Oxygen-doped CZTSSe / CdS heterojunction defect state passivation method

Abstract

The invention provides a defect state passivation method for an oxygen-doped CZTSSe / CdS heterojunction. Oxygen doping is formed in a CZTSSe / CdS heterojunction region, so that carrier recombination in a junction is inhibited, and passivation of a film layer and an interface defect state is realized; doped oxygen atoms occupy sulfur vacancy points in the CdS film, the VS defect is passivated, and charge recombination is reduced; the Fermi level position of the CdS film is improved through oxygen doping, good energy band alignment at a CZTSSe / CdS interface is achieved, and the transport capacity of charges is improved; the method is simple and effective to operate and low in cost, not only is beneficial to improving the performance of the CZTSSe solar cell, but also meets the requirements of large-scale batch production, and has relatively strong popularization significance.

Description

Technical Field

[0001] The invention relates to the field of thin-film solar cells, and in particular to a method for passivating defect states of oxygen-doped CZTSSe / CdS heterojunctions. Background Art

[0002] Inorganic materials (GaAs, CIGS and CdTe) have been widely used in the absorption layer of thin-film solar cells, but their toxic components (Cd, As) and expensive rare elements (In, Ga) have hindered their large-scale commercialization. Cu2ZnSn(S,Se)4 (CZTSSe) materials, which have a similar structure to CIGS materials, are considered to be promising absorption layer materials because they are environmentally friendly and have rich elemental composition, which can avoid the above problems. In addition, CZTSSe materials have the advantages of high absorption coefficient, good material stability and adjustable band gap, and have the potential to prepare low-cost and high-efficiency thin-film solar cells.

[0003] At present, the power conversion efficiency of CZTSSe solar cells has achieved a breakthrough of 15%, but there is still a certain gap compared with the efficiency of inorganic thin-film solar cells based on GaAs, CIGS and CdTe absorption layers. One of the key factors restricting the efficiency improvement of CZTSSe solar cells is the serious carrier recombination caused by defects in the CZTSSe / CdS heterojunction and poor band alignment. Therefore, defect passivation of the CZTSSe / CdS heterojunction is an effective way to break through the cell efficiency.

[0004] The reported schemes for improving CZTSSe / CdS heterojunction are as follows: improving the film quality by optimizing the selenization process or chemical water bath deposition process, indirectly improving the heterojunction quality and reducing the carrier recombination in the junction; treating the CZTSSe surface with a highly corrosive acid solution to remove its secondary phase, residual selenium, etc., improving the CZTSSe / CdS interface quality and reducing the interface recombination; performing a long heterojunction annealing on the CZTSSe / CdS heterojunction to promote the mutual diffusion of elements such as Zn, Sn, and Cd at the interface, thereby enhancing the heterojunction quality, reducing carrier recombination, and improving its transport capacity. However, the difficult etching technology, strong corrosiveness, and long annealing steps will lead to problems such as poor repeatability, unsafety, and long preparation cycle in the preparation process of CZTSSe solar cells. Therefore, the development of a CZTSSe / CdS heterojunction defect passivation technology that is simple to operate, safe and effective, and has a short cycle is conducive to the breakthrough of CZTSSe solar cell efficiency and the advancement of its commercialization process. Summary of the invention

[0005] The purpose of the present invention is to provide a method for passivating defect states of oxygen-doped CZTSSe / CdS heterojunctions, which uses a strong oxidation technology to treat the CZTSSe / CdS heterojunction to passivate its defect states and effectively improve the power conversion efficiency of CZTSSe solar cells.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present invention is: an oxygen-doped CZTSSe / CdS heterojunction defect state passivation method, forming oxygen doping in the CZTSSe / CdS heterojunction region, inhibiting carrier recombination, and realizing the passivation of film layer and interface defect states; in the CdS film layer, the doped oxygen atoms occupy the sulfur vacancy sites and passivate the sulfur vacancy defects; oxygen doping increases the Fermi level position of the CdS film, realizes the band alignment at the CZTSSe / CdS interface, promotes carrier transport, and reduces interface recombination.

[0007] Preferably, the method comprises the following steps: S1. Prepare CZTSSe precursor film on a clean substrate, and obtain a CZTSSe absorber layer film with good crystallinity by high-temperature selenization technology; S2, preparing a CdS buffer layer on the CZTSSe absorption layer film by a chemical water bath deposition method to form a CZTSSe / CdS heterojunction; S3. Oxygen doping of CZTSSe / CdS heterojunction is performed using oxidation technology.

