The band gap of Zn(O,S) and (Zn,Mg)O buffer layers are varied with the objective of changing the conduction band alignment at the buffer layer/CuGaSe(2) interface. To achieve this, alternative buffer layers are deposited using atomic layer deposition. The optimal compositions for CuGaSe(2) solar cells are found to be close to the same for (Zn,Mg)O and the same for Zn(O,S) as in the CuIn(0.7)Ga(0.3)Se(2) solar cell case. At the optimal compositions the solar cell conversion efficiency for (Zn,Mg)O buffer layers is 6.2% and for Zn(O,S) buffer layers it is 3.9% compared to the CdS reference cells which have 5-8% efficiency. (C) 2008 Elsevier B.V. All rights reserved.