A PERC-copper-zinc-tin-sulfur tandem solar cell and its fabrication method

Abstract

This invention discloses a PERC-copper-zinc-tin-sulfur tandem solar cell and its fabrication method. The cell includes a bottom cell, a top cell, a connecting layer between the bottom and top cells, a transition layer, a window layer, and a top electrode on the top cell. The top cell is copper-zinc-tin-sulfur; the connecting layer is a tunneling layer formed by an ultrathin silicon oxide layer and a MoSxOy layer. Fabrication: S1, cleaning and texturing the P-type silicon wafer; S2, diffusion to form a phosphosilicate glass layer on the front side, and alkaline polishing on the back side; S4, oxidation to form an ultrathin silicon oxide layer on the front side; S5, deposition of a second passivation layer and a first passivation layer on the back side; S6, fabrication of the bottom electrode; S7, deposition of a MoSxOy layer on the ultrathin silicon oxide layer using magnetron sputtering to form the connecting layer; S8, deposition of copper-zinc-tin-sulfur on the connecting layer using magnetron sputtering to form the top cell; S9, deposition of a transition layer and a window layer sequentially on the top cell using magnetron sputtering; S10, finally printing electrode paste on the window layer, heating and sintering to obtain the tandem solar cell.

Description

Technical Field

[0001] This invention relates to the field of solar cell fabrication technology and device technology, specifically to a PERC-copper-zinc-tin-sulfur tandem solar cell and its fabrication method. Background Technology

[0002] Solar power generation is considered an inexhaustible and clean energy source, and is seen as an effective way to solve the energy crisis, reduce environmental pollution, and address global warming. In the current photovoltaic power generation market, crystalline silicon solar cells dominate. Currently, PERC cells, a type of silicon-based solar cell, account for approximately 80% of the global solar energy market, offering the best cost-performance ratio. PERC cells have a theoretical maximum efficiency of 24.5%, and mass-produced efficiencies have generally reached over 23.3%, leaving little room for further cost reduction and efficiency improvement. However, N-type HJT and Topcon cells have already achieved mass-produced efficiencies of 24% and above, and their production costs are approaching those of PERC cells. Therefore, the representative P-type cell is nearing its end in all aspects.

[0003] Tandem solar cells offer an effective solution to this problem. Traditional single-cell PERC cells have a bandgap of around 1.1 eV, smaller than the optimal bandgap of 1.4 eV, meaning they cannot utilize high-energy photons below 400 nm, resulting in a loss of approximately 20% of spectral energy. Tandem solar cells, through matching cells with different bandgap values, achieve better and more comprehensive light absorption.

[0004] Copper-zinc-tin-sulfur (CZTS) is a direct bandgap semiconductor with a bandgap of approximately 1.5 eV, which matches the solar spectrum well. In the visible light band, its absorption coefficient reaches as high as 10⁴ cm⁻¹. -1 This technology can effectively absorb and utilize incident light. Furthermore, compared to traditional copper indium gallium selenide (CIGS), copper zinc tin sulfide (CZTS) raw materials are abundant, making it a promising candidate material for solar cell absorber layers. CZTS cells are a relatively mature technology; their bandgap can complement that of PERC cells, achieving better light absorption. In addition, CZTS cell fabrication is largely compatible with current PERC cell fabrication processes, and the material cost is very low, making it an effective solution for reducing costs and increasing efficiency in PERC cell production. Summary of the Invention

[0005] The purpose of this invention is to provide a novel PERC-copper-zinc-tin-sulfur tandem solar cell and its fabrication process. Based on the existing PERC cell structure and equipment, this invention fabricates a copper-zinc-tin-sulfur cell on the top layer, forming a tandem solar cell that better utilizes sunlight, improves cell efficiency, reduces cell cost, and makes better use of existing equipment.

[0006] This invention is achieved through the following technical solution:

[0007] A PERC-copper-zinc-tin-sulfur tandem solar cell is characterized in that the tandem solar cell includes a bottom cell, a top cell, a connecting layer disposed between the bottom cell and the top cell, and a transition layer, a window layer and a top electrode sequentially disposed on the top cell; the top cell is a copper-zinc-tin-sulfur cell; and the connecting layer is a tunneling layer formed by an ultrathin silicon oxide layer and a MoSxOy layer.

