Method for monitoring passivation effect of back contact battery based on undercut morphology

Abstract

The invention discloses a method for monitoring the passivation effect of a back contact battery based on undercut morphology. The production line process flow of the back contact battery comprises the following steps: preparing an N-type silicon wafer, performing primary texturing, performing alkali polishing, preparing a P-type polycrystalline silicon layer, performing double-sided boron diffusion, performing P1 laser, performing RCA cleaning, preparing an N-type polycrystalline silicon layer, performing double-sided phosphorus diffusion, performing P2 laser, performing acid etching, performing secondary texturing, plating antireflection films on the front surface and the back surface, metallizing and sintering. The method comprises the following steps: selecting a silicon wafer subjected to RCA and / or secondary texturing, and observing the undercut morphology of the silicon wafer; if it is observed that the undercut morphology width is larger than D, laser process parameters and / or alkali washing process parameters are / is adjusted reversely; if it is observed that the undercut morphology width does not exceed D, the silicon wafer is kept to be continuously produced according to the original production line technological process; the step of adjusting the laser process parameters comprises the step of adjusting the power of P1 laser and / or P2 laser to be increased or reduced; the adjustment of the alkali washing process parameters comprises the adjustment of the RCA and / or the temperature increase and the time reduction during the secondary texturing.

Description

Technical Field

[0001] This invention relates to the field of novel crystalline silicon solar cell processing technology, specifically to a method for monitoring the passivation effect of back contact cells based on undercut morphology. Background Technology

[0002] With technological breakthroughs and mass production implementation, back contact batteries (BC batteries) are now fully ready for mass production and are entering the mass market. The methods for monitoring their passivation effect are also increasing, such as using the WCT-120 tester to monitor their minority carrier lifetime, or adjusting and monitoring their process through photoluminescence and electroluminescence. The fundamental reason for this is to monitor the passivation effect of the battery cells during the back contact battery manufacturing process. However, these monitoring methods can only provide conclusive results; they cannot understand the reasons for differences in test results from the perspective of the battery structure itself. In other words, current monitoring methods for the passivation effect of back contact batteries cannot directly reveal the internal differences of the battery, and the conclusive results they provide cannot offer guidance on how to optimize the passivation effect of back contact batteries.

[0003] In the manufacturing process of back contact batteries, multiple laser grooving and wet etching processes will be carried out, which will form undercut. The main reasons for this are as follows: (1) Laser process: Due to uneven laser energy distribution and improper laser parameter settings, such as unreasonable laser power, pulse frequency, scanning speed and other process parameters, undercut will be formed after the same wet process; (2) Material characteristics: The silicon wafers and passivation films used in the battery have certain differences in physical and chemical properties. These differences may lead to different absorption and reaction of materials to laser, resulting in different removal rates of bottom materials during etching compared to top materials, ultimately forming undercut; (3) Wet alkaline washing process: After the same laser process, different process settings such as time, temperature, equipment bubbling, and circulation during wet alkaline washing may ultimately form undercut.

[0004] The undercut will have the following effects on BC batteries: (1) Effects on battery performance: Undercut may damage the structural integrity of the back of the battery, affecting the electrical performance of the battery. For example, it may lead to poorer isolation between the N and P regions, increasing the risk of leakage, thereby reducing the open circuit voltage, short circuit current and fill factor of the battery, and ultimately affecting the conversion efficiency of the battery; (2) Effects on production yield: If the undercut is severe, it will lead to an increase in the scrap rate of the battery cells, because undercut may damage the internal structure of the battery, making it prone to failure in subsequent testing and use, thereby reducing the number of good products produced, EL defects in finished product monitoring, and the yield dropping to below 95%, increasing production costs, and poor battery contact, resulting in product downgrading; (3) Effects on reliability: Undercut may reduce the mechanical strength of the battery, making it more prone to cracks during packaging and use, affecting the long-term reliability and stability of the battery. It can be seen that undercut has a decisive effect on the electrical performance, yield and reliability of BC batteries. At present, there is no testing equipment that can directly obtain the effect of undercut on recombination loss. Even the quokka simulation only considers the recombination coefficient. Summary of the Invention

