Interface effects on the external quantum efficiency of organic bulk heterojunction photodetectors

We investigate the effects of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and LiF interfacial layers on the efficiency of organic bulk heterojunction photodetectors fabricated with blends of regioregular poly(3-hexylthiophene-2,5-diyl) as electron donor and {6}-1-[3-(methoxycarbonyl)propyl]-{5}-1-phenyl-[5,6]-C61 as electron acceptor. At high reverse bias voltage, we find that the efficiency of these devices is limited only by the rate of creating excitons in the organic layer. Upon correction for the optical loss at the interfacial layers, the internal quantum efficiency can approach 100% in this highly disordered network of donor-acceptor molecular heterojunctions.