Stress-induced large-area lift-off of crystalline Si films

A new implantation-free lift-off process is presented. We deposit a layer with mismatched thermal expansion coefficient with respect to the substrate. Upon cooling, the differential contraction induces a large stress field which is released by the initiation and the propagation of a crack parallel to the surface. The principle is demonstrated on both single and multi-crystalline silicon. Films with an area of 25 cm² and a thickness of 30–50 μm have been obtained. Some Si layers were further processed into solar cells. An energy conversion efficiency of 9.9% was reached on a 1 cm² sample. PACS 62.20.Mk; 68.55.Jk; 68.60.Bs; 84.60.Jt