A planar fused-ring electron acceptor (IC-C6IDT-IC) based on indacenodithiophene is designed and synthesized. IC-C6IDT-IC shows strong absorption in 500–800 nm with extinction coefficient of up to 2.4 × 10<sup>5sup> M<sup>–1sup> cm<sup>–1sup> and high electron mobility of 1.1 × 10<sup>–3sup> cm<sup>2sup> V<sup>–1sup> s<sup>–1sup>. The as-cast polymer solar cells based on IC-C6IDT-IC without additional treatments exhibit power conversion efficiencies of up to 8.71%.