In summary, we investigated hybrid PEI/TiO2 as a protection layer for metal oxide photoanodes that significantly enhances the stability of these materials for solar water oxidation. The hybrid TiO2 layer was formed on the interfacial PEI layer during the ALD process, and we observed distinct energetics associated with a new defect state resulting from the partial reduction of Ti 4+ in TiO2. Furthermore, the unique properties of the PEI layer (e.g., preventing unfavorable band bending) facilitated selective-hole transfer between the metal oxide and TiO2 layer. Addressing the challenges related to unfavorable hole-selective contact, the metal oxide photoanode modified with the hybrid TiO2 demonstrated feasibility in solar water oxidation with long-term stability.