Photovoltaic Charge Generation Visualized at the Nanoscale:  A Proof of Principle

We report for the first time a nanoscale resolved proof of principle of the photovoltaic activity in phase-segregated electron acceptor−donor blend architectures as obtained by Kelvin probe force microscopy. The explored length scale is truly important for organic solar cells since it is comparable to the mean exciton diffusion length. We chose a blend of regioregular poly(3-hexylthiophene) (P3HT) and N,N‘-bis(1-ethylpropyl)-3,4:9,10-perylenebis(dicarboximide) (PDI) as model systems, acting as electron donor and electron acceptor, respectively. In this work, we demonstrate that the same type of molecular assemblies, obtained from a given electron-accepting material on the same sample, shows different surface potential changes upon white-light illumination when in physical contact with the donor materials or isolated from it. Although excitons are generated by light absorption in all the PDI clusters, we unambiguously proved that only the ones which are in physical contact with P3HT exhibit an appreciable charge transfer because of the existence of a complementary electron donor phase. Such a direct observation is novel and of general applicability and can also be extended to other bicomponent materials for plastic photovoltaics.