A method and system for testing solar cells

Abstract

The application provides a solar cell testing method and a testing system, and relates to the technical field of photovoltaics. The solar cell testing method comprises the following steps: obtaining a lossless current density of a solar cell under the condition that external quantum efficiency is 1; the solar cell comprises a silicon substrate and a front film located on the light side of the silicon substrate; obtaining a loss current density lost by the solar cell; the loss current density comprises a reflection loss current density lost due to reflection, a front film absorption loss current density lost due to light absorbed by the front film, a transmission loss current density lost due to light transmitted through the solar cell and a collection loss current density lost due to collection of the silicon substrate; and subtracting the loss current density from the lossless current density to obtain a short-circuit current density of the solar cell. The application does not need to use a probe or other electrically connected testing pieces, and has high accuracy.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic technology, and in particular to a testing method and testing system for solar cells. Background Technology

[0002] Accurately measuring the various electrical performance parameters of a solar cell is fundamental to evaluating its performance.

[0003] Currently, the electrical performance of solar cells is usually tested by contact testing. This involves using a test fixture and conductive materials such as probes to connect to the main grid of the solar cell. After illumination, the current is collected to test the electrical performance of the solar cell.

[0004] However, in contact testing, good contact current collection is mainly achieved by pressing conductive materials such as probes against the solar cell. This results in the test fixture applying pressure to the solar cell, which has a certain probability of damaging the solar cell's electrodes or even passivation layer, affecting the actual efficiency of the solar cell. Using a small number of probe arrays for testing can lead to a significant increase in external resistance due to excessive transmission distance, affecting tests such as short-circuit current density. For back-contact solar cells, using overly dense probe arrays carries the risk of short circuits caused by incorrect positive and negative electrode connections. Furthermore, contact testing is susceptible to errors due to poor probe contact. Therefore, existing contact testing methods have certain limitations. Summary of the Invention

[0005] This invention provides a testing method and system for solar cells, aiming to solve the limitations of existing contact testing methods for solar cells, such as the risk of damaging the electrodes or even the passivation layer.

[0006] A first aspect of the present invention provides a method for testing solar cells, comprising:

[0007] To obtain the lossless current density of a solar cell with an external quantum efficiency of 1; the solar cell includes: a silicon substrate and a front film located on the light-facing side of the silicon substrate;

[0008] The loss current density of the solar cell is obtained; the loss current density includes: reflection loss current density due to reflection, front film absorption loss current density due to light absorbed by the front film, transmission loss current density due to light transmitted through the solar cell, and collection loss current density due to collection by the silicon substrate.

[0009] The short-circuit current density of the solar cell is obtained by subtracting the loss current density from the lossless current density.

[0010] In this embodiment of the invention, the lossless current density, reflection loss current density, front film absorption loss current density, transmission loss current density, and collection loss current density can all be obtained non-contactly. Therefore, the solar energy testing method of this application does not require the use of probes or other electrically connected test pieces. Thus, the electrodes and passivation layer of the solar cell are basically not at risk of being damaged by probes, and the actual efficiency of the solar cell will not be affected. Since probes are basically not used, the problem of excessive transmission distance caused by a small number of probe arrays leading to a significant increase in external resistance will not be avoided. For back-contact solar cells, since probes are basically not used, the risk of short circuits caused by incorrect positive and negative electrode connections due to the use of overly dense probes will not be introduced, and the difficulty of precise alignment between probes and test points of the solar cell will be avoided. Therefore, the solar cell testing method provided by this application can be applied to various types of solar cells and has a wide range of applications, even for back-contact solar cells without a main grid. Since probes are rarely used, there is no risk of testing errors due to poor probe contact. Furthermore, with an external quantum efficiency of 1, the lossless current density of a solar cell is the ideal current density that a solar cell can achieve across the entire wavelength range without considering all losses. The reflection loss current density, front film absorption loss current density, parasitic absorption loss current density, transmission loss current density, and collection loss current density basically cover all the current densities lost by the solar cell. Therefore, the short-circuit current density of the solar cell obtained by subtracting the loss current density from the lossless current density is highly accurate.

[0011] Optionally, the solar cell further includes: a front metal electrode located on the side of the front film opposite to the silicon substrate; the loss current density further includes: metal shading loss current density lost due to light blocked by the front metal electrode.

[0012] Optionally, the solar cell further includes: a back film located on the backlight side of the silicon substrate; at least one of the front film, the back film, and the silicon substrate includes a heavily doped portion;

[0013] The loss current density also includes the parasitic absorption loss current density due to parasitic absorption by the heavily doped portion.

[0014] Optionally, obtaining the loss current density of the solar cell includes:

[0015] The reflectivity R(λ) of the solar cell at various wavelengths λ was measured.

[0016] The reflection loss current density JLoss was calculated. R , Wherein, q is the charge of an electron, λ1 is the lower limit of the wavelength of light absorbed by the solar cell, and λ2 is the upper limit of the wavelength of light absorbed by the solar cell; The current density of the solar cell is measured under STC standard test conditions when the solar cell is irradiated with spectral irradiation at various wavelengths according to a specified spectrum.

[0017] Optionally, obtaining the loss current density of the solar cell includes:

[0018] The reflectivity R(λ) of the solar cell at various wavelengths λ was measured.

[0019] The thickness d of the front film and the extinction coefficient k of the front film at various wavelengths were measured.

[0020] The absorbance A1(λ) of the front film for each wavelength was calculated.

[0021] The absorption loss current density JLoss of the front membrane was calculated. front , Wherein, q is the charge of an electron, λ1 is the lower limit of the wavelength of light absorbed by the solar cell, λ2 is the upper limit of the wavelength of light absorbed by the solar cell, and eQE ideal (λ) represents the external quantum efficiency under ideal conditions; the... The current density of the solar cell is measured under STC standard test conditions when the solar cell is irradiated with spectral irradiation at various wavelengths according to a specified spectrum.

[0022] Optionally, obtaining the loss current density of the solar cell includes:

[0023] The reflectivity R(λ) of the solar cell at various wavelengths λ was measured.

[0024] The doping concentration N and the thickness D of each heavily doped portion in the solar cell were measured; the doping concentration N of the heavily doped portion is greater than or equal to 1E18 atoms / cm. 3 ;

[0025] For each of the heavily doped regions, the absorbance A2(λ) of the heavily doped region at each wavelength is calculated. Where X and Y are both fitting coefficients;

[0026] For each of the heavily doped portions, the current density JLoss lost due to parasitic absorption by the heavily doped portion is calculated. NIR1 , Wherein, q is the charge of an electron, λ1 is the lower limit of the wavelength of light absorbed by the solar cell, λ2 is the upper limit of the wavelength of light absorbed by the solar cell, and EQE ideal (λ) represents the external quantum efficiency under ideal conditions; the... The current density of the solar cell is given by irradiating it with various wavelengths under specified spectral irradiation conditions according to STC standard testing; Abb(λ) is the absorptivity of the silicon substrate for each wavelength.

