A novel procedure based on the reactive evaporation method was developed to deposit highly transparent thin films of i-ZnO and n(+)-ZnO in-situ. The opto-electrical properties of the ZnO films were optimized for using them as TCO layer in solar cells. The optimization of the preparation parameters was achieved through a figure of merit defined in terms of both, the transmittance and the resistivity. n(+)-ZnO films with resistivities around 8 x 10(-4) Omega cm and i-ZnO films with resistivities around 10(5) Omega cm and transmittances greater than 80% (in the visible region) were obtained with this method. The applicability of the i-ZnO and n(+)-ZnO thin films in photovoltaic devices has been demonstrated by using them as interdiffusion barrier and TCO layer in CulnS(2) based solar cells. Conversion efficiencies of 9.1% were achieved with CIS based solar cells using ZnO thin films deposited by reactive evaporation. (C) 2012 Elsevier B.V. All rights reserved.