We have fabricated photodetectors based on electron-accepting and electron-donating organic materials. Multiple heterojunetions between the donor and acceptor layers were introduced. The thickness of the donor and acceptor materials was controlled in the molecular scale. By keeping the total thickness of the devices the same, we have studied the performance of the photodetectors as a function of the number of such molecular-level interfaces. The results showed that the number of donor-acceptor interfaces enhanced exciton dissociation but, at the same time, hindered charge transport by introducing energy barriers. We have shown that a trade-off between the two effects existed at an optimum number of donor acceptor interfaces, where the device showed better photodetector performance. (c) 2006 Elsevier B.V. All rights reserved.