A thin layer of CdS of about 200 angstrom enhances the solar conversion efficiency of CdS/CdTe solar cells from 8% to 15%. A similar enhancement of the efficiency is observed on other solar cells, based on CuInSe2 or similar compounds. The reason for this efficiency enhancement that is typical for CdS, but not observed with similar semiconductors, is briefly described. The technical and economical importance of these solar cells on the energy conversion market is summarized. (C) 2010 Elsevier Ltd. All rights reserved.