[0027] The parasitic absorption loss current density JLoss of the solar cell due to parasitic absorption by all the heavily doped portions is obtained by summing the parasitic absorption current densities corresponding to the parasitic absorption by the heavily doped portions. NIR .

[0028] Optionally, X is 1E-6 to 1E-13, and Y is 1 to 3.

[0029] Optionally, obtaining the loss current density of the solar cell includes:

[0030] The transmittance T(λ) of the solar cell at various wavelengths λ was measured.

[0031] The transmission loss current density JLoss was calculated. T , Wherein, q is the charge of an electron, λ1 is the lower limit of the wavelength of light absorbed by the solar cell, and λ2 is the upper limit of the wavelength of light absorbed by the solar cell; The current density of the solar cell is measured under STC standard test conditions when the solar cell is irradiated with spectral irradiation at various wavelengths according to a specified spectrum.

[0032] Optionally, obtaining the loss current density of the solar cell includes:

[0033] The photoluminescence intensity (PLI) of the solar cell was measured at a range of 0.01 standard solar intensity to 0.1 standard solar intensity.

[0034] The collection loss current density JLoss was calculated. base JLoss base =JLoss standard ×PLI standard / PLI; where JLoss standard The basic collection loss of the silicon substrate; the PLI standard The photoluminescence intensity value is the equivalent light intensity under the excess carrier concentration corresponding to the short-circuit current of the solar cell.

[0035] Optionally, the wavelength of light absorbed by the solar cell is in the range of 300 nm to 1200 nm; and / or,

[0036] The wavelengths are obtained by stepping values, which range from 0.5 nm to 20 nm.

[0037] Optionally, the PLI standard The range is 2000 to 5000.

[0038] Optionally, the testing method for the solar cell further includes:

[0039] Starting from 0.02 standard solar irradiance, the photoluminescence intensity values ​​(PLI) of the solar cell were measured at equal light intensity steps from 0.02 standard solar irradiance to 0.06 standard solar irradiance.

[0040] The equivalent current density Jeq, J, of the solar radiation intensity corresponding to each photoluminescence intensity value PLI was calculated. eq =J sc ×(1-f); where J sc The short-circuit current density of the solar cell; f is the solar intensity corresponding to one of the multiple photoluminescence intensity values ​​PLI.

[0041] The equivalent voltages V' corresponding to the multiple photoluminescence intensity values ​​PLI are calculated, and V' = V t ×ln(PLI)-[ln(C)×V t ]; where V t C is the thermal voltage of the solar cell at 25°C; C is the coefficient used for testing and calibrating the photoluminescence intensity value.

[0042] The equivalent voltage-current curve is obtained by fitting multiple equivalent current densities Jeq and multiple equivalent voltages V'.

[0043] Based on several positive and several negative equivalent current densities at certain points in the equivalent voltage-current curve, and the corresponding equivalent voltage V', the slope r of the selected partial points is obtained through linear fitting, and the series resistance Rs of the solar cell is calculated.

[0044] Using V = V′ - J eq ×R s The equivalent voltages V' are converted into actual voltages V;

[0045] The actual voltage-current curves are obtained by plotting multiple equivalent current densities Jeq and multiple actual voltages V, and the fill factor of the solar cell is obtained.

[0046] Optionally, the testing method for the solar cell further includes:

[0047] The photoluminescence intensity value PLI of the solar cell was measured under one standard solar radiation intensity.

[0048] The open-circuit voltage V of the solar cell is determined using the photoluminescence intensity value PLI corresponding to a standard solar radiation intensity. oc V oc =V t ×ln(PLI)-[ln(C)×V t ].

[0049] Optionally, the testing method for the solar cell further includes:

[0050] The short-circuit current density, the fill factor, and the open-circuit voltage V of the solar cell are used to measure the short-circuit current density, the fill factor, and the open-circuit voltage V of the solar cell. oc The product of these three factors is determined as the photoelectric conversion efficiency of the solar cell.

[0051] A second aspect of the present invention provides a testing system for solar cells, comprising:

[0052] A lossless current density acquisition module is used to acquire the lossless current density of a solar cell when the external quantum efficiency is 1; the solar cell includes: a silicon substrate and a front film located on the light-facing side of the silicon substrate;

[0053] The loss current density acquisition module is used to acquire the loss current density lost by the solar cell; the loss current density includes: reflection loss current density lost due to reflection, front film absorption loss current density lost due to light absorbed by the front film, transmission loss current density lost due to light transmitted through the solar cell, and collection loss current density lost due to collection by the silicon substrate.

[0054] The calculation module is used to obtain the short-circuit current density of the solar cell by subtracting the loss current density from the lossless current density.

[0055] Optionally, the loss current density acquisition module includes: a PL tester, a reflectivity tester, a transmittance tester, and a film thickness refractive index tester.

[0056] The above-mentioned testing methods and systems for solar cells have the same or similar beneficial effects, and will not be repeated here to avoid repetition. Attached Figure Description

[0057] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. 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.

[0058] Figure 1 A flowchart illustrating the steps of a solar cell testing method according to an embodiment of the present invention is shown;

[0059] Figure 2 A schematic diagram showing the current density of a solar cell according to an embodiment of the present invention is provided.

[0060] Figure 3 A flowchart illustrating the steps of another solar cell testing method according to an embodiment of the present invention is shown;

[0061] Figure 4 A schematic diagram of the photoluminescence intensity (PLI) values ​​of high-energy solar cells measured under different solar radiation intensities is shown in an embodiment of the present invention.

[0062] Figure 5 An equivalent voltage-current curve obtained by fitting in an embodiment of the present invention is shown;

[0063] Figure 6 The actual voltage and current curves in an embodiment of the present invention are shown. Detailed Implementation

[0064] 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, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0065] This invention provides a testing method for solar cells, referring to... Figure 1 The testing method for this solar cell may include the following steps.

[0066] Step 101: Obtain the lossless current density of the solar cell when the external quantum efficiency is 1; the solar cell includes: a silicon substrate and a front film located on the light-facing side of the silicon substrate.

[0067] The solar cells mentioned in this application may be bifacial solar cells, back-contact solar cells, gridless back-contact solar cells, etc., and no specific limitation is made on the type of solar cell.

[0068] A solar cell may include: a silicon substrate, a front film located on the light-facing side of the silicon substrate, and a back film located on the back-facing side of the silicon substrate. The doping type and crystal type of the silicon substrate are not specifically limited. During normal operation of the solar cell, the side of the silicon substrate that primarily absorbs light is the light-facing side, and the back-facing side is opposite to the light-facing side. The front film located on the light-facing side of the silicon substrate refers to all film layers in the solar cell located on the light-facing side of the silicon substrate, excluding the front metal electrode located on the light-facing side of the silicon substrate. For example, the front film may include a front passivation layer, etc. The specific film layers included in the front film are not limited. The back film located on the back-facing side of the silicon substrate refers to all film layers in the solar cell located on the back-facing side of the silicon substrate, excluding the back metal electrode located on the back-facing side of the silicon substrate. For example, the back film may include a front passivation layer, etc. The specific film layers included in the back film are not limited.

