Interface Engineering of TiO₂ Photoelectrode Coatings Grown by Atomic Layer Deposition on Silicon

Titanium dioxide (TiO₂) can protect photoelectrochemical (PEC) devices from corrosion, but the fabrication of high-quality TiO₂ coatings providing long-term stability has remained challenging. Here, we compare the influence of Si wafer cleaning and postdeposition annealing temperature on the performance of TiO₂/n⁺-Si photoanodes grown by atomic layer deposition (ALD) using tetrakis(dimethylamido)titanium (TDMAT) and H₂O as precursors at a growth temperature of 100 °C. We show that removal of native Si oxide before ALD does not improve the TiO₂ coating performance under alkaline PEC water splitting conditions if excessive postdeposition annealing is needed to induce crystallization. The as-deposited TiO₂ coatings were amorphous and subject to photocorrosion. However, the TiO₂ coatings were found to be stable over a time period of 10 h after heat treatment at 400 °C that induced crystallization of amorphous TiO₂ into anatase TiO₂. No interfacial Si oxide formed during the ALD growth, but during the heat treatment, the thickness of interfacial Si oxide increased to 1.8 nm for all of the samples. Increasing the ALD growth temperature to 150 °C enabled crystallization at 300 °C, which resulted in reduced growth of interfacial Si oxide followed by a 70 mV improvement in the photocurrent onset potential.