A II-VI compound thin film / silicon parallel stacked solar cell

Abstract

The present invention discloses a II-VI compound thin film / silicon parallel stacked solar cell, which includes a II-VI compound thin film top solar cell with an overall thickness of less than 1 micron, a spectral response range of 300nm to 690-800nm, and a transmittance that can be adjusted by 20% to 60%, and a crystalline silicon bottom solar cell with a basic structure of p-i-n or n-i-p. The top solar cell and the bottom solar cell are connected by electrodes in parallel, and the bonding stack is achieved by transparent polymer materials. The present invention solves the thermal impact of the high temperature process on the bottom solar cell during the production of the top solar cell and avoids the production of complex tunnel junctions. The present invention can make the most of the mature production process of solar cells, save costs, and can also make the most of the solar spectrum of 300nm to 1100nm to meet different application scenarios, especially the needs under weak light conditions.

Description

Technical Field

[0001] The present invention relates to a design of a solar cell structure, and in particular to a method for producing a laminated solar cell based on parallel integration of II-VI compound thin-film solar cells and crystalline silicon solar cells by utilizing a currently mature preparation process. Background Art

[0002] Currently, the conversion efficiency of single-junction solar cells is increasing increasingly slowly, gradually approaching its theoretical efficiency limit. For each photovoltaic material with a given bandgap width, its spectral response range covers only a small portion of the solar spectrum, meaning it can only convert sunlight energy within a certain wavelength range into electrical energy. To improve the photoelectric conversion efficiency of solar cells, it is necessary to carefully manage the photons they absorb to ensure that more photons are absorbed and collected by the cell. Semiconductor materials with an ideal bandgap are often selected, first ensuring absorption of visible light between 380nm and 780nm. Furthermore, the absorption of shorter and longer wavelengths is then enhanced. An effective approach is to integrate photovoltaic materials with different bandgap widths to create a band structure with a gradient bandgap. This allows high-energy photons to be absorbed by the upper material with the higher bandgap, while lower-energy photons can pass through the upper material and be absorbed by the lower material with the lower bandgap. In practical design, a common approach is to construct a single-junction subcell for each absorbing semiconductor. These subcells are then connected in series, resulting in double-junction, triple-junction, or even multi-junction tandem solar cells. Tandem solar cells broaden the cell's spectral response to sunlight, reducing light energy loss and achieving efficient sunlight utilization.

[0003] These multi-junction solar cells often require tunnel junctions between sub-cells. In-situ growth of multi-junction solar cells requires strict consideration of the compatibility of the material properties of each film layer, the compatibility of the deposition technology, and the repeatability of the fabrication process. Guaranteeing material quality during the fabrication of complex multi-material systems is difficult. These scientific and technological challenges hinder the practical application of multi-junction solar cells.

[0004] Multi-junction solar cells integrated in series require extremely precise management of light and electricity, and finely distribute the transmitted light of each upper layer of sub-cells to ensure that the output current of each lower layer of sub-cells is the same as that of each upper layer of sub-cells. This greatly increases the design complexity and manufacturing difficulty of the cells, and also limits the improvement of the short-circuit current density of the cells.

[0005] In the application and development of photovoltaic materials, crystalline silicon with a band gap of 1.1eV can absorb photons with energy greater than 1.1eV (i.e., light with a wavelength shorter than 1100nm). Correspondingly, the short-circuit current density of crystalline silicon cells can be as high as 42.50mA / cm2 This is unmatched by any other solar cell. This is one of the reasons why most multi-junction solar cells use crystalline silicon cells as the base cell. It is also noted that significant research progress has been made in II-VI compound thin-film solar cells, represented by cadmium telluride. The conversion efficiency of small-area cells has exceeded 22%, reaching an extreme in short-wave response, offering a clear advantage over other solar cells. However, progress in further expanding their long-wave response has been limited.

[0006] Based on the comprehensive advantages of II-VI compound thin film solar cells and crystalline silicon solar cells, the connection methods of their integrated construction of stacked solar cells are analyzed, and a structural design of a II-VI compound thin film / silicon parallel stacked solar cell is proposed. Summary of the Invention

[0007] The purpose of the present invention is to design a new structure and new connection method of solar cells that can effectively utilize the solar spectrum using existing technologies, improve the conversion efficiency of solar cells, and broaden the outdoor applications of solar cells.

