A hole-selective hybrid TiO 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 TiO protective overlayers, deposited by atomic layer deposition, are conductive for holes via a defect band in the TiO. However, when coated on simply prepared, low-cost photoanodes such as metal oxides, no charge transfer is observed through amorphous TiO. Here, we report a hybrid polyethyleneimine/TiO layer that facilitates hole transfer from model oxides BiVO and FeO, 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/TiO acts as a hole-selective interface, improving the optoelectronic properties of the photoanode devices. These polyethyleneimine/TiO modified photoanodes exhibit high photostability for solar water oxidation over 400 h.