Non-contact testing method and sorting method for open-circuit voltage of solar cell

Abstract

The invention relates to the technical field of solar cells, and discloses a non-contact testing method and a sorting method for open-circuit voltage of a solar cell. The test method comprises the following steps: selecting s > = 3 standard sheets; dividing a to-be-detected battery piece (a to-be-detected piece) and a standard piece into m areas which are greater than or equal to 5; measuring the PL brightness Lsm of each area of the standard film and the PL brightness L'm of each area of the to-be-measured film; according to the direct proportion relation between the PL brightness and the open-circuit voltage, the open-circuit voltage Vsm of each area of the standard film is obtained by combining the Lsm; according to the direct proportion relation between the PL brightness and the open-circuit voltage, obtaining the open-circuit voltage V'm formula of each area of the to-be-measured chip: V'm = Vsm * L'm / Lsm; and combining Lsm, Vsm, L'm and the formula to obtain s standard sheets, respectively calibrating s open-circuit voltage V's data of the tested to-be-tested sheets, and averaging to obtain the open-circuit voltage V'data of the to-be-tested sheets, so that the defect of contact test sorting of an IV tester is avoided, the consumed time is short, and the test sorting result is accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of solar cells, and in particular to a non-contact testing method and a sorting method for the open-circuit voltage of solar cells. Background Art

[0002] To cope with the cyclical fluctuations in the photovoltaic industry, the most significant research directions and achievements in cost reduction are currently focused on silicon costs and non-silicon silver costs, including:

[0003] 1) Continuous thinning of silicon wafers. Before 2015, the thickness of P-type monocrystalline silicon wafers remained stable at 200μm. From 2015 to 2018, the thickness of silicon wafers dropped to 180μm. From 2019 to 2021, N-type silicon wafers began to gradually dominate the market, and the thickness of monocrystalline silicon wafers dropped to 170μm. After 2022, the thickness of silicon wafers dropped rapidly. Currently, the mainstream TOPCon solar cells in the market use N-type monocrystalline silicon wafers with a thickness of 130μm. The cost of silicon wafers accounts for a large proportion of the manufacturing cost of TOPCon solar cells, usually 60-70%. Therefore, reducing the thickness of silicon wafers can effectively reduce the manufacturing cost of solar cells.

[0004] 2) Reduce silver consumption. The main grid on the front of the solar cell (the main grid is made of silver paste) is gradually changing to a multi-bus bar (MBB), even a super-many bus bar (SMBB), and gradually to a zero bus bar (0BB) structure. MBB and SMBB use thin and narrow main grids instead of the traditional thick and sparse main grids, which can improve carrier collection capacity and reduce silver paste consumption. The 0BB structure is more direct, removing the main grid and retaining only the thin grid, which directly reduces silver paste consumption. The purpose of this is to: first, reduce silver paste consumption; second, increase the light-receiving area on the front of the solar cell, allowing more light to enter the cell, further increasing the current density, and improving cell efficiency. In the manufacturing cost of TOPCon solar cells, the cost of silver generally accounts for 60-70% of the non-silicon cost and 16-25% of the overall solar cell cost. Therefore, reducing silver consumption can also effectively reduce costs.

[0005] After manufacturing, any type of solar cell requires testing and sorting to categorize or grade the cells based on their electrical performance. (This is because solar cells with different electrical properties, when used in the same solar module manufacturing process, can produce defects such as differences in brightness and EL (electroluminescence). Although busbar-less solar cells (OBB cells) offer significant advantages in reducing costs and improving efficiency, traditional current-voltage (IV) testers (used to test certain electrical properties of solar cells) are unable to effectively measure the IV performance of OBB cells, and therefore are unable to sort them. This is because IV testers typically use Ohm's theorem (I=U / R) to place a cell in the tester and install probe rows on the top and bottom of the cell, equal to the number of busbars on the top and bottom surfaces of the cell. During testing, the probe rows are pressed against the cell's busbars, and the current / voltage values ​​are measured by the voltage / current changes. However, current IV testers set the number of probe rows based on the number of busbars. Fine grid lines are thinner, making accurate testing of the fine grid much more difficult than that of the main grid. Furthermore, the fine grid can withstand less pressure, current, and voltage than the main grid, making it more susceptible to damage. Therefore, compared to traditional solar cells with a main grid, 0BB cells lack a main grid, making it more difficult to test the grid lines with a probe array. Furthermore, thinning the cells further increases the risk of damage to the 0BB cells.

[0006] Currently, there are two main effective methods for testing the IV performance of 0BB cells: 1. Increasing the number of probe rows allows for data collection. 2. Replacing the probe rows of conventional IV testers with bougies allows the larger contact area to allow the bougies to contact more fine grids, collecting fine grid currents to achieve IV performance testing. However, while IV testing can be completed for both 0BB cells and MBB, SMBB, and other cells by increasing the number of probe rows or replacing them with bougies, this introduces new challenges, as described below, hindering the detection and sorting of solar cells with different electrical properties:

[0007] 1. Increasing the number and contact area of ​​probe rows increases the amount of light blocking the solar cell surface. Solar cells convert light energy into electricity. Furthermore, IV testing of solar cells involves providing a standard light source, and then collecting current / voltage data through the probe rows to perform IV performance testing. Therefore, increasing the amount of light blocking by the probe rows directly leads to IV test inaccuracy.

