Metallization treatment process of solar cell

Abstract

The invention provides a metallization treatment process of a solar cell. The metallization treatment process comprises the following steps: sequentially drying and sintering a semiconductor substrate with conductive slurry formed on the surface to obtain a cell; the sintering treatment comprises a melting constant-temperature sintering area and a peak constant-temperature sintering area located behind the melting constant-temperature sintering area, the sintering temperature of the melting constant-temperature sintering area is smaller than that of the peak constant-temperature sintering area, and the temperature difference between the melting constant-temperature sintering area and the peak constant-temperature sintering area is 670-770 DEG C. According to the metallization treatment process provided by the invention, the sintering temperature in the melting constant-temperature sintering region is maintained in a relatively low temperature range, so that the diffusion speed of the inorganic glass component in the conductive slurry to the surface of the semiconductor substrate can be slowed down; according to the invention, the inorganic glass component can be prevented from passing through the passivation layer to perform redundant diffusion to the inside of the semiconductor substrate as much as possible, and the uncontrollable widening of the metal electrode covering the surface of the semiconductor substrate is reduced, so that the photoelectric conversion efficiency of the solar cell is improved.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power generation technology, and more specifically, to a metallization process for solar cells. Background Technology

[0002] Traditional solar cell metallization processes involve high-temperature sintering to create metal-semiconductor contacts and form metal electrodes. The contact quality between the metal electrode and the semiconductor substrate affects the transport efficiency of photogenerated carriers. Poor contact quality leads to increased contact resistance in the solar cell. Encapsulating solar cells with high contact resistance results in severe hotspot effects, where localized temperature increases cause performance degradation and pose significant safety hazards. Furthermore, different morphologies formed after the metal electrode contacts the semiconductor substrate surface also affect cell performance.

[0003] Therefore, optimizing the metallization process of solar cells to improve their performance is an urgent problem to be solved in the field of photovoltaic power generation technology. Summary of the Invention

[0004] This application provides a metallization process for solar cells, which can improve the photoelectric conversion efficiency of solar cells.

[0005] Specifically, this application is implemented through the following technical solution:

[0006] This application provides a metallization process for solar cells, including:

[0007] A semiconductor substrate with a conductive paste formed on its surface is sequentially dried and sintered to obtain a battery cell. The sintering process includes a melt-isothermal sintering zone and a peak-isothermal sintering zone located after the melt-isothermal sintering zone. The sintering temperature of the melt-isothermal sintering zone is lower than the sintering temperature of the peak-isothermal sintering zone, and the temperature difference between the melt-isothermal sintering zone and the peak-isothermal sintering zone is 670-770°C.

[0008] Optionally, the temperature of the melting isothermal sintering zone is 80–130°C, and the temperature of the peak isothermal sintering zone is 800–850°C.

[0009] Optionally, the sintering time of the melt isothermal sintering zone is not less than the sintering time of the peak isothermal sintering zone.

[0010] Optionally, the sintering time of the melting isothermal sintering zone is 12-16 s, and the sintering time of the peak isothermal sintering zone is 12-16 s.

[0011] Optionally, the sintering process further includes a heating transition sintering zone disposed between the melting isothermal sintering zone and the peak isothermal sintering zone; the sintering temperature of the heating transition sintering zone is lower than the sintering temperature of the peak isothermal sintering zone, and the temperature difference between the two zones is 100 to 200°C.

[0012] Optionally, the sintering temperature of the heating transition sintering zone is 700–780°C; and / or, the sintering time of the heating transition sintering zone is 3–4 seconds.

[0013] Optionally, the sintering process further includes a cooling transition sintering zone located after the peak isothermal sintering zone; the sintering temperature of the cooling transition sintering zone is lower than the sintering temperature of the peak isothermal sintering zone, and the temperature difference between the two zones is 100 to 400°C.

