Wide band gap CuGaSe2 solar cell absorption layer film and preparation method thereof

Abstract

The invention discloses a wide band gap CuGaSe2 solar cell absorption layer thin film and a preparation method thereof, and relates to the technical field of solar cells. The method comprises the specific steps that a CuGaSe2 thin film with the thickness of 500 nm, a Sb2Se3 thin film with the thickness of 100 nm and a CuGaSe2 thin film with the thickness of 500 nm are sequentially deposited on a Mo back electrode, and a CuGaSe2 / Sb2Se3 / CuGaSe2 prefabricated film is formed; then, the prefabricated film is placed in a tubular furnace for annealing treatment, CuGaSe2 crystal grain growth is promoted through decomposition and volatilization of Sb2Se3 at the high temperature, and the CuGaSe2 absorption layer thin film with the large crystal grain size is obtained. According to the absorption layer film prepared by the method, the grain growth effect is optimal during annealing at 550 DEG C, the average grain size is increased from 0.2 mu m to 0.7 mu m, no secondary phase exists, the forbidden bandwidth is 1.7 eV, the absorption coefficient is greater than 105 cm <-1 >, and the absorption layer film is suitable for being used as a top battery absorption layer material of a laminated battery. According to the invention, the preparation process is optimized, the problems of low crystallinity, small grain size and limited performance of the wide band gap CuGaSe2 thin film in the traditional method are solved, and a new scheme is provided for the preparation of the efficient thin film solar cell.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar cells, and particularly relates to a wide-bandgap CuGaSe2 solar cell absorber layer thin film and a preparation method thereof. Background Art

[0002] Compared with traditional crystalline silicon solar cells, thin-film solar cells have advantages such as good low-light performance and can be made into flexible cells, and are suitable for scenarios that require flexibility such as car roofs and wearable devices. With the in-depth research, the efficiency of thin-film solar cells represented by cadmium telluride (CdTe), gallium arsenide (GaAs), copper indium gallium selenide (CIGS), perovskite, etc. has been continuously improved, gradually approaching the Shockley-Queisser limit of single pn-junction solar cells. The tandem solar cell is composed of a high-efficiency bottom cell and a wide-bandgap top cell connected in series. Under illumination, the top cell first absorbs high-energy photons, and the remaining low-energy photons then pass through the top cell and are absorbed by the bottom cell. The bottom cell usually uses conventional bandgap materials to improve the absorption efficiency of low-energy photons; while the top cell uses wide-bandgap materials to better utilize high-energy photons, thereby significantly improving the overall photoelectric conversion efficiency. The tandem solar cell improves the comprehensive utilization rate of light energy through this structure of hierarchical absorption of high- and low-energy photons. In tandem solar cells, the research on the bottom cell is relatively rich, while the top cell usually needs to use wide-bandgap materials, and there is less research on it and the preparation difficulty is relatively large.

[0003] CuGaSe2 is a direct-bandgap semiconductor with a high light absorption coefficient and a wide bandgap, and is suitable as the top cell material of tandem solar cells. The CuGaSe2 thin film can be deposited by magnetron sputtering of a ternary copper gallium selenide target. This deposition method can reduce the secondary phases formed by complex chemical reactions during the preparation process and generate a large-area uniform CuGaSe2 thin film with a single phase. However, the thin film obtained by magnetron sputtering has a low crystallinity and small grain size. The small grain size will generate a large number of grain boundaries, and the defects at the grain boundaries are easy to form recombination centers, resulting in carrier scattering and reducing the mobility, which in turn hinders the diffusion and collection of carriers and limits the improvement of battery performance. Annealing treatment is required to promote the crystallization growth of the thin film. To obtain a dense and highly crystalline CuGaSe2 absorber layer thin film, H2Se gas needs to be added to the annealing atmosphere. However, H2Se has a high cost, and is toxic and corrosive. At present, there is still a lack of a simple and effective method to directly prepare the CuGaSe2 absorber layer thin film, which has become a key problem that researchers in this field are committed to solving. Summary of the Invention

[0004] Aiming at the defects existing in the prior art, the present invention discloses a wide-bandgap CuGaSe2 solar cell absorption layer thin film and a preparation method thereof. By doping Sb2Se3 into the CuGaSe2 thin film and utilizing the decomposition and volatilization of Sb2Se3 during annealing to promote the growth of CuGaSe2 grains, the obtained CuGaSe2 absorption layer thin film has excellent characteristics such as large grain size, flat surface, high absorption coefficient, and a wide bandgap suitable for the top cell. The preparation method of the CuGaSe2 absorption layer thin film comprises the following steps:

