Method for modifying Mo / CZTSSe back interface by CuO sacrificial layer

Abstract

The invention discloses a method for modifying a Mo / CZTSSe back interface by a CuO sacrificial layer, which is characterized in that the CuO sacrificial layer is introduced at the Mo / CZTSSe back interface to realize the modification of the back interface. The introduction of the CuO sacrificial layer can prevent Se from diffusing to the substrate, reduce the thickness of MoSe2 and reduce the contact resistance of a back interface, and meanwhile, Cu ions diffuse to the CZTSSe thin film to form a CuxSey liquid phase, so that the crystal growth can be promoted, and the quality of the thin film can be improved. By means of the treatment, the quality of a back interface and the quality of a CZTSSe absorption layer can be improved at the same time, series resistance and carrier recombination are effectively reduced, the performance of the CZTSSe solar cell is greatly improved, the cell efficiency is improved to 10.57% from 9.23%, and a new thought is provided for preparation of the efficient CZTSSe solar cell.

Description

Technical Field

[0001] The invention belongs to the field of thin-film solar cells, and in particular relates to a method for modifying a Mo / CZTSSe back interface with a CuO sacrificial layer. Background Art

[0002] Copper zinc selenium sulfur selenide (CZTSSe) semiconductor material has the advantages of adjustable energy gap, rich and non-toxic composition elements, and high absorption coefficient. It is one of the most promising thin-film solar cell absorber materials in recent years. At present, the photoelectric conversion efficiency (PCE) of the most advanced CZTSSe thin-film solar cell has exceeded 15%, but there is still a big gap with its theoretical efficiency (33%). The relatively low open circuit voltage (V OC ) and fill factor (FF) are the main reasons that limit the performance improvement of CZTSSe solar cells. At the Mo / CZTSSe back interface, too thick MoSe2 will lead to a large series resistance (R s ), deteriorating the device FF. In addition, the mismatched band arrangement at the CZTSSe / Mo interface will hinder carrier transport, leading to increased electron-hole recombination and deteriorating solar cell performance.

[0003] The reported methods of passivating the CZTSSe / Mo interface include: ① introducing a high-conductivity, high-stability barrier layer to inhibit the generation of MoSe2, but also preventing the diffusion of Na and deteriorating the quality of CZTSSe crystals; ② introducing a sacrificial layer, such as Ag, Bi, etc., to reduce carrier recombination, but also reducing the quality of CZTSSe crystals due to hindering the diffusion of Na; ③ introducing a "self-assembled open-pore" intermediate layer, such as ultra-thin Al2O3, etc., to eliminate the holes on the back interface and inhibit the generation of MoSe2, but its low conductivity increases the series resistance of the device. Therefore, a back interface modification method that introduces a sacrificial layer on the back interface without deteriorating the quality of CZTSSe crystals will overcome the drawbacks of the current sacrificial layer scheme and effectively improve the performance of CZTSSe solar cells. Summary of the invention

[0004] The purpose of the present invention is to provide a method for modifying the Mo / CZTSSe back interface with a CuO sacrificial layer, which can simultaneously improve the quality of the back interface and the CZTSSe absorption layer and effectively improve the performance of CZTSSe solar cells.

[0005] To achieve the above object, the present invention adopts the following technical solution: A method for modifying the back interface of Mo / CZTSSe with a CuO sacrificial layer is to introduce a layer of CuO as a sacrificial layer at the back interface of Mo / CZTSSe to achieve modification of the back interface; wherein the introduction of the CuO sacrificial layer can prevent Se from diffusing into the substrate, reduce the thickness of MoSe2, and reduce the contact resistance of the back interface; at the same time, Cu ions diffuse into the CZTSSe film, which can promote its crystal growth and improve the film quality; the method specifically comprises the following steps: (1) Clean the substrate and blow dry; (2) preparing a CuO sacrificial layer on the substrate surface and performing post-annealing treatment; (3) A CZTSSe precursor is prepared on a CuO sacrificial layer, and then a CZTSSe absorption layer is formed by high-temperature selenization treatment.

[0006] Furthermore, the substrate in step (1) is a Mo foil substrate.

[0007] Furthermore, the method for preparing the CuO sacrificial layer in step (2) includes magnetron sputtering, thermal evaporation, and solution spin coating.

[0008] Furthermore, the thickness of the CuO sacrificial layer prepared in step (2) is 50-125 nm.

[0009] Furthermore, the post-annealing treatment in step (2) is carried out in an inert gas atmosphere at 150° C. for 20 min.

[0010] Furthermore, the preparation method of the CZTSSe precursor in step (3) includes magnetron sputtering, solution spin coating, and electrodeposition.

[0011] Furthermore, the high temperature selenization treatment in step (3) is carried out in a nitrogen environment at 550° C. for 15 minutes.

