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

CuFeO2 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 CuFeO2 and compare results to those for Fe2O3. Cathodic photocurrent, which is only observed in CuFeO2, 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 CuFeO2 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.