Symmetric doping method of zinc-based oxide semiconductor nanocrystals and applications thereof

Abstract

The application discloses a symmetric doping method of zinc-based oxide semiconductor nanocrystals and application thereof, and comprises the following steps: preparing surface hydroxylated zinc oxide nanocrystals, which are N type; realizing conversion of the zinc oxide nanocrystals from N type to P type by amino silane functionalization on the surface hydroxylated zinc oxide nanocrystals of N type, and obtaining zinc oxide nanocrystals of P type; and the application can further obtain zinc oxide nanocrystals with different carrier concentrations by metal ion doping, and can adjust the work function in a wide range. The obtained nanocrystals can be applied to design light emitting diodes, can be used as a carrier transport layer or a quantum well potential barrier layer in a multi-quantum well structure, and can be used to prepare a multi-layer structure by a solution method, including a multi-quantum well light emitting layer structure; the nanocrystals are further doped with metal ions or alloyed to match light emitting layer materials with different work functions, and can effectively inhibit fluorescence quenching, and realize all-inorganic QLED.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oxide semiconductor and quantum dot light emitting diode, in particular to P-type zinc oxide nanocrystal and its application. BACKGROUND

[0002] The manufacturing process of authoritative semiconductors such as silicon (Si) and gallium arsenide (GaAs) has problems of high energy consumption and high operating cost. Metal oxide nanocrystal semiconductors can be prepared by low-temperature chemical method, have a wide band gap of electronic energy band, and have excellent light transmittance, and are important optoelectronic and information technology materials for developing low-carbon economy. In the electronic structure of metal oxides, the conduction band bottom is contributed by the delocalized orbit of metal atoms, and the valence band top is contributed by the localized orbit of oxygen atoms, so metal oxides generally have good electron mobility, but the hole mobility is relatively low. The development of chip technology requires the use of the same material system and symmetrical doping effect [1] , for example, silicon-based CMOS uses a combination of NMOS and PMOS, making device integration easier and reducing energy consumption. It is currently difficult to prepare high-performance wide-bandgap P-type metal oxide semiconductors by alloying or doping, so there is a lack of excellent bipolar metal oxide semiconductor materials. If metal oxides are used as both electron transport materials and hole transport materials, the device power consumption is often high due to the unbalanced transport characteristics.

[0003] Zinc oxide has good electron transport capability and can be applied to electroluminescent devices. However, due to the aforementioned asymmetric doping effect, the carrier transport capability of P-type zinc oxide nanocrystals is poor. Most of the reported P-type zinc oxide is in the form of single crystal materials or nanowires, which are not suitable for QLED applications. The preparation method of bulk materials is mainly pulse laser deposition, molecular beam epitaxy, MOCVD, and atomic layer epitaxy, which is a gas phase method with high cost, and the carrier concentration is still significantly lower than that of the corresponding N-type semiconductor materials. Zinc oxide nanomaterials prepared by sol-gel method are mainly doped by sodium ions or nitrogen elements, but due to the limited doping concentration, the compensation effect of intrinsic defects, deep level defects and bistable structure, the P-type doping has not achieved the expected effect [2] . The existing P-type oxide semiconductor with relatively high performance needs to be formed into high-quality crystals through high-temperature process, which limits the application of devices. Due to the above material technology problems, the current quantum dot electroluminescent diode (QLED) and organic light emitting diode (OLED) still use a complex material system of organic carrier transport layer as the main carrier transport layer, such as using PEDOT:PSS, TFB, PTAA as hole transport material, and using TPBi, B2, etc. as electron transport material [3-7]This not only restricts device integration, but also limits the performance and lifetime of QLED devices. QLED is a kind of LED device using quantum dots as the light-emitting layer. In order to improve the probability of carrier forming excitons and thus improve the light-emitting efficiency, LEDs usually use quantum well structures, usually multi-layered multi-quantum well (MQW) structures [8-9] Quantum well (QW) refers to the use of higher bandgap semiconductors on both sides of the light-emitting layer to spatially confine electrons and holes through the formation of I-type heterojunctions, thereby improving the radiative recombination rate of the quantum dot light-emitting layer and achieving the purpose of enhancing light-emitting efficiency. Compared with LEDs, the main advantage of QLED is that it can fully utilize the batch production of quantum dot materials by chemical methods, and the cost of the solution device process used is also relatively low. However, due to the lack of wide-bandgap bipolar semiconductor materials, especially the lack of nanocrystalline semiconductors suitable for solution preparation and application [10-11] , it is difficult for existing QLED to realize multi-quantum well device structures. Moreover, most known and scalable MQW and superlattice structures are epitaxially grown. Although the commercialization of epitaxial MQW and superlattices has made important progress, their integration onto any substrate has inherent difficulties, thus limiting their application range

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[0017] Based on the deficiencies of the prior art, the application discloses a symmetric doping method of zinc-based oxide semiconductor nanocrystals and obtains P-type zinc oxide nanocrystals, the nanocrystals can be used to prepare a carrier transport layer with nanoscale thickness by a low-cost solution method and can be prepared in a large area, and are applied to design semiconductor devices such as light-emitting diodes, thin-film solar cells and multifunctional integrated chips. The application also provides application of the P-type zinc oxide nanocrystals as barrier layers of quantum wells in a multi-quantum well structure to construct a high-performance quantum dot electroluminescent diode.

