Effect of laser marks and residual stress in wafers on the propensity for performance loss due to cracking in solar cells

In this study, silicon wafers were marked with four different kinds of laser marks. Initial characterization of the wafers was performed to measure various parameters such as minority lifetime, residual stress, wafer thickness, Photoluminescence, and Resonance Ultrasound Imaging. The wafers were consequently processed into solar cells. EL, PL and RUV measurements were also performed on solar cells, in addition to the flash I-V measurements to determine solar cell performance parameters. Cells were laminated into custom modules and the modules were passed through static and dynamic mechanical loading tests according to IEC 61215. A procedure to quantify the performance loss due to cell cracking for each cell was developed and applied for each cell that experienced significant cracking after mechanical loading tests. Following correlations were explored: (i) Propensity of power loss due to cell cracks and residual stress at wafer level (ii) Types of laser marks and their effects on parameters measured in various wafer and cell characterization techniques.