For bulk heterojunction (BHJ) organic photodetectors (OPDs), it was found that the direct contact between the deposited electrode and the photoactive organic layer leads to severe quenching of excitons. Improved device architectures hence involve the incorporation of charge transport layers, such as metal oxide layers, between electrodes and the active layer, allowing substantially higher internal efficiencies to be achieved. We show here that through appropriate surface modification of the underlying metal oxide layer, i.e. through hydrogen annealing, a novel light trapping scheme for the photoactive layer deposited on top of the metal oxide layer is developed. This is achieved via optimization of polymer morphology and chain alignment in OPD devices through the formation of an extended interfacial hydrogen bonding network acting as nucleation site for enhanced chain alignment within the bulk material.