[0014] Optionally, the sintering temperature of the cooling transition sintering zone is 500–700°C; and / or, the sintering time of the cooling transition sintering zone is 3–4 seconds.

[0015] Optionally, the melting isothermal sintering zone includes a first upper temperature zone and a first lower temperature zone; the temperature of the first lower temperature zone is greater than or equal to the temperature of the first upper temperature zone, and the temperature difference between the first lower temperature zone and the first upper temperature zone is less than 50°C.

[0016] And / or, the peak isothermal sintering zone includes a second upper temperature zone and a second lower temperature zone; the temperature of the second lower temperature zone is greater than or equal to the temperature of the second upper temperature zone, and the temperature difference between the second lower temperature zone and the second upper temperature zone is less than 80°C.

[0017] Optionally, the sintering temperature of the melting isothermal sintering zone is lower than the temperature of the drying treatment.

[0018] The technical solution provided in this application can achieve the following beneficial effects:

[0019] This application provides a metallization process for solar cells. By maintaining the sintering temperature in the molten isothermal sintering zone at a relatively low temperature range, the diffusion rate of inorganic glass components in the conductive paste to the surface of the semiconductor substrate can be slowed down. This not only minimizes redundant diffusion of inorganic glass components through the passivation layer into the semiconductor substrate, but also reduces the uncontrollable widening of the metal electrode covering the surface of the semiconductor substrate, thereby improving the photoelectric conversion efficiency of the solar cell. Attached Figure Description

[0020] Figure 1 This is a comparison chart of the sintering curves formed by the actual sintering temperature changing over time between the metallization process provided in Example 1 of this application and the metallization process provided in Comparative Example 1.

[0021] Figure 2 This is a comparison chart of the sintering curves formed by the actual sintering temperature change over time between the metallization process provided in Examples 2-4 of this application and the metallization process provided in Comparative Example 2.

[0022] Figure 3 This is a comparison of the morphology of the semiconductor silicon substrate provided in Embodiment 1 of this application before and after sintering in a rapid metallization process.

[0023] Figure 4 This is a comparison of the morphology of the semiconductor silicon substrate provided in Comparative Example 1 (i.e., the control group) before and after sintering in the metallization process. Detailed Implementation

[0024] The technical solution of this application will now be described in detail with reference to the accompanying drawings.

[0025] This application provides a metallization process for solar cells, comprising: sequentially drying and sintering a semiconductor substrate with a conductive paste formed on its surface to obtain a solar cell; the sintering process includes a molten isothermal sintering zone and a peak isothermal sintering zone located after the molten isothermal sintering zone, wherein the sintering temperature of the molten isothermal sintering zone is lower than the sintering temperature of the peak isothermal sintering zone, and the temperature difference between the molten isothermal sintering zone and the peak isothermal sintering zone is 670–770°C.

[0026] A semiconductor substrate refers to a substrate formed after performing at least some of the following processes on a semiconductor substrate, such as a silicon wafer: cleaning, texturing, diffusion, and coating. A conductive paste is then formed on at least one surface of this semiconductor substrate through coating steps such as spraying or printing. The semiconductor substrate with the conductive paste on its surface is first dried to evaporate the organic solvents in the conductive paste, and then sintered to allow the inorganic portion of the conductive paste, after removing the organic solvents, to adhere tightly to the surface of the semiconductor substrate, forming a metal electrode. Traditional solar cell metallization processes use high initial temperatures for melting and sintering, and a peak sintering region appears when the sintering temperature reaches its maximum. Because the melting and sintering temperature remains high, the inorganic portion of the conductive paste, such as inorganic glass components, after removing the organic solvents, quickly falls onto the surface of the semiconductor substrate, forming significant uncontrolled broadening. This increases the light-blocking area of ​​the metal electrode and reduces the photoelectric conversion efficiency.

