Feasibility of using thin crystalline silicon films epitaxially grown at 165 °C in solar cells: A computer simulation study

Abstract

We have previously reported on the successful deposition of heterojunction solar cells whose thin intrinsic crystalline absorber layer is grown using the standard radio frequency plasma enhanced chemical vapour deposition process at 165 °C on highly doped P-type (100) crystalline silicon substrates. The structure had an N-doped hydrogenated amorphous silicon emitter deposited on top of the intrinsic epitaxial silicon layer. However to form the basis of a solar cell, the epitaxial silicon film must be chiefly responsible for the photo-generated current of the structure and not the underlying crystalline silicon substrate. In this article we use detailed electrical-optical modelling to calculate the minimum thickness of the epitaxial silicon layer for this to happen. We have also investigated by modelling the influence of the a-Si:H/epitaxial-Si and epitaxial-Si/c-Si interface defects, the thickness of the epitaxial silicon layer and its volume defect density on cell performance. Finally by varying the input parameters and considering various light-trapping schemes, we show that it is possible to attain a conversion efficiency in excess of 13% using only a 5 micron thick epitaxial silicon layer.