Atomic Layer Deposited TiO2–IrOx Alloys Enable Corrosion Resistant Water Oxidation on Silicon at High Photovoltage

We synthesized by atomic layer deposition (ALD) TiO 2 –IrO x alloys that enable high photovoltages and catalyze water oxidation on silicon metal–insulator–semiconductor (MIS) photoanodes. The ratio of TiO 2 to IrO x was precisely controlled by varying the number of ALD cycles for each precursor. Silicon with a 2 nm surface SiO 2 layer was coated with TiO 2 –IrO x alloys ranging in composition from 18 to 35% iridium relative to the sum of titanium and iridium concentrations. IrO x catalyzed oxygen evolution and imparted a high work function to the TiO 2 –IrO x alloys, enabling photovoltages during water oxidation that exceeded 600 mV. TiO 2 imparted stability and inhibited corrosion of the underlying silicon light absorber. After annealing in forming gas (5% H 2 /95% N 2 ), TiO 2 –IrO x alloys were stable for 12 h of continuous water oxidation in 1 M H 2 SO 4 . Key properties of the MIS junction affecting electrochemical operation were also extracted by electrochemical impedance spectroscopy. This work demonstrates that alloying by ALD is a promising approach for designing corrosion resistant Schottky contacts with optimized electronic and materials properties for catalyzed, solar driven water oxidation.