Unveiling Electronic\nStructure, Band Alignment, and\nCharge Carrier Kinetics of Copper Sulfide

In this work, we synthesize pure\ncovellite copper sulfide\n(CuS)\nnanostructures using a hydrothermal approach, adjusting the copper\nstoichiometry to investigate their structural, optical, and electrochemical\nproperties. Time-resolved photoluminescence reveals nanosecond-range\nexcited state lifetimes, while femtosecond transient absorption spectroscopy\nshows that hole absorption dominates over photoinduced electrons with\nrelaxation kinetics influenced by copper stoichiometry. We examine\nthe impact on band edges and stability through cyclic voltammetry,\nfinding that the optical band gap of the CuS nanostructures aligns\nclosely with electrochemical values, approximately 1.9 to 1.8 eV.\nUltraviolet photoelectron spectroscopy confirms changes in the valence\nband maxima, with varying stoichiometry elevating the valence band\nedge, indicating a near-metallic nature for CuS. Our study enables\nprecise engineering of these nanostructures, positioning CuS as a\npromising low-cost material for energy harvesting and optoelectronic\napplications, including photovoltaics, photocatalysis, and energy\nstorage.