三点、四点法机械性能测试建模及其在太阳电池中的应用

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

用三点弯曲和四点弯曲测试方法分别测试了单晶硅片和双面电池两种不同样片的机械性能,通过建立模型,探讨了不同的弯曲测试方法对样片的最大弯曲位移、最大载荷和断裂强度的影响.研究表明:三点弯曲和四点弯曲测试测量的最大弯曲位移相差不大,但对单晶硅片而言,三点弯曲测试方法测量结果离散度较大,四点弯曲测试方法测量结果离散度较小.然而不论是单晶硅片还是双面电池,四点弯曲测试方法均能通过分散载荷的方式而增加样片的承载能力,四点弯曲测试方法计算得出的断裂强度较小于三点弯曲测试的结果.

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.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.