Method for preparing gradient absorption layer and solar cell using gradient absorption layer

Abstract

The invention provides a method for preparing a gradient absorption layer and a solar cell using the absorption layer, and the method for preparing the CIGS gradient absorption layer comprises the following two steps: 1, preparing a low-temperature amorphous CIGS prefabricated layer: sputtering a CIGS quaternary target material in an argon environment through a magnetron sputtering method, an amorphous CIGS prefabricated layer with the thickness of 40-100 nm is deposited on the molybdenum electrode layer at low temperature; and 2, preparing a high-temperature crystalline CIGS gradient absorption layer, namely sputtering and depositing a wide-band-gap copper-indium-gallium-sulfur regulation and control layer near the front surface or the back surface of the CIGS absorption layer when the high-temperature crystalline CIGS absorption layer is deposited by adopting a magnetron sputtering method, and then annealing to prepare the CIGS gradient absorption layer. Therefore, the preparation method has the advantages that the problem that the efficiency of the prepared CIGS thin film solar cell is low due to the fact that element distribution of a common CIGS absorption layer subjected to sputtering deposition is difficult to control, a V-shaped gradient band gap cannot be effectively formed and the defect density is high is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of thin-film solar cells, and mainly relates to a method for preparing a gradient absorption layer and a solar cell using the absorption layer. Background Art

[0002] With the rapid development of modern society, human demand for energy has risen rapidly. At the same time, the environmental degradation caused by fossil energy has become increasingly prominent. People urgently need to find environmentally friendly new energy to replace fossil energy. Copper indium gallium selenide (CIGS) thin-film solar cells have the characteristics of high efficiency, stable performance, and adjustable band gap. It is a type of solar cell that has developed rapidly in recent years. At present, the commonly used methods for preparing CIGS light absorption layer films are mainly multi-source co-evaporation and sputtering-selenization. Although relatively efficient CIGS thin-film solar cells can be prepared by co-evaporation, the co-evaporation method has problems such as high process difficulty, low yield, and low raw material utilization. The sputtering-selenization process can prepare CIGS thin films on a large area. It has the advantages of high raw material utilization, high density of precursor films, good component uniformity, and adjustable chemical ratio of elements. However, the selenization process requires the use of highly toxic H 2 Se gas or Se vapor, and has the disadvantages of long time, high energy consumption and low yield.

[0003] In recent years, in order to avoid the problems of co-evaporation and sputtering-selenization, sputtering film formation using CIGS quaternary target has become a new method for preparing CIGS light absorption layer. Since CIGS quaternary compound has been formed in the prefabricated film deposited by sputtering using CIGS quaternary target, the use of highly toxic H 2 Se gas or Se vapor is used to post-selenize the deposited film, which can greatly simplify the battery preparation process and reduce the maintenance cost of the equipment. However, the industrial development of quaternary target sputtering CIGS thin film solar cells is much slower than that of crystalline silicon solar cells, mainly because its open circuit voltage (V OC ) is less than 60% of the Shockley Quiesser theoretical limit. The use of a V-shaped gradient bandgap absorber layer (large bandgap on the front and rear surfaces and narrow bandgap in the middle layer) is an effective means to improve device performance. However, when depositing the CIGS absorber layer by magnetron sputtering, the high-temperature preparation process required will lead to a chaotic distribution of elements in the absorber layer, making it difficult to achieve a gradient bandgap at the front and rear interfaces. The body defect density of the prepared absorber layer is also high, which brings difficulties to the preparation of high-efficiency CIGS thin-film solar cells. Therefore, it is particularly important to provide a method for preparing a CIGS absorber layer with a gradient bandgap and low carrier recombination characteristics based on selenium-free sputtering technology to improve the efficiency of CIGS thin-film solar cells. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a gradient absorption layer and a solar cell using the absorption layer, so as to solve the problem that the element distribution of the CIGS absorption layer deposited by conventional sputtering is difficult to control, the V-shaped gradient band gap cannot be effectively formed, and the defect density is high, thereby resulting in low efficiency of the prepared CIGS thin film solar cell.

