Wide bandgap copper gallium selenide light absorption layer and preparation method thereof, and solar cell

Abstract

The present invention provides a wide bandgap copper gallium selenide light absorption layer and a preparation method thereof, wherein the wide bandgap copper gallium selenide light absorption layer comprises a copper gallium selenide thin film layer and an indium gallium thin film layer covered on the copper gallium selenide thin film layer, wherein an InGaO2 thin film layer is formed on the interface between the copper gallium selenide thin film layer and the indium gallium thin film layer through an annealing process. Cu Antisite defects. The preparation method includes: heating a substrate to a first temperature, co-evaporating gallium and selenium on the substrate; increasing the temperature of the substrate to a second temperature, co-evaporating copper and selenium on the substrate; maintaining the temperature of the substrate at the second temperature, co-evaporating indium, gallium, and selenium on the substrate; maintaining the temperature of the substrate at the second temperature, annealing the substrate in a selenium atmosphere to prepare a wide-bandgap copper-gallium-selenide light-absorbing layer. The present invention also provides a solar cell including the wide-bandgap copper-gallium-selenide light-absorbing layer. The wide-bandgap copper-gallium-selenide light-absorbing layer provided by the present invention can obtain a higher-efficiency solar cell while having a wide bandgap, and can be better suited for stacked solar cells.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar cells, and in particular relates to a wide bandgap copper gallium selenide light absorption layer and a preparation method thereof, and also relates to a solar cell comprising the wide bandgap copper gallium selenide light absorption layer. Background Art

[0002] In recent years, with the rapid development of photovoltaic technology, the efficiency of various single-junction solar cells has gradually approached the theoretical efficiency limit of this system. Further improving the efficiency of single-junction cells through technological advancement will become extremely difficult. Tandem solar cells can connect absorber layers matching different spectral bands in series to increase the cell's absorption bandwidth of the sunlight spectrum. Furthermore, the absorber layers with different band gaps in tandem solar cells absorb photons of different energies, reducing thermal relaxation losses caused by excess energy from high-energy photons exceeding the band gap, maximizing the conversion of light energy into electrical energy and significantly improving photoelectric conversion efficiency.

[0003] The mainstream double-junction tandem cell requires a narrow-bandgap bottom cell and a wide-bandgap top cell. However, materials for wide-bandgap top cells are extremely scarce. To match the narrow-bandgap bottom cell absorber layer, such as p-type crystalline silicon with a 1.1eV bandgap or p-type copper indium selenide with a 1.0eV bandgap, the top cell must be a p-type material with a bandgap between 1.6eV and 1.7eV. For a long time, expensive III-V materials were the only viable option. Finding high-efficiency, low-cost p-type wide-bandgap top cell materials is key to the future development of double-junction tandem cells.

[0004] The band gap of CIGS (copper indium gallium selenide) can be flexibly adjusted in the range of 1.0-2.5eV. The most efficient CIGS solar cell currently has a band gap of 1.15eV, corresponding to a Ga / Ga+In ratio of 0.3. In order to obtain a higher band gap, the current mainstream research direction internationally is to achieve it through cation and anion replacement. In terms of cation replacement, the main approach is to increase the Ga component content to increase the absorption band gap of the CIGS material. If all the In in CuInGaSe2 is replaced by Ga to form copper gallium selenide (CGSe), the band gap of CGSe can reach 1.7eV. However, experiments by multiple research units have found that the efficiency of solar cells decreases with increasing Ga content.

