Design narrow band gap small-molecule acceptors with unilateral vinylene π-bridge for high-performance optoelectronic devices

Abstract

Narrow band gap (NBG) small-molecule acceptors (SMAs) are crucial for enhancing the performance of organic solar cells (OSCs) and near-infrared organic photodetectors (NIR OPDs). Two novel SMAs, namely BTP-1V-4F and BTP-1V-4Cl, were developed via a synergistic strategy combining unilateral vinylene π-bridge introduction and terminal halogen atom modulation. The unilateral vinylene π-bridge not only effectively extends the intramolecular conjugated electron cloud distribution, promoting a narrowed bandgap and a redshifted absorption, but also synergistically suppresses molecular disorder in conjunction with the terminal halogen atoms, thereby optimizing the orderly packing. The results revealed that although BTP-1V-4Cl possesses a narrower bandgap and stronger crystallinity, BTP-1V-4F exhibits better compatibility with the donor material and achieves a more ordered and well-proportioned crystalline morphology in the blends. Consequently, BTP-1V-4F devices deliver superior performance. The NBG OSCs achieved a power conversion efficiency (PCE) of 14.2% with the open-circuit voltage of 0.8 V. Meanwhile, the NIR OPDs exhibited a remarkable specific detectivity (D * ) of 3.85×10 13 Jones with an ultralow dark current density (JD) of 5.22×10 -10 A cm -2 and a responsivity of 0.497 A W -1 at 870 nm and -1 V bias. This work demonstrates the promise of the BTP-1V-4X series for semi-transparent cells, tandem cells, and photodetectors.