Reverse saturation current density J of the back aluminum metal region of the battery 0 Testing method

Abstract

The present invention relates to a test method for the reverse saturation current density J0 of the back aluminum metal region of a battery, comprising the following steps: (1) Laser grooving, printing aluminum wires, and sintering are performed on the back surface of a battery substrate sample to form a main grid region, a secondary grid region, and a non-printed region; (2) A PL imager takes a PL image of the battery substrate sample; (3) An image processing software is used to automatically read the luminance values of multiple coordinate points on the PL image simultaneously. The positions where the coordinate points are automatically read are the positions around the non-printed region and the central position; the luminance values corresponding to the main grid region, the secondary grid region, and the non-printed region are denoted as P B , P F , P N ; Divide P B by P F respectively, and calculate the ratio to obtain the luminance percentages denoted as R N , R B , R F ; (4) A battery structure design simulation software is used to perform data simulation to obtain the relationship curve between the luminance percentage and J0; Substitute the values of R B and R F into the relationship curve to obtain J0 of the main grid region and J0 of the secondary grid region.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and particularly relates to a test method for the reverse saturation current density J 0 of the back aluminum metal region of the battery. Background Art

[0002] According to the crystal structure differences of silicon-based materials, they can be divided into monocrystalline silicon solar cells, polycrystalline silicon solar cells, and amorphous silicon solar cells. Conventional batteries print metal aluminum on the back surface to play a field passivation role. Although the aluminum back field (i.e., back aluminum, Al-BSF, etc.) can prevent minority carriers from migrating to the back surface and has good passivation and gettering effects, with the progress of technology, the main reasons restricting efficiency improvement are the high recombination rate and low reflectivity of the back surface of the silicon wafer. In order to reduce costs and increase efficiency, the silicon wafer is gradually thinned, but the sintering process after aluminum back field printing will cause problems such as an increase in the warpage of the battery chip and an acceleration of the back surface recombination rate. The PERC battery can well solve this problem.

[0003] The PERC battery (passivated emitter rear contact battery) adopts an inverted pyramid structure design on the front surface, and both the front surface and the back surface are passivated with an oxide layer to reduce carrier recombination. It deposits a passivation dielectric film on the back surface of the conventional battery, playing a good field passivation role; secondly, in order to reduce metal contact recombination, a local opening method is used for contact, greatly reducing the back surface recombination speed; finally, the back surface is polished to improve the light reflection of the back surface. At the same time, with the successful development of the PERC battery aluminum paste product, people have turned their attention to the research on the double-sided power generation of PERC batteries, and have successfully produced PERC batteries with an efficiency of 23.9%, and they have become the mainstream products in the market. The back surface of the double-sided PERC battery adopts an aluminum grid line structure, replacing the full aluminum back field of the conventional PERC battery, and has the advantages of double-sided power generation, high reliability of the double-glass encapsulated component, low aluminum paste consumption, and high compatibility with traditional battery technologies.

[0004] One of the important ways to improve the efficiency of the PERC battery is to reduce various recombination rates. In the prior art, there is usually no relatively convenient means to evaluate J 0 in the relevant region. For example, Chinese Patent CN20211055548.2 discloses a test method and system for the metal-induced recombination value of the back aluminum of the PERC battery, and Chinese Patent CN201911304205.8 discloses a test method for the surface recombination current density distribution of a double-sided symmetric passivated silicon wafer. They mainly achieve the same algorithm through different samples or the same sample under different test conditions, and their operation processes and calculations are relatively cumbersome. There is no relatively convenient, fast, and reliable method in the prior art to evaluate the metal-induced recombination situation in each region of the back aluminum. Summary of the Invention

[0005] To solve the technical problem of obtaining the metal composite situation of each area of the back aluminum conveniently, quickly and reliably, the reverse saturation current density J of the metal area of the battery back aluminum is provided. 0 The test method. The method of the present invention can obtain the brightness ratio of each area of the back aluminum by using simple image processing, and substituting it into the known quokka simulation software can obtain the corresponding J 0 data, which can be used to accurately and quickly evaluate the recombination rate J of the metal area of the back aluminum 0 , which can be used to assist technicians to quickly and conveniently understand the recombination situation of BSF and find out the strategy to deal with the high J of BSF 0 .

