Side-chain Engineering for Efficient Non-fullerene Polymer Solar Cells Based on Wide-bandgap Polymer Donor
In this work, a new wide bandgap polymer of PSBZ based on thienyl substituted benzodithiophene (BDTT) as donor unit and difluorobenzotriazole (BTz-2F) as acceptor unit was synthesized for photovoltaic applications. Compared to the analogous polymer J61 with linear dodecylthio side chains in BDTT unit and long-sized 2-hexyldecyl side chain in BTz-2F, PSBZ possesses branched 2-butyloctyl side chains to increase steric hindrance of BDTT unit and short-sized 2-butyloctyl side chain to decrease steric hindrance of BTz-2F unit for more efficient charge separation and transport in the devices. As a result, PSBZ exhibited stronger π-π interaction and smaller stacking spacing leading to a higher extinction coefficient of 1.48 × 105 cm-1 and a high hole mobility of 8.56 × 10-3 cm2/Vs. Compared to the analogous polymer J61 with a power conversion efficiency (PCE) of 9.53% and a short-circuit current density (Jsc) of 17.43 mA cm-2, the PSBZ:ITIC-based polymer solar cells yielded a higher PCE of 10.5% with a higher Jsc of 19.0 mA cm-2. The results show that our design strategy is successful for improving photovoltaic performance by the side chain engineering.