Microstructure Manipulation Achieves Superior Efficiency of GeTe-Based Thermoelectric Modules

GeTe has good thermoelectric performance at relatively high temperatures, but the low-symmetry structure near room temperature and phase transition limit its service stability for power generation applications. Here, the thermoelectric properties and mechanical hardness of GeTe are improved by microstructure manipulation and phase transition engineering. The incorporation of Cr, Pb, and Sb into the GeTe lattice modulates the phase transition, increasing the cubic phase fraction from 49% to 73% at 300 K. These modifications introduce shear strains and refined herringbone structures, enhancing phonon scattering while simultaneously improving carrier mobility through dislocation accumulation and band convergence. Consequently, the optimal materials achieve a maximum zT of 2.1 at 700 K and an average zT of 1.5 across the 300-773 K temperature range, along with a Vickers hardness of 1.88 GPa. Paired with n-type PbTe, the fabricated seven-pair module achieves a superior efficiency of 9.7% under a 500 K temperature gradient. This study demonstrates microstructure manipulation is a promising strategy for GeTe-based thermoelectric applications.