[0008] In order to achieve the above object, the structural feature of the present invention is to include the following steps:

[0009] A. Make the top cell on the ultra-white glass substrate with a thickness of 1 to 3 mm: first deposit a thickness of ~100 nm, a transmittance greater than 90%, and a resistivity of ~10 -3 Ω.cm n-type transparent conductive film, then deposited with a thickness of ~10nm, with a transmittance greater than 90% and a resistivity of ~10 6 Ω.cm high-resistance transparent conductive film, followed by depositing an n-type window layer film with a thickness of 50nm and a transmittance adjustable by 50% to 90% on the high-resistance transparent conductive film, followed by depositing a p-type II-VI compound absorption layer film with a thickness of 100nm to 600nm and a band gap adjustable by 1.55eV to 1.8eV on the n-type window layer film, and then heat-treating the absorption layer film, and then etching away the oxide film on the surface of the absorption layer. After cleaning, a copper-containing back field layer film with a thickness of 100nm to 100nm is deposited on the absorption layer film, and then a thin metal back electrode film with a thickness of 150nm is deposited on the back field layer film. The overall thickness of the top cell is less than 1 micron;

[0010] B. Cleaning the edge of the negative electrode of the top cell obtained in step A, leaving only the transparent conductive film to form a negative electrode region;

[0011] C. Connect the thin metal back electrode of the top cell obtained in step A in parallel at both ends of the top cell to form a positive electrode region;

[0012] D. Use a crystalline silicon cell with a pin or nip structure as the bottom cell, and form a strip electrode on the upper side close to the top cell. The pattern and position of the strip electrode are the same as the pattern and position of the thin metal back electrode of the top cell;

[0013] E. After completing the above steps, the long-wave transmittance is not less than 90%, the curing temperature is not more than 160℃, and after curing, it can withstand the temperature of -45℃ to 85℃, and the insulation resistivity is greater than 10 15 The top cell and bottom cell are bonded and cured with a transparent polymer material of Ω.cm;

[0014] F. Connect the positive electrode area of ​​the top cell to the positive electrode area of ​​the bottom cell, and connect the negative electrode area of ​​the top cell to the negative electrode area of ​​the bottom cell to form parallel channels, thereby completing the production of a II-VI compound thin film / silicon parallel stacked solar cell. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic diagram of the solar cell structure and one of the electrode connection methods of the present invention, wherein 1 is incident light, 2 is the top cell glass substrate, 3 is the top cell transparent conductive film, which is the negative electrode region, 4 is the top cell high-resistance transparent conductive film, 5 is the top cell window layer film, 6 is the top cell II-VI compound absorption layer film, 7 is the top cell back field layer film, 8 is the top cell thin strip metal back electrode film, 9 is the transparent polymer adhesive layer, 10 is the bottom cell strip electrode, 11 is the bottom cell p-type layer, 12 is the bottom cell i-type layer, 13 is the bottom cell n-type layer, 14 is the bottom cell back electrode, which is the negative electrode region, 15 is the top cell and the bottom cell negative electrode region connected in parallel, and 16 is the top cell and the bottom cell positive electrode region connected in parallel.

[0016] Figure 2 This is a schematic diagram of the solar cell structure and the second electrode connection method of the present invention, wherein 1 is incident light, 2 is the top cell glass substrate, 3 is the top cell transparent conductive film, which is the negative electrode region, 4 is the top cell high-resistance transparent conductive film, 5 is the top cell window layer film, 6 is the top cell II-VI compound absorption layer film, 7 is the top cell back field layer film, 8 is the top cell thin strip metal back electrode film, 9 is the transparent polymer adhesive layer, 10 is the bottom cell strip electrode, 11 is the bottom cell p-type layer, 12 is the bottom cell i-type layer, 13 is the bottom cell n-type layer, 15 is the top cell and the bottom cell negative electrode region connected in parallel, 16 is the top cell and the bottom cell positive electrode region connected in parallel, and 17 is the bottom cell back electrode, which is the positive electrode region.

