Impact of Tabula Rasa and Phosphorus Diffusion Gettering on 21% Heterojunction Solar Cells Based on n-Type Czochralski-Grown Upgraded 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.