Efficiency potential of RGS silicon from current R&D production

Abstract

Ribbon Growth on Substrate (RGS) is a low cost silicon ribbon material for photovoltaics. The RGS growth technique allows the direct growth of wafers with a very high production speed of one wafer per second. An industrial compatible cost effective screen printing process results in an efficiency of 13.1% for an untextured RGS cell. Based on this efficiency the silicon consumption per WPeak for a 300 μm thick RGS wafer calculates to 5.4 g/WPeak which is about 50% lower compared to standard block cast mc silicon material where a silicon loss of more than 50% appears due to ingot casting and wafering by wire saw. The silicon reduction is even more pronounced by the use of thinner RGS wafers. For efficiency demonstration a laboratory type high efficiency photolithography based process results in 14.4% efficiency on smaller cell size, which is the highest solar cell efficiency reached on RGS silicon so far. In this paper the applied cell processes as well as cell results are discussed by means of spectral response as well as spatially resolved LBIC measurements showing the characteristics of this multi-crystalline silicon ribbon material.