[0005] There is an ordered defect reconstruction layer (ODC layer) on the surface and crystal interface of traditional CIGS materials. This structure has a fixed lattice structure and energy band structure, which can greatly reduce the recombination probability of carriers at the crystal interface. There are a lot of In in this ordered defect reconstruction layer. CuAntisite defects, however, in order to obtain copper gallium selenide with a high bandgap width, all In in CuInGaSe2 is replaced by Ga. The ordered defect reconstruction layer mentioned above is difficult to form at the interface, and the electron-hole recombination at the surface and crystal interface cannot be suppressed, thereby reducing the battery efficiency. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the present invention provides a wide bandgap copper gallium selenide light absorption layer and a preparation method thereof, and a solar cell, to solve the problem in the prior art of reduced cell efficiency in order to obtain copper gallium selenide with a high bandgap width.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0008] A wide bandgap copper gallium selenide light absorption layer comprises a copper gallium selenide thin film layer and an indium gallium thin film layer covered on the copper gallium selenide thin film layer, wherein the interface between the copper gallium selenide thin film layer and the indium gallium thin film layer is formed by an annealing process. Cu Antiposition defect.

[0009] Preferably, the atomic ratio of gallium to the sum of indium and gallium in the indium gallium thin film layer is (0.3-0.7):1.

[0010] Preferably, the atomic ratio of gallium to the sum of indium and gallium in the indium gallium thin film layer is (0.5-0.7):1.

[0011] Preferably, the wide bandgap copper gallium selenide light absorption layer has a thickness of 1.0 μm to 3.0 μm.

[0012] The present invention also provides a method for preparing the wide bandgap copper gallium selenide light absorption layer as described above, comprising the following steps:

[0013] S10, heating the substrate to a first temperature, and co-evaporating gallium and selenium on the substrate;

[0014] S20, raising the temperature of the substrate to a second temperature, and co-evaporating copper and selenium on the substrate;

[0015] S30, maintaining the temperature of the substrate at a second temperature, and co-evaporating indium, gallium, and selenium on the substrate;

[0016] S40, maintaining the temperature of the substrate at a second temperature, performing an annealing treatment on the substrate in a selenium atmosphere, and preparing the wide bandgap copper gallium selenide light absorption layer on the substrate;

[0017] Wherein, in step S30, when indium, gallium and selenium are co-evaporated, the atomic ratio of gallium to the sum of indium and gallium is controlled to be (0.3-0.7):1.

[0018] Preferably, in step S30, when indium, gallium and selenium are co-evaporated, the atomic ratio of gallium to the sum of indium and gallium is controlled to be (0.5-0.7):1.

[0019] Preferably, the annealing time of the annealing treatment is 15 minutes to 20 minutes.

[0020] Preferably, the first temperature is 340°C to 380°C, and the second temperature is 500°C to 600°C.

[0021] Preferably, the substrate comprises a molybdenum metal layer, and when co-evaporating gallium and selenium in step S10, selenium vapor is first introduced to form a molybdenum selenide layer on the surface of the molybdenum metal layer, and then gallium vapor is introduced to co-evaporate gallium and selenium on the molybdenum selenide layer.

[0022] An embodiment of the present invention further provides a solar cell, which includes the wide bandgap copper gallium selenide light absorption layer as described above.

[0023] The wide bandgap copper gallium selenide light absorption layer and its preparation method provided by the embodiment of the present invention are based on the traditional three-step co-evaporation process for preparing copper indium gallium selenide. In the first co-evaporation step, Ga is completely replaced with In, thereby obtaining a copper gallium selenide (CGSe) thin film after the second co-evaporation of Cu, thereby increasing the bandgap width of the light absorption layer; In is introduced again in the third co-evaporation step, and an In-rich Indium Gallium thin film layer is covered on the copper gallium selenide thin film layer, and then an annealing process is performed to form an In-rich Indium Gallium thin film layer at the interface between the copper gallium selenide thin film layer and the Indium Gallium thin film layer. Cu Antisite defects form a reconstructed phase structure at the crystal interface that is beneficial to charge separation and inhibits interface recombination. The copper gallium selenide light absorption layer obtained in this way can obtain a higher efficiency solar cell on the basis of having a wide bandgap, and can be better suitable for stacked solar cells. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the structure of a thin-film solar cell prepared in an embodiment of the present invention;

