Tuning Acceptor Properties via O/S Heteroatom Bridging in Extended-Conjugation Central Cores toward Efficient Organic Solar Cells

Abstract

The substituent units on acceptors with extended-conjugation central cores play a crucial role in enhancing the device efficiency of organic solar cells (OSCs). The subtle variation of substituent units can result in obvious alteration in efficiency, which demonstrates that it is necessary to reveal the intrinsic correlation between molecular structure and device performance. In this work, by altering bridging atoms (O vs S) between central core and peripheral substituent units, we designed and synthesized two acceptors, namely CHE-O and CHE-S. Theoretical calculations and experimental results demonstrate that such minor change in chemical structure significantly affects molecular packing behavior and blend morphology, ultimately leading to obvious alteration in efficiency. Among them, CHE-O with O bridge exhibits superior packing behavior and more favorable phase separation morphology, thus achieving 19.30% efficiency in PM6: CHE-O-based device in comparison with 16.89% of PM6: CHE-S system. This study demonstrates that fine-tuning substituent units on the central core can effectively regulate photovoltaic properties, which is important for designing acceptor materials.