Post-processing method for improving efficiency of battery piece

Abstract

The invention provides a post-processing method for the efficiency of a battery piece, and the method comprises the steps: selecting to apply a corresponding bias voltage to a substrate of the battery piece according to the electrical property of charges needing to be injected into a dielectric film of the battery piece; irradiating the dielectric film with laser, and injecting required charges into the dielectric film; and carrying out charge fixation. According to the method, effective passivation of the surface of the battery piece can be achieved, the method is simple and rapid, the charge polarity and the charge concentration can be flexibly adjusted, and the conversion efficiency of the battery piece can be remarkably improved.

Description

Technical Field

[0001] The invention relates to the field of solar cells, and in particular to a post-processing method for improving the efficiency of a solar cell. Background Art

[0002] With the improvement of crystalline silicon manufacturing technology, the carrier lifetime of the substrate silicon wafer is no longer the key factor restricting the improvement of battery efficiency. However, the influence of the passivation of the battery surface on the conversion efficiency is becoming more and more obvious. In order to reduce surface recombination and improve conversion efficiency, the passivation technology of photovoltaic crystalline silicon cells came into being, mainly including chemical passivation and field passivation.

[0003] At present, it is common to enhance the passivation effect by using film layers of different materials, such as silicon oxide, aluminum oxide, silicon nitride, etc., or a stacked structure. Among them, the fixed negative charge of the aluminum oxide film layer and the fixed positive charge of the silicon nitride film layer can play a field passivation role. However, these existing technologies still have some problems and limitations.

[0004] First, the conditions for generating fixed charges are relatively complex. Taking the fixed negative charge of aluminum oxide as an example, it usually requires an additional high-temperature annealing process to form, which increases the complexity and energy consumption of the process. Secondly, the polarity of the charge generated in the prior art is difficult to adjust, and the charge generation concentration cannot be directly adjusted. This fixed characteristic limits the optimization space of the passivation effect, and the passivation parameters cannot be flexibly adjusted according to different types of battery structures.

[0005] In addition, existing passivation methods often need to be performed in the early stages of battery manufacturing, and there may be compatibility issues with subsequent process steps (such as laser enhanced contact technology LECO). This limitation of the process sequence may affect the retention of the passivation effect or add additional process steps to maintain the passivation effect.

[0006] Finally, traditional surface passivation methods, such as hydrogen passivation, tend to lose effectiveness over time because hydrogen atoms easily detach from the silicon surface. This instability in passivation can greatly affect the long-term performance and reliability of solar cells.

[0007] These problems lead to the limitation of existing passivation technology in improving the efficiency of solar crystalline silicon cells, especially the challenge of further improving the efficiency of high-efficiency cells. Therefore, developing a passivation method that can flexibly adjust the charge characteristics, is easy to integrate into existing production lines, and has long-term stability has become an important topic in the current field of solar cell manufacturing technology. Summary of the invention

[0008] The purpose of the present invention is to provide a post-processing method for improving the efficiency of a battery cell, so as to solve the problem that the fixed charge passivation mechanism in the prior art has a poor effect.

[0009] To achieve the above object, the present invention proposes a post-processing method for improving the efficiency of a cell, comprising the following steps:

[0010] According to the electrical properties of the charge to be injected into the dielectric film of the cell, a corresponding bias voltage is applied to the substrate of the cell;

[0011] irradiating the dielectric film with laser to inject desired charges into the dielectric film;

[0012] Charge fixation.

[0013] Furthermore, when negative charge needs to be injected, a positive bias voltage is applied to the wafer stage of the battery cell; when positive charge needs to be injected, a negative bias voltage is applied to the wafer stage of the battery cell.

[0014] Furthermore, the bias voltage ranges from 5V to 30V.

[0015] Furthermore, the laser irradiation is performed by using pulsed laser.

[0016] Specifically, the power of the laser is 20-500W.

[0017] Furthermore, the laser irradiation comprises a plurality of cycles, each cycle comprising a laser irradiation step and a laser off step. Specifically, the number of cycles of the laser irradiation is 10-50 times, the laser irradiation time in the laser irradiation step is 1-3 seconds, and the laser off time in the laser irradiation step is 0.5-1 second.