[0025] Figure 2 is a flow chart of a method for preparing a wide bandgap copper gallium selenide light absorption layer in an embodiment of the present invention;

[0026] Figure 3 is a SEM cross-sectional view of a bandgap copper gallium selenide light absorption layer prepared in an embodiment of the present invention;

[0027] Figure 4 4 is a volt-ampere curve of the thin-film solar cell prepared in an embodiment of the present invention. DETAILED DESCRIPTION

[0028] To make the objectives, technical solutions, and advantages of the present invention more apparent, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. Examples of these preferred embodiments are illustrated in the accompanying drawings. The embodiments of the present invention shown in and described with reference to the accompanying drawings are merely exemplary, and the present invention is not limited to these embodiments.

[0029] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, the accompanying drawings only show structures and / or processing steps closely related to the solutions according to the present invention, while other details that are not closely related to the present invention are omitted.

[0030] The embodiment of the present invention first provides a wide bandgap copper gallium selenide light absorption layer, comprising a copper gallium selenide thin film layer and an indium gallium thin film layer covering the copper gallium selenide thin film layer, wherein the interface between the copper gallium selenide thin film layer and the indium gallium thin film layer is formed by an annealing process. Cu Antisite defects form a reconstructed phase structure at the crystal interface that is beneficial to charge separation and inhibits interface recombination.

[0031] In a preferred embodiment, the atomic ratio of gallium to the sum of indium and gallium (Ga / Ga+In) in the indium gallium thin film layer is (0.3-0.7):1, and a more preferred ratio is (0.5-0.7):1.

[0032] In a preferred solution, the thickness of the wide bandgap copper gallium selenide light absorption layer is 1.0 μm to 3.0 μm.

[0033] An embodiment of the present invention further provides a method for preparing the wide bandgap copper gallium selenide light absorption layer as described above, the method comprising the following steps:

[0034] S10, heating the substrate to a first temperature, and co-evaporating gallium and selenium on the substrate.

[0035] S20, raising the temperature of the substrate to a second temperature, and co-evaporating copper and selenium on the substrate.

[0036] S30, maintaining the temperature of the substrate at a second temperature, and co-evaporating indium, gallium, and selenium on the substrate.

[0037] S40, maintaining the temperature of the substrate at a second temperature, performing annealing treatment on the substrate in a selenium atmosphere, and preparing the wide bandgap copper gallium selenide light absorption layer on the substrate.

[0038] Specifically, in step S30, when indium, gallium and selenium are co-evaporated, the atomic ratio of gallium to the sum of indium and gallium (Ga / Ga+In) is controlled to be (0.3-0.7):1, and a more preferred ratio is (0.5-0.7):1.

[0039] In a preferred embodiment, the annealing time of the annealing treatment is 15 minutes to 20 minutes.

[0040] In a specific solution, the first temperature is 340°C to 380°C, and the second temperature is 500°C to 600°C.

[0041] In a preferred embodiment, the substrate includes a molybdenum metal layer. During the co-evaporation of gallium and selenium in step S10, selenium vapor is first introduced to form a molybdenum selenide layer on the surface of the molybdenum metal layer. Gallium vapor is then introduced to co-evaporate gallium and selenium on the molybdenum selenide layer. Uniformly selenizing the molybdenum metal layer first allows the subsequently prepared copper gallium selenide light absorption layer to better bond to the molybdenum metal layer.

[0042] An embodiment of the present invention further provides a solar cell, wherein the solar cell utilizes the wide-bandgap copper gallium selenide light absorption layer described above as a light absorption layer. Furthermore, a preferred embodiment of the present invention further provides a tandem solar cell, wherein the top cell of the tandem solar cell utilizes a solar cell including the wide-bandgap copper gallium selenide light absorption layer provided by an embodiment of the present invention.