[0069] With an external quantum efficiency (EQE) of 1, the lossless current density (Jideal) of a solar cell is the ideal current density achievable across the entire wavelength range without considering all losses. Since solar cells typically absorb light in the wavelength range of 300nm-1200nm, the lossless current density (Jideal) can also be considered the ideal current density achievable within this long range without considering all losses. The lossless current density (Jideal) is usually a design parameter of the solar cell and can be obtained from its design specifications. For example, the value of the lossless current density (Jideal) can be 46.3 mA / cm². 2 (mA per square centimeter) -46.5mA / cm 2 .

[0070] Step 102: Obtain the current loss density of the solar cell; the current loss density includes: reflection loss current density due to reflection, front film absorption loss current density due to light absorbed by the front film, transmission loss current density due to light transmitted through the solar cell, and collection loss current density due to collection by the silicon substrate.

[0071] The reflection loss current density JLoss is due to reflection. R This mainly refers to the current density lost due to light reflected off the surface of the solar cell that is not absorbed by the solar cell. The current density lost due to light absorbed by the front film (JLoss) is the current density lost due to absorption by the front film. front This mainly refers to the current density lost due to light that is absorbed by the front film but not by the silicon substrate.

[0072] Step 103: Subtract the lost current density from the lossless current density to obtain the short-circuit current density of the solar cell.

[0073] Figure 2 The horizontal axis represents the wavelength of light that the solar cell can absorb, in nm. Figure 2 The vertical axis represents different proportions of the lossless current density of the solar cell. Figure 2 In the figure, the area corresponding to a ordinate of 1.0 represents the lossless current density (Jideal) of the solar cell. Specifically, the inventors discovered that for back-contact solar cells without a front metal electrode and with heavily doped portions, the current density loss is mainly due to reflection loss (JLoss). R (like Figure 2 The area shown in S1), and the front film absorption loss current density JLoss due to the light absorbed by the front film. front (like Figure 2 The area shown in S2), and the transmission loss current density JLoss due to the light loss transmitted through the solar cell. T (like Figure 2 The area shown in S3), the parasitic absorption loss current density JLoss of this solar cell due to parasitic absorption by the heavily doped portion. NIR (like Figure 2 The area shown in S4), and the collection loss current density JLoss due to the collection on the silicon substrate. base (like Figure 2 (The area shown in S5). Due to the collection loss current density JLoss caused by the silicon substrate. base Usually smaller, so in Figure 2 The difference is not obvious enough; the collection loss current density JLoss base The corresponding wavelength range is typically 620nm to 1200nm. Figure 2 The S in the gray area represents the short-circuit current density of the back-contact solar cell.

[0074] It should be noted that since this back-contact solar cell does not have a front metal electrode to block the light, the metal shading loss current density of this back-contact solar cell due to the light being blocked by the front metal electrode is 0.

[0075] This application is based on the above. Figure 2This study reveals a method for obtaining the short-circuit current density of solar cells. The non-contact current density, reflection loss current density, front film absorption loss current density, parasitic absorption loss current density, transmission loss current density, and collection loss current density can all be obtained non-contactly. Therefore, the solar cell testing method of this application does not require the use of probes or other electrically connected test pieces. Thus, the electrodes and passivation layer of the solar cell are essentially not at risk of being damaged by probes, and the actual efficiency of the solar cell will not be affected. Since probes are largely not used, the problem of excessive transmission distance leading to a significant increase in external resistance due to a small number of probe arrays is avoided. For back-contact solar cells, the absence of probes also avoids the risk of short circuits caused by misaligned positive and negative connections due to overly dense probe arrays, and eliminates the difficulty of precise alignment between probes and the test points of the solar cell. Therefore, the solar cell testing method provided in this application is applicable to various types of solar cells, with a wide range of applications, even for back-contact solar cells without a main grid. Moreover, when the external quantum efficiency is 1, the lossless current density of a solar cell is the ideal current density that a solar cell can achieve across the entire wavelength range without considering all losses. The reflection loss current density, front film absorption loss current density, parasitic absorption loss current density, transmission loss current density, and collection loss current density basically cover all the current densities lost by the solar cell. Therefore, the short-circuit current density of the solar cell obtained by subtracting the loss current density from the lossless current density is highly accurate.

[0076] Optionally, the solar cell may further include: a front metal electrode located on the side of the front film facing away from the silicon substrate, or in other words, the front film is located between the silicon substrate and the front metal electrode. The loss current density of the solar cell may further include: the metal shading loss current density Jloss caused by light blocked by the front metal electrode. metal Based on the lossless current density minus all the aforementioned loss current densities, it is also necessary to subtract the metal shielding loss current density Jloss from the lossless current density. metal Only then can the short-circuit current density of the solar cell be obtained. For solar cells that include a front metal electrode, the shading of the front metal electrode is also considered, resulting in a more accurate short-circuit current density.

[0077] It should be noted that for solar cells including a front metal electrode, the metal shading loss current density Jloss is the current density lost by the solar cell due to the light blocked by the front metal electrode. metal This is one of the design parameters of the solar cell and can be obtained from the design parameters of the solar cell. For example, when testing bifacial solar cells (such as TOPCon cells), the metal shading loss current density Jloss is...metal Jloss can be obtained in the following way: metal = Jideal × Shading Ratio, where the shading ratio is the proportion of the area of ​​the metal shading on the light-facing surface to the total area of ​​the light-facing surface. Therefore, for solar cells including the front metal electrode, the metal shading loss current density can also be obtained non-contactly.

[0078] Optionally, at least one of the front film, the back film, and the silicon substrate may include a heavily doped portion. The doping concentration N of the heavily doped portion is greater than or equal to 1E¹⁸ atoms / cm². 3 This can be because only the front film includes the heavily doped portion, only the rear film includes the heavily doped portion, only the silicon substrate includes the heavily doped portion, both the front and rear films include the heavily doped portion, both the front film and the silicon substrate include the heavily doped portion, both the silicon substrate and the rear film include the heavily doped portion, or both the front film, rear film and silicon substrate include the heavily doped portion. The loss current density also includes the parasitic absorption loss current density due to parasitic absorption by the heavily doped portion.

[0079] The following is combined Figure 3 Further explanation of step 102 above. Optionally, obtaining the aforementioned reflection loss current density in step 102 may include steps 1021 to 1022.

[0080] Step 1021: Measure the reflectivity R(λ) of the solar cell at various wavelengths λ.

[0081] The reflectivity R(λ) of a solar cell at various wavelengths λ can be measured using relevant reflectivity testing instruments. Optionally, a reflectivity tester can conveniently and accurately measure the reflectivity R(λ) of a solar cell at various wavelengths λ. Here, "variable wavelengths λ" typically refers to the entire wavelength range, more specifically, the range of wavelengths of light that the solar cell can absorb. Optionally, the reflectivity R(λ) of the solar cell can be measured at various wavelengths λ within the wavelength range of 300nm to 1200nm, which basically covers the range of wavelengths that various solar cells can absorb. Optionally, a certain step wavelength can be used, ranging from 0.5nm to 20nm, which can appropriately reduce the number of wavelengths that need to be measured, thereby reducing workload and improving testing efficiency, without significantly affecting testing accuracy.

