A photovoltaic effect whose positive polarity is on SnO2 was found on CuInSe2, (or related materials)/SnO2 thin film structures. The CuInSe2 films were deposited by means of a simple and low cost method using the close-spaced vapour transport by iodine in a closed tube. The source temperature was increased during the depositions from 400-450 degrees C to 550-650 degrees C, depending on the material. By lighting through SnO2, open circuit voltages of the order of 350 mV or more and short circuit current densities of the order of 30 mA cm(-2) were obtained. The interpretation proposed is the formation of a doping gradient in the CuInSe2 films, due to the deposition conditions. The films are p(+) type next to SnO2 and p(-) or n type at the surface, where an n-type phase appears, formed from III-VI compounds. Moreover, there is probably an interaction between SnO2, iodine and CuTnSe(2), resulting in an n-doped layer in the film (perhaps due to Sn diffusion), adding to the first doping profile.