[0018] To achieve the purpose, the application adopts the following technical scheme:

[0019] The application first discloses a symmetric doping method of zinc-based oxide semiconductor nanocrystals (the doping method is not limited to doping of a real chemical element, but refers to a method for achieving a target polarity), and the method has the following characteristics: surface-hydroxylated zinc oxide nanocrystals are prepared, and the zinc oxide nanocrystals are N-type; amino-silane functionalization is performed on the N-type surface-hydroxylated zinc oxide nanocrystals to inhibit formation of oxygen vacancies of the zinc oxide nanocrystals, increase a work function of the zinc oxide nanocrystals and enhance a hole transport capacity, so that the zinc oxide nanocrystals are converted from N-type to P-type, and P-type amino-silane functionalized ZnO nanocrystals are obtained, which are denoted as AP-ZnO.

[0020] Further, the AP-ZnO is doped with metal M ions to obtain AP-ZnO:M; by adjusting the doping element and / or doping concentration of the metal M ions, the work function and carrier concentration of the AP-ZnO are adjusted, so that the AP-ZnO can realize energy level matching when applied to an optoelectronic device, the electron and hole transport capacities in the device are similar, and thus the quantum efficiency of the device is improved.

[0021] Based on the method, the application further provides zinc oxide nanocrystals, including surface-hydroxylated zinc oxide nanocrystals of N-type, amino-silane functionalized zinc oxide nanocrystals of P-type and AP-ZnO nanocrystals doped with metal M ions. A dispersion liquid of the nanocrystals can be directly made into a thin film by a solution spin coating technology and is used in a quantum dot light-emitting diode QLED. The thin film made of the AP-ZnO is denoted as an AP-ZnO thin film, the thin film made of the AP-ZnO:M is denoted as an AP-ZnO:M thin film, and the thin film made of the surface-hydroxylated zinc oxide nanocrystals is denoted as a ZnO thin film.

[0022] The application further provides a quantum dot light emitting diode, which comprises a hole transport layer, a light emitting layer, an electron transport layer and a cathode arranged on the surface of an ITO transparent conductive glass anode layer by layer; the electron transport layer is the AP-ZnO film, the AP-ZnO:M film, the laminated film composed of the AP-ZnO film and the ZnO film, or the laminated film composed of the AP-ZnO:M film and the ZnO film, wherein the laminated film is directly contacted with the light emitting layer by the AP-ZnO film or the AP-ZnO:M film.

[0023] Furthermore, the hole transport layer is the AP-ZnO film, the laminated film composed of the ZnO film and the AP-ZnO film, or the laminated film composed of the ZnO film and the AP-ZnO:M film, wherein the laminated film is directly contacted with the anode by the ZnO film.

[0024] Furthermore, the light emitting layer comprises n layers of quantum dot light emitting films, and n≥1; when n≥2, the AP-ZnO film or the AP-ZnO:M film is inserted between the adjacent quantum dot light emitting films as a barrier layer, thereby forming a QLED containing a multi-quantum well light emitting layer.

[0025] Compared with the prior art, the application has the following beneficial effects:

[0026] 1. The application realizes the symmetric doping of zinc-based oxide semiconductor nanocrystals by controlling the work function and carrier concentration of zinc oxide nanocrystals through the amino silane functionalization to inhibit oxygen vacancies and possible strain effects; meanwhile, the doping ratio can be improved when the nanocrystals are doped with metal M ions in the subsequent process based on the lattice strain effect caused by the amino silane functionalization, so that efficient electronic structure regulation is realized based on chemical composition.

[0027] 2. The P-type amino silane functionalized zinc oxide nanocrystals applied in QLED can further control the work function through Nd, Ga and other metal ion doping to realize the balance of carrier injection, and can be set as an interface layer between the light emitting layer and the electron transport layer to improve the light emitting efficiency or brightness of the device.

[0028] 3. The combination of two or more light emitting layers and interface layers forms a double quantum well or multi-quantum well light emitting layer structure, which can significantly improve the carrier injection efficiency.

[0029] 4. The method according to the application can simultaneously obtain N-type zinc oxide nanocrystals with excellent electron transport performance and P-type zinc oxide nanocrystals with excellent hole transport performance, so that the same type of zinc-based oxide semiconductor can be used in the same chip, which has the advantages of process integration, simple structure, low manufacturing power consumption and low cost.

[0030] 5、The prepared P-type zinc oxide nanocrystals can replace traditional organic semiconductors as a hole transport layer, inhibit fluorescence quenching, can be applied to various types of quantum dot light emitting materials, can meet the design requirements of more extensive semiconductor devices, and can greatly reduce the cost. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 (a) is the Mott-Schottky plot of the ZnO nanocrystals prepared in Example 1 in 0.1M Na2SO4 under dark conditions; Figure 1 (b) is the Mott-Schottky plot of the AP-ZnO nanocrystals prepared in Example 1 in 0.1M Na2SO4 under dark conditions.

[0032] Figure 2 The electrochemical potential plot of the AP-ZnO nanocrystals prepared in Example 1.

