Entropy engineering enabled atomically dispersed Cu doping leading to an exceptionally high thermoelectric figure of merit in n-type lead chalcogenides

Abstract

High-entropy lead chalcogenides usually exhibit high ZT values at a very narrow temperature window because the highly disordered lattice structure trades electrical conductivity for low lattice thermal conductivity (κ_lat). Here, we construct a new entropy-engineered n-type lead chalcogenide of Cu_0.004Pb_1−xSn_xSe_0.5Te_0.25S_0.25 (x = 0–0.1). Remarkably, Sn doping plainly fixes the lattice by homogenizing the charge density difference in the vicinity of Cu atoms. This facilitates Cu atoms atomically dispersing into the interstice of the matrix, removing dislocation and nanoscale precipitates that are commonly found in low-entropy lead chalcogenides. The completely dissolved Cu atoms dynamically optimized the carrier concentration over the temperature range of 300–723 K. As a result, the Cu_0.004Pb_0.99Sn_0.01Se_0.5Te_0.25S_0.25 shows a maximum power factor of ∼21 μW cm⁻¹ K⁻² at 300 K and an average power factor of ∼19 μW cm⁻¹ K⁻² from 300–723 K, rivaling the low-entropy lead compounds with ordered lattice structures. Importantly, the atomically dispersed interstitial Cu atom also markedly shortens the phonon mean free path, suppressing the minimum κ_lat to ∼0.2 W m⁻¹ K⁻¹ at 723 K which strikes the theoretical minimum. The synergistically optimized charge and thermal transport properties collectively give rise to a benchmark room temperature ZT of ∼0.6, which monotonously increases to ∼1.7 at 723 K, surpassing all the n-type entropy-engineered and low-entropy lead chalcogenides.