Quinoidal Nitrogen-Bridged Terthiophene Acceptors Enabling Broadband Spectral Response Reaching 1.4 µm in SWIR Organic Photodetectors

Organic photodetectors (OPDs) capable of detecting short-wavelength infrared (SWIR) radiation beyond the silicon cutoff (≈1.1 µm) have attracted significant attention due to their potential applications, such as machine vision, remote sensing, medical imaging, artificial intelligence, etc. However, designing organic materials with high sensitivity in the SWIR range remains challenging. Here, a new series of ultra-narrow bandgap small molecular acceptors, 5MTT-F, 5MCN-F, and 5MCN-Cl, based on a nitrogen-bridged terthiophene core, designed to promote planarity, π-delocalization, and quinoidal characteristics, is reported. Systematic modulation of π-bridges and terminal groups enable precise tuning of energy levels and absorption profiles, extending the photoresponse up to ≈1400 nm with optical bandgaps as low as 0.85 eV. OPDs fabricated with these acceptors and the donor polymer PCE10-0F exhibit excellent performance, with 5MTT-F device achieving a responsivity of 0.12 A·W⁻¹ and a specific detectivity of 1.69 × 10¹² Jones at 1.1 µm. Notably, 5MCN-based OPDs demonstrate broadband SWIR detection with detectivities of 8.98 × 10¹⁰ Jones up to 1.3 µm. This work presents a viable molecular design strategy for achieving efficient SWIR OPDs and deepening the understanding of structure–property–performance relationships in organic semiconductors for broadband infrared detection.