[0033] Figure 3 The XPS full spectrum of the ZnO and AP-ZnO nanocrystals prepared in Example 1.

[0034] Figure 4 The XPS spectrum of O1s of the ZnO and AP-ZnO nanocrystals prepared in Example 1.

[0035] Figure 5 (a) is the voltage and current density curve of the single hole device with ZnO, AP-ZnO and ZnO / AP-ZnO combined structure as a hole transport layer in Example 2; Figure 5 (b) is the voltage and current density curve of the single electron device with ZnO, AP-ZnO and ZnO / AP-ZnO combined structure as an electron transport layer in Example 2.

[0036] Figure 6 (a) is the voltage and current density curve of the single hole device with AP-ZnO as a hole transport layer in Example 3; Figure 6 (b) is the voltage and current density curve of the single electron device with AP-ZnO / ZnO as an electron transport layer in Example 3.

[0037] Figure 7 (a) is the voltage and current density curve of the single quantum well QLED based on the all-inorganic carrier transport layer in Example 3; Figure 7 (b) is the voltage and current density curve of the double quantum well QLED based on the all-inorganic carrier transport layer in Example 3.

[0038] Figure 8 The voltage and luminous intensity curve of the double quantum well QLED based on the all-inorganic carrier transport layer in Example 3.

[0039] Figure 9 EL spectra of the double quantum well QLED based on all-inorganic carrier transport layers in Example 3.

[0040] Figure 10 Voltage vs. current density curves of the single electron device with AP-ZnO:Nd / Al injecting electrons and tuning in Example 4.

[0041] Figure 11 Voltage vs. current density curves of the QLED device with AP-ZnO:Na / Ag injecting electrons efficiently in Example 5.

[0042] Figure 12 Voltage vs. luminance curves of the QLED device with AP-ZnO:Na / Ag injecting electrons efficiently in Example 5.

[0043] Figure 13 EL spectra of the QLED device with AP-ZnO:Na / Ag injecting electrons efficiently in Example 5 at different voltages.

[0044] Figure 14 EQE of the QLED device with AP-ZnO:Na / Ag injecting electrons efficiently in Example 5.

[0045] Figure 15 Voltage vs. current density curves of the all-inorganic QLED device with AP-ZnO:Na / Ag injecting electrons efficiently in Example 6.

[0046] Figure 16 Voltage vs. luminance curves of the all-inorganic QLED device with AP-ZnO:Na / Ag injecting electrons efficiently in Example 6.

[0047] Figure 17 EL spectra of the all-inorganic QLED device with AP-ZnO:Na / Ag injecting electrons efficiently in Example 6 at different voltages.

[0048] Figure 18 Voltage vs. current density curves of the single hole device with efficient hole injection structure based on AP-ZnO and silver electrode in Example 7.

[0049] Figure 19 Voltage vs. current density curves of the single electron device with efficient electron injection structure based on AP-ZnO and silver electrode in Example 7.

[0050] Figure 20 PL spectra of the light-emitting layer under different substrates in Example 8. DETAILED DESCRIPTION

[0051] In order to make the objects, technical solutions and advantages of the present application clearer, the following will clearly and completely describe the present application with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only part of, rather than all of, the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0052] Example 1, Preparation and characterization of P-type AP-ZnO nanocrystals

[0053] 1. Synthesis of surface hydroxylated ZnO nanocrystals

[0054] 30 mL of dimethyl sulfoxide (DMSO) and 3 mmol of zinc acetate dihydrate were mixed and stirred at room temperature for 30 min, and then a solution containing 5.5 mmol of tetramethylammonium hydroxide (TMAH) in ethanol (10 mL) was added dropwise to the solution within 5 min, and the stirring was continued at room temperature for 24 h to obtain a clear colloid.

[0055] The obtained clear colloid was mixed with ethyl acetate at a volume ratio of 1:2, and then centrifuged to wash, and the obtained precipitate was dispersed in ethanol at a concentration of 0.3686 mol / L to obtain an ethanol dispersion of surface hydroxylated ZnO nanocrystals (hereinafter referred to as ZnO ethanol solution).

[0056] 2. Synthesis of water dispersion system of AP-ZnO nanocrystals

[0057] 0.74 mmol of ZnO in the ZnO ethanol solution obtained in step 1 was measured, and 0.057 mmol of APTMS was added, and the reaction was stirred for 12 h, and then the reaction liquid was centrifuged, and the obtained precipitate was washed by a mixed solvent of ethyl acetate and ethanol (volume ratio of 2:1) and then centrifuged to remove unreacted aminosilane; the obtained precipitate was dispersed in pure water to prepare a water dispersion system of aminosilane functionalized ZnO nanocrystals at a concentration of 0.1229 mol / L, which was recorded as a water dispersion system of AP-ZnO nanocrystals (hereinafter referred to as AP-ZnO aqueous solution).