[0008] 2. Difficulty aligning the probe rows with the gate lines. Although increasing the number of probe rows can complete IV testing, aligning the probe rows with the gate lines (such as fine gates) is still difficult and time-consuming.

[0009] 3. Easy to crush the cell. As mentioned above, thinning has become a trend, and cell wafers are getting thinner and thinner. Whether increasing the number of probe rows or replacing them with probe bars, as long as they are used to press fine grids for IV testing, there is a possibility that the probe rows or probe bars will not press accurately, causing uneven force on the surface of the thinned cell wafer, which can easily lead to cell fragmentation.

[0010] 4. The increase in the number of probes (or probe rows) leads to an increase in the probability of probe errors, an increase in probe row loss, and an increase in test costs.

[0011] In addition, as described in publication number CN103364704A, a method for predicting the open circuit voltage of a polycrystalline silicon wafer is based on the PL image calculation formula and the parameters α and β to substitute the result into the open circuit voltage prediction formula, thereby inferring the open circuit voltage result. Therefore, the prior art CN103364704A is a "theoretical (PL brightness calculation formula) → theoretical (open circuit voltage prediction formula)" method; and this theory → theory prediction method ignores the impact of the actual environment (such as edge effects, and environmental factors such as temperature and humidity) on the test results; moreover, this theory → theory prediction method does not have an error correction mechanism. Therefore, the open circuit voltage prediction method of the prior art CN103364704A has the defects of high prediction and error correction time cost, and poor stability and accuracy of the prediction results; and furthermore, it is impossible to sort the battery cells based on the prediction results of its open circuit voltage. Summary of the Invention

[0012] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a non-contact testing method and a sorting method for the open-circuit voltage of solar cells.

[0013] Based on this, the present invention discloses a non-contact test method for the open circuit voltage of a solar cell, comprising the following steps:

[0014] Step 1: Select s standard cells, where s≥3; the PL brightness and open-circuit voltage of the standard cells are recorded as Ls and Vs respectively; and the PL brightness and open-circuit voltage of the cell to be tested are recorded as L' and V' respectively;

[0015] Step 2: Divide the surface of the cell to be tested and each standard cell into m areas, where m ≥ 5; use PL brightness test equipment to test and obtain the PL brightness Ls of each area of ​​the standard cell. m and the PL brightness L' of each area of ​​the cell to be tested m data;

[0016] Step 3: Based on the proportional relationship between the PL brightness of the cell and the open circuit voltage, combined with the PL brightness Ls of each area of ​​the standard cell m Data, get the open circuit voltage Vs corresponding to each area of ​​the standard battery cellm The open circuit voltage of each region of the cell to be tested is recorded as V' m According to the proportional relationship between the PL brightness of the cell and the open circuit voltage, we can get formula (4) V' m =Vs m ×L' m / Ls m ;

[0017] Step 4: PL brightness Ls of each area of ​​the standard cell m and open circuit voltage Vs m Data, and the PL brightness L' of each area of ​​the cell to be tested m The data is combined with formula (4) to obtain s open circuit voltage V's data of the cell to be tested after s standard cells are calibrated and tested. The average value of the s open circuit voltage V's data is taken to obtain the open circuit voltage V' data of the cell to be tested.

[0018] Preferably, in step 1, the standard cell is a first-class standard cell certified by an authoritative organization in the photovoltaic industry.

[0019] Preferably, in step 1, the standard cell is a secondary standard cell calibrated with a primary standard cell.

[0020] Further preferably, in step 1, the calibration step of the secondary standard cell includes:

[0021] Step 11: Use several primary standard battery cells to calibrate the IV tester;

[0022] Step 12: Use a calibrated IV tester to test the conversion efficiency and open circuit voltage of the secondary standard battery cell.

[0023] Preferably, in step 1, the selected standard battery cell meets the following conditions:

[0024] The material type, size and appearance of the standard cell are consistent with those of the cell to be tested, the spectral response of the standard cell is consistent with that of the cell to be tested, the electrical performance temperature coefficient of the standard cell is matched with that of the cell to be tested, and the electrical performance of the selected standard cell is stable without light decay or environmental aging.

[0025] Preferably, in step 2, the middle and edges of the surface of each battery cell are divided into regions.