[0005] A method for preparing a gradient absorption layer comprises the following two steps: Step 1: Preparation of low-temperature amorphous CIGS prefabricated layer: Using magnetron sputtering method to sputter CIGS quaternary target in argon environment, a layer of amorphous CIGS prefabricated layer with a thickness of 40 nm~100 nm is deposited on the molybdenum electrode layer at low temperature, and the deposition temperature is 10℃~50℃; Step 2: Preparation of high-temperature crystalline CIGS gradient absorption layer: When the high-temperature crystalline CIGS absorption layer is deposited by magnetron sputtering, a wide-bandgap copper indium gallium sulfide regulation layer is sputtered and deposited near the front surface or back surface of the CIGS absorption layer, and then annealing is performed to obtain the CIGS gradient absorption layer, and the substrate temperature for annealing is 350°C~650°C.

[0006] According to a method for preparing a CIGS gradient absorption layer of the present invention, the high-temperature crystalline CIGS absorption layer is prepared by sputtering a CIGS target in an argon environment using a magnetron sputtering method.

[0007] According to a method for preparing a gradient absorption layer of the present invention, during the preparation, the argon pressure in the vacuum chamber is 0.2 Pa~1.0 Pa, and the sputtering power is 0.1 W / cm 2 ~8 W / cm 2 .

[0008] According to a method for preparing a gradient absorption layer of the present invention, the wide bandgap copper indium gallium sulfide regulation layer is prepared by sputtering a copper indium gallium sulfide target in an argon environment using a magnetron sputtering method.

[0009] According to a method for preparing a gradient absorption layer of the present invention, during the preparation, the argon pressure in the vacuum chamber is 0.2 Pa~1.0 Pa, and the sputtering power is 0.1 W / cm 2 ~8 W / cm 2 , the thickness is 0.3%~15% of the total thickness of the absorption layer.

[0010] According to a method for preparing a gradient absorption layer of the present invention, the total thickness of the CIGS gradient absorption layer is 1000nm~3000nm, and the position and depth of the band gap minimum (gap) can be adjusted by adjusting the position and thickness of the copper indium gallium sulfide layer, so as to avoid the charge barrier caused by the inappropriate front gradient starting position and the undesirable band gap gap. The sputtering deposition of a wide band gap copper indium gallium sulfide layer near the front surface or the back surface refers to depositing a copper indium gallium sulfide film at a position where the distance to the front surface accounts for 0%-30% of the total thickness of the absorption layer, or at a position where the distance to the back surface accounts for 0%-30% of the total thickness of the absorption layer, and the thickness of the copper indium gallium sulfide layer accounts for 0.3%-15% of the total thickness of the absorption layer.

[0011] A solar cell, whose absorption layer is prepared based on the above method for preparing a CIGS absorption layer. The present invention provides a method for preparing a CIGS thin-film solar cell based on the above CIGS gradient absorption layer, which comprises the following steps: (a) Preparation of a molybdenum electrode layer: depositing a molybdenum electrode layer with a thickness of 200 to 1000 nm on a substrate by magnetron sputtering; the substrate is a soda-lime glass substrate, a stainless steel substrate or a polyimide substrate; (b) Preparation of CIGS absorption layer: on the molybdenum electrode layer, a CIGS absorption layer is prepared based on the method for preparing a CIGS absorption layer according to claims 1 to 6; (c) Preparation of buffer layer: a buffer layer with a thickness of 40-200 nm is prepared on the CIGS absorption layer by chemical water bath method or magnetron sputtering method; the buffer layer material can be cadmium sulfide film, zinc sulfide film, indium sulfide film or composite film of cadmium sulfide and zinc sulfide; (d) Preparation of the window layer: a high resistance layer with a thickness of 80 to 200 nm is prepared on the buffer layer by magnetron sputtering, and a transparent conductive layer with a thickness of 100 to 400 nm is prepared on the high resistance layer by magnetron sputtering; the high resistance layer may be intrinsic zinc oxide (i-ZnO), and a transparent conductive layer with a thickness of 100 to 400 nm is prepared on the high resistance layer by magnetron sputtering; (e) Preparation of metal grid electrode: A patterned metal grid electrode is prepared by using a mask plate using a vacuum evaporation method to obtain the CIGS thin-film solar cell; the metal grid electrode can be one or more of gold, silver, aluminum, copper, and nickel. Considering the cost and performance, the metal grid electrode can preferably be a double-layer structure of aluminum and nickel, wherein the thickness of the aluminum layer is 70~200 nm and the thickness of the nickel layer is 3~20 nm.

