Preparation method of copper-indium-gallium-selenium thin film solar cell

Abstract

The application provides a preparation method of a copper-indium-gallium-selenium thin film solar cell, which comprises the following steps: providing a substrate, preparing a metal back electrode layer on the substrate, preparing a copper-indium-gallium-selenium absorption layer on the metal back electrode layer, placing the copper-indium-gallium-selenium absorption layer in an electrolyte containing alkali metal elements, diffusing the alkali metal elements in the electrolyte to the copper-indium-gallium-selenium absorption layer through an electrochemical ion extraction process, preparing a buffer layer on the copper-indium-gallium-selenium absorption layer, preparing a window layer on the buffer layer, preparing a metal top electrode layer on the window layer, and obtaining the copper-indium-gallium-selenium thin film solar cell. According to the technical scheme of the application, the alkali metal post-treatment of the CIGS absorption layer is carried out through the electrochemical ion extraction process, the alkali metal elements in the electrolyte are diffused to the surface layer and the interior of the CIGS absorption layer, the carrier concentration of the CIGS absorption layer is increased, the open-circuit voltage and the fill factor of the device are improved, and thus the efficiency of the copper-indium-gallium-selenium thin film solar cell is improved.

Description

Technical Field

[0001] This invention belongs to the field of solar cell technology, specifically relating to a method for preparing a copper indium gallium selenide thin-film solar cell. Background Technology

[0002] Copper indium gallium selenide (CIGS) thin-film solar cells are a type of high-efficiency thin-film solar cell, characterized by high stability, low cost, and long lifespan. The basic structure of a CIGS thin-film solar cell includes a substrate, a back electrode, a light-absorbing layer, a buffer layer, a window layer, and a metal electrode layer stacked sequentially. The light-absorbing layer is a compound semiconductor thin film composed of copper, indium, gallium, and selenium.

[0003] Existing research has shown that doping the CIGS absorber layer with a small amount of alkali metal elements (such as Na and K) can effectively improve the conversion efficiency of CIGS thin-film solar cells. Regarding the methods of doping the CIGS absorber layer with alkali metals, the main methods currently include: (1) diffusion from the substrate to achieve alkali metal doping; (2) doping the back electrode with alkali metals or preparing an alkali metal pre-layer on the back electrode, allowing the alkali metal to slowly diffuse into the CIGS absorber layer in subsequent processes. All of the above alkali metal doping methods require high-temperature process conditions to ensure sufficient diffusion of the alkali metals. High-temperature process conditions require precise control of process parameters, increasing the process difficulty; otherwise, the high temperature may adversely affect the structure of the CIGS absorber layer (especially the crystal structure), failing to achieve the goal of improving the efficiency of CIGS thin-film solar cells. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a method for preparing copper indium gallium selenide thin-film solar cells to solve the problem of how to dope alkali metals into the CIGS absorber layer under low temperature and relatively easy process conditions.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] A method for fabricating a copper indium gallium selenide (CIGS) thin-film solar cell includes the following steps:

[0007] S10. Provide a substrate and use a magnetron sputtering process to prepare a metal back electrode layer on the substrate;

[0008] S20. A copper indium gallium selenide (CIGS) absorber layer is formed on the metal back electrode layer using a co-evaporation process.

[0009] S30. The copper indium gallium selenide (CIGS) absorber layer is placed in an electrolyte containing alkali metal elements, and the alkali metal elements in the electrolyte are diffused into the CIGS absorber layer through an electrochemical ion extraction process.

[0010] S40. A buffer layer is formed on the copper indium gallium selenide absorber layer by applying a chemical bath deposition process.

[0011] S50. A window layer is formed on the buffer layer using a magnetron sputtering process.

[0012] S60. A metal top electrode layer is formed on the window layer using a thermal evaporation process to obtain the copper indium gallium selenide thin-film solar cell.

[0013] In the specific scheme, the electrochemical ion extraction process includes: using the copper indium gallium selenide (CIGS) absorber layer as the negative electrode and providing a conductive electrode as the positive electrode, charging the CIGS absorber layer in the electrolyte, so that the alkali metal elements in the electrolyte diffuse to the CIGS absorber layer.

[0014] In the specific scheme, the charging current for the copper indium gallium selenide (CIGS) absorber layer is 80 μA to 120 μA, and the charging time T is T = S × t; where S is the area of ​​the CIGS absorber layer immersed in the electrolyte, and the time constant t = 15 s / cm 2 ~20s / cm 2 .

