A high-performance “fueled” photodetector based on few-layered 2D ternary chalcogenide NiGa2S4

Abstract

Few-layered binary 2D transition metal chalcogenides have been comprehensively employed in photodetector systems thanks to their intrinsic band gap structure and a high in-plane charge carrier mobility. Their rich chemistry is further broadened when considering ternary 2D chalcogenide materials, giving the possibility to prepare isomorphic materials characterized by various metal distributions within the framework of a crystal structure. Whereas the “inverse” A^(τ)B^(Ω)(τ)₂X₄ hexagonal structures (e.g. ZnIn₂S₄) have been widely studied in photocatalysis, “normal” A^II(Ω) B^III(τ)₂X^VI₄ phases have not been considered so far. In this study, a NiGa₂S₄ photodetector has been prepared by drop-casting the exfoliated crystals onto ITO glass. Their photoresponse has been analyzed either in the absence or in the presence of an electron donor species (EtOH) in the electrolyte solution. Ethanol acts as a fuel in the PEC photodetector system boosting their performance by a factor of ∼x49 in terms of the responsivity at a given wavelength. Moreover, the spectral response is expanded from blue to far IR wavelengths, reaching responsivity values from 48 to 7 mA W⁻¹. The dynamics of photogenerated electrons and holes has been studied using laser flash photolysis. The stability of the “fueled” PEC photodetector has been evaluated through long-term tests which have shown a stable response over extended periods. It is anticipated that the present work can provide fundamental insight into the field of PEC semiconductor-based photodetectors, offering an extendable strategy to engineer high-performance PEC devices.