[0027] By limiting the temperature difference between the molten isothermal sintering zone and the peak isothermal sintering zone within the aforementioned range, this application can maintain the sintering temperature in the molten isothermal sintering zone at a lower temperature range. This slows down the diffusion rate of inorganic glass components in the conductive paste to the surface of the semiconductor substrate. This not only minimizes redundant diffusion of inorganic glass components into the semiconductor substrate after they erode through the passivation layer, but also reduces the uncontrollable widening of the metal electrode covering the surface of the semiconductor substrate, optimizes the morphology of the metal electrode, and reduces the area of ​​light obstruction by the metal electrode, thereby improving the photoelectric conversion efficiency of the solar cell.

[0028] In some embodiments, the temperature of the molten isothermal sintering zone is 80–130°C, and the temperature of the peak isothermal sintering zone is 800–850°C. Therefore, by setting the temperature of the molten isothermal sintering zone within the above range, the sintering temperature before reaching the peak sintering zone is significantly reduced, thus lowering energy consumption and production costs during the sintering process. Simultaneously, by controlling the peak isothermal sintering zone within the above temperature range, the insufficient thermal dynamics of the inorganic glass components in the conductive paste during the sintering process in the molten isothermal sintering zone can be compensated for, and the metallic silver in the conductive paste can be rapidly precipitated from the etched area, forming a eutectic phase after co-fusion with silicon atoms in the semiconductor silicon wafer, ensuring good ohmic contact of the metal electrodes.

[0029] It should be noted that the temperature ranges of the aforementioned melting isothermal sintering zone and peak isothermal sintering zone refer to the pre-set sintering temperature ranges, specifically the temperature ranges pre-set by the sintering equipment used in the metallization process, and not the actual sintering temperature ranges during the sintering process.

[0030] In some embodiments, the sintering time of the molten isothermal sintering zone is not less than the sintering time of the peak isothermal sintering zone. This ensures that the temperature change curve over time in the molten isothermal sintering zone tends to be flat, allowing the inorganic glass components in the conductive paste to more uniformly cover the contact area, thus improving the contact quality between the metal electrode and the semiconductor substrate. In some embodiments, the sintering time of the molten isothermal sintering zone is 12–16 s, and the sintering time of the peak isothermal sintering zone is 12–16 s. This ensures that metal electrodes with superior morphology and high-performance solar cells can be formed while maintaining a relatively short isothermal sintering process in both the molten isothermal sintering zone and the peak isothermal sintering zone, improving production efficiency and the throughput of the metallization process.

[0031] In some embodiments, the sintering process further includes a heating transition sintering zone disposed between the molten isothermal sintering zone and the peak isothermal sintering zone; the sintering temperature of the heating transition sintering zone is lower than the sintering temperature of the peak isothermal sintering zone, and the temperature difference between the two zones is 100–200°C. This serves as a temperature buffer between the heating process from the molten isothermal sintering zone and the peak isothermal sintering zone, mitigating the effects of temperature cross-contamination. In some embodiments, the sintering temperature of the heating transition sintering zone is 700–780°C; and / or, the sintering time of the heating transition sintering zone is 3–4 seconds. This ensures that the molten isothermal sintering zone can heat up more stably to the peak isothermal sintering zone, improving sintering efficiency.

[0032] In some embodiments, the sintering process further includes a cooling transition sintering zone disposed after the peak isothermal sintering zone; the sintering temperature of the cooling transition sintering zone is lower than that of the peak isothermal sintering zone, and the temperature difference between the two zones is 100–400°C. This serves as a cooling buffer after the peak isothermal sintering zone, preventing internal stress defects in the solar cells caused by excessively rapid cooling. In some embodiments, the sintering temperature of the cooling transition sintering zone is 500–700°C; and / or, the sintering time of the cooling transition sintering zone is 3–4 seconds. This ensures a more stable cooling process in the peak isothermal sintering zone, providing a buffer for subsequent cooling to room temperature and improving sintering efficiency.

