A tungsten-doped indium oxide evaporation target material, a preparation method therefor, and use thereof

Abstract

The application belongs to the technical field of metal oxide target material, and discloses a tungsten-doped indium oxide evaporation target material, a preparation method and application thereof. The preparation raw material of the tungsten-doped indium oxide target material comprises indium oxide and tungsten oxide. The indium oxide is micron-grade indium oxide powder, and the D50 of the indium oxide powder is 10-200 microns. The tungsten oxide is nanometer-grade tungsten oxide powder, and the D50 of the tungsten oxide powder is 10-100 nanometers. The tungsten-doped indium oxide target material has a relative density suitable for RPD process film coating and has good electrical conductivity. The oxide film obtained by using the IWO target material of the application for RPD film coating has high light transmittance and is suitable for preparing photovoltaic solar cells. The application also provides a preparation method and application of the IWO target material.

Description

Technical Field

[0001] This invention relates to the field of metal oxide target technology, and in particular to a tungsten-doped indium oxide vapor deposition target, its preparation method, and its application. Background Technology

[0002] Currently, transparent conductive oxide (TCO) thin films have become a key material in the field of photovoltaic solar cells, especially in the fabrication of high-efficiency solar cells. These TCO films have attracted widespread attention due to their ability to effectively collect the charge generated by light while allowing sunlight to pass through, thereby improving solar energy conversion efficiency. TCO films are typically prepared using methods such as reactive plasma deposition (RPD), chemical vapor deposition (CVD), physical vapor deposition (PCD), electrochemical deposition, and inkjet printing. Among these, the RPD method has received particular attention due to its unique advantages, including higher deposition rates, superior film quality, and higher target utilization. In the field of photovoltaic solar cells, TCO films prepared using the RPD method can not only improve the photoelectric conversion efficiency of solar cells but also reduce production costs, which is of great significance for achieving cost-effective solar cell products. Therefore, RPD technology shows broad application prospects in solar cell manufacturing and is one of the important directions for current and future solar cell technology research and development. Unlike PVD magnetron sputtering, RPD generally uses a porous target with a relative density of about 60%. This is because during RPD coating, a target with too high a density is prone to cracking, while a target with too low a density is prone to dust splashing or structural collapse, thus failing to obtain a high-quality thin film.

[0003] Indium tin oxide (ITO) targets are widely used for depositing thin films due to their high transmittance, good electrical conductivity, and stability in various environments. Furthermore, ITO film processing technology is mature, enabling uniform deposition on large-area substrates. However, the high cost, sensitivity to water vapor, and rigidity of ITO targets in flexible solar cells limit their application. Therefore, researchers are seeking alternative TCO materials to replace ITO targets, with indium tungsten oxide (IWO) targets becoming a research focus due to their potential advantages in chemical stability, environmental stability, and suitability for flexible cell processes. The high mobility and high transmittance of IWO targets across the entire solar spectrum also give them a significant advantage over ITO in photovoltaic applications. However, IWO thin films present certain challenges in terms of conductivity and coating process complexity. Currently, the high-temperature sintering effect in the preparation process of IWO targets is not ideal. Tungsten oxide is prone to sublimation above 850℃, and volatilization is particularly severe above 1250℃. Therefore, tungsten oxide will volatilize during the sintering process, and the composition is unstable. In particular, it is more difficult to control the composition content and uniformity of targets for preparing porous structures for RPD coating.

[0004] Therefore, it is urgent to improve and optimize the existing IWO target materials and their preparation methods to enhance doping uniformity and the photoelectric effect of the prepared oxide films. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides a tungsten-doped indium oxide (IWO) target. The tungsten-doped indium oxide target of this invention has a relative density between 55% and 63%, making it highly suitable for RPD (Reverse Diode) deposition processes. Furthermore, it exhibits low resistivity and good electrical conductivity. The oxide film obtained by RPD deposition using the IWO target of this invention has high light transmittance and is suitable for application in the fabrication of photovoltaic solar cells.

[0006] The present invention also provides a method for preparing a tungsten-doped indium oxide target.