[0082] For example, starting from 300nm, the reflectivity R(λ) at each wavelength λ can be measured sequentially in step wavelengths of 0.5nm, 1nm, 3nm, 5nm, 9nm, 10nm, 12.5nm, 15nm, 17nm, 18nm, 19nm, and 20nm, until the reflectivity R(λ) at a wavelength of 1200nm is measured.

[0083] Step 1022: Calculate the reflection loss current density JLoss. R , Wherein, q is the charge of an electron, λ1 is the lower limit of the wavelength of light absorbed by the solar cell, and λ2 is the upper limit of the wavelength of light absorbed by the solar cell; The current density of the solar cell is measured under STC standard test conditions when the solar cell is irradiated with spectral irradiation at various wavelengths according to a specified spectrum.

[0084]

[0085] In Formula 1, q represents the charge of one electron, specifically 1.6 × 10⁻⁶. -19 Coulomb. λ1 is the lower limit of the wavelength of light absorbed by the solar cell, and λ2 is the upper limit of the wavelength of light absorbed by the solar cell. Optionally, λ1 is 300 nm and λ2 is 1200 nm. R(λ) is the reflectivity of the solar cell at each wavelength λ measured in step 1021 above. AM1.5G refers to the spectral irradiance I at each wavelength under the STC standard test conditions, specifically a light intensity of 1000 W / m². 2 The ambient temperature of the solar cell is 25℃. Under STC standard test conditions, the solar cell is irradiated at various wavelengths with a specified spectral irradiance I. The current density J of the solar cell is calculated as J = I / E, where E is the photon energy, and E varies with wavelength. The reflection loss current density JLoss can be accurately calculated by integrating the equation in Formula 1. R .

[0086] Through the aforementioned steps 1021 and 1022, the reflection loss current density JLoss can be accurately obtained in a non-contact manner. R .

[0087] Optionally, in step 102, the aforementioned pre-membrane absorbs the loss current density JLoss. front The acquisition may include steps 1023 to 1026.

[0088] Step 1023: Measure the reflectivity R(λ) of the solar cell at various wavelengths λ.

[0089] Step 1023 can be referred to the aforementioned step 1021. To avoid repetition, it will not be described again here.

[0090] Step 1024: Measure the thickness d of the front film and the extinction coefficient k of the front film at various wavelengths.

[0091] The direction of the film thickness d is parallel to the direction of the solar cell thickness. Optionally, the film thickness d and the extinction coefficient k of the front film at various wavelengths can be measured using a film thickness refractive index meter. Here, each wavelength λ usually refers to the entire wavelength range, more specifically, the wavelength range of light that the solar cell can absorb. Optionally, it can be various wavelengths within the 300nm to 1200nm wavelength range of the solar cell. Optionally, in measuring the extinction coefficient k of the front film at various wavelengths, a certain step wavelength can be used. This step wavelength range can be 0.5nm to 20nm, which can appropriately reduce the number of wavelengths that need to be measured, thereby reducing workload and improving testing efficiency, without significantly affecting testing accuracy.

[0092] Step 1025: Calculate the absorbance A1(λ) of the front film for each wavelength.

[0093]

[0094] Here, the absorption rate A1(λ) of the front membrane at each wavelength can be accurately calculated using the k value at each wavelength.

[0095] Step 1026: Calculate the absorption loss current density JLoss of the front membrane. front , Wherein, q is the charge of an electron, λ1 is the lower limit of the wavelength of light absorbed by the solar cell, λ3 is the upper limit of the wavelength of light absorbed by the silicon substrate and the front film in the solar cell, and EQE ideal (λ) represents the external quantum efficiency under ideal conditions; the... The current density of the solar cell is measured under STC standard test conditions when the solar cell is irradiated with spectral irradiation at various wavelengths according to a specified spectrum.

[0096]

[0097] In Formula 3, q ​​is the same as before, representing the charge of an electron. λ1 is the lower limit of the wavelength of light absorbed by the solar cell, and λ2 is the upper limit of the wavelength of light absorbed by the solar cell. As mentioned earlier, λ1 can be 300 nm and λ2 can be 1200 nm. For the wavelength range of 900 nm to 1200 nm, the corresponding front film absorption loss current density is almost zero. Therefore, preferably, λ1 can be 300 nm and λ2 can be 900 nm, which can reduce the amount of calculation.

[0098] EQE in Equation 3 ideal (λ) represents the external quantum efficiency under ideal conditions, which can be a fixed value of 1. In Equation 3... The current density of the solar cell is measured under STC standard test conditions when the solar cell is irradiated with spectral irradiation at various wavelengths according to a specified spectrum. Please refer to the aforementioned records; to avoid repetition, they will not be repeated here.

[0099] Through the aforementioned steps 1023 to 1026, the front membrane absorption loss current density JLoss can be accurately obtained in a non-contact manner. front .

[0100] Optionally, if the solar cell includes a heavily doped portion, the current loss density further includes the parasitic absorption loss current density due to parasitic absorption of the heavily doped portion. In this case, step 102 also needs to obtain the parasitic absorption loss current density JLoss. NIR The aforementioned parasitic absorption loss current density JLoss NIR The acquisition may include steps 1027 to 10211.

[0101] Step 1027: Measure the reflectivity R(λ) of the solar cell at various wavelengths λ.

[0102] Step 1027 can be referred to the aforementioned step 1021. To avoid repetition, it will not be described again here.

[0103] Step 1028: Measure the doping concentration N and thickness D of each heavily doped portion in the solar cell; the doping concentration N of the heavily doped portion is greater than or equal to 1E18 atoms / cm. 3 .

[0104] The heavily doped portion here refers to a doping concentration N greater than or equal to 1E18 atoms / cm². 3The doped layer is located in at least one of the light-facing side, the back-facing side, and the silicon substrate. Optionally, the doping concentration N and the thickness D of each heavily doped portion in the back film of the solar cell can be measured using a doping concentration meter (such as ECV).

[0105] Step 1029: For each heavily doped portion, calculate the absorbance A2(λ) of the heavily doped portion for each wavelength. Where X and Y are both fitting coefficients.

[0106]

[0107] In Formula 4, X and Y are fitting coefficients related to the properties of the heavily doped portion and will not change after the solar cell is finalized. Optionally, X can be from 1E-6 to 1E-13, and Y can be from 1 to 3. For example, X can be 1E-6, 1E-7, 1E-8, 1E-9, 1E-10, 1E-11, 1E-12, or 1E-13, and Y can be 1, 1.3, 1.5, 2, 2.5, 3, 2.6, 1.9, or 2.8. In step 1029, the number of A2(λ) is typically calculated for each heavily doped portion.

