New benzodithiophene fused electron acceptors for benzodithiophene-based polymer

We designed and synthesised two fused electron acceptors based on 6,6,12,12-tetrakis (3-hexylphenyl)-indacenobis (benzodithiophene) with two-dimensional alkylthiophene or alkylthiothiophene substituents, named ETBDTIC and ESTBDTIC, respectively. ESTBDTIC exhibited red-shift absorption and deeper the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels compared with ETBDTIC. The ESTBDTIC based device exhibited slightly lower open-circuit voltage (Voc) because of its deeper LUMO level that originated from the electron-withdrawing thioalkyl group, while short-circuit current density (Jsc) and fill factor (FF) of ESTBDTIC were much higher than the Jsc and FF of ETBDTIC. The ETBDTIC -based device displayed power conversion efficiency (PCE) of 5.11% with a Voc of 0.96 V, Jsc of 11.24 mA/cm2, and FF of 47.30%; the corresponding values of ESTBDTIC -based device were 7.78%, 0.92 V, 13.92 mA/cm2, and 60.50%. The electronic properties, charge transport, crystallinity, film morphology, and surface energy, and photovoltaic characteristics were studied.