[0058] Mott-Schottky was used to determine the conductivity type of ZnO nanocrystals and AP-ZnO nanocrystals by electrochemical impedance spectroscopy (EIS), and a classic three-electrode system was used for all electrochemical experiments, the reference electrode was Ag / AgCl, the counter electrode was a platinum wire electrode, ZnO and AP-ZnO nanocrystals were coated on ITO conductive glass to prepare a working electrode to be tested, the electrolyte solution was 0.1 M Na2SO4 solution, and the test environment was dark. Figure 1As shown in (a), the Mott-Schottky curves reveal that ZnO nanocrystals exhibit a positive tangent slope on the straight line of the Mott-Schottky curve, indicating the characteristics of an n-type semiconductor. According to... Figure 1 (b) shows the Mott-Schottky curves. The AP-ZnO nanocrystals exhibit negative tangent slopes on the straight lines of the Mott-Schottky curves, indicating their p-type semiconductor characteristics. Simultaneously, the HOMO energy levels of the AP-ZnO nanocrystals were measured using cyclic voltammetry on an electrochemical workstation. Calculations and comparisons with the HOMO levels of ZnO nanocrystals reported in existing literature were performed based on… Figure 2 It can be seen that the HOMO energy level of AP-ZnO nanocrystals is higher than that of ZnO nanocrystals, which is more conducive to electron injection and transport.

[0059] In addition, ZnO and AP-ZnO nanocrystalline films were prepared on ordinary glass by spin coating, and then XPS tests were performed. Figures 3-4 As can be seen, compared with surface-hydroxylated zinc oxide, aminosilane-functionalized zinc oxide has a lower number of oxygen vacancies (Vo), indicating that its work function is increased.

[0060] Example 2: Symmetrical carrier transport based on ZnO nanocrystalline semiconductor

[0061] This embodiment tests the hole and electron injection capabilities of three carrier transport layers—ZnO, AP-ZnO, and ZnO / AP-ZnO stacks—using single-electron and single-hole devices. The single-electron device uses an ITO / ETL / CsPbBr3 / TPBi / LiF / Al structure, with Al as the anode during testing. The single-hole device uses an ITO / HTL / CsPbBr3 / TAPC / MoO3 / Al structure, with ITO as the anode during testing. The ETL or HTL uses ZnO, AP-ZnO, and ZnO / AP-ZnO stacks (with ZnO in contact with ITO) as the electron or hole transport layer in the single-electron and single-hole devices, respectively.

[0062] The preparation method of the single-electron device is as follows: the patterned etched indium tin oxide (ITO) glass (16 mm*16 mm, 1.1 mm thick) is ultrasonically treated in a beaker containing a mixed solution of ITO cleaning solution and deionized water at a volume ratio of 1:20 for 20 min, then immersed in ultrasonic water for 20 min, finally washed with deionized water to remove the surface residual impurities, dried with nitrogen, then placed on a hot stage to remove the surface residual water, and treated with ultraviolet ozone (UV-Zone) for 15 min. On the ITO glass substrate, ZnO ethanol solution or AP-ZnO aqueous solution is filtered through a 0.45 μm filter, spin-coated at a speed of 3000 rpm for 30 s, and then annealed at 150°C for 20 min to prepare two electron transport layers, respectively. Alternatively, ZnO ethanol solution and AP-ZnO aqueous solution are spin-coated on the ITO glass substrate in sequence to obtain a stacked zinc oxide layer as the electron transport layer. Then, the CsPbBr3 light-emitting layer is prepared by spin-coating at 3000 rpm for 30 s. The TPBi (40 nm) electron transport layer and LiF (1 nm) / Al (100 nm) cathode are deposited by shadow mask in high vacuum (<5*10 -6 Torr).

[0063] The preparation method of the single-electron device is as follows: the patterned etched indium tin oxide (ITO) glass (16 mm*16 mm, 1.1 mm thick) is ultrasonically treated in a beaker containing a mixed solution of ITO cleaning solution and deionized water at a volume ratio of 1:20 for 20 min, then immersed in ultrasonic water for 20 min, finally washed with deionized water to remove the surface residual impurities, dried with nitrogen, then placed on a hot stage to remove the surface residual water, and treated with ultraviolet ozone (UV-Zone) for 15 min. On the ITO glass substrate, ZnO ethanol solution or AP-ZnO aqueous solution is filtered through a 0.45 μm filter, spin-coated at a speed of 3000 rpm for 30 s, and then annealed at 150°C for 20 min to prepare two electron transport layers, respectively. Alternatively, ZnO ethanol solution and AP-ZnO aqueous solution are spin-coated on the ITO glass substrate in sequence to obtain a stacked zinc oxide layer as the electron transport layer. Then, the CsPbBr3 light-emitting layer is prepared by spin-coating at 3000 rpm for 30 s. The TPBi (40 nm) electron transport layer and LiF (1 nm) / Al (100 nm) cathode are deposited by shadow mask in high vacuum (<5*10 -6 Torr).

[0064] As Figure 5As shown, ZnO as a common electron transport material has strong electron transport ability and weak hole injection ability, but the AP-ZnO prepared by the application has strong hole transport ability and weak electron transport ability, which also shows that the AP-ZnO with P-type semiconductor characteristics obtained by surface ligand modification of ZnO can be used as a hole transport material in electroluminescent devices.

