Photoelectrochemistry of core–shell tandem junction n–p+-Si/n-WO3 microwire array photoelectrodes

Abstract

Tandem junction (n–p⁺-Si/ITO/WO₃/liquid) core–shell microwire devices for solar-driven water splitting have been designed, fabricated and investigated photoelectrochemically. The tandem devices exhibited open-circuit potentials of E_oc = −1.21 V versus E⁰′(O₂/H₂O), demonstrating additive voltages across the individual junctions (n–p⁺-Si E_oc = −0.5 V versus solution; WO₃/liquid E_oc = −0.73 V versus E⁰′(O₂/H₂O)). Optical concentration (12×, AM1.5D) shifted the open-circuit potential to E_oc = −1.27 V versus E⁰′(O₂/H₂O) and resulted in unassisted H₂ production during two-electrode measurements (anode: tandem device, cathode: Pt disc). The solar energy-conversion efficiencies were very low, 0.0068% and 0.0019% when the cathode compartment was saturated with Ar or H₂, respectively, due to the non-optimal photovoltage and band-gap of the WO₃ that was used in the demonstration system to obtain stability of all of the system components under common operating conditions while also insuring product separation for safety purposes.