[0007] The present invention also provides a TCO thin film.

[0008] The present invention also proposes applications of the aforementioned IWO target and TCO thin film.

[0009] In a first aspect, the present invention provides a tungsten-doped indium oxide target, wherein the raw materials for preparation include indium oxide and tungsten oxide;

[0010] Wherein, the indium oxide is micron-sized indium oxide powder, and the D50 of the indium oxide powder is 10-200 μm;

[0011] The tungsten oxide is nano-sized tungsten oxide powder, and the D50 of the tungsten oxide powder is 10-100 nm.

[0012] According to specific embodiments of the present invention, the IWO target material provided by the present invention has at least the following beneficial effects:

[0013] The IWO target material of this invention has a relative density between 55% and 63%, making it highly suitable for coating in RPD processes. The resistivity of this target material is between 2 and 6 × 10⁻⁶. -2 With a resistivity between Ω·cm, it exhibits good electrical conductivity; the oxide film obtained by RPD deposition using the IWO target of this invention has high light transmittance and is suitable for application in the preparation of photovoltaic solar cells.

[0014] According to some embodiments of the present invention, the raw materials for preparation include 92-98 parts of indium oxide and 2-8 parts of tungsten oxide by mass.

[0015] According to some embodiments of the present invention, the D50 of the indium oxide powder is 20-100 μm.

[0016] According to some embodiments of the present invention, the D50 of the tungsten oxide powder is 20-50 nm.

[0017] A second aspect of the present invention provides a method for preparing a tungsten-doped indium oxide target as described in the first aspect of the present invention, comprising the following steps:

[0018] S1. Indium oxide and tungsten oxide are separately dispersed in an organic solution, the dispersions are mixed, irradiated with ultraviolet light, and annealed to obtain powder;

[0019] S2. The powder is molded and sintered to obtain the IWO precursor.

[0020] S3. Crush the IWO precursor, sieve, grind, and spray granulate to obtain IWO powder;

[0021] S4. The IWO powder is molded and sintered to obtain an IWO target material.

[0022] According to specific embodiments of the present invention, the method for preparing the IWO target material provided by the present invention involves fully and uniformly dispersing the tungsten oxide nanoparticles in a liquid environment, combined with ultraviolet light irradiation, to allow the tungsten oxide nanoparticles to fully and uniformly adhere to the surface of the indium oxide particles in the liquid environment. This surface modification method allows the doped oxide and the substrate particles to be fully premixed, thereby giving the target material high uniformity. Consequently, the oxide film obtained by coating using this target material has high light transmittance. Furthermore, the method for preparing the IWO target material of the present invention eliminates the need for traditional high-temperature sintering, significantly reducing the volatilization rate of the easily volatile tungsten oxide during high-temperature sintering, thus making the composition content of the target material more controllable. Moreover, the IWO target material prepared using the method of the present invention has a target material relative density suitable for RPD process coating, which is beneficial for obtaining a higher deposition rate, better film quality, and higher target material utilization.

[0023] According to some embodiments of the present invention, the organic solution in step S1 includes at least one of methanol, ethanol, isopropanol or polyvinylpyrrolidone.

[0024] According to some embodiments of the present invention, the dispersion method in step S1 is ultrasonic dispersion.

[0025] According to some embodiments of the present invention, the frequency of the ultrasonic dispersion is 20 to 60 kHz.

[0026] According to some embodiments of the present invention, the parameters of the ultraviolet light irradiation in step S1 are: wavelength 100-400 nm, intensity 30-150 μW / cm². 2 The time is 7 to 13 hours.

[0027] This invention discovers that irradiating indium oxide micron particles and tungsten oxide nanoparticles in a liquid-phase dispersion environment with ultraviolet light of appropriate intensity helps the tungsten oxide nanoparticles to adhere fully and uniformly to the indium oxide micron particles, avoids the agglomeration of tungsten oxide particles, improves the doping uniformity of the subsequently prepared target material, and helps prevent cracking of the sintered body. The prepared target material is more suitable for coating in the RPD process.

