Diffusion Of Phosphorous In Black Silicon

Black silicon is a promising texturing method for solar cells since it suppresses optical reflection in a broad spectral range. This relaxes the usual antireflection requirements on the coatings used for surface passivation of silicon. Fabrication of n-type emitters requires diffusion of phosphorous through the nanostructures of black silicon, which may need different optimal conditions as compared to diffusion through e.g. pyramidal wet-etched structures due to the different characteristic dimensions. In addition, the diffusion process should ideally not deteriorate the antireflective properties of black silicon. Here, we have investigated the effect of temperature and time during the doping process on optical reflectance and sheet resistance of black silicon. Doping temperatures of 875 degrees C and lower result in negligible increase of reflectance as compared to pristine black silicon. In addition, the sheet resistance of black silicon emitters is confirmed to be lower than that of planar Si under identical annealing conditions.