Silicon heterojunction solar cells: Influence of H2-dilution on cell performance

Surface passivation of hydrogenated amorphous silicon (a-Si:H) films is critically influenced by the hydrogen/silane ratio during PECVD deposition. Das et al. (2008) studied this effect with respect to the crystal orientation of c-Si wafer substrates. We revisit the effect of the hydrogen/silane ratio and observe modifications compared to their study: we obtain VOC-values >710 mV and find for textured and on (1 1 1)-oriented substrate surfaces that the effective carrier lifetime and VOC-values of solar cells benefit from increasing the hydrogen/silane ratio. The implied open-circuit voltages from lifetime measurements on our samples agree well with the final solar cell open-circuit voltages. We achieve high surface passivation, resulting in VOC>710 mV and efficiencies up to 19.4% for 4 cm2 solar cells.