[0033] In some embodiments, the melting isothermal sintering zone includes a first upper temperature zone and a first lower temperature zone; the temperature of the first lower temperature zone is greater than or equal to the temperature of the first upper temperature zone, and the temperature difference between the first lower temperature zone and the first upper temperature zone is less than 50°C. Therefore, by using an upper temperature zone and a lower temperature zone to sinter the battery cell simultaneously, the battery cell can be heated more uniformly. In some embodiments, the peak isothermal sintering zone includes a second upper temperature zone and a second lower temperature zone; the temperature of the second lower temperature zone is greater than or equal to the temperature of the second upper temperature zone, and the temperature difference between the second lower temperature zone and the second upper temperature zone is less than 80°C.

[0034] It should be noted that the "temperature difference" mentioned above refers to the temperature difference between different sintering zones at the same upper and lower temperature ranges. For example, the temperature difference between the molten isothermal sintering zone and the peak isothermal sintering zone is 670–820℃, which means the temperature difference between the first upper temperature zone of the molten isothermal sintering zone and the second upper temperature zone of the peak isothermal sintering zone is 670–820℃; or, the temperature difference between the first lower temperature zone of the molten isothermal sintering zone and the second lower temperature zone of the peak isothermal sintering zone is 670–820℃.

[0035] In some embodiments, the sintering temperature of the melt-isothermal sintering zone is lower than the drying temperature. Therefore, by connecting the melt-isothermal sintering zone and the drying zone of the drying process, a low-temperature sintering process can be maintained continuously in the melt-isothermal sintering zone to slow down the diffusion rate of the inorganic glass components in the conductive paste to the surface of the semiconductor substrate. Exemplarily, the drying temperature can be selected from 100 to 300°C, but it is not limited to this.

[0036] Traditional solar cells are typically dried and sintered in multi-chamber sintering furnaces. Most existing production lines use sintering furnaces with 16 chambers. The first six chambers (chambers 1-6) are used for drying, while the last ten chambers (chambers 7-16) are used for sintering. Since each chamber is approximately the same length, each chamber creates a temperature zone of equal length.

[0037] When using a traditional 16-chamber sintering furnace, the limited temperature adjustment window results in a small temperature difference between adjacent temperature zones after temperature modulation. Because traditional temperature modulation methods employ variable temperature control in most chambers of the melting sintering zone before reaching the peak sintering temperature (peak isothermal sintering zone), temperature fluctuations between adjacent zones are significant, increasing the risk of temperature cross-contamination. Furthermore, the prolonged temperature change time is detrimental to maintaining optimal microstructure of the grid lines. Extending the melting sintering zone duration requires increasing the number of chambers, necessitating the introduction of new sintering furnaces with more chambers, such as 18 chambers. However, this introduces significant drawbacks, including higher procurement costs and insufficient space in existing production lines for assembly.

[0038] The semiconductor substrate with conductive paste formed on its surface was dried and sintered sequentially using a 16-chamber sintering furnace. Each chamber was 0.8m long. The first 6 chambers (chambers 1-6) were used for drying, and the last 10 chambers (chambers 7-16) were used for sintering.

[0039] Example 1

[0040] S1. The semiconductor silicon substrate with conductive paste formed on its surface is first transported to the first 6 chambers of the sintering furnace through a conveyor belt with a speed of 15.6 m / min for drying treatment. The drying temperatures of the first 6 chambers are 390℃, 370℃, 340℃, 280℃, 240℃ and 200℃, respectively, and the drying time of each temperature zone is 3.1s.

[0041] S2. Then, the dried semiconductor silicon substrate is transported to chambers 7 to 16 via a conveyor belt at a speed of 15.6 m / min for sintering. Chambers 7 to 10 are four melting isothermal sintering zones, chamber 11 is a heating transition sintering zone, chambers 12 to 15 are four peak isothermal sintering zones, and chamber 16 is a cooling transition sintering zone.