[0028] According to some embodiments of the present invention, the parameters of the ultraviolet light irradiation in step S1 are: wavelength 200-300 nm, intensity 60-120 μW / cm². 2 The time is 8 to 12 hours.

[0029] According to some embodiments of the present invention, the annealing method in step S1 is to anneal in an annealing furnace at 300-500°C under an argon atmosphere for 0.5-2 hours.

[0030] According to some embodiments of the present invention, the compression molding pressure in step S2 is 1 to 2 MPa.

[0031] According to some embodiments of the present invention, the sintering method in step S2 is to raise the temperature to 800-850°C at a heating rate of 1-3°C / min under an oxygen atmosphere or an air atmosphere, and hold the temperature for 2-3 hours.

[0032] According to some embodiments of the present invention, the sieving in step S3 is sieving through a 60-200 mesh sieve.

[0033] According to some embodiments of the present invention, the sieving in step S3 is sieving through a sieve of 80 to 160 mesh.

[0034] According to some embodiments of the present invention, the grinding method in step S3 is to add zirconia balls, pure water and dispersant to the sieved IWO precursor powder and ball mill for 12 to 18 hours.

[0035] According to some embodiments of the present invention, the molding pressure in step S4 is 20-30 MPa.

[0036] According to some embodiments of the present invention, the sintering in step S4 is as follows: in an oxygen sintering furnace, the temperature is raised to 600-650°C at a heating rate of 1-3°C / min for degreasing, and held for 2-3 hours; then the temperature is raised to 850-900°C at a heating rate of 0.5-2°C / min, and held for 3-4 hours; then the temperature is raised to 1050-1150°C at a heating rate of 0.5-1°C / min, and held for 2-3 hours; and then cooled to room temperature.

[0037] In this invention, the sintering of the target material does not require the traditional high temperature of over 1200℃. The maximum sintering temperature is only 1150℃, which can effectively avoid the volatilization of tungsten oxide, control the most suitable relative density of the target material, improve the uniformity of the target material and ensure the stability of the target material composition, thereby improving the quality of the target material and the oxide film prepared therefrom.

[0038] In a third aspect, the present invention provides a TCO thin film, wherein the raw material for preparing the TCO thin film is the tungsten-doped indium oxide target described in the first aspect of the present invention.

[0039] The TCO thin film is prepared as follows:

[0040] According to some embodiments of the present invention, a TCO thin film is obtained by coating the tungsten-doped indium oxide target described in the first aspect of the present invention using reactive plasma deposition (RPD).

[0041] A fourth aspect of the present invention provides the application of the tungsten-doped indium oxide target described in the first aspect of the present invention and the TCO thin film described in the third aspect of the present invention in solar cells.

[0042] The tungsten-doped indium oxide target of the present invention has a suitable relative density and good electrical conductivity, and the composition content is controllable and the doping uniformity is high. The oxide film obtained by RPD process has high light transmittance, which can effectively improve the photoelectric conversion efficiency of solar cells, reduce production costs, and realize high cost-effective solar cell products.

[0043] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Detailed Implementation

[0044] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0045] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0046] Example 1

[0047] This embodiment provides a highly uniform IWO vapor deposition target and its preparation method.

[0048] The raw materials for preparing the IWO target in this embodiment are 92 parts by mass of indium oxide and 8 parts by mass of tungsten oxide;

[0049] The indium oxide is micron-sized indium oxide powder with a D50 of 20–100 μm, and the tungsten oxide is nano-sized tungsten oxide powder with a D50 of 20–50 nm.

[0050] The preparation method of the IWO target material in this embodiment is as follows:

[0051] 1) Take the above-mentioned mass fractions of nano-sized tungsten oxide powder and micron-sized indium oxide powder, disperse them separately in 99.9% ethanol, and sonicate them (40kHz) until the particles are uniformly dispersed to the naked eye. Then, mix the two dispersions and irradiate the mixed dispersion with a UV lamp. The irradiation parameters are: UV wavelength 254nm, intensity 90μW / cm². 2 The irradiation time was 12 hours. After the ultraviolet light irradiation was completed, the mixed dispersion was placed in an annealing furnace at 400°C under an argon atmosphere for 1 hour to collect indium oxide powder with surface-modified tungsten oxide nanoparticles.