[0018] Furthermore, the post-processing method for improving the efficiency of the battery cell further includes subjecting the battery cell to a laser enhanced contact process before irradiating the dielectric film with a laser.

[0019] Furthermore, the post-processing method for improving the efficiency of the cell also includes forming a barrier layer between the substrate and the dielectric film before irradiating the dielectric film with a laser. Specifically, the step of forming the barrier layer includes forming a silicon oxide layer or an aluminum oxide layer between the substrate and the dielectric film of the cell.

[0020] Compared with the prior art, the post-processing method for improving the efficiency of solar crystalline silicon cells provided by the present invention has at least the following beneficial effects:

[0021] According to the electrical properties of the charge to be injected into the dielectric film of the cell, a corresponding bias voltage is applied to the substrate of the cell; the dielectric film is irradiated with a laser to inject the required charge into it; and the charge is fixed. This method can effectively passivate the surface of the cell. In addition, this method is simple and fast, and can flexibly adjust the charge polarity and charge concentration, which can significantly improve the conversion efficiency of the cell.

[0022] In addition, the method of the present invention is to fix the charge of the dielectric film after LECO, and combined with the setting of the bias voltage of the wafer stage and the optimization of the laser irradiation parameters, the effect and stability of fixed charge injection can be further improved. The combination of these technical features can not only enhance the performance of the battery cell, but also improve production efficiency and reduce manufacturing costs, providing a new technical solution for the large-scale production of solar cells.

[0023] The method of the present invention can be directly carried out after the existing LECO process, requiring little modification of the existing equipment, and the process can be perfectly integrated without adding more costs. The technology is perfectly compatible and only requires fine-tuning of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the overall process in one embodiment of the present invention;

[0025] Figure 2 It is a schematic diagram of the actual operation of an embodiment of the present invention.

[0026] In the figure, 1, dielectric film; 2, barrier layer; 3, substrate; 4, wafer stage. DETAILED DESCRIPTION

[0027] A post-processing method for improving the efficiency of a cell of the present invention will be described in more detail below in conjunction with the accompanying drawings, wherein preferred embodiments of the present invention are shown. It should be understood that those skilled in the art may modify the present invention described herein while still achieving the beneficial effects of the present invention. Therefore, the following description should be understood as being widely known to those skilled in the art and not as a limitation of the present invention.

[0028] In the description of this specification, "one embodiment" or "some embodiments" etc. means that one or more embodiments of this specification include a specific feature, structure or characteristic described in conjunction with the embodiment. Therefore, the phrases "in one embodiment", "in some embodiments", "in some other embodiments", "in some other embodiments", etc. appearing in different places in this specification do not necessarily refer to the same embodiment, but mean "one or more but not all embodiments", unless otherwise specifically emphasized in other ways.

[0029] The present invention is described in more detail by way of example in the following paragraphs. Advantages and features of the present invention will become more apparent from the following description.

[0030] Please refer to Figure 1 The present invention provides a post-processing method for improving the efficiency of a battery cell, comprising the following steps:

[0031] According to the electrical properties of the charge to be injected into the dielectric film 1 of the cell, a corresponding bias voltage is applied to the substrate 3 of the cell; the dielectric film 1 is irradiated with a laser to inject the required charge therein; and the charge is fixed.

[0032] The technical solution of the present invention is described in detail below in conjunction with specific embodiments.

[0033] In a specific embodiment, if Figure 2 As shown, the post-processing method for injecting fixed charges into the dielectric film 1 on the surface of the cell is to apply a corresponding bias voltage to the wafer stage 4 and then irradiate the cell with a laser to achieve the required charge injection.

[0034] The cell mentioned in this embodiment can be a conventional crystalline silicon solar cell, on the surface of which a dielectric film 1 has been deposited. The dielectric film 1 can be a silicon nitride film or other commonly used passivation film, and its preparation method belongs to the conventional means of those skilled in the art, which will not be described here.

