An electro-injection process for N-type monocrystalline heterojunction solar cells

Abstract

This invention discloses an electro-injection process for N-type monocrystalline heterojunction solar cells. The process steps are as follows: A certain number of heterojunction solar cells are stacked in series with their P-sides facing the same direction; the solar cells are heated to the electro-injection annealing temperature and maintained at this temperature until the electro-injection is completed; a constant current source is applied to both ends of the cell or the series-stacked cell group, with the current flowing from the P-type end of the cell's PN junction and out from the N-type end; compressed air is used to cool the cell, maintaining a constant temperature during the current injection; and the constant current source is maintained for a certain duration. This invention, by electro-injecting charge carriers into the finished cell, changes the quasi-Fermi level of electrons, effectively improving the passivation effect of hydrogen atoms on the recombination centers of the cell matrix, and effectively improving the photoelectric conversion efficiency of the cell. The low-temperature electro-injection process, with temperatures generally below 150℃, results in better internal temperature uniformity of the cell, shorter process time, higher production capacity, lower energy consumption, flexible injection methods, and lower industrialization costs.

Description

Technical Field

[0001] This invention relates to the field of heterojunction solar energy technology, and more particularly to an electro-injection process for heterojunction solar cells. Background Technology

[0002] Photovoltaic solar energy, as a clean and renewable energy source, has always attracted much attention. Improving efficiency and reducing costs remains a constant theme in the photovoltaic industry and a primary goal for all photovoltaic companies. Traditional electro-injection technology is used for boron-doped P-type PERC cells (Passivated Emitter Rear Cells) because the high oxygen content in silicon wafers produced by the Czochralski method forms boron-oxygen (BO) complexes with the doped boron inside the wafer under illumination, hindering cell conversion efficiency. Traditional electro-injection applies a forward-biased DC current across the PN junction of the cell to passivate the photogenerated BO complexes, achieving an effect against light-induced degradation (LID). Conventional electro-injection is a high-temperature process, with annealing temperatures generally exceeding 180°C, resulting in poor internal temperature uniformity within the cell. The conventional electro-injection process is time-consuming, and as the industry increasingly recognizes the effects of light and elevated temperature-induced degradation (LID), the process time will further increase, impacting mass production capacity.

[0003] For an N-type monocrystalline heterojunction solar cell, heterojunction cells possess high conversion efficiency, a short manufacturing process, high bifaciality, and are free from light-induced degradation and potential-induced degradation, making them considered the next generation of high-efficiency solar cells with the greatest potential for mass production. Regarding the PN junction formation process, N-type monocrystalline heterojunction cells utilize low-temperature deposition of an ultrathin amorphous silicon film to form the PN junction, which differs significantly from the high-temperature diffusion-formed PN junctions of mainstream PERC cells. Traditional low-temperature electro-injection processes for passivating the boron-oxygen complex in P-type cells have a significant destructive effect on the PN junction formed by the low-temperature process in heterojunction cells. Therefore, a novel low-temperature electro-injection process is needed to improve the cell's conversion efficiency by passivating internal impurities and structural defects in the heterojunction solar cell. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides an electro-injection process for heterojunction solar cells. Using an N-type monocrystalline heterojunction cell as the substrate, and under a relatively low electro-injection annealing temperature, a suitable forward-biased DC current is injected. This process enhances the passivation effect of hydrogen atoms on recombination centers such as impurities and defects inside the cell within a short time, effectively improving the cell's open-circuit voltage Voc, fill factor FF, and conversion efficiency Eff.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: an electro-injection process for heterojunction solar cells, the process steps of which are as follows:

[0006] A certain number of heterojunction solar cells are stacked in series with their P-sides facing the same direction.

[0007] The solar cell is heated to the electro-injection annealing temperature and held at that temperature until the electro-injection is completed;

[0008] A constant current source is applied to both ends of the battery or series-stacked battery pack. The current flows in from the P-type end of the battery PN junction and flows out from the N-type end. Compressed air is used to cool the battery and maintain a constant temperature during current injection.

[0009] At the electrical injection annealing temperature, a constant current source is injected for a certain period of time.

[0010] Furthermore, the thickness of the solar cells is selected to be 90-180μm, and the number of cells that can be stacked is 1-600.

[0011] Furthermore, the electro-injection annealing temperature is 50℃-150℃.

[0012] Furthermore, the constant current source has a current range of 0.1A to 15A, the temperature remains constant during current injection, and the temperature uniformity deviation between battery cells is less than 5℃.

[0013] Furthermore, the duration of the constant current source injection is 20 minutes to 120 minutes.

[0014] As can be seen from the above description of the structure of the present invention, compared with the prior art, the present invention has the following advantages:

[0015] 1. This invention improves the passivation effect of hydrogen atoms on the recombination center of the battery matrix by injecting charge carriers into the finished battery and changing the quasi-Fermi level of electrons, thereby effectively improving the photoelectric conversion efficiency of the battery.

[0016] 2. This invention adopts a low-temperature electric injection process, with temperatures generally below 150°C. The internal temperature uniformity of the battery is good, the temperature uniformity deviation between cells is less than 5°C, the process time is short, 1-600 battery cells can be stacked, the production capacity is high, the energy consumption is low, the injection method is flexible, and the industrialization cost is low. Attached Figure Description

[0017] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0018] Figure 1The following is a diagram showing the conversion efficiency distribution of monocrystalline silicon cells before and after the treatment of this invention: (1) Vertical filling represents the conversion efficiency distribution before treatment; (2) Horizontal filling represents the conversion efficiency distribution after treatment, wherein the efficiency levels E1 to E6 increase by 0.20%.

