Combined Theoretical and Experimental Investigations of Atomic Doping To Enhance Photon Absorption and Carrier Transport of LaFeO₃ Photocathodes

Perovskite-type lanthanum iron oxide, LaFeO₃, is a p-type semiconductor that can achieve overall water splitting using visible light while maintaining photostability. These features make LaFeO₃ a promising photocathode candidate for various photoelectrochemical cells. Currently, the photoelectrochemical performance of a LaFeO₃ photocathode is mainly limited by considerable bulk electron-hole recombination. This study reports a combined theoretical and experimental investigation on atomic doping of LaFeO₃, in particular, substitutional doping of La³⁺ with K⁺, to increase its charge transport properties and decrease electron-hole recombination. The computational results show that K doping enhances not only the charge transport properties but also photon absorption below the bandgap energy of the pristine LaFeO₃. The effect of K doping was systematically investigated by comparing the electronic and atomic structures, majority carrier density, hole-polaron formation, and optical properties of pristine and K-doped LaFeO₃. The computational results were then verified by experimentally characterizing the crystal structures, compositions, optical properties, and photoelectrochemical properties of LaFeO₃ and K-doped LaFeO₃ electrodes. For this purpose, pristine LaFeO₃ and K-doped LaFeO₃ were prepared as high-surface-area, high-purity photoelectrodes having the same morphology to accurately and unambiguously evaluate the effect of K doping. Here, the combined computational and experimental investigations presented in this study provide useful insights into the effect of composition tuning of LaFeO₃ and other p-type oxides with a perovskite structure.