Investigation of pentaarylazafullerenes as acceptor systems for bulk-heterojunction organic solar cells

In a comparative study a novel class of pentaarylazafullerene derivatives is investigated as acceptor material in solution-processed organic solar cells. Due to their raised lowest unoccupied molecular orbital (LUMO) compared to phenyl-C61-butyric acid methyl ester (PC61BM) the orbital matching to P3HT is optimized so that an increased open-circuit voltage (VOC) compared to the standard PC61BM acceptor is gained. However, the performance of pentaarylazafullerene solar cells is limited by rather low short circuit currents (JSC) and fill factors (FF) which can be partially improved by using 1-methylnaphtalene as additive. Within this series the azafullerenes with phenoxyphenyl and phenoxymethyl addends 1 and 3 show the best results with encouraging VOCs of >800 mV and power conversion efficiencies (PCEs) of 0.9%.