Phase transition suppression for enhanced thermoelectric performance in rhombohedral GeSe

Temperature-driven phase transitions are commonly observed in high-performance thermoelectric materials. However, the practical deployment of thermoelectric generators requires a comprehensive evaluation of material performance under wide and continuously varying temperature gradients. In particular, such phase transitions can markedly compromise the operational stability and energy-conversion efficiency of thermoelectric systems. Therefore, controlling or suppressing these phase transitions is essential for ensuring reliable device performance. In this work, we demonstrate the suppression of a metastable phase transition in rhombohedral GeSe, enabling a substantial enhancement in its thermoelectric properties. The GeSe–AgInTe2 solid solution undergoes a phase transition near 650 K, which severely deteriorates its electrical transport behavior. We show that this detrimental transition can be effectively suppressed by partially substituting In with Sb. The resulting improvement in electrical transport, together with intrinsically low thermal conductivity arising from multiple phonon-scattering centers, leads to a pronounced enhancement in thermoelectric performance. Consequently, the average ZT (ZTave) in the range of 573–773 K increases from ∼0.38 to ∼0.91. These findings establish phase-transition engineering as a viable strategy for reliable, high-efficiency thermoelectric generators capable of operating across broad temperature windows.