Synergistic Effects of Chlorination and Branched Alkyl Side Chain on the Photovoltaic Properties of Simple Nonfullerene Acceptors with Quinoxaline as the Core.

To date, the fused-ring electron acceptors show the best photovoltaic performances, and the development of simple nonfullerene acceptors via intramolecular noncovalent interactions can reduce synthetic costs. In this work, four simple nonfullerene acceptors with an A-D-A'-D-A configuration, QCIC1, QCIC2, QCIC3, and QCIC4, are synthesized. They own the same conjugated backbone (A': quinoxaline; D: cyclopentadithiophene; A: dicyano-indanone) but different halogen atoms and alkyl side chains. Due to the chlorination on the end-groups and the most and/or longest branched alkyl side chains on the backbone, the blended film composed of QCIC3 and donor PBDB-T exhibits the strongest π-π stacking and the most suitable phase-separation domains among the four blended films. Therefore, the QCIC3 based organic solar cells yield the highest power conversion efficiency of 10.55%. This work provides a pathway to optimize the molecular arrangements and enhance the photovoltaic property of simple electron acceptors through subtle chemical modifications.