Mitigating the Trade-Off between Bandgap Narrowing and Trap-Limited Transport for Low-Noise Organic Short-Wave Infrared Photodetectors

Solution-processed organic photodetectors present a promising route to short-wave infrared detection; however, accessing the spectral region beyond 1200 nm requires sub-1.0 eV organic absorbers, typically achieved through strong intramolecular charge transfer, enhanced quinoidal character, and extended π-conjugation; whereas, conformational and energetic disorder in such narrow-bandgap systems can contribute to trap-mediated transport losses and elevated dark current.

This study introduces Fc2BS and Fc2BT, narrow-bandgap nonfullerene acceptors differing solely in the π-bridge unit (benzoselenadiazole vs benzothiadiazole), to examine how chalcogen substitution influences bandgap narrowing and trap-related transport in sub-1.0 eV organic absorbers. Fc2BS achieves an optical bandgap of 0.98 eV with absorption extending to 1263 nm, where benzoselenadiazole substitution is associated with reduced structural and energetic disorder relative to benzothiadiazole.