Disordered Order Enables High Out-of-Plane ZT in PbSnS₂ Crystals

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 PbSnS₂ 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 PbSnS₂-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.