[0008] Specifically, the PERC-copper-zinc-tin-sulfur tandem solar cell designed in this invention comprises, from bottom to top, a bottom cell, a connecting layer with a tunneling structure, a top cell, a transition layer, a window layer, and a top electrode. The window layer serves both as an anti-reflective layer (silicon nitride) and a conductive layer.

[0009] Furthermore, a PERC-copper-zinc-tin-sulfur tandem solar cell: the bottom cell includes, from bottom to top, a bottom electrode, a first passivation layer, a second passivation layer, a P-type silicon wafer, a phosphosilicate glass layer, and the ultrathin silicon oxide layer; the bottom electrode penetrates the first passivation layer and the second passivation layer and is in contact with the P-type silicon wafer.

[0010] Furthermore, in a PERC-copper-zinc-tin-sulfur tandem solar cell, the first passivation layer is a SiNx layer, and the thickness of the first passivation layer is 65-120 nm.

[0011] Furthermore, in a PERC-copper-zinc-tin-sulfur tandem solar cell, the second passivation layer is an AlOx layer, and the thickness of the second passivation layer is 5-10 nm.

[0012] Furthermore, a PERC-copper-zinc-tin-sulfur tandem solar cell: the P-type silicon wafer has a thickness of 120-250 μm and a resistivity of 0.4-1.5 Ω / cm.

[0013] Furthermore, a PERC-copper-zinc-tin-sulfur tandem solar cell: the thickness of the ultrathin silicon oxide layer (SiOx) is 1-3 nm.

[0014] Furthermore, a PERC-copper-zinc-tin-sulfur tandem solar cell: the thickness of the MoSxOy layer is 2-6 nm.

[0015] Furthermore, a PERC-copper-zinc-tin-sulfur tandem solar cell: the transition layer is a cadmium sulfide (CdS) layer, and the thickness of the transition layer is 10-100 nm.

[0016] Furthermore, a PERC-copper-zinc-tin-sulfur tandem solar cell: the window layer is a zinc oxide layer (ZnO), and the thickness of the window layer is 60-200 nm.

[0017] A method for fabricating a PERC-copper-zinc-tin-sulfur tandem solar cell, characterized in that the method comprises the following steps in sequence:

[0018] S1. Clean and texturize the P-type silicon wafer;

[0019] S2. The texturized P-type silicon wafer is subjected to front diffusion to form a phosphosilicate glass layer, and then the back side is alkaline polished.

[0020] S3. Front oxidation, forming the ultrathin silicon oxide layer on the phosphosilicate glass layer;

[0021] S4. A second passivation layer and a first passivation layer are deposited sequentially on the back side;

[0022] S5. Laser drilling, screen printing, sintering, and preparation of the bottom electrode;

[0023] S6. Using magnetron sputtering, the MoSxOy layer is deposited on the ultrathin silicon oxide layer to form the connecting layer of the tunneling structure; specifically, the MoSxOy layer is a gradient layer, with the S element gradually increasing from the bottom to the top during the deposition process, and the S / (Mo+S+O element ratio) is 10-40%; the O / Mo element ratio on the target can be set to 1.5 (MoSxOy). 1.5 The sulfur element in the gradient layer is achieved by introducing different hydrogen sulfide gases during the magnetron sputtering process, while maintaining the temperature within the range of 300±20 degrees Celsius.

[0024] S7. Using magnetron sputtering, copper-zinc-tin-sulfur (CZTS) is deposited on the connecting layer to obtain the top-layer cell, and the thickness of the top-layer cell is 1-3 μm and the band gap is 1.4-1.7 eV; specifically, the band gap of the top-layer cell can be adjusted to 1.4-1.7 eV by the doping ratio of sulfur, copper, etc. in the target material.

[0025] S8. Using magnetron sputtering, the transition layer and the window layer are deposited sequentially on the top-layer battery.

[0026] S9. Finally, electrode paste is screen-printed on the window layer and sintered by heating to obtain the tandem solar cell; wherein: the heating and sintering is carried out by heating from room temperature to 900°C within 1-5 minutes.

