The effects of ethane plasma annealing on grain boundary barrier heights, minority carrier lifetimes and capture cross-sections and trap energy levels have been observed through measurements of photoconductance voltage and decay time onp-type Wacker polycrystalline silicon samples, of mm grain-size. It has been found that ethane plasma annealing significantly reduces the grain boundary heights, increases the minority carrier lifetimes and reduces minority carrier capture cross-sections by filling the deep trap levels in the band gap. It is suggested that ethane and other saturated hydrocarbons may prove useful for passivation of grain boundaries in polycrystalline solar cells and other electronic devices.