[0012] According to a solar cell described in the present invention, in the step (a), for a stainless steel substrate or a polyimide substrate, before the deposition of the molybdenum electrode layer in the step (a), a barrier layer with a thickness of 50 to 400 nm is first deposited on the substrate by magnetron sputtering or PECVD, and the barrier layer is preferably a silicon oxide film, a titanium nitride film or a silicon nitride film; a molybdenum layer doped with sodium metal is then deposited on the barrier layer by magnetron sputtering, and the target material used for the deposition of the sodium molybdenum layer is a target material made of a mixture of sodium molybdate and molybdenum, the sodium molybdate content in the target material is 0.5% to 10%, the sputtering pressure is 0.2 to 1 Pa, and the sputtering power is 0.2 to 4 W / cm 2 . Then the deposition of the pure molybdenum electrode layer is carried out.

[0013] According to a solar cell described in the present invention, for a soda-lime glass substrate, when a pure molybdenum electrode layer is deposited by a DC magnetron sputtering method, a layer of molybdenum with a thickness of 400 nm to 700 nm is first deposited under a higher Ar gas pressure of 1.5 to 3 Pa, and then a layer of molybdenum with a thickness of 100 nm to 400 nm is deposited under a lower Ar gas pressure of 0.2 to 1 Pa. The molybdenum film deposited under the high Ar gas pressure has tensile stress, good adhesion to the substrate, but high resistivity; the molybdenum film deposited under the low Ar gas pressure has tensile stress, poor adhesion to the substrate, but low resistivity. By sputtering and depositing the molybdenum layer under two Ar gas pressures, it is helpful to obtain a molybdenum electrode layer with relatively excellent adhesion and conductivity.

[0014] According to the solar cell described in the present invention, the transparent conductive layer in the step (d) can be one of aluminum-doped zinc oxide (AZO), indium tin oxide (ITO), boron-doped zinc oxide, molybdenum-doped indium oxide (IMO), zinc-doped indium oxide (IZO) or titanium-doped indium oxide (ITiO).

[0015] The beneficial effects of the present invention are: (1) The present invention adopts a magnetron sputtering process to prepare the absorption layer of the CIGS thin-film solar cell. There is no need for post-annealing under selenium atmosphere conditions, and the equipment requirements are relatively low. The obtained product has controllable performance and good consistency, and is suitable for industrial production.

[0016] (2) The method described in the present invention can obtain CIGS absorption layers with different S / (S+Se) ratios and different gradient band gaps by adjusting the position and thickness of the wide band gap copper indium gallium sulfide control layer.

[0017] (3) The CIGS absorption layer prepared by the method of the present invention has good crystallinity, a V-shaped gradient band gap distribution, a low defect density, and good absorption in the visible light region, which is beneficial to improving the photoelectric conversion efficiency of solar cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 are SEM cross-sectional images of CIGS absorber layers prepared in Example 1 and Comparative Example 1; Figure 2 is the half-width fitting result of the (112) crystal plane diffraction peak of the XRD spectra of the samples of Examples 1 to 3; Figure 3 This is the XPS depth analysis S / (S+Se) result of the CIGS gradient absorption layer of the sample in Example 7. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] The purpose of the present invention is to provide a method for preparing a CIGS gradient absorption layer, and to use the method to prepare a CIGS thin-film solar cell, so as to solve the problem that the element distribution of the CIGS absorption layer deposited by conventional sputtering is difficult to control, the V-shaped gradient band gap cannot be effectively formed, and the defect density is high, thereby resulting in low efficiency of the prepared CIGS thin-film solar cell.

[0021] To achieve the above objectives, the present invention provides a method for preparing a CIGS gradient absorption layer, which comprises the following steps: (a) Preparation of low-temperature amorphous CIGS pre-layer: CIGS quaternary target is sputtered by magnetron sputtering in an argon environment, and a layer of amorphous CIGS pre-layer with a thickness of 40 nm-100 nm is deposited on the molybdenum electrode layer at a low temperature (10 ℃-50 ℃).

[0022] (b) Preparation of CIGS gradient absorption layer: When the high-temperature crystalline CIGS absorption layer is deposited by magnetron sputtering, a wide-bandgap copper indium gallium sulfide regulation layer is sputtered and deposited near the front surface or back surface of the CIGS absorption layer, and then high-temperature annealing is performed to obtain the CIGS gradient absorption layer.

[0023] The high-temperature crystalline CIGS absorption layer was prepared by magnetron sputtering CIGS target in an argon environment. The argon pressure in the vacuum chamber was 0.2 Pa-1.0 Pa and the sputtering power was 0.1 W / cm 2 - 8 W / cm 2 , the substrate temperature is 350℃-650℃.

