Molecular Engineering of Olefin-Bridged Fully Non-Fused Ring Electron Acceptors for Enhanced Near-Infrared Absorption and Mobility

Fully nonfused ring electron acceptors (NFREAs) have attracted growing attention as cost-effective alternatives to fused-ring electron acceptors (FREAs) in organic solar cells (OSCs). However, their molecular frameworks, linked entirely by single bonds, typically result in wider bandgaps, limited near-infrared (NIR) absorption, and poor electron mobility, leading to inferior performance compared to FREAs. In this work, we propose a molecular engineering strategy to design olefin-bridged NFREAs (OB-NFREAs) by introducing olefin bridges into the fully nonfused backbone of TBT-26. Theoretical calculations indicate that all OB-NFREAs, namely D-O1, D-O2, and D-O3, demonstrate a significant enhancement in optoelectronic performance. The olefin double bonds extend π-conjugation, reduce the bandgap, and improve molecular planarity. Consequently, the absorption edge of the absorption range of OB-NFREAs expands from 300 to 900 nm (TBT-26) to 300-1200 nm (D-O3), with a significant redshift of the absorption peak to 895 nm and 1.8-fold increase in integrated absorption intensity. Moreover, electron mobility is substantially enhanced, with D-O1 reaching 1.14 × 10^-3 cm² V^-1 s^-1, which is more than an order of magnitude higher than that of TBT-26. These results indicate that rational olefin bridge design can enhance π-π stacking, facilitate more efficient charge transfer, improve electron mobility, and redshift the absorption spectrum. Fine-tuning olefin bridges is thus a powerful strategy for constructing NFREAs with high mobility and strong NIR absorption, paving the way for next-generation organic photovoltaic materials.