Stress and temperature coupling effects on dislocation density reduction in multicrystalline silicon

Abstract

In multicrystalline silicon (mc-Si), the presence of dislocation-rich areas limits solar cell conversion efficiencies. Previous studies have demonstrated that dislocation densities higher than 106 cm-2 can dramatically decrease the minority carrier lifetime. High dislocation densities, and their decoration with impurities, can limit minority carrier lifetime even after phosphorous diffusion or hydrogen passivation. We previously proposed a method to remove dislocations from mc-Si by high-temperature annealing, demonstrating dislocation density reductions of 95% approximately. We demonstrated that the dependence of dislocation density reduction on annealing temperature is much more pronounced that the dependence on annealing time. In this contribution, we propose stress as an additional mechanism to enhance dislocation density reduction. We discuss the relationship between temperature, stresses and dislocation density in string ribbon.