Bismuth‐Tin Core–Shell Particles From Liquid Metals: A Novel, Highly Efficient Photothermal Material that Combines Broadband Light Absorption with Effective Light‐to‐Heat Conversion

Abstract This study presents a pioneering investigation of hybrid bismuth‐tin (BiSn) liquid metal particles for photothermal applications. It is shown that the intrinsic core–shell structure of liquid metal particles can be instrumentalized to combine the broadband absorption characteristics of defect‐rich nano‐oxides and the high light‐to‐heat conversion efficiency of metallic particles. Even though bismuth or tin does not show any photothermal characteristics alone, optimization of the core–shell structure of BiSn particles leads to the discovery of novel, highly efficient photothermal materials. Particles with optimized structures can absorb 85% of broadband light and achieve over 90% photothermal conversion efficiency. It is demonstrated that these particles can be used as a solar absorber for solar water evaporation systems owing to their broadband absorption capability and become a non‐carbon alternative enabling scalable applications. We also showcased their use in polymer actuators in which a near‐infrared (NIR) response stems from their oxide shell, and fast heating/cooling rates achieved by the metal core enable rapid response and local movement. These findings underscore the potential of BiSn liquid metal‐derived core–shell particles for diverse applications, capitalizing on their outstanding photothermal properties as well as their facile and scalable synthesis conditions.