Fig. 7. (a) Photocurrent density and (b) incident photon-to-current efficiency recorded for 20 μm thick TiO₂ nanotube layers sensitized with different CdS coating thicknesses (2.5, 5 and 10 nm). (c) Diffuse reflectance spectra of TiO₂ nanotube layers with a CdS coating of different thickness: 2.5, 5 and 10 nm.