[0024] The wide bandgap copper indium gallium sulfide control layer was prepared by magnetron sputtering copper indium gallium sulfide target in an argon environment. The argon pressure in the vacuum chamber was 0.2 Pa-1.0 Pa and the sputtering power was 0.1 W / cm 2 - 8 W / cm 2 , the substrate temperature is 350℃-650℃, and the thickness is 0.3%-15% of the total thickness of the absorption layer.

[0025] The total thickness of the CIGS gradient absorption layer is 1000 nm-3000 nm.

[0026] By adjusting the position and thickness of the copper indium gallium sulfide layer, the position and depth of the band gap minimum (gap) can be controlled to avoid the charge barrier caused by the inappropriate front gradient starting position and the undesirable band gap gap. Sputtering a wide-gap copper indium gallium sulfide layer near the front surface or the back surface means depositing a copper indium gallium sulfide film at a distance from the front surface accounting for 0%-30% of the total thickness of the absorption layer, or at a distance from the back surface accounting for 0%-30% of the total thickness of the absorption layer, and the thickness of the copper indium gallium sulfide layer accounts for 0.3%-15% of the total thickness of the absorption layer.

[0027] In order to improve the photoelectric conversion efficiency of CIGS thin-film solar cells prepared by selenium-free magnetron sputtering, the present invention provides a method for preparing a CIGS thin-film solar cell based on the above-mentioned CIGS gradient absorption layer, which comprises the following steps: (a) Preparation of molybdenum electrode layer: A molybdenum electrode layer with a thickness of 200-1000 nm was deposited on the substrate by magnetron sputtering; (b) Preparation of CIGS gradient absorption layer: The CIGS gradient absorption layer was prepared by the above method; (c) Preparation of buffer layer: A buffer layer with a thickness of 40-200 nm is prepared on the CIGS absorption layer by chemical water bath method or magnetron sputtering method; (d) Preparation of window layer: a high resistance layer with a thickness of 80-200 nm is prepared on the buffer layer by magnetron sputtering, and a transparent conductive layer with a thickness of 100-400 nm is prepared on the high resistance layer by magnetron sputtering; (e) Preparation of metal grid electrode: A patterned metal grid electrode is prepared by using a vacuum evaporation method and a mask plate, thus obtaining a CIGS thin-film solar cell.

[0028] In step (a), the substrate is a soda-lime glass sheet, a thin stainless steel sheet or a polyimide sheet.

[0029] For stainless steel or polyimide substrates, before the deposition of the molybdenum electrode layer in the above step (a), a barrier layer with a thickness of 50 to 400 nm is first deposited on the pretreated substrate by magnetron sputtering or PECVD, and the barrier layer is preferably a silicon oxide film, a titanium nitride film or a silicon nitride film; a molybdenum layer doped with sodium metal is then deposited on the barrier layer by magnetron sputtering, and the target material used for the deposition of the sodium molybdenum layer is a target material made of a mixture of sodium molybdate and molybdenum (the content of sodium molybdate in the target material is 0.5% to 10%), the sputtering pressure is 0.2 to 1 Pa, and the sputtering power is 0.2 to 4 W / cm 2 . Then the deposition of the pure molybdenum electrode layer is carried out.

[0030] For soda-lime glass substrates, when a pure molybdenum electrode layer is deposited by DC magnetron sputtering, a layer of molybdenum with a thickness of 400 nm-700 nm is first deposited under a higher Ar gas pressure of 1.5~3 Pa, and then a layer of molybdenum with a thickness of 100 nm-400 nm is deposited under a lower Ar gas pressure of 0.2~1 Pa. The molybdenum film deposited under high Ar gas pressure conditions presents tensile stress, has good adhesion to the substrate, but has a high resistivity; the molybdenum film deposited under low Ar gas pressure conditions presents tensile stress, has poor adhesion to the substrate, but has a low resistivity. By sputtering and depositing the molybdenum layer under two Ar gas pressure conditions, it is helpful to obtain a molybdenum electrode layer with excellent adhesion and conductivity.

[0031] The buffer layer material in step (c) may be a cadmium sulfide film, a zinc sulfide film, an indium sulfide film, or a composite film of cadmium sulfide and zinc sulfide.

[0032] In step (d), the high resistance layer may be intrinsic zinc oxide (i-ZnO), and a transparent conductive layer with a thickness of 100-400 nm is prepared on the high resistance layer by magnetron sputtering; The TCO layer in step (d) may be aluminum-doped zinc oxide (AZO), ITO, boron-doped zinc oxide, molybdenum-doped indium oxide (IMO), zinc-doped indium oxide (IZO), or titanium-doped indium oxide (ITiO).