[0035] It is worth noting that the selection of the dielectric film 1 has an important influence on the injection effect of the fixed charge. For example, aluminum oxide films usually have a higher negative fixed charge density, while silicon nitride films usually have a positive fixed charge. In this embodiment, a suitable dielectric film 1 material can be selected according to the specific structure of the battery cell and the required passivation effect. For example, for a battery cell with a P-type substrate 3, an aluminum oxide film is more likely to be selected. At this time, it is necessary to inject negative charges into the dielectric film 1 on the surface of the substrate 3. The injection of negative charges can also effectively block the minority carriers (electrons) in the P-type substrate 3 from reaching the surface of the substrate 3, thereby reducing surface recombination, increasing the minority carrier lifetime, and thus improving the efficiency of the battery cell.

[0036] When applying a bias voltage to the substrate 3 of the cell, the bias voltage is selected according to the electrical properties of the charge to be injected. In this embodiment, the cell is placed on the wafer stage 4, and applying a bias voltage to the substrate 3 can be achieved by simply applying a corresponding bias voltage to the wafer stage 4.

[0037] Specifically, when negative charge needs to be injected, a positive bias voltage can be applied to the wafer stage 4; when positive charge needs to be injected, a negative bias voltage can be applied to the wafer stage 4. The bias voltage range is 5-30V, preferably, it can be set to 10-20V, for example, 15V. The above bias voltage range can ensure that there is sufficient electric field strength to drive the injection of charge without causing damage to the battery cell.

[0038] Furthermore, the bias voltage value can be fine-tuned according to the specific conditions of the cell. For example, for a thicker dielectric film 1, a slightly higher bias voltage may be required to ensure sufficient electric field strength; while for a thinner dielectric film 1, a lower bias voltage may be used to avoid breakdown. In actual operation, the optimal bias voltage value can also be determined through a series of experiments to achieve the best charge injection effect.

[0039] While applying the bias voltage, the surface of the dielectric film 1 is laser irradiated to inject charges therein. The laser power used for the laser irradiation is 20-500W, preferably, it can be set to 100-300W, for example, 200W. Laser irradiation can excite the generation of electron-hole pairs inside the cell, and under the action of the bias voltage electric field, the carriers will be separated and injected into the dielectric film 1, so that the required charges are retained in the dielectric film 1.

[0040] The wavelength selection of the laser irradiation is also an important consideration. Generally, a wavelength that can be effectively absorbed by silicon can be selected, such as a near-infrared laser of 1064 nm. Lasers of this wavelength can penetrate the dielectric film 1 and generate electron-hole pairs in the silicon substrate 3. At the same time, the penetration depth of the laser also needs to be considered to ensure that the generated carriers can be effectively driven into the dielectric film 1 by the electric field.

[0041] In this embodiment, the laser irradiation is performed by pulsed laser irradiation. The laser irradiation includes multiple cycles, and each cycle includes laser irradiation including a laser irradiation step and a laser shut-off step. Specifically, the number of cycles of the laser irradiation is 10-50 times, and preferably, it can be set to 20-30 times. The laser irradiation time in the laser irradiation step is 1-3 seconds, and the laser shut-off time in the laser shut-off step is 0.5-1 second. This pulsed laser irradiation can avoid overheating of the battery cell and improve the efficiency of charge injection.

[0042] Furthermore, the parameters of laser irradiation can be adjusted according to the thermal characteristics of the cell and the required charge injection amount. For example, for heat-sensitive cells, the number of cycles can be increased, but the time and power of each irradiation can be reduced; while for situations where a large amount of charge injection is required, the irradiation time or power can be appropriately increased. This flexible adjustment can make the post-processing method of this embodiment applicable to cells of various types and structures.

[0043] Before the fixed charge injection step, the cell is subjected to a laser enhanced contact (LECO) process. The LECO process can improve the contact characteristics of the cell and further improve the cell efficiency. The specific parameters of the LECO process can be adjusted according to the specific conditions of the cell, which is a common method used by those skilled in the art and will not be described in detail here.

[0044] It is worth noting that the LECO process can be well combined with the post-processing method proposed in this embodiment. The LECO process forms a good ohmic contact and reduces the contact resistance by locally melting the silicon and metal contact layers. The post-processing method proposed in this embodiment mainly acts on the non-metallic contact area of ​​the cell to improve the surface passivation effect. The two processes are perfectly compatible in technology, and the combination of the two can comprehensively improve the performance of the cell.

