Solar cell film contact resistance testing method

Abstract

The invention provides a method for testing the contact resistance of a solar cell film, which comprises the following steps of: preparing a plurality of multi-layer stacked test samples with different thicknesses, and alternately depositing an amorphous silicon film and a transparent conductive oxide film on a glass substrate of each sample to form a horizontal laminated structure; respectively arranging silver electrodes on the left side and the right side of each sample for performing voltage-current volt-ampere test, and recording the total resistance of each sample in a specified voltage range and the change condition of the total resistance along with the thickness of the film layer; electrode contact resistance is measured and deducted; reversely deducing the resistance value when the thickness of the film layer is 0 through an extrapolation method to obtain the contact resistance between the film layers; and calculating the contact resistance of a single interface according to the number of contact interfaces of the amorphous silicon film and the transparent conductive oxide film in the sample. The method is suitable for a test system under different manufacture procedures and thickness changes, and quantitative extraction of the contact resistance between the amorphous silicon and the TCO is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photovoltaics, in particular to a method for testing the contact resistance of a solar cell thin film. BACKGROUND

[0002] Heterojunction solar cells benefit from its excellent surface passivation technology, this structure helps to reduce the interface recombination, improve the lifetime of carriers, with high open-circuit voltage, high conversion efficiency, however, in the process of monitoring, there are some problems, the resistance between the film layers cannot be effectively and accurately measured, especially the contact resistance of amorphous silicon film and transparent conductive oxide film, the resistance between the two contact surfaces due to incomplete contact, the contact resistance of the textured silicon substrate due to incomplete contact is more affected, this resistance will hinder the transmission of current through the contact surface, resulting in energy loss and signal transmission quality decline.

[0003] Because the contact resistance of single amorphous silicon film and TCO is small in order of magnitude, direct testing will cause great error, at present, there is no good evaluation method for the measurement of contact resistance of heterojunction solar cells, one is to simulate through simulation software, and one is to estimate the resistance of each film layer and contact resistance by fitting the whole cell string resistance through IV curve, these methods cannot obtain true and accurate results. SUMMARY

[0004] In view of the above, the present application provides a method for testing the contact resistance of a solar cell thin film, a testing system which is controllable in structure, has clear physical quantity response and is suitable for different processes and thickness changes, so as to realize quantitative extraction of the contact resistance between amorphous silicon and TCO.

[0005] The present application specifically adopts the following technical scheme: a method for testing the contact resistance of a solar cell thin film, comprising the following steps: S1, preparing a plurality of multilayer stacked test samples with different thicknesses, each sample being formed by alternately depositing amorphous silicon thin film and transparent conductive oxide thin film on a glass substrate to form a horizontal layer structure; S2, silver electrodes are arranged on the left and right sides of each sample respectively for voltage-current voltammetry test, and the total resistance of each sample in a specified voltage range and the change of the total resistance with the film thickness are recorded; S3, measuring and deducting the electrode contact resistance; S4, obtaining the film layer and film layer contact resistance by extrapolation method to deduce the resistance value when the film thickness is 0; S5, calculating the contact resistance of a single interface according to the number of contact interfaces of amorphous silicon thin film and transparent conductive oxide thin film in the sample.

[0006] As a further improved technical solution, the contact resistance of the electrode and the film layer is measured, the electrode is directly contacted with the film layer, the resistance value at this time is measured, the measurement is repeated multiple times, and the average value is taken as the contact resistance value of the electrode and the film layer, so as to exclude the interference in the subsequent test.

[0007] As a further improved technical solution, in step S2, the total resistance is taken as the ordinate, and the film layer thickness is taken as the abscissa, and a curve of the total resistance changing with the film layer thickness is drawn.

[0008] As a further improved technical solution, in the S4, the resistance value when the film layer thickness is 0 is extracted, and the ordinate intercept is the contact resistance of the amorphous silicon film layer and the transparent conductive oxide film layer.

[0009] As a further improved technical solution, the number of layers in each sample is an integer greater than 3, and the number of contact interfaces in each sample is the number of layers minus 1.

[0010] As a further improved technical solution, the thin film preparation adopts plasma enhanced chemical vapor deposition and magnetron sputtering method, which are respectively used for depositing amorphous silicon layer and TCO layer, and the deposition parameters of each sample are controlled to be constant to ensure the consistency of the sample quality.

[0011] As a further improved technical solution, in step S4, linear fitting is performed, and the linear fitting equation is R 间 =kD 总 +b, wherein R 间 is the interlayer resistance, D 总 is the total thickness of the sample, b represents the sum of all interface contact resistances, and k is the contribution of the unit film layer thickness to the total resistance.

[0012] As a further improved technical solution, the single interface contact resistance R 单 =b / number of interfaces.

[0013] As a further improved technical solution, the sample is equivalent to a material with uniform resistivity, and the transverse current test is used to reflect the vertical interface contact resistance.

