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

摘要

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 (Fe-i) 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 Fe-i, 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 Fe-i from the bulk.