[0017] Figure 3This is a planar schematic diagram of the edge cleaning of the negative electrode edge area of ​​the top battery of the present invention, wherein 3 is the transparent conductive film of the top battery, the white area shown is the edge cleaning area, 7 is the back field layer film of the top battery, 8 is the thin metal back electrode film of the top battery, and 18 is the positive electrode area of ​​the top battery.

[0018] Figure 4 It is a planar schematic diagram of the upper side of the bottom battery of the present invention, wherein 10 is the strip electrode of the bottom battery, 11 or 13 is the p- or n-type layer of the bottom battery, 19 is the electrode area of ​​the bottom battery, when 11 is the p-type layer of the bottom battery, 19 is the positive electrode area of ​​the bottom battery, and when 13 is the n-type layer of the bottom battery, 19 is the negative electrode area of ​​the bottom battery. DETAILED DESCRIPTION

[0019] In order to make the advantages, technical solutions and implementation effects of the present invention more clear and feasible, the present invention is further described below. The preparation of all materials is described using conventional techniques, but is not limited to this description. It should be understood that the specific examples provided herein are only for better explanation of the present invention and do not limit the present invention.

[0020] A solar cell comprising a II-VI compound thin film / silicon parallel stack, the structure of which comprises the following steps:

[0021] A. Make the top cell on the ultra-white glass substrate with a thickness of 1 to 3 mm: first deposit a thickness of ~100 nm, a transmittance greater than 90%, and a resistivity of ~10 -3 Ω.cm n-type transparent conductive film, then deposited with a thickness of ~10nm, with a transmittance greater than 90% and a resistivity of ~10 6 Ω.cm high-resistance transparent conductive film, followed by depositing an n-type window layer film with a thickness of 50nm and a transmittance adjustable by 50% to 90% on the high-resistance transparent conductive film, followed by depositing a p-type II-VI compound absorption layer film with a thickness of 100nm to 600nm and a band gap adjustable by 1.55eV to 1.8eV on the n-type window layer film, and then heat-treating the absorption layer film, and then etching away the oxide film on the surface of the absorption layer. After cleaning, a copper-containing back field layer film with a thickness of 100nm to 100nm is deposited on the absorption layer, and then a thin metal back electrode film with a thickness of 150nm is deposited on the back field layer film. The overall thickness of the top cell is less than 1 micron;

[0022] B. Clean the edge of the negative electrode of the top battery obtained in step A, and remove the high-resistance transparent conductive film / n-type window layer film / p-type II-VI compound absorption layer film / p-type window layer film in the area. + Type back field layer film / back electrode layer film (positive electrode) to form a negative electrode region;

[0023] C. Connecting the thin metal back electrode film of the top cell obtained in step A in parallel at both ends of the top cell to form a positive electrode region;

[0024] D. Use a crystalline silicon cell with a pin or nip structure as the bottom cell, and form a strip electrode on the upper side close to the top cell. The pattern and position of the strip electrode are the same as the pattern and position of the thin metal back electrode of the top cell;

[0025] E. After completing the above steps, the light transmittance is not less than 90%, the curing temperature is not more than 160℃, and after curing, it can withstand the temperature of -45℃ to 85℃, and the insulation resistance is greater than 10 15 The top cell and bottom cell are bonded and cured with a transparent polymer material of Ω.cm;

[0026] F. Connect the positive electrode area of ​​the top cell to the positive electrode area of ​​the bottom cell, and connect the negative electrode area of ​​the top cell to the negative electrode area of ​​the bottom cell to form parallel channels, thereby completing the production of a II-VI compound thin film / silicon parallel stacked solar cell.

[0027] Example 1

[0028] A II-VI compound thin film / silicon parallel stacked solar cell, comprising the preparation of a II-VI compound thin film top solar cell, the preparation of a silicon bottom solar cell, and the parallel stacking of the top cell and the bottom cell:

