We have fabricated and characterized some donor/acceptor type photovoltaic devices. While zinc phthalocyanine has been the donor material, a series of acceptor materials with identical backbone but different strength has been chosen. The role of function groups in acceptor material on photovoltaic device characteristics has been studied under different illumination intensities. Origin of the open-circuit voltage has been discussed considering ionization potential of donor and electron affinity of the acceptor material. Nonlinear increase of short-circuit current on light intensity has been observed and discussed in terms of conductance switching of acceptor material via electroreduction. (C) 2003 Elsevier B.V. All rights reserved.