[0065] Example 3, QLED solution method device process based on ZnO full inorganic carrier transport layer

[0066] According to the experimental results of Example 2, another single electron and single hole device is designed to verify the electron injection ability of the AP-ZnO / ZnO stack and the hole injection ability of the AP-ZnO nanocrystal. The structure of the single electron device is ITO / ZnO / CsPbBr3 / AP-ZnO / ZnO / Al, and ITO is used as the anode; the structure of the single hole device is ITO / AP-ZnO / CsPbBr3 / MoO3 / Al, and ITO is used as the anode; since the water resistance of the light-emitting layer material CsPbBr3 is limited and the water contact angle is large, there is a certain difficulty in spin coating the AP-ZnO aqueous solution on the light-emitting layer CsPbBr3, so the CsPbBr3 layer is subjected to argon plasma etching.

[0067] According to Figure 6 It can be seen that the electron injection ability of the AP-ZnO / ZnO stack is comparable to the hole injection ability of the AP-ZnO, and has similar device performance parameters, so the following designed QLED uses AP-ZnO / ZnO as the electron transport layer and AP-ZnO as the hole transport layer.

[0068] According to the above results, an electroluminescent device is designed, and the device structure is ITO / AP-ZnO / EML / AP-ZnO / ZnO / Al, wherein AP-ZnO is used as a hole transport layer, AP-ZnO / ZnO stack is used as an electron transport layer, and EML uses CsPbBr3 single quantum well and CsPbBr3 / AP-ZnO / CsPbBr3 double quantum well, respectively.

[0069] The specific manufacturing steps of the electroluminescent device are as follows:

[0070] 1. Substrate treatment: The patterned etched indium tin oxide (ITO) glass (16mm*16mm, thickness 1.1mm) is ultrasonically treated in a beaker containing a mixture of ITO cleaning solution and deionized water in a volume ratio of 1:20 for 20min, then immersed in plasma water for 20min, finally washed with deionized water to remove surface impurities, dried with nitrogen, and then placed on a hot stage for annealing, and then treated with ultraviolet ozone (UV-Zone) for 15min.

[0071] 2. Hole transport layer preparation: The AP-ZnO aqueous solution was filtered through a 0.45 μm water filter, and spin-coated onto the ITO glass substrate at a speed of 3000 rpm for 30 s. The AP-ZnO layer was obtained by annealing at 150 °C for 20 min, thereby obtaining the hole transport layer.

[0072] 3. Light-emitting layer preparation: The CsPbBr3 quantum dot solution was spin-coated on the AP-ZnO substrate at a speed of 2000 rpm for 30 s, and annealed at 60 °C for 15 min.

[0073] 4. Plasma etching: After the preparation of the perovskite quantum dot film, the surface of the peroviskite quantum dot film was treated. In this embodiment, the surface of the peroviskite quantum dot film was treated with argon plasma for 25 s to enhance the solvent resistance and reduce the water contact angle of the surface of the light-emitting layer.

[0074] 5. AP-ZnO layer preparation: The surface of the peroviskite quantum dot film was passivated with an amino-silane zinc oxide nanocrystal barrier layer. The AP-ZnO aqueous solution was filtered through a 0.45 μm water filter, and spin-coated onto the light-emitting layer substrate at a speed of 5000 rpm for 30 s. The AP-ZnO layer was obtained by annealing at 60 °C for 20 min.

[0075] 6. Preparation of the top zinc oxide nanocrystal electron transport layer and the electrode Al: The ZnO ethanol solution was spin-coated on the above-mentioned AP-ZnO interface layer at a speed of 3000 rpm for 30 s, and annealed at 60 °C for 15 min. The Al cathode was deposited by shadow mask in a high vacuum (<5 x 10 -6 Torr) to obtain a single quantum well QLED.

[0076] The steps 3-5 were repeated once to obtain a double quantum well QLED (i.e., in the order of 1, 2, 3, 4, 5, 3, 4, 5, 6), and more times to obtain a multi-quantum well QLED. In this embodiment, the single quantum well and the double quantum well were used for comparison.

[0077] According to Figures 7-9 It can be seen that the single quantum well device has a large leakage current, while the double quantum well device has a small leakage current and better performance. According to the experimental observation, the single quantum well device is not lit, while the double quantum well device is lit, and the light-emitting peak is at 520 nm, which is green light, and the turn-on voltage is 3.5 V. The reason why the single quantum well device has a large leakage current and is not lit is that the energy levels of the materials on both sides of the device cannot effectively block the electrons and holes, resulting in an increase in non-radiative recombination. The double quantum well device can effectively confine the electrons and holes in the quantum well, thereby increasing the radiative recombination. Increasing the number of quantum wells is beneficial to achieving carrier balance.

[0078] Example 4, fine-tuning of carrier transport based on doped AP-ZnO

[0079] This embodiment regulates the electron transport ability of AP-ZnO by doping it with Nd ions, with doping concentrations of 0%, 20%, and 80%, respectively. A stack of zinc oxide carrier transport layers is made using Nd-doped AP-ZnO, and a single electron device is prepared to verify the influence of the electron transport ability. The structure of the single electron device is ITO / ZnO / CsPbBr3@ZnO / AP-ZnO:Nd / Al. During testing, ITO is used as the anode, and p-CsPbBr3@ZnO is argon plasma treated CsPbBr3@ZnO (the specific preparation method of CsPbBr3@ZnO can be referred to in patent CN115975631A). In addition, a control group is prepared, and the structure of the single electron device is ITO / ZnO / CsPbBr3@ZnO / TPBi / LiF / Al.