[0045] In addition, before injecting the charge, a barrier layer 2 may be formed between the substrate 3 of the cell and the dielectric film 1. The barrier layer 2 may be a silicon oxide layer or an aluminum oxide layer. Specifically, a silicon oxide layer with a thickness of 1-10 nm may be grown on the surface of the silicon substrate 3 by thermal oxidation, or an aluminum oxide layer with a thickness of 5-20 nm may be deposited by atomic layer deposition (ALD). The barrier layer 2 may prevent the injected charge from being lost to the substrate 3, thereby avoiding the loss of the charge in the dielectric film 1 and ensuring the long-term stability of the field passivation.

[0046] The formation process of the barrier layer 2 requires special attention. For the silicon oxide layer, dry oxygen oxidation or wet oxygen oxidation is usually used. Dry oxygen oxidation can be carried out at a temperature of 900-1100°C, and the oxidation time is adjusted according to the required oxide layer thickness, usually ranging from a few minutes to tens of minutes. Wet oxygen oxidation can be carried out at a lower temperature (such as 800-900°C), and the oxidation speed is faster, but the quality of the oxide layer formed may be slightly lower than that of dry oxygen oxidation.

[0047] For the aluminum oxide layer, atomic layer deposition (ALD) is an ideal choice. ALD can be performed at relatively low temperatures (such as 200-300°C) and can deposit about 0.1nm of aluminum oxide per cycle. Therefore, to form a 5-20nm aluminum oxide layer, 50-200 ALD cycles are required. The advantage of ALD is that it can form a very uniform and dense film, which is very important for blocking charge loss.

[0048] The thickness control of barrier layer 2 is also a key factor. If barrier layer 2 is too thin, it may not effectively prevent charge loss; if it is too thick, it may affect other properties of the battery cell. Therefore, it is necessary to determine the optimal thickness of barrier layer 2 through experiments to strike a balance between charge stability and battery performance.

[0049] The post-processing method of this embodiment can be flexibly applied to different types of crystalline silicon solar cells. For example, for cells with a P-type substrate 3, negative charges can be injected to achieve field passivation; for cells with an N-type substrate 3, positive charges can be injected. The type and amount of injected charges can also be precisely controlled by adjusting the polarity and magnitude of the bias voltage and the parameters of the laser irradiation, thereby optimizing the passivation effect of the cell.

[0050] It is worth noting that the amount of charge injection also needs to be carefully controlled. Too little charge may not provide sufficient field passivation effect, while too much charge may lead to the formation of an inversion layer, which in turn increases surface recombination. Therefore, it is necessary to precisely control the amount of injected charge by adjusting the bias voltage and laser irradiation parameters.

[0051] In actual operation, the effect of charge injection can be evaluated by measuring the open circuit voltage (Voc), short circuit current density (Jsc) and fill factor (FF) of the cell. Generally, successful charge injection will lead to a significant increase in Voc, while Jsc will also increase. If Voc is found to increase but Jsc decreases, it may mean that too much charge is injected and needs to be reduced appropriately.

[0052] Another advantage of the method of the present invention is its controllability and repeatability. Since the charge injection process is controlled by externally applied bias voltage and laser irradiation, the processing parameters can be easily adjusted and optimized to suit different battery structures and materials. This flexibility makes the method adaptable to new battery technologies that may emerge in the future.

[0053] In industrial production, the method of the present invention can be easily integrated into existing battery production lines. For example, a charge injection station including a bias voltage power supply and a laser system can be added after the PECVD deposition of the dielectric film 1. The entire process can be completed in tens of seconds without significantly increasing the production time. In addition, since the method does not require high temperature treatment or complex chemical processes, it has low energy consumption, is environmentally friendly, and conforms to the sustainable development concept of the modern solar energy industry.

[0054] The post-processing method provided in this embodiment has significant technical effects. First, the method can be carried out in the final stage of battery cell preparation, is simple to operate, and is easy to integrate into existing production lines. Second, through the combination of bias voltage and laser irradiation, fast and efficient fixed charge injection can be achieved, and the entire processing process can be completed within tens of seconds, greatly improving production efficiency. In addition, the method can accurately control the type and amount of injected charge, making the passivation effect more excellent.