[0029] A. Make the top cell on the ultra-white glass substrate with a thickness of 1 to 3 mm: first deposit a thickness of ~100 nm, a transmittance greater than 90%, and a resistivity of ~10 -3 Ω.cm n-type transparent conductive film, related materials include Cd2SnO4, In2O3:SnO2, SnO2:F, etc., related preparation technologies include magnetron sputtering, thermal decomposition, plasma sputtering, pulsed laser deposition, etc.; then deposited thickness ~10nm, transmittance greater than 90%, resistivity ~10 6Ω.cm high-resistance transparent conductive film SnO2, related preparation technologies include magnetron sputtering, thermal decomposition, plasma sputtering, pulsed laser deposition, atomic layer deposition, etc.; then depositing a n-type window layer film with a thickness of ~50nm and a transmittance adjustable by 50% to 90% on the SnO2, the materials include ZnS or CdS or CdSTe or CdSe or ZnMgO, related preparation technologies include magnetron sputtering, chemical pool water bath, pulsed laser deposition, vacuum thermal evaporation, close space sublimation method, etc.; then on the n-type window layer film A p-type II-VI compound absorption layer film with a thickness of 100nm to 600nm and an adjustable band gap of 1.55ev to 1.8eV is deposited on the substrate. The materials include ZnTe, CdTe, CdSe, CdZnTe, CdSTe, CdSeTe, etc. The relevant preparation technologies include magnetron sputtering, pulsed laser deposition, vacuum thermal evaporation, near-space sublimation, etc. The absorption layer film is then heat-treated using a box annealing furnace, a tunnel annealing furnace, etc. The typical conditions are: in an atmosphere of group VII elements, such as Cl - , temperature 350 ℃ ~ 450 ℃, time 15 minutes ~ 30 minutes, the environment can be vacuum or oxygen-containing atmosphere; then etch away the oxide film on the surface of the absorption layer, the method used may be wet etching: bromine + methanol solution (wherein the volume content of bromine is 1‰ ~ 2%), time 2 seconds ~ 10 seconds; or dry plasma etching; after cleaning, deposit a copper-containing back field layer film with a thickness of ~ 100nm on the absorption layer film, the material includes ZnTe: Cu or CuCl, and the related preparation technologies include magnetron sputtering, pulsed laser deposition, vacuum thermal evaporation, etc.; next, the back field layer film is deposited on Heat treatment is performed in a vacuum environment at a temperature of 250°C to 350°C for 5 to 20 minutes. Finally, a thin metal back electrode film with a thickness of 150 nm is deposited on the back field layer film. Materials include Ti, Cr, Au, Ni, Mo, Al, etc. Related preparation techniques include sputtering, vacuum thermal evaporation, screen printing, etc. The thin metal back electrode can be obtained by mask plate, laser scribing or photolithography. The overall thickness of the top cell is less than 1 micron, the spectral response range is 300 nm to 690 to 800 nm, and the transmittance of the entire top cell can be adjusted by 20% to 60%.

[0030] B. Cleaning the edge of the negative electrode of the top battery obtained in step A, retaining the transparent conductive film, to form a negative electrode region;

[0031] C. Connect the thin metal back electrode of the top cell obtained in step A in parallel at both ends of the top cell to form a positive electrode region;

[0032] D. Use a crystalline silicon cell with a pin or nip structure as the bottom cell, and form a strip electrode on the upper side close to the top cell. The pattern and position of the strip electrode are the same as the pattern and position of the thin metal back electrode of the top cell;

[0033] E. After completing the above steps, use a transparent polymer material to bond the top cell and the bottom cell and cure them;

[0034] F. Connect the positive electrode area of ​​the top cell to the positive electrode area of ​​the bottom cell, and connect the negative electrode area of ​​the top cell to the negative electrode area of ​​the bottom cell to form parallel channels, thereby completing the production of a II-VI compound thin film / silicon parallel stacked solar cell.

[0035] Example 2

[0036] A II-VI compound thin film / silicon parallel stacked solar cell, comprising the preparation of a II-VI compound thin film top solar cell, the preparation of a silicon bottom solar cell, and the parallel stacking of the top cell and the bottom cell:

[0037] A. Referring to step A of Example 1, complete the production of the top battery;

[0038] B. Clean the edge of the negative electrode of the top battery obtained in step A, and remove the high-resistance transparent conductive film / n-type window layer film / p-type II-VI compound absorption layer film / p-type window layer film by laser scribing. + Type back field layer film / back electrode layer film (positive electrode), the laser reference parameters include: wavelength 531nm, frequency 10KHz, current 23A, power 120~750mJ, by retaining only the transparent conductive film to form the negative electrode region;