[0043] The wide bandgap copper gallium selenide light absorption layer and its preparation method provided in the above embodiment are based on the traditional three-step co-evaporation process for preparing copper indium gallium selenide. In the first co-evaporation step, Ga is used to completely replace In, thereby obtaining a copper gallium selenide (CGSe) thin film after the second co-evaporation of Cu, thereby increasing the bandgap width of the light absorption layer; In is introduced again in the third co-evaporation step, and an In-rich Indium Gallium thin film layer is covered on the copper gallium selenide thin film layer, and then an annealing process is performed to form an In-rich Indium Gallium thin film layer at the interface between the copper gallium selenide thin film layer and the Indium Gallium thin film layer. Cu Antisite defects form a reconstructed phase structure at the crystal interface that is beneficial to charge separation and inhibits interface recombination. The copper gallium selenide light absorption layer obtained in this way can obtain a higher efficiency solar cell on the basis of having a wide bandgap, and can be better suitable for stacked solar cells.

[0044] Example 1

[0045] This embodiment provides a thin film solar cell, wherein the light absorption layer in the thin film solar cell adopts the wide bandgap copper gallium selenide light absorption layer provided by the embodiment of the present invention. The structure of the thin film solar cell is as follows: Figure 1 As shown, combined Figure 1 , the preparation process of the thin film solar cell comprises the following steps:

[0046] Step S1: providing a supporting substrate 1 and forming a bottom electrode layer 2 on the supporting substrate 1.

[0047] Specifically, a cleaned soda-lime glass substrate is used as the supporting substrate 1 and placed in a magnetron sputtering chamber, and a Mo bottom electrode layer 2 with a thickness of 500 nm is sputtered and deposited using a Mo target.

[0048] Step S2 , preparing a copper gallium selenide light absorption layer 3 on the bottom electrode layer 2 .

[0049] Specifically, the copper gallium selenide light absorbing layer 3 is a wide bandgap copper gallium selenide light absorbing layer, combined with Figure 2 As shown, in this embodiment, the wide bandgap copper gallium selenide thin film absorption layer is prepared by a three-step co-evaporation method, including the following steps:

[0050] S10, heating the substrate to a first temperature, and co-evaporating gallium and selenium on the substrate.

[0051] That is, the first step of co-evaporation deposition specifically includes: heating the substrate obtained in step S1 to 360°C, raising the temperature of the Ga source to the evaporation temperature of Ga at 965°C, so that Ga changes from solid to gaseous state and becomes Ga vapor, and then keeping warm for 20 minutes. Open the main valve of the Se source 1 minute in advance, and let Se vapor in. The Se source furnace is opened in advance to allow the Se in the Se furnace to be fully released in the furnace. The main baffle is manually opened 30 seconds in advance to allow Se to fall on the Mo metal layer to form a layer of molybdenum selenide first, so that the Mo layer is uniformly selenized. Then open the beam source furnace baffle of the Ga source, let Ga vapor in, and co-evaporate gallium and selenium on the Mo metal layer; wherein, if Figure 2 As shown, the time for co-evaporation of gallium and selenium in this embodiment is 36 minutes.

[0052] S20, raising the temperature of the substrate to a second temperature, and co-evaporating copper and selenium on the substrate.

[0053] That is, the second step of co-evaporation deposition, specifically including: closing the baffle of the gallium beam source furnace after the first step of deposition. Raise the temperature of the Cu source to 1200°C, the evaporation temperature of Cu, so that Cu changes from solid to gas, and becomes Cu vapor, and Cu vapor is introduced into the furnace. Raise the temperature of the substrate from 360°C to 600°C, and then maintain the temperature of the substrate at 600°C to deposit Cu to form a copper gallium selenide film. During the deposition of Cu, when a 0.1°C cooling point is observed, the deposition of Cu is terminated. That is, when the stoichiometric ratio of Cu to Ga reaches 1:1, continue to evaporate copper, selenium and copper will generate copper selenide, and the liquid phase copper selenide will absorb heat and undergo a short cooling phenomenon, which lasts for about 6s to 10s. When a short cooling phenomenon is observed, it means that the growth of copper is completed. At this time, lower the temperature of the copper source, turn off the copper source, and terminate the deposition of Cu. Among them, if Figure 2 As shown, the time for co-evaporation of copper and selenium in this embodiment is 18 minutes.

