A Fused Ring Electron Acceptor with Decacyclic Core Enables over 13.5% Efficiency for Organic Solar Cells

Abstract Extending π‐conjugation of donor units in fused ring electron acceptors (FREAs) promises to reinforce intramolecular charge transfer for smaller bandgaps, and enhances intermolecular interactions for higher charge mobility. Despite these advantages, power conversion efficiencies (PCEs) of FREAs with a large planar donor core are still below 12%. Herein, a fused decacyclic donor unit, IDC, is developed, and the FREA, IDCIC, whose optical bandgap is 1.45 eV, is synthesized. The FTAZ:IDCIC‐based organic solar cell (OSC) with a binary additive, chloronaphthalene and 1,8‐diiodooctane (CN thus FTAZ:IDCIC‐based OSCs with 0.25% CN&DIO obtain moderate domain size and high domain purity simultaneously, achieving the least charge recombination for the highest J SC (21.98 mA cm −2 ) and fill factor (FF) (71.03%).