[0052] 2) The powder obtained in step 1) is subjected to a single molding process with a molding pressure of 2 MPa. The preform obtained by molding is placed in an oxygen atmosphere (or an air atmosphere) for calcination. The temperature is increased to 800℃ at a heating rate of 1.5℃ / min and held for 2 hours to obtain the IWO precursor.

[0053] 3) The precursor obtained in step 2) is crushed, and IWO precursor powder is collected after passing through a 160-mesh sieve. 60wt% of zirconia balls, 150wt% of pure water and 2wt% of dispersant are added and mixed. The mixture is then ground thoroughly for 12 hours. The ground powder is then spray-dried to obtain IWO powder.

[0054] 4) The IWO powder obtained in step 3) is molded into a blank with a molding pressure of 20 MPa. Then, it is placed in an oxygen sintering furnace and heated to 600°C at a heating rate of 2°C / min for degreasing and held for 2 hours. After degreasing, the temperature is increased to 850°C at a heating rate of 1°C / min and held for 3.5 hours. Then, the temperature is increased to 1050°C at a heating rate of 0.5°C / min and held for 2.5 hours. After cooling to room temperature, a highly uniform IWO vapor deposition target blank is obtained. The sintered blank is cut and surface ground to obtain an IWO vapor deposition target block with a diameter of 30 mm and a height of 40 mm.

[0055] Example 2

[0056] This embodiment provides a highly uniform IWO vapor deposition target and its preparation method.

[0057] The difference between this embodiment and Embodiment 1 is that the raw materials for preparing the IWO target in this embodiment are 93.5 parts by mass of indium oxide and 6.5 parts by mass of tungsten oxide, and the ultraviolet irradiation time in step 1) is 11 hours.

[0058] Example 3

[0059] This embodiment provides a highly uniform IWO vapor deposition target and its preparation method.

[0060] The difference between this embodiment and Embodiment 1 is as follows: In this embodiment, the raw materials for preparing the IWO target are 95 parts by mass of indium oxide and 5 parts by mass of tungsten oxide. In step 1), the ultraviolet irradiation time is 10.5 h; in step 2), the molding pressure is 1.5 MPa and the temperature is raised to 850 °C; in step 3), the target is passed through an 80-mesh sieve and the grinding time is 14 h; in step 4), the temperature is raised to 650 °C for degreasing and held for 2.5 h, then the temperature is raised to 850 °C and held for 3.5 h, and finally the temperature is raised to 1150 °C.

[0061] Example 4

[0062] This embodiment provides a highly uniform IWO vapor deposition target and its preparation method.

[0063] The difference between this embodiment and embodiment 3 is that the raw materials for preparing the IWO target in this embodiment are 96.5 parts by mass of indium oxide and 3.5 parts by mass of tungsten oxide, and the ultraviolet irradiation time in step 1) is 9 hours.

[0064] Example 5

[0065] This embodiment provides a highly uniform IWO vapor deposition target and its preparation method.

[0066] The difference between this embodiment and Embodiment 3 is as follows: In this embodiment, the raw materials for preparing the IWO target are 98 parts by mass of indium oxide and 2 parts by mass of tungsten oxide. The ultraviolet irradiation time in step 1) is 8 hours; the molding pressure in step 2) is 1 MPa; the grinding time in step 3) is 18 hours after passing through an 80-mesh sieve; and in step 4) the temperature is raised to 650°C for degreasing and held for 3 hours, then the temperature is raised to 900°C and held for 3.5 hours, and finally the temperature is raised to 1150°C.

[0067] Comparative Example 1

[0068] This comparative example provides a highly uniform IWO vapor deposition target and its preparation method.

[0069] The difference between this comparative example and Example 3 is that the ultraviolet irradiation time in step 1) of this comparative example is 5 hours.

