Impact of Tabula Rasa and Phosphorus Diffusion Gettering on 21% Heterojunction Solar Cells Based on n-Type Czochralski-Grown Upgrade Metallurgical-Grade Silicon

This paper investigates the impact of tabula rasa (TR) and phosphorus diffusion gettering (PDG), both in isolation and in combination, for improving the electronic quality of n-type Czochralski grown Upgraded Metallurgical-Grade (UMG) silicon wafers. We have found that the bulk lifetimes of the UMG wafers were affected by both oxygen precipitate nuclei and mobile metallic impurities. Thus, we achieved the best bulk lifetimes after subjecting the UMG wafers to a TR step prior to a PDG step. Further, we report silicon heterojunction solar cells results based on the UMG wafers subjected to a TR step prior to a PDG step. The best in-house measured efficiencies were 21.2 % and 20.8 % for the UMG wafers from the middle and tail regions of the ingot, respectively.This work has been supported by the Australian Renewable Energy Agency (ARENA) through the Australian Centre for Advanced Photovoltaics (ACAP), and project RND009. Support was also provided by the Engineering Research Center Program of the National Science Foundation and the Office of Energy Efficiency and Renewable Energy of the Department of Energy under NSF Cooperative Agreement No. EEC-1041895