gamma-Ester-Functionalized 1,1-Dicyanomethylene-3-indanone End-Capped Nonfullerene Acceptors for High-Performance, Annealing-Free Organic Solar Cells

Abstract

Modifying the end-capping groups in nonfullerene acceptors (NFAs) is an effective strategy for modulating their properties and that of the entire NFAs. This study reports the synthesis of a novel gamma-ester-functionalized IC end-capping group (IC-gamma e) and its incorporation into the benzothiadiazole-fused central core, yielding isomer-free IC-gamma e end-capped NFAs, such as Y-IC-gamma e, Y-FIC-gamma e, and Y-ClIC-gamma e. The resultant NFAs exhibited similar absorption profiles but upshifted the lowest unoccupied molecular orbital energy level compared with those of the ester-free analogues, such as Y6 and Y7. Without thermal annealing, an excellent power conversion efficiency (PCE) of 16.4% is realized in the annealing-free OSC based on Y-FIC-gamma e with the PM6 donor polymer, which outperforms the OSCs based on Y-IC-gamma e and Y-ClIC-gamma e. In addition, the OSCs based on asymmetric Y-FIC-gamma e and Y-ClIC-gamma e have higher thermal stability with more than 83% PCE retention at an elevated temperature after 456 h than the symmetric Y-IC-gamma e case. In this study, we not only establish the structure-property relationship regarding the ester functionality and symmetricity tuning on the NFAs but also diagnose the reasons for the best-performing Y-FIC-gamma e-based OSCs, providing useful information for a novel high-performing NFA design strategy.