A method for improving the grain size of cuprous oxide thin films and its application

Abstract

The present invention relates to the technical field of cuprous oxide film preparation, and in particular to a method for improving the grain size of cuprous oxide films and its application. The method comprises placing a cleaned quartz glass sheet into the coating chamber of a magnetron sputtering apparatus, evacuating the chamber, and heating the quartz glass sheet to a set temperature; introducing a flow protective atmosphere into the chamber, and using a DC power supply and a high-purity silver target to sputter a silver thin film buffer layer on the quartz glass sheet, so that a buffer layer silver film is obtained on the quartz glass sheet; then using a high-purity copper target to sputter a cuprous oxide film on the silver film: introducing oxygen to start sputtering; after completion, the gas is discharged, the chamber is opened, and the obtained product is taken out. The method proposed by the present invention uses magnetron sputtering coating technology to prepare a buffer layer silver film on a substrate, which can improve the crystallinity of the cuprous oxide film, reduce defects, and significantly improve the grain size of the cuprous oxide film. In addition, the method of the present invention can reduce the preparation cost of large-grain cuprous oxide films.

Description

Technical Field

[0001] The present invention relates to the technical field of cuprous oxide film preparation, in particular to a method for improving the grain size of cuprous oxide film and application thereof. Background Art

[0002] The information disclosed in the background of the invention is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Cuprous oxide is a direct bandgap semiconductor with a band gap of 2.1 eV and a theoretical photoelectric conversion efficiency of up to 20%. Currently, the main method for preparing cuprous oxide thin films is to deposit cuprous oxide on a substrate. For example, patent document 201511025986.9 discloses a method for preparing cuprous oxide thin films, comprising the following steps: placing a copper source in a reaction boat, which is then placed in a quartz reaction tube; placing a cleaned and dried substrate on a substrate holder, which is then placed in the quartz reaction tube; opening the copper source gas line to allow inert gas to pass through the reaction boat and into the quartz reaction tube, with the outlet of the reaction boat facing the substrate surface; opening the oxygen source gas line to allow inert gas carrying the oxygen source to enter the quartz reaction tube; heating the quartz reaction tube, thereby heating the reaction boat and substrate within the quartz reaction tube; adjusting the operating temperature of the reaction boat and substrate, setting the growth time, and depositing the cuprous oxide thin film on the substrate to complete the preparation. However, the highest actual photoelectric conversion efficiency of cuprous oxide thin films currently prepared is relatively low (generally only 3.83%), which is still far from the theoretical photoelectric conversion efficiency of 20%, which limits the application of cuprous oxide solar cells. Summary of the Invention

[0004] The low actual photoelectric conversion efficiency of cuprous oxide films is primarily due to the high nucleation rate of cuprous oxide films, resulting in numerous and fine grains. This in turn creates numerous grain boundaries, where hole carriers recombine with electrons, causing a decrease in carrier concentration and, consequently, reduced conversion efficiency. To address this issue, the present invention provides a method for increasing the grain size of cuprous oxide films and its application. This method can produce large-grain cuprous oxide films at a low cost, thereby improving their actual photoelectric conversion efficiency.

[0005] In order to achieve the above-mentioned purpose of the invention, the technical means adopted by the present invention are:

[0006] First, the present invention discloses a method for improving the grain size of a cuprous oxide film: a pure silver film or a silver film containing trace impurities (oxygen, nitrogen, etc.) is prepared on a substrate as a buffer layer, and then a cuprous oxide film is sputtered on the buffer layer.

[0007] The lattice constant of silver is close to that of cuprous oxide, and the lattice mismatch is small, and both are cubic structures, so it is easy to produce epitaxial growth relationship. In addition, ohmic contact is formed between silver and cuprous oxide, which is conducive to photovoltaic device improving efficiency, reducing interface contact resistance, and avoiding loss of carriers between interfaces. Although the present invention also attempts to adopt copper, indium phosphide, magnesium oxide etc. as buffer layer, copper and cuprous oxide form Schottky contact, and interface contact resistance is very large, which is unfavorable for device improving efficiency, and magnesium oxide itself has poor conductivity. For this reason, the present invention selects silver as buffer film.

