“Materials for solar fuels: Coupling efficient water splitting catalysts and high-performance photovoltaics by atomic layer deposition”
Atomic layer deposition (ALD), a cyclic form of chemical vapor deposition that occurs via a series of self-limiting chemisorption reactions, is an increasingly important enabler of nanotechnology and advanced energy technologies. Exciting energy-related applications of ALD that have emerged in recent years include surface passivation of photovoltaics, electrode coating for advanced batteries, and catalyst synthesis. In this presentation, I will summarize recent research in which ALD has been used to promote stable photoelectrolysis of water for solar fuel synthesis. ALD-grown TiO2 layers are found to be particularly effective in inhibiting oxidative corrosion of high-quality semiconductor absorbers and in electronically coupling these semiconductors to efficient catalysts for oxygen evolution, the kinetically-limiting step in water splitting. In addition, ALD is used to alloy TiO2 with transition metal oxides that are themselves good catalysts for water oxidation and that exhibit a high work function. These layers produce high photovoltages in excess of 600 mV in n-Si Schottky MIS junction water splitting photoanodes. Such ALD-grown metal oxide alloys have the potential to become “all-in-one” catalyst/protection/hole-selective contact layers for photoelectrochemical devices. Finally, results obtained from a novel multijunction silicon photoelectrochemical cell incorporating ALD-TiO2 protection and exhibiting > 10% solar-to-hydrogen efficiency will be described.