Hole Thermalization Dynamics Facilitate Ultrafast Spatial Charge Separation in CuFeO₂ Solar Photocathodes

CuFeO 2 is an earth-abundant metal oxide semiconductor showing promising efficiency as a solar photocathode. Using extreme ultraviolet (XUV) and optical spectroscopy, we track the element-specific electron and hole dynamics in CuFeO 2 and compare results to those for Fe 2 O 3 . Cathodic photocurrent, which is only observed in CuFeO 2, is shown to correlate with ultrafast (500 fs) hole thermalization from O 2p to hybridized Cu 3d states, leading to spatial charge separation within the CuFeO 2 lattice. These results are supported by DFT calculations confirming strong covalency of Cu 3d and O 2p states at the valence band edge. The ability to elucidate site-specific charge carrier dynamics in real time provides valuable insights for the rational design of catalysts for efficient solar energy harvesting.