Sintering and light injection integrated processing method for back contact solar cell

Abstract

The invention relates to the technical field of crystalline silicon solar cell manufacturing, in particular to a back contact solar cell sintering and light injection integrated processing method, which is carried out in a sintering and light injection integrated furnace and comprises the following steps of: S1) sintering: transmitting a cell printed with metal slurry to pass through a sintering area with temperature gradient, performing drying and high-temperature sintering to enable the metal slurry and a silicon substrate of the battery piece to form ohmic contact; wherein in the section where the organic matter is intensively decomposed in the sintering area, the strength of the sweeping airflow higher than the strength of the inlet and the strength of the sweeping airflow at the outlet are applied, so that decomposition products are effectively discharged; s2) performing light injection: heating the sintered battery piece obtained in the step S1) in a light injection heating area, and then performing illumination in a light injection heat preservation area; in the light injection heat preservation area, the supply flow of compressed air is kept to be zero or close to zero; and S3) cooling: transmitting the battery piece subjected to light injection in the step S2) to pass through a light injection cooling area, and cooling at the rotating speed of a fan less than or equal to 180 rpm. The method has the advantages that the hydrogen passivation effect can be remarkably improved, and the photoelectric conversion efficiency of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of crystalline silicon solar cell manufacturing technology, and in particular to an integrated method for sintering and light injection of back-contact solar cells. Background Technology

[0002] Back-contact solar cells have become an important development direction for high-performance crystalline silicon solar cells due to their advantages such as no grid lines obstructing the front side and high efficiency. In the manufacturing process of back-contact cells, a metal paste is typically screen-printed and then sintered to form the back electrode. Subsequently, light injection is performed, using high temperature and light to increase carrier concentration and passivate defects within the silicon wafer.

[0003] To further improve the passivation effect and UV degradation resistance of batteries, the industry often employs high-hydrogen processes in the passivation layer (such as the alumina layer). However, high-hydrogen processes result in a high hydrogen content in the film layer. During the subsequent high-temperature sintering and photo-implantation processes, some hydrogen ions will escape too quickly, which not only reduces the passivation effect but may also damage the outer silicon nitride passivation film, leading to "film bursting." In addition, existing sintering-photo-implantation processes also have the following problems: First, if the organic components in the metal paste cannot be completely removed during sintering, they will remain in the furnace cavity, contaminating the battery cells, affecting the grid line contact quality, and leading to poor sintering and reduced efficiency; second, during the heating stage of photo-implantation, hydrogen atoms may be excited prematurely and cannot effectively migrate to silicon lattice defects for passivation, resulting in low hydrogen utilization.

[0004] The aforementioned issues collectively affect key performance parameters such as the fill factor and series resistance of the battery, ultimately limiting the improvement of the conversion efficiency of back-contact solar cells. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide an integrated processing method for sintering and light injection of back contact solar cells. This method can ensure the efficient and directional discharge of organic matter in the complex slurry on the back of the back contact cell, avoiding cross-contamination. By shutting off the compressed air in the light injection area, a stable thermal environment is created, which allows hydrogen atoms to be effectively activated by strong light and migrate to the defect area around the back finger electrode for efficient passivation. This significantly reduces the series resistance and increases the parallel resistance, thereby greatly improving the fill factor and photoelectric conversion efficiency.

[0006] This invention is achieved through the following technical solution: On one hand, it provides an integrated sintering and light injection method for back-contact solar cells, which is carried out in a sintering-light injection integrated furnace and includes the following steps: Step S1) Sintering The solar cells printed with metal paste are conveyed through a sintering zone with a temperature gradient for drying and high-temperature sintering, so that the metal paste forms an ohmic contact with the silicon substrate of the solar cells; wherein, in the section of the sintering zone where organic matter is concentrated and decomposed, a purge airflow intensity higher than that at its inlet and outlet is applied to effectively remove the decomposition products. Step S2) Light Injection The sintered solar cell obtained in step S1) is heated in the light injection heating zone and then irradiated in the light injection heat preservation zone; in the light injection heat preservation zone, the supply flow rate of compressed air is maintained at zero or close to zero. Step S3) Cooling The solar cell obtained after light injection in step S2) is conveyed through the light injection cooling zone and cooled by a fan speed of ≤180 rpm.

