Scattering, Diffraction, and Geometric Light Trapping in Thin Film Amorphous Silicon Solar Cells on Plastic Substrates

In this study we compare light trapping in hydrogenated amorphous silicon (a-Si:H) solar cells deposited directly onto polycarbonate (PC) at low temperature (<130°C). To that end, we embossed PC substrates with 400 nm and 10 μm square based pyramids to induce light trapping based on diffraction and on geometric effects. As a comparison, we deposited a-Si:H cells on flat glass substrates and on Asahi U-type TCO glass. The cells on PC generate current densities comparable (slightly higher) than cells on Asahi TCO glass, but suffer from a slightly lower Voc, resulting in cells with an initial efficiency of 6.8% and 7.4% on sub-micron pyramid and micro-pyramid structured PC substrates respectively, compared to 7.6% for cells on Asahi. This shows great potential for a-Si:H cells deposited directly onto cheap plastics.