Highly efficient charge separation in model Z-scheme TiO2/TiSi2/Si photoanode by micropatterned titanium silicide interlayer

Atomic layer deposited (ALD) TiO2 is an attractive material for improving the photoactivity and chemical stability of semiconductor electrodes in artificial photosynthesis. Using photoelectrochemical (PEC) measurements, we show that an interfacial, topographically microstructured TiSi2 layer inside the TiO2/Si heterojunction improves the charge carrier separation and shifts the water dissociation onset potential to more negative values. These observations are correlated with the X-ray photoelectron spectroscopy (XPS) and ultra-violet photoelectron spectroscopy (UPS) measurements, which reveal an increased band bending due to the TiSi2 interlayer. Combined with the UV-Vis absorption results, the photoelectron spectroscopy measurements allow the reconstruction of the complete energy band diagram for the TiO2/TiSi2/Si heterojunction and the calculation of the valence and conduction band offsets. The energy band alignment and improvements in PEC results reveal that the charge transfer across the heterojunction follows a Z-scheme model, where the metal-like TiSi2 islands act as recombination centers at the interface. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.