Improving surface passivation on very thin substrates for high efficiency silicon heterojunction solar cells

Abstract

Silicon solar cells are now less than 3% absolute from the theoretical efficiency limit. Advanced passivated contact architectures have demonstrated surface saturation current densities close to 1 fA/cm2. We have optimized the thin intrinsic hydrogenated amorphous silicon layer by controlling the deposition temperature and the silane-to-hydrogen dilution ratio. Thin wafers were used as a testbed to increase the sensitivity to surface passivation. By optimizing the intrinsic layer, we reduced the surface saturation current densities from 1.7 fA/cm2 to 0.6 fA/cm2 on textured wafers with thicknesses ranging between 40 and 180 μm. Implied open-circuit voltages over 760 mV were accomplished on p-i/c-Si/i-n structures deposited on n-type CZ wafers with wafer thicknesses below 50 μm. Further, we demonstrated experimentally the potential of using very thin wafers by manufacturing screen-printed silicon heterojunction solar cells on 40 μm thick standalone wafers while achieving an efficiency of 20.48%.