[0014] The solar cell thin film contact resistance test method provided by the application can amplify the signal by stacking multiple layers, can reflect the characteristics of the vertical interface by equivalent transverse resistance, can flexibly set the film layer thickness and the total number of layers according to the experimental requirements, can balance the test accuracy and the process feasibility, is suitable for laboratory research and development and industrial quality monitoring, does not need complex modeling or additional calibration, the linear regression fitting is intuitive and reliable, is suitable for standardized process application, is suitable for the interface contact resistance measurement of various types of TCO (such as ITO, AZO and FTO) and various types of a-Si:H process conditions, and has good method migration and universality. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The sample structure is a 6-layer structure. DETAILED DESCRIPTION

[0016] The application will be further described below in conjunction with the accompanying drawings and examples. It should be understood that the specific examples described herein are intended to be illustrative only and are not a limitation on the present application.

[0017] The solar cell thin film contact resistance testing method of the present application comprises: S1, preparing a plurality of multilayer stack test samples with different thicknesses, each sample being formed by alternately depositing amorphous silicon thin films and transparent conductive oxide thin films on a glass substrate to form a horizontal layer structure.

[0018] The number of layers in each sample is an integer greater than 3, such as any of 4, 5, 6, 7, 8, 9, 10, 20, 21, 22, 30, etc. The number of contact interfaces in each sample is one less than the number of layers. The present application does not limit the parity of the number of layers, but the key is that the sample has a known number of TCO / a-Si interfaces, and the deposition thickness of each layer is consistent and the structure is regular.

[0019] The deposition parameters (such as gas flow, power, temperature, etc.) of each sample are controlled to be constant to ensure that the sample quality is consistent and the preparation steps of each sample are as follows: Select a glass substrate of appropriate size, and clean it with organic solvents such as acetone and alcohol by ultrasonic cleaning to remove organic impurities and particles on the surface. Then, rinse it with deionized water and dry it in a drying oven. Place the cleaned glass substrate in an amorphous silicon thin film deposition device, and use plasma enhanced chemical vapor deposition (PECVD) or physical vapor deposition (PVD) such as magnetron sputtering to deposit an amorphous silicon thin film on the substrate. Control the deposition parameters to make the thickness of the thin film reach the set value, such as 100 nm, 80 nm, 60 nm, 40 nm or 20 nm, etc. On the deposited amorphous silicon thin film, deposit a transparent conductive oxide thin film TCO such as indium tin oxide (ITO) or aluminum zinc oxide (AZO) by magnetron sputtering or chemical vapor deposition, and control the deposition process parameters to obtain the required TCO film thickness. In this embodiment, the TCO film layer and the amorphous silicon film layer have the same thickness.

[0020] Stack the above-mentioned amorphous silicon thin film and TCO thin film in sequence to form a multilayer composite structure. For example, a 6-layer structure is a sample with 3 layers of amorphous silicon and 3 layers of TCO. The sample is stacked from bottom to top as follows: glass substrate, deposited amorphous silicon layer, TCO layer, amorphous silicon layer, TCO layer, amorphous silicon layer, and TCO layer.

[0021] A plurality of samples were prepared, for example, 6-layer structures, each of which was formed by 3 layers of amorphous silicon thin film and 3 layers of transparent conductive film (TCO) stacked alternately, the thickness of the amorphous silicon thin film and the TCO film being 100 nm, 80 nm, 60 nm, 40 nm, and 20 nm respectively, 5 samples of each thickness were prepared to ensure experimental repeatability.

[0022] S2, silver electrodes were arranged on the left and right sides of each sample respectively for voltage-current voltammetry test, the total resistance of each sample in the specified voltage range was recorded, and the change of the total resistance with the thickness of the film layer was recorded.

[0023] The prepared multi-layer film samples were placed in a constant temperature and humidity test environment, the temperature was controlled at 25°C±0.5°C, the humidity was controlled at 40%±5%, the voltammetry test equipment was prepared, Keithley 2400 source meter was used as the voltammetry test equipment, the output end of the source meter was connected with the silver electrodes at both ends of the sample to form a closed loop. The voltage was applied in sections in the range of-1V to +1V, the current was measured, the I-V curve was drawn, and the total resistance was extracted by the slope Electrode arrangement: 3 silver electrodes were arranged on the left and right sides of the sample to be tested, the electrode size was 5 mm long, 2 mm wide, and 0.5 mm thick. The electrode spacing was 2 mm. The sample to be tested was regarded as a regular cuboid pattern, and each film layer was equivalent to a uniform whole, and the internal resistivity was equal.

[0024] According to the measurement results, the curve of the total resistance changing with the thickness of the film layer was drawn with the thickness of the film layer as the horizontal coordinate and the total resistance as the vertical coordinate.

[0025] S3, the electrode contact resistance was measured and deducted.

[0026] The contact resistance between the electrode and the film layer was measured by the four-probe method. The Ag electrode was directly pressed on the surface of the TCO film, two voltage sampling probes (inner probes) were arranged in the center of the contact area, two current injection probes (outer probes) were arranged symmetrically at the two sides of the Ag and TCO junction, and the distance between the contact edge and the two current injection probes was 0.5-1 mm. A constant current was input, and the steady-state voltage value was recorded. According to Ohm's law, the contact resistance was calculated. Each group of samples was measured for not less than 10 times, and the average value was taken as the contact resistance between the electrode and the film layer. The resistance between the film layers was calculated as follows: 间 = R 总 - R 电极平均 .

