Superstrate-type CuInSe2-based thin film solar cells by a low-temperature process using sodium compounds

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°C. Even at relatively low substrate temperatures, sodium compounds enhanced the (1 1 2) 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 Voc, = 430 mV, Jsc = 29.4 mA/cm2 and FF = 0.60. The light soaking and forward bias effects were observed for these cells.