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 cm² V^-1 s^-1 . Most importantly, its thin film exhibits a low trap density of 5.55 × 10¹⁶ 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 10¹³ Jones at 400-1000 nm wavelength region with a peak specific detectivity of 4.65 × 10¹³ Jones at 880 nm. This performance is among the best reported for self-powered NIR OPDs.