[0027] S4, the resistance value when the thickness of the film layer is 0 is obtained by extrapolation, and the contact resistance between the film layer and the film layer is obtained.

[0028] The sample is equivalent to a material with uniform resistivity, and the transverse current test reflects the vertical contact resistance between interfaces. Although the actual test is a horizontal electrode structure, the horizontal resistance is obtained, but since the current needs to cross multiple interfaces for transmission, the transverse resistance contains the contact resistance contribution of each amorphous silicon and TCO interface. Under the premise that the sample structure is regular, the thickness of each layer is consistent, and the interface quality is uniform, the change trend of the transverse resistance can be regarded as the equivalent expression of the vertical interface contact resistance. By adjusting the total film thickness and linearly fitting to extrapolate to D 总 =0, the total contact resistance can be accurately extracted.

[0029] The resistance value when the film layer thickness is 0 is extracted, and the vertical axis intercept is the contact resistance of the amorphous silicon film layer and the transparent conductive oxide film layer.

[0030] Linear fitting is performed, and the linear fitting equation is R 间 =kD 总 +b, where R 间 is the interlayer resistance, D 总 is the total thickness of the sample, b represents the total of all interface contact resistances, k is the contribution of unit film thickness to the total resistance, the slope k=△R / △b, and the slope k and b are calculated by entering the measured data into the formula.

[0031] S5, according to the number of contact interfaces of the amorphous silicon thin film and the transparent conductive oxide thin film in the sample, the contact resistance of a single interface is calculated.

[0032] Where the single interface contact resistance R 单 =b / interface number.

[0033] In addition, the above examples are only used to illustrate the present application and do not limit the technical solutions described in the present application. The understanding of the specification should be based on the skilled person in the art. Although the present application has been described in detail with reference to the above examples, those skilled in the art should understand that the skilled person in the art can still modify or equivalently replace the present application, and all technical solutions and improvements that do not deviate from the spirit and scope of the present application should be covered within the scope of the claims of the present application.

Claims

1. A method for testing the contact resistance of a solar cell thin film, characterized in that: Includes the following steps: S1. Prepare several multilayer stacked test samples of different thicknesses. For each sample, amorphous silicon thin film and transparent conductive oxide thin film are alternately deposited on a glass substrate to form a horizontal stacked structure. S2. Silver electrodes are set on the left and right sides of each sample to perform voltage-current voltammetry tests, and the total resistance of each sample within the specified voltage range and the change of total resistance with film thickness are recorded. S3. Measure and subtract the electrode contact resistance; S4. By extrapolating, the resistance value when the film thickness is 0 is calculated to obtain the contact resistance between the film layers. S5. Calculate the contact resistance of a single interface based on the number of contact interfaces of the amorphous silicon thin film and the transparent conductive oxide thin film in the sample.

2. The method for testing the contact resistance of solar cell thin films according to claim 1, characterized in that: To measure the contact resistance between the electrode and the film, the electrode is placed in direct contact with the film, and the resistance value is measured. This measurement is repeated multiple times, and the average value is taken as the contact resistance value between the electrode and the film to eliminate interference in subsequent tests.

3. The method for testing the contact resistance of solar cell thin films according to claim 1, characterized in that: In step S2, the curve of total resistance versus film thickness is plotted with film thickness as the x-axis and total resistance as the y-axis.

4. The method for testing the contact resistance of solar cell thin films according to claim 1, characterized in that: In step S4, the resistance value when the film thickness is 0 is extracted, and the vertical intercept is the contact resistance between the amorphous silicon film and the transparent conductive oxide film.

5. The method for testing the contact resistance of solar cell thin films according to claim 1, characterized in that: The number of layers in each sample is an integer greater than 3, and the number of contact interfaces in each sample is the number of layers minus 1.

6. The method for testing the contact resistance of solar cell thin films according to claim 1, characterized in that: The thin film was prepared using plasma-enhanced chemical vapor deposition and magnetron sputtering, respectively, for the deposition of amorphous silicon and TCO layers. The deposition parameters for each sample were kept constant to ensure consistent sample quality.

7. The method for testing the contact resistance of solar cell thin films according to claim 4, characterized in that: In step S4, a linear fit is performed, and the linear fit equation is R. 间 =kD 总 +b represents the total thickness of the sample, where R 间 D is the interlayer resistance. 总 Let be the total thickness of the sample, b represent the sum of the contact resistances of all interfaces, and k represent the contribution of the unit film thickness to the total resistance.

8. The method for testing the contact resistance of solar cell thin films according to claim 7, characterized in that: Single interface contact resistance R 单 =b / number of interfaces.

9. The method for testing the contact resistance of solar cell thin films according to claim 1, characterized in that: The sample is treated as a material with uniform resistivity, and the vertical contact resistance between the interfaces is reflected by transverse current testing.

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