[0026] Preferably, in step 3, the process of determining the proportional relationship between the PL brightness of the cell and the open circuit voltage is specifically as follows:

[0027] Step 31: The calculation formula of the open circuit voltage V of the battery cell is as follows (1):

[0028]

[0029] In formula (1), n ​​is the diode ideal factor, k is the Boltzmann constant, T is the absolute temperature, q is the electron charge, and I ph is the photocurrent, I0 is the diode saturation current; n, k, T, q in formula (1) are all constants, I ph Affected by the IV tester light source, it can remain constant, so the variable that affects the open circuit voltage V is the diode saturation current I0; and according to formula (1), the reciprocal of the diode saturation current 1 / I0 is proportional to the open circuit voltage V, expressed as 1 / I0∝V;

[0030] Step 32: The calculation formula of the diode saturation current I0 is as shown in the following formula (2):

[0031]

[0032] In formula (2), q is the electron charge, n i is the intrinsic carrier concentration, N D 、N A are the impurity concentrations of the donor and acceptor, respectively, D n 、D p are the diffusion coefficients of electrons and holes, τ n , τ p are the minority carrier lifetimes of electrons and holes, respectively; q and D in formula (2) n 、D p is a constant, N D 、N A , τ n , τ p It is related to the doping concentration and passivation ability of the cell and can remain constant. Therefore, according to formula (2), the minority carrier lifetime τ is proportional to the inverse of the diode saturation current 1 / I0, expressed as τ∝1 / I0;

[0033] Step 33: Combined with the above, the PL brightness L is proportional to the minority carrier lifetime τ, expressed as L∝τ; that is, L∝τ∝1 / I0∝V, so the PL brightness L is proportional to the open-circuit voltage V, that is, L∝V.

[0034] Further preferably, in step 3, according to the proportional relationship between the PL brightness of the cell and the open circuit voltage, formula (3) is obtained: Vs m / V' m =Ls m / L' m , formula (3) is transformed to get formula (4) V' m =Vs m ×L' m / Lsm .

[0035] Preferably, the step 4 specifically includes:

[0036] Step 41: PL brightness Ls of each area of ​​one standard cell m and open circuit voltage Vs m Data, and the PL brightness L' of each area of ​​the cell to be tested m The data, combined with formula (4), can be used to obtain the open circuit voltage V' of each area of ​​the cell to be tested after the calibration test of the standard cell. m Data, open circuit voltage V' of each region m The data is averaged to obtain the open circuit voltage V's data of the cell to be tested after the calibration test of the standard cell.

[0037] Step 42, repeat step 41 to obtain s-1 open circuit voltage V's data of the battery cell to be tested after the remaining s-1 standard battery cells are calibrated and tested; average the s open circuit voltage V's data to obtain the open circuit voltage V' data of the battery cell to be tested.

[0038] The present invention also discloses a non-contact sorting method for open-circuit voltage of solar cells, comprising the following steps:

[0039] Step 1: Using the non-contact test method for the open circuit voltage of a solar cell described above in the present invention, obtain the open circuit voltage V' data of the cell to be tested;

[0040] Step 2: sort the cells to be tested according to the open circuit voltage V' data of the cells to be tested and the cell sorting rules.

[0041] Compared with the prior art, the present invention has at least the following beneficial effects:

[0042] The present invention avoids many disadvantages of contact testing and sorting using an IV tester by performing non-contact testing and sorting on the battery cells to be tested: 1. Since the open-circuit voltage of the battery cell to be tested is tested non-contactly, there is no pressing and electrical contact of the probe row or probe on the battery cell to be tested during the IV test. Therefore, there is no shading phenomenon caused by the probe row or probe during the non-contact test, and the non-contact test results of the open-circuit voltage of the battery cell to be tested are more accurate. 2. Since the PL brightness test process is extremely simple and does not require the use of a probe row structure, there is no need for pressing needles, testing, spring reset and other actions, so the test time is shortened, which can greatly improve the work efficiency of non-contact testing and sorting. 3. For thin-film battery cells, there is no risk of the probe row or probe crushing the battery cell during non-contact testing and sorting. 4. During the non-contact test of the open-circuit voltage of the battery cell to be tested, a large number of probe row structures are discarded, and the cost and time generated by probe loss and maintenance are greatly reduced.

[0043] Moreover, compared with the prior art CN103364704A, the non-contact testing method of the present invention has more advantages in terms of test time compression and test result stability and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a structural diagram of dividing the surface of a solar cell into five areas in step 2 of a non-contact test method for the open-circuit voltage of a solar cell according to this embodiment.

[0045] Figure 2 1 is a data diagram comparing the open circuit voltage of the non-contact high voltage measured by the non-contact testing method of this embodiment and the actual high voltage measured by the existing IV tester.

[0046] Figure 3 1 is a data diagram comparing the open circuit voltage of the non-contact medium voltage measured by the non-contact testing method of this embodiment and the actual medium voltage measured by the existing IV tester.

[0047] Figure 4 1 is a data diagram comparing the open circuit voltage of the non-contact low voltage measured by the non-contact testing method of this embodiment and the actual low voltage measured by the existing IV tester.