[0033] The metal gate electrode in step (e) may be one or more of gold, silver, aluminum, copper, and nickel. Considering the cost and performance, the metal gate electrode may preferably be an Al / Ni double-layer structure, wherein the Al layer is 70-200 nm thick and the Ni layer is 3-20 nm thick.

[0034] The present invention adopts a direct sputtering process in a selenium-free atmosphere to prepare a high-efficiency CIGS thin-film solar cell, innovatively inserts a copper indium gallium sulfide regulation layer with a wide bandgap characteristic and a defect passivation function on the surface or in the middle of the CIGS absorption layer, and controls the thickness of the wide-bandgap copper indium gallium sulfide thin film regulation layer and the introduction position in the CIGS absorption layer to achieve precise regulation of the V-shaped bandgap and defect passivation characteristics of the absorption layer, thereby improving the open circuit voltage and fill factor of the battery, and obtaining a high-efficiency CIGS thin-film solar cell.

[0035] Example 1 In the first step, after cleaning the soda-lime glass substrate, a pure molybdenum electrode layer was deposited using a DC magnetron sputtering method. First, a layer of molybdenum with a thickness of 600 nm was deposited under an Ar gas pressure of 2 Pa, and then a layer of molybdenum with a thickness of 200 nm was deposited under an Ar gas pressure of 0.5 Pa to obtain a molybdenum electrode with a total thickness of 0.8 μm.

[0036] In the second step, a low-temperature amorphous CIGS layer was deposited on the molybdenum electrode layer using a CIGS quaternary target by magnetron sputtering. The substrate temperature during preparation was room temperature, the argon flow rate was 10 sccm, and the sputtering power density was 0.12 W / cm 2 , the sputtering pressure is 0.5 Pa and the thickness is 80 nm.

[0037] In the third step, the substrate temperature was raised to 580 °C, and a high-temperature crystalline CIGS layer was further deposited using a CIGS quaternary target by magnetron sputtering. The argon flow rate during deposition was 10 sccm, and the sputtering power density was 2.4 W / cm 2 , the sputtering pressure is 0.5 Pa, and the thickness is 2010 nm.

[0038] The fourth step is to transfer the sample with the CIGS layer deposited above into a sputtering chamber equipped with a copper indium gallium sulfide target to prepare a 10 nm thick copper indium gallium sulfide film, wherein the argon flow rate is 10 sccm, the sputtering pressure is 0.5 Pa, and the sputtering power is 1.6 W / cm 2 .

[0039] After sputtering, the sample was subjected to vacuum in-situ annealing at 580 °C for 10 min to complete the preparation of a gradient CIGS absorption layer with a total thickness of 2100 nm.

[0040] Step 5: Preparation of the buffer layer: The CdS buffer layer is prepared by a chemical water bath method. After cadmium acetate, sodium citrate, thiourea and ammonia water are mixed in a certain order, the thickness of the buffer layer is controlled by adjusting the temperature of the water bath and the immersion time of the absorption layer in the solution. The thickness of the prepared CdS buffer layer is 50 nm.

[0041] Step 6: Preparation of the window layer: A 100 nm thick intrinsic ZnO layer is firstly sputtered and deposited on the CdS buffer layer by magnetron sputtering, and then a 400 nm thick aluminum-doped zinc oxide (AZO) layer is sputtered and deposited; The seventh step is the preparation of metal gate line electrodes: the patterned metal nickel (Ni) and metal aluminum (Al) gate line electrodes are prepared using a vacuum evaporation method using a mask.

[0042] The CIGS thin film solar cell is obtained.

[0043] Example 2 In the first step, after cleaning the soda-lime glass substrate, a pure molybdenum electrode layer was deposited using a DC magnetron sputtering method. First, a layer of molybdenum with a thickness of 600 nm was deposited under an Ar gas pressure of 2 Pa, and then a layer of molybdenum with a thickness of 200 nm was deposited under an Ar gas pressure of 0.5 Pa to obtain a molybdenum electrode with a total thickness of 0.8 μm.

[0044] In the second step, a low-temperature amorphous CIGS layer was deposited on the molybdenum electrode layer using a CIGS quaternary target by magnetron sputtering. The substrate temperature during preparation was room temperature, the argon flow rate was 10 sccm, and the sputtering power density was 0.12 W / cm 2 , the sputtering pressure is 0.5 Pa and the thickness is 80 nm.

