Achieving Photomultiplication in Dye‐Sensitized Narrowband Photodetectors by Electron Injection through a Thin Hole‐Transporting Layer

Narrowband photodetectors (NBPDs) that response to light with specific wavelength are attractive in imaging fields. Organic materials meet the demand of NBPDs well as active layer due to their tunable and the narrowband-absorption properties. However, the responsivity is generally low caused by the hard exciton diffusion as well as severe recombination. Herein, a narrowband-absorption BODIPY dye is synthetized and applied in vertical-structural NBPDs as sensitizer bonding with the mesoporous titanium dioxide (mp-TiO2). The close bonding between BODIPY dyes and mp-TiO2 effectively enhances the dissociation of excitons. Importantly, the NBPDs present high photomultiplication, the first observation in such dye-sensitized devices, which is due to the electron injection induced by a thin layer of Spiro-OMeTAD covered on the hump parts of mp-TiO2. The NBPDs exhibit high external quantum efficiency (EQE) of 534% at 510 nm with a full-width at half-maximum (FWHM) of 45 nm, a low dark current of 7.0 × 10-5 mA cm-2, and a high detectivity (D*) of 1.5 × 1013 cm Hz1/2 W-1 (Jones) at −3 V. Besides, the devices own response speed within several milliseconds and excellent stability. The work proposes a strategy to fabricate photomultiplication-type NBPDs by using intrinsic narrowband-absorption dyes as active layer.