Fullerene derivative acceptors for high performance polymer solar cells

Polymer solar cells (PSCs) are composed of a blend film of a conjugated polymer donor and a soluble fullerene derivative acceptor sandwiched between a PEDOT:PSS coated ITO positive electrode and a low work function metal negative electrode. The conjugated polymer donor and the fullerene derivative acceptor are the key photovoltaic materials for high performance PSCs. For the acceptors, although [6,6]-phenyl-C-61-butyric acid methyl ester (PC60BM) and its corresponding C-70 derivative PC70BM are dominantly used as the acceptors in PSC at present, several series of new fullerene derivatives with higher-lying LUMO energy level and better solubility were reported in recent years for further improving the power conversion efficiency of the PSCs. In this perspective paper, we reviewed the recent research progress on the new fullerene derivative acceptors, including various PC60BM-like C-60 derivatives, PC60BM bisadduct, PC70BM bisadduct, indene-C-60 bisadduct and indene-C-70 bisadduct, trimetallic nitride endohedral fullerenes and other C-60 derivatives with multi side chains. The synthesis and physicochemical properties of PC60BM and PC70BM were also introduced considering the importance of the two fullerene acceptors.