[0015] In a specific embodiment, the electrolyte includes a solvent and a compound containing an alkali metal element dissolved in the solvent.

[0016] In the specific scheme, the alkali metal element is K or Na, and the compound containing the alkali metal element is KPF6, KF, KCl, NaF, or NaCl.

[0017] In the specific embodiment, the concentration of the compound containing the alkali metal element in the electrolyte is 0.05 mol / L to 0.1 mol / L.

[0018] In the specific scheme, the solvent is a mixed solvent of EC:DMC:EMC = 1:1:1 Vol%.

[0019] In a specific embodiment, the metal back electrode layer includes a first Mo thin film layer and a second Mo thin film layer stacked sequentially on the substrate; the metal top electrode layer includes a first Ni thin film layer, an Al thin film layer and a second Ni thin film layer stacked sequentially on the window layer.

[0020] In the specific scheme, the buffer layer is a CdS buffer layer.

[0021] In the specific scheme, the window layer includes an i-ZnO thin film layer and an AZO thin film layer stacked sequentially on the buffer layer.

[0022] The method for fabricating a copper indium gallium selenide (CIGS) thin-film solar cell provided in this invention involves forming a CIGS absorber layer on a metal back electrode layer, followed by an alkali metal post-treatment of the CIGS absorber layer using an electrochemical ion extraction process. This process allows alkali metal elements from the electrolyte to diffuse into the surface and interior of the CIGS absorber layer, increasing the carrier concentration and improving the open-circuit voltage (Voc) and fill factor (FF) of the device, thereby enhancing the efficiency of the CIGS thin-film solar cell. The electrochemical ion extraction process can be performed at low temperatures (e.g., room temperature), which is less complex than existing high-temperature diffusion processes and avoids potential adverse effects on the structure of the CIGS absorber layer due to high temperatures. Attached Figure Description

[0023] Figure 1 This is a process flow diagram of the fabrication process of copper indium gallium selenide thin-film solar cells in the embodiments of the present invention;

[0024] Figure 2 This is a JV curve obtained from electrical testing of a battery sample in an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Examples of these preferred embodiments are illustrated in the drawings. The embodiments of the present invention shown in and described with reference to the drawings are merely exemplary, and the present invention is not limited to these embodiments.

[0026] It should also be noted that, in order to avoid obscuring the invention with unnecessary details, only the structures and / or processing steps closely related to the solution according to the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0027] This invention provides a method for preparing a copper indium gallium selenide (CIGS) thin-film solar cell. (See attached document.) Figure 1 The preparation method includes the following steps:

[0028] Step S10: Provide a substrate and use magnetron sputtering to prepare a metal back electrode layer on the substrate.

[0029] In the specific scheme, the substrate is first cleaned, then placed inside the chamber of the sputtering equipment and the vacuum level is evacuated to a specified pressure before sputtering. In a preferred embodiment, the substrate is selected as soda-lime glass, and the material of the metal back electrode layer is molybdenum (Mo). The metal back electrode layer includes a first Mo thin film layer and a second Mo thin film layer sequentially stacked on the substrate.

[0030] The first Mo thin film layer is prepared using a high-voltage, low-power process, while the second Mo thin film layer is prepared using a high-power, low-voltage process. This results in better adhesion and meets the conductivity requirements.

[0031] Step S20: A copper indium gallium selenide (CIGS) absorber layer is formed on the metal back electrode layer using a co-evaporation process.

[0032] In the specific scheme, the substrate after sputtering to form a metal back electrode layer is placed in the chamber of the MBE equipment, and a copper indium gallium selenide absorber layer is deposited on the substrate using a three-step co-evaporation process.

[0033] S30. Place the copper indium gallium selenide (CIGS) absorber layer in an electrolyte containing alkali metal elements, and use an electrochemical ion extraction process to diffuse the alkali metal elements in the electrolyte into the CIGS absorber layer.

[0034] In the specific scheme, the electrochemical ion extraction process includes: using a copper indium gallium selenide (CIGS) absorber layer as the negative electrode and a conductive electrode as the positive electrode, charging the CIGS absorber layer in an electrolyte, thereby allowing alkali metal elements in the electrolyte to diffuse into the CIGS absorber layer. It should be noted that using the CIGS absorber layer as the negative electrode specifically refers to using the substrate after the CIGS absorber layer is formed in step S20 as the negative electrode, and the voltage is applied between the conductive electrode (positive electrode) and the metal back electrode layer on the substrate (negative electrode).