[0080] The preparation method of the Nd-doped AP-ZnO aqueous solution is as follows: the AP-ZnO nanocrystals prepared in Example 1 are configured into an aqueous solution with a concentration of 10 mg / mL, then an aqueous solution of NdCl3 with a concentration of 10 mg / mL is prepared, and then 20% and 80% of the mass ratio of NdCl3 aqueous solution is added to the AP-ZnO aqueous solution, respectively, and stirred for a certain time to obtain the AP-ZnO:Nd aqueous solution.

[0081] The preparation steps of the single electron device are as follows: ZnO solution is spin-coated on a clean ITO glass substrate as a bottom electron transport layer, then CsPbBr3@ZnO solution is spin-coated on the ZnO substrate to prepare an EML layer, argon plasma etching is performed to increase the water resistance and reduce the water contact angle, then AP-ZnO aqueous solution with different Nd doping concentrations is spin-coated after the EML to prepare AP-ZnO:Nd as a top electron transport layer, and Al is deposited by shadow mask in high vacuum (<5x10 -6 Torr).

[0082] The preparation method of the control group single electron device is as follows: ZnO solution is spin-coated on a clean ITO glass substrate as a bottom electron transport layer, then CsPbBr3@ZnO solution is spin-coated on the ZnO substrate to prepare an EML layer, then TPBi (40 nm), LiF (1 nm), and Al (100 nm) are deposited by shadow mask in high vacuum (<5x10 -6 Torr).

[0083] According to Figure 10It can be obtained that one of the benefits of Nd doping is that the JV characteristic curve of the device is smoother, and the electron injection current density is greatly improved with the increase of Nd doping concentration, reaching a maximum at a doping concentration of about 20%, and the carrier transport capacity is comparable to that of the traditional electron transport material TPBi. In addition, according to the XPS of AP-ZnO:Nd nanocrystals with different doping ratios, it is found that the oxygen vacancies decrease with the increase of the doping ratio, which at the same time verifies that the AP-ZnO can regulate its carrier transport capacity by doping metal ions. This feature can be beneficial to the design of electroluminescent devices with relatively balanced carrier transport in the later stage, so as to obtain high-performance devices.

[0084] Example 5, combination of AP-ZnO doping and metal electrode to realize large range adjustable carrier transport performance

[0085] In this embodiment, AP-ZnO doped with Na ions is used as the electron transport layer, and the device structure is ITO / PEDOT:PSS / PTAA / EML / AP-ZnO:Na / Ag, where EML is InMP-CsPbBr3 (for specific preparation method, refer to patent CN 112251221A).

[0086] The specific preparation method of AP-ZnO:Na is as follows: the AP-ZnO nanocrystals prepared in Example 1 are configured into a 10 mg / mL aqueous solution, then a 10 mg / mL aqueous solution of NaCl is configured, then added into the AP-ZnO aqueous solution according to a mass ratio of 5%, and fully stirred for a certain time to obtain an AP-ZnO:Na aqueous solution.

[0087] The preparation method of the electroluminescent device is as follows: the patterned etched indium tin oxide (ITO) glass is ultrasonically treated in a beaker containing ITO cleaning solution and deionized water at a volume ratio of 1:20 for 20 min, then soaked in plasma water for 20 min, and finally washed with deionized water to remove the surface residual impurities, dried with nitrogen, and then placed on a hot stage for annealing to evaporate the residual water, and then treated with ultraviolet ozone (UV-Zone) for 15 min. The PEDOT:PSS solution is filtered through a 0.22 μm water filter, spin-coated on the ITO glass substrate at a speed of 4000 rpm for 40 s, and annealed at 120°C for 15 min. The PTAA chlorobenzene solution with a concentration of 5 mg / mL is filtered through a 0.45 μm organic filter, spin-coated at a speed of 3000 rpm for 40 s, and annealed at 120°C for 15 min. The light-emitting layer of InMP-CsPbBr3 is prepared by spin-coating at 2000 rpm for 30 s, annealed at 60°C for 15 min, and then etched by argon plasma for 25 s. The AP-ZnO:Na aqueous solution with a concentration of 10 mg / mL is filtered through a 0.45 μm water filter, spin-coated at a speed of 5000 rpm for 30 s, and annealed at 60°C for 15 min; the metal Ag is evaporated by shadow mask in high vacuum (<5×10 -6 Torr).

[0088] In this embodiment, AP-ZnO:Na is used as the electron transport layer, and the electroluminescent device is prepared by a full solution method. As shown in FIG. 6, the electroluminescent device shows good performance, and the EQE of the device is up to 2.16%. Figures 11-14 The electroluminescent device shows no change in the emission peak position under different bias voltages. In addition, the turn-on voltage of the light-emitting device is 4.5 V, and the maximum luminance of the device is 752 cd / m 2 2 at 8.5 V. The CIE color coordinates of the device are (0.11, 0.78), showing a pure and saturated green light color. According to this embodiment, it can be seen that AP-ZnO:Na can be used as a good electron transport layer material in the electroluminescent device.