[0005] S1: Place the substrate with the Mo back electrode deposited in the magnetron sputtering chamber, and sputter the copper gallium selenide target to obtain a CuGaSe2 thin film with a thickness of 500 nm;

[0006] S2: Place the CuGaSe2 thin film in a thermal evaporation device, and thermally evaporate Sb2Se3 under high vacuum conditions to deposit a 100 nm Sb2Se3 thin film, obtaining a CuGaSe2 / Sb2Se3 thin film;

[0007] S3: Place the CuGaSe2 / Sb2Se3 thin film in the magnetron sputtering chamber, and sputter the copper gallium selenide target again to deposit a 500 nm thick CuGaSe2 thin film, obtaining a CuGaSe2 / Sb2Se3 / CuGaSe2 preform;

[0008] S4: Place the CuGaSe2 / Sb2Se3 / CuGaSe2 preform in a tube furnace. The heating program of the tube furnace is set to a heating rate of 10 °C / min. After heating to the set temperature of 510 - 570 °C, keep it warm for 30 min, and then cool down. After the temperature drops to room temperature, take out the sample. By promoting the growth of CuGaSe2 grains through the decomposition and volatilization of Sb2Se3 during high-temperature annealing, a CuGaSe2 absorption layer thin film with a large grain size is obtained.

[0009] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0010] Firstly, by doping Sb2Se3 into the CuGaSe2 thin film and utilizing the decomposition and volatilization of Sb2Se3 during high-temperature annealing, the average grain size of the CuGaSe2 absorption layer thin film is significantly increased from 0.2 μm to 0.7 μm, and there is no residual Sb2Se3 in the CuGaSe2 absorption layer thin film, reducing the number of grain boundaries, improving the carrier mobility and diffusion length, and enhancing the cell efficiency. In addition, the preparation process is optimized to avoid using toxic H2Se gas, reducing the cost and safety risks, which is conducive to large-scale production. The light absorption coefficient of the absorption layer thin film prepared by annealing at 550 °C is greater than 10 5 cm -1, with a band gap of 1.7 eV, no secondary phase, suitable as the top cell material for tandem solar cells, optimizing the hierarchical absorption of the solar spectrum, and providing important material support for the development of tandem solar cells. Description of the Drawings

[0011] Figure 1 is the flowchart of the preparation method of the wide-bandgap CuGaSe2 solar cell absorption layer thin film of the present invention.

[0012] Figure 2 is the morphology of the CuGaSe2 absorption layer thin film obtained by annealing after doping with Sb2Se3 in Examples 1-4 of the present invention.

[0013] Figure 3 is the Raman shift of the CuGaSe2 absorption layer thin film obtained by annealing after doping with Sb2Se3 in Examples 1-4 of the present invention.

[0014] Figure 4 is the XRD pattern of the CuGaSe2 absorption layer thin film obtained by annealing after doping with Sb2Se3 in Examples 1-4 of the present invention.

[0015] Figure 5 is the full width at half maximum of the main strong peak of the XRD of the CuGaSe2 absorption layer thin film obtained by annealing after doping with Sb2Se3 in Examples 1-4 of the present invention.

[0016] Figure 6 is the morphology of the CuGaSe2 absorption layer thin film obtained by annealing without doping with Sb2Se3 in Comparative Example 1. Detailed Description of the Invention

[0017] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0018] Example 1

[0019] Step S1: Place the substrate with the Mo back electrode deposited in the magnetron sputtering chamber, and sputter the copper gallium selenide target (atomic ratio of Cu:Ga:Se = 0.9:1.0:2.0) at room temperature using a radio frequency (RF) power supply to obtain a "copper-poor and selenium-rich" composition, and obtain a 500-nm-thick CuGaSe2 thin film;

[0020] Step S2: Place the CuGaSe2 thin film in a thermal evaporation device, put the Sb2Se3 powder into the evaporation boat, heat the evaporation boat under high vacuum conditions, and Sb2Se3 volatilizes and Deposit at a rate on CuGaSe2. After depositing a 100-nm-thick Sb2Se3 thin film, a thin film with the structure of CuGaSe2 / Sb2Se3 is obtained;

