Valence Band Modification and Enhanced Phonon‐Phonon Interactions for High Thermoelectric Performance in GeTe

Abstract The strong coupling between carrier and phonon transport in thermoelectric (TE) materials severely limits improvements to the figure of merit (ZT). In this work, an approach is proposed to weaken electron‐phonon coupling, effectively enhancing the TE performance of GeTe. Alloying with Zn₄Sb₃ reduces excessive carrier concentration (n_H), widens the bandgap, and promotes band convergence, synergistically improving charge carrier transport and ensuring a high power factor. Additional Pb doping further optimizes n_H, boosting the power factor even more. Moreover, phonon transport is suppressed through Pb doping, as reflected in enhanced acoustic‐optical interactions due to the crossing of optical and acoustic modes, and a reduction in sound group velocity. This reinforced strong phonon scattering, combined with multi‐scale hierarchical nano/microstructures in the matrix, significantly reduces lattice thermal conductivity. As a result, a high ZT of 2.1 is achieved at 753 K in Ge_0.9Pb_0.1Te+0.9%Zn₄Sb₃. Alongside optimized mechanical performance, a high power density of 1.46 W cm⁻² is realized at a temperature difference of 350 K in the fabricated 7‐pair TE module. The findings demonstrate the effectiveness of a stepwise optimization strategy for developing high‐performance TE materials.