[0039] C. Connect the thin metal back electrode of the top cell obtained in step A in parallel at both ends of the top cell to form a positive electrode region;

[0040] D. Use a crystalline silicon cell with a pin or nip structure as the bottom cell, and form a strip electrode on the upper side close to the top cell. The pattern and position of the strip electrode are the same as the pattern and position of the thin metal back electrode of the top cell;

[0041] E. After completing the above steps, use a transparent polymer material to bond the top cell and the bottom cell and cure them;

[0042] F. Connect the positive electrode area of ​​the top cell to the positive electrode area of ​​the bottom cell, and connect the negative electrode area of ​​the top cell to the negative electrode area of ​​the bottom cell to form parallel channels, thereby completing the production of a II-VI compound thin film / silicon parallel stacked solar cell.

[0043] Example 3

[0044] A II-VI compound thin film / silicon parallel stacked solar cell, comprising the preparation of a II-VI compound thin film top solar cell, the preparation of a silicon bottom solar cell, and the parallel stacking of the top cell and the bottom cell:

[0045] A. Referring to step A of Example 1, complete the production of the top battery;

[0046] B. Cleaning the edge of the negative electrode of the top cell obtained in step A, leaving only the transparent conductive film to form a negative electrode region;

[0047] C. Connect the thin metal back electrodes of the top cell obtained in step A in parallel at both ends of the top cell to form a positive electrode region. The positive electrode region can be obtained using the mask plate used in step A, or can be obtained by screen printing alone, or by wire welding;

[0048] D. Use a crystalline silicon cell with a pin or nip structure as the bottom cell, and form a strip electrode on the upper side close to the top cell. The pattern and position of the strip electrode are the same as the pattern and position of the thin metal back electrode of the top cell;

[0049] E. After completing the above steps, use a transparent polymer material to bond the top cell and the bottom cell and cure them;

[0050] F. Connect the positive electrode area of ​​the top cell to the positive electrode area of ​​the bottom cell, and connect the negative electrode area of ​​the top cell to the negative electrode area of ​​the bottom cell to form parallel channels, thereby completing the production of a II-VI compound thin film / silicon parallel stacked solar cell.

[0051] Example 4

[0052] A II-VI compound thin film / silicon parallel stacked solar cell, comprising the preparation of a II-VI compound thin film top solar cell, the preparation of a silicon bottom solar cell, and the parallel stacking of the top cell and the bottom cell:

[0053] A. Referring to step A of Example 1, complete the production of the top battery;

[0054] B. Cleaning the edge of the negative electrode of the top cell obtained in step A, leaving only the transparent conductive film to form a negative electrode region;

[0055] C. Connect the thin metal back electrode of the top cell obtained in step A in parallel at both ends of the top cell to form a positive electrode region;

[0056] D. Select crystalline silicon cells with a pin or nip structure as the bottom cell. The bottom cell is mainly based on mainstream crystalline silicon cells, including crystalline silicon cells with optimized back electrodes, such as PERC, PERL and PERT solar cells; they can also include passivated crystalline silicon cells, such as SHJ and TOPCon solar cells; they can also include crystalline silicon cells with improved light utilization efficiency, such as grooved buried gate, IBC and silicon ball solar cells; the above-mentioned crystalline silicon solar cells form strip electrodes on the upper side near the top cell. The pattern and position of the strip electrodes are the same as the pattern and position of the thin metal back electrode of the top cell;

[0057] E. After completing the above steps, use a transparent polymer material to bond the top cell and the bottom cell and cure them;

[0058] F. Connect the positive electrode area of ​​the top cell to the positive electrode area of ​​the bottom cell, and connect the negative electrode area of ​​the top cell to the negative electrode area of ​​the bottom cell to form parallel channels, thereby completing the production of a II-VI compound thin film / silicon parallel stacked solar cell.