[0054] S30, maintaining the temperature of the substrate at a second temperature, and co-evaporating indium, gallium, and selenium on the substrate.

[0055] The third step of co-evaporation deposition: After the second step of deposition is completed, close the copper beam source furnace baffle. Raise the temperature of the In source and Ga source to the evaporation temperature of In at 820°C and the evaporation temperature of Ga at 900°C, respectively, so that In and Ga change from solid to gaseous, becoming In vapor and Ga vapor respectively. Maintain the temperature of the substrate at 600°C, introduce Ga vapor and In vapor into the furnace, and co-evaporate the InGaSe thin film layer on the CuGaSe thin film layer. In this embodiment, the Ga / Ga+In ratio is 0.5:1 during the third step of co-evaporation deposition, as shown in FIG. Figure 2 As shown, the co-steaming time is 14 min.

[0056] S40, maintaining the temperature of the substrate at a second temperature, performing annealing treatment on the substrate in a selenium atmosphere, and preparing the wide bandgap copper gallium selenide light absorption layer on the substrate.

[0057] Specifically, the substrate temperature is maintained at 600°C, and the substrate is annealed in a Se atmosphere. After that, each source is turned off and the temperature is lowered. When the substrate temperature drops to 300°C, the Se source main baffle is closed. When the substrate temperature drops below 200°C, the prepared wide bandgap copper gallium selenide light absorption layer can be taken out. Figure 2 As shown, the annealing time is 15 min.

[0058] The entire process of preparing the wide bandgap copper gallium selenide light absorption layer is carried out in an atmosphere containing sufficient Se. The evaporation temperature of Se during the entire process is 650-660° C., at which solid Se can be converted into gaseous Se vapor.

[0059] The wide bandgap copper gallium selenide light absorption layer prepared above was scanned by electron microscope, and the following results were obtained: Figure 3 The SEM image of the cross section of the bandgap copper gallium selenide light absorbing layer is shown. It can be seen from the figure that the microstructure of the copper gallium selenide light absorbing layer obtained in this embodiment is a large-area uniform polycrystalline thin film with a grain size of 200nm to 1μm.

[0060] Step S3, refer to Figure 1 A cadmium sulfide buffer layer 4, a window layer 5 and a top electrode layer 6 are formed on the copper gallium selenide light absorption layer 3 to obtain the thin film solar cell.

[0061] The specific preparation processes for the cadmium sulfide buffer layer 4, the window layer 5, and the top electrode layer 6 can be carried out in accordance with existing techniques. For example, the cadmium sulfide buffer layer 4 can be formed using a chemical bath deposition method; the window layer 5 can be an intrinsic zinc oxide (IZO) layer and an aluminum-doped zinc oxide (AZO) layer formed using a magnetron sputtering process; and the top electrode layer 6 can be a metal top electrode layer formed using a magnetron sputtering process.

[0062] In this embodiment, the thin film solar cell prepared in the above embodiment is subjected to electrical testing. Figure 4 This is the volt-ampere characteristic curve obtained from the test. Figure 4 The volt-ampere characteristic curve shown in FIG. 1 shows that the open circuit voltage (Voc) of the thin-film solar cell prepared in the above embodiment is 837 mV and the short circuit current (Isc) is 19.0 mA / cm 2 , the fill factor (FF) is 66.1%, the efficiency (Eff) is 10.5%, and it has good electrical performance.

