Ultra-Sensitive Short-Wave Infrared Organic Photodetectors Enabled by a π-Conjugation Extended Proquinoid Electron Acceptor

Short-wavelength infrared (SWIR) light detection technologies have attracted considerable attention due to their broad applications in bioimaging, sensing, and optical communication. Despite this promise, achieving high-performance organic SWIR photodetectors (SWIR OPDs) remains a major challenge due to intrinsically weak photoresponse and sensitivity in this spectral region. Herein, a novel proquinoid-type non-fullerene acceptor (NFA), denoted as TQC-4Cl is reported, which exhibits an ultra-narrow band gap of 1.01 eV and a broad spectral response extending beyond 1200 nm, enabled via an aromatic-quinoid transformation strategy. Thermal annealing of the TQC-4Cl film significantly enhanced crystallinity and molecular ordering. Consequently, the optimized TQC-4Cl-based SWIR OPDs exhibit an exceptionally low dark current density (J_d) of 4.38 × 10⁻⁸ A cm⁻²_, noise current of 466 fA (at 4 Hz), and a high external quantum efficiency (EQE) of 13.66% at 1200 nm at −0.5 V bias, resulting in a shot-noise limited specific detectivity (D_sh*) of 1.06 × 10¹² Jones and a noise current-based specific detectivity (D_n*) of 2.84 × 10¹¹ Jones under the same bias conditions. The ideal phase-separated morphology and high crystallinity of the photoactive layer provide the beneficial condition enabling efficient charge extraction, suppressed bimolecular recombination, and reduced energetic disorder. Furthermore, the devices demonstrated long-term operational stability at 85 °C, underscoring their superior thermal durability. This study not only marks the advancement toward the realization of highly sensitive and thermally robust SWIR OPDs but also contributes to the rational molecular design strategies for ultra-narrow bandgap organic semiconductors for next-generation optoelectronic devices.