Sensitive short-wavelength infrared photodetection with a quinoidal ultralow band-gap n-type organic semiconductor

It is fundamentally challenging to achieve high responsivity and detectivity for organic photodetectors (OPDs) in the short-wavelength infrared (SWIR) region due to the challenges in designing ultralow band-gap organic semiconductors with a low energetic disorder and trap density. Herein, we report a quinoidal, ultralow band-gap, n-type small molecule with an absorption onset of up to 1,243 nm. The quinoidal central core contributes to reduced thermally generated carriers via decreasing energetic disorder and trap density. As a result, the self-powered OPD exhibited a detectivity of over 1012 Jones in 400–1,200 nm. Particularly, at 1,100 nm, the detection limit of commercial silicon photodetectors, an external quantum efficiency of 18.9% and a detectivity of 3.81 × 1012 Jones are achieved under zero bias, which renders the device the best self-powered OPD in photovoltaic mode below the silicon band gap to date. This work opens an avenue to develop sensitive SWIR photodetection technology based on organic semiconductors.