[0027] Specifically, the PERC-copper-zinc-tin-sulfur tandem solar cell prepared by the present invention comprises, from bottom to top, the following layers arranged in sequence: a bottom electrode on the back of the silicon wafer, a first passivation layer (SiNx), a second passivation layer (AlOx), a P-type silicon wafer, a phosphosilicate glass layer on the front of the silicon wafer, an ultrathin silicon oxide layer, a MoSxOy layer, a copper-zinc-tin-sulfur top cell, a transition layer (CdS), a window layer (ZnO), and a top electrode.

[0028] The beneficial effects of this invention are:

[0029] (1) The PERC-copper-zinc-tin-sulfur tandem solar cell designed in this invention can utilize incident light more efficiently and further improve the cell efficiency.

[0030] (2) The underlying battery in this invention can be based on the existing PERC battery production line process and equipment without any additional modifications or additions, and its cost is low.

[0031] (3) The copper-zinc-tin-sulfur top-layer battery deposited in this invention is prepared by magnetron sputtering throughout the process, which is simple; in addition, the thickness of the top-layer battery is only a few micrometers, and the cost is extremely low.

[0032] (4) There is no existing technology to realize the stacking scheme of PERC+CZTS. The present invention adopts a special connecting layer structure, which can achieve efficient tunneling with the bottom cell and form a good back passivation effect with the top cell (CZTS). The present invention creatively adopts a gradient MoSxOy layer structure before CZTS coating, which can form a good tunneling structure with the ultrathin silicon oxide layer and also form a good back contact with the bottom of CZTS, assisting CZTS to form a chalcopyrite structure.

[0033] (5) The copper-zinc-tin-sulfur thin-film solar cell provided by the present invention is a novel thin-film technology, similar to perovskite cells. However, it has a problem with the preparation route. Existing copper-zinc-tin-sulfur cells are basically prepared by co-evaporation, where copper, zinc, tin and sulfur sources are stacked at high temperature and proportionally doped to form an absorption layer. This process is difficult to control and wasteful. The present invention creatively prepares the top layer cell material into powder in advance, then grinds it into a target material, and completes the preparation by sputtering at room temperature. Finally, the film structure is optimized by annealing to eliminate the sputtering effect. This solution makes the preparation process simple and controllable with extremely low energy consumption. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the structure of a PERC-copper-zinc-tin-sulfur tandem solar cell designed according to the present invention.

[0036] The diagram is labeled as follows: 1 bottom cell, 2 top cell, 3 connecting layer, 4 MoSxOy layer, 5 transition layer (cadmium sulfide layer), 6 window layer (zinc oxide layer), 7 top electrode, 1-1 bottom electrode, 1-2 first passivation layer (SiNx layer), 1-3 second passivation layer (AlOx layer), 1-4 P-type silicon wafer, 1-5 phosphosilicate glass layer, 1-6 ultrathin silicon oxide layer (SiOx). Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0038] In the description of this invention, it should be understood that the terms "upper," "lower," "left," "right," "top," and "bottom," etc., indicating orientation or positional relationships, are merely for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature. Moreover, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein.

[0039] A method for fabricating PERC-copper-zinc-tin-sulfur tandem solar cells is provided, and the specific fabrication steps are as follows:

[0040] S1. Clean and texturize the P-type silicon wafer; the thickness of the P-type silicon wafer is 120-250μm, the resistivity is 0.4-1.5Ω / cm, and the size is selected as 156.75*156.75—210*210mm;

[0041] S2. The texturized P-type silicon wafer is subjected to front diffusion to form a phosphosilicate glass layer, and then the back side is alkaline polished.

[0042] S3, front oxidation, forming an ultra-thin silicon oxide layer with a thickness of 1-3nm on the phosphosilicate glass layer;

[0043] S4. Sequentially deposit a second passivation layer (AlOx) and a first passivation layer (SiNx) on the back side of the silicon wafer;

[0044] S6. Laser drilling, screen printing, sintering, and preparation of the bottom electrode, wherein the bottom electrode penetrates the first passivation layer and the second passivation layer and contacts the P-type silicon wafer.

