Multi‐Scale Lattice Strain Engineering Enables Reduced Deformation Potential and High Thermoelectric Performance in GeTe Alloys

Chemical doping is a widely adopted strategy for optimizing carrier concentration and tailoring the electronic band structure in thermoelectric (TE) materials. However, in intrinsically cation‐deficient systems such as p ‐type GeTe, its effectiveness is often limited because the coexistence of abundant Ge vacancies and aliovalent dopants intensifies charge‐carrier scattering, thereby deteriorating carrier mobility ( µ ). Herein, we report a facile dopant‐free strategy to enhance the TE performance of Ge 0.94 Bi 0.06 Te through the construction of multi‐scale lattice strain. Increasing lattice symmetry and preserving ordered domain boundaries, combined with reduced deformation potential and prolonged carrier relaxation time, thereby improving µ and further boosting weighted mobility ( µ W ) and power factor. Moreover, the engineered multi‐scale lattice defects strongly suppress lattice thermal conductivity ( κ lat ), yielding an increased µ W / κ lat ratio within the optimal carrier concentration range, indicating weakened electron‐phonon coupling. Consequently, the peak figure of merit ( ZT ) of 2.21 and average ZT of 1.4 over 303–803 K are achieved. Furthermore, a single‐stage TE device fabricated using this material attains a conversion efficiency of 7.83% at a temperature difference of 400 K. This work highlights the effectiveness of strain engineering in decoupling electronic and phononic transport and demonstrates its broad applicability for developing high‐performance TE materials.