Realizing Ultrahigh Thermoelectric Performance in n‐Type PbSe Through Lattice Planification and Introducing Liquid‐Like Cu Ions

Abstract The coupling relationship between electrical and thermal transports makes it rather challenging to enhance thermoelectric performance. Here, electrical and thermal transports are successfully decoupled to realize high performance in n‐type PbSe by utilizing a stepwise strategy. First, the PbSe lattice is plained with extra Pb to compensate for the intrinsic Pb vacancies, which can weaken defect scattering and improve carrier mobility to ≈1230 cm² V⁻¹ s⁻¹. The room‐temperature power factor triples and reaches ≈32 µW cm⁻¹ K⁻², and ZT is significantly enhanced to ≈0.6 in Pb_1.006Se. Subsequently, liquid‐like interstitial Cu ions are introduced to inhibit heat conduction without damaging electrical transport. While maintaining a high power factor of ≈25 µW cm⁻¹ K⁻², Cu ions strongly suppress phonon transport at high temperature, leading to an ultralow lattice thermal conductivity of ≈0.28 W m⁻¹ K⁻¹ in Pb_1.006Cu_0.006Se, only 30% of the Cu‐free PbSe. Eventually, a remarkable peak ZT of ≈1.8 at 773 K is achieved along with a high average ZT of ≈1.1 from 300 to 823 K in Pb_1.006Cu_0.006Se. An outstanding experimental conversion efficiency of ≈7.1% is obtained in the single‐leg device, demonstrating great potential for PbSe as low‐ to mid‐temperature thermoelectrics.