Activation of hematite photoanodes for solar water splitting: Effect of FTO deformation

The sintering at 800°C is found to induce the diffusion of Sn from the F-doped SnO₂ (FTO) into the hematite lattice, enhancing the photoelectrochemical cell (PEC) properties of the hematite photoanodes, but this diffusion also has detrimental effects on the conductivity of the FTO substrate. In the present research we examined the role of FTO deformation during the activation of hematite photoanodes synthesized on FTO substrates. The incorporation of Sn dopants from the FTO substrates in the hematite lattice was confirmed by X-ray photoelectron spectroscopy and was found to increase with sintering time. Further from the extended X-ray absorption fine structure analysis, it was found that the diffused Sn atoms affected the metal sites of the hematite lattice. Increased diffusion of Sn into the hematite lattice caused structural disordering of the FTO, but optimum sintering time compensated for the structural disordering and improved the ordering. Under high-temperature annealing at 800°C, the FTO substrates underwent a stoichiometric change that directly affected their electrical conductivity; their resistivity was doubled after 20 min of sintering. Activation of hematite photoanodes by high-temperature sintering entails a kinetic competition between Sn dopant diffusion from the FTO substrate into the hematite and the resulting thermal deformation and conductivity loss in the FTO substrates.