Synergistic Effects of Polymer Donor Backbone Fluorination and Nitrogenation Translate into Efficient Non-Fullerene Bulk-Heterojunction Polymer Solar Cells

State-of-the-art non-fullerene bulk-heterojunction (BHJ) polymer solar cells outperform the more extensively studied polymer–fullerene BHJ solar cells in terms of efficiency, thermal- and photo-stability. Considering the strong light absorption in near infrared region (600–1000 nm) for most of efficient acceptors, the exploration of high-performing large bandgap (LBG) polymer donors with complementary optical absorption ranging from 400 nm to 700 nm remains critical. In this work, the strategy of concurrently incorporating fluorine (–F) and unsaturated nitrogen (–N) substituents along the polymer backbones is used to develop LBG polymer donor PB[N][F]. Results show that the F– and N–substituted polymer donor PB[N][F] realizes up to 14.4% efficiency in BHJ photovoltaic devices when paired with a benchmark molecule acceptor Y6, which largely outperforms the analogues PB with efficiency of only 3.6% and PB[N] with efficiency of 11.8%. Systematic examinations show that synergistic effects of polymer backbone ...