[0035] In the preferred embodiment, graphite is selected as the conductive electrode for the positive electrode.

[0036] The charging current for charging the copper indium gallium selenide (CIGS) absorber layer is preferably 80 μA to 120 μA, for example, 80 μA, 90 μA, 100 μA, 110 μA, or 120 μA, with 100 μA being the most preferred. The charging time T is given by T = S × t, where S is the area of ​​the CIGS absorber layer immersed in the electrolyte, and the time constant t = 15 s / cm. 2 ~20s / cm 2 In a preferred embodiment, t = 17.6 s / cm 2 .

[0037] The electrolyte comprises a solvent and a compound containing an alkali metal element dissolved in the solvent. The alkali metal element is preferably K or Na, and the compound containing the alkali metal element is, for example, KPF6, KF, KCl, NaF, or NaCl; in a preferred embodiment, the compound containing the alkali metal element is KPF6.

[0038] The concentration of the compound containing the alkali metal element in the electrolyte is selected to be 0.05 mol / L to 0.1 mol / L, preferably 0.1 mol / L. The solvent is preferably a mixed solvent of EC:DMC:EMC = 1:1:1 Vol%, that is, a mixed solvent in which the volume ratio of EC (ethylene carbonate), DMC (dimethyl carbonate) and EMC (ethyl methyl carbonate) is 1:1:1.

[0039] Furthermore, after the electrochemical ion extraction process is completed, the substrate is removed and the surface of the copper indium gallium selenide absorber layer is cleaned with dimethyl carbonate to remove residual electrolyte.

[0040] Step S40: A buffer layer is formed on the copper indium gallium selenide absorber layer using a chemical bath deposition process.

[0041] In a preferred embodiment, the buffer layer is made of cadmium sulfide (CdS). The substrate sample processed in step S30 is immersed in ultrapure water and then placed in a reaction vessel containing ammonia, cadmium sulfate, and thiourea solution. The reaction is carried out under heating to form a CdS buffer layer on the copper indium gallium selenide absorber layer.

[0042] Furthermore, after the CdS buffer layer is formed, the resulting sample is placed in an annealing furnace for annealing treatment.

[0043] Step S50: A window layer is formed on the buffer layer using a magnetron sputtering process.

[0044] In a preferred embodiment, the window layer comprises an intrinsic zinc oxide (i-ZnO) layer and an aluminum-doped zinc oxide (AZO) layer sequentially disposed. The intrinsic zinc oxide (i-ZnO) layer is sputtered by first performing low-power sputtering followed by high-power sputtering. The low-power sputtering first forms a loose layer, which can better bond with the CdS buffer layer and is less prone to detachment. The aluminum-doped zinc oxide (AZO) layer is sputtered using higher power.

[0045] Step S60: Apply thermal evaporation process to prepare a metal top electrode layer on the window layer to obtain a copper indium gallium selenide thin film solar cell.

[0046] In a preferred embodiment, the metal top electrode layer comprises a first Ni thin film layer, an Al thin film layer, and a second Ni thin film layer sequentially stacked on the window layer.

[0047] The method for fabricating copper indium gallium selenide (CIGS) thin-film solar cells provided in the above embodiments involves forming a CIGS absorber layer on a metal back electrode layer, followed by alkali metal post-treatment doping of the CIGS absorber layer through an electrochemical ion extraction process. This allows alkali metal elements in the electrolyte to diffuse to the surface and interior of the CIGS absorber layer, increasing the carrier concentration of the CIGS absorber layer and improving the open-circuit voltage (Voc) and fill factor (FF) of the device, thereby improving the efficiency of the copper indium gallium selenide thin-film solar cell.

[0048] Alkali metal post-processing can passivate crystallization and lattice defects in the absorption layer without altering the CIGS structure, and can reduce the device's quality factor and reverse saturation current, thereby improving device performance. Alkali metal post-processing also widens the band gap of the CIGS surface, reduces the maximum valence band value, and the lower hole concentration further suppresses carrier recombination at the interface, which is another important reason for improving open-circuit voltage and conversion efficiency.

[0049] Among them, the electrochemical ion extraction process can be carried out at low temperature (e.g., room temperature), which is less difficult than the existing high temperature diffusion process and can avoid the adverse effects on the structure of the CIGS absorber layer caused by high temperature.

