Asymmetric Alkoxy and Alkyl Substitution on Nonfullerene Acceptors Enabling High‐Performance Organic Solar Cells

Abstract

In this paper, a strategy of asymmetric alkyl and alkoxy substitution is applied to state-of-the-art Y-series nonfullerene acceptors (NFAs), and it achieves great performance in organic solar cell (OSC) devices. Since alkoxy groups can have a significant influence on the material properties of NFAs, alkoxy substitution is applied to the Y6 molecule in a symmetric manner. The resulting molecule (named Y6-2O), despite showing improved open-circuit voltage (Voc), yields extremely poor performance due to low solubility and excessive aggregation properties, a change that is due to the conformational locking effect of alkoxy groups. In contrast, asymmetric alkyl and alkoxy substitution on Y6, yields a molecule named Y6-1O that can maintain the positive effect of Voc improvement and obtain reasonably good solubility. The resulting molecule Y6-1O enables highly efficient nonfullerene OSCs with 17.6% efficiency and the asymmetric side-chain strategy has the potential to be applied to other NFA-material systems to further improve their performance.