Speaker
Sheridan Few
Description
Recently, much attention has been paid to the formation of charge transfer (CT) states at the donor : acceptor interface in organic photovoltaic materials, and to their role in charge pair generation.1 However, until now few theoretical studies have addressed the electronic properties of CT states in detail. In this work, we use density functional theory (DFT) methods to study the energies and properties of CT states of a complex consisting of an oligomer of a donor polymer (poly-3-hexyl-thiophene (P3HT), Poly((9,9-dioctylfluorenyl-2,7-diyl)-alt-5,5-(40,70-di-2-thienyl-20,10,30-benzothiadiazole)) (PFODTBT), and the thiophene-isoindigo based polymer, P3TI) and an acceptor molecule (fullerene derivatives phenyl C61 butyric acid methyl ester (PCBM), phenyl C71 butyric acid methyl ester (PC71BM), and bis-indenofullerene ICBA). The effects of position, relative orientation, and specific chemical structure of the molecules on charge distribution, absorption and emission spectra, and overlap of electronic states between the molecules are studied. Results are analysed in comparison with electroluminescence data on polymer:fullerene blends containing different fullerene derivatives. We discuss how studies on this model system help to elucidate the role of charge transfer states in charge generation and so help develop design rules for better photovoltaic materials.
