Near-Infrared Small Molecule Acceptor Enabled High-Performance Nonfullerene Polymer Solar Cells with Over 13% Efficiency

One of the most promising approaches to achieve high-performance polymer solar cells (PSCs) is to develop nonfullerene small molecule acceptors (SMAs) with an absorption extending to the near-infrared (NIR) region. In this work, two novel SMAs, namely, BTTIC and BTOIC, are designed and synthesized, with optical bandgaps (E-g(opt)) of 1.47 and 1.39 eV, respectively. Desipte the narrow E-g(opt), the PBDB-T:BTTIC- and PBDB-T:BTOIC-based PSCs can maintain high V(OC)s of over 0.90 and 0.86 V, respectively, with low energy losses (E-loss) < 0.6 eV. Meanwhile, due to the favorable morphology of the PBDB-T:BTTIC blend, balanced carrier mobilities are achieved. The high external quantum efficiencies enable a high power conversion efficiency (PCE) up to 13.18% for the PBDB-T:BTTIC-based PSCs. In comparison, BTOIC shows an excessive crystallization propensity owing to its oxyalkyl side groups, which eventually leads to a relatively low PCE for the PBDB-T:BTOIC-based PSCs. Overall, this work provides insights into the design of novel NIR-absorbing SMAs for nonfullerene PSCs.