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

Tin monosulfide (SnS), as a narrow band gap semiconductor for visible-light harvesting, nevertheless the easy formation of secondary phases such as Sn2S3 and SnS2 severely restricts its photoelectrochemical properties. Herein, we proposed a novel two-step strategy to fabricate phase-pure SnS photoelectrode with tunable conductivity on Ti foil substrate and carefully investigated the formation mechanism and photoelectrochemical properties. The tunable conductivity is determined by Na2SO4 pretreatment before annealing, which is supported by the EDS, XPS, and EPR characterizations. Na+ adsorbed to the edge of the precursor SnS2 nanosheets forming a dangling bond adsorption will protect S2- against reacting with the trace oxygen in the CVD system within a certain temperature range (< 525 ℃), thereby reducing the generation of S vacancies to adjust the S/Sn ratio and further regulating the conductivity type. Moreover, the anodic photocurrent density of SnS thin films was about 0.32 mA/cm2 at 1.23 V vs. RHE with the separation and injection efficiency of 1.22 % and 72.78 % and a maximum cathodic photocurrent density can reach approximately -0.36 mA/cm2 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.