Hierarchical growth of SnO₂ nanostructured films on FTO substrates: Structural defects induced by Sn(ii) self-doping and their effects on optical and photoelectrochemical properties

Direct hydrothermal growth of Sn(ii)-doped SnO₂ films on fluorine-doped tin oxide (FTO) substrates results in the formation of upstanding SnO₂ nanosheet arrays covered by hierarchical SnO₂ nanoflowers. The n-type semiconductor films show extended photoresponse in the visible spectrum arising from the coexistence of Sn(ii) dopant ions and oxygen vacancies in these hierarchical SnO₂ nanostructures, which leads to a narrowed bandgap. Photoluminescence spectroscopy revealed that the emission in the UV, blue and red spectral ranges is related to the evolution of Sn(ii) dopants and oxygen vacancies with annealing temperature, whereas oxygen vacancies are mostly responsible for visible emission. The Sn(ii)-doped SnO ₂ films show higher photocurrent when sensitized with narrow bandgap CdS nanoparticles, serving as efficient electron acceptors.