Ferroelectric-Modulated Photocathode BiFeO3 (BFO) Thin Film Heterostructures via Rare-Earth Substitutions

Ferroelectric polarization in the p-type bismuth ferrite (BFO) thin film heterostructures is effectively modulated through the choice of crystal facet orientations (i.e., (001)-facet and (111)-facet), polarization directions (i.e., upward polarization and downward polarization), and rare-earth (RE) doping (i.e., 7% Nd, 10% Sm, and 7% Gd). The manipulated ferroelectricity tunes the efficiency of charge separation, transfer, and recombination in photoelectrochemical (PEC) water splitting significantly. Among all the samples, the 7% Gd-doped BFO (BGFO) heterostructure coupled with (111)-facet and upward polarization exhibits the highest ferroelectric polarization and charge dynamics due to its lowest oxygen vacancy concentration and electrical leakage. Thus, the BGFO is most effective in facilitating separation and transport of charge carriers and shielding charge recombination, leading to the increased incident photon-to-current efficiency (IPCE), interfacial charge accumulation, and downward band bending at the BGFO/electrolyte interface in the PEC water reduction.