Push–Pull Type Non-Fullerene Acceptors for Polymer Solar Cells: Effect of the Donor Core

There has been a growing interest in the design and synthesis of non-fullerene acceptors for organic solar cells that may overcome the drawbacks of the traditional fullerene-based acceptors. Herein, two novel push-pull (acceptor-donor-acceptor) type small-molecule acceptors, that is, ITDI and CDTDI, with indenothiophene and cyclopentadithiophene as the core units and 2-(3-oxo-2,3-dihydroinden-1-ylidene)malononitrile (INCN) as the end-capping units, are designed and synthesized for non-fullerene polymer solar cells (PSCs). After device optimization, PSCs based on ITDI exhibit good device performance with a power conversion efficiency (PCE) as high as 8.00%, outperforming the CDTDI-based counterparts fabricated under identical condition (2.75% PCE). We further discuss the performance of these non-fullerene PSCs by correlating the energy level and carrier mobility with the core of non-fullerene acceptors. These results demonstrate that indenothiophene is a promising electron-donating core for high-performance non-fullerene small-molecule acceptors.