Minority carrier lifetime monitoring in a buried contact solar cells process using MC-SI

Abstract

The buried contact solar cell is produced in industry using monocrystalline silicon. The low shading losses and the selective emitter design can lead to high efficiencies. The buried contact solar cell process features two diffusion steps, one of them is a high temperature step at 950°C. Compared to a standard screen print process the hydrogen passivation scheme also differs. In this paper we investigate the evolution of minority carrier lifetime of several multicrystalline silicon materials during processing and compare the final lifetime after the buried contact process to the final lifetime of a neighboring wafer after a standard screen print process. Solar grade feedstock (Elkem SoG) from a metallurgical process route produced by Elkem Solar AS has the potential for a reduction of costs per watt-peak in photovoltaics and is therefore in the focus of our investigation. The solar grade reference material A shows high lifetimes after a standard screen print process. In the buried contact process, lifetime drops after the high temperature POCl3 diffusion and can be recovered partly by hydrogenation. In Elkem SoG silicon wafers, the phosphorous gettering continues even in the high temperature POCl3 diffusion, resulting in high lifetimes also after the buried contact solar cell process.