Microwave annealing passivation treatment method for photovoltaic cell

Abstract

The invention discloses a microwave annealing and passivating treatment method for a photovoltaic cell, which comprises the following steps of: placing the pretreated photovoltaic cell in a microwave oven cavity, heating the cell to 350-550 DEG C in a microwave field with the frequency of 0.5-5GHz and the power of 0.5-4kW, and keeping the temperature for at least 1 minute; and taking out the photovoltaic cell, cooling to room temperature, detecting and packaging. The microwave annealing technology is used, efficient hydrogen passivation and defect repair can be achieved, hydrogen atom migration is activated at the low temperature within the low time, grain boundary and dislocation defects are rapidly filled, and carrier recombination is reduced.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaic cells, and specifically to a microwave annealing passivation treatment method for photovoltaic cells. Background Art

[0002] The passivation technology of photovoltaic cells is the core link to improve the photoelectric conversion efficiency, but the existing methods have significant limitations. Traditional chemical passivation relies on a large amount of chemical reagents (such as TMA, ozone), resulting in high costs and environmental pollution; plasma enhanced chemical vapor deposition (PECVD) can achieve hydrogen passivation, but the equipment is complex and the maintenance cost is high. Thermal oxidation passivation requires high-temperature treatment (such as 500 - 600 °C), with high energy consumption and easy to cause thermal damage to the materials. In addition, traditional heating methods (such as hot plates or diffusion furnaces) have temperature gradient problems, resulting in uneven passivation layers and affecting the carrier lifetime.

[0003] In recent years, although low-temperature passivation processes can partially improve the efficiency, their passivation effects are limited by the insufficient migration of hydrogen atoms and have limited ability to repair deep defects. Photo-injection passivation does not require high temperature, but requires complex equipment and a long processing time, making it difficult to scale up. Although hydrogen passivation has been proven to significantly improve the battery performance, it relies on high-temperature annealing (500 - 600 °C) or long-time plasma treatment (several hours), with high energy consumption and the risk of defect regeneration.

[0004] Therefore, there is an urgent need for an efficient, uniform and environmentally friendly passivation technology to solve the bottlenecks of traditional methods in terms of energy consumption, uniformity and material compatibility. Summary of the Invention

[0005] In view of this, the present invention provides a microwave annealing passivation treatment method for photovoltaic cells to solve the problems raised in the above background art.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] On the one hand, the present invention discloses a microwave annealing passivation treatment method for photovoltaic cells, including the following steps:

[0008] S1. Place the pretreated photovoltaic cell in the microwave oven cavity, and use a microwave field with a frequency of 0.5 - 5 GHz and a power of 0.5 - 4 kW to heat the cell to 350 - 550 °C, and maintain it at this temperature for at least 1 minute;

[0009] S2. Take out the photovoltaic cell, cool it to room temperature and detect and package it.

[0010] As a further scheme of the present invention: in step S1, the pretreatment is: perform surface purging on the photovoltaic cell that has completed the coating process to remove impurities.

[0011] As a further solution of the present invention: in step S1, the heating rate is 10-50 °C / second, and the temperature uniformity deviation ≤ ±5 °C

[0012] As a further solution of the present invention: the frequency of the microwave field is 2.45-3 GHz, the power is 2-3 kW, the temperature is 400-500 °C, and the heat preservation time is 2-5 minutes.

[0013] As a further solution of the present invention: the photovoltaic cells are laid flat in a single layer or stacked in multiple layers at intervals in the microwave oven cavity, and the distance between adjacent cells is 2.5-3.5 mm of the cell thickness.

[0014] As a further solution of the present invention: the photovoltaic cell is any one of TOPCon, BC, HJT or perovskite photovoltaic cells.

[0015] In the second aspect, the present invention discloses a photovoltaic cell obtained by the microwave annealing passivation treatment method of the above photovoltaic cell.

[0016] The hydrogen atoms come from the residual hydrogen element in the battery preparation process. The microwave field excites the carriers to accelerate the directional migration of hydrogen atoms, forming Si-H or metal-hydrogen bonding structures. Under the action of the microwave field, the hydrogen atoms inside the battery migrate to the defect sites to form a hydride passivation layer, inhibiting carrier recombination.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] 1. The microwave heating annealing technology can achieve efficient hydrogen passivation and defect repair, activate the migration of hydrogen atoms at a lower temperature and time, enable them to quickly fill grain boundary and dislocation defects, and reduce carrier recombination.