[0006] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0007] The test method of the reverse saturation current density J of the metal area of the battery back aluminum 0 includes the following steps:

[0008] (1) Prepare a battery substrate sample that has been laser grooved on the back surface, printed with only aluminum wires and sintered; the battery substrate sample forms a metal area and a non-metal area where the aluminum wires are printed;

[0009] The metal area is divided into a longitudinal main grid area (Busbar_BSF) and a transverse sub-grid area (Finger_BSF), and the non-metal area is a non-printed area where no aluminum wires are printed (the non-printed area is a back silver area containing multiple arrays. The sample in the method of the present invention does not involve the production of back silver, so the J of the metal area can be evaluated); 0

[0010] (2) Use a PL imager to take a PL image of the battery substrate sample;

[0011] (3) Use image processing software to perform image processing on the PL image to obtain brightness values, and automatically read the brightness values of multiple coordinate points on the PL image at the same time. The positions where the coordinate points are automatically read are the surrounding positions and the central position around the non-printed area. The coordinate points at the surrounding positions are automatically read in the main grid area and the sub-grid area, and the coordinate points at the central position are automatically read in the non-printed area;

[0012] The brightness value corresponding to the main grid area is denoted as P B , the brightness value corresponding to the sub-grid area is denoted as P F , and the brightness value corresponding to the non-printed area is denoted as P N ;

[0013] Dividing P B by P F respectively by P N, the calculated luminance percentages for the ratio calculation are denoted as R B and R F ;

[0014] (4) Input the process parameters related to the battery into the battery structure design simulation software to perform data simulation to obtain the relationship curve between the luminance percentage and J 0 .

[0015] Substitute the values of R B and R F obtained in step 3 into the relationship curve to obtain J 0 in the main grid area and J 0 .

[0016] Furthermore, the metal-free surface of the battery substrate sample is the light-receiving surface during shooting.

[0017] Furthermore, the image processing software is Image J software; the battery structure design simulation software is quokka simulation software.

[0018] Furthermore, the process parameters related to the battery include basic battery structure parameters, substrate material parameters, front surface parameters of the battery, back surface parameters of the battery, and optical parameters. For example, the resistivity and thickness of the silicon wafer, the number of grid lines and grid line width printed with aluminum wires on the back surface, the actual and virtual line lengths and aperture diameters of the laser openings, etc. The more detailed the parameter input, the better the accuracy and reliability of the simulated curve.

[0019] Furthermore, it also includes testing J 0 of the entire back surface, calculating the average value of P B and P F , dividing by P N , and denoting the calculated luminance percentage for the ratio calculation as R 整体 . Substitute the value of R 整体 into the relationship curve to obtain J 0 of the entire back surface.

[0020] Advantageous technical effects:

[0021] The calculation of the recombination rate of the metal and non-metal regions on the back surface of the present invention does not require complex operations, only requires the operator to be proficient in operating the relevant software. At the same time, there is no need to prepare special screen plates or laser processes, and sample preparation can be directly achieved on the production line. The method of the present invention can realize the differential calculation of J 0 in the main grid area and the secondary grid area of the metal region, and can also calculate J 0 of the entire back surface. The operation method is simple, fast, and the calculated J 0 has good reliability. Description of the Drawings

[0022] Figure 1 It is a cross-sectional SEM image of a BSF (aluminum back surface field cell). The present invention tests the reverse saturation current in the metal region (abbreviated as J in the metal region) for the composite situation of this part. 0 )

[0023] Figure 2 It is a schematic structural diagram of a battery substrate sample, where 1 is the lateral sub-grid region, 2 is the longitudinal main-grid region, and 3 is the non-printing region.

[0024] Figure 3 It is a flowchart of the test method for J in the back aluminum metal region of the battery of the present invention. 0

[0025] Figure 4 It is a PL imaging diagram of the battery substrate sample printed with aluminum paste A in Example 2.

[0026] Figure 5 In Example 2, the ImageJ image processing software is used to automatically read the luminance values of coordinate points of the battery substrate sample; where A is the automatic reading effect diagram of the luminance value coordinate points in the main-grid region, B is the automatic reading effect diagram of the luminance value coordinate points in the sub-grid region, C is the automatic reading effect diagram of the luminance value coordinate points in the non-printing region, and D is the automatic reading effect diagram of the overall coordinate points on the back surface.

