A hole-selective hybrid TiO₂ layer for stable and low-cost photoanodes in solar water oxidation

The use of conductive and corrosion-resistant protective layers represents a key strategy for improving the durability of light absorber materials in photoelectrochemical water splitting. For high performance photoanodes such as Si, GaAs, and GaP, amorphous TiO₂ protective overlayers, deposited by atomic layer deposition, are conductive for holes via a defect band in the TiO₂. However, when coated on simply prepared, low-cost photoanodes such as metal oxides, no charge transfer is observed through amorphous TiO₂. Here, we report a hybrid polyethyleneimine/TiO₂ layer that facilitates hole transfer from model oxides BiVO₄ and Fe₂O₃, enabling access to a broader scope of available materials for practical water oxidation. A thin polyethyleneimine layer between the light absorber and the hybrid polyethyleneimine/TiO₂ acts as a hole-selective interface, improving the optoelectronic properties of the photoanode devices. These polyethyleneimine/TiO₂ modified photoanodes exhibit high photostability for solar water oxidation over 400 h.