Highly efficient large area (10.5%, 1376 cm(2)) thin-film CdS/CdTe solar cell sub-module has been fabricated. Very recently we also have fabricated a very large area sub-module of aperture area 5413 cm(2) exhibiting a conversion efficiency of 8.4%. Such a high efficiency has been achieved by depositing all the constituent films such as SnO2: F, CdS and CdTe having greater uniformity and better quality under atmospheric pressure conditions. A post deposition treatment of CdTe surface with CdCl2 has been optimized to improve the overall solar cell output performance significantly. (C) 2001 Elsevier Science B.V. All rights reserved.