In our systems case the potential of the non-illuminated (dark) surface becomes positive with respect to illuminated surface, because positive charged current carriers have the larger mobility. The kinetics of the respective photovoltaic signal VPH(t) is similar to the VPH(t) relationships (Fig. ). The appearance of positive electric charges on the free surface of the investigated PPC films during their light irradiation therefore most likely due to diffusion of the photogenerated holes away from the irradiated ITO contact toward the free surface. This confirms the p-type photoconductivity character of investigated PPCs .