The morphology of CdS layers grown by chemical bath deposition (CBD) and high vacuum evaporation (HVE) have been investigated. The grains of CBD-CdS are more compact and smooth than those of HVE-CdS. The annealing and CdCl2 treatment cause grain growth, which is stronger for the CdCl2 treated samples. The grain-size of the as-deposited CdTe on CBD-CdS is about 5 times larger than of those grown on HVE-CdS. The structural and electrical properties of CdTe/CdS solar cells are strongly dependent on the CdS. The grain size of CdCl2 treated CdTe layers are similar, irrespective of the transparent conducting oxide substrate and CdS deposition method. The efficiency of solar cells on thin CBD-CdS is low (about 5.6%) because of pin-holes and a large intermixing of CdTe-CdS. The cells on HVE-CdS yield a higher current density despite thicker HVE-CdS as compared to CBD-CdS. The efficiency of solar cells on HVE-CdS is 12.3%. (C) 2001 Elsevier Science B.V. All rights reserved.