Optimization of Hybrid Photoelectrodes for Solar Water-Splitting

The "Hybrid Photoelectrode", a multi-junction thin film device for producing hydrogen through solar-powered water-splitting, is presented. In this monolithically stacked device configuration, an outer semiconductor-electrolyte junction acts in conjunction with underlying photovoltaic solid state-junctions to generate sufficient photovoltage and photocurrent for unassisted water photoelectrolysis. An initial prototype device, consisting of an amorphous-silicon-based photovoltaic tandem junction coated with a reactively sputtered tungsten trioxide film, exhibited stable solar-to-hydrogen (STH) conversion in acidic media at 0.6% efficiency. An efficiency of 2.2% STH is projected for a device based on recently developed tungsten trioxide films and existing thin-film-silicon tandem devices. The potential for further efficiency increase by materials and device optimizations is discussed.