Ultrathin Bi₂O₂S nanosheet near-infrared photodetectors

Recently, a zipper two-dimensional (2D) material Bi₂O₂Se belonging to the layered bismuth oxychalcogenide (Bi₂O₂X: X = S, Se, Te) family, has emerged as an alternate candidate to van der Waals 2D materials for high-performance electronic and optoelectronic applications. This hints towards exploring the other members of the Bi₂O₂X family for their true potential and bismuth oxysulfide (Bi₂O₂S) could be the next member for such applications. Here, we demonstrate for the first time, the scalable room-temperature chemical synthesis and near-infrared (NIR) photodetection of ultrathin Bi₂O₂S nanosheets. The thickness of the freestanding nanosheets was around 2-3 nm with a lateral dimension of ∼80-100 nm. A solution-processed NIR photodetector was fabricated from ultrathin Bi₂O₂S nanosheets. The photodetector showed high performance, under 785 nm laser illumination, with a photoresponsivity of 4 A W^-1, an external quantum efficiency of 630%, and a normalized photocurrent-to-dark-current ratio of 1.3 × 10¹⁰ per watt with a fast response time of 100 ms. Taken together, the findings suggest that Bi₂O₂S nanosheets could be a promising alternative 2D material for next-generation large-area flexible electronic and optoelectronic devices.