Magnetic Studies of Photovoltaic Processes in Organic Solar Cells

In this paper, we use magnetic field effects of photocurrent (MFEPC) to study the photovoltaic processes in pristine conjugated polymer, bulk heterojunction, and double-layer solar cells, respectively, based on poly(3-alkylthiophene) (P3HT). The MFEPCreveals that the photocurrent generation undergoes the dissociation in polaron pair states and the charge reaction in excitonic states in pristine conjugated polymers. As for the bulk-heterojunction solar cells consisting of electron donor P3HT and electron acceptor [6,6]-phenyl C61-butyric acid methyl ester (PCBM), the MFEPCindicates that the dissociated electrons and holes inevitably form the intermolecular charge-transfer (CT) complexes at donor and acceptor interfaces. Essentially, the photocurrent generation relies on the further dissociation of intermolecular CT complexes. Moreover, we use double-layer solar cell to further study the intermolecular CT complexes with well-controlled donor-acceptor interfaces based on double-layer P3HT/TiOxdesign. We find that the increase in free energies can significantly reduce the density of CT complexes upon thermal annealing.