[0005] The purpose of this invention is to address the problem that existing methods for monitoring the passivation effect of BC batteries cannot intuitively understand the intrinsic differences of the batteries and can only provide conclusive results on the quality of passivation. However, these conclusive results cannot provide guidance on how to optimize the passivation effect of BC batteries. Therefore, this invention proposes a method for monitoring the passivation effect of BC batteries based on undercut morphology. This method is a novel means of monitoring the passivation effect, which can thoroughly understand the passivation dependence of BC batteries and thus guide the optimization and improvement of the electrical performance parameters of BC batteries.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] This invention provides a method for monitoring the passivation effect of back contact batteries based on undercut morphology. The production line process of the back contact batteries includes the following steps:

[0008] N-type silicon wafer → First texturing → Alkali polishing → Preparation of P-type polycrystalline silicon layer → Double-sided boron diffusion → P1 laser → RCA cleaning → Preparation of N-type polycrystalline silicon layer → Double-sided phosphorus diffusion → P2 laser → Acid etching → Second texturing → Anti-reflection coating on front and back sides → Metallization → Sintering.

[0009] The specific monitoring method is as follows: Select silicon wafers that have undergone RCA cleaning and / or secondary texturing, dry their surfaces, and then perform microscopic morphology testing to observe the undercut morphology of the silicon wafers.

[0010] If the undercut width of the silicon wafer is observed to be greater than D, the laser process parameters and / or the alkaline washing process parameters are adjusted in reverse. If the undercut width of the silicon wafer is observed to be no more than D, the silicon wafer is kept in the original production line process flow to continue the production of back contact cells.

[0011] Among them, the reverse adjustment of laser process parameters includes: increasing or decreasing the power of P1 laser and / or P2 laser; the reverse adjustment of alkaline washing process parameters includes: increasing the temperature and decreasing the time during RCA cleaning and / or secondary texturing.

[0012] Specifically, a smaller undercut morphology width results in less recombination in the battery, leading to better passivation, which in turn improves the battery's electrical performance.

[0013] Furthermore, a method for monitoring the passivation effect of back contact cells based on undercut morphology is proposed: two different silicon wafers after RCA cleaning and secondary texturing are selected respectively, and their surfaces are dried and microstructure tests are performed to observe the undercut morphology of the two silicon wafers.

[0014] If the undercut morphology width of the silicon wafer that has only undergone RCA cleaning is observed to be greater than D, then the P1 laser power is adjusted in reverse to increase or decrease and / or the temperature and cleaning time during RCA cleaning are adjusted in reverse to increase and decrease; otherwise, no adjustment is made.

[0015] If the width of the undercut morphology of the silicon wafer after secondary texturing is observed to be greater than D, then the P2 laser power is adjusted in reverse to increase or decrease and / or the temperature and texturing time during secondary texturing are adjusted in reverse to increase and decrease. Otherwise, no adjustment is made.

[0016] Furthermore, a method for monitoring the passivation effect of back contact cells based on undercut morphology is proposed: if the undercut morphology width of the silicon wafer that has only undergone RCA cleaning is observed to be greater than D, then the P1 laser power is adjusted to increase or decrease, and the temperature and cleaning time during RCA cleaning are adjusted to increase and decrease respectively; otherwise, no adjustment is made.

[0017] If the width of the undercut morphology of the silicon wafer after secondary texturing is observed to be greater than D, then the P2 laser power is adjusted in reverse to increase or decrease, and the temperature and texturing time during secondary texturing are adjusted in reverse to increase and decrease. Otherwise, no adjustment is made.

[0018] Furthermore, a method for monitoring the passivation effect of back contact batteries based on undercut morphology is proposed: the value of D is not more than 3.0 μm.

[0019] Specifically, in the method of this invention, the value of D can be freely set. The smaller the value, the better it is for improving the electrical performance and reliability of the back contact battery. However, the smaller the value of D, the greater the cost of reverse optimization of the production line. A balance can be struck based on the actual requirements for the electrical performance and reliability of the back contact battery.

[0020] Furthermore, a method for monitoring the passivation effect of back contact cells based on undercut morphology is provided: a location near the middle and / or edge of the silicon wafer after RCA cleaning and / or secondary texturing is selected as the test location for micromorphology testing, and at least 2 points are tested at each test location, and the average value is taken as the width of the undercut.

