A High Efficiency Si Photoanode Protected by Few-Layer MoSe₂

To date, the performance of semiconductor photoanodes has been severely limited by oxidation and photo-corrosion. Here, a report is given on the use of earth-abundant MoSe₂ as a surface protection layer for Si-based photoanodes. Large area MoSe₂ film was grown on p⁺-n Si substrate by molecular beam epitaxy. It is observed that the incorporation of few-layer (≈3 nm) epitaxial MoSe₂ can significantly enhance the performance and stability of Si photoanode. The resulting MoSe₂/p⁺-n Si photoanode produces a light-limited current density of 30 mA cm⁻² in 1 M HBr under AM 1.5G one sun illumination, with a current-onset potential of 0.3 V versus reversible hydrogen electrode (RHE). The applied bias photon-to-current efficiency (ABPE) reaches up to 13.8%, compared to the negligible ABPE values (<0.1%) for a bare Si photoanode under otherwise identical experimental conditions. The photoanode further produced stable voltage of ≈0.38 V versus RHE at a photocurrent density of ≈2 mA cm⁻² for ≈14 h under AM 1.5G one sun illumination. This work shows the extraordinary potential of two-dimensional transitional metal dichalcogenides in photoelectrochemical application and will contribute to the development of low cost, high efficiency, and highly stable Si-based photoelectrodes for solar hydrogen production.