Surface characterisation of wafers for silicon-heterojunction solar cells

Silicon-heterojunction cells represent a fast-growing, very promising field in photovoltaics. The key issues from the scientific and technological point of view are directly related to the quality of the junction interface (i.e., to that of the wafer surface just before thin-film deposition). The chemical purity of this surface and its dependence on HF chemical etching have been studied by XPS. Possible surface damage has been checked by SEM. Polished, rough and textured wafers have been tested. Textured samples have impurities derived from the previous pyramid-etching process. A brief (2 min) dipping in very diluted (only 1%) HF is enough to remove the 5-nm native-oxide layer. More aggressive treatments only increase surface reactivity. No surface damage is appreciated in the SEM images, not even in those of the samples etched with the highest concentrations and/or for the longest times.