N-type PbSe thermoelectric materials encounter challenges in improving the power factor due to the single-band structure near the Fermi level, which obstructs typical band convergence. The primary strategy for enhancing the thermoelectric figure of merit (ZT) for n-type PbSe involves reducing lattice thermal conductivity (κ lat ) by introducing various defect structures. However, lattice mismatches resulting from internal defects within the matrix can diminish carrier mobility, thereby affecting electrical transport properties. In this study, n-type AgCuTe-alloyed PbSe systems achieve a peak ZT value of ≈1.5 at 773 K. Transmission electron microscopy reveals nanoprecipitates of Ag 2 Te, the room temperature second phase of AgCuTe, within the PbSe matrix. Meanwhile, a unique semi-coherent phase boundary is observed between the PbSe matrix and the Ag 2 Te nanoprecipitates. This semi-coherent phase interface effectively scatters low-frequency phonons while minimizing damage to carrier mobility. Additionally, the dynamic doping effect of Cu atoms from the decomposition of AgCuTe within the matrix further optimize the high-temperature thermoelectric performance. Overall, these factors significantly enhance the ZT across the whole temperature range. The ZT value of ≈1.5 indicates high competitiveness compared to the latest reported n-type PbSe materials, suggesting that these findings hold promise for advancing the development of efficient thermoelectric systems.
Endotaxial nanostructures can reduce lattice thermal conductivity through enhancing phonon scattering without affecting electrical transport, leading to a high thermoelectric performance. On the other hand, band engineering can enhance electrical transport by improving the Seebeck coefficient through valence band convergence and the resonance level. In this paper, the synergistic effect of band engineering and endotaxial nanostructures was implemented in SnTe thermoelectric materials by alloying with AgCuTe and doping with Indium. The positron annihilation lifetime spectra show that the vacancy concentration in SnTe was reduced after alloying with AgCuTe, which led to a decreasing hole concentration and improved carrier mobility. Additionally, the diffusion of Ag in the matrix during the preparation can facilitate valence band convergence. Therefore, the power factor of SnTe is greatly increased to 18 μW cm−1 K−2 at 800 K, which can be further increased to 21.4 μW cm−1 K−2 at 800 K after In doping due to resonance level formation. Meanwhile, Cu2Te endotaxial nanostructures also can be observed in the TEM image after SnTe alloying with AgCuTe. So, the lattice thermal conductivity significantly reduced to 0.93 W m−1 K −1 in In-doped and AgCuTe-alloyed SnTe. Finally, we obtain an enhanced ZT value of 1.14 in Sn1.02In0.01Te–1%AgCuTe at 800 K.
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