Synthesis and photovoltaic properties of biindene-C70 monoadduct as acceptor in polymer solar cells

A new fullerene derivative, biindene-C70 monoadduct (BC70MA), was synthesized by [4+2] cycloaddition reaction between 1,1′-biindene and C70, for the application as acceptor in polymer solar cells (PSCs). BC70MA is soluble in common organic solvents such as tetrahydrofuran, chloroform, toluene, o-dichlorobenzene, etc., and shows stronger absorption in the visible region and a slightly up-shifted lowest unoccupied molecular orbital (LUMO) energy level than that of PCBM. PSCs were fabricated with BC70MA as acceptor and poly(3-hexylthiophene) (P3HT) as donor for investigating the photovoltaic properties of BC70MA. The power conversion efficiency of the PSC based on P3HT/BC70MA (1:1, w/w) with the additive of 3% octane-1,8-dithiol and thermal annealing at 110 °C for 10 min reached 3.44% with open circuit voltage of 0.64 V, short circuit current of 8.02 mA/cm2 and fill-factor of 0.67, under the illumination of AM1.5, 100 mW/cm2.