[0055] More importantly, the effect of the method of this embodiment has long-term stability. Traditional surface passivation methods, such as hydrogen passivation, tend to weaken over time because hydrogen atoms are easily detached from the silicon surface. The method of this embodiment injects fixed charges, which are not easily lost due to the presence of the barrier layer 2, so the passivation effect can be maintained for a long time.

[0056] The barrier layer 2 used in the method of this embodiment can not only prevent the loss of injected charge, but also provide additional chemical passivation effect. For example, the silicon oxide layer can effectively passivate the dangling bonds on the silicon surface, while the aluminum oxide layer or the silicon oxide layer can provide additional negative fixed charges. This dual passivation effect (chemical passivation and field passivation) can further improve the performance of the cell.

[0057] In addition, another advantage of the method of this embodiment is its adjustability. By changing the bias voltage and laser irradiation parameters, the amount and distribution of injected charges can be precisely controlled. This flexibility allows the method to adapt to different types of battery structures and materials, and even achieve different passivation effects in different areas of the same battery. For example, different types or amounts of charges can be injected into the front and back of the battery to optimize the overall performance.

[0058] Finally, the method of this embodiment also has a potential cost advantage. Since the method can be fine-tuned and implemented on existing LECO (laser enhanced contact) equipment, no additional new equipment is needed, which further reduces the implementation cost.

[0059] A key advantage of the method of this embodiment is its perfect compatibility with existing LECO technology. After the LECO process, the fixed charge injection process of the present invention can be directly carried out, and only the parameters such as laser power and frequency need to be fine-tuned. This integrated processing method not only simplifies the production process, but also makes full use of existing equipment and improves production efficiency.

[0060] In summary, the post-processing method for improving the efficiency of solar crystalline silicon cells provided by the present invention combines bias voltage and laser irradiation to inject fixed charges into the dielectric film on the surface of the cell, thereby achieving effective passivation of the cell surface. This method is simple and fast, can flexibly adjust the charge polarity and charge concentration, and can significantly improve the conversion efficiency of the cell.

[0061] In addition, the method of the present invention is to fix the charge of the dielectric film after LECO, and combined with the setting of the bias voltage of the wafer stage and the optimization of the laser irradiation parameters, the effect and stability of fixed charge injection can be further improved. The combination of these technical features can not only enhance the performance of the battery cell, but also improve production efficiency and reduce manufacturing costs, providing a new technical solution for the large-scale production of solar cells.

[0062] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A post-processing method for improving the efficiency of a cell, characterized in that: The following steps are involved: According to the electrical properties of the charge to be injected into the dielectric film of the cell, a corresponding bias voltage is applied to the substrate of the cell; irradiating the dielectric film with laser to inject desired charges into the dielectric film; Charge fixation.

2. The post-processing method for improving the efficiency of a battery cell according to claim 1, characterized in that: When negative charge needs to be injected, a positive bias voltage is applied to the wafer stage of the battery cell; when positive charge needs to be injected, a negative bias voltage is applied to the wafer stage of the battery cell.

3. The post-processing method for improving the efficiency of a battery cell according to claim 1 or 2, characterized in that: The bias voltage ranges from 5V to 30V.

4. The post-processing method for improving the efficiency of a battery cell according to claim 1, characterized in that: The laser irradiation is performed by using a pulsed laser.

5. The post-processing method for improving the efficiency of a battery cell according to claim 1 or 4, characterized in that: The power of the laser irradiation is 20-500W.

6. The post-processing method for improving the efficiency of a battery cell according to claim 1 or 4, characterized in that: The laser irradiation comprises a plurality of cycles, and each cycle comprises a laser irradiation step and a laser off step.

7. The post-processing method for improving the efficiency of a battery cell according to claim 6, characterized in that: The number of cycles of the laser irradiation is 10-50 times.

8. The post-processing method for improving the efficiency of a battery cell according to claim 6, characterized in that: The laser irradiation time in the laser irradiation step is 1-3 seconds; the laser off time in the laser off step is 0.5-1 second.

9. The post-processing method for improving the efficiency of a battery cell according to claim 1, characterized in that: Before the dielectric film is irradiated with laser, the cell is subjected to laser enhanced contact process.

10. The post-processing method for improving the efficiency of a battery cell according to claim 1, characterized in that: Before irradiating the dielectric film with laser, a barrier layer is formed between the substrate and the dielectric film.

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