TiO2/TiO2:Er bilayers for improved light harvesting in photoelectrochemical processes

Enhanced light harvesting as a strategy to increase photocurrent of titanium dioxide-based photoanodes for hydrogen generation is the main focus of this work. Single TiO 2 :Er layers and heterostructures composed of TiO 2 :Er 3+ and undoped TiO 2 have been obtained by means of reactive radio frequency magnetron sputtering from Ti/Er and Ti metallic targets. Increasing the concentration of Er 3+ leads to amorphization of TiO 2 . X-ray photoelectron and X-ray absorption spectra collected with synchrotron radiation, as well as Rutherford backscattering spectra, reveal that Er 3+ ions are distributed homogenously in the TiO 2 lattice. Top TiO 2 layer, which is found to be of a mixed anatase and rutile structure from grazing incidence X-ray diffraction, acts as an anti-reflective coating. Diffuse reflectance and transmittance spectra measured with an integrating sphere confirm the increase in surface roughness and enhanced light scattering. As a result, bilayers exhibit photocurrent values up to 10 times higher than single layers. • Enhanced light harvesting is observed for TiO 2 /TiO 2 :Er thin film heterostructures. • 10-fold increase in photocurrent for bilayers is due to columnar growth of TiO 2 . • Increased surface roughness of top TiO 2 layer improves light scattering. • Crystallized TiO 2 on top of amorphous TiO 2 :Er acts as anti-reflective coating.