Dielectric rear side passivation on Ribbon Growth on Substrate (RGS) solar cells

Abstract

Ribbon Growth on Substrate (RGS) silicon wafers are cast directly from the melt onto reusable substrates. With a high production speed in the order of one wafer per second and the avoidance of material loss due to wire-sawing like in the block-casting technology, RGS is a cost-effective material. The wafers are multicrystalline with typical grain sizes between 0.1 mm to 1 mm. Up to now, the adapted solar cell process contained an open rear side metallization realized by an Al-grid [1]. This had to be implemented because of increased process induced shunting in cell areas with Al back side metallization. For rear side passivation and avoidance of possible shunting, two new cell back side designs are tested and compared to the RGS baseline process. In this work, silicon carbide as a dielectric passivation layer and its properties regarding a co-firing temperature step and the application of such a layer in the RGS solar cell process is investigated. It is found that a cell process for RGS containing a dielectric layer on the cell rear side in connection with Laser Fired Contacts (LFCs) enhances the cell performance by reducing the area of possibly contacted shunting paths further and thus increasing the parallel resistance of the solar cells. The gain in efficiency is hereby less attributed to the improved rear side passivation quality for this material with a limited diffusion length.