High‐Yield Synthesis and Electrochemical and Photovoltaic Properties of Indene‐C70 Bisadduct

[6, 6]‐Phenyl‐C61‐butyric acid methyl ester (PC60BM) is the widely used acceptor material in polymer solar cells (PSCs). Nevertheless, the low LUMO energy level and weak absorption in visible region are its two weak points. For enhancing the solar light harvest, the soluble C70 derivative PC70BM has been used as acceptor instead of PC60BM in high efficiency PSCs in recent years. But, the LUMO level of PC70BM is the same as that of PC60BM, which is too low for the PSCs based on the polymer donors with higher HOMO level, such as poly (3‐hexylthiophene) (P3HT). Here, a new soluble C70 derivative, indene‐C70 bisadduct (IC70BA), is synthesized with high yield of 58% by a one‐pot reaction of indene and C70 at 180 °C for 72 h. The electrochemical properties and electronic energy levels of the fullerene derivatives are measured by cyclic voltammetry. The LUMO energy level of IC70BA is 0.19 eV higher than that of PC70BM. The PSC based on P3HT with IC70BA as acceptor shows a higher Voc of 0.84 V and higher power conversion efficiency (PCE) of 5.64%, while the PSC based on P3HT/PC60BM and P3HT/PC70BM displays Voc of 0.59 V and 0.58 V, and PCE of 3.55% and 3.96%, respectively, under the illumination of AM1.5G, 100 mW cm−2. The results indicate that IC70BA is an excellent acceptor for the P3HT‐based PSCs and could be a promising new acceptor instead of PC70BM for the high performance PSCs based on narrow bandgap conjugated polymer donor.