An n‐Type All‐Fused‐Ring Molecule with Photoresponse to 1000 nm for Highly Sensitive Near‐Infrared Photodetector

Abstract Most of all‐fused‐ring π‐conjugated molecules have wide or medium bandgap and show photo response in the visible range. In this work, an all‐fused‐ring n‐type molecule, which exhibits an ultrasmall optical bandgap of 1.22 eV and strong near‐infrared (NIR) absorption with an onset absorption wavelength of 1013 nm is reported. The molecule consists of 14 aromatic rings and has electron donor–acceptor characteristics. It exhibits excellent n‐type properties with low‐lying HOMO/LUMO energy levels of −5.48 eV/−3.95 eV and high electron mobility of 7.0 × 10 −4 cm 2 V −1 s −1 . Most importantly, its thin film exhibits a low trap density of 5.55 × 10 16 cm −3 because of the fixed molecular conformation and consequently low conformation disorder. As a result, organic photodetector (OPD) based on the compound exhibits a remarkably low dark current density ( J d ) of 2.01 × 10 −10 A cm −2 at 0 V. The device shows a shot‐noise‐limited specific detectivity ( D sh *) of exceeding 10 13 Jones at 400–1000 nm wavelength region with a peak specific detectivity of 4.65 × 10 13 Jones at 880 nm. This performance is among the best reported for self‐powered NIR OPDs.