Silicon epitaxy below 200°C: Toward micrometer-scale thin film silicon solar cells

Low temperature plasma processes provides a tool box for etching, texturing and deposition of a wide range of materials. Here we present a bottom up approach to grow crystalline silicon films by standard RF-PECVD at temperatures below 200°C. Recently, proof was made that thin film epi-Si can match wafer-based solar cells efficiency, while being transferable to a foreign substrate [1]. This offer the possibility of cost saving through wafer re-use and material reduction scenario. But most epitaxial conditions need temperature above 600°C, whereas our approach offers the additional advantage of cost reduction through standard industrial RF-PECVD equipment and low thermal budget. Both structural and electronic properties of the epitaxial layers are investigated. High crystalline quality and stress level are deduced from HRTEM and Raman measurement. We build heterojunction solar cells with intrinsic epitaxial absorber in the range of few µm, grown by RF-PECVD at 165 °C on highly doped (100) substrate, in the wafer equivalent approach [2]. Achievement of a fill factor as high as 79% is a proof that excellent quality of epitaxial layers can be produced at such low temperatures. The possibility of reaching 10% conversion efficiency in few microns Si solar cells is discussed. [2] J. H. Petermann, D. Zielke, J. Schmidt, F. Haase, E. G. Rojas, et R. Brendel, Progress in Photovoltaics: Research and Applications (s. d.). [3] R. Cariou, M. Labrune, et P. Roca i Cabarrocas, Solar Energy Materials and Solar Cells 95, 2260-2263 (2011).