[0048] Figure 5 for Figure 2-4 An integrated diagram of three sets of open circuit voltage comparison data. DETAILED DESCRIPTION

[0049] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0050] Example

[0051] A non-contact test method for the open-circuit voltage of a solar cell according to this embodiment includes the following steps:

[0052] Step 1: Select s standard cells (referred to as standard cells), where s≥3. The PL brightness and open-circuit voltage of the standard cells are recorded as Ls and Vs, respectively; and the PL brightness and open-circuit voltage of the cell to be tested are recorded as L' and V', respectively. For example, when the number of standard cells selected is s=3, the PL brightness of these three standard cells are recorded as L1, L2, and L3, respectively, and the open-circuit voltages of these three standard cells are recorded as V1, V2, and V3, respectively.

[0053] In one example of this embodiment, the standard sample selected in step 1 is a first-level standard sample. Each company's first-level standard samples are certified by authoritative organizations in the photovoltaic industry, such as Rhine, TUV, and ISFH. Therefore, the electrical performance data (such as cell conversion efficiency and open-circuit voltage) of the first-level standard samples are known.

[0054] In another example of this embodiment, the standard chip selected in step 1 is a secondary standard chip calibrated with a primary standard cell (for example, a calibrated secondary standard chip with a conversion efficiency of 26.0% and a medium voltage M (0.734-0.737mV)). Furthermore, when the standard chip selected in step 1 is a secondary standard chip, it is necessary to calibrate the secondary standard chip multiple times using a primary standard chip obtained from an authoritative organization. The calibration steps for the secondary standard chip include:

[0055] Step 11: Use a test device (e.g., an IV tester) to perform a cross-test (e.g., a cross-test of conversion efficiency) on several first-level standard wafers to verify the repeatability and accuracy of the test device (this process is referred to as calibrating the test device using several first-level standard wafers). For example, use several first-level standard wafers with a conversion efficiency of 26.0% to calibrate the test device (e.g., an IV tester) so that the test results stabilize at 26.0%.

[0056] Step 12: Then, use the calibrated test equipment to test the conversion efficiency and open-circuit voltage of the secondary standard chip multiple times, and take the average of the data from multiple tests to obtain the conversion efficiency and open-circuit voltage of the secondary standard chip.

[0057] In step 1, the selected labels must meet the following conditions:

[0058] a) The label must be consistent with the material type, size and appearance of the battery cell to be tested.

[0059] b) The electrical performance temperature coefficient of the standard chip (such as open circuit voltage temperature coefficient β, short circuit current temperature coefficient α, etc.) must match the battery cell to be tested to ensure test accuracy at different temperatures.

[0060] c) The spectral response of the standard chip must be consistent with that of the cell to be tested to avoid measurement errors caused by spectral mismatch, such as calibration under the AM1.5G standard spectrum.

[0061] d) In addition, the electrical properties of the standard chip (such as conversion efficiency, IV curve, etc.) must be stable over a long period of time, with little to no light decay or environmental aging.

[0062] In step 1, the number of standard slices s is at least 3. This is because the existence of test error is taken into account:

[0063] a) Calibration with only one standard slide will prevent any random errors from being detected because there is only one set of data to compare. b) Calibration with two standard slides will generate two sets of data. If an error occurs, it is still impossible to determine whether the error originated from slide L1 or slide L2 because it is impossible to determine which set of data is the correct value and which is the error value. c) Calibration with three standard slides significantly reduces the probability of error because the test results contain both positive and negative errors. The probability of simultaneous errors in the test results of three standard slides is already very low, and the probability of simultaneous positive or negative errors is even lower. Therefore, at least three standard slides are required. Of course, the number of standard slides can be increased to increase accuracy.

[0064] Step 2: Divide the surface of each standard sheet into m areas, where m ≥ 5. In line with the standard sheet, the surface of the cell to be tested is also divided into m areas. Use PL brightness test equipment to test and obtain the PL brightness Ls of each area of ​​the standard cell. m and the PL brightness L' of each area of ​​the cell to be tested m data.

[0065] In step 2, the center and edges of each cell surface are divided into regions. Figure 1 As shown in the figure, when m=5, the five areas are located at the upper left 1, upper right 2, lower left 3, lower right 4, and center 5 of the surface of the standard sheet respectively; taking standard sheet s as an example, the PL brightness data of the five areas of standard sheet s are recorded as Ls1, Ls2, Ls3, Ls4, and Ls5 respectively; and the PL brightness data of each area of ​​the battery cell to be tested are recorded as L'1, L'2, L'3, L'4, and L'5 respectively.

[0066] In step 2, the number of divided regions m on the surface of the cell to be tested and each standard wafer is at least 5. Of course, the number of divided regions on the standard wafer and the cell to be tested can be increased to ensure higher accuracy. In step 2, the number of divided regions and the number of regions on the standard wafer and the cell to be tested must be consistent.