[0008] Preferably, the preparation method of the CZTSSe precursor film in S1 includes magnetron sputtering, solution spin coating, spraying or electrodeposition.

[0009] Preferably, the substrate in S1 is molybdenum-coated soda-lime glass, molybdenum foil, molybdenum-coated metal foil or molybdenum-coated polyimide.

[0010] Preferably, the thickness of the CZTSSe absorption layer in S1 is 2000-4000 nm.

[0011] Preferably, the thickness of the CdS buffer layer in S2 is 60-100 nm.

[0012] Preferably, the oxidation technology in S3 includes ultraviolet ozone treatment technology or oxygen environment thermal annealing technology.

[0013] Compared with the prior art, the present invention has the following beneficial effects: (1) In the CZTSSe / CdS heterojunction processed by the present invention, the CdS buffer layer obtains higher optical transmittance, thereby improving the light utilization rate of the solar cell.

[0014] (2) The CZTSSe / CdS heterojunction interface processed by the present invention obtains a suitable conduction band offset value (0.1 eV), which promotes electron transport capability while reducing carrier recombination.

[0015] (3) The method of oxygen doping passivation of CZTSSe / CdS heterojunction defect states of the present invention is simple to operate, safe and effective, has a short processing cycle, and is easy to realize industrialization. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic diagram of the structure of the CZTSSe solar cell of the present invention; Figure 2 Schematic diagram of the energy band of oxygen-doped CZTSSe / CdS heterojunction in an embodiment of the present invention; Figure 3 The SEM cross-sectional view and EDS element distribution diagram of the CZTSSe solar cell in the embodiment of the present invention; Figure 4 is the CZTSSe solar cell in the embodiment of the present invention. J — V Graph. DETAILED DESCRIPTION

[0017] The following is combined with Figure 1-4 , the technical solution of the present invention is specifically described.

[0018] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0019] 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 application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should also be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0020] The present embodiment provides a method for passivating defect states of oxygen-doped CZTSSe / CdS heterojunctions, wherein oxygen doping is formed in the CZTSSe / CdS heterojunction region to suppress carrier recombination and achieve passivation of film layer and interface defect states; in the CdS film layer, doped oxygen atoms occupy sulfur vacancy sites to passivate sulfur vacancy defects; oxygen doping increases the Fermi level position of the CdS film, achieves band alignment at the CZTSSe / CdS interface, promotes carrier transport, and reduces interface recombination.

[0021] In this embodiment, the method includes the following steps: S1. Prepare CZTSSe precursor film on a clean substrate, and obtain a CZTSSe absorber layer film with good crystallinity by high-temperature selenization technology; S2, preparing a CdS buffer layer on the CZTSSe absorption layer film by a chemical water bath deposition method to form a CZTSSe / CdS heterojunction; S3. Oxygen doping of CZTSSe / CdS heterojunction is performed using oxidation technology.

[0022] In this embodiment, the method for preparing the CZTSSe precursor film in S1 includes magnetron sputtering, solution spin coating, spraying or electrodeposition.

[0023] In this embodiment, the substrate in S1 is molybdenum-coated soda-lime glass, molybdenum foil, molybdenum-coated metal foil or molybdenum-coated polyimide.

[0024] In this embodiment, the thickness of the CZTSSe absorption layer in S1 is 2000-4000 nm.

[0025] In this embodiment, the thickness of the CdS buffer layer in S2 is 60-100 nm.

[0026] In this embodiment, the oxidation technology in S3 includes ultraviolet ozone treatment technology or oxygen environment thermal annealing technology.

[0027] This embodiment provides a CZTSSe solar cell, such as Figure 1 , starting from the substrate, it includes a base 1, a CZTSSe absorption layer 2, a CdS buffer layer 3, an ITO window layer 4 and an Ag electrode 5 in sequence.

[0028] In this embodiment, the substrate is a Mo foil substrate with a thickness less than 0.1 mm and a purity greater than 99.99%.

[0029] This embodiment provides a method for preparing a CZTSSe solar cell, comprising the following steps: (1) Treatment of Mo foil substrate: The impurities on the surface of Mo foil were removed by electrochemical method, and the residual cleaning solution was removed by ultrapure water.

