High Thermoelectric Performance in Low‐Cost Cu ₈ SiS <i> _x </i> Se _6‐ <i> _x </i> Argyrodite

Abstract Cu‐based argyrodites have attracted attention as thermoelectric materials for energy harvesting. However, phase transitions and low energy conversion performance limit their applications.This work explores the great thermoelectric performance of Cu 8 SiS x Se 6‐ x argyrodite with stabilized high‐symmetry cubic phase at above 282 K. The suppression of the phase transition below room temperature is realized due to the increase of the configurational entropy caused by the substitution of Se by S in Cu 8 SiS x Se 6‐ x . As a result, a significant enhancement of weighted mobility is achieved for materials without the phase transition due to clean grain boundary contacts. In turn, samples with disordered or dirty grain boundaries lead to a lower and increasing trend of weighted mobility for materials with phase transition in the operating temperature range. The developed argyrodites exhibit excellent thermoelectric performance due to the improved power factor of up to 4.2 µWcm −1 K −2 and ultralow lattice thermal conductivity of 0.18 Wm −1 K −1 at 773 K, which is derived from the peculiar chemical bonding with a large number of different Si‐Se, Se‐Cu, and Cu‐Cu interactions. The dimensionless thermoelectric figure of merit zT for Cu 8 SiS 3 Se 3 argyrodite reaches a value of 1.24, offering this material as a low‐cost and Te‐free alternative for thermoelectric energy conversion applications.