[0027] Figure 6 It is the automatic reading effect diagram of the overall coordinate points on the back surface of the PL imaging diagram of the battery substrate sample printed with aluminum paste B in Example 3 under the ImageJ image processing software.

[0028] Figure 7 It is the automatic reading effect diagram of the overall coordinate points on the back surface of the PL imaging diagram of the battery substrate sample printed with aluminum paste C in Example 4 under the ImageJ image processing software.

[0029] Figure 8 It is a curve relationship diagram of the luminance ratio and J0 simulated by the quokka simulation software according to the input process parameters. Specific embodiments

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments and drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0031] Unless otherwise specifically stated, the numerical values set forth in these embodiments do not limit the scope of the present invention. Technologies and methods known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such technologies and methods should be regarded as part of the specification. In all examples shown and discussed herein, any specific values should be construed as merely exemplary and not as limiting. Accordingly, other examples of the exemplary embodiments may have different values.

[0032] For the experimental methods without specific conditions noted in the following embodiments, they are generally determined according to national standards; if there is no corresponding national standard, they are carried out according to general international standards or the standard requirements proposed by relevant enterprises. Unless otherwise specified, all parts are by weight and all percentages are by weight percentage.

[0033] Reverse saturation current density J of the metal region 0 Hereinafter referred to as J of the metal region 0 。

[0034] Example 1

[0035] Input process parameters related to the battery into the quokka simulation software for battery structure design for data simulation. The battery process parameters in this embodiment adopt the process parameters of 10BB PERC products, and the process parameters include basic parameters of the battery structure, substrate material parameters, front surface parameters of the battery, back surface parameters of the battery, optical parameters, and so on.

[0036] After simulation, the relationship curve between the light luminance percentage r_PL and J 0 is obtained, and the relationship curve is as Figure 8 shown.

[0037] Example 2

[0038] Testing method for J of the back aluminum metal region of the battery 0 is as shown in Figure 3 and includes the following steps:

[0039] (1) Prepare a battery substrate sample that has been laser grooved on the back surface and only printed with aluminum wires (using aluminum paste A) and sintered. The structural schematic diagram of the battery substrate sample is as Figure 2 shown: The battery substrate forms a metal region and a non-metal region where the aluminum wires are printed; the metal region is divided into a longitudinal main grid region 2 (Busbar_BSF) and a transverse sub-grid region 1 (Finger_BSF), and the non-metal region is a non-printed region 3 where no aluminum wires are printed, and the non-printed region 3 is used for printing the back silver, and the preparation of the sample in the present invention does not involve the back silver;

[0040] (2) Use a PL imager to take a picture of the battery substrate sample to obtain a PL imaging diagram, and the PL imaging diagram is as Figure 4As shown;

[0041] (3) using Image J image processing software to process the PL image to obtain the brightness value, and automatically reading the brightness values ​​of multiple coordinate points on the PL image at the same time, the positions where the coordinate points are automatically read are the surrounding positions and the center position around the non-printing area 3, the coordinate points of the surrounding positions are automatically read in the longitudinal direction of the main grid area 2 and the transverse direction of the secondary grid area 1, and the coordinate points of the center position are automatically read in the center of the non-printing area 3; (the automatic reading of the coordinate points is achieved by writing the relevant program language of the Image J image processing software to realize the output of the brightness value after marking multiple coordinate points in each area);

[0042] The coordinate points of the main grid area 2, the auxiliary grid area 1 and the non-printing area 3 are automatically read as follows: Figure 5 As shown in A, B, and C, Figure 5 D is the automatic reading effect diagram of the overall coordinate points on the back surface;

[0043] The brightness value corresponding to the main grid area 2 is recorded as P B , the corresponding brightness value of the auxiliary grid area 1 is recorded as P F , and the brightness value corresponding to the non-printing area 3 is recorded as P N ;

[0044] P B With P F Divide by P N , and the percentage of brightness is calculated as R B , R F ; That is, P B ÷P N =R B , P F ÷P N =R F ;

[0045] P B With P F Take the average and divide by P N The percentage of brightness calculated by ratio is recorded as R 整体 ; that is, [average(P B , P F )]÷P N =R 整体 ;

[0046] Table 1 PL imaging data of printed aluminum paste A

[0047]

[0048] (4) R obtained in step 3 B , RF Substitute the value of R 整体 into r_PL of the relationship curve in Example 1 to obtain the main grid region J 0 and the secondary grid region J 0 . The relevant J 0 data results are shown in Table 4.

