The present disclosure is directed to an optimized structure for an exciton-based photovoltaic cell, in which the bulk heterojunction between the electron donor (typically an organic polymeric semiconductor) and an electron acceptor (e.g., silicon or titanium or titania) minimizes the necessary exciton travel distance to the heterojunction in three dimensions. The configuration is arrayed in three dimensions, such that one member of the heterojunction pair, such as the electron acceptor is in the form of a number of nanoscale channels, extending to an electrode. The channels extend through a photovoltaic matrix material in a predetermined three-dimensional configuration.