Broadening spectral responses and achieving environmental stability in SnS₂/Ag-NPs/HfO₂ flexible phototransistors

Layered two-dimensional (2D) materials have gained popularity thanks to their atomically thin physique and strong coupling with light. Here, we investigated a wide band gap (≥ 2 eV) 2D material, i.e., tin disulfide (SnS₂), and decorated it with silver nanoparticles, Ag-NPs, for broadband photodetection. Our results show that the SnS₂/Ag-NPs devices exhibit broadband photodetection ranging from the ultraviolet to near-infrared (250-1050 nm) spectrum with decreased rise/decay times from 8/20 s to 7/16 s under 250 nm wavelength light compared to the bare SnS₂ device. This is attributed to the localized surface plasmon resonance effect and the wide band gap of SnS₂ crystal. Furthermore, the HfO₂-passivated SnS₂/Ag-NPs devices exhibited high photodetection performance in terms of photoresponsivity (∼12 500 A W^-1), and external quantum efficiency (∼6 × 10⁶%), which are significantly higher compared to those of bare SnS₂. Importantly, after HfO₂ passivation, the SnS₂/Ag-NPs photodetector maintained the stable performance for several weeks with merely ∼5.7% reduction in photoresponsivity. Lastly, we fabricated a flexible SnS₂/Ag-NPs photodetector, which shows excellent and stable performance under various bending curvatures (0, 20, and 10 mm), as it retains ∼80% of its photoresponsivity up to 500 bending cycles. Thus, our study provides a simple route to realize broadband and stable photoactivity in flexible 2D material-based devices.