[0059] Example 5

[0060] A II-VI compound thin film / silicon parallel stacked solar cell, comprising the preparation of a II-VI compound thin film top solar cell, the preparation of a silicon bottom solar cell, and the parallel stacking of the top cell and the bottom cell:

[0061] A. Referring to step A of Example 1, complete the production of the top battery;

[0062] B. Cleaning the edge of the negative electrode of the top cell obtained in step A, leaving only the transparent conductive film to form a negative electrode region;

[0063] C. Connect the thin metal back electrode of the top cell obtained in step A in parallel at both ends of the top cell to form a positive electrode region;

[0064] D. Use a crystalline silicon cell with a pin or nip structure as the bottom cell, and form a strip electrode on the upper side close to the top cell. The pattern and position of the strip electrode are the same as the pattern and position of the thin metal back electrode of the top cell;

[0065] E. After completing the above steps, adopt a long-wave transmittance of not less than 90% (690nm ~ 1100nm), the curing temperature shall not exceed 160℃, and after curing, it shall be able to withstand the temperature of -45℃ ~ 85℃, and the insulation resistivity shall be greater than 10 15 The top cell and bottom cell are bonded and cured using a transparent polymer material of Ω.cm. Common transparent polymer materials include polystyrene, polymethyl methacrylate, polycarbonate, ethylene vinyl acetate, poly-4-methyl-1-pentene, polysulfone, etc. Curing is performed using vacuum lamination technology.

[0066] F. Connect the positive electrode area of ​​the top cell to the positive electrode area of ​​the bottom cell, and connect the negative electrode area of ​​the top cell to the negative electrode area of ​​the bottom cell to form parallel channels, thereby completing the production of a II-VI compound thin film / silicon parallel stacked solar cell.

Claims

1. A II-VI compound thin film / silicon parallel stacked solar cell, characterized in that The top cell structure includes the following: n-type negative electrode transparent conductive film / high resistance transparent conductive film / n-type window layer film / p-type II-VI compound absorption layer film / p + The top cell is composed of a thin film of back field layer / positive back electrode layer. The overall thickness of the top cell is less than 1 micron. The band gap of the top cell absorption layer can be adjusted from 1.55ev to 1.8eV. The spectral response range is from 300nm to 690~800nm. The transmittance of the entire top cell can be adjusted from 20% to 60%. The basic structure of the bottom cell is a pin or nip crystalline silicon cell. The top cell and the bottom cell are bonded with a transparent polymer material, and the electrode areas of the two are connected in parallel.

2. A II-VI compound thin film / silicon parallel stacked solar cell according to claim 1, characterized in that The thickness of the top cell n-type transparent conductive film is 100nm, the transmittance is greater than 90%, and the resistivity is 10 -3 Ω.cm, the thickness of the high-resistance transparent conductive film is ~10nm, the transmittance is greater than 90%, and the resistivity is ~10 6 Ω.cm, the thickness of the n-type window layer film is ~50nm, the transmittance can be adjusted from 50% to 90%, the thickness of the p-type II-VI compound absorption layer film is 100nm to 600nm, the band gap can be adjusted from 1.55ev to 1.8eV, p + The back field layer film is a copper-containing material with a thickness of 100 nm, and the back electrode layer film is a metal thin strip electrode with a thickness of 150 nm.

3. A II-VI compound thin film / silicon parallel stacked solar cell according to claim 1, characterized in that It is necessary to clean the edge area of ​​the negative electrode of the top battery to form a negative electrode area.

4. A II-VI compound thin film / silicon parallel stacked solar cell according to claim 1, characterized in that The back electrode of the top cell needs to form a thin strip metal back electrode, which forms a positive electrode region in parallel at both ends of the top cell, and the pattern and position of the thin strip metal back electrode are the same as the pattern and position of the strip electrode of the bottom cell.

5. The II-VI compound thin film / silicon parallel stacked solar cell according to claim 1, characterized in that The transparent polymer material used for bonding the top cell and the bottom cell has a long-wave transmittance of not less than 90%, a long-wave wavelength range of 690nm to 1100nm, a maximum curing temperature of no more than 160°C, and can withstand temperatures of -45°C to 85°C after curing. The insulation resistivity is greater than 10 15 Ω.cm and other characteristics.

6. The II-VI compound thin film / silicon parallel stacked solar cell according to claim 1, characterized in that The positive electrode region of the top battery is connected to the positive electrode region of the bottom battery, and the negative electrode region of the top battery is connected to the negative electrode region of the bottom battery, forming parallel channels.

Images