Biindene-C60 adducts for the application as acceptor in polymer solar cells with higher open-circuit-voltage

Two C60 derivatives, biindene-C60 monoadduct (BC60MA) and biindene-C60 bisadduct (BC60BA), were synthesized by an one-pot reaction of 1, 1′-biindene and C60, for the application as acceptor materials in Polymer Solar Cells (PSCs). The two C60 derivatives possess good solubility in toluene and o-dichlorobenzene, and the solubility of BC60BA is even better than that of BC60MA. The electrochemical properties and the LUMO energy levels of the two fullerene derivatives were investigated by cyclic voltammetry. The LUMO energy levels of BC60MA and BC60BA were 0.06 and 0.17 eV higher (up-shifted) than that of PCBM, respectively. The PSCs based on P3HT as donor and BC60MA or BC60BA as acceptor exhibited higher Voc of 0.68 and 0.82 V, respectively, which is benefited from the higher LUMO energy levels of the C60 derivatives. The power conversion efficiency of the PSC based on P3HT/BC60MA was 2.21% after annealing at 140 °C for 5 min.