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Charge and energy transfer are competing processes in photoexcited organic donor/acceptor systems. By inserting a thin interlayer of a wide band gap organic semiconductor in a poly(3-hexylthiophene)/fullerene heterojunction, we were able to selectively suppress electron transfer. External quantum efficiency measurements show that device performance is unaffected by the presence of the interlayer. These results can be explained by two-step exciton dissociation where energy transfer of excitons from the donor to the acceptor is followed by hole transfer to the donor. The same interlayer was shown to decrease the photocurrent in a heterojunction where this energy transfer pathway is forbidden.