A novel two-step strategy to fabricate phase-pure SnS photoelectrodes with tunable conductivity: formation mechanism and photoelectrochemical properties

Tin monosulfide (SnS) is a narrow band gap semiconductor for visible-light harvesting, however the easy formation of secondary phases such as Sn2S3 and SnS2 severely restricts its photoelectrochemical (PEC) properties. Herein, we propose a novel two-step strategy to fabricate phase-pure SnS photoelectrodes with tunable conductivity on Ti foil substrate and carefully investigated the formation mechanism and PEC properties. The tunable conductivity is determined by Na2SO4 pretreatment before annealing, which is supported by energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and electron paramagnetic resonance characterizations. Na+ adsorbed to the edge of the precursor SnS2 nanosheets forming a dangling bond adsorption will protect S2- against reaction with the trace oxygen in the chemical vapor deposition system within a certain temperature range (<525 degrees C), thereby reducing the generation of S vacancies to adjust the S/Sn ratio and further regulate the conductivity type. Moreover, the anodic photocurrent density of SnS thin films was about 0.32 mA cm(-2) at 1.23 V vs reversible hydrogen electrode (RHE) with the separation and injection efficiency of 1.22% and 72.78% and a maximum cathodic photocurrent density reaching approximately -0.36 mA cm(-2) at 0 V vs RHE with the separation and injection efficiency 1.15% and 5.44% respectively. The method shown in this work provides an effective approach to control the electrical conductivity of SnS thin films with considerable photocurrent response for phase-pure SnS.