Stable passivations for high-efficiency silicon solar cells

Initial designs of single-crystal silicon point-contact solar cells have shown a degradation in their efficiency after being exposed to concentrated sunlight. The main mechanism appears to be an increase in recombination centers at the Si/SiO₂ interface due to ultraviolet light photoinjecting electrons from the silicon conduction band into the silicon dioxide that passivates the cell´s front surface. Trichloroethane, texturization, and aluminum during the forming gas anneal all contribute to the instability of the interface. A reasonably good resistance to UV light can be obtained by putting a phosphorus diffusion at the surface and can be improved further by stripping off the deposited oxide after the diffusion and regrowing a dry thermal oxide. A second technique, which utilizes ultrathin oxides and thin polysilicon films and can yield stable point-contact solar cells that are more efficient at higher concentrations, is also described