Facile Modification of a Noncovalently Fused-Ring Electron Acceptor Enables Efficient Organic Solar Cells

Electron acceptors with nonfused aromatic cores (NCAs) have aroused increasing interest in organic solar cells due to the low synthetic complexity and flexible chemical modification, but the corresponding device performance still lags behind. Herein, we designed and synthesized two new quinoxaline-based NCAs, namely, QOC6-4H and QOC6-4Cl. Although both NCAs show good backbone coplanarity, QOC6-4Cl with chlorinated end groups exhibits higher extinction coefficient, enhanced crystallinity, and more compact pi-pi stacking, which is correlated with the stronger intermolecular interactions induced by chlorine atoms. Benefiting from the broader and stronger optical absorption, improved carrier mobilities, and suppressed charge recombination, a notable power conversion efficiency (PCE) of 12.32% with a distinctly higher short-current density (J(sc)) of 22.91 mA cm(-2) and a fill factor (FF) of 69.01% could be obtained for the PBDB-T:QOC6-4Cl-based device. The PCEs of PBDB-T:QOC6-4H were only lower than 8%, which could mainly be attributed to the unsymmetric charge transport. Our work proves that the chlorination of end groups is a facile and effective strategy to enhance the intermolecular interactions and thus the photovoltaic performance of NCAs, and a careful modulation of the intermolecular interactions plays a vital role in further developing both high-performance and low-cost organic photovoltaic materials.

Automated summary

The study introduces two new quinoxaline-based NCAs, QOC6-4H and QOC6-4Cl, with the latter showing improved optical absorption, carrier mobilities, and charge recombination suppression. The device based on PBDB-T:QOC6-4Cl achieved a notable power conversion efficiency and higher short-current density, demonstrating that chlorination of end groups is an effective strategy to enhance intermolecular interactions and photovoltaic performance of NCAs.