Superstrate-type solar cells with a Au/CuInSe2(CIS)/InxSey/ZnO:Al/glass structure were investigated, The CIS films were deposited by coevaporation method with intentionally incorporated Na2S at a substrate temperature of 350 degrees C. Even at relatively low substrate temperatures, sodium compounds enhanced the (112) preferred orientation of the chalcopyrite structure, and also improved the cell performance. The InxSey buffer layers disappeared after CIS deposition by interdiffusion. Preliminary cells yielded an efficiency of 7.5% with V-OC = 430 mV, J(SC) = 29.4 mA/cm(2) and FF = 0.60. The light soaking and forward bias effects were observed for these cells.