[0019] 2. The microwave field acts directly on the interior of the material, eliminating the temperature gradient and ensuring the uniformity of the passivation layer. Compared with PECVD (requiring multi-layer deposition), this process can form a dense passivation layer in a single treatment, and the passivation layer has good uniformity.

[0020] 3. The present invention uses microwave annealing, with the energy consumption only being 30% of that of traditional heat treatment, and no chemical reagents are required, reducing carbon emissions and pollution risks. This process is compatible with single-crystalline silicon, polycrystalline silicon and thin-film batteries, and can be extended to the preparation of the tunneling oxide layer of TOPCon batteries, with strong versatility.

[0021] 4. By optimizing the microwave power (0.5-4 kW) and frequency (0.5-5 GHz), defect regeneration during high-temperature treatment is reduced. Description of the Drawings

[0022] Figure 1 It is the photoluminescence image at different stages during the microwave annealing of the battery in Example 1;

[0023] Figure 2 The relationship curves of the surface load current and carrier lifetime with the microwave annealing time in Example 1;

[0024] Figure 3 The relationship curves of the effective carrier lifetime and open circuit voltage with the microwave annealing time in Example 1;

[0025] Figure 4 The relationship curves of the surface load current and carrier lifetime with the traditional tube annealing time in the comparative example. Detailed implementation manners

[0026] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below in conjunction with specific embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the disclosure of the present invention more thorough and comprehensive.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0028] Example 1

[0029] This example discloses a microwave passivation treatment method for monocrystalline silicon cells. An N-type monocrystalline silicon photovoltaic cell (size 156×156 mm) is used, and the step method is as follows:

[0030] (1) Pretreatment: Blow the surface of the cell with 99.99% high-purity nitrogen to remove particulate contaminants.

[0031] (2) Microwave heating: Place the cell horizontally in a single layer in a microwave oven, with the cell surface 30 cm away from the microwave source; start the microwave generator, the frequency of the microwave field is 2.45 GHz, the power is 3 kW, and the temperature is raised to 450 °C within 5 seconds (calibrated by an infrared thermometer), and keep the temperature constant for 5 minutes. During this period, the power is dynamically adjusted through a closed-loop system (fluctuation < 5%).

[0032] (3) Cooling: Take out the cell and let it cool naturally to room temperature (about 10 minutes).

[0033] Record the photoluminescence of the cell at each time point during microwave heating. The results are shown in Figure 1 ; Figure 1 The light gray to dark black area in indicates the increase in passivation degree. At different microwave annealing times (1–6 min), the PL images of the AlOx layer polycrystalline silicon contact cells show that with the increase of the microwave annealing time, the passivation effect gradually improves, and the cell shows a uniform passivation effect after annealing for 4 minutes.

[0034] Figure 2 The left figure shows the curve of the surface load current of different dielectric layer solar cells varying with the microwave time during microwave annealing, and Figure 2 The right figure shows the carrier lifetime of SiNy-structured solar cells at different microwave heating time points; it can be seen that after 1 minute of microwave annealing, the J0 of SiNy and AlOx / SiNy solar cells decreases significantly, indicating that the surface passivation effect has been greatly improved. The SiNy-structured solar cells exhibit the best carrier lifetime after 1 minute, and the lifetime of the AlOx-structured solar cells also increases.

[0035] Figure 3 The left figure shows the curve of the effective carrier lifetime varying with the microwave annealing time, and, Figure 3 The right figure shows the curve of the open-circuit voltage varying with the microwave annealing time. It can be seen that as the annealing time increases, the lifetime gradually increases and reaches saturation at 4 minutes. The surface recombination current J0 and the implied open-circuit voltage (iVoc) also improve with the increase of the annealing time and tend to be stable after 4 minutes, indicating that microwave annealing can effectively improve the surface passivation effect of solar cells.

[0036] Example 2

[0037] This example discloses a method for microwave passivation treatment of polycrystalline silicon solar cells. Polycrystalline silicon solar cells (size 156×156 mm) are used, and the step method is as follows:

[0038] (1) Pretreatment: Blow the surface of the solar cells with 99.99% high-purity nitrogen to remove particulate contaminants.

[0039] (2) Microwave heating: Stack 10 solar cells in the microwave oven with a layer spacing of 3 mm; start the microwave generator, the frequency of the microwave field is 5 GHz, the power is 4 kW, and the temperature is raised to 400 °C within 5 seconds (calibrated by an infrared thermometer), and keep the temperature constant for 8 minutes. During this period, the power is dynamically adjusted through a closed-loop system (fluctuation < 5%).