[0021] Step S3: Place the CuGaSe2 / Sb2Se3 thin film in a magnetron sputtering chamber, and use a radio frequency (RF) power supply to sputter a copper gallium selenide target (atomic ratio of Cu:Ga:Se = 0.9:1.0:2.0) at room temperature, and deposit a 500-nm-thick CuGaSe2 thin film again to obtain a preform film with the structure of CuGaSe2 / Sb2Se3 / CuGaSe2;

[0022] Step S4: Put the CuGaSe2 / Sb2Se3 / CuGaSe2 preform film into a graphite box, then place the graphite box in a tube furnace. After pumping the pressure in the quartz tube to 0.1 Pa, introduce argon to adjust the air pressure to atmospheric pressure, repeat three times, and then introduce flowing argon. Set the heating degree of the tube furnace to a heating rate of 10 °C / min. After heating to the working temperature of 550 °C, keep it warm for 30 min, and then cool down. After the temperature drops to room temperature, take out the sample. Promote the growth of CuGaSe2 grains through the decomposition and volatilization of Sb2Se3 during high-temperature annealing to obtain a CuGaSe2 absorption layer thin film with large grain size.

[0023] Figure 1 is the flow chart of the preparation method of Embodiment 1 of the present invention.

[0024] Figure 2 The 550 °C in the figure corresponds to the morphology of the CuGaSe2 absorption layer thin film obtained by annealing after doping Sb2Se3 in Embodiment 1 of the present invention, and the average grain size reaches 0.7 μm.

[0025] Figure 3 The 550 °C in the curve corresponds to the Raman shift curve of the CuGaSe2 absorption layer thin film obtained by annealing after doping Sb2Se3 in Embodiment 1 of the present invention, which is consistent with the peak position of CuGaSe2.

[0026] Figure 4 The 550 °C in the curve corresponds to the XRD pattern of the CuGaSe2 absorption layer thin film obtained by annealing after doping Sb2Se3 in Embodiment 1 of the present invention, which is consistent with the main diffraction peaks of CuGaSe2 and there is no secondary phase.

[0027] Figure 5 The full width at half maximum of the main strong peak corresponding to 550 °C is the full width at half maximum of the main strong peak of the XRD of the CuGaSe2 absorption layer thin film obtained by annealing after doping Sb2Se3 in Embodiment 1 of the present invention. Its lowest full width at half maximum of 0.086° means that the absorption layer thin film has high crystallinity.

[0028] Embodiment 2

[0029] Step S1 is the same as step S1 in Example 1;

[0030] Step S2 is the same as step S2 in Example 1;

[0031] Step S3 is the same as step S3 in Example 1;

[0032] Step S4: Place the CuGaSe2 / Sb2Se3 / CuGaSe2 prefabricated film into a graphite box, then place the graphite box in a tube furnace. After pumping the pressure in the quartz tube to 0.1 Pa, introduce argon to adjust the air pressure to atmospheric pressure. Repeat this three times, and then introduce flowing argon. Set the heating degree of the tube furnace to a heating rate of 10 °C / min. After heating to the working temperature of 510 °C, hold for 30 min, and then cool down. After the temperature drops to room temperature, take out the sample. Promote the growth of CuGaSe2 grains through the decomposition and volatilization of Sb2Se3 during high-temperature annealing to obtain a CuGaSe2 absorption layer film with large grain size. Except that the working temperature is changed to 510 °C, other conditions in step S4 are the same as those in step S4 in Example 1.

[0033] Example 3

[0034] Step S1 is the same as step S1 in Example 1;

[0035] Step S2 is the same as step S2 in Example 1;

[0036] Step S3 is the same as step S3 in Example 1;

[0037] Step S4: Place the CuGaSe2 / Sb2Se3 / CuGaSe2 prefabricated film into a graphite box, then place the graphite box in a tube furnace. After pumping the pressure in the quartz tube to 0.1 Pa, introduce argon to adjust the air pressure to atmospheric pressure. Repeat this three times, and then introduce flowing argon. Set the heating degree of the tube furnace to a heating rate of 10 °C / min. After heating to the working temperature of 530 °C, hold for 30 min, and then cool down. After the temperature drops to room temperature, take out the sample. Promote the growth of CuGaSe2 grains through the decomposition and volatilization of Sb2Se3 during high-temperature annealing to obtain a CuGaSe2 absorption layer film with large grain size. Except that the working temperature is changed to 530 °C, other conditions in step S4 are the same as those in step S4 in Example 1.

