Fine-tuning blend morphology via alkylthio side chain engineering towards high performance non-fullerene polymer solar cells

Two medium bandgap polymers (ffQx-TS1, ffQx-TS2) were designed and synthesized to investigate the influence of different alkylthio side chain on the morphology and photovoltaic performance of non-fullerene polymer solar cells (PSCs). Both polymers exhibit similar molecular weights and comparable the highest occupied molecular orbital (HOMO) energy level. However, the polymer with straight alkylthio chain delivers a root-mean-square (RMS) of 0.86 nm, which is slightly lower than that with branched chain (1.40 nm). The lower RMS benefits the ohmic contact between the active lay and interface layer, thus enhanced short circuit current (J(sc)) (from 13.54 mA cm(-1) to 15.25 mA cm(-1)) could be obtained. Due to the enhancement of J(sc), better power conversion efficiency (PCE) of 7.69% for ffQx-TS2 could be realized. These results indicated that alkylthio side chain engineering is a promising method to improve photovoltaic performance. (C) 2018 Elsevier B.V. All rights reserved.