[0008] Secondly, the present invention discloses the application of the product prepared by the method for improving the grain size of the cuprous oxide thin film in the field of solar cells.

[0009] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0010] (1) The method proposed in the present invention adopts magnetron sputtering coating technology, which can prepare large-grain cuprous oxide films at a low cost, thereby improving the actual photoelectric conversion efficiency of cuprous oxide.

[0011] (2) The silver buffer layer can improve the crystallinity of the cuprous oxide film, reduce defects, improve the crystallization quality, and significantly increase the grain size of cuprous oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0013] Figure 1 This is a process flow chart of cuprous oxide prepared in Examples 2-4 of the present invention.

[0014] Figure 2 These are XRD images of cuprous oxide prepared in Examples 1 and 2 of the present invention.

[0015] Figure 3 This is a SEM image of cuprous oxide prepared in Example 1 of the present invention.

[0016] Figure 4 These are SEM images of cuprous oxide prepared in Examples 2-4 of the present invention, wherein Figures ac represent Examples 2-4, respectively. DETAILED DESCRIPTION

[0017] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0018] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0019] As previously mentioned, the highest practical photoelectric conversion efficiency of cuprous oxide thin films currently produced is relatively low, far from the theoretical photoelectric conversion efficiency of 20%. This limits the application of cuprous oxide solar cells. Therefore, the present invention proposes a method for increasing the grain size of cuprous oxide thin films based on a pre-silvered buffer layer. This method is now further described.

[0020] As a further technical solution, the substrate includes a single crystal silicon wafer, a quartz glass wafer, etc.

[0021] As a further technical solution, the substrate is ultrasonically cleaned with acetone and ethanol and then sputtered to remove impurities on the surface of the substrate.

[0022] As a further technical solution, the method for preparing the silver film buffer layer on the substrate is magnetron sputtering; specifically, a layer of silver film is sputtered on the substrate using a high-purity silver target.

[0023] As a further technical solution, during the preparation of the silver film, the background vacuum is evacuated to ≤3.5×10 -4 Pa, and then the substrate is heated to 480-550 ° C and sputtered in an argon atmosphere. The sputtering parameters are: DC power supply, target power of 8-13 W, sputtering time of 18-30 min, sputtering pressure of 0.3-0.8 Pa, and argon flow rate of 35-45 sccm.

[0024] As a further technical solution, the method of sputtering the cuprous oxide film on the buffer layer is: using a high-purity copper target for sputtering in an argon atmosphere, with a background vacuum of ≤3.5×10 -4 Pa, sputtering parameters are: RF power supply, target power is 35-48W, sputtering time is 12-18min, sputtering pressure is 0.3-0.8Pa, total flow rate of argon and oxygen is 35-45sccm, and O2 content is 5-10%.

[0025] As a further technical solution, the thickness of the silver target and the copper target are both 3-6 mm and the diameter is 40-55 mm.

[0026] The following combination Figure 1-4 The present invention will be further described.

[0027] Example 1

[0028] A method for increasing the grain size of a cuprous oxide film comprises the following steps:

[0029] (1) Ultrasonic cleaning of quartz glass sheets with acetone and ethanol for 10 min each, and set aside.

[0030] (2) Place the quartz glass sheet obtained in step (1) into the coating chamber of the magnetron sputtering apparatus, and then evacuate the chamber until the background vacuum is ≤3.5×10 -4 Pa; then heat the quartz glass plate to 500°C and maintain this temperature;

[0031] (3) A cuprous oxide film is sputtered on the quartz glass sheet of step (3) using a high-purity copper target: oxygen is introduced, and the total flow rate of argon and oxygen is 40 sccm, the O2 content is 5%, and the sputtering parameters are: RF power supply, target power 40 W, sputtering time 15 min, and sputtering pressure 0.5 Pa; after completion, the gas is discharged, the chamber is opened, and the obtained product is taken out.

