A critical review on the fracture of ultra-thin photovoltaics silicon wafers

Abstract

Silicon-based solar photovoltaics cells are an important way to utilize solar energy. Diamond wire slicing technology is the main method for producing solar photovoltaics cell substrates. In order to reduce production costs and improve the production efficiency, the solar photovoltaics cell substrates silicon wafers are developing in the direction of large size and ultra-thin, and the diamond wire slicing technology is developing in the direction of high wire speed and fine wire diameter. These aspects cause an increase in the fracture probability of silicon wafer during the processing and increase costs. In this paper, a comprehensive review has been conducted on silicon wafer fracture with the latest research. Firstly, the strength characteristics of ideal crystalline silicon are summarized and discussed. The ideal crystalline silicon has a large mechanical strength, and the tensile strength in the non-dissociation direction is more than 10 GPa, while the fracture strength of silicon wafers is only 100 MPa–500 MPa. This is because there is subsurface damage on the wafers during slicing processing. Then the testing methods and statistical methods of silicon wafer fracture strength are introduced. The testing methods mainly include 3-point bending test, 4-point bending test, and biaxial bending test. Collecting load-displacement data during bending test can further calculate the fracture stress of silicon wafers through linear stress analytical formulas and finite element methods. Then, the Weibull function is used for statistical analysis to obtain the fracture strength of the silicon wafer. Finally, the research literatures on the theoretical modeling of silicon wafer fracture strength and the calculation model of silicon wafer fracture probability under different load conditions are introduced. This review contributes to a comprehensive understanding of the mechanical strength degradation and fracture mechanism of silicon wafers, and provides critical insights for future research interests.