Bead-on-a-string PbTe nanowires stabilize high-mobility n-type transport for mid-temperature thermoelectrics

PbTe is a benchmark mid-temperature material, yet its n-type performance remains constrained by low conduction-band degeneracy, impurity-induced mobility degradation and deleterious interfacial carrier scattering. Here, a solution-processable solvothermal injection strategy is reported to construct Bi-doped PbTe bead-on-a-string nanowires that integrate Bi-induced band-edge reconstruction with ordered couple phonon scattering. Nonclassical nucleation and oriented attachment produced phase-pure polycrystalline nanowires with an aspect ratio of approximately 100, uniform Bi incorporation and near-coherent nanodomains after spark plasