Exciton diffusion is at the heart of operation of most organic optoelectronic devices, and is currently the most limiting factor to achieve high efficiency. It is deeply related to molecular organization, as it depends on inter-molecular distances and orbital overlap. However, there is no clear guideline on how to improve exciton diffusion regarding molecular design and structure. Here we use single-crystal charge-transfer interfaces to probe favorable exciton diffusion. Photoresponse measurements on interfaces between perylenediimides and rubrene show higher photocurrent yield (+50%) and extended spectral coverage (+100 nm) when exists an increased dimensionality of the percolation network and stronger orbital overlap. This is achieved by very short inter-stack distances in different directional axes, which favors exciton diffusion by a Dexter mechanism. Even if the core of the molecule shows strong deviation from planarity, the similar electrical resistance of the different systems, planar and non-planar, shows that electronic transport is not compromised. These results highlight the impact of molecular organization in device performance, and the necessity of optimizing it to take full advantage of the materials properties.