[0021] Furthermore, a method for monitoring the passivation effect of back contact batteries based on undercut morphology is proposed: microscopic morphology testing of silicon wafers is performed using scanning electron microscopy.

[0022] Furthermore, a method for monitoring the passivation effect of back contact batteries based on undercut morphology includes: adjusting the process parameters of alkaline washing in reverse, which further includes: adjusting the solution composition during RCA cleaning and / or secondary texturing to reduce the corrosion rate.

[0023] The beneficial effects of this invention are:

[0024] The method proposed in this invention involves observing the undercut morphology of silicon wafers after RCA cleaning and / or secondary texturing. When the width of the undercut morphology exceeds the expected width D, it can guide the optimization of the RCA cleaning and secondary texturing processes on the back contact battery production line, as well as the upstream P1 and P2 laser processes. This optimizes the back contact battery production line process, ensuring that the optimized process produces back contact batteries with good passivation, eliminates abnormalities, and ultimately improves the overall electrical performance and reliability of the back contact batteries obtained from the production line.

[0025] This invention provides a method for monitoring the undercut morphology of silicon wafers during the BC battery manufacturing process. This allows for timely adjustments to the production line process, preventing severe undercutting issues and avoiding an increase in battery scrap rates. This reduces production costs, and once the undercutting is improved, the battery contact will be better, preventing product degradation.

[0026] The method proposed in this invention is a method for monitoring the passivation effect of back contact batteries based on undercut morphology, specifically for back contact batteries produced on production lines. This method is a novel means of monitoring passivation effect, which can thoroughly understand the passivation dependence of back contact batteries, thereby guiding the optimization and improvement of the electrical performance parameters and reliability of back contact batteries produced on production lines. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figures 1-2 The image shows the undercut topography of silicon wafers after RCA cleaning on the back contact battery production line.

[0029] Figures 3-4 This is a bottom-section morphology of a silicon wafer after cleaning using the RCA cleaning process on a back-contact battery production line, optimized according to Embodiment 1 of the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] In the description of this invention, it should be understood that the terms "upper," "lower," "left," "right," "top," and "bottom," etc., indicating orientation or positional relationships, are merely for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature. Moreover, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein.

[0032] Currently, the production process of existing back contact batteries (BC batteries) generally includes the following steps: N-type silicon wafer → primary texturing → alkaline polishing → preparation of P-type polycrystalline silicon layer → double-sided boron diffusion → P1 laser → RCA cleaning → preparation of N-type polycrystalline silicon layer → double-sided phosphorus diffusion → P2 laser → acid etching → secondary texturing → front and back anti-reflection coating → metallization → sintering.

[0033] The power of the original P1 laser on the production line is generally around 20-25W (preferably 23W), the temperature of the original RCA cleaning is generally 65-70℃ (preferably 68℃), and the cleaning (alkaline cleaning) time is generally around 900-1100 seconds (preferably 1000 seconds).

[0034] Specifically, after the P1 laser, the silicon wafer enters the RCA cleaning tank and undergoes alkaline washing to remove the P-poly (P-type polycrystalline silicon layer) in the laser area, while retaining the P-poly in the non-laser area. This creates a height difference between the laser and non-laser areas, forming a P-laser area, which prepares the ground for subsequent processes. After the P2 laser, the silicon wafer undergoes texturing, during which the laser area is washed away, and a GAP texture is formed, thus creating a P-GAP / N-GAP area on the back side.

[0035] Example 1

[0036] This embodiment 1 provides a method for monitoring the passivation effect of back contact batteries based on undercut morphology. The production line process of the back contact batteries includes the following steps in sequence:

[0037] N-type silicon wafer → First texturing → Alkali polishing → Preparation of P-type polycrystalline silicon layer → Double-sided boron diffusion → P1 laser → RCA cleaning → Preparation of N-type polycrystalline silicon layer → Double-sided phosphorus diffusion → P2 laser → Acid etching → Second texturing → Anti-reflection coating on front and back sides → Metallization → Sintering.

