Peculiarities of the photovoltaic properties of films based on photoconducting polymer and organic dye in samples with free surfaces and between electric contacts

Composite films based on a carbazolyl-containing oligomer with polymethine dye additives exhibit a change in the magnitude and sign of the photovoltaic response on the passage from the samples with free surfaces to sandwich structures. It is concluded that the photovoltaic effect in the former case is determined by the diffusion of positive charge carriers possessing higher mobility, while in the latter case this effect is controlled by a significant drift of carriers in the electric field created by different work functions of the charge-collecting electrodes. It is shown that the photovoltaic effect also takes place in a nonphotoconducting polymer (polyvinyl ethylal). However, neither the sign nor magnitude of the effect in this case change on the passage from the samples with free surfaces to sandwich structures.