[0050] Example 1

[0051] This embodiment provides a specific example of a method for fabricating a copper indium gallium selenide (CIGS) thin-film solar cell, which is carried out according to the following steps:

[0052] (1) Fabrication of the metal back electrode layer

[0053] Soda-lime glass with dimensions of 10cm×10cm×2mm was selected as the substrate. The substrate was first rinsed with deionized water, using a semiconductor cleaning agent for auxiliary cleaning, with a rinsing time exceeding 10 minutes. After cleaning, the glass substrate was placed in an ultrasonic cleaner and ultrasonically cleaned for 40 minutes, followed by rinsing with deionized water for 10 minutes. The substrate was then dried and placed inside the sputtering chamber, where a vacuum was evacuated to the specified pressure before sputtering.

[0054] Sputtering is performed using DC magnetron sputtering in a sputtering apparatus to sequentially deposit a first Mo thin film layer and a second Mo thin film layer on a soda-lime glass substrate, forming a metal back electrode layer. The thickness of the first Mo thin film layer is approximately 300 nm, and the thickness of the second Mo thin film layer is approximately 1000 nm.

[0055] (2) Preparation of copper indium gallium selenide absorber layer

[0056] The substrate, after sputtering to form a metal back electrode layer, is placed in the chamber of the MBE device, and a copper indium gallium selenide (CIGS) absorber layer is deposited on the substrate using a three-step co-evaporation process. The specific process for this step follows existing techniques, resulting in a 1 μm thick CIGS absorber layer.

[0057] (3) Alkali metal post-treatment of copper indium gallium selenide absorber layer by electrochemical method

[0058] The glass substrate with the copper indium gallium selenide (CIGS) absorber layer formed was cut into two pieces, each measuring 10cm × 5cm × 2mm. A small piece of the CIGS absorber layer was scraped off from a corner of one of the samples to expose the Mo electrode layer. A wire was connected to the exposed Mo electrode layer as the negative electrode, and a graphite electrode was used as the positive electrode. The positive and negative electrodes were placed in an electrolytic cell using a 0.1mol / L KPF6 in EC:DMC:EMC = 1:1:1 Vol%. The area of ​​the negative electrode material submerged in the electrolyte was 5cm × 4.5cm. Charging was performed using a current of 100μA for 22.5cm. 2 ×17.6s / cm 2 =396s.

[0059] After processing, the negative electrode material is removed and its surface is cleaned with 99.5% dimethyl carbonate to remove residual electrolyte.

[0060] (4) Preparation of cadmium sulfide buffer layer

[0061] Weigh 0.184 g of chromium sulfate and place it in 60 mL of deionized water. Stir for 15 min and label the solution A. Weigh 5.694 g of thiourea and place it in 150 mL of deionized water. Stir for 15 min and label the solution B. Weigh 425 mL of deionized water and place it in a reaction vessel. Weigh 45 mL of ammonia water and place it in a beaker. Mix the ammonia water with solution A and pour the mixture into the reaction vessel. Rinse the sample obtained in step (3) with solution B and collect the rinse solution B in the reaction vessel. Place the sample surface down in the reaction vessel and place it in a water bath (the water bath temperature is set at 67°C, and a magnetic stirrer is used for stirring. The heating power is 500 W). After reacting for 9 min, remove the sample and rinse it quickly with a large amount of deionized water. Then, anneal it in an oven at 160°C for 2 min. In this embodiment, the thickness of the cadmium sulfide buffer layer is set to 50 nm.

[0062] (5) Preparation of window layer

[0063] A window layer was fabricated on the buffer layer using radio frequency magnetron sputtering. The window layer consisted of an intrinsic zinc oxide (i-ZnO) layer and an aluminum-doped zinc oxide (AZO) layer sequentially disposed. Specifically, a 50 nm thick i-ZnO layer was fabricated using an intrinsic ZnO target (99.99% purity), and a 200 nm thick AZO layer was fabricated using a ZnO:Al2O3 target (doped with 2 wt% Al2O3).