[0049] Example 3

[0050] Testing method for the aluminum metal region J 0 of the battery back, the process flow is as Figure 3 shown, including the following steps:

[0051] (1) Prepare a battery substrate sample that has been laser grooved on the back surface and only printed with aluminum wires (using aluminum paste B) and sintered. The structural schematic diagram of the battery substrate sample is as Figure 2 shown: The battery substrate forms a metal region and a non-metal region for printing aluminum wires; the metal region is divided into a longitudinal main grid region 2 (Busbar_BSF) and a transverse secondary grid region 1 (Finger_BSF), and the non-metal region is a non-printed region 3 where no aluminum wires are printed. The non-printed region 3 is used for printing the back silver. In the present invention, the preparation of the sample does not involve the back silver;

[0052] (2) Use a PL imager to take a picture of the battery substrate sample to obtain a PL imaging diagram. The PL imaging diagram is as Figure 4 shown;

[0053] (3) Use Image J image processing software to perform image processing on the PL imaging diagram to obtain luminance values. Automatically read the luminance values of multiple coordinate points on the PL imaging diagram at the same time. The positions where the coordinate points are automatically read are the surrounding positions and the central position of the non-printed region 3. The coordinate points at the surrounding positions are automatically read in the longitudinal main grid region 2 and the transverse secondary grid region 1, and the coordinate points at the central position are automatically read at the center of the non-printed region 3; (The automatic reading of the coordinate points is achieved by writing relevant programming languages for the Image J image processing software to mark multiple coordinate points in each region and then output the luminance values);

[0054] The effect diagram of automatically reading the coordinate points of the luminance values of the main grid region 2, the secondary grid region 1, and the non-printed region 3 is as Figure 6 shown;

[0055] The luminance value corresponding to the main grid region 2 is denoted as P B , the luminance value corresponding to the secondary grid region 1 is denoted as P F , and the luminance value corresponding to the non-printed region 3 is denoted as P N ;

[0056] Compare P B with P FDivide by P respectively N , and the luminance percentages obtained by ratio calculation are denoted as R B 、R F ; that is, P B ÷P N = R B , P F ÷P N = R F ;

[0057] Take the average value of P B and P F and then divide by P N , and the luminance percentage obtained by ratio calculation is denoted as R 整体 ; that is, [average(P B , P F )]÷P N = R 整体 ;

[0058] Table 2 Data related to the PL imaging diagram of printed aluminum paste B

[0059]

[0060] (4) Substitute the values of R B , R F and R 整体 into r_PL of the relationship curve in Example 1 to obtain the main grid region J 0 , the secondary grid region J 0 , and the relevant J 0 data results are shown in Table 4.

[0061] Example 4

[0062] Test method for J 0 in the back aluminum metal region of the battery, and the process flow is as Figure 3 shown, including the following steps:

[0063] (1) Prepare a battery substrate sample with only aluminum wires printed (using aluminum paste C) after laser grooving on the back surface and sintered. The structural schematic diagram of the battery substrate sample is as Figure 2 shown: The battery substrate forms a metal region and a non-metal region for printing aluminum wires; the metal region is divided into a longitudinal main grid region 2 (Busbar_BSF) and a transverse secondary grid region 1 (Finger_BSF), and the non-metal region is a non-printing region 3 where no aluminum wires are printed. The non-printing region 3 is used for printing back silver, and the preparation of the sample in the present invention does not involve back silver;

[0064] (2) Use a PL imager to take a PL imaging diagram of the battery substrate sample, and the PL imaging diagram is as Figure 4 shown;

[0065] (3) Use the Image J image processing software to process the PL imaging map to obtain the luminance values. Automatically read the luminance values at multiple coordinate points on the PL imaging map simultaneously. The positions where the coordinate points are automatically read are the surrounding positions and the central position around the non-printing area 3. The coordinate points at the surrounding positions are automatically read in the longitudinal main grid area 2 and the transverse sub-grid area 1, and the coordinate points at the central position are automatically read at the center of the non-printing area 3; (The automatic reading of the coordinate points is achieved by writing relevant programming languages for the Image J image processing software to mark multiple coordinate points in each area and then output the luminance values);

