Cheng, W.-H.; Richter, M.H.; May, M.M.; Ohlmann, J.; Lackner, D.; Dimroth, F.; Hannappel, T.; Atwater, H.A; Lewerenz, H.-J.: Monolithic Photoelectrochemical Device for Direct Water Splitting with 19% Efficiency. ACS Energy Letters 3 (2018), p. 1795-1800
Open Accesn Version

Efficient unassisted solar water splitting, a pathway to storable renewable energy in the form of chemical bonds, requires optimization of a photoelectrochemical device based on photovoltaic tandem heterojunctions. We report a monolithic photocathode device architecture that exhibits significantly reduced surface reflectivity, minimizing parasitic light absorption and reflection losses. A tailored multifunctional crystalline titania interphase layer acts as a corrosion protection layer, with favorable band alignment between the semiconductor conduction band and the energy level for water reduction, facilitating electron transport at the cathode−electrolyte interface. It also provides a favorable substrate for adhesion of high-activity Rh catalyst nanoparticles. Under simulated AM 1.5G irradiation, solar-to-hydrogen efficiencies of 19.3 and 18.5% are obtained in acidic and neutral electrolytes, respectively. The system reaches a value of 0.85 of the theoretical limit for photoelectrochemical water splitting for the energy gap combination employed in the tandem-junction photoelectrode structure.