Two-Dimensional Gallium Sulfide Nanoflakes for UV-Selective Photoelectrochemical-type Photodetectors

Two-dimensional (2D) transition-metal monochalcogenides have been recently predicted to be potential photo(electro)catalysts for water splitting and photoelectrochemical (PEC) reactions. Differently from the most established InSe, GaSe, GeSe, many other monochalcogenides, bulk GaS has a large band gap of ca. 2.5 eV, which increases up more than 3.0 eV with decreasing its thickness due quantum confinement effects. Therefore, 2D fills void between small-band-gap semiconductors insulators, resulting interest realization van der Waals type-I heterojunctions in photocatalysis, as well development UV light-emitting diodes, wells, optoelectronic devices. Based on theoretical calculations electronic structure function layer number reported literature, we experimentally demonstrate, first time, PEC properties liquid-phase exfoliated nanoflakes. Our results indicate that solution-processed GaS-based PEC-type photodetectors outperform corresponding solid-state photodetectors. In fact, morphology flakes intrinsically minimizes distance photogenerated charges surface area at redox reactions occur, limiting electron-hole recombination losses. The latter are instead deleterious standard configurations. Consequently, display relevant UV-selective photoresponse. particular, they attain responsivities 1.8 mA W-1 1 M H2SO4 (at 0.8 V vs reversible hydrogen electrode -RHE-), 4.6 Na2SO4 0.9 RHE), 6.8 KOH 1.1 RHE) under 275 nm illumination wavelength an intensity 1.3 mW cm-2.