[0012] Compared with the prior art, the present invention has the following beneficial effects: The present invention utilizes the method of modifying the back interface by using a CuO sacrificial layer, which can inhibit the downward diffusion of Se elements and effectively reduce the thickness of MoSe2; at the same time, the diffusion of Cu ions promotes the crystallization process of the CZTSSe absorption layer, which can improve the quality of the CZTSSe film and increase the battery efficiency from 9.23% to 10.57%. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Surface SEM comparison of Mo / CuO / CZTSSe (A) prepared in Example and Mo / CZTSSe (B) prepared in Comparative Example.

[0014] Figure 2Cross-sectional SEM comparison images of Mo / CuO / CZTSSe (A) prepared in the example and Mo / CZTSSe (B) prepared in the comparative example and their local magnified images.

[0015] Figure 3 Schematic diagram of the structure of the CZTSSe solar cell constructed in the embodiment (A) and the SEM cross-sectional view of the finished cell (B), wherein 1 is a Mo foil substrate, 2 is a CuO sacrificial layer (this layer disappears after high-temperature selenization), 3 is a CZTSSe absorption layer, 4 is a CdS buffer layer, 5 is an ITO window layer, and 6 is an Ag electrode.

[0016] Figure 4 EDS characterization diagram of Cu element in the CZTSSe solar cell constructed in the embodiment and the CZTSSe solar cell constructed in the comparative example.

[0017] Figure 5 CZTSSe solar cells constructed with CuO sacrificial layers of different thicknesses J - V curve. DETAILED DESCRIPTION

[0018] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0019] 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.

[0020] 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 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.

[0021] In this embodiment, the substrate used is a Mo foil substrate with a thickness of less than 0.1 mm and a purity of greater than 99.99%. The CuO sacrificial layer is prepared by magnetron sputtering. The CZTSSe precursor is prepared by solution spin coating. Example

[0022] The preparation steps of flexible CZTSSe solar cells are as follows: (1) Prepare the substrate: clean and dry the Mo foil, fix it on the sample holder, and place it on the sputtering machine sample substrate; (2) Install the target: Install the CuO (99.99%) target at the RF source target position; (3) Pre-sputtering: Close the chamber door, turn on the vacuum pump, and evacuate the chamber to 7×10 -4 Pa, fill with argon to 3 Pa, the RF source output power is 40 W, turn on the RF source, after ignition, adjust the gas pressure to 0.3 Pa, maintain for 3 to 7 minutes, so that the sputtering rate is stable; (4) Sputtering CuO film: After the pre-sputtering, turn on the substrate rotation and substrate baffle, and then start to deposit the CuO film on the sample surface. The thickness of the CuO film is controlled according to the sputtering time (the sputtering time is 17 min, 25 min, 33 min, and 42 min, and the corresponding CuO film thickness is 50 nm, 75 nm, 100 nm, and 125 nm, respectively); (5) Open the chamber and take out the sample: After sputtering, turn off the substrate rotation and substrate baffle, fill the chamber with air to atmospheric state, open the chamber door, and take out the sample; (6) Preparation of CuO sacrificial layer: The obtained sample was transferred to a glove box filled with argon and annealed on a hot plate at 150 °C for 20 min to obtain Mo / CuO with good crystallinity.

[0023] (7) Preparation of CZTSSe absorption layer: A CZTSSe precursor solution was prepared, and a CZTSSe pre-layer was prepared on the obtained Mo / CuO sample by spin coating. The sample was then transferred to a rapid thermal annealing furnace filled with nitrogen and maintained at 550°C for 15 min to obtain a crystallized CZTSSe absorption layer.

[0024] (8) Preparation of CdS buffer layer: A CdS layer was deposited on the surface of the CZTSSe absorption layer using a chemical water bath method. The reaction temperature was 70 °C and the reaction time was 20 min. A CdS film with a thickness of 80 nm was obtained.

[0025] (9) Preparation of ITO window layer: The ITO layer was deposited on the CdS buffer layer by magnetron sputtering. The process parameters were: background vacuum degree <1.0×10 -3 Pa, the sputtering gas is argon, the working vacuum is 0.3 Pa, the RF sputtering power is 40 W, the sputtering time is 40 min, and the thickness is 230~260 nm.

[0026] (10) Preparation of Ag electrode: Ag electrode was prepared on the window layer by vacuum evaporation technology. Process parameters: vacuum degree was less than 2×10 -4 Pa, the evaporation rate is 3 Å / s, and the deposition thickness is 500 ~800nm.

[0027] Comparative Example The preparation steps of flexible CZTSSe solar cells are as follows: (1) Preparation of CZTSSe absorption layer: Prepare CZTSSe precursor solution, and prepare CZTSSe prefabricated layer on the cleaned and dried Mo foil by spin coating. Then transfer it to a rapid thermal annealing furnace filled with nitrogen and keep it at 550°C for 15 min to obtain a crystallized CZTSSe absorption layer.