[0070] Comparative Example 2

[0071] This comparative example provides a highly uniform IWO vapor deposition target and its preparation method.

[0072] The difference between this comparative example and Example 3 is that the ultraviolet irradiation time in step 1) of this comparative example is 15 hours.

[0073] Comparative Example 3

[0074] This comparative example provides a highly uniform IWO vapor deposition target and its preparation method.

[0075] The difference between this comparative example and Example 3 is that the highest sintering temperature in step 4) of this comparative example is 1350°C.

[0076] Comparative Example 4

[0077] This comparative example provides a highly uniform IWO vapor deposition target and its preparation method.

[0078] The difference between this comparative example and Example 3 is that the ultraviolet irradiation step is omitted in step 1) of this comparative example, and the two oxide powders are mixed by dry method.

[0079] Comparative Example 5

[0080] This comparative example provides a highly uniform IWO vapor deposition target and its preparation method.

[0081] The difference between this comparative example and Example 1 is that the raw materials for preparing the IWO target in this comparative example are 90 parts by mass of indium oxide and 10 parts by mass of tungsten oxide.

[0082] In this comparative example, cracking occurred during sintering in step 4) of the preparation process.

[0083] Test case

[0084] The IWO targets prepared in each embodiment and comparative example were tested for their volatility, relative density, and resistivity. The average light transmittance of the thin films obtained by RPD deposition using the IWO targets was also tested. The doping ratios, some preparation processes, and test results for each embodiment and comparative example are shown in Table 1.

[0085] Testing methods for each indicator:

[0086] 1) Target material volatility: Measure the difference in target material mass before and after sintering / target material mass before sintering;

[0087] 2) Relative density: tested using the wax sealing method;

[0088] 3) Target resistivity: measured with a resistivity meter;

[0089] 4) Average light transmittance: tested using a UV-Vis spectrophotometer;

[0090] The method for preparing oxide thin films by RPD deposition is as follows: IWO targets from each embodiment and comparative example are placed in a water-cooled crucible of the RPD equipment, with white glass as the sample substrate, and the vacuum pressure is evacuated to 0.4 × 10⁻⁶. -3 Below Pa, an argon-oxygen mixture is introduced, with an oxygen content of 20%–30% and an oxygen flow rate of 80 sccm. After filling, the chamber pressure is 0.3 Pa, and the DCG current is 120–180 A. The electron gun rotation and tilt angles are adjusted, and the plasma beam is focused onto the target surface and stabilized before coating begins. The deposited film is then annealed in an air atmosphere to obtain an IWO transparent conductive film with a thickness of 100–110 nm.

[0091] Table 1. Doping ratios, preparation processes, and test results for each embodiment and comparative example.

[0092]

[0093] The test results above show that the target evaporation rate is low during the preparation of IWO targets using the method of this invention, all below 5%, and the relative density of the prepared targets is between 55% and 63%, making them very suitable for RPD coating processes. The resistivity of the IWO targets prepared by the method of this invention is between 2 and 6 × 10⁻⁶. -2 With resistivity between Ω·cm, it exhibits low electrical conductivity and good conductivity. Furthermore, the oxide film obtained by RPD deposition using the IWO target material of this invention exhibits high light transmittance, with an average light transmittance exceeding 88%, making it suitable for photovoltaic solar cell fabrication. Examples 1-5 using this invention control the oxide doping ratio and UV lamp irradiation time to obtain a uniformly doped IWO target material with suitable density without cracking. The sintered target material demonstrates excellent resistivity and density, and the processed vapor-deposited target material can be stably used for RPD deposition, resulting in a significantly improved average transmittance of the obtained film.

[0094] In Comparative Example 1, due to insufficient UV irradiation time, tungsten oxide nanoparticles failed to adhere sufficiently and uniformly to the surface of indium oxide particles in the liquid phase environment. The resulting IWO target had a low relative density of only 40%. Furthermore, the uneven doping of tungsten oxide led to excessively high resistivity of the IWO target and a decrease in the average light transmittance of the film, significantly reducing the performance of the oxide film. The IWO target prepared in this comparative example was also unsuitable for RPD deposition. Conversely, in Comparative Example 2, the extended UV irradiation time may have caused further agglomeration and growth of tungsten oxide nanoparticles after attachment to the surface of indium oxide micron particles, resulting in excessively large interparticle gaps. This also resulted in a low target density, making it unsuitable for RPD deposition, and the average light transmittance of the deposited oxide film also decreased.