[0030] (2) Preparation of CZTSSe absorption layer: A CZTSSe precursor film was prepared on a clean substrate by solution spin coating, and then a well-crystallized CZTSSe absorption layer was obtained by high-temperature selenization technology. The selenization temperature was 560°C and the time was 12 to 15 minutes.

[0031] (3) Preparation of CdS buffer layer: The CdS layer was deposited on the surface of the CZTSSe absorption layer using a chemical water bath method. The reaction temperature was 60-70 °C, the deposition time was 14-18 min, and the thickness of the CdS film was 75 nm.

[0032] (4) Oxidation treatment of CZTSSe / CdS heterojunction: In a UV-ozone device, the Mo / CZTSSe / CdS sample was exposed to UV light and ozone environment. The oxygen doping amount was controlled by the treatment time, which was 0 min, 10 min, 15 min, and 20 min, respectively.

[0033] (5) Preparation of ITO window layer: The ITO film layer was deposited on the CZTSSe / CdS heterojunction by sputtering. The process parameters were: sputtering gas was Ar, working pressure was 0.5 Pa, RF sputtering power was 90 W, sputtering time was 48~54 min, and the thickness was 220~260 nm.

[0034] (4) Preparation of Ag electrode: Ag electrode was prepared on the window layer by vacuum evaporation technology. The process parameters were as follows: vacuum degree was less than 1×10 -4 Pa, the evaporation rate is 1 Å / s, and the thickness is 500~800 nm.

[0035] Figure 3 This is a SEM cross-sectional view of the CZTSSe solar cell in this embodiment. It can be seen that from bottom to top, they are: CZTSSe absorption layer, CdS buffer layer, ITO window layer; from the EDS line scan results, it can be seen that oxygen is successfully doped into the CZTSSe / CdS heterojunction.

[0036] Figure 4 The box plot of the power conversion efficiency of the CZTSSe / CdS heterojunction of the CZTSSe solar cell in this embodiment at different processing times and the best device J—V When the treatment time is 15 min, the CZTSSe solar cell has the best performance, with a maximum efficiency of 10.83%, which is 15.34% higher than the maximum efficiency of the control group device, proving the effectiveness of the oxygen-doped passivation CZTSSe / CdS heterojunction defect state method of the present invention.

[0037] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A method for passivating defect states of oxygen-doped CZTSSe / CdS heterojunctions, characterized in that: Oxygen doping is formed in the CZTSSe / CdS heterojunction region to inhibit carrier recombination and achieve passivation of film layer and interface defect states; in the CdS film layer, the doped oxygen atoms occupy the sulfur vacancy sites and passivate the sulfur vacancy defects; Oxygen doping increases the Fermi level position of CdS film, achieves band alignment at the CZTSSe / CdS interface, promotes carrier transport, and reduces interface recombination.

2. A method for passivating defect states of oxygen-doped CZTSSe / CdS heterojunctions, characterized in that: The steps include: S1. Prepare CZTSSe precursor film on a clean substrate, and obtain a CZTSSe absorber layer film with good crystallinity by high-temperature selenization technology; S2, preparing a CdS buffer layer on the CZTSSe absorption layer film by a chemical water bath deposition method to form a CZTSSe / CdS heterojunction; S3. Oxygen doping of CZTSSe / CdS heterojunction is performed using oxidation technology.

3. A method for passivating defect states of oxygen-doped CZTSSe / CdS heterojunctions, characterized in that: The preparation method of the CZTSSe precursor film in S1 includes magnetron sputtering, solution spin coating, spraying or electrodeposition.

4. A method for passivating defect states of oxygen-doped CZTSSe / CdS heterojunctions, characterized in that: The substrate in S1 is molybdenum-coated soda-lime glass, molybdenum foil, molybdenum-coated metal foil or molybdenum-coated polyimide.

5. A method for passivating defect states of oxygen-doped CZTSSe / CdS heterojunctions, characterized in that: The thickness of the CZTSSe absorption layer in S1 is 2000-4000 nm.

6. A method for passivating defect states of oxygen-doped CZTSSe / CdS heterojunctions, characterized in that: The thickness of the CdS buffer layer in S2 is 60-100 nm.

7. A method for passivating defect states of oxygen-doped CZTSSe / CdS heterojunctions, characterized in that: The oxidation technology in S3 includes ultraviolet ozone treatment technology or oxygen environment thermal annealing technology.

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