Scattering Intensity Regulation via Intrinsic S Vacancies in [CuS ₂ ▫] Motif for Optimized Initial Thermoelectric Performance in Cu─Sb─S System

Abstract The Cu─Sb─S system has garnered significant attention as thermoelectric (TE) material due to the low lattice thermal conductivity ( κ _lat ), cost‐effectiveness, and low toxicity. Herein, an intrinsic switch is demonstrated to optimize the initial properties before doping, which controls the intensity of phonon and carrier scattering simultaneously. The degree of filling of the S‐site at the co‐vertex junction of the [CuS ₃ ] triangles plays a crucial role in determining both electrical and thermal transport properties. Scattering intensity reaches a maximum with the formation of [CuS ₂ ▫] motifs and a minimum when the [CuS ₂ ▫] is fully filled. However, neither condition achieves optimal performance. The partially filled sample, Cu ₃ SbS _3.1 , exhibits enhanced carrier transport while facilitating phonon scattering at a high level by preserving significant thermal vibration of Cu atoms. This optimal balance achieved by modulating the scattering intensity endows the pristine Cu ₃ SbS _3.1 with an intrinsic zT value of 0.7, which is far superior to that of other members in the Cu─Sb─S system. Additionally, zT and its average value are improved through Cd doping, reaching 1.07 and 0.70, respectively. This strategy regulates intrinsic scattering intensity to enhance initial TE properties and provide optimized materials for further development.