[0108] Step 10210: For each of the heavily doped portions, calculate the parasitic absorption loss current density JLoss. NIR1 , Wherein, q is the charge of an electron, λ1 is the lower limit of the wavelength of light absorbed by the solar cell, and λ2 is the upper limit of the wavelength of light absorbed by the solar cell; the EQE ideal (λ) represents the external quantum efficiency under ideal conditions; the... The current density of the solar cell is given by irradiating the solar cell with various wavelengths under specified spectral irradiation conditions according to STC standard test conditions; Abb(λ) is the light absorption rate of the silicon substrate.

[0109] In Formula 5, q is the same as before, representing the charge of an electron. λ2 is the upper limit of the wavelength of light absorbed by the solar cell, and λ1 is the lower limit of the wavelength of light absorbed by the solar cell. As mentioned earlier, λ2 can be 1200 nm, and λ1 can be 300 nm. For the 300 nm-900 nm wavelength range, the parasitic absorption loss current density is almost zero. Therefore, the integration calculation can be performed from 300 nm to 1200 nm, or preferably directly from 900 nm to 1200 nm, which can reduce the computational load. EQE in Formula 5... ideal (λ) represents the external quantum efficiency under ideal conditions, which can be a fixed value of 1. In Equation 5... The current density of the solar cell is measured under STC standard test conditions when the solar cell is irradiated with spectral irradiation at various wavelengths according to a specified spectrum. Refer to the aforementioned records; to avoid repetition, they will not be repeated here. Abb(λ) represents the absorptivity of the silicon substrate for each wavelength, existing as a wavelength-to-absorption ratio (similar to reflectivity and external quantum efficiency EQE), and is a constant value given a fixed solar cell structure. For example, for back-contact solar cells, the average value of Abb(λ) in the wavelength range of 900nm to 1200nm is approximately 0.6 to 0.7. When the heavily doped portion is located only on the light-facing side of the silicon substrate, Abb(λ) is 0. In step 10210, the number of heavily doped portions typically yields several JLoss values. NIR1 .

[0110] Step 10211: Sum the parasitic absorption loss current densities corresponding to all the heavily doped portions to obtain the parasitic absorption loss current density JLoss of the solar cell due to parasitic absorption by the heavily doped portions. NIR .

[0111] This involves summing the parasitic absorption loss current density corresponding to each heavily doped portion of a solar cell. Through steps 1027 to 10211, the parasitic absorption loss current density JLoss can be accurately obtained in a contactless manner. NIR .

[0112] Optionally, the aforementioned transmission loss current density JLoss in step 102 T The acquisition may include steps 10212 to 10213.

[0113] Step 10212: Measure the transmittance T(λ) of the solar cell at various wavelengths λ.

[0114] The transmittance T(λ) of a solar cell at various wavelengths λ can be measured using a relevant transmittance meter. Optionally, a transmittance meter can conveniently and accurately measure the transmittance T(λ) of a solar cell at various wavelengths λ. Here, "various wavelengths λ" usually refers to the entire wavelength range, more specifically, the range of wavelengths of light that the solar cell can absorb. Optionally, the transmittance T(λ) of the solar cell can be measured at various wavelengths λ within the wavelength range of 300nm to 1200nm, which basically covers the range of wavelengths that various solar cells can absorb. Optionally, a certain step wavelength can be used, ranging from 0.5nm to 20nm, which can appropriately reduce the number of wavelengths that need to be measured, thereby reducing workload and improving testing efficiency, without significantly affecting the testing accuracy.

[0115] Step 10213: Calculate the transmission loss current density JLoss using Formula 6. T , Wherein, q is the charge of an electron, λ1 is the lower limit of the wavelength of light absorbed by the solar cell, and λ2 is the upper limit of the wavelength of light absorbed by the solar cell; The current density of the solar cell is measured under STC standard test conditions when the solar cell is irradiated with spectral irradiation at various wavelengths according to a specified spectrum.

[0116]

[0117] In Formula 6, q is the same as before, representing the charge of an electron. λ2 is the upper limit of the wavelength of light absorbed by the solar cell, and λ1 is the lower limit of the wavelength of light absorbed by the solar cell. As mentioned earlier, λ2 can be 1200nm and λ1 can be 300nm. For the 300nm-900nm wavelength band, the transmission loss current density is almost zero. Therefore, the integration calculation can be performed from 300nm to 1200nm, or preferably directly from 900nm to 1200nm, which can reduce the amount of calculation. In Formula 6... The current density of the solar cell is measured under STC standard test conditions when the solar cell is irradiated with spectral irradiation at various wavelengths according to a specified spectrum. Please refer to the aforementioned records; to avoid repetition, they will not be repeated here.

[0118] Through the aforementioned steps 10212 and 10213, the transmission loss current density JLoss can be accurately obtained in a non-contact manner. -T .

[0119] Optionally, in step 102, the aforementioned collection loss current density JLoss baseThe acquisition may include steps 10214 to 10215.

[0120] Step 10214: Measure the photoluminescence intensity (PLI) of the solar cell at a standard solar intensity of 0.01 to 0.1.

[0121] The photoluminescence intensity (PLI) of the solar cell can be measured at a solar intensity of 0.01 to 0.1 solar irradiance using a photoluminescence instrument. Alternatively, the PLI of the solar cell can be measured at a solar intensity of 0.01 to 0.1 solar irradiance using a photoluminescence meter.

[0122] Step 10215: Calculate the collection loss current density JLoss using Formula 7. base JLoss base =JLoss standard ×PLI standard / PLI; where JLoss standard The basic collection loss of the silicon substrate; the PLI standard The photoluminescence intensity value is the equivalent light intensity under the excess carrier concentration corresponding to the short-circuit current of the solar cell.

[0123]

[0124] In formula 7, JLoss standard For the basic collection loss of this silicon substrate, the PLI standard The JLoss value represents the photoluminescence intensity value of the equivalent light intensity under the excess carrier concentration corresponding to the short-circuit current of the solar cell. standard A fixed value of 0.1 mA / cm can be used. 2 Within the range of 0.01 to 0.1 solar irradiance, the excess carrier concentration varies relatively little. When the solar cell is in a short-circuit state, its excess carrier concentration is at 1E¹³ cm⁻¹. -3 Up to 1E14cm -3 The light intensity corresponding to this concentration is approximately 0.01 to 0.1 times the standard solar intensity. Therefore, the PLI obtained by measuring this light intensity is the standard photoluminescence intensity at the equivalent light intensity under the excess carrier concentration corresponding to the short-circuit current. Simultaneously, experiments show that the PLI... standard The Jloss calculated under different irradiances is obtained when the PLI of the solar cell under test is tested with the same irradiance as that of the solar cell under test. base The values ​​are not significantly different. Optional, PLI standard The value can range from 2000 to 5000.

[0125] More specifically, Where Δn is the photon injection rate, q is the charge of one electron (as mentioned earlier), and W is the thickness of the solar cell, all of which are constants. Where ni is the intrinsic carrier concentration, N A Let PLI be the doping concentration of the silicon substrate, which is a fixed value. Therefore, we can deduce that PLI ∝ τ, and thus, we can obtain...

