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VOLUME 62 (1995) | ISSUE 5 | PAGE 407
Photovoltaic effect in asymmetrical donor-acceptor organic superlattices
We predict a novel photovoltaic mechanism in donor-acceptor super-lattices. We consider an asymmetrical organic superlattice such as... D-A-N-D-A-N-D-A-N..., where D, A and N indicate layers of materials which are, respectively, donor, acceptor and neither donor nor acceptor, all neutral in the ground state. In such a structure, the lowest-lying electronic excitations are charge-transfer excitons (CTEs) at the D-A interfaces, with electrons displaced from the donor to the acceptor side. We show that the excitation of CTEs under illumination is accompanied by the appearance of a macroscopic voltage drop along the growth direction. The resulting average electric field can separate and drive the photogenerated free carriers (partly coming from the ionization of the CTEs themselves), producing a photovoltaic current.