Shallow doping at multiple energy levels to boost the photoelectrochemical activity of water-splitting α-Fe2O3 electrodes

Hematite (α-Fe₂O₃), an n-type semiconducting material, is considered one of the most promising photoanodes for water splitting, yet exhibits unsatisfactory photoelectrochemical (PEC) activity stemming from poor conductivity and inferior charge carrier transport. Doping is an effective strategy to improve conductivity and enhance carrier transport in α-Fe₂O₃. However, there is a limit of the doping method, because some dopants will pin the Fermi level via defect complexes and aggregate carrier recombination, leading to positive shift of onset potential and depressed saturated photocurrent. Herein, a strategy based on shallow dopants locating at multiple energy levels is developed to surpass the restriction by introducing niobium (Nb) into the titanium-doped Fe₂O₃ (Ti-Fe₂O₃) through post-treatment. The resulting Nb/Ti-Fe₂O₃ composite film is confirmed to further increase the carrier concentration of Ti-Fe₂O₃ and exhibit a 625% increase in saturated water-splitting photocurrent without positively shifted photocurrent onset. This study paves a new way for further advancement of the PEC water splitting.