[0095] In Comparative Example 3, the excessively high sintering temperature of the target material made it easier for tungsten oxide to volatilize during sintering, resulting in a low relative density of the target material, high resistivity, and a decrease in the average light transmittance of the oxide film. Comparative Example 4 used a dry mixing method, but this conventional method resulted in poor uniformity of the two oxide powders, making it difficult to achieve high uniformity doping in the preparation of tungsten-doped indium oxide targets. This also led to excessively high target resistivity and reduced average film transmittance, making it unsuitable for RPD coating. In Comparative Example 5, the excessively high tungsten oxide doping amount (10 wt%) caused excessive tungsten oxide nanoparticles, leading to excessive lattice distortion in the target material and cracking during sintering.

[0096] Compared to existing ITO targets used in heterojunction and perovskite solar cells, this invention, through tungsten doping, produces a target with a relative density of 55%–63%. Simultaneously, surface modification in a liquid-phase environment ensures thorough premixing of the doped oxide with the substrate particles. Furthermore, by controlling the ultraviolet irradiation time, the resulting target exhibits high uniformity, and the oxide film prepared by RPD demonstrates excellent uniformity and high average light transmittance. This target, applied to photovoltaic heterojunction cells and perovskite cells, exhibits good light transmittance and is suitable for RPD coating, thereby improving cell conversion efficiency.

[0097] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof can be combined with each other unless otherwise specified.

Claims

1. A method for preparing a tungsten-doped indium oxide target, characterized in that, Includes the following steps: S1. 92-98 parts by mass of indium oxide and 2-8 parts by mass of tungsten oxide are separately dispersed in an organic solution. The mixed dispersions are irradiated with ultraviolet light and annealed to obtain powder. The indium oxide is micron-sized indium oxide powder with a D50 of 10-200 μm; the tungsten oxide is nano-sized tungsten oxide powder with a D50 of 10-100 nm. The ultraviolet irradiation parameters are: wavelength 100-400 nm, intensity 30-150 μW / cm². 2 Time: 7-13 hours; S2. The powder is molded and sintered to obtain the IWO precursor. S3. Crush the IWO precursor, sieve, grind, and spray granulate to obtain IWO powder; S4. The IWO powder is molded and sintered to obtain an IWO target material; The sintering process is as follows: in an oxygen sintering furnace, the temperature is raised to 600-650℃ at a heating rate of 1-3℃ / min for degreasing, and held for 2-3 hours. Then, the temperature is raised to 850-900℃ at a heating rate of 0.5-2℃ / min and held for 3-4 hours. Finally, the temperature is raised to 1050-1150℃ at a heating rate of 0.5-1℃ / min and held for 2-3 hours, and then cooled to room temperature.

2. The preparation method according to claim 1, characterized in that, The sieving process described in step S3 involves passing the material through a 60-200 mesh sieve.

3. The preparation method according to claim 1, characterized in that, The molding pressure in step S2 is 1~2MPa, and / or the molding pressure in step S4 is 20~30MPa.

4. A TCO thin film, characterized in that, The raw material for preparing the TCO thin film is the tungsten-doped indium oxide target obtained by the preparation method of the tungsten-doped indium oxide target according to any one of claims 1 to 3.

5. The TCO film according to claim 4, characterized in that, The TCO thin film is prepared as follows: The tungsten-doped indium oxide target prepared by the method described in any one of claims 1 to 3 is coated with a film using reactive plasma deposition to obtain a TCO thin film.

6. The application of the tungsten-doped indium oxide target prepared by the method of any one of claims 1 to 3 or the TCO thin film of any one of claims 4 to 5 in solar cells.

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