Manipulating Atomic Disorder and Mesoscale Architectures for High‐Efficiency Thermoelectric Modules

ABSTRACT Decoupling electron and phonon transport remains the central challenge in designing high‐performance thermoelectric materials for low‐grade heat recovery. Conventional optimization strategies for Bi ₂ Te ₃ ‐based alloys typically isolate defect engineering from microstructure modulation, often leading to performance trade‐offs. Here, we demonstrate a strategy that simultaneously manipulates atomic disorder and mesoscale architectures via an in situ solid‐state reaction in p‐type Bi _0.5 Sb _1.5 Te ₃ . By incorporating PbTiO ₃ precursors, we trigger a thermodynamically driven reaction: at the atomic scale, Pb atoms substitutionally occupy Sb sites to induce chemical disorder and optimize the Fermi level; at the mesoscale, residual Ti species segregate to form PbTiO ₃ @TiO ₂ core–shell precipitates. This hierarchical structural engineering acts as a frequency‐selective barrier, drastically reducing lattice thermal conductivity without compromising carrier mobility. Consequently, the 0.5 mol% composite achieves a peak figure of merit of 1.47 at 333 K. Translating this material‐level breakthrough into a device, we fabricated a thermoelectric module that delivers a conversion efficiency of ∼7% and an output power of 13.1 mW under a temperature difference of 180 K. This work establishes a generalizable protocol for functionalizing thermoelectric systems via coupled defect chemistry and interface engineering, bridging the gap between fundamental transport physics and practical energy harvesting.