[0045] In the third step, the substrate temperature was raised to 580 °C, and a high-temperature crystalline CIGS layer was further deposited using a CIGS quaternary target by magnetron sputtering. The argon flow rate during deposition was 10 sccm, and the sputtering power density was 2.4 W / cm 2 , the sputtering pressure is 0.5 Pa, and the thickness is 1990 nm.

[0046] The fourth step is to transfer the sample with the CIGS layer deposited above into a sputtering chamber equipped with a copper indium gallium sulfide target to prepare a 10 nm thick copper indium gallium sulfide film, wherein the argon flow rate is 10 sccm, the sputtering pressure is 0.5 Pa, and the sputtering power is 0.8 W / cm 2 .

[0047] In the fifth step, the sample was transferred back to the sputtering chamber containing the CIGS target and a 20 nm thick CIGS film was deposited. The argon flow rate was 10 sccm, the sputtering pressure was 0.5 Pa, and the sputtering power was 1.6 W / cm 2 .

[0048] After sputtering, the sample was subjected to vacuum in-situ annealing at 580 °C for 10 min to complete the preparation of a gradient CIGS absorption layer with a total thickness of 2100 nm.

[0049] Step 6 Preparation of buffer layer: The CdS buffer layer is prepared by chemical water bath method. After cadmium acetate, sodium citrate, thiourea and ammonia water are mixed in a certain order, the thickness of the buffer layer is controlled by adjusting the temperature of the water bath and the immersion time of the absorption layer in the solution. The thickness of the prepared CdS buffer layer is 50 nm.

[0050] Step 7: Preparation of the window layer: A 100 nm thick intrinsic ZnO layer is firstly sputtered and deposited on the CdS buffer layer by magnetron sputtering, and then a 400 nm thick aluminum-doped zinc oxide (AZO) layer is sputtered and deposited; Step 8: Preparation of metal gate line electrodes: Use vacuum evaporation method to prepare patterned metal nickel (Ni) and metal aluminum (Al) gate line electrodes using a mask.

[0051] The CIGS thin film solar cell is obtained.

[0052] Embodiment 3-5 The total thickness of the crystalline CIGS absorption layer and the copper indium gallium sulfide film was fixed to 2020 nm, and the deposition thickness of the copper indium gallium sulfide film was changed (to 30, 60 and 100 nm, respectively, and the corresponding thickness of the third crystalline CIGS absorption layer was 1990, 1960 and 1920 nm, respectively). The other processes were the same as in Example 1.

[0053] Embodiment 6-8 The deposition position of the copper indium gallium sulfide film was changed (40, 60 and 100 nm from the upper surface of the absorption layer, respectively; the corresponding thicknesses of the third-step high-temperature crystalline CIGS absorption layer and the fifth-step re-deposited CIGS absorption layer were 1970 and 40 nm, 1950 and 60 nm, and 1910 and 100 nm, respectively). The other processes were the same as in Example 2.

[0054] Comparative Example 1 In the first step, after cleaning the soda-lime glass substrate, a pure molybdenum electrode layer was deposited using a DC magnetron sputtering method. First, a layer of molybdenum with a thickness of 600 nm was deposited under an Ar gas pressure of 2 Pa, and then a layer of molybdenum with a thickness of 200 nm was deposited under an Ar gas pressure of 0.5 Pa to obtain a molybdenum electrode with a total thickness of 0.8 μm.

[0055] In the second step, a low-temperature amorphous CIGS layer was deposited on the molybdenum electrode layer using a CIGS quaternary target by magnetron sputtering. The substrate temperature during preparation was room temperature, the argon gas flow rate was 10 sccm, the sputtering power density was 0.12 W / cm2, the sputtering pressure was 0.5 Pa, and the thickness was 80 nm.

[0056] In the third step, the substrate temperature is raised to 580 °C, and a high-temperature crystalline CIGS layer is further deposited using a CIGS quaternary target by magnetron sputtering. During deposition, the argon flow rate is 10 sccm, the sputtering power density is 2.4 W / cm2, the sputtering pressure is 0.5 Pa, and the thickness is 2020 nm.

[0057] After sputtering, the sample was subjected to vacuum in-situ annealing at 580 °C for 10 min to complete the preparation of a gradient CIGS absorption layer with a total thickness of 2100 nm.

