Impurity Gettering by Boron‐ and Phosphorus‐Doped Polysilicon Passivating Contacts for High‐Efficiency Multicrystalline Silicon Solar Cells

Abstract

Highly doped polysilicon (poly‐Si) on ultra‐thin oxide layers are highlighted as they allow both carrier collection efficiency with a low contact resistivity and an excellent surface passivation. Their integration at the rear surface of a high‐quality single‐crystalline silicon solar cell allows to achieve a record conversion efficiency of 25.7% for a double‐side contacted device. However, so far, only a very few studies investigate the interactions between poly‐Si passivating contacts and low‐quality cheaper silicon wafers. Thus, this study focuses on the external gettering response of both boron (B) and phosphorus (P) in situ doped poly‐Si passivating contacts on high‐performance multicrystalline silicon. Wafers are extracted from five ingot heights and experience P‐ and B‐doped poly‐Si passivating contact fabrication processes. Subsequently, the bulk carrier lifetime and interstitial iron (Fei) concentration are characterized and compared with conventional POCl3 and BCl3 thermal diffusion steps, and as‐cut references. The P‐doped poly‐Si contact fabrication process results in gettering more than 99% of the Fei, which leads to an increase in the bulk carrier lifetime. Interestingly, the B‐doped poly‐Si contact also develops a substantial external gettering action, and allows removing 96% of the Fei from the bulk.