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)/In_xSe_y,/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 In_xSe_y 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/cm² and FF = 0.60. The light soaking and forward bias effects were observed for these cells.