[0038] The specific monitoring method is as follows: Select a silicon wafer that has been cleaned by RCA, blow dry its surface, select the positions near the middle and the edge as test positions, and then perform micro-morphology testing by scanning electron microscope (SEM) to observe the undercut morphology of the silicon wafer. Specifically, test 2 points at each test position on the silicon wafer and take the average value as the width of the undercut.

[0039] If the undercut width of the silicon wafer is observed to be greater than D (set to D = 3.0 μm), the power of the P1 laser is reduced in reverse, while the temperature of the RCA cleaning is increased and the cleaning time is reduced in reverse. If the undercut width of the silicon wafer is observed to be less than or equal to the set value of D, the silicon wafer is kept in the original production line process to continue the production of back contact cells.

[0040] Specifically, a silicon wafer that has undergone RCA cleaning (cleaning temperature 65-70℃, cleaning time 900-1100 seconds) on an existing back-contact battery production line was subjected to microscopic morphology testing (the test location was selected near the center of the silicon wafer, and two points were tested at this location; the average value was taken as the width of the undercut). The undercut morphology of the silicon wafer was observed, and the results showed that the morphology of test point 1 on the silicon wafer was as follows: Figure 1 As shown, the morphological results of test point 2 are as follows: Figure 2 As shown, the undercut width (P-GAP area undercut width) of test point 1 is approximately 2.7 μm and the depth is approximately 14.3 μm. The undercut width of test point 2 is approximately 4.1 μm and the depth is approximately 14.3 μm. It is calculated that the undercut morphology width of the silicon wafer after RCA cleaning on the existing back contact cell production line is approximately 3.4 μm (greater than the set D value). If production continues according to the existing back contact cell production line process, it is easy to cause poor electrical performance and reliability of the resulting BC cell.

[0041] Therefore, in order to obtain BC batteries with better electrical performance and reliability, based on the above observation results of the undercut morphology width of silicon wafers after RCA cleaning on the original back contact battery production line, the power of P1 laser can be reduced, and the temperature and cleaning time of RCA cleaning can be increased and decreased, respectively. Specifically, the power of P1 laser can be adjusted to 18-20W (19W specifically selected) and the temperature of RCA cleaning can be adjusted to 72-75℃ (74℃ specifically selected) and the cleaning (alkaline cleaning) time can be adjusted to 80-450 seconds (450 seconds specifically selected) based on the original production line process parameters. After adjusting the process parameters of P1 laser and RCA cleaning, the silicon wafers after RCA cleaning are selected for micromorphology testing (the position near the middle of the silicon wafer is selected as the test position, and two points are tested at this test position, and the average value is taken as the undercut width) to observe the undercut morphology of the silicon wafer. The results show that the morphology of test point 1 on the silicon wafer is as follows. Figure 3 As shown, the morphological results of test point 2 are as follows: Figure 4 As shown, the undercut width of test point 1 is about 1.8 μm and the depth is about 5.7 μm, while the undercut width of test point 2 is about 1.6 μm and the depth is about 6.1 μm. Therefore, it can be calculated that the undercut morphology width of the silicon wafer after RCA cleaning on the back contact cell production line after process adjustment is about 1.7 μm.

[0042] As can be seen, after optimization by the method of the present invention, the undercut width of the silicon wafer after RCA cleaning is significantly reduced (from 3.4 μm to 1.7 μm on the original production line). The reduction in the undercut width of the silicon wafer means that the silicon wafer has achieved better passivation. The improved passivation effect can bring better electrical performance and reliability to BC cells.

[0043] test:

[0044] The electrical performance of BC batteries produced using the original BC battery production line process and BC batteries produced using the optimized production line process of Example 1 (i.e., two types of BC batteries, one before and one after the production line process optimization) were tested, and the results are as follows:

[0045] Voc_(mV) Isc_(A) FF_(%) pFF_(%) <![CDATA[Jo_(fA / cm 2 )]]> Efficiency (%) Before optimization 735.67 13.90 78.67 84.27 7.40 24.03 After optimization 736.75 13.93 79.74 84.62 7.11 24.45

[0046] It can be seen that after the production line process of BC batteries is optimized by the reverse guidance of the method of this invention, the current, opening voltage, filling capacity, pFF and other electrical performance parameters of the produced BC batteries can be improved to a certain extent compared with the original production line process. The overall efficiency of BC batteries can be improved by about 0.42%, Voc by about 1.1mV, current by about 30mA, FF by about 1.1%, and Jo by about 0.29fA / cm 2 Therefore, this monitoring method can be fully utilized in the production process of BC batteries to monitor the bottom cutting of the batteries, thereby adjusting the laser parameters and RCA cleaning process on the BC battery production line, improving the passivation effect of the batteries, and enhancing the electrical performance and reliability of BC batteries.