[0063] In summary, the wide bandgap copper gallium selenide light absorption layer and its preparation method provided by the embodiment of the present invention are based on the traditional three-step co-evaporation process for preparing copper indium gallium selenide. In the first co-evaporation step, Ga is used to completely replace In, thereby obtaining a copper gallium selenide (CGSe) thin film after the second co-evaporation of Cu, thereby increasing the bandgap width of the light absorption layer; In is introduced again in the third co-evaporation step, and an In-rich Indium Gallium thin film layer is covered on the copper gallium selenide thin film layer, and then an annealing process is performed to form an In-rich Indium Gallium thin film layer at the interface between the copper gallium selenide thin film layer and the Indium Gallium thin film layer. Cu Antisite defects form a reconstructed phase structure at the crystal interface that is beneficial to charge separation and inhibits interface recombination. While ensuring the bandgap width of the copper gallium selenide light absorption layer, the solar cells prepared using this wide-bandgap copper gallium selenide light absorption layer have excellent efficiency, achieving an improvement in the efficiency of wide-bandgap CGSe solar cells, and can be better used as the top cell of a stacked solar cell.

[0064] The above is only a specific implementation method of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application. These improvements and modifications should also be regarded as the scope of protection of the present application.

Claims

1. A wide bandgap copper gallium selenide light absorption layer, characterized in that: The copper gallium selenide film layer and the indium gallium film layer are covered on the copper gallium selenide film layer, and the interface between the copper gallium selenide film layer and the indium gallium film layer is formed by an annealing process. Cu Antisite defects form a reconstructed phase structure at the crystal interface that is beneficial to charge separation and inhibits interface recombination.

2. The wide bandgap copper gallium selenide light absorbing layer according to claim 1, characterized in that: The atomic ratio of gallium to the sum of indium and gallium in the indium gallium thin film layer is (0.3-0.7):

1.

3. The wide bandgap copper gallium selenide light absorbing layer according to claim 2, characterized in that: The atomic ratio of gallium to the sum of indium and gallium in the indium gallium thin film layer is (0.5-0.7):

1.

4. The wide bandgap copper gallium selenide light absorbing layer according to any one of claims 1 to 3, characterized in that: The thickness of the wide bandgap copper gallium selenide light absorption layer is 1.0 μm to 3.0 μm.

5. A method for preparing a wide bandgap copper gallium selenide light absorbing layer according to claim 1, characterized in that: The following steps are involved: S10, heating the substrate to a first temperature, and co-evaporating gallium and selenium on the substrate; S20, raising the temperature of the substrate to a second temperature, and co-evaporating copper and selenium on the substrate; S30, maintaining the temperature of the substrate at a second temperature, and co-evaporating indium, gallium, and selenium on the substrate; S40, maintaining the temperature of the substrate at a second temperature, performing an annealing treatment on the substrate in a selenium atmosphere, and preparing the wide bandgap copper gallium selenide light absorption layer on the substrate; Wherein, in step S30, when indium, gallium and selenium are co-evaporated, the atomic ratio of gallium to the sum of indium and gallium is controlled to be (0.3-0.7):

1.

6. The preparation method according to claim 5, characterized in that In step S30, when indium, gallium and selenium are co-evaporated, the atomic ratio of gallium to the sum of indium and gallium is controlled to be (0.5-0.7):

1.

7. The preparation method according to claim 5, characterized in that The annealing time of the annealing treatment is 15 min to 20 min.

8. The preparation method according to any one of claims 5 to 7, characterized in that: The first temperature is 340°C to 380°C, and the second temperature is 500°C to 600°C.

9. The preparation method according to claim 8, characterized in that The substrate includes a molybdenum metal layer. When co-evaporating gallium and selenium in step S10, selenium vapor is first introduced to form a molybdenum selenide layer on the surface of the molybdenum metal layer, and then gallium vapor is introduced to co-evaporate gallium and selenium on the molybdenum selenide layer.

10. A solar cell, characterized in that: The method comprises the wide bandgap copper gallium selenide light absorption layer as described in any one of claims 1 to 4.

Images