[0042] The sintering time for each temperature zone is 3.1s, the total sintering time for the melting isothermal sintering zone is 12.4s, the total sintering time for the peak isothermal sintering zone is 12.4s, and the total sintering time is 31s.

[0043] Examples 2-4

[0044] The difference from Example 1 is that the temperature of chambers 7 to 16 is different, while other experimental conditions are the same as in Example 1.

[0045] Comparative Example 1

[0046] S1. The semiconductor silicon substrate with conductive paste formed on its surface is first transported to the first 6 chambers of the sintering furnace through a conveyor belt with a speed of 14.0 m / min for drying treatment. The drying temperatures of the first 6 chambers are 390℃, 370℃, 340℃, 280℃, 240℃ and 200℃ respectively, and the drying time of each temperature zone is 3.5s.

[0047] S2. Then, the dried semiconductor silicon substrate is transported to the 7th to 16th chambers via a conveyor belt at a speed of 14.0 m / min for sintering. Among them, the 7th to 11th chambers are 5 melting temperature-changing sintering zones, the 12th to 15th chambers are 4 peak temperature isothermal sintering zones, and the 16th chamber is a cooling transition sintering zone.

[0048] The sintering time for each temperature zone is 3.5s, the total sintering time for the peak isothermal sintering zone is 14s, and the total sintering time is 35s.

[0049] Comparative Example 2

[0050] The difference from Comparative Example 1 is that the temperature of chambers 7 to 16 is different, while the other experimental conditions are the same as those in Comparative Example 1.

[0051] The set sintering temperatures for each temperature zone in Examples 1-4 and Comparative Examples 1-2 are shown in Table 1 below.

[0052] Table 1

[0053]

[0054]

[0055]

[0056] Please see Figure 1 and Figure 2 The actual temperatures of each chamber temperature zone in the sintering furnaces of Examples 1-4 and Comparative Examples 1-2 were measured using a MOLE temperature measuring instrument equipped with platinum-rhodium alloy thermocouple temperature sensors, and sintering curves showing the actual temperature changing over time were generated. It should be noted that due to differences in the internal structure of the sintering furnaces, the actual temperatures of each temperature zone within the sintering furnace differ to some extent from the preset temperatures.

[0057] from Figure 1 and Figure 2 As shown in the sintering curves, the metallization process provided in Examples 1-4 of this application, after drying, first undergoes low-temperature sintering in a molten isothermal sintering zone with a lower temperature range. During this process, the temperature change curve over time in the molten isothermal sintering zone tends to be flat and is maintained for a relatively long time. Then, the sintering temperature is gradually increased to reach the peak isothermal sintering zone, resulting in a large temperature difference between the molten isothermal sintering zone and the peak isothermal sintering zone. In contrast, the metallization process provided in Comparative Examples 1-2, after drying, directly and gradually increases the sintering temperature to reach the peak sintering zone, and the temperature change curve over time in the molten sintering zone tends to be steeper.

[0058] Please see Figure 3 and Figure 4 The morphology images of the semiconductor silicon substrates of Example 1 and Comparative Example 1 before and after sintering were obtained using a Zeta-3D microscope. In the images, the length of the red dashed line extending horizontally represents the width (linewidth) of the metal gate electrode, and the length of the red dashed line extending vertically represents the height (lineheight) of the metal gate electrode. The linewidth and lineheight of the morphology were measured three times using a diagonal measurement method, and the average values ​​of the morphology test data are shown in Table 2 below. After assembling the semiconductor substrates with conductive paste layers disclosed in Examples 1-4 and Comparative Examples 1-2 into solar cells, the cell performance was tested using a solar simulator (Halm photovoltaic tester), and the obtained electrical performance data are shown in Table 3 below.