[0038] Example 4

[0039] Step S1 is the same as step S1 in Example 1;

[0040] Step S2 is the same as step S2 in Example 1;

[0041] Step S3 is the same as step S3 in Example 1;

[0042] Step S4: Place the CuGaSe2 / Sb2Se3 / CuGaSe2 prefabricated film in a graphite box, then place the graphite box in a tube furnace. Pump the pressure in the quartz tube to 0.1 Pa and then introduce argon to adjust the air pressure to atmospheric pressure. Repeat this three times and then introduce flowing argon. Set the heating degree of the tube furnace to a heating rate of 10 °C / min. After heating to the working temperature of 570 °C, hold for 30 min, and then cool down. After the temperature drops to room temperature, take out the sample. Promote the growth of CuGaSe2 grains through the decomposition and volatilization of Sb2Se3 during high-temperature annealing to obtain a CuGaSe2 absorption layer film with large grain size. Except that the working temperature is changed to 570 °C, other conditions in step S4 are the same as those in step S4 of Example 1.

[0043] Comparative Example 1

[0044] Step S1: Place the substrate with the deposited Mo back electrode in a magnetron sputtering chamber. Sputter a copper gallium selenide target (atomic ratio of Cu:Ga:Se = 0.9:1.0:2.0) at room temperature using a radio frequency (RF) power supply to obtain a "copper-poor and selenium-rich" composition and obtain a 1000-nm-thick CuGaSe2 prefabricated film.

[0045] Step S2: Place the CuGaSe2 prefabricated film in a graphite box, then place the graphite box in a tube furnace. Pump the pressure in the quartz tube to 0.1 Pa and then introduce argon to adjust the air pressure to atmospheric pressure. Repeat this three times and then introduce flowing argon. Set the heating degree of the tube furnace to a heating rate of 10 °C / min. After heating to 550 °C, hold for 30 min, and then cool down. After the temperature drops to room temperature, take out the sample to obtain a CuGaSe2 absorption layer film.

[0046] Figure 6 It is the morphology of the CuGaSe2 absorption layer film obtained by annealing without doping Sb2Se3 in Comparative Example 1, with an average grain size of 0.2 μm and a relatively small grain size.

Claims

1. A preparation method of a wide-bandgap CuGaSe2 solar cell absorption layer thin film, characterized in that, It includes the following steps: (1) Sputter-deposit a CuGaSe2 thin film on a Mo back electrode by magnetron sputtering; (2) Thermally evaporate and deposit an Sb2Se3 thin film on the CuGaSe2 thin film to obtain a CuGaSe2 / Sb2Se3 thin film; (3) Sputter-deposit a CuGaSe2 thin film again by magnetron sputtering to obtain a CuGaSe2 / Sb2Se3 / CuGaSe2 preform; (4) Anneal the CuGaSe2 / Sb2Se3 / CuGaSe2 preform, and promote the growth of CuGaSe2 grains through the decomposition and volatilization of Sb2Se3 during high-temperature annealing to obtain a CuGaSe2 absorption layer thin film with large grain size.

2. The preparation method according to claim 1, characterized in that, In the step of sputter-depositing the CuGaSe2 thin film by magnetron sputtering in step (1), the atomic ratio of the copper gallium selenide target is Cu:Ga:Se = 0.9:1.0:2.0 to obtain a "copper-poor and selenium-rich" (Cu / Ga < 1, Se / (Cu+Ga) > 1) composition, and the thickness of the deposited CuGaSe2 thin film is 500 nm.

3. The preparation method according to claim 1, wherein In the step of depositing the Sb2Se3 thin film on the CuGaSe2 thin film described in step (2), the deposition rate of the Sb2Se3 thin film is The deposition thickness is 100 nm.

4. The preparation method according to claim 1, wherein, In the step of sputter-depositing the CuGaSe2 thin film by magnetron sputtering in step (3), the atomic ratio of the copper gallium selenide target is Cu:Ga:Se = 0.9:1.0:2.0, and the thickness of the deposited CuGaSe2 thin film is 500 nm.

5. The preparation method according to claim 1, characterized in that, In the annealing step of step (4), the annealing temperature is 510 - 570 °C, the heating rate is 10 °C / min, the holding time is 30 min, the annealing atmosphere is argon, and Sb2Se3 decomposes and volatilizes during high-temperature annealing to promote the growth of CuGaSe2 grains.

6. A wide-bandgap CuGaSe2 solar cell absorber layer thin film, characterized in that, Prepared by using the preparation method according to any one of claims 1 - 5.

7. Application of the CuGaSe2 thin film according to claim 6 in the top cell of a tandem solar cell.

Images