[0066] The effect diagrams of the automatic reading of the coordinate points of the luminance values in the main grid area 2, the sub-grid area 1, and the non-printing area 3 are respectively as Figure 7 shown;

[0067] The luminance value corresponding to the main grid area 2 is denoted as P B , the luminance value corresponding to the sub-grid area 1 is denoted as P F , and the luminance value corresponding to the non-printing area 3 is denoted as P N ;

[0068] Divide P B by P F respectively, and the calculated luminance percentages of the ratio are denoted as R N , R B , R F ; that is, P B ÷P N = R B , P F ÷P N = R F ;

[0069] Take the average of P B and P F , and then divide by P N , and the calculated luminance percentage of the ratio is denoted as R 整体 ; that is, [average(P B , P F )]÷P N = R 整体 ;

[0070] Table 3 Data related to the PL imaging map of the printed aluminum paste C

[0071]

[0072] (4) Take the R B , R F and R 整体Substituting the numerical value into r_PL of the relationship curve in Example 1 can obtain the main grid region J 0 and the secondary grid region J 0 . The relevant J 0 data results are shown in Table 4.

[0073] Table 4 Relevant J in Examples 2 - 4 0 data

[0074]

[0075] As can be seen from Table 4, the aluminum paste B used in Example 2 has a relatively low reverse saturation current density J 0 value, which means that using the aluminum paste B in Example 2 has a lower recombination rate. If necessary, the R 整体 data in Tables 1 - 3 can be substituted into Figure 8 the curve to calculate the overall J 0 .

[0076] The method of the present invention can calculate the recombination rate of the back aluminum metal region J 0 quickly, efficiently and conveniently, and can assist technicians in judging the quality of the materials used.

[0077] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. Test method for the reverse saturation current density J of the aluminum metal region on the battery back 0 ​ It is characterized in that it includes the following steps: (1) The back surface of the battery substrate sample is successively subjected to laser grooving, aluminum wire printing, and sintering to form a metal area and a non-metal area with printed aluminum wires; The metal area is divided into a longitudinal main grid area (2) and a transverse sub-grid area (1), and the non-metal area is a non-printed area (3) without printed aluminum wires; (2) Use a PL imager to take a picture of the battery substrate sample to obtain a PL imaging diagram; (3) Use image processing software to automatically read the luminance values of multiple coordinate points on the PL imaging diagram at the same time. The positions where the coordinate points are automatically read are the surrounding positions and the central position around the non-printed area (3). The coordinate points at the surrounding positions are automatically read in the main grid area (2) and the sub-grid area (1), and the coordinate points at the central position are automatically read in the non-printed area (3); The luminance values corresponding to the main gate region (2), the sub-gate region (1), and the non-printing region (3) are respectively denoted as P B , P F , P N ; Divide P B and P F by P N respectively, and the luminance percentages obtained by ratio calculation are respectively denoted as R B , R F ; (4) Input process parameters related to the battery into the battery structure design simulation software to perform data simulation to obtain the relationship curve between the percentage of luminance and J 0 ; Substitute the R obtained in step 3 B and R F values into the relationship curve to obtain the main gate region J 0 and the sub-gate region J 0 .

2. The test method for the reverse saturation current density J of the aluminum back metal region of the battery according to claim 1 0 ​ It is characterized in that the metal-free surface of the battery substrate sample is the light-receiving surface when the PL imager takes pictures.

3. The test method for the reverse saturation current density J of the back aluminum metal region of the battery according to claim 1 0 ​ It is characterized in that the image processing software is Image J software; the battery structure design simulation software is quokka simulation software.

4. The test method for the reverse saturation current density J of the aluminum back metal region of the battery according to claim 1 0 ​ It is characterized in that the process parameters related to the battery include basic battery structure parameters, substrate material parameters, battery front surface parameters, battery back surface parameters, and optical parameters.

5. The test method for the reverse saturation current density J of the aluminum back metal region of the battery according to any one of claims 1-4 0 ​ It is characterized in that It also includes measuring J for the entire back surface 0 , for P B With P F After taking the average value and dividing by P N , the calculated luminance percentage for the ratio calculation is denoted as R 整体 , Substitute the value of R 整体 into the relationship curve to obtain J for the entire back surface 0 .

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