High‐Entropy‐Alloy Nanoparticles with Enhanced Interband Transitions for Efficient Photothermal Conversion

Photothermal materials with broadband optical absorption and high conversion efficiency are intensively pursued to date. Here, proposing by the d‐d interband transitions, we report an unprecedented high‐entropy alloy FeCoNiTiVCrCu nanoparticles that the energy regions below and above the Fermi level (±4 eV) have been fully filled by the 3d transition metals, which realizes an average absorbance greater than 96 % in the entire solar spectrum (wavelength of 250 to 2500 nm). Furthermore, we also calculated the photothermal conversion efficiency and the evaporation rate towards the steam generation. Due to its pronounced full light capture and ultrafast local heating, our high‐entropy‐alloy nanoparticle‐based solar steam generator has over 98 % efficiency under one sun irradiation, meanwhile enabling a high evaporation rate of 2.26 kg m−2 h−1. A strategy toward the optimization of photothermal conversion materials with broad optical absorption and high conversion efficiency via the d‐d interband transitions is demonstrated. The high‐entropy‐alloy nanoparticles could realize an excellent solar harvesting performance especially compositing with up to seven 3d elements in a single phase, ascribing to the fully filled energy regions below and above the Fermi level.