[0058] Step 4: Preparation of the buffer layer: The CdS buffer layer is prepared by a chemical water bath method. After cadmium acetate, sodium citrate, thiourea and ammonia water are mixed in a certain order, the thickness of the buffer layer is controlled by adjusting the temperature of the water bath and the immersion time of the absorption layer in the solution. The thickness of the prepared CdS buffer layer is 50 nm.

[0059] Step 5: Preparation of the window layer: A 100 nm thick intrinsic ZnO layer is firstly sputtered and deposited on the CdS buffer layer by magnetron sputtering, and then a 400 nm thick aluminum-doped zinc oxide (AZO) layer is sputtered and deposited; The sixth step is the preparation of metal gate line electrodes: the patterned metal nickel (Ni) and metal aluminum (Al) gate line electrodes are prepared using a vacuum evaporation method using a mask.

[0060] The CIGS thin film solar cell is obtained.

[0061] The microstructure and battery performance parameters of the prepared samples were characterized. Figure 1 , Figure 2 As shown in Tables 1 and 2. Figure 1 The SEM images of the CIGS gradient absorption layer are obtained by sputtering and depositing 0 nm, 10 nm, 100 nm and 1000 nm thick copper indium gallium sulfide wide band gap film layers on the surface of the CIGS film using the process conditions of Comparative Example 1 and Examples 1 to 3, and then annealing. Figure 2 It is the half-height width fitting result of XRD test (112) of samples of Example 1, Example 6, Example 8 and Comparative Example 1. Figure 1 and Figure 2The results show that after adding the copper indium gallium sulfide wide bandgap deposition layer, the grain size of the obtained CIGS absorption layer becomes significantly larger, and the half-width results of the XRD test also verify this conclusion. Table 1 shows the battery efficiency parameters of Example 1, Examples 3 to 5 and Comparative Example 1. The results show that when the thickness of the copper indium gallium sulfide film in Example 3 is 30 nm, the device efficiency is the highest, and the battery efficiency reaches 16.72%. Table 2 shows the battery efficiency parameters of Example 1, Example 2, and Examples 6 to 8. The results show that when the copper indium gallium sulfide film deposition position in Example 6 is 40 nm away from the top of the absorption layer, the efficiency is the highest, reaching 18.44%. This is because the notch position of the V-shaped structure is in the depletion region, which is conducive to reducing recombination and improving V OC . Figure 3 This is the XPS deep etching result of the sample of Example 6. Obvious high S content can be observed at the top and bottom of the absorption layer, indicating that the change in the S / (S+Se) element content of the absorption layer presents a V-shaped change, which corresponds to a V-shaped structure of the band gap.

[0062] Table 1 Performance parameters of CIGS thin film solar cells prepared under the process conditions of Examples 1-5 and Comparative Example 1 Table 2 Performance parameters of CIGS thin film solar cells prepared under the process conditions of Examples 1-2 and 6-8 Example 9 The difference between this embodiment and embodiment 1 is that the sputtering gas pressure of the copper indium gallium sulfide film in the fourth step is 1 Pa.

[0063] Example 10 The difference between this embodiment and embodiment 1 is that the sputtering power of the copper indium gallium sulfide film in the fourth step is 2.4 W / cm 2 .

[0064] Table 3 shows the cell efficiency parameters of Example 1, Example 9 and Example 10. The results show that the sputtering pressure and sputtering power of the copper indium gallium sulfur film in Example 1 are 0.5 Pa and 1.6 W / cm 2 This is because excessively high sputtering pressure and power density will cause changes in the composition and phase of the absorption layer, leading to the formation of harmful deep energy level defects.

[0065] Table 3 Performance parameters of CIGS thin film solar cells prepared under the process conditions of Examples 1 and 9-10 The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a gradient absorption layer, characterized in that: It includes the following two steps: Step 1: Preparation of low-temperature amorphous CIGS prefabricated layer: Using magnetron sputtering method to sputter CIGS quaternary target in argon environment, a layer of amorphous CIGS prefabricated layer with a thickness of 40 nm~100 nm is deposited on the molybdenum electrode layer at low temperature, and the deposition temperature is 10℃~50℃; Step 2: Preparation of high-temperature crystalline CIGS gradient absorption layer: When the high-temperature crystalline CIGS absorption layer is deposited by magnetron sputtering, a wide-bandgap copper indium gallium sulfide regulation layer is sputtered and deposited near the front surface or back surface of the CIGS absorption layer, and then annealing is performed to obtain the CIGS gradient absorption layer, and the substrate temperature for annealing is 350°C~650°C.

