High Thermoelectric Performance in PbSe–NaSbSe₂ Alloys from Valence Band Convergence and Low Thermal Conductivity

Abstract

PbSe is an attractive thermoelectric material due to its favorable electronic structure, high melting point, and lower cost compared to PbTe. Herein, the hitherto unexplored alloys of PbSe with NaSbSe 2 (NaPb m SbSe m+2 ) are described and the most promising p-type PbSe-based thermoelectrics are found among them. Surprisingly, it is observed that below 500 K, NaPb m SbSe m+2 exhibits unorthodox semiconducting-like electrical conductivity, despite possessing degenerate carrier densities of ≈10 20 cm −3 . It is shown that the peculiar behavior derives from carrier scattering by the grain boundaries. It is further demonstrated that the high solubility of NaSbSe 2 in PbSe augments both the thermoelectric properties while maintaining a rock salt structure. Namely, density functional theory calculations and photoemission spectroscopy demonstrate that introduction of NaSbSe 2 lowers the energy separation between the L-and Σ-valence bands and enhances the power factors under 700 K. The crystallographic disorder of Na + , Pb 2+ , and Sb 3+ moreover provides exceptionally strong point defect phonon scattering yielding low lattice thermal conductivities of 1-0.55 W m −1 K −1 between 400 and 873 K without nanostructures. As a consequence, NaPb 10 SbSe 12 achieves maximum ZT ≈1.4 near 900 K when optimally doped. More importantly, NaPb 10 SbSe 12 maintains high ZT across a broad temperature range, giving an estimated record ZT avg of ≈0.64 between 400 and 873 K, a significant improvement over existing p-type PbSe thermoelectrics.

Strong Valence Band Convergence to Enhance Thermoelectric Performance in PbSe with Two Chemically Independent Controls

“…The occurrence of a maximum in the Hall coefficient T H signifies the convergence temperature of the two valence bands [10, 15] . For Ag‐doped and SrSe alloyed sample, the T H is ≈550 K, which is the lowest temperature reported in PbSe‐based material systems, [5b, 10, 13b, 15] indicating the smallest Δ E V value obtained [10] . And from the PYSA measurement, Δ E v is reduced from ≈0.25 for pure PbSe to ≈0.18 eV for both SrSe‐ and BaSe‐alloyed samples at room temperature.…”

“…These results are supported by temperature‐dependent Hall coefficients (Figures S11a and S12a ) and Photoemission Yield Spectroscopy in Air (PYSA) data (Figure S4). The occurrence of a maximum in the Hall coefficient T H signifies the convergence temperature of the two valence bands [10, 15] . For Ag‐doped and SrSe alloyed sample, the T H is ≈550 K, which is the lowest temperature reported in PbSe‐based material systems, [5b, 10, 13b, 15] indicating the smallest Δ E V value obtained [10] .…”

Strong Valence Band Convergence to Enhance Thermoelectric Performance in PbSe with Two Chemically Independent Controls

“…The occurrence of amaximum in the Hall coefficient T H signifies the convergence temperature of the two valence bands. [10,15] ForA g-doped and SrSe alloyed sample,t he T H is % 550 K, which is the lowest temperature reported in PbSe-based material systems, [5b,10, 13b,15] indicating the smallest DE V value obtained. [10] And from the PYSA measurement, DE v is reduced from % 0.25 for pure PbSe to % 0.18 eV for both SrSe-and BaSe-alloyed samples at room temperature.Aswe will present below,t his significant energy band convergence contributes to the significant enhancement of the Seebeck coefficients.…”

Long periodic ripple in a 2D hybrid halide perovskite structure using branched organic spacers

“…Photoemission yield spectroscopy in air (PYSA) was performed on both systems to nd the VBM directly. 53 The CBM can then be added by summing the VBM and the bandgap. Fig.…”