Isomers of IC70BA and Their Photovoltaic Performance in Polymer Solar Cells.

Indene-C70 derivatives were synthesized, including indene-C70 mono-adduct (IC70MA), indene-C70 bis-adduct (IC70BA) and indene-C70 tris-adduct (IC70TA). All as-prepared fullerene adducts are in fact a mixture of isomers. The IC70BA mixture was further separated by high-performance liquid chromatography (HPLC) and two different IC70BA isomers were obtained. With the addition of the increased number of indene, the lowest unoccupied molecular orbital (LUMO) energy level of the C70 derivatives is also increased. IC70BA and its isomers have a slight difference in LUMO energy level, but show great differences in the absorption spectra. Polymer solar cells (PSCs) devices were fabricated under the same conditions with P3HT as donor, IC70BA and its isomer as acceptor, to examine the influence of the regioisomers on photovoltaic performance. The two IC70BA isomers exhibited varying power conversion efficiency (PCE) values of 2.80 and 3.18%, respectively, suggesting the molecular structure of the fullerene derivatives have an effect on polymer solar cells properties.