[0126]

[0127] Through the aforementioned steps 10214 to 10215, the aforementioned collection loss current density JLoss can be accurately obtained in a contactless manner. base .

[0128] This invention also provides another method for testing solar cells, combined with Figure 3 The testing method for this solar cell may include the following steps.

[0129] Step 201: Obtain the lossless current density of the solar cell when the external quantum efficiency is 1; the solar cell includes: a silicon substrate and a front film located on the light-facing side of the silicon substrate.

[0130] Step 202: Obtain the loss current density of the solar cell; the loss current density includes: reflection loss current density due to reflection, front film absorption loss current density due to light absorbed by the front film, transmission loss current density due to light transmitted through the solar cell, and collection loss current density due to collection by the silicon substrate.

[0131] Step 203: Subtract the lost current density from the lossless current density to obtain the short-circuit current density of the solar cell.

[0132] Steps 201 to 203 can refer to the aforementioned steps 101 to 103 and can achieve the same or similar beneficial effects. To avoid repetition, they will not be described again here.

[0133] Step 204: Starting from 0.02 standard solar intensity, the multiple photoluminescence intensity values ​​(PLI) of the solar cell are measured at equal light intensity steps from 0.02 standard solar intensity to 0.06 standard solar intensity.

[0134] The number of photoluminescence intensity values ​​(PLIs) measured here can be greater than or equal to 10, with equal solar intensity steps. For example, if 10 tests are performed at solar intensities ranging from 0.02 to 0.06 standard solar intensities, the intensity step value would be (0.06-0.02) / 10 = 0.004 standard solar intensities. Ten photoluminescence intensity values ​​(PLIs) of the solar cell are obtained by measuring at 10 standard solar intensities.

[0135] It should be noted that the test can also be performed 10 times at a light intensity of 0.03 to 0.05 standard solar irradiance. The light intensity step value is (0.05-0.03) / 10 = 0.002 standard solar irradiance. Ten photoluminescence intensity values ​​(PLI) of the solar cell are obtained by measuring at 10 standard solar irradiances.

[0136] Figure 4 The photoluminescence intensity (PLI) values ​​of high-performance solar cells were measured under different solar radiation intensities. Figure 4 The horizontal axis represents different solar irradiance levels, and the vertical axis represents the photoluminescence intensity (PLI) value corresponding to each standard solar irradiance. Figure 4 One standard solar radiation intensity is 1000 W / m². 2 . Reference Figure 4 Multiple tests were conducted at standard solar irradiance levels ranging from 0.03 to 0.06, yielding multiple photoluminescence intensity values ​​(PLI).

[0137] Step 205: Calculate the equivalent current density Jeq, J, of the solar radiation intensity corresponding to each photoluminescence intensity value PLI. eq =J sc ×(1-f); where J sc is the short-circuit current density of the solar cell; f is the solar intensity corresponding to one of the multiple photoluminescence intensity values ​​PLI.

[0138] J eq =J sc ×(1-f)(Formula 8)

[0139] In Formula 8, Jeq is the equivalent current density of solar radiation corresponding to each of the aforementioned photoluminescence intensity values ​​PLI, J sc The given value is the short-circuit current density of the aforementioned solar cell. Here, f represents the solar radiation intensity corresponding to one of the aforementioned photoluminescence intensity values ​​(PLI). f here is a proportional value. Both Jeq and f correspond to the solar radiation intensity at f.

[0140] Step 206: Calculate the equivalent voltage V' corresponding to the plurality of photoluminescence intensity values ​​PLI, where V' = V t×ln(PLI)-[ln(C)×V t ]; where V t is the thermal voltage of the solar cell at 25°C; C is the coefficient used for testing and calibrating the photoluminescence intensity value.

[0141] V' = V t ×ln(PLI)-[ln(C)×V t ](Formula 9)

[0142] In Formula 9, C is the coefficient used for testing and calibrating the photoluminescence intensity value, and its value can range from 1E-8 to 1E-9. t The thermal voltage of the solar cell at 25°C is a fixed value of 0.025683V (volts).

[0143] Step 207: Fit the equivalent voltage-current curves using multiple equivalent current densities Jeq and multiple equivalent voltages V'.

[0144] In addition to the existing multiple equivalent current densities Jeq and multiple equivalent voltages V', interpolation can be performed here, such as inserting 100 to 300 pairs of equivalent current densities Jeq and equivalent voltages V'. There is no specific limitation on whether to interpolate.

[0145] Step 208: Based on several positive and several negative equivalent current densities and the corresponding equivalent voltage V' at some points in the equivalent voltage-current curve, linear fitting is performed to obtain the slope r of the selected partial points, and the series resistance Rs of the solar cell is calculated.

[0146] Figure 5 This is the equivalent voltage-current curve obtained through fitting. Figure 5 The horizontal axis represents the equivalent voltage V', from... Figure 4 The photoluminescence intensity value was obtained by PLI conversion calculation. Figure 5 The ordinate is the equivalent current density Jeq, from Figure 4 The value is calculated based on the solar intensity and the measured Jsc. The slope is calculated at the open-circuit voltage Voc point (i.e., Jeq = 0), yielding the series resistance. This resistance is used to correct the voltage V in the subsequent IV curve. For example, Figure 5 In the middle, R s The value referred to is the obtained series resistance. It should be noted that the number of positive and negative equivalent current densities used for linear fitting here is greater than or equal to 20.

[0147] Step 209, use V = V′ - J eq ×R sThe equivalent voltages V' are converted into actual voltages V.

[0148] Step 210: Plot the actual voltage-current curve using multiple equivalent current densities Jeq and multiple actual voltages V, and obtain the fill factor of the solar cell.

[0149] Figure 6 That is, to use Figure 5 A real voltage-current curve is obtained by plotting multiple equivalent current densities Jeq and multiple actual voltages V.

[0150] Step 211: Measure the photoluminescence intensity value PLI of the solar cell under a standard solar light intensity.

[0151] The photoluminescence intensity (PLI) of the solar cell can be measured using a PL meter under a standard solar intensity.

[0152] Step 212: Determine the open-circuit voltage V of the solar cell using the photoluminescence intensity value PLI corresponding to a standard solar radiation intensity. oc V oc =V t ×ln(PLI)-[ln(C)×V t ]; where C is the coefficient used for testing and calibrating the photoluminescence intensity value, and V t The thermal voltage of the solar cell at 25°C is given.

[0153] C and V here t All of these can be referred to in the aforementioned relevant records. To avoid repetition, they will not be repeated here. Here, the open-circuit voltage V of the solar cell is accurately determined without contact. oc .

[0154] Step 213: The short-circuit current density, fill factor, and open-circuit voltage V of the solar cell are... oc The product of these three factors is determined as the photoelectric conversion efficiency of the solar cell.

