Si/TiO_2 Tandem-Junction Microwire Arrays for Unassisted Solar-Driven Water Splitting

Tandem-junction microwire array photoelectrodes have been fabricated by coating np^+-Si radial homojunction microwire arrays sequentially with fluorine-doped tin oxide (FTO) and titanium dioxide (TiO_2). These photoelectrodes effected unassisted water splitting under simulated 1 Sun conditions with an open-circuit potential (E_(oc)) of −1.5 V vs the formal potential for oxygen evolution, E^(0′)(OH^−/O_2), a current density at E = E^(0′)(OH^−/O_2) of 0.78 mA cm^(−2), a fill factor ( ff ) = 0.51, and a photovoltaic-biased photoelectrochemical ideal regenerative cell efficiency of 0.6%