[0007] Furthermore, the sintering zone sequentially includes a drying zone and a sintering zone; the temperature of the drying zone is 50-250℃; and the peak temperature of the sintering zone is 600-860℃.

[0008] Furthermore, within the sintering zone, the heating rate of the solar cell from 500°C to the peak temperature is controlled between 80°C / s and 150°C / s.

[0009] Furthermore, the process of applying a purge gas flow rate higher than that at its inlet and outlet is as follows: in the sintering zone, the purge gas flow rate for discharging organic matter is 100-400 m³ / h, while the purge gas flow rate in its inlet and outlet areas is 50-150 m³ / h.

[0010] Furthermore, the purging gas flow is compressed air, with a flow rate of 30-80 L / min in the sintering zone and a flow rate of 10-40 L / min in its inlet and outlet regions.

[0011] Furthermore, in step S2), the light injection insulation zone is divided into multiple independently controlled illumination units, and the light irradiance of each illumination unit is independently controlled at 20-40 solar constants.

[0012] Preferably, in step S1), the metal paste is silver paste.

[0013] Preferably, the back contact cell is an IBC cell, the structure of which includes: a silicon substrate, and alternating p-type doped regions and n-type doped regions formed on the back side of the substrate, wherein a hydrogen passivation layer is covered on the doped regions, and the p-type electrode and the n-type electrode respectively pass through the hydrogen passivation layer to form ohmic contacts with the corresponding doped regions.

[0014] Beneficial effects This invention implements a differentiated exhaust strategy in the sintering zone, increasing the organic exhaust flow rate in the middle section to 100-400 m³. 3 The flow rate of the exhaust gas in this area is increased to 30-80 L / min, while the flow rates at the inlet and outlet are reduced, resulting in a distribution that is "strong in the middle and weak at both ends". This directional and gradient exhaust layout effectively guides the concentrated discharge of organic decomposition products, significantly reduces furnace contamination and process fluctuations, and ensures uniformity of metal contact.

[0015] This invention increases the heating rate of the solar cell from 500°C to the peak temperature in the sintering region to ≥80°C / s. This extremely high heating rate shortens the high-temperature process and suppresses premature hydrogen escape from the hydrogen passivation layer. In a light-injection environment without airflow interference, strong light irradiation precisely activates hydrogen atoms, promoting their directional migration to grain boundaries and defects to form stable Si-H bonds, achieving efficient bulk and surface passivation. Photogenerated carriers form a favorable concentration gradient under high-intensity light irradiation, further optimizing carrier collection and transport paths.

[0016] Therefore, the process of this invention significantly improves the hydrogen passivation effect and photoelectric conversion efficiency of back-contact solar cells. Attached Figure Description

[0017] Figure 1 This is a process flow diagram illustrating the integrated sintering and light injection method for back-contact solar cells in this invention. Figure 2 This is a schematic diagram illustrating the back-contact solar cell structure of the present invention; Figure 3 This is a simplified schematic diagram illustrating the integrated sintering and photoinjection equipment of the present invention, showing the various functional areas of the equipment and its key control components.

[0018] In the diagram: 1-Silicon substrate; 2-Tunneling oxide layer; 3-Polycrystalline silicon layer; 4-Alumina passivation layer; 5-Silicon nitride passivation layer; 6-Silver electrode; 7-Compressed air flow rate in the light injection heating zone; 8-Compressed air flow rate in the heat preservation zone; 9-Cooling fan in the light injection cooling zone; 10-Waste air flow rate at the inlet of the drying zone; 11-Waste air flow rate in the sintering zone of the sintering furnace; 12-Waste air flow rate at the tail end of the sintering zone; 13-LED light source in the light injection heat preservation zone; 14-Battery cell; 15-Organic exhaust at the inlet of the drying zone; 16-Organic exhaust in the sintering zone of the sintering furnace; 17-Organic exhaust at the tail end of the sintering zone; 18-Compressed air flow rate in the drying zone; 19-Compressed air flow rate in the sintering zone. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer.

