Thin film CdS/CdTe solar cells with high efficiencies above 15% were produced by vacuum evaporation at substrate temperatures lower than 400 degrees C. The junction quality was found to be improved by introducing an In (or Sn)-oxide buffer layer on the transparent conducting oxide film, and V-oc greater than 0.84 V and FF greater than 75% could be obtained. Furthermore, the two-step CdS formation method was found to be effective for obtaining high-efficiency cells on a sodalime glass.