[0155] Specifically, the conversion efficiency of a solar cell is Eta, where Eta = Jsc × Voc × FF, and FF is the fill factor of the solar cell. This application achieves contactless acquisition of the solar cell's conversion efficiency. Therefore, the solar cell testing method of this application eliminates the need for probes or other electrically connected test pieces. Consequently, the electrodes and passivation layer of the solar cell are virtually free from the risk of damage by probes, thus not affecting the actual efficiency of the solar cell. Since probes are largely eliminated, the problem of excessively long transmission distances due to a small number of probe arrays is avoided, preventing a significant increase in external resistance. For back-contact solar cells, the absence of probes also avoids the risk of short circuits caused by misaligned positive and negative connections due to overly dense probe arrays, and eliminates the difficulty of precise alignment between probes and the test points on the solar cell. Therefore, the solar cell testing method provided in this application is applicable to various types of solar cells, with a wide range of applications, even for back-contact solar cells without a main grid. Moreover, when the external quantum efficiency is 1, the lossless current density of a solar cell is the ideal current density that a solar cell can achieve across the entire wavelength range without considering all losses. The reflection loss current density, front film absorption loss current density, parasitic absorption loss current density, transmission loss current density, and collection loss current density basically cover all the current densities lost by the solar cell. Therefore, the short-circuit current density of the solar cell obtained by subtracting the loss current density from the lossless current density is highly accurate.

[0156] Especially for back-contact solar cells without a main grid, since the test methods in this application are all non-contact, they do not introduce the risk of short circuits caused by incorrect positive and negative electrode connections due to the use of overly dense probes, nor do they avoid the difficulty of more precise alignment between the probes and the test points of the back-contact solar cell. They also do not cause a significant increase in external resistance due to excessive transmission distance caused by a small number of probe rows. The electrodes and passivation layer of the solar cell are basically not at risk of being damaged by the probes, and the actual efficiency of the solar cell will not be affected.

[0157] This application also provides a testing system for solar cells, which can implement any of the aforementioned testing methods for solar cells. The testing system for solar cells may include: a non-destructive current density acquisition module for acquiring the non-destructive current density of the solar cell when the external quantum efficiency is 1; the solar cell includes: a silicon substrate and a front film located on the light-facing side of the silicon substrate; a loss current density acquisition module for acquiring the loss current density lost by the solar cell; the loss current density includes: reflection loss current density lost due to reflection, front film absorption loss current density lost due to light absorbed by the front film, transmission loss current density lost due to light transmitted through the solar cell, and collection loss current density lost due to collection by the silicon substrate; and a calculation module for subtracting the loss current density from the non-destructive current density to obtain the short-circuit current density of the solar cell.

[0158] Optionally, the loss current density acquisition module includes: a PL meter, a doping concentration meter, a reflectivity meter, a transmittance meter, and a film thickness and refractive index meter. (See reference...) Figure 3 The photoluminescence intensity (PL) meter here can be used to measure the photoluminescence intensity (PLI) value of a solar cell. In cases where the solar cell includes a heavily doped portion, the doping concentration meter is used to test the doping concentration N and thickness D of the heavily doped portion. The reflectivity meter is used to measure the reflectivity of the solar cell at various wavelengths λ. The transmittance meter is used to measure the transmittance T(λ) of the solar cell at various wavelengths λ. The film thickness refractive index meter is used to measure the film thickness d of the front film and the extinction coefficient k of the front film at various wavelengths.

[0159] In determining the short-circuit current of a solar cell, a reflectivity meter and a transmittance meter can be integrated into a single instrument. When the solar cell includes heavily doped portions, the concentration N of the heavily doped portion does not vary significantly after product finalization and can be a fixed value. The thickness D of the heavily doped portion can be obtained from film thickness measurements obtained in the preceding processes. During the determination of the short-circuit current of the solar cell, measurements of the loss current density, open-circuit voltage Voc, and fill factor FF can all be performed on a PL (Photometric Photovoltaic Power) meter.

[0160] It should be noted that this testing system can implement any of the aforementioned solar cell testing methods and has the same or similar beneficial effects as any of the aforementioned solar cell testing methods. The relevant parts can be referred to each other. In order to avoid repetition, they will not be described again here.

[0161] Using the non-contact testing method provided in this application, such as Figure 3The test method shown is used to test a gridless back-contact solar cell, including a heavily doped portion, to determine the short-circuit current, open-circuit voltage, fill factor, and photoelectric conversion efficiency of the gridless back-contact solar cell. The parameters of the determined short-circuit current of the gridless back-contact solar cell are shown in Table 1 below.

[0162] Table 1: Parameters for determining short-circuit current in this application

[0163]

[0164] Referring to Table 1, since this gridless back-contact solar cell has no front metal electrode, the metal shading loss current density Jloss-metal due to light blocked by the front metal electrode is 0. Therefore, Jsc = Jideal - Jloss T -JLoss R -JLoss front -Jloss NIR -Jloss base =46.47-2.42-0.95-0.24-0.94-0.07=41.85mA / cm 2 .

[0165] The electrical performance of the gridless back-contact solar cell was tested using existing contact testing methods, compared with the non-contact testing method provided in this application. Figure 3 The test method shown was used to test back-contact solar cells without a main grid. The test results of the two are compared in Table 2 below.

[0166] Table 2: Comparison of Electrical Performance Test Results

[0167]

[0168] As shown in Table 2 above, the test results obtained using the test method of this application are quite similar to those obtained using existing contact testing methods, indicating that the non-contact testing method provided in this application is reliable and accurate. More importantly, compared to existing contact testing methods, this application's non-contact testing will not damage the solar cell and has a wider range of applications.

[0169] It should be noted that, for the sake of simplicity, the method embodiments are all described as a series of actions. However, those skilled in the art should understand that the embodiments of this application are not limited to the described order of actions, because according to the embodiments of this application, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also understand that the embodiments described in the specification are all preferred embodiments, and the actions involved are not necessarily essential to the embodiments of this application.

[0170] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0171] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk), and includes several instructions to cause a terminal (which may be a mobile phone, computer, server, air conditioner, or network device, etc.) to execute the methods described in the various embodiments of the present invention.

[0172] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A method for testing solar cells, characterized in that, include: A non-contact method is used to obtain the lossless current density of a solar cell with an external quantum efficiency of 1. The solar cell includes a silicon substrate and a front film located on the light-facing side of the silicon substrate. When the solar cell includes a front metal electrode located on the side of the front film away from the silicon substrate, the front film refers to all film layers in the solar cell located on the light-facing side except for the front metal electrode. When the solar cell does not include the front metal electrode, the front film refers to all structures in the solar cell located on the light-facing side. The loss current density of the solar cell is obtained in a non-contact manner; the loss current density includes: reflection loss current density due to reflection, front film absorption loss current density due to light absorbed by the front film, transmission loss current density due to light transmitted through the solar cell, and collection loss current density due to collection by the silicon substrate. The short-circuit current density of the solar cell is obtained by subtracting the loss current density from the lossless current density.

2. The test method for solar cells according to claim 1, characterized in that, The solar cell further includes: the front metal electrode; the loss current density further includes: the metal shading loss current density lost due to light being blocked by the front metal electrode.

