Dual electron donor/electron acceptor character of a conjugated polymer in efficient photovoltaic diodes

The authors report efficient photovoltaic diodes which use poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(3-hexylthien-5-yl)-2,1,3-benzothiadiazole]-2('),2(')-diyl) (F8TBT) both as electron acceptor, in blends with poly(3-hexylthiophene), and as hole acceptor, in blends with (6,6)-phenyl C-61-butyric acid methyl ester. In both cases external quantum efficiencies of over 25% are achieved, with a power conversion efficiency of 1.8% under simulated sunlight for optimized F8TBT/poly(3-hexylthiophene) devices. The ambipolar nature of F8TBT is also demonstrated by the operation of light-emitting F8TBT transistors. The equivalent p- and n-type operation in this conjugated polymer represent an important extension of the range of useful n-type materials which may be developed. (C) 2007 American Institute of Physics.