Three-point and four-point mechanical bending test modeling and application in solar cells

Abstract

<sec>Silicon (Si)-wafer-based solar cells have dominated the global market with a share exceeding 90% due to their abundant source material and well-known physical and chemical properties. The brittleness of silicon material limits its further applications. It is necessary to investigate the material strength properties of Si wafer and/or Si solar cells, which can guide the fabrication process of Si solar cells to avoid breaking the Si wafers. The Si material strength properties have been extensively investigated by the methods of three-point bending test and four-point bending test. However, the difference between these two methods has not been studied so far.</sec><sec>In this work, the mechanical strength properties of monocrystalline silicon (c-Si) wafer and bifacial c-Si solar cells are measured by three-point bending test and four-point bending test respectively. The average value of the maximum bending displacements has a little discrepancy between the results of the three-point bending test and four-point bending test methods. It is worth noting that the degree of dispersion of the Si wafer test results of the three-point bending test is larger than those of the four-point bending test. And the results of the dispersion of the Si bifacial solar cells, obtained from the two bending test methods, show no difference between them due to the existence of metalized electrodes. Whether the measured sample is Si wafer or Si solar cell, the average value of the maximum load, obtained from the four-point bending test, is higher than that from the three point-bending test method, and the average value of the fracture strength, obtained from the four-point bending test, is lower than that from the three-point bending test method. By establishing the models of different beams, the applied load gets dispersed through two bars of the four-point bending test method, whereas the applied load is directly applied to the sample through one bar of the three-point bending test method, which can explain the relatively large difference between these two test methods.</sec>