Origin of the open-circuit voltage in multilayer heterojunction organic solar cells

From temperature dependent studies of pentacene/C-60 solar cells in the dark, the reverse saturation current is found to be thermally activated with a barrier height that corresponds to the difference in energy between the highest occupied molecular orbital of the donor and the lowest unoccupied molecular orbital of the acceptor corrected for vacuum level misalignments and the presence of charge-transfer states. From the reverse saturation current in the dark and the short-circuit current under illumination, the open-circuit voltage can be predicted. Examination of several donor materials supports the relationship between reverse saturation current, this barrier height, and open-circuit voltage.