[0067] Furthermore, the region division rules in this embodiment should distinguish between the edge and center of the cell surface (e.g., the standard cell, the cell under test). This is because the "edge effect" can cause differences in performance between the edge and center of the cell during the manufacturing process (e.g., the center of the cell is smoother than the edge during coating, the center is more uniformly doped than the edge during doping, and the edge is more damaged than the center during etching). The accumulation of these differences between the center and edge of the cell ultimately leads to different performance across different regions of the cell surface. Therefore, calibrating and testing data from the center of the standard cell with data from the edge of the cell under test (e.g., open-circuit voltage) will result in test errors. Using data from corresponding regions of the standard cell and the cell under test with similar performance for performance calibration and testing can effectively reduce test and sorting errors for the cell under test. Therefore, dividing the cell surface (including the standard cell and the cell under test) into multiple regions for testing and sorting helps improve the test accuracy of the open-circuit voltage of the cell under test and reduce test and sorting errors. Therefore, in step 2 of this embodiment, the test areas on the surfaces of the standard wafer and the cell to be tested are carefully divided.

[0068] It should be noted that the existing technology directly measures the PL brightness of the entire cell, without dividing the cell surface into regions. This is because PL brightness is typically used as an analytical test method and does not require high precision. In contrast, this embodiment uses the PL brightness of the reference sample and the cell under test (as well as the reference sample's open-circuit voltage) as a bridge for non-contact testing of the cell under test's open-circuit voltage, which requires higher precision.

[0069] Step 3: Based on the proportional relationship between the PL brightness of the cell and the open circuit voltage, combined with the PL brightness Ls of each area of ​​the standard cell m Data, get the open circuit voltage Vs corresponding to each area of ​​the standard battery cell m The open circuit voltage of each region of the cell to be tested is recorded as V' m For example, when m=5, taking the standard sheet s as an example, the open circuit voltage data of the five regions of the standard sheet s are recorded as Vs1, Vs2, Vs3, Vs4, and Vs5 respectively; and the PL brightness data of each region of the cell to be tested are recorded as L'1, L'2, L'3, L'4, and L'5 respectively.

[0070] Step 3 also includes: according to the proportional relationship between the PL brightness of the cell and the open circuit voltage, formula (4) V' is obtained m =Vs m ×L' m / Ls m .

[0071] The operating principle of an IV tester for crystalline silicon solar cells is primarily based on the photoelectric effect and circuit measurement principles. Specifically, when standard sunlight simulated by the IV tester strikes a crystalline silicon solar cell, photons interact with the crystalline silicon material, and the photon energy is absorbed by the crystalline silicon, generating electron-hole pairs. Under the influence of the cell's internal electric field, the electrons and holes are separated, with electrons migrating to the negative electrode and holes to the positive electrode, thereby generating a photogenerated current. The probes in the probe array collect the current and voltage data generated by the cell. This data is integrated by existing software programs to output key cell parameters such as short-circuit current, open-circuit voltage, maximum power point current, maximum power point voltage, fill factor, and conversion efficiency.

[0072] For solar cell testing and sorting, the primary data used is the cell's conversion efficiency and open-circuit voltage. Specifically, after IV testing, cells are first binned based on conversion efficiency, with cells of the same efficiency grouped as Group A. Cells in Group A are then divided into three groups based on their open-circuit voltage: high voltage (H), medium voltage (M), and low voltage (L).

[0073] Therefore, open circuit voltage is a further basis for cell sorting. Furthermore, the key factors affecting short-circuit current are light intensity, spectral distribution, cell test temperature, cell material and structure, and cell area. Therefore, for standard cells and test environments, short-circuit current does not vary much, so the main factor affecting cell sorting is open circuit voltage.

[0074] Based on this, in step 3, the process of determining the proportional relationship between the PL brightness of the cell and the open circuit voltage is specifically as follows:

[0075] Step 31: The calculation formula of the open circuit voltage V of the battery cell is as follows (1):

[0076]

[0077] In formula (1), n ​​is the diode ideal factor, k is the Boltzmann constant, T is the absolute temperature, q is the electron charge, and I ph is the photocurrent, and I0 is the diode saturation current.

[0078] In formula (1), n, k, T, and q are all constants. ph Affected by the IV tester's light source, the diode saturation current I0 remains constant, so the variable that affects the open-circuit voltage V is the diode saturation current I0. Furthermore, according to formula (1), the inverse of the diode saturation current, 1 / I0, is proportional to the open-circuit voltage V, expressed as 1 / I0∝V.

[0079] Step 32: The calculation formula of the diode saturation current I0 is as shown in the following formula (2):

[0080]

[0081] In formula (2), q is the electron charge, n i is the intrinsic carrier concentration, N D 、N A are the impurity concentrations of the donor and acceptor, respectively, D n 、D p are the diffusion coefficients of electrons and holes, τ n , τ p are the minority carrier lifetimes of electrons and holes, respectively.

[0082] q and D in formula (2) n 、D p is a constant, N D 、N A , τ n , τ p It is related to the doping concentration and passivation ability of the cell and can remain constant. Therefore, according to formula (2), the minority carrier lifetime τ is proportional to the inverse of the diode saturation current 1 / I0, expressed as τ∝1 / I0.