[0019] Figure 2 To characterize the interaction between the injection current, injection temperature, and injection time used in this invention, the optimal injection parameters for improving conversion efficiency were explored using computer-aided design of experiments (DOE). Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Example 1

[0022] An electro-injection process for a heterojunction solar cell, comprising the following steps:

[0023] 1. Stack 400 M2 type heterojunction solar cells with a surface area of ​​156.75mm × 156.75mm in series, with the P-side facing the same direction;

[0024] 2. Heat the series-connected battery pack to the temperature required for electric injection annealing, such as 130°C, and use compressed air for cooling and temperature control to maintain the temperature uniformity of the battery pack within the annealing temperature at less than 5°C.

[0025] 3. A constant current source I with a value of 5A is applied to the series-connected battery pack. The current flows in from the P terminal of the PN junction of the battery and flows out from the N terminal of the PN junction.

[0026] 4. At the electric injection annealing temperature, maintain a constant current injection for 30 minutes.

[0027] Example 2

[0028] An electro-injection process for a heterojunction solar cell, comprising the following steps:

[0029] 1. Stack 400 M2 type heterojunction solar cells with a surface area of ​​156.75mm × 156.75mm in series, with the P-side facing the same direction;

[0030] 2. Heat the series-connected battery pack to the required temperature for electrical injection, such as 90°C, and use compressed air for cooling and temperature control while maintaining the battery pack; at this annealing temperature, maintain the temperature uniformity deviation within the battery pack to less than 5°C;

[0031] 3. A constant current source I with a value of 5A is applied to the series-connected battery pack. The current flows in from the P terminal of the PN junction of the battery and flows out from the N terminal of the PN junction.

[0032] 4. At the electric injection annealing temperature, maintain a constant current injection for 70 minutes.

[0033] Examples 1 and 2 compare the electro-injection treatment conditions under constant current 5A injection, relative high temperature of 130℃ for a short time of 30 minutes, and relative low temperature of 90℃ for a long time of 70 minutes. The experimental results are shown in Table 1. Table 1 shows that after electro-injection treatment, the average photoelectric conversion efficiency of the cells in Example 1 increased by 0.247%, the fill factor (FF) increased by 0.677%, and the open-circuit voltage increased by 1.7mV. In Example 2, the average photoelectric conversion efficiency of the cells increased by 0.281%, the fill factor (FF) increased by 0.714%, and the open-circuit voltage increased by 1.9mV.

[0034] Table 1. Comparison of electrical performance parameters of solar cells before and after electro-injection treatment using the technical solution of this invention.

[0035] project Isc / A Uoc / V FF / % Eff / % Pmpp / W Before electro-injection 0 0 0 0 0 Example 1 -0.007 0.0017 0.677 0.247 0.060 Example 2 0.004 0.0019 0.714 0.281 0.069

[0036] As a preferred option, the electro-injection current is 4.5-5.5A, the electro-injection temperature is 100-120℃, and the injection time is 40-60 minutes. For different coating processes, the electro-injection process parameters that can stably improve efficiency can be confirmed by interactive experiments.

[0037] In summary, this invention effectively enhances the passivation effect of hydrogen atoms on the recombination centers of the battery matrix by injecting charge carriers into the finished battery and simultaneously changing the quasi-Fermi level of electrons, thereby effectively improving the photoelectric conversion efficiency of the battery. It adopts a low-temperature electric injection process, with temperatures generally below 150°C, resulting in good internal temperature uniformity of the battery and an inter-cell temperature uniformity deviation of less than 5°C. The process time is short, and 1-600 battery cells can be stacked, resulting in high production capacity, low energy consumption, flexible injection methods, and low industrialization costs.

[0038] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electric injection process for N-type monocrystalline heterojunction solar cells, characterized in that: The process steps are as follows: A certain number of heterojunction solar cells are stacked in series with their P-sides facing the same direction. The solar cell is heated to the electro-injection annealing temperature and held at that temperature until the electro-injection is completed; A constant current source is applied to both ends of the series-stacked battery pack. The current flows in from the P-type end of the battery PN junction and flows out from the N-type end. Compressed air is used to cool the battery and maintain a constant temperature during current injection. The temperature uniformity deviation between battery cells is less than 5℃. At the electrical injection annealing temperature, a constant current source is injected for a certain duration; The electro-injection annealing temperature is 90℃—150℃; The current range of the constant current source is 4.5A–5.5A; The duration of the constant current source injection is 20 to 120 minutes.

2. The electric injection process for an N-type monocrystalline heterojunction solar cell according to claim 1, characterized in that: The thickness of the solar cells is 90-180μm, and the number of cells stacked is 1-600.

3. The electric injection process for an N-type monocrystalline heterojunction solar cell according to claim 1, characterized in that: The electro-injection annealing temperature is 100℃-120℃.

4. The electric injection process for an N-type monocrystalline heterojunction solar cell according to claim 1, characterized in that: The duration of the constant current source injection is 30 to 70 minutes.

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