[0021] Example 1 A method for integrating sintering and light injection of back-contact solar cells is disclosed. This method is carried out in an integrated sintering-light injection furnace, which is sequentially divided into the following functional areas: a sintering furnace drying zone, a sintering furnace sintering zone, a light injection heating zone, a light injection heat preservation zone, and a light injection cooling zone. Figure 3 As shown, each functional area consists of multiple sub-temperature zones with independently controllable process parameters; among them, the sintering zone of the sintering furnace includes pre-sintering and main sintering.

[0022] 1. The flow rate of organic discharge 3 in the sintering zone of the sintering furnace is set to 100-400 m³ / h, and the flow rate of organic discharge 2 at the inlet of the drying zone and organic discharge 4 at the tail end of the sintering zone is set to 50-150 m³ / h. 2. The exhaust air flow rate 11 in the sintering zone of the sintering furnace is set to 30-80 L / min, the exhaust air flow rate 10 at the inlet of the drying zone and the exhaust air flow rate 12 at the tail end of the sintering zone are set to 10-40 L / min, and the air flow rate 5 in the drying zone and the air flow rate 6 in the sintering zone are set to 10-80 L / min. Under the above conditions, the organic solvents, volatiles of the carrier, and pyrolysis products in the slurry are efficiently discharged from the furnace cavity to avoid contamination of the product in subsequent steps. The EDS energy dispersive spectroscopy analysis of the finished product shows that it does not contain carbon elements, indicating that organic components do not remain in the finished battery. 3. The heating rate from 500℃ to the peak temperature in the sintering zone is 80℃~150℃ / s. At this heating rate, the viscosity of the glass phase in the slurry decreases at a stable rate. Under the action of capillary force and interfacial tension, the silver particles rotate and shift, forming a denser packing structure, reducing the porosity of the electrode, thereby giving the electrode better conductivity and reducing resistance. SEM scanning of the electrode cross-section shows that the electrode is dense and free of voids, and the electrode does not burn through the polycrystalline silicon layer, thus preventing corrosion of the silicon substrate.

[0023] 4. The irradiance of the LED light source 13 injected into the heat preservation area is set to 20-40 suns. Under this intensity of light, the valence state of hydrogen atoms is adjusted, and hydrogen atoms move directionally toward the silicon base, passivating defects. Through electrical performance testing, the open circuit voltage does not decrease significantly. Through EL testing, there is no blackening phenomenon. Through 3D microscopy testing, no "film bursting" phenomenon is generated on the surface of the passivation layer, indicating that the hydrogen passivation effect is good. 5. The compressed air flow rate 7 in the light injection heating zone and the compressed air flow rate 8 in the heat preservation zone are set to 0 L / min to stabilize the temperature of the heating zone. The peak temperature of the heating zone is measured by the furnace temperature gauge. The temperature repeatability and uniformity of this zone are both within 6℃, while the temperature repeatability and uniformity of the prior art are greater than 12℃, indicating that the temperature stability of the present invention is significantly improved. 6. The cooling fan 9 in the light injection cooling zone is set to a speed of 60-180 rpm. At this speed, the temperature of the finished solar cells can be controlled within 60℃, which will not affect the subsequent testing process. At the same time, the temperature of the light-irradiated zone is relatively stable, avoiding the deterioration of the passivation effect caused by excessive cooling rate. The furnace temperature gauge pulls the furnace temperature, and the temperature of the heat preservation zone 13 is maintained above 300℃.

[0024] The table below shows the organic discharge flow rate settings for the example:

[0025] The following table shows the compressed air flow rate settings for the embodiment:

[0026] The following table shows the irradiation intensity settings for the embodiments:

[0027] The following table shows the compressed air flow rate settings for the embodiment:

