Entropy and Enthalpy Co‐Tuning Strategy in Cu_2‐yAg_y(In_0.06Sn_0.94)Se₂S System toward Excellent Thermoelectric Performance

Abstract

With the reduction in size, nanoparticles (NPs) exhibit unique chemical and physical properties due to surface effects and size‐dependent electronic bands. However, a significant challenge that limits their practical application is the tendency for grain growth at elevated temperatures. Herein, an entropic and enthalpic‐co‐stabilization strategy is employed in a series of high‐entropy Cu2‐yAgy(In0.06Sn0.94)Se2S materials. Remarkably, the grain size of these materials remains at 70 nm even after repeated tests up to 873 K. This stability has enabled to achieve an ultra‐low thermal conductivity (κtot) of 0.22 W m−1 K−1, a record‐high peak zT value of 1.76, and a high average zT value of 0.54 for nanostructured Cu1.73Ag0.27(In0.06Sn0.94)Se2S. Additionally, a high thermoelectric conversion efficiency of 4.5% for the segmented single‐leg module and 3.8% for the 2‐pair module at ΔT ≈ 460 K are achieved with the Cu2SnSe3‐based material, marking its debut in thermoelectric power generation. These findings provide a paradigm to stabilize grain size and improve the thermoelectric performance of nano‐sized high‐entropy materials (HEMs), presenting a promising avenue for substantial advancements across various applications.