Correlative Raman-Voltage Microscopy Revealing the Localized Structure-Stress Relationship in Silicon Solar Cells

Knowledge of localized strain at the micrometer scale is essential for tailoring the electrical and mechanical properties of ongoing thinning of crystal silicon (c-Si) solar cells. Thinning c-Si wafers below 110 μm are susceptible to cracking in manufacturing due to the nonuniform stress distribution at a micrometer region, necessitating a rigorous technique to reveal the localized stress distribution correlating with its device electrical output. In this context, a Raman microscopy integrated with a photovoltage mapping setup with high resolution to the submicrometer scale is developed to acquire correlative Raman-voltage of the localized physical properties at the microcracks on the rear side of c-Si solar cells. By integrating photoelectrical, mechanical, and theoretical simulations, we elucidated the evolution of the microcracks. The localized stresses cause significant electrical output degradation in c-Si solar cells. In addition, theoretical simulations and experimental characterization indicate that the etched rear side acts as a more intense stress concentrator, resulting in an asymmetrical stress distribution between the rear and front sides of c-Si solar cells. This finding provides valuable insights into the origin of microcracks in c-Si solar cells and serves as a metrology tool for microscale mapping of strain-engineered photovoltaic modules.