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.