[0040] (3) Cooling: Take out the solar cells and let them cool naturally to room temperature.

[0041] Example 3

[0042] This example discloses a method for microwave passivation treatment of thin-film solar cells. Perovskite thin-film solar cells (flexible substrate, size 156×156 mm) are used, and the step method is as follows:

[0043] (1) Pretreatment: Blow the surface of the solar cells with 99.99% high-purity nitrogen to remove particulate contaminants.

[0044] (2) Microwave heating: Place the battery horizontally in a single layer in a microwave oven, with the battery surface 25 cm away from the microwave source; Start the microwave generator, with the frequency of the microwave field being 0.5 GHz and the power being 0.8 kW, heat up to 350 °C within 5 seconds (calibrated by an infrared thermometer), maintain a constant temperature for 2 minutes, and dynamically adjust the power through a closed-loop system during this period (fluctuation < 5%).

[0045] (3) Cooling: Take out the battery and let it cool naturally to room temperature.

[0046] Comparative example

[0047] This comparative example discloses a method for microwave passivation treatment of monocrystalline silicon cells. An N-type monocrystalline silicon photovoltaic cell (size 156 × 156 mm) is used, and the step method is as follows:

[0048] (1) Pretreatment: Blow the surface of the battery with 99.99% high-purity nitrogen to remove particulate contaminants.

[0049] (2) Tube furnace heating: Place the battery horizontally in a single layer in a tube furnace, with the battery surface 30 cm away from the heat source, thermally oxidize at 850 °C in the tube furnace for 30 minutes, and introduce oxygen during this period.

[0050] (3) Cooling: Take out the battery and let it cool naturally to room temperature (about 10 minutes).

[0051] Figure 4 Shows the relationship between the surface load current and the carrier lifetime and the tube annealing time in this embodiment; The left figure shows the change trend of the surface recombination current J0 after different traditional annealing times. The cell with an AlOx layer shows the best surface passivation effect at 20 minutes, while the SiNy and AlOx / SiNy cells are slightly inferior. In the right figure, for the effective carrier lifetime, the cell with an SiNy layer only reaches an effect close to microwave annealing after 30 minutes of traditional annealing.

[0052] Although this specification is described according to the implementation manners, not every implementation manner only contains an independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other implementation manners that can be understood by those skilled in the art.

[0053] Therefore, the above-mentioned are only the preferred embodiments of this application, and are not used to limit the scope of implementation of this application; that is, all equivalent transformations made according to the scope of the claims of this application are within the protection scope of the claims of this application.

Claims

1. A microwave annealing passivation treatment method for a photovoltaic cell, characterized in that, The following steps are involved: S1. Place the pretreated photovoltaic cell in a microwave oven cavity, heat the cell to 350-550°C using a microwave field with a frequency of 0.5-5 GHz and a power of 0.5-4 kW, and maintain the temperature for at least 1 minute. S2. Take out the photovoltaic cell, cool it to room temperature, and inspect the package.

2. The microwave annealing passivation treatment method for a photovoltaic cell according to claim 1, wherein In step S1, the pretreatment is: cleaning the surface of the photovoltaic cell that has completed the coating process to remove impurities.

3. The microwave annealing passivation treatment method for a photovoltaic cell according to claim 1, characterized in that, In step S1, the heating rate is 10-50°C / second, and the temperature uniformity deviation is ≤±5°C.

4. The microwave annealing passivation treatment method for a photovoltaic cell according to claim 1, wherein, The frequency of the microwave field is 2.45-3 GHz, the power is 2-3 kW, the temperature is 400-500° C., and the holding time is 2-5 minutes.

5. The microwave annealing passivation treatment method for a photovoltaic cell according to claim 1, characterized in that, The photovoltaic cells are laid flat in a single layer or stacked in multiple layers in the microwave oven cavity, with the distance between adjacent cells being 2.5-3.5 mm of the cell thickness.

6. The microwave annealing passivation treatment method for a photovoltaic cell according to claim 1, characterized in that, The photovoltaic cell is any one of a TOPCon cell, a BC cell, a HJT cell or a perovskite photovoltaic cell.

7. A photovoltaic cell obtained by the microwave annealing passivation treatment method for a photovoltaic cell according to any one of claims 1 to 6.

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