Side-chain engineering could tune the crystallinity, solubility and aggregation styles of fused-ring electron acceptors (FREAs), and thus could influence the morphology and charge carrier mobility of blend films as well as the final device performances. Herein, we developed a novel FREA called spiro-IDT-O-IC, which is composed of a spiro-bridged IDT core and two 1,1-dicyanomethylene-3-indanone (IC) terminal units. Similar acceptor molecule IDT-O-IC with four 4-octyloxyphenyl side chains is also prepared for the control experiment. The absorptions, energy levels, molecular configurations, and electronic wave functions of these two acceptor molecules have been comparatively studied. Polymer solar cells (PSCs) fabricated with PBDB-T:spiro-IDT-O-IC as the active layer demonstrated a PCE of 6.23% with a J_sc of 11.76 mA/cm², a V_oc of 0.84 V and an FF of 0.63. To the best of our knowledge, this is the first report that a spiro-bridged ladder type core was used for the fabrication of fused ring acceptors.