[0083] Furthermore, when a solar cell is illuminated by light with energy greater than the bandgap of its semiconductor material, electrons in the semiconductor absorb the photon energy and transition from the valence band to the conduction band, forming non-equilibrium carriers. These excited electrons are unstable and can transition back to the valence band in a very short time through radiative or non-radiative recombination. During radiative recombination, the electrons release excess energy in the form of photons, a phenomenon known as photoluminescence (PL). The brightness of PL is closely related to the recombination of minority carriers (minority carriers) in the solar cell. The more minority carriers generated by illumination, the longer the minority carrier lifetime and the brighter the PL brightness. Therefore, by analyzing changes in the PL signal, we can derive changes in the minority carrier lifetime in the corresponding region. Therefore, the PL brightness, L, is directly proportional to the minority carrier lifetime, τ.

[0084] Step 33: Combine steps 31 and 32, and consider that the PL brightness L is proportional to the minority carrier lifetime τ, expressed as L∝τ; that is, L∝τ∝1 / I0∝V, so the PL brightness L is proportional to the open-circuit voltage V, that is, L∝V.

[0085] In step 3, according to the proportional relationship between the PL brightness of the cell and the open circuit voltage, formula (3) is obtained:

[0086] Vs m / V' m =Ls m / L'm (3);

[0087] Then, by simply transforming formula (3), we get the following formula (4):

[0088] V' m =Vs m ×L' m / Ls m (4).

[0089] Step 4: According to the PL brightness Ls of each area of ​​one of the standard films m and open circuit voltage Vs m Data, and the PL brightness L' of each area of ​​the cell to be tested m The data is combined with formula (4) to calculate the open circuit voltage V' of each area of ​​the cell to be tested after the calibration test of this piece of standard chip. m (For example, when m=5, we get V'1, V'2, V'3, V'4, V'5, etc.); and then calculate the open circuit voltage V' of each region. m The data is averaged. Taking m=5 as an example, the open circuit voltage V's data of the cell to be tested after the calibration test of the standard cell can be calculated according to the following formula (5).

[0090] V's=(V'1+V'2+V'3+V'4+V'5) / 5(5).

[0091] It should be noted that the prior art generally uses a primary standard to calibrate the color, appearance, and conversion efficiency of a secondary standard. However, this embodiment also utilizes the open-circuit voltage and PL brightness data of the standard (the open-circuit voltage and PL brightness data of the primary standard, or the calibrated open-circuit voltage and PL brightness data of the secondary standard), as well as the PL brightness data of the cell to be tested. The PL brightness data of the standard and the cell to be tested serve as an intermediate bridge, and combined with the proportional relationship between PL brightness and open-circuit voltage, the open-circuit voltage of the cell to be tested is calibrated.

[0092] Step 5. To avoid test errors caused by large PL brightness differences between a certain area of ​​the standard cell and the cell to be tested, repeat step 4 to obtain s-1 open-circuit voltage V's data of the cell to be tested after calibration and testing of the remaining s-1 standard cells; then take the average of the obtained s open-circuit voltage V's data to obtain the open-circuit voltage V' data of the cell to be tested.

[0093] A non-contact sorting method for open-circuit voltage of solar cells according to this embodiment includes the following steps:

[0094] Step 1: Using the non-contact test method for the open-circuit voltage of a solar cell described in steps 1-5 of this embodiment, obtain the open-circuit voltage V' data of the cell to be tested;

[0095] Step 2: sort the cells to be tested according to the open circuit voltage V' data of the cells to be tested and the existing cell sorting rules.

[0096] In summary, the present embodiment provides a non-contact testing method and sorting method for the open-circuit voltage of a solar cell. By analyzing the influencing factors of the key test parameters of the cell IV tester and combining the principle analysis and formula derivation process of the above step 3, a proportional relationship between the PL brightness L and the open-circuit voltage V is obtained. Thus, the PL brightness data is used as a bridge, and combined with an error correction mechanism (such as s pieces of standard cells are used to calibrate and test the s open-circuit voltage V's data of the cell to be tested, and the average value is taken to obtain the open-circuit voltage V' data of the cell to be tested; for example, the surface of each cell is divided into m areas to avoid test errors), the open-circuit voltage of the cell to be tested is tested non-contactly, thereby achieving accurate sorting of the open-circuit voltage of the cell to be tested.

[0097] Performance Testing

[0098] To verify the stability and accuracy of the non-contact testing method and sorting method for the open circuit voltage of a solar cell according to an embodiment of the present invention, three cell samples with open circuit voltages in the high voltage, medium voltage, and low voltage ranges were selected. Referring to the non-contact testing method for the open circuit voltage of a solar cell according to this embodiment (the number of standard cells s = 3, the number of areas divided on the surface of each cell m = 5), the open circuit voltages of the three cell samples were tested non-contactly, and the following results were obtained: Figure 2-5 The non-contact test data of three groups of open circuit voltages are shown in Figure 1. The open circuit voltages of the three battery cell samples are directly tested using an existing IV tester, and the results are as follows: Figure 2-5 The measured data of the three groups of open circuit voltages shown are the measured high voltage, the measured medium voltage, and the measured low voltage.

