Disordered Order Enables High Out‐of‐Plane <i>ZT</i> in PbSnS₂ Crystals

Abstract High‐performance thermoelectric materials enable waste heat recovery, providing an effective avenue for sustainable development. The concept of “phonon‐glass electron‐crystal” is considered as an ideal approach to achieve high‐performance thermoelectric materials. However, achieving this perfect state remains a significant challenge due to the coupled transport parameters. In this work, long‐range order and short‐range disorder (disordered order) in n‐type PbSnS 2 crystals are successfully realized through alloying Se, which enable the synergistic optimization of electron and phonon transport. The improvement of crystal symmetry weakens the distortion of the average long‐range order, leading to a high carrier mobility and promoted electrical transport performance. Meanwhile, the local structure analyzed by X‐ray absorption fine structure spectra reveals a strengthened short‐range disorder, resulting in the enhanced phonon scattering and thus ultralow lattice thermal conductivity. As a result, the disordered order enables a high ZT ≈ 1.7 in PbSnS 2 ‐Cl‐30%Se crystal at 733 K along the out‐of‐plane direction. Moreover, the single‐leg device fabricated using this crystal produces a power generation efficiency of ≈7.2% at temperature difference of 378 K. This work demonstrates the realistic feasibility of disordered order to fulfill the ideal “phonon‐glass electron‐crystal” thermoelectric material, which opens up new avenues for performance optimization.