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 SnO2 films show higher photocurrent when sensitized with narrow bandgap CdS nanoparticles, serving as efficient electron acceptors.