[0064] (6) Fabrication of the metal top electrode layer

[0065] A prepared photomask is placed over the sample surface. By adjusting the beam position and electron beam current, the metal placed in the crucible is evaporated, and Ni, Al, and Ni metal sources are deposited sequentially. A first Ni thin film layer, an Al thin film layer, and a second Ni thin film layer are then sequentially formed on the window layer. The thickness of the first Ni thin film layer is [missing information]. The thickness of the Al thin film is The thickness of the second Ni thin film layer is

[0066] Based on the above preparation process steps (1) to (6), a copper indium gallium selenide (CIGS) thin-film solar cell was prepared in this embodiment, and the cell sample is denoted as Alkali-PDT. In comparison, a comparative CIGS thin-film solar cell was also prepared in this embodiment according to the above preparation process steps (1), (2) and (4) to (6), and the cell sample is denoted as No-PDT. That is, the No-PDT cell sample omits the alkali metal post-treatment step (3) compared to the Alkali-PDT cell sample.

[0067] In this embodiment, electrical tests were performed on the Alkali-PDT and No-PDT battery samples respectively, and the results were as follows: Figure 2 The JV curve shown is as follows. Figure 2 As shown, the Alkali-PDT battery sample obtained through alkali metal post-treatment in this embodiment exhibits a significant improvement in overall device performance, particularly in the open-circuit voltage (Voc). This improvement in open-circuit voltage is likely due to the increased carrier concentration. Specifically, the Alkali-PDT battery sample obtained through alkali metal post-treatment in this embodiment has an open-circuit voltage (Voc) of 679 mV and a short-circuit current density (Isc) of 34.2 mA / cm². 2 The fill factor (FF) is 76.21% and the efficiency (Eff) is 17.73%.

[0068] The above description is only a specific embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for preparing a copper indium gallium selenide thin-film solar cell, characterized in that, Including the following steps: S10. Provide a substrate and use a magnetron sputtering process to prepare a metal back electrode layer on the substrate; S20. A copper indium gallium selenide (CIGS) absorber layer is formed on the metal back electrode layer using a co-evaporation process. S30. The copper indium gallium selenide (CIGS) absorber layer is placed in an electrolyte containing alkali metal elements, and the alkali metal elements in the electrolyte are diffused into the CIGS absorber layer by an electrochemical ion extraction process. S40. A buffer layer is formed on the copper indium gallium selenide absorber layer by applying a chemical bath deposition process. S50. A window layer is formed on the buffer layer using a magnetron sputtering process. S60. A metal top electrode layer is formed on the window layer by applying a thermal evaporation process to obtain the copper indium gallium selenide thin-film solar cell. The electrochemical ion extraction process includes: using the copper indium gallium selenide (CIGS) absorber layer as the negative electrode and a conductive electrode as the positive electrode, charging the CIGS absorber layer in the electrolyte, so that the alkali metal elements in the electrolyte diffuse into the CIGS absorber layer.

2. The method for preparing a copper indium gallium selenide thin-film solar cell according to claim 1, characterized in that, The charging current for the copper indium gallium selenide (CIGS) absorber layer is 80 μA to 120 μA, and the charging time T is T = S × t; where S is the area of ​​the CIGS absorber layer immersed in the electrolyte, and the time constant t = 15 s / cm. 2 ~20s / cm 2 .

3. The method for preparing a copper indium gallium selenide thin-film solar cell according to claim 1 or 2, characterized in that, The electrolyte comprises a solvent and a compound containing an alkali metal element dissolved in the solvent.

4. The method for preparing a copper indium gallium selenide thin-film solar cell according to claim 3, characterized in that, The alkali metal element is K or Na, and the compound containing the alkali metal element is KPF6, KF, KCl, NaF, or NaCl.

5. The method for preparing a copper indium gallium selenide thin-film solar cell according to claim 4, characterized in that, The concentration of the compound containing the alkali metal element in the electrolyte is 0.05 mol / L to 0.1 mol / L.

6. The method for preparing a copper indium gallium selenide thin-film solar cell according to claim 4, characterized in that, The solvent is a mixed solvent of EC:DMC:EMC = 1:1:1 Vol%.

7. The method for preparing a copper indium gallium selenide thin-film solar cell according to claim 1, characterized in that, The metal back electrode layer includes a first Mo thin film layer and a second Mo thin film layer stacked sequentially on the substrate; the metal top electrode layer includes a first Ni thin film layer, an Al thin film layer and a second Ni thin film layer stacked sequentially on the window layer.

8. The method for preparing a copper indium gallium selenide thin-film solar cell according to claim 1, characterized in that, The buffer layer is a CdS buffer layer.

9. The method for preparing a copper indium gallium selenide thin-film solar cell according to claim 1, characterized in that, The window layer includes an i-ZnO thin film layer and an AZO thin film layer stacked sequentially on the buffer layer.

Images