Photoelectrochemical properties of orthorhombic and metastable phase SnS nanocrystals synthesized by a facile colloidal method

• A facile method to synthesize two different phases of SnS having different morphological and optical properties.
• The phases and morphologies of SnS nanocrystal can be controlled by adding capping surfactant hexamethyldisilazane (HMDS).
• As we know, this is the first metastable SnS photoanode for application in a photoelectrochemical cell.

SnS of orthorhombic (OR) and metastable (SnS) phases were synthesized by using a simple and facile colloidal method. The tin precursor was synthesized using tin oxide (SnO) and oleic acid (OA), while the sulfur precursor was prepared using sulfur powder (S) and oleyamine (OLA). The sulfur precursor was injected into the tin precursor and the prepared SnS nanocrystals were precipitated at a final reaction temperature of 180 °C. The results show that hexamethyldisilazane (HMDS) can be successfully used as a surfactant to synthesize monodisperse 20 nm metastable SnS nanoparticles, while OR phase SnS nanosheets were obtained without HMDS. The direct bandgap observed for the metastable SnS phase is higher (1.66 eV) as compared to the OR phase (1.46 eV). The large blueshift in the direct bandgap of metastable SnS is caused by the difference in crystal structure. The blueshift in the direct band gap value for OR-SnS could be explained by quantum confinement in two dimensions in the very thin nanosheets. SnS thin films used as a photo anode in a photoelectrochemical (PEC) cell were prepared by spin coating on the fluorine-doped tin oxide (FTO) substrates. The photocurrent density of the SnS (metastable SnS)/FTO and SnS (OR)/FTO are 191.8 μA/cm2 and 57.61 μA/cm2 at an applied voltage of − 1 V at 150 W, respectively. These narrow band gap and low cost nanocrystals can be used for applications in future optoelectronic devices.