3. The test method for solar cells according to claim 1, characterized in that, The solar cell further includes: a back film located on the backlight side of the silicon substrate; the back film refers to all film layers in the solar cell located on the backlight side except for the back metal electrode located on the backlight side; at least one of the front film, the back film, and the silicon substrate includes a heavily doped portion; The loss current density also includes the parasitic absorption loss current density due to parasitic absorption by the heavily doped portion.

4. The test method for solar cells according to claim 1, characterized in that, The process of obtaining the loss current density of the solar cell includes: The reflectivity R(λ) of the solar cell at various wavelengths λ was measured. The reflection loss current density was calculated. Wherein, q is the charge of an electron, λ1 is the lower limit of the wavelength of light absorbed by the solar cell, and λ2 is the upper limit of the wavelength of light absorbed by the solar cell; The current density of the solar cell is measured under STC standard test conditions when the solar cell is irradiated with spectral irradiation at various wavelengths according to a specified spectrum.

5. The test method for solar cells according to claim 1, characterized in that, The process of obtaining the loss current density of the solar cell includes: The reflectivity R(λ) of the solar cell at various wavelengths λ was measured. The thickness d of the front film and the extinction coefficient k of the front film at various wavelengths were measured. The absorption rates of the front film for each wavelength were calculated. ; The absorption loss current density of the front membrane was calculated. Wherein, q is the charge of an electron, λ1 is the lower limit of the wavelength of light absorbed by the solar cell, and λ2 is the upper limit of the wavelength of light absorbed by the solar cell. The external quantum efficiency under ideal conditions; The current density of the solar cell is measured under STC standard test conditions when the solar cell is irradiated with spectral irradiation at various wavelengths according to a specified spectrum.

6. The test method for solar cells according to claim 3, characterized in that, The process of obtaining the loss current density of the solar cell includes: The reflectivity R(λ) of the solar cell at various wavelengths λ was measured. The doping concentration N and the thickness D of each heavily doped portion in the solar cell were measured; the doping concentration N of the heavily doped portion is greater than or equal to 1E18 atoms / cm. 3 ; For each of the heavily doped regions, the absorption rate of the heavily doped region at each wavelength is calculated. Where X and Y are both fitting coefficients; For each of the heavily doped portions, the current density lost due to parasitic absorption by the heavily doped portion is calculated. , Wherein, q is the charge of an electron, λ1 is the lower limit of the wavelength of light absorbed by the solar cell, and λ2 is the upper limit of the wavelength of light absorbed by the solar cell. The external quantum efficiency under ideal conditions; The current density of the solar cell is given by irradiating it with various wavelengths under specified spectral irradiation conditions according to STC standard testing; Abb(λ) is the absorptivity of the silicon substrate for each wavelength. The parasitic absorption loss current density of the solar cell due to parasitic absorption by all the heavily doped portions is obtained by summing the parasitic absorption current densities corresponding to the parasitic absorption by the heavily doped portions. .

7. The test method for solar cells according to claim 1, characterized in that, The process of obtaining the loss current density of the solar cell includes: The transmittance T(λ) of the solar cell at various wavelengths λ was measured. The transmission loss current density was calculated. Wherein, q is the charge of an electron, λ1 is the lower limit of the wavelength of light absorbed by the solar cell, and λ2 is the upper limit of the wavelength of light absorbed by the solar cell; The current density value of the solar cell is determined by irradiating the solar cell with various wavelengths under specified spectral irradiation conditions according to STC standard test conditions.

8. The test method for solar cells according to claim 1, characterized in that, The process of obtaining the loss current density of the solar cell includes: The photoluminescence intensity (PLI) of the solar cell was measured at a range of 0.01 standard solar intensity to 0.1 standard solar intensity. The collection loss current density was calculated. ;in, The basic collection loss of the silicon substrate; The photoluminescence intensity value is the equivalent light intensity under the excess carrier concentration corresponding to the short-circuit current of the solar cell.

9. The test method for solar cells according to any one of claims 4 to 7, characterized in that, The solar cell absorbs light with wavelengths ranging from 300 nm to 1200 nm; and / or, The wavelengths are obtained by stepping values, which range from 0.5 nm to 20 nm.

10. The test method for solar cells according to any one of claims 1 to 8, characterized in that, Also includes: Starting from 0.02 standard solar irradiance, the photoluminescence intensity values ​​(PLI) of the solar cell were measured at equal light intensity steps from 0.02 standard solar irradiance to 0.06 standard solar irradiance. The equivalent current density Jeq of the solar radiation intensity corresponding to each photoluminescence intensity value PLI was calculated. ; wherein, the J sc The short-circuit current density of the solar cell; f is the solar intensity corresponding to one of the multiple photoluminescence intensity values ​​PLI. The equivalent voltages V' corresponding to the multiple photoluminescence intensity values ​​PLI were calculated. Among them, V t C is the thermal voltage of the solar cell at 25°C; C is the coefficient used for testing and calibrating the photoluminescence intensity value. The equivalent voltage-current curve is obtained by fitting multiple equivalent current densities Jeq and multiple equivalent voltages V'. Based on several positive and several negative equivalent current densities at certain points in the equivalent voltage-current curve, and the corresponding equivalent voltage V', the slope r of the selected partial points is obtained through linear fitting, and the series resistance Rs of the solar cell is calculated. ; use The equivalent voltages V' are converted into actual voltages V; The actual voltage-current curves are obtained by plotting multiple equivalent current densities Jeq and multiple actual voltages V, and the fill factor of the solar cell is obtained.

11. The test method for solar cells according to claim 10, characterized in that, Also includes: The photoluminescence intensity value PLI of the solar cell was measured under one standard solar radiation intensity. The open-circuit voltage V of the solar cell is determined using the photoluminescence intensity value PLI corresponding to a standard solar radiation intensity. oc , .

12. A testing system for solar cells, characterized in that, include: A non-contact current density acquisition module is used to acquire the non-contact current density of a solar cell with an external quantum efficiency of 1. The solar cell includes a silicon substrate and a front film located on the light-facing side of the silicon substrate. When the solar cell includes a front metal electrode located on the side of the front film away from the silicon substrate, the front film refers to all film layers in the solar cell located on the light-facing side except for those located on the front metal electrode. When the solar cell does not include the front metal electrode, the front film refers to all structures in the solar cell located on the light-facing side. The loss current density acquisition module is used to acquire the loss current density of the solar cell in a non-contact manner; the loss current density includes: reflection loss current density due to reflection, front film absorption loss current density due to light absorbed by the front film, transmission loss current density due to light transmitted through the solar cell, and collection loss current density due to collection by the silicon substrate. The calculation module is used to obtain the short-circuit current density of the solar cell by subtracting the loss current density from the lossless current density.

13. The solar cell testing system according to claim 12, characterized in that, The loss current density acquisition module includes: a PL tester, a reflectivity tester, a transmittance tester, and a film thickness refractive index tester.

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