Gradient Doping Of Sulfur In Sb2se3 Nanowire Arrays As Photoelectrochemical Photocathode With A 2% Half-Cell Solar-To-Hydrogen Conversion Efficiency

Exploring Sb2Se3 as a photoelectrochemical (PEC) photocathode for water reduction has recently attracted much attention, mainly due to its excellent photophysical properties and perfect band structure matching with water reduction potential. Whereas significant achievements have been made in improving its photocurrent density, the PEC performance remains poor mostly due to the low onset potential or low fill factor. Here, we fabricated S doped Sb2Se3 nanowire arrays with a gradient S concentration (grad-S:Sb2Se3). Gradient S doping creating a cascade valence band structure in Sb2Se3 simultaneously enhances its onset potential and fill factor. Light-trapping effects in nanowire geometry improve the light harvesting efficiency. A further deposition of a thin TiO2 layer is utilized to passivate the detrimental surface defects and form a buried junction with grad-S:Sb2Se3. By employing the prepared grad-S:Sb2Se3 nanowire arrays as the photocathode for water reduction, we achieved a high onset potential of 0.42V vs RHE, a fill factor of 34%, and a record high half-cell solar-to-hydrogen conversion efficiency of 2% from Sb2Se3-based photocathodes.