Bulk carrier lifetime surpassing 600 us in Upgraded Metallurgical-grade Silicon multicrystalline wafers after Phosphorus Diffusion Gettering

TL;DR

This paper demonstrates that optimized phosphorus diffusion gettering significantly enhances bulk carrier lifetimes in upgraded metallurgical-grade silicon wafers, achieving record lifetimes over 600 microseconds, thus improving their suitability for high-efficiency solar cells.

Contribution

It introduces optimized PDG processes for UMG-Si that substantially increase carrier lifetimes, surpassing previous records and enabling better solar cell performance.

Findings

Carrier lifetimes increased by 20 to 250 times

Record bulk lifetime over 645 microseconds achieved

Enhanced UMG-Si suitability for high-efficiency solar cells

Abstract

Upgraded metallurgical-grade (UMG) Si is obtained via a purification route alternative to the one used for conventional polysilicon and with significantly reduced environmental impact. Additionally, despite a lower purity level in the feedstock than polysilicon, UMG-Si has demonstrated potential for the fabrication of highly efficient and low-cost solar cells. Low initial bulk carrier lifetimes recorded in UMG-Si bare wafers can be improved by means of an adequate Phosphorus Diffusion Gettering (PDG) process to the level of mc-Si. In this letter, optimized PDG processes for UMG-Si are reported, resulting in increased values between 20 and 250 times the original carrier lifetimes and record figures above 645 us.