[0032] Example 2

[0033] refer to Figure 1 A method for increasing the grain size of a cuprous oxide film comprises the following steps:

[0034] (1) Ultrasonic cleaning of quartz glass sheets with acetone and ethanol for 10 min each, and set aside.

[0035] (2) Place the quartz glass sheet obtained in step (1) into the coating chamber of the magnetron sputtering apparatus, and then evacuate the chamber until the background vacuum is ≤3.5×10 -4 Pa; then heat the quartz glass plate to 500°C and maintain this temperature;

[0036] (3) Argon gas with a flow rate of 40 sccm was introduced into the chamber as a protective atmosphere, and a high-purity silver target (thickness 5 mm, diameter 50 mm) was used to sputter a buffer layer on a quartz glass sheet. The sputtering parameters were: DC power supply, target power 10 W, sputtering time 20 min, and sputtering pressure 0.5 Pa. After completion, a buffer layer silver film was obtained on the quartz glass sheet;

[0037] (4) Next, a cuprous oxide film is sputtered on the silver film of step (3) using a high-purity copper target: oxygen is introduced, and the total flow rate of argon and oxygen is 45 sccm, the O2 content is 10%, and the sputtering parameters are: RF power supply, target power of 40 W, sputtering time of 15 min, and sputtering pressure of 0.5 Pa; after completion, the gas is discharged, the chamber is opened, and the obtained product is taken out.

[0038] Example 3

[0039] refer to Figure 1 A method for increasing the grain size of a cuprous oxide film comprises the following steps:

[0040] (1) Ultrasonic cleaning of quartz glass sheets with acetone and ethanol for 10 min each, and set aside.

[0041] (2) Place the quartz glass sheet obtained in step (1) into the coating chamber of the magnetron sputtering apparatus, and then evacuate the chamber until the background vacuum is ≤3.5×10 -4 Pa; then heat the quartz glass plate to 550°C and maintain this temperature;

[0042] (3) Argon gas with a flow rate of 35 sccm was introduced into the chamber as a protective atmosphere, and a high-purity silver target (thickness 5 mm, diameter 50 mm) was used to sputter a buffer layer on a quartz glass sheet. The sputtering parameters were: DC power supply, target power 8 W, sputtering time 18 min, and sputtering pressure 0.8 Pa. After completion, a buffer layer silver film was obtained on the quartz glass sheet;

[0043] (4) Then, a cuprous oxide film is sputtered on the silver film in step (3) using a high-purity copper target: oxygen is introduced, and the total flow rate of argon and oxygen is 45 sccm, the O2 content is 5%, and the sputtering parameters are: RF power supply, target power of 35 W, sputtering time of 18 min, and sputtering pressure of 0.8 Pa; after completion, the gas is discharged, the chamber is opened, and the obtained product is taken out.

[0044] Example 4

[0045] refer to Figure 1 A method for increasing the grain size of a cuprous oxide film comprises the following steps:

[0046] (1) The single crystal silicon wafer (100) is ultrasonically cleaned with acetone and ethanol for 10 minutes respectively, and then set aside.

