A 50–70 nm thickness TiO2 compact blocking layer was deposited
on the cleaned FTO substrates by treating in a 50 mM TiCl4 aqueous
solution at 70 °C for 30 min in order to improve the mechanical and
adhesion strength. The substrates were then rinsed with deionized
water and ethanol, at last heated at 500 °C for 30 min