[0047] Specifically, the method of the present invention can fundamentally understand the factors affecting the difference in passivation effect of the battery (excessive undercut) by observing the undercut morphology of the silicon wafer during the BC battery production process. This allows for timely adjustments to these factors affecting the passivation effect, thus solving the problem of poor passivation effect at its source.

[0048] This monitoring method differs from traditional methods for monitoring the passivation effect of BC batteries. Instead of directly providing a conclusive result on the quality of the passivation effect, this method provides an intuitive understanding of the factors affecting the passivation effect. It can predict the future trend of the passivation effect during the BC battery production process (excessive undercut indicates that the battery is trending towards poor passivation), thereby guiding the optimization of the BC battery production line process and providing guidance on how to optimize the passivation effect of BC batteries.

[0049] The method provided by this invention is a macroscopic monitoring method, for example, guiding the adjustment of laser power by increasing or decreasing it, and guiding the adjustment of temperature and time during RCA cleaning and / or secondary texturing. The specific increase or decrease in laser power and the adjustment parameters of RCA cleaning and secondary texturing can be determined by actual production line measurements to achieve the optimal adjustment results. The solution composition during RCA cleaning and / or secondary texturing can also be adjusted to reduce the corrosion rate, thereby reducing undercut.

[0050] Example 2

[0051] This embodiment 2 provides a method for monitoring the passivation effect of back contact batteries based on undercut morphology. The difference between embodiment 2 and embodiment 1 is as follows:

[0052] As a preferred option, in order to ensure the best electrical performance and reliability of the BC cells produced on the production line, Example 2 simultaneously selected to observe the undercut morphology of silicon wafers after RCA cleaning and secondary texturing; specifically, two different silicon wafers after RCA cleaning and secondary texturing on the production line can be selected respectively, and their surfaces can be dried and microscopic morphology tests can be performed to observe the undercut morphology of the two silicon wafers.

[0053] Specifically, if the undercut morphology width of the silicon wafer after RCA cleaning is observed to be greater than D, then the P1 laser power is adjusted in reverse to increase or decrease, and the temperature and cleaning time during RCA cleaning are adjusted in reverse to increase and decrease; otherwise, no adjustment is made. If the undercut morphology width of the silicon wafer after secondary texturing is observed to be greater than D, then the P2 laser power is adjusted in reverse to decrease, and the temperature and texturing time during secondary texturing are adjusted in reverse to increase and decrease; otherwise, no adjustment is made.

[0054] Specifically, in Example 2, by simultaneously selecting to observe the undercut morphology of the silicon wafer after RCA cleaning and secondary texturing, the observation results can guide the optimization of RCA cleaning process parameters and P1 laser process parameters, as well as the optimization of secondary texturing process parameters and P2 laser process parameters.

[0055] If only the silicon wafers after RCA cleaning or only the silicon wafers after secondary texturing are tested for morphology, although the overall electrical performance and reliability of BC cells produced on the production line can be improved to some extent, testing only the silicon wafers after RCA cleaning means that it can only guide the optimization of RCA cleaning process parameters and P1 laser process parameters, without clarifying whether the secondary texturing process parameters and P2 laser process parameters need to be optimized. It may also lead to problems such as poor passivation effect of silicon wafers due to poor secondary texturing process parameters and P2 laser process parameters.