[0099] Will Figure 2-5 The three sets of data shown are compared with the non-contact high voltage and measured high voltage data, the non-contact medium voltage and measured medium voltage data, and the non-contact low voltage and measured low voltage data. The comparison results all show that the open circuit voltage directly measured by the existing IV tester and the open circuit voltage non-contact tested by a non-contact testing method for the open circuit voltage of a solar cell in an embodiment of the present invention have an error of no more than 0.4mV.

[0100] At present, mainstream manufacturers in the market usually use 1mV as the basis for grading open-circuit voltage of cells with the same conversion efficiency. Taking a conversion efficiency of 25.0% as an example, the open-circuit voltage sorting interval between high-voltage cells with a conversion efficiency of 25.0%, medium-voltage cells with a conversion efficiency of 25.0%, and low-voltage cells with a conversion efficiency of 25.0% is 1mV.

[0101] Therefore, the open circuit voltage of a solar cell tested by the non-contact method according to the embodiment of the present invention is highly accurate and meets the current requirements for open circuit voltage classification.

[0102] Moreover, the present invention avoids many disadvantages of contact testing and sorting using IV testers by performing non-contact testing and sorting on the battery cells to be tested: 1. Since the open-circuit voltage of the battery cell to be tested is tested non-contactly, there is no pressing and electrical contact of the probe row or probe on the battery cell to be tested during the IV test process. Therefore, there is no shading phenomenon caused by the probe row or probe during the non-contact test process, and the non-contact test results of the open-circuit voltage of the battery cell to be tested are more accurate. 2. Since the PL brightness test process is extremely simple and does not require the use of a probe row structure, there is no need for pressing needles, testing, spring reset and other actions, so the test time is shortened, which can greatly improve the work efficiency of non-contact testing and sorting. 3. For thin-film battery cells, there is no risk of the probe row or probe crushing the battery cell during non-contact testing and sorting. 4. During the non-contact test of the open-circuit voltage of the battery cell to be tested, a large number of probe row structures are discarded, and the cost and time generated by probe loss and maintenance are greatly reduced.

[0103] Furthermore, the non-contact test method for the open-circuit voltage of a solar cell of the present invention has the following advantages over the prior art (such as the method for predicting the open-circuit voltage of a polycrystalline silicon wafer provided in publication number CN103364704A):

[0104] The prior art CN103364704A uses the PL image calculation formula and parameters α and β to substitute the result into the open-circuit voltage prediction formula to infer the open-circuit voltage result. The basic concept of the present invention is to use the known electrical properties of the standard cell, using PL brightness data as an intermediate bridge, and combining the proportional relationship between PL brightness and open-circuit voltage to calibrate the open-circuit voltage of the cell under test.

[0105] Therefore, the key difference between the present invention and the prior art CN103364704A is:

[0106] The prior art CN103364704A uses a "theoretical (PL brightness calculation formula) → theoretical (open-circuit voltage prediction formula)" method. The present invention, on the other hand, uses a "realistic (measured electrical properties of a standard cell) → real (open-circuit voltage of the cell under test)" method. Therefore, compared to the prior art CN103364704A, the present invention's non-contact solar cell open-circuit voltage measurement method offers higher precision and accuracy.

[0107] Because the theory→theory calculation method ignores the influence of the actual environment on the test results, such as the edge effect mentioned in the previous question, and the influence of environmental factors such as temperature and humidity on the test results. Moreover, this theory→theory calculation method does not have the error correction mechanism in the present invention, which uses multiple standard pieces to calibrate and correct the same test results. In addition, the test method of the embodiment of the present invention only needs to be tested once (the PL brightness of standard pieces A, B, and C are measured together) to complete multiple n (n≥3) calibration tests of the open circuit voltage of the battery cell to be tested. Therefore, this error correction mechanism basically does not extend the test time, and the test time is greatly compressed. If the prior art CN103364704A wants to complete n calibration tests, it needs to test n times, calculate n times, and compare the results before completing the comparison and error correction.

[0108] Therefore, the present invention is superior to the prior art CN103364704A in terms of both test time compression and stable and accurate test results.

[0109] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they become aware of the basic creative concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0110] The technical solution provided by the present invention is introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A non-contact test method for the open circuit voltage of a solar cell, characterized in that: The method includes the following steps: Step 1: Select s standard cells, where s≥3; the PL brightness and open-circuit voltage of the standard cells are recorded as Ls and Vs respectively; and the PL brightness and open-circuit voltage of the cell to be tested are recorded as L' and V' respectively; Step 2: Divide the surface of the cell to be tested and each standard cell into m areas, where m ≥ 5; use PL brightness test equipment to test and obtain the PL brightness Ls of each area of ​​the standard cell. m and the PL brightness L' of each area of ​​the cell to be tested m data; Step 3: Based on the proportional relationship between the PL brightness of the cell and the open circuit voltage, combined with the PL brightness Ls of each area of ​​the standard cell m Data, get the open circuit voltage Vs corresponding to each area of ​​the standard battery cell m The open circuit voltage of each region of the cell to be tested is recorded as V' m According to the proportional relationship between the PL brightness of the cell and the open circuit voltage, we can get formula (4) V' m =Vs m ×L' m / Ls m ; Step 4: PL brightness Ls of each area of ​​the standard cell m and open circuit voltage Vs m Data, and the PL brightness L' of each area of ​​the cell to be tested m The data is combined with formula (4) to obtain s open circuit voltage V's data of the cell to be tested after s standard cells are calibrated and tested. The average value of the s open circuit voltage V's data is taken to obtain the open circuit voltage V' data of the cell to be tested.

