Electrochemical surface charge-inversion from semi-insulating Sb₂Se₃ photoanodes and abrupt photocurrent generation for water splitting

Binary chalcogenide Sb₂Se₃ shows dominantly p-type electrical conductivity and poor photocathodic performance; however, its narrow band gap and low work function suggest satisfactory conditions for the generation of the inversion state at the surface if used as a photoanode. We propose a fabrication design for the synthesis of n-type Sb₂Se₃ by suppressing the formation of antisite Sb_Se defects, where excessively thick Se layers deposited on the electrodeposited Sb-Se precursors and high N₂ pressure are introduced during the annealing step. Surprisingly, the linear sweep voltage (LSV) measurement from the n-type Sb₂Se₃ shows remarkably enhanced photocurrent density (up to approximately 5 mA cm^-2 at 1.23 V vs. a reversible hydrogen electrode) under light illumination, which is the highest performance among pristine binary photoelectrodes yet recorded. In addition, the LSV curve exhibits non-typical behavior with a significant increase of the photocurrent at the specific potential. The measured current density under light illumination and no dark current indicate a vigorous photoactive reaction from photogenerated carriers. Here, the abrupt increase in photocurrent density is attributed to the conduction path of hole carriers originating from the charge inversion state with p-type conductivity at the surface, allowing significant carrier injection into the electrolyte. Based on electrochemical analyses, the mechanism that results in outstanding photocurrent gain from the novel n-type Sb₂Se₃ photoanodes was proposed and their further development possibilities via additional improvements were presented.