[0047] (2) The single crystal silicon wafer (100) obtained in step (1) is placed in the coating chamber of the magnetron sputtering apparatus, and then evacuated to a background vacuum of ≤3.5×10 -4 Pa; then heating the single crystal silicon wafer (100) to 480° C. and maintaining this temperature;

[0048] (3) Argon gas with a flow rate of 45 sccm is introduced into the chamber as a protective atmosphere, and a high-purity silver target (thickness 5 mm, diameter 50 mm) is used to sputter a buffer layer on the single crystal silicon wafer (100). The sputtering parameters are: DC power supply, target power of 13 W, sputtering time of 30 min, and sputtering pressure of 0.3 Pa. After completion, a buffer layer silver film is obtained on the single crystal silicon wafer (100);

[0049] (4) Next, a cuprous oxide film is sputtered on the silver film of step (3) using a high-purity copper target: oxygen is introduced, and the total flow rate of argon and oxygen is 35 sccm, the O2 content is 8%, and the sputtering parameters are: RF power supply, target power of 48 W, sputtering time of 12 min, and sputtering pressure of 0.3 Pa; after completion, the gas is discharged, the chamber is opened, and the obtained product is taken out.

[0050] Performance Testing

[0051] (1) Figure 2 The figures show the XRD patterns of the cuprous oxide prepared in Examples 1 and 2. It can be seen from the figures that the method of the present invention can successfully prepare cuprous oxide, and that the cuprous oxide and the silver buffer layer have a definite epitaxial orientation relationship, indicating that the silver buffer layer can control the nucleation, growth, and crystallization quality of the cuprous oxide.

[0052] (2) The cuprous oxide films prepared in Examples 1-4 were observed under a scanning electron microscope (magnification of 10k). The results are as follows: Figure 3 and 4 As shown, Figure 3 This is an SEM image of cuprous oxide prepared in Example. It can be seen that the particle size of cuprous oxide is about 20 nm without a buffer layer. Figure 4 Figures ac are SEM images of the cuprous oxide prepared in Examples 2, 3, and 4, respectively. It can be seen that the grain size of the cuprous oxide film with the silver buffer layer is approximately 1-2 μm. Comparing the grain sizes of the cuprous oxide prepared in Example 1 with those in Examples 2-4, the difference is 50-100 times, an increase of nearly two orders of magnitude. This demonstrates that the silver buffer layer significantly increases the grain size of the cuprous oxide, thereby significantly reducing the grain boundary area of ​​the cuprous oxide film, thereby significantly improving the photoelectric conversion efficiency of the cuprous oxide film.

[0053] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for increasing the grain size of a cuprous oxide film, characterized in that: The steps are: preparing a silver film as a buffer layer on a substrate, and then sputtering a cuprous oxide film on the buffer layer to obtain; The method for preparing the silver film buffer layer on the substrate is magnetron sputtering; A high-purity silver target is used to sputter a silver film on the substrate; The thickness of the silver target is 3-6 mm and the diameter is 40-55 mm; During the preparation of the silver film, the background vacuum was evacuated to ≤3.5×10 -4 Pa, then the substrate is heated to 480-550 ° C and sputtered in an argon atmosphere. The sputtering parameters are: DC power supply, target power of 8-13 W, sputtering time of 18-30 min, sputtering pressure of 0.3-0.8 Pa, and argon flow rate of 35-45 sccm; The method of sputtering cuprous oxide film on the buffer layer is as follows: using a high-purity copper target to sputter in an argon atmosphere, with a background vacuum of ≤3.5×10 -4 Pa, sputtering parameters are: RF power supply, target power is 35-48W, sputtering time is 12-18min, sputtering pressure is 0.3-0.8Pa, total flow rate of argon and oxygen is 35-45sccm, and O2 content is 5-10%.

2. The method for increasing the grain size of a cuprous oxide thin film according to claim 1, wherein: The copper target has a thickness of 3-6 mm and a diameter of 40-55 mm.

3. The method for increasing the grain size of a cuprous oxide thin film according to claim 1, wherein: The substrate is a single crystal silicon wafer or a quartz glass wafer.

4. The method for increasing the grain size of a cuprous oxide thin film according to claim 1, wherein: The substrate is ultrasonically cleaned with acetone and ethanol before being sputtered.

5. Application of a product prepared by the method for increasing the grain size of a cuprous oxide thin film according to any one of claims 1 to 4 in the field of solar cells.

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