[0045] S6. A MoSxOy layer with a thickness of 2-6 nm is deposited on the ultrathin silicon oxide layer using a magnetron sputtering process, and the two form the connecting layer of the tunnel structure.

[0046] S7. Copper-zinc-tin-sulfur is deposited on the bonding layer using a magnetron sputtering process to obtain the top-layer battery, and the band gap of the top-layer battery is 1.4-1.7 eV.

[0047] S8. Using magnetron sputtering, a cadmium sulfide transition layer and a zinc oxide window layer are sequentially deposited on the top-layer battery.

[0048] S9. Finally, electrode paste is screen-printed on the window layer and sintered by heating to obtain the tandem solar cell; wherein: the heating and sintering is carried out by heating from room temperature to 900°C within 1-5 minutes.

[0049] Example 1

[0050] like Figure 1As shown, a PERC-copper-zinc-tin-sulfur tandem solar cell is characterized in that the tandem solar cell includes a bottom cell 1, a top cell 2 with a thickness of 2μm, a connecting layer 3 disposed between the bottom cell 1 and the top cell 2, and a cadmium sulfide transition layer 5, a zinc oxide window layer 6, and a top electrode 7 sequentially disposed on the top cell 2; wherein: the top cell 2 is a copper-zinc-tin-sulfur cell; the connecting layer 3 is a tunneling layer formed by an ultrathin silicon oxide layer 1-6 and a MoSxOy layer 4; the thickness of the transition layer 5 is 60nm; and the thickness of the window layer 6 is 100nm. Wherein: the bottom battery 1 includes, from bottom to top, a bottom electrode 1-1, a first passivation layer (SiNx) 1-2 with a thickness of 80nm, a second passivation layer (AlOx) 1-3 with a thickness of 5nm, a P-type silicon wafer 1-4 with a thickness of 180μm, a phosphorus silicon glass layer 1-5, and an ultrathin silicon oxide layer 1-6 with a thickness of 2nm; the bottom electrode 1-1 penetrates the first passivation layer 1-2 and the second passivation layer 1-3 and is in contact with the P-type silicon wafer 1-4.

[0051] The method for fabricating the PERC-copper-zinc-tin-sulfur tandem solar cell in Example 1 above is provided, and the fabrication process includes the following specific steps:

[0052] S1. Clean and texturize P-type silicon wafers 1-4; the thickness of the P-type silicon wafers is 180μm, the resistivity is 0.4-1.5Ω / cm, and the size is 156.75*156.75mm.

[0053] S2. Perform front-side diffusion on the texturized P-type silicon wafers 1-4 to form phosphosilicate glass layers 1-5, and then perform back-side alkaline polishing.

[0054] S3, front oxidation, forming an ultrathin silicon oxide layer 1-6 with a thickness of 2nm on the phosphorus silica glass layer 1-5;

[0055] S4. Sequentially deposit a 5nm thick second passivation layer 1-3 and an 80nm thick first passivation layer 1-2 on the back side of the silicon wafer.

[0056] S5. Laser drilling, screen printing, sintering, to prepare the bottom electrode 1-1, and the bottom electrode 1-1 penetrates the first passivation layer 1-2 and the second passivation layer 1-3 and contacts the P-type silicon wafer;

[0057] S6. Using magnetron sputtering, a 4nm thick MoSxOy layer 4 is deposited on the ultrathin silicon oxide layer 1-6. The ultrathin silicon oxide layer 1-6 and the MoSxOy layer 4 form a tunneling structure connecting layer 3.

[0058] S7. Using magnetron sputtering, copper-zinc-tin-sulfur is deposited on the connecting layer 3 to obtain the top battery 2 with a thickness of 2μm.

[0059] S8. Using magnetron sputtering, a 60nm thick transition layer (CdS)5 and a 100nm thick window layer (ZnO)6 are sequentially deposited on the top layer battery 2.

[0060] S9. Finally, electrode paste is screen-printed on window layer 6, and then heated and sintered to obtain the tandem solar cell; wherein: the heating and sintering is carried out by heating from room temperature to 900°C in 3 minutes.