[0028] (2) Preparation of CdS buffer layer: A CdS layer was deposited on the surface of the CZTSSe absorption layer using a chemical water bath method. The reaction temperature was 70 °C and the reaction time was 20 min. A CdS film with a thickness of 80 nm was obtained.

[0029] (3) Preparation of ITO window layer: The ITO layer was deposited on the CdS buffer layer by magnetron sputtering. The process parameters were: background vacuum degree <1.0×10 -3 Pa, the sputtering gas is argon, the working vacuum is 0.3 Pa, the RF sputtering power is 40 W, the sputtering time is 40 min, and the thickness is 230~260 nm.

[0030] (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 2×10 -4 Pa, the evaporation rate is 3 Å / s, and the deposition thickness is 500 ~800nm.

[0031] Figure 1 The surface SEM comparison of Mo / CuO / CZTSSe (CuO layer thickness 75 nm) prepared in the example and Mo / CZTSSe prepared in the comparative example. It can be seen from the figure that the surface morphology of the Mo / CuO / CZTSSe absorption layer is uniform, flat and dense, and the quality is high, while the surface morphology of the CZTSSe absorption layer without CuO modification is poor and has holes.

[0032] Figure 2 This is a cross-sectional SEM comparison of Mo / CuO / CZTSSe (CuO layer thickness is 75 nm) prepared in the example and Mo / CZTSSe prepared in the comparative example. As can be seen from the figure, the thickness of the MoSe2 layer in the Mo / CuO / CZTSSe structure is significantly lower than that of the MoSe2 layer in the Mo / CZTSSe structure, so it can effectively reduce the series resistance and carrier recombination, and the CZTSSe crystal size formed in the Mo / CuO / CZTSSe structure is larger than that of Mo / CZTSSe, and its crystallinity is also better.

[0033] Figure 3The schematic diagram of the structure of the CZTSSe solar cell constructed in the embodiment (A) and the SEM cross-sectional view of the finished cell (B). As can be seen from the figure, the finished product contains Mo foil, CZTSSe absorption layer, CdS buffer layer, ITO window layer, and Ag electrode (the CuO sacrificial layer disappears after high-temperature selenization).

[0034] Figure 4 The EDS diagram of Cu element in the CZTSSe solar cell prepared in the example (CuO layer thickness is 75 nm) and the CZTSSe solar cell constructed in the comparative example can reflect the distribution of Cu element in different samples. It can be seen from the figure that the sample with CuO added has more Cu content in the macrocrystalline layer, and the Cu formed by it x Se y Liquid phase is an important factor in promoting grain growth.

[0035] Figure 5 CZTSSe solar cells constructed with CuO sacrificial layers of different thicknesses J - V It can be seen from the figure that when the thickness of the CuO sacrificial layer is 75 nm, the performance is optimal and the maximum efficiency reaches 10.57%.

[0036] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for modifying the Mo / CZTSSe back interface with a CuO sacrificial layer, characterized in that: The following steps are involved: (1) Clean the substrate and blow dry; (2) preparing a CuO sacrificial layer on the substrate surface and performing post-annealing treatment; (3) A CZTSSe precursor is prepared on a CuO sacrificial layer, and then a CZTSSe absorption layer is formed by high-temperature selenization treatment.

2. The method for modifying the Mo / CZTSSe back interface with a CuO sacrificial layer according to claim 1, characterized in that: The substrate in step (1) is a Mo foil substrate.

3. The method for modifying the Mo / CZTSSe back interface with a CuO sacrificial layer according to claim 1, characterized in that: The method for preparing the CuO sacrificial layer in step (2) includes magnetron sputtering, thermal evaporation, and solution spin coating.

4. The method for modifying the Mo / CZTSSe back interface with a CuO sacrificial layer according to claim 1, characterized in that: The thickness of the CuO sacrificial layer prepared in step (2) is 50-125 nm.

5. The method for modifying the Mo / CZTSSe back interface with a CuO sacrificial layer according to claim 1, characterized in that: The post-annealing treatment in step (2) is carried out in an inert gas atmosphere at 150° C. for 20 minutes.

6. The method for modifying the Mo / CZTSSe back interface with a CuO sacrificial layer according to claim 1, characterized in that: The preparation method of the CZTSSe precursor in step (3) includes magnetron sputtering, solution spin coating, and electrodeposition.

7. The method for modifying the Mo / CZTSSe back interface with a CuO sacrificial layer according to claim 1, characterized in that: The high temperature selenization treatment in step (3) is carried out in a nitrogen environment at 550° C. for 15 minutes.

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