[0056] Testing only the silicon wafers after secondary texturing means that the optimization of secondary texturing and P2 laser process parameters can only be guided backward, without clarifying whether the RCA cleaning and P1 laser process parameters also need optimization. This could lead to poor passivation of the silicon wafers due to unsuitable RCA cleaning and P1 laser process parameters. Therefore, it is preferable to simultaneously observe the undercut morphology of the silicon wafers after RCA cleaning and secondary texturing. The observation results can guide the optimization of RCA cleaning and P1 laser process parameters, as well as the optimization of secondary texturing and P2 laser process parameters, thereby maximizing the optimization of existing production line processes and significantly improving the electrical performance and reliability of BC cells produced on the production line.

[0057] The above-described preferred embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of the invention. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A method for monitoring the passivation effect of back contact batteries based on undercut morphology, characterized in that, The production line process for the back contact battery includes the following steps in sequence: N-type silicon wafer → First texturing → Alkali polishing → Preparation of P-type polycrystalline silicon layer → Double-sided boron diffusion → P1 laser → RCA cleaning → Preparation of N-type polycrystalline silicon layer → Double-sided phosphorus diffusion → P2 laser → Acid etching → Second texturing → Anti-reflection coating on front and back sides → Metallization → Sintering. The specific monitoring method is as follows: Select silicon wafers that have undergone RCA cleaning and / or secondary texturing, dry their surfaces, and then perform microscopic morphology testing to observe the undercut morphology of the silicon wafers. If the undercut width of the silicon wafer is observed to be greater than D, the laser process parameters and / or the alkaline washing process parameters are adjusted in reverse. If the undercut width of the silicon wafer is observed to be no more than D, the silicon wafer is kept in the original production line process flow to continue the production of back contact cells. Among them, the reverse adjustment of laser process parameters includes: increasing or decreasing the power of P1 laser and / or P2 laser; the reverse adjustment of alkaline washing process parameters includes: increasing the temperature and decreasing the time during RCA cleaning and / or secondary texturing.

2. The method for monitoring the passivation effect of back contact batteries based on undercut morphology according to claim 1, characterized in that, Two different silicon wafers that have undergone RCA cleaning and secondary texturing were selected respectively. After their surfaces were dried, their microstructure was tested to observe the undercut morphology of the two silicon wafers. If the undercut morphology width of the silicon wafer that has only undergone RCA cleaning is observed to be greater than D, then the P1 laser power is adjusted in reverse to increase or decrease and / or the temperature and cleaning time during RCA cleaning are adjusted in reverse to increase and decrease; otherwise, no adjustment is made. If the width of the undercut morphology of the silicon wafer after secondary texturing is observed to be greater than D, then the P2 laser power is adjusted in reverse to increase or decrease and / or the temperature and texturing time during secondary texturing are adjusted in reverse to increase and decrease. Otherwise, no adjustment is made.

3. The method for monitoring the passivation effect of back contact batteries based on undercut morphology according to claim 2, characterized in that, If the undercut morphology width of the silicon wafer that has only undergone RCA cleaning is observed to be greater than D, then the P1 laser power is adjusted in reverse to increase or decrease, and the temperature and cleaning time during RCA cleaning are adjusted in reverse to increase and decrease; otherwise, no adjustment is made. If the width of the undercut morphology of the silicon wafer after secondary texturing is observed to be greater than D, then the P2 laser power is adjusted in reverse to increase or decrease, and the temperature and texturing time during secondary texturing are adjusted in reverse to increase and decrease. Otherwise, no adjustment is made.

4. A method for monitoring the passivation effect of a back contact battery based on undercut morphology according to any one of claims 1 to 3, characterized in that, The value of D does not exceed 3.0 μm.

5. A method for monitoring the passivation effect of a back contact battery based on undercut morphology according to any one of claims 1 to 3, characterized in that, Select locations near the center and / or edge of the silicon wafer as test sites for micromorphology testing, and test at least 2 points at each test site, taking the average value as the width of the undercut.

6. The method for monitoring the passivation effect of back contact batteries based on undercut morphology according to claim 5, characterized in that, The microstructure of silicon wafers was tested using a scanning electron microscope.

7. The method for monitoring the passivation effect of back contact batteries based on undercut morphology according to claim 1, characterized in that, Reverse adjustment of alkaline washing process parameters also includes: adjusting the solution composition during RCA cleaning and / or secondary texturing to reduce the corrosion rate.

Images