Silicon nanostructures on Si(111) substrates were prepared by photoelectrochemical dissolution in diluted ammonium fluoride containing solutions and under optical real-time control by Brewster-angle reflectometry. Subsequent Pt-electrodeposition resulted in formation of local Schottky-barriers and surface passivation by an ultra-thin SiO_2 film. Efficiencies of the monolithic system for photoelectrochemical solar energy conversion and for photoelectrocatalytic evolution of hydrogen were investigated in dependence of the preceding surface preparation. Smooth nanotopographies on n-type Si(111), consisting of recurrent structures with 2nm average height, showed highest device performance while an increasing aspect ratio of the structures reduced the efficiency. As possible cause, lower densities of Pt-contacts on stronger corrugated surfaces were observed. Comparable results were obtained for p-type Si(111) in corresponding experiments for hydrogen reduction.
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