[0028] A method for integrating sintering and light injection of back-contact solar cells, such as... Figure 1 As shown, it includes the following steps: Step S1) Sintering The solar cells printed with metal paste are conveyed through a sintering zone with a temperature gradient for drying and high-temperature sintering, so that the metal paste forms an ohmic contact with the silicon substrate of the solar cells; wherein, in the section of the sintering zone where organic matter is concentrated and decomposed, a purge airflow intensity higher than that at its inlet and outlet is applied to effectively remove the decomposition products. Specifically, such as Figure 3As shown, the battery cell 14 is fed into the furnace via a conveying mechanism. First, it passes through the drying zone, where the organic carrier in the slurry volatilizes at a temperature of 50-250°C and is discharged by the organic exhaust vent 15 at the entrance of the drying zone. It then enters the pre-sintering zone and sintering zone, where the temperature rises to a peak of 600-860°C. The heating rate from 500°C to the peak temperature in the sintering zone is 80°C~150°C / s. During this stage, the resin binder in the slurry completely decomposes, and the volatiles and pyrolysis products are discharged through the organic exhaust vent 16 in the sintering zone and the organic exhaust vent 17 at the tail end of the sintering zone. The organic exhaust flow rate of the organic exhaust vent 17 at the tail end of the sintering zone is greater than that of the organic exhaust vent 16 in the sintering zone, and the compressed air flow rate 19 in the sintering zone is greater than that in the drying zone, forming a "strong in the middle, weak at both ends" distribution. This achieves a directional and gradient exhaust layout that effectively guides the concentrated discharge of organic decomposition products; as shown... Figure 2 As shown, in the sintering zone, glass powder melts and etches through the back alumina passivation layer 4 and silicon nitride passivation layer 5, so that the silver paste comes into contact with the doped polycrystalline silicon layer 3 and forms a silver electrode 6. The electrode does not penetrate the tunnel oxide layer 2 and directly contacts the silicon substrate 1. After sintering is completed, the battery enters the multifunctional zone, and the surface temperature of the battery gradually decreases to 310℃-100℃.

[0029] Example: The above method is used to manufacture an N-type back-contact solar cell with dimensions of 182.3mm * 105mm, such as... Figure 2 As shown, the silicon substrate 1 has a thickness of 50-300 μm, and the back tunneling layer is a tunneling oxide layer 2 with a thickness of 1-10 nm. Electrons can tunnel into the polycrystalline silicon layer 3, while holes are blocked, thereby reducing the contact recombination current. The appropriate thickness can ensure the tunneling effect of electrons. The back conductive layer is a cross-arranged P-type silicon substrate. + Polycrystalline silicon layer 3 consists of P-type doped polycrystalline silicon layers and N+-type doped polycrystalline silicon layers, wherein P... + The thickness of the N-type doped polycrystalline silicon layer is 150nm-550nm. + The doped polycrystalline silicon layer is 50nm-350nm thick. The polycrystalline silicon layer provides chemical passivation to the back side of the silicon substrate, reducing carrier recombination caused by surface defects. During the metallization sintering process, the polycrystalline silicon layer comes into contact with the silver paste to prevent the silicon substrate from being corroded by the paste and reduce carrier recombination loss in the metal contact area of ​​the back surface. The back passivation layer is an aluminum oxide passivation layer 4 with a thickness of 1-20nm, which plays a role in chemical passivation and reduces the carrier recombination rate. The back passivation layer is a silicon nitride passivation layer 5 with a thickness of 20-200nm, which plays a role in anti-reflection and chemical passivation. It also includes a silver electrode 6, which is used to collect the current generated by photogenerated carriers (electrons and holes) and transmit it to the external circuit. Step S2) Light Injection The sintered solar cell obtained in step S1) is heated in the light injection heating zone and then irradiated in the light injection heat preservation zone; in the light injection heat preservation zone, the supply flow rate of compressed air is maintained at zero or close to zero. Specifically, after sintering, the solar cell enters the light injection region and is heated to 350℃-600℃ in the light injection heating region, activating hydrogen atoms in the passivation layer (such as silicon nitride). Subsequently, it is subjected to high-intensity illumination (LED light source) in the light injection heat preservation region, with an equivalent light intensity of 20–40 suns and a wavelength typically 400nm–1200nm. Photogenerated charge carriers modulate defect state charges, promoting the bonding of hydrogen atoms with dangling bonds within the silicon bulk, achieving both bulk and surface passivation.

[0030] Step S3) Cooling The solar cell obtained after light injection in step S2) is conveyed through the light injection cooling zone and cooled by a fan speed of ≤180 rpm.