[0059] Table 2

[0060]

[0061]

[0062] Table 3

[0063]

[0064] As shown in Tables 2 and 3, the improved metallization process in Example 1 of this application can effectively reduce the line height of the metal electrode after sintering. The gate line width of the metal electrode remains essentially unchanged before and after sintering, effectively controlling the uncontrollable widening of the metal electrode and avoiding unnecessary damage to the passivation layer. In contrast, the gate line width of the metal electrode in Comparative Example 1 changed by approximately 3 μm before and after sintering. After optimizing the morphology of the metal electrode, Examples 1-4 of this application can reduce the area of ​​light obstruction by the metal electrode, thereby improving the short-circuit current, open-circuit voltage, and photoelectric conversion efficiency of the battery.

[0065] Furthermore, by adopting the metallization process provided in Embodiments 1-4 of this application, the dwell time of the battery cells in each chamber can be shortened. That is, by increasing the belt speed of the conveyor belt by 10% to 20% to shorten the dwell time, the production efficiency of the metallization process can be improved, and the final rapid high-temperature metallization can be achieved. The metallization process provided in Embodiments 1-4 of this application can increase the single-track throughput by approximately 10,300 cells within 24 hours.

[0066] The above embodiments can be combined with each other without conflicting with the technical means described therein. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A metallization process for solar cells, characterized in that, include: A semiconductor substrate with a conductive paste formed on its surface is dried and sintered sequentially to obtain a battery cell; The sintering process includes a melting isothermal sintering zone and a peak isothermal sintering zone located after the melting isothermal sintering zone. The sintering temperature of the melting isothermal sintering zone is lower than the sintering temperature of the peak isothermal sintering zone, and the temperature difference between the melting isothermal sintering zone and the peak isothermal sintering zone is 670-770°C.

2. The metallization process according to claim 1, characterized in that, The temperature of the melting isothermal sintering zone is 80–130°C, and the temperature of the peak isothermal sintering zone is 800–850°C.

3. The metallization process according to claim 1, characterized in that, The sintering time of the melt isothermal sintering zone is not less than the sintering time of the peak isothermal sintering zone.

4. The metallization process according to claim 3, characterized in that, The sintering time of the melting isothermal sintering zone is 12-16 s, and the sintering time of the peak isothermal sintering zone is 12-16 s.

5. The metallization process according to any one of claims 1 to 4, characterized in that, The sintering process further includes a heating transition sintering zone disposed between the melting isothermal sintering zone and the peak isothermal sintering zone; the sintering temperature of the heating transition sintering zone is lower than the sintering temperature of the peak isothermal sintering zone, and the temperature difference between the two zones is 100 to 200°C.

6. The metallization process according to claim 5, characterized in that, The sintering temperature of the heating transition sintering zone is 700-780℃; and / or the sintering time of the heating transition sintering zone is 3-4s.

7. The metallization process according to any one of claims 1 to 4, characterized in that, The sintering process further includes a cooling transition sintering zone located after the peak constant temperature sintering zone; the sintering temperature of the cooling transition sintering zone is lower than the sintering temperature of the peak constant temperature sintering zone, and the temperature difference between the two zones is 100 to 400°C.

8. The metallization process according to claim 7, characterized in that, The sintering temperature of the cooling transition sintering zone is 500-700℃; and / or the sintering time of the cooling transition sintering zone is 3-4s.

9. The metallization process according to any one of claims 1 to 4, characterized in that, The melting isothermal sintering zone includes a first upper temperature zone and a first lower temperature zone; the temperature of the first lower temperature zone is greater than or equal to the temperature of the first upper temperature zone, and the temperature difference between the first lower temperature zone and the first upper temperature zone is less than 50°C. And / or, the peak isothermal sintering zone includes a second upper temperature zone and a second lower temperature zone; the temperature of the second lower temperature zone is greater than or equal to the temperature of the second upper temperature zone, and the temperature difference between the second lower temperature zone and the second upper temperature zone is less than 80°C.

10. The metallization process according to any one of claims 1 to 4, characterized in that, The sintering temperature of the melting isothermal sintering zone is lower than the temperature of the drying treatment.

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