Rational Terminal Engineering Enabled Vulnerable Exocyclic-Vinyl-Free Nonfullerene Acceptors for Sensitive and Durable Near-Infrared Organic Photodetectors

The advancement of acceptor-donor-acceptor (A-D-A)-type nonfullerene acceptors (NFAs) has significantly enhanced the near-infrared organic photodetector (NIR OPD) performance. However, structural instability arising from vulnerable exocyclic vinyl bridges between donor (D) and acceptor (A) units remains a critical challenge for both material and device durability. Herein, we break this bottleneck through a pioneering terminal engineering strategy and present the judicious design and synthesis of novel electron-withdrawing 2-(2-bromo-3-cyano-8<i>H</i>-indeno[2,1-<i>b</i>]thiophen-8-ylidene)malononitrile (ITC2H) toward exocyclic-vinyl-free NFAs. Compared with the classical NFA (BTP-IC2H), the ITC2H-flanked derivative BTP-ITC2H exhibits not only enhanced chemical/photostability but also improved crystallinity, broadened and red-shifted absorption spectrum, optimized miscibility with polymer donor, and reduced reorganization energy. These synergistic advantages yield an optimized nanomorphology with suppressed trap states and favorable charge transport dynamics. The resulting self-powered OPD achieves a dark current density (<i>J</i>_d) of 3.3 × 10^-11 A cm^-2 and noise-limited specific detectivity (<i>D</i>*_sh) surpassing 10¹³ Jones across 310-910 nm, coupled with a linear dynamic range (LDR) of 141 dB and superior thermal stability. The generality of this design paradigm is demonstrated by extending ITC2H to its halogenated analogues, enabling response extension to 1300 nm with a <i>J</i>_d of 3.87 × 10^-11 A cm^-2 and <i>D</i>*_sh approaching 10¹³ Jones even at 1200 nm, underscoring their versatility for diverse applications. The molecular engineering paradigm in this work provides critical insights into structure-stability-performance relationships, advancing the development of robust and efficient organic optoelectronics for practical implementation.