Multicrystalline silicon solar cells from RST ribbon process

Abstract

The aim of Solarforce is the achievement of high efficiency solar cells made out of ≤100 µm thick multicrystalline silicon wafers produced by the Ribbon on Sacrificial Template (RST) process. For a first evaluation of the RST material, solar cells were fabricated on p-type RST wafers with different processes. The first conclusion is that the density of silicon carbide inclusions has to be lowered to obtain better FF values, and in turn a better homogeneity in cell performances. Secondly, conversion efficiency is found to be limited around 14% by low bulk minority carrier lifetime values, limiting both Voc and Leff. ICP-MS analyses on RST material show that this lifetime may be improved with the possible achievement of low metallic impurity content in the wafers, under 1 ppb wt. Further enhancement is also shown to be possible with the n doping of RST material, a well controlled process in ribbon growth.