Indium Selenide/Indium Tin Oxide Hybrid Films for Solution-Processed Photoelectrochemical-Type Photodetectors in Aqueous Media

2D metal monochalcogenides have recently attracted interest for photoelectrochemical (PEC) applications in aqueous electrolytes. Their optical bandgap in the visible and near-infrared spectral region is adequate for energy conversion and photodetection/sensing. Their large surface-to-volume ratio guarantees that the charge carriers are photogenerated at the material/electrolyte interface, where redox reactions occur, minimizing recombination processes. However, solution-processed photoelectrodes based on these materials exhibit energy conversion efficiencies that are far from the current state of the art expressed by established technologies. This work reports a systematic morphological, spectroscopic, and PEC characterization of solution-processed films of photoactive InSe flakes for PEC-type photodetectors. By optimizing the thickness and hybridizing InSe flakes with electrically conductive Sn:In₂O₃ (ITO) nanocrystals, photoanodes with a significant photoanodic response in both acidic and alkaline media are designed, reaching responsivity up to 60.0 mA W⁻¹ (external quantum efficiency = 16.4%) at +0.4 V versus RHE under visible illumination. In addition, a strategy based on the use of sacrificial agents (i.e., 2-propanol and Na₂SO₃) is proposed to improve the stability of the InSe and ITO/InSe photodetectors. Our data confirm the potential of 2D InSe for PEC energy conversion and sensing applications, remarking the challenges related to InSe stability during anodic operation.