Bis(pyrrolidino)[60]fullerenes: promising photostable fullerene-based acceptors suppressing light-induced absorber degradation pathways

Two novel highly soluble bis(pyrrolidino)[60]fullerenes were synthesized and investigated as promising electron acceptor materials for organic solar cells. Reduced electron affinity of bis(pyrrolidino)[60]fullerenes as compared to the reference [60]PCBM enabled a spectacular increase in open-circuit voltage of organic bulk heterojunction solar cells by ~200 mV while using model P3HT and PCDTBT electron donor polymers. In addition to the improved optoelectronic properties, bis(pyrrolidino)[60]fullerenes were found to be resistant towards the photochemical cross-linking in contrast to conventional [60]PCBM and conjugated polymers. Most importantly, the designed fullerene derivatives efficiently suppressed photooxidation of conjugated polymers as revealed by ESR spectroscopy, which features a tremendous potential of applying these materials in the development of efficient and durable organic photovoltaics.