Crystalline thin-film Si cells from layer transfer using porous Si (PSI-process)

We fabricate thin-film Si cells by photolithography-free layer transfer processes. The confirmed power conversion efficiency of a 25.5 mum-thick cell that is textured with random upright pyramids is 15.4 %. Upright pyramids are, however, difficult to form in ultra-thin Si films. We therefore introduce an alternative process that yields random inverted pyramids on the front surface without chemical etching of the thin epitaxial film. This novel process applies an epitaxial emitter to speed up the fabrication process when compared to a thermally diffused emitter.