Dithienobenzothiadiazole-Bridged Nonfullerene Electron Acceptors for Efficient Organic Solar Cells

Advances of small-molecular acceptors (SMAs) recently have motivated the development of high-performance organic solar cells (OSCs). The SMAs featuring A–D–C–D–A framework have attracted numerous attention due to their facile tunability on chemical structures and in commercial synthesis. In this work, dithienobenzothiadiazol (DTBT) was utilized as the center (C) unit of A–D–C–D–A SMAs and three corresponding SMAs named DTBCIC-Cl, DTBCIC-F, and DTBCIC-H were synthesized by altering the terminal groups. The variation of terminal groups endowed SMAs with different performances, including optical absorbance, energy levels, and molecular packing, etc. In comparison to DTBCIC-H, DTBCIC-Cl and DTBCIC-F obtained by halogenation showed red-shift absorption, well matched energy levels with the polymer donor PM6, as well as closer molecular packing, rendering the blend films based on PM6:DTBCIC-Cl and PM6:DTBCIC-F wide absorption and improved morphology. High power conversion efficiency of 12.71% was thus obtained for OSCs based on DTBCIC-Cl. The results prove that optimization of SMAs via altering terminal groups provides a promising design strategy to obtain high-performance A–D–C–D–A SMAs.