The particular properties Of Cu2S-CdS heterojunctions are revealed. The effects of lattice mismatch on epitaxy as well as wet-and dry-topotaxy are discussed and preconditions for successful application of topotaxy are elaborated. The influence of surface treatments of the cells and of additional semiconducting or metallic layers of monolayer-range thicknesses at the surface is demonstrated. The junction formation technology and the surface treatments appear to be relevant also to other photovoltaic devices. (C) 2003 Elsevier Science B.V. All rights reserved.