Transparent Ta2O5 Protective Layer for Stable Silicon Photocathode under Full Solar Spectrum

Protective layers are always required for Si-based photoelectrodes to achieve long-term stability in solar water splitting, for which TiO2, with excellent chemical stability and the effectiveness of charge carrier transfer, is commonly used. However, previous reports found that the performance of the TiO2-protected photoelectrode would deteriorate with the formation of Ti3+ traps, which was rarely investigated. This paper demonstrates that AM 1.5G illumination facilitates generation of Ti3+ in TiO2, since TiO2 could be excited by the highly energetic UV photons, and describes the replacement of the classical photoresponsive TiO2 with completely transparent and chemically inert Ta2O5 layers to improve the photostability. Finally, this pn(+)-Si/Ta2O5/Pt photoelectrode shows a long-term stability over 200 h, a saturated photocurrent density of similar to 34.7 mA cm(-2), and the maximum applied bias photon-to-current efficiency of 8.1%, largely surpassing the TiO2-protected counterparts. With improved stability, Ta2O5 could be highlighted as a new candidate for the protection of unstable semiconductors.