In this study, performance improvement of CIGS-based submodules using a sputtered ZnO:5.7wt% Ga2O3 (5.7GZO) as window layers is reported. Preheating treatment at 200degreesC for 15 min is applied to the parts before the deposition of GZO window layers. This contributes to increase the optical transparency (% T) of GZO window considering the % T of about +5% and to improve the J(sc) of about +4mA/cm(2). Deposition of a high-resistivity, intrinsic ZnO (i-ZnO) thin layer on the Zn(O,S,OH)(x) buffer layer before 5.7GZO window deposition contributes to improve the properties of pn hetero-junction quality and increase the optical transparency, V-oc and FF. (C) 2002 Published by Elsevier Science B.V.