the quantum dot light-emitting diode; the organic substance containing halogen element is selected from at least one of trifluorobenzene, trifluoromethylbenzene, trifluoromethylphenol, trichloromethylphenol, trifluoromethylphenylthiol, trichlorobenzene and trifluoromethoxybenzene; the solvent in the treatment liquid is selected from one or more of methanol, ethanol, chlorobenzene, toluene and butanol; the concentration of the organic substance containing halogen element is 0.1-5 mg / ml.
2. The method for fabricating a quantum dot light-emitting diode according to claim 1, characterized in that, the temperature of the heating treatment is 50-300 ℃; and / or, the time of the heating treatment is 5-30 min.
3. The method for fabricating a quantum dot light-emitting diode according to claim 1, characterized in that, in the step of forming the hole transport layer on the first electrode, the thickness of the hole transport layer is 15-100 nm.
4. The method for fabricating a quantum dot light-emitting diode according to claim 1, characterized in that, before the step of forming the hole transport layer on the first electrode, the method further comprises the steps of: forming a hole injection layer on the first electrode, and forming the hole transport layer on the hole injection layer; and / or, before the step of forming the second electrode on the quantum dot light-emitting layer, the method further comprises the steps of: forming an electron transport layer on the quantum dot light-emitting layer, and forming the second electrode on the electron transport layer.
5. A quantum dot light emitting diode prepared by the method of any one of claims 1-4, comprising: A first electrode, a second electrode, a quantum dot light-emitting layer between the first electrode and the second electrode, and a hole transport layer between the first electrode and the quantum dot light-emitting layer, wherein the hole transport layer is composed of TFB, and the surface of the hole transport layer close to the quantum dot light-emitting layer side is provided with an organic substance containing halogen element.
Citation Information
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