Variations of the back surface field in silicon thin-film solar cells with interdigitated front grid

Crystalline Si Thin-Film Solar Cells (c-Si TFC) based on a silicon-on-insulator structure (SOI) were realized with an interdigitated front contact grid. Efficiencies of up to 19.2% on a 46µm thick silicon layer and 18.5% on a 30µm thick silicon layer were achieved. These layer systems were grown epitaxially on the 200nm thick seeding layer on top of an implanted compact SiO2 intermediate layers. Various simulations were performed to study the influence of the back surface field (BSF) as well as of the grid finger distance and the finger width, respectively on the solar cell performance. It could be shown that the best results were obtained on thin (2µm) but very highly doped BSFs as well as on thick (8.5µm) and less highly doped BSFs. Solar cells with n-doped BSFs were much worse compared to p+ BSFs. This might be a result of a lower crystallographic quality of the highly n-doped layers which act as seeding layers for the subsequent epi-growth. The finger-to-finger distance of the grid hardly affects the overall cell performance in a wide range, which is a promising result for a potential screen-printing process of an interdigitated front-grid in the future.