[0061] The above-described preferred embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of the invention. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A PERC-copper-zinc-tin-sulfur tandem solar cell, characterized in that, The tandem solar cell includes a bottom cell (1), a top cell (2), a connecting layer (3) disposed between the bottom cell (1) and the top cell (2), and a transition layer (5), a window layer (6), and a top electrode (7) sequentially disposed on the top cell (2); the top cell (2) is a copper-zinc-tin-sulfur cell; the connecting layer (3) is a tunneling layer formed by an ultrathin silicon oxide layer (1-6) and a MoSxOy layer (4); The fabrication method of PERC-copper-zinc-tin-sulfur tandem solar cells includes the following steps: S1. Clean and texturize the P-type silicon wafers (1-4); S2. The texturized P-type silicon wafer (1-4) is subjected to front diffusion to form a phosphosilicate glass layer (1-5), and then the back side is subjected to alkaline polishing. S3. Front oxidation, forming the ultrathin silicon oxide layer (1-6) on the phosphosilicate glass layer (1-5); S4. A second passivation layer (1-3) and a first passivation layer (1-2) are deposited sequentially on the back side; S5. Laser drilling, screen printing, sintering, and preparation of the bottom electrode (1-1); S6. Using magnetron sputtering, the MoSxOy layer (4) is deposited on the ultrathin silicon oxide layer (1-6) to form a tunneling structure connection layer (3); Among them, the MoSxOy layer (4) is a gradient layer. During the deposition process, the S element gradually increases from the bottom layer to the top layer. The S / (Mo+S+O) element ratio is 10-40%. The O / Mo element ratio is set to 1.5 on the target. The S element of the gradient layer is achieved by introducing different hydrogen sulfide gases during the magnetron sputtering process, and the temperature is maintained at 300±20℃. S7. Copper, zinc, tin and sulfur are deposited on the connecting layer (3) by magnetron sputtering to obtain the top battery (2), and the thickness of the top battery (2) is 1 to 3 μm and the band gap is 1.4 to 1.7 eV. S8. Using magnetron sputtering, the transition layer (5) and the window layer (6) are deposited sequentially on the top battery (2); S9. Finally, electrode paste is screen printed on the window layer (6), and sintered by heating to obtain the tandem solar cell. The heating and sintering is carried out by heating from room temperature to 900°C within 1 to 5 minutes.

2. The PERC-copper-zinc-tin-sulfur tandem solar cell according to claim 1, characterized in that, The bottom battery (1) includes, from bottom to top, a bottom electrode (1-1), a first passivation layer (1-2), a second passivation layer (1-3), a P-type silicon wafer (1-4), a phosphosilicate glass layer (1-5), and the ultrathin silicon oxide layer (1-6); the bottom electrode (1-1) penetrates the first passivation layer (1-2) and the second passivation layer (1-3) and is in contact with the P-type silicon wafer (1-4).

3. A PERC-copper-zinc-tin-sulfur tandem solar cell according to claim 2, characterized in that, The first passivation layer (1-2) is a SiNx layer, and the thickness of the first passivation layer (1-2) is 65-120 nm.

4. A PERC-copper-zinc-tin-sulfur tandem solar cell according to claim 2, characterized in that, The second passivation layer (1-3) is an AlOx layer, and the thickness of the second passivation layer (1-3) is 5-10 nm.

5. A PERC-copper-zinc-tin-sulfur tandem solar cell according to claim 2, characterized in that, The thickness of the P-type silicon wafer (1-4) is 120-250 μm and the resistivity is 0.4-1.5 Ω / cm.

6. A PERC-copper-zinc-tin-sulfur tandem solar cell according to claim 2, characterized in that, The thickness of the ultrathin silicon oxide layer (1-6) is 1-3 nm.

7. A PERC-copper-zinc-tin-sulfur tandem solar cell according to claim 1, characterized in that, The thickness of the MoSxOy layer (4) is 2-6 nm.

8. A PERC-copper-zinc-tin-sulfur tandem solar cell according to claim 1, characterized in that, The transition layer (5) is a cadmium sulfide layer, and the thickness of the transition layer (5) is 10-100 nm.

9. A PERC-copper-zinc-tin-sulfur tandem solar cell according to claim 1, characterized in that, The window layer (6) is a zinc oxide layer, and the thickness of the window layer (6) is 60-200 nm.

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