Effective lifetime variations significant for process evaluation or just an artifact of wafer size and quality? : An attempt to quantify material induced variations

Abstract

Small sample size and usage of sister wafers in photovoltaics research are quite common. Regarding sample size, edge effects and reduced thermal mass may influence applicability of scientific findings to industrial wafers. Therefore, an extended investigation of these effects performed on various Si materials for solar cells can help to evaluate possible drawbacks of small-sized research samples. In addition to problems with inversion-based passivation mechanisms, edge recombination effects can significantly reduce lifetimes. These effects are more detrimental for small-sized samples due to a higher edge-to-area ratio. Furthermore, a comparison of sister wafers including their degradation and regeneration behavior should help to quantify the uncertainty due to wafer quality variations. Comparable lifetimes without significant variations are shown with annealed sister wafers. However, fired p-type Cz-Si sister wafers are prone to BO and LeTID degradation. Therefore, differing initial lifetimes can be explained by different states of degradation at the start of investigation. Normalized defect densities show comparable maxima referring to regenerated lifetimes. Keywords: Defect Density, Degradation, Lifetime