2. The method for preparing a gradient absorption layer according to claim 1, characterized in that: The high temperature crystalline CIGS absorption layer is prepared by sputtering a CIGS target in an argon environment using a magnetron sputtering method.

3. The method for preparing a gradient absorption layer according to claim 2, characterized in that: During the preparation, the argon pressure in the vacuum chamber was 0.2 Pa-1.0 Pa, and the sputtering power was 0.1 W / cm 2 ~8 W / cm 2 .

4. The method for preparing a gradient absorption layer according to claim 1, characterized in that: The wide bandgap copper indium gallium sulfide regulation layer is prepared by sputtering a copper indium gallium sulfide target in an argon environment using a magnetron sputtering method.

5. The method for preparing a gradient absorption layer according to claim 4, characterized in that: During the preparation, the argon pressure in the vacuum chamber was 0.2 Pa-1.0 Pa, and the sputtering power was 0.1 W / cm 2 ~8 W / cm 2 , the thickness is 0.3%~15% of the total thickness of the absorption layer.

6. The method for preparing a gradient absorption layer according to claim 1, characterized in that: The total thickness of the CIGS gradient absorption layer is 1000 nm to 3000 nm.

7. A solar cell, wherein the absorption layer is prepared by the method for preparing a CIGS absorption layer according to claims 1 to 6, characterized in that: The present invention provides a method for preparing a CIGS thin-film solar cell based on the above-mentioned CIGS gradient absorption layer, which comprises the following steps: (a) Preparation of a molybdenum electrode layer: a molybdenum electrode layer with a thickness of 200 to 1000 nm is deposited on a substrate by magnetron sputtering; the substrate is a soda-lime glass substrate, a stainless steel substrate or a polyimide substrate; (b) Preparation of CIGS absorption layer: on the molybdenum electrode layer, a CIGS absorption layer is prepared based on the method for preparing a CIGS absorption layer according to claims 1 to 6; (c) Preparation of buffer layer: a buffer layer with a thickness of 40-200 nm is prepared on the CIGS absorption layer by chemical water bath method or magnetron sputtering method; the buffer layer material is cadmium sulfide film, zinc sulfide film, indium sulfide film or composite film of cadmium sulfide and zinc sulfide; (d) Preparation of the window layer: a high resistance layer with a thickness of 80 to 200 nm is prepared on the buffer layer by magnetron sputtering, and a transparent conductive layer with a thickness of 100 to 400 nm is prepared on the high resistance layer by magnetron sputtering; the high resistance layer is intrinsic zinc oxide (i-ZnO), and a transparent conductive layer with a thickness of 100 to 400 nm is prepared on the high resistance layer by magnetron sputtering; (e) Preparation of metal grid electrode: A patterned metal grid electrode is prepared by using a vacuum evaporation method using a mask plate to obtain the CIGS thin-film solar cell; the metal grid electrode can preferably be a double-layer structure of aluminum and nickel, wherein the thickness of the aluminum layer is 70~200 nm and the thickness of the nickel layer is 3~20 nm.

8. A solar cell according to claim 7, characterized in that: In the step (a), for the stainless steel substrate or the polyimide substrate, before the molybdenum electrode layer is deposited in the step (a), a barrier layer with a thickness of 50 to 400 nm is first deposited on the substrate by magnetron sputtering or PECVD; a molybdenum layer doped with sodium metal is then deposited on the barrier layer by magnetron sputtering, and the target material used for the deposition of the sodium molybdenum layer is a target material made of a mixture of sodium molybdate and molybdenum, the sputtering pressure is 0.2 to 1 Pa, and the sputtering power is 0.2 to 4 W / cm 2 Then, a pure molybdenum electrode layer is deposited.

9. A solar cell according to claim 7, characterized in that: In the step (a), for the soda-lime glass substrate, when a pure molybdenum electrode layer is deposited by DC magnetron sputtering, a layer of molybdenum with a thickness of 400 nm to 700 nm is first deposited under a higher Ar gas pressure of 1.5 to 3 Pa, and then a layer of molybdenum with a thickness of 100 nm to 400 nm is deposited under a lower Ar gas pressure of 0.2 to 1 Pa.

10. A solar cell according to claim 7, characterized in that: The transparent conductive layer in step (d) is one of aluminum-doped zinc oxide, indium tin oxide, boron-doped zinc oxide, molybdenum-doped indium oxide, zinc-doped indium oxide or titanium-doped indium oxide.

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