Hole-Selective Hybrid TiO2 Layer towards Long-Term Stability of 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 (a-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 a-TiO2. Here, we report a hybrid polyethyleneimine (PEI)/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 PEI layer between the light absorber and the hybrid PEI/TiO2 acts as a hole-selective interface, improving the optoelectronic properties of the photoanode devices. These PEI/TiO2 modified photoanodes exhibit high photostability for solar water oxidation (~2 mA cm-2 for > 120 h).