2. The non-contact test method for open circuit voltage of a solar cell according to claim 1, characterized in that: In step 1, the standard cell is a first-class standard cell certified by an authoritative organization in the photovoltaic industry.

3. The non-contact test method for open circuit voltage of a solar cell according to claim 1, characterized in that: In step 1, the standard cell is a secondary standard cell calibrated with a primary standard cell.

4. The non-contact test method for open circuit voltage of a solar cell according to claim 3, characterized in that: In step 1, the calibration steps of the secondary standard cell include: Step 11: Use several primary standard battery cells to calibrate the IV tester; Step 12: Use a calibrated IV tester to test the conversion efficiency and open circuit voltage of the secondary standard battery cell.

5. The non-contact test method for open circuit voltage of a solar cell according to claim 1, characterized in that: In step 1, the selected standard battery cell meets the following conditions: The material type, size and appearance of the standard cell are consistent with those of the cell to be tested, the spectral response of the standard cell is consistent with that of the cell to be tested, the electrical performance temperature coefficient of the standard cell is matched with that of the cell to be tested, and the electrical performance of the selected standard cell is stable without light decay or environmental aging.

6. The non-contact test method for open circuit voltage of a solar cell according to claim 1, characterized in that: In step 2, the center and edges of the surface of each battery cell are divided into regions.

7. The non-contact test method for open circuit voltage of a solar cell according to claim 1, characterized in that: In step 3, the process of determining the proportional relationship between the PL brightness of the cell and the open circuit voltage is specifically as follows: Step 31: The calculation formula of the open circuit voltage V of the battery cell is as follows (1): In formula (1), n ​​is the diode ideal factor, k is the Boltzmann constant, T is the absolute temperature, q is the electron charge, and I ph is the photocurrent, I0 is the diode saturation current; n, k, T, q in formula (1) are all constants, I ph Affected by the IV tester light source, it can remain constant, so the variable that affects the open circuit voltage V is the diode saturation current I0; and according to formula (1), the reciprocal of the diode saturation current 1 / I0 is proportional to the open circuit voltage V, expressed as 1 / I0∝V; Step 32: The calculation formula of the diode saturation current I0 is as shown in the following formula (2): In formula (2), q is the electron charge, n i is the intrinsic carrier concentration, N D 、N A are the impurity concentrations of the donor and acceptor, respectively, D n 、D p are the diffusion coefficients of electrons and holes, τ n , τ p are the minority carrier lifetimes of electrons and holes, respectively; q and D in formula (2) n 、D p is a constant, N D 、N A , τ n , τ p It is related to the doping concentration and passivation ability of the cell and can remain constant. Therefore, according to formula (2), the minority carrier lifetime τ is proportional to the inverse of the diode saturation current 1 / I0, expressed as τ∝1 / I0; Step 33: Combined with the above, the PL brightness L is proportional to the minority carrier lifetime τ, expressed as L∝τ; that is, L∝τ∝1 / I0∝V, so the PL brightness L is proportional to the open-circuit voltage V, that is, L∝V.

8. A non-contact test method for open circuit voltage of a solar cell according to claim 1 or 7, characterized in that: In step 3, according to the proportional relationship between the PL brightness of the cell and the open circuit voltage, formula (3) is obtained: Vs m / V' m =Ls m / L' m , formula (3) is transformed to get formula (4) V' m =Vs m ×L' m / Ls m .

9. The non-contact test method for open circuit voltage of a solar cell according to claim 1, characterized in that: The step 4 specifically includes: Step 41: PL brightness Ls of each area of ​​one standard cell m and open circuit voltage Vs m Data, and the PL brightness L' of each area of ​​the cell to be tested m The data, combined with formula (4), can be used to obtain the open circuit voltage V' of each area of ​​the cell to be tested after the calibration test of the standard cell. m Data, open circuit voltage V' of each region m The data is averaged to obtain the open circuit voltage V's data of the cell to be tested after the calibration test of the standard cell. Step 42, repeat step 41 to obtain s-1 open circuit voltage V's data of the battery cell to be tested after the remaining s-1 standard battery cells are calibrated and tested; average the s open circuit voltage V's data to obtain the open circuit voltage V' data of the battery cell to be tested.

10. A non-contact sorting method for open circuit voltage of solar cells, characterized in that: The steps include: Step 1: using the non-contact test method for open-circuit voltage of a solar cell according to any one of claims 1 to 9 to obtain open-circuit voltage V' data of the cell to be tested; Step 2: sort the cells to be tested according to the open circuit voltage V' data of the cells to be tested and the cell sorting rules.

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