Polymer Based Nanostructured Donor-Acceptor Heterojunction Photovoltaic Devices

Bulk heterojunction photovoltaic devices based on blends of conjugated polymers and fullerenes have achieved efficiencies of 3.5% under AM1.5 illumination. This is a result of efficient exciton dissociation at donor--acceptor interfaces. However, the intimate blending of the electron and hole transporting species leads to detrimental charge carrier recombination in the bulk of these devices. Weare investigating a solution to this problem by fabricating nanostructured oxide--conjugated polymer composite structures. Porous SnO2 films with pore diameters of~100 nm have been fabricated. Intercalation of polymers into the pores by adsorption from solution yielded structures with approximately 75% of the free volume filled with polymer. The resulting composite structures are promisingcandidates for developing polymer-based solar cells with short carrier-to-electrode path lengths while retaining high optical absorption, thus leading to increased efficiencies. Additionally, a carboxylic acid fullerene derivative was shown to bind to the SnO2 surface, a necessary step in creating a nanostructured electron-accepting surface.