A Quinoidal J-Aggregated Indacendiselenophene Exhibiting High Responsivity in Ultra-Narrowband Organic Photodetection

Organic semiconductors that exhibit narrowband absorption in the near-infrared (NIR) region are highly sought after for photodetector applications, yet achieving such behavior intrinsically remains a considerable challenge. We report a novel fused quinoidal tetracyanoindacenodiselenophene material (QIDSe-C16) that forms solid-state J-aggregates producing a remarkably sharp absorption band with a full width at half-maximum (FWHM) of 27 nm centred at 772 nm, closely matching that of its sulfur analogue (QIDT-C16). Despite exhibiting similar optical and electrochemical characteristics, selenium substitution enhances charge-carrier mobility and significantly improves device performance. Optimized organic phototransistors (OPTs) based on QIDSe-C16 display ambipolar transport and excellent photoresponsivity, reaching 289 A W^-1 at 780 nm illumination, which is an order of magnitude higher than QIDT-C16-based devices and among the best so-far reported values. Our findings demonstrate that controlling solid-state aggregation through heteroatom engineering offers an effective route to narrowband, filter-free NIR photodetectors that combine spectral selectivity with high charge transport.