[0089] Example 6: Full inorganic QLED by injecting holes through n-type ZnO / AP-ZnO:Nd semiconductor stack structure

[0090] The embodiment takes ZnO / AP-ZnO:Nd stack as the hole transport layer, and AP-ZnO:Na as the electron transport layer, and the device structure is ITO / ZnO / AP-ZnO:Nd / EML / AP-ZnO:Na / Ag, wherein the doping concentration of Nd in AP-ZnO:Nd is 15%, and the embodiment is denoted as AP-ZnO:Nd-15%, and the specific synthesis method is shown in embodiment 4; the doping concentration of AP-ZnO:Na is 5%, and the specific synthesis method is shown in embodiment 5; and the EML adopts CsPbBr3.

[0091] The specific device preparation method is as follows: the patterned etched indium tin oxide (ITO) glass is ultrasonically treated in a beaker of ITO cleaning solution and deionized water in a volume ratio of 1:20 for 20 min, then immersed in plasma water for ultrasonic treatment for 20 min, finally washed with deionized water to remove the surface residual impurities, dried with nitrogen, and then placed on a hot stage for annealing to evaporate the residual water, and then treated with ultraviolet ozone (UV-Zone) for 15 min. The ZnO ethanol solution is filtered through a 0.45 μm organic filter, spin-coated on the glass substrate of ITO at a speed of 3000 rpm for 30 s, and annealed at 150°C for 20 min. The AP-ZnO:Nd-15% aqueous solution with a concentration of 10 mg / mL is filtered through a 0.45 μm water filter, spin-coated at a speed of 3000 rpm for 30 s, and annealed at 150°C for 20 min. The luminescent layer of CsPbBr3 is prepared by spin-coating at 2000 rpm for 30 s, annealed at 60°C for 15 min, and then etched by argon plasma for 25 s. The AP-ZnO:Na aqueous solution with a concentration of 10 mg / mL is filtered through a 0.45 μm water filter, spin-coated at a speed of 5000 rpm for 30 s, and annealed at 60°C for 15 min; the metal Ag is evaporated by shadow mask in high vacuum (<5×10 -6 Torr).

[0092] In the same chip, the surface hydroxylated zinc oxide nanocrystals with hole transport properties and the Nd-doped surface amino silane passivated zinc oxide nanocrystals are used as the hole transport layer, and the Na-doped surface amino silane passivated zinc oxide is used as the electron transport layer, which has the advantages of process integration, simple structure, low manufacturing power consumption and low cost. As shown in Figure 15 As shown in the figure, in the low voltage region, the current density is low, and then the current rises rapidly, showing good device performance. According to Figure 17It can also be seen that the emission peak position does not change under different bias, and the CIE coordinates are (0.08, 0.78), showing a pure and saturated green light color. According to examples 5 and 6, it is shown that the doped AP-ZnO can not only inject holes efficiently, but also inject electrons efficiently. The structure of ITO / ZnO / AP-ZnO is conducive to realizing carrier balance and supporting a new working mode of bidirectional bias.

[0093] Example 7, universality of AP-ZnO carrier transport layer to energy level matching of light-emitting layer

[0094] This example uses AP-ZnO and silver electrode for different light-emitting layers to realize efficient carrier injection. The hole injection ability is verified by a single hole device, and the structure is: ITO / PEDOT:PSS / PTAA / EML / AP-ZnO / Ag, and Ag is used as anode during testing; the electron injection ability is verified by a single electron device, and the structure of the single electron device is: ITO / ZnO / EML / AP-ZnO:Nd / Ag, and ITO is used as anode during testing; wherein EML is CsPbBr3, ExMP-CsPbBr3 (for specific preparation method, refer to patent CN 111088045 A), InMP-CsPbBr3.

[0095] The preparation method of the single hole device is as follows: the PEDOT:PSS solution is filtered through a 0.22 μm water filter, and is spin-coated on a clean ITO glass substrate at a speed of 4000 rpm for 40 s, and is annealed at 120°C for 15 min; the PTAA chlorobenzene solution with a concentration of 5 mg / mL is filtered through a 0.45 μm organic filter, and is spin-coated at a speed of 3000 rpm for 30 s, and is annealed at 120°C for 15 min. Different light-emitting layers are prepared by spin-coating at 2000 rpm for 30 s, annealing at 60°C for 15 min, and then etching by argon plasma for 25 s. The AP-ZnO aqueous solution with a concentration of 10 mg / mL is filtered through a 0.45 μm water filter, and is spin-coated at a speed of 5000 rpm for 30 s, and is annealed at 60°C for 15 min; the metal Ag is evaporated by shadow mask in high vacuum (<5×10 -6 Torr).

[0096] The preparation method of the single-electron device is as follows: spin-coating a ZnO ethanol solution on a clean ITO glass substrate as a bottom electron transport layer, then spin-coating a CsPbBr3 solution on the ZnO film, annealing at 60°C for 20 min to prepare an EML layer, and performing argon plasma etching for 25 s, then spin-coating an AP-ZnO aqueous solution doped with 15% Nd on the EML to obtain AP-ZnO:Nd as a top electron transport layer, and evaporating Ag by shadow mask in a high vacuum (<5×10 -6 Torr).

[0097] According to Figures 18-19 It can be seen that the AP-ZnO can achieve efficient carrier injection for different light-emitting layers. For hole injection, the hole injection ability of CsPbBr3 is slightly weaker than that of the other light-emitting layers, because there is a problem of relatively mismatched energy levels between AP-ZnO and CsPbBr3, and the hole injection barrier is relatively large, which makes the hole injection ability slightly weaker than that of the other two. This problem can be solved by adjusting the plasma etching time to change the energy level of the light-emitting layer and reduce the hole injection barrier. The electron injection ability of different light-emitting layers does not have a large gap.

[0098] Example 8: AP-ZnO carrier transport layer inhibits light-emitting layer quenching

[0099] This example studies the fluorescence intensity of the light-emitting layer under different substrates. The specific test method is as follows: ZnO, AP-ZnO, ZnO / AP-ZnO stack and PTAA substrates are prepared on ordinary glass substrates by spin-coating technology, then a CsPbBr3 quantum dot solution is spin-coated on the ordinary glass substrates and the prepared substrates at a spin-coating parameter of 3000 rpm / 30 s, and annealed at 60°C for 10 min, then the fluorescence intensity of each sample is tested by a fluorescence spectrometer.

[0100] As Figure 20It can be seen that after the ZnO is passivated by the amino silane, the oxygen vacancies are reduced, and the fluorescence quenching is inhibited. Meanwhile, compared with the conventional organic material PTAA, the fluorescence intensity of the quantum dot film under the AP-ZnO substrate is almost twice that of the quantum dot film under the PTAA substrate, and the PL is enhanced. This also indicates that the work function between the light-emitting layer and the AP-ZnO is more matched than that between the light-emitting layer and the PTAA, which is beneficial to the improvement of the subsequent electroluminescent device efficiency. According to the hole transport capacity of the single-hole device in the above-mentioned embodiment, the AP-ZnO is a good hole transport material, so it is feasible to replace the organic carrier transport material with the AP-ZnO, and the device efficiency will be greatly improved.

[0101] The above merely illustrates the embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A symmetric doping method for zinc-based oxide semiconductor nanocrystals, characterized in that: Surface-hydroxylated zinc oxide nanocrystals were prepared in the N-type configuration. By functionalizing the N-type surface-hydroxylated zinc oxide nanocrystals with aminosilane, the work function and hole transport capability of the zinc oxide nanocrystals were increased, thereby realizing the conversion of zinc oxide nanocrystals from the N-type to the P-type, and obtaining P-type aminosilane-functionalized zinc oxide nanocrystals, denoted as AP-ZnO.

2. The method according to claim 1, characterized in that: AP-ZnO is doped with metal M ions to obtain AP-ZnO:M. By controlling the metal M ion doping element and / or doping concentration, the work function and carrier concentration of AP-ZnO can be controlled, so that AP-ZnO can achieve energy level matching when applied to optoelectronic devices, making the electron and hole transport capabilities in the device similar, thereby improving the quantum efficiency of the device.

3. Zinc oxide nanocrystals obtained by the method of claim 1 or 2.

4. A zinc oxide nanocrystalline thin film, characterized in that: The film is made using the zinc oxide nanocrystals described in claim 3; the film made using AP-ZnO is referred to as AP-ZnO film, the film made using AP-ZnO:M is referred to as AP-ZnO:M film, and the film made using surface-hydroxylated zinc oxide nanocrystals is referred to as ZnO film.

5. The application of the zinc oxide nanocrystalline thin film according to claim 4 in quantum dot light-emitting diodes (QLEDs).

6. A quantum dot light-emitting diode, characterized in that: A hole transport layer, a light-emitting layer, an electron transport layer, and a cathode are sequentially deposited on the surface of an ITO transparent conductive glass anode. The electron transport layer is an AP-ZnO thin film, an AP-ZnO:M thin film, a stacked thin film composed of an AP-ZnO thin film and a ZnO thin film, or a stacked thin film composed of an AP-ZnO:M thin film and a ZnO thin film, wherein the stacked thin film is in direct contact with the light-emitting layer by an AP-ZnO thin film or an AP-ZnO:M thin film. The AP-ZnO thin film, AP-ZnO:M thin film, and ZnO thin film are the AP-ZnO thin film, AP-ZnO:M thin film, and ZnO thin film as described in claim 4.

7. The quantum dot light-emitting diode according to claim 6, characterized in that: The hole transport layer is an AP-ZnO thin film, or a stacked thin film composed of a ZnO thin film and an AP-ZnO thin film, or a stacked thin film composed of a ZnO thin film and an AP-ZnO:M thin film, wherein the stacked thin film is in direct contact with the anode by the ZnO thin film; the AP-ZnO thin film, AP-ZnO:M thin film and ZnO thin film are the AP-ZnO thin film, AP-ZnO:M thin film and ZnO thin film as described in claim 4.

8. The quantum dot light-emitting diode according to claim 6 or 7, characterized in that: The light-emitting layer comprises n quantum dot light-emitting films, n≥1; when n≥2, an AP-ZnO film or AP-ZnO:M film as described in claim 4 is inserted between adjacent quantum dot light-emitting films as a barrier layer to form a QLED containing a multi-quantum-well light-emitting layer.

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