Use of ultrathin oxides and thin polycrystalline silicon films for stable high-efficiency silicon solar cells

Initial designs of single-crystal point-contact solar cells showed a degradation in their efficiency due to photoinjected hot-electron damage. We have examined the ultraviolet stability of ultrathin oxides covered by a thin polycrystalline silicon film and a thick oxide. Optical modeling has shown that these oxide/polycrystalline silicon/oxide stacks can have extremely good antireflection properties which offset the absorption losses from the polycrystalline silicon. Experiments have determined that these stacks are stable under ultraviolet exposure and that the polycrystalline silicon is absorbing less light than predicted. Point-contact solar cells fabricated with this technique have achieved efficiencies as high as 24.4% under 36 W/cm2 of concentrated sunlight.