[0031] Specifically, to ensure stable temperature control in the light injection heating zone and the insulation zone, the compressed air flow rate 7 in the light injection heating zone and the compressed air flow rate 8 in the insulation zone are set to 0, and the speed of the cooling fan 9 in the light injection cooling zone is set to 60-180 rpm to ensure a stable atmosphere in the cavity. Finally, the solar cells are discharged after cooling to room temperature in the cooling zone, completing all processing.

[0032] Comparative Example 1 In the control group, conventional sintering furnace technology was used to sinter the back electrode slurry of the solar cell precursor. Solar cells from the control group were obtained.

[0033] Effect Example The table below shows a performance comparison between the batteries in the examples and the comparative examples: First comparison:

[0034] Second comparison:

[0035] The comparison results show that the embodiment exhibits a significant increase in fill factor and a conversion efficiency improvement of over 0.11%. This invention increases the heating rate of the solar cell from 500°C to the peak temperature in the sintering region to ≥80°C / s. This extremely high sintering heating rate shortens the high-temperature process and suppresses premature hydrogen escape from the hydrogen passivation layer. In a light injection environment without airflow interference, strong light irradiation can precisely activate hydrogen atoms, promoting their directional migration to grain boundaries and defects to form stable Si-H bonds, achieving efficient bulk passivation and surface passivation. Photogenerated carriers form a favorable concentration gradient under high-intensity light irradiation, further optimizing the carrier collection and transport path.

[0036] Therefore, the process of this invention significantly improves the hydrogen passivation effect and photoelectric conversion efficiency of back-contact solar cells.

[0037] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for integrating sintering and light injection of back-contact solar cells, wherein the method is carried out in a sintering-light injection integrated furnace, characterized in that, Includes the following steps: Step S1) Sintering The solar cells printed with metal paste are conveyed through a sintering zone with a temperature gradient for drying and high-temperature sintering, so that the metal paste forms an ohmic contact with the silicon substrate of the solar cells; wherein, in the section of the sintering zone where organic matter is concentrated and decomposed, a purge airflow intensity higher than that at its inlet and outlet is applied to effectively remove the decomposition products. Step S2) Light Injection The sintered solar cell obtained in step S1) is heated in the light injection heating zone and then irradiated in the light injection heat preservation zone; in the light injection heat preservation zone, the supply flow rate of compressed air is maintained at zero or close to zero. Step S3) Cooling The solar cell obtained after light injection in step S2) is conveyed through the light injection cooling zone and cooled by a fan speed of ≤180 rpm.

2. The method according to claim 1, characterized in that, The sintering zone includes a drying zone, a pre-sintering zone, and a sintering zone in sequence; the temperature of the drying zone is 150-300℃; and the peak temperature of the pre-sintering zone and the sintering zone is 700-900℃.

3. The method according to claim 2, characterized in that, Within the sintering zone, the heating rate of the solar cell from 500°C to the peak temperature is controlled between 80°C / s and 150°C / s.

4. The method according to claim 1, characterized in that, The process of applying a purge gas flow rate higher than that at its inlet and outlet is as follows: in the sintering zone, the purge gas flow rate for discharging organic matter is 100-400 m³ / h, while the purge gas flow rate in its inlet and outlet areas is 50-150 m³ / h.

5. The method according to claim 4, characterized in that, The purging airflow is compressed air, with a flow rate of 30-80 L / min in the sintering zone and 10-40 L / min in its inlet and outlet regions.

6. The method according to claim 1, characterized in that, In step S2), the light injection insulation zone is divided into multiple independently controlled illumination units, and the light irradiance of each illumination unit is independently controlled at 20-40 solar constants.

7. The method according to claim 1, characterized in that, In step S1), the metal paste is silver paste.

8. The method according to any one of claims 1-7, characterized in that, The back contact cell is an IBC cell, and its structure includes: a silicon substrate, and alternating p-type doped regions and n-type doped regions formed on the back side of the substrate. A hydrogen passivation layer covers the doped regions, and the p-type electrode and n-type electrode respectively pass through the hydrogen passivation layer to form ohmic contacts with the corresponding doped regions.

Images