Antireflective porous-silicon coatings for multicrystalline solar cells: the effects of chemical etching and rapid thermal processing

In this paper, the emitter of multicrystalline silicon solar cells has been chemically etched in order to form porous silicon (PS) layers, usually kno wn as stain-etched PS, to be used at the same time as a selective emitter a nd as an efficient antireflective layer. The optical behaviour of the solar cells in the 250-850 nm wavelength range (5-1.45 eV range) was determined before and after PS formation, resulting in a notable reduction of reflecta nce after PS formation and a corresponding increase in cell efficiency. The different morphologies of the silicon emitter and metallic contacts, befor e and after PS formation, were analysed by scanning electron microscopy and atomic force microscopy. Furthermore, the electrical properties of both th e emitter region and the contacts were investigated, as well as the most si gnificant solar cell parameters before and after PS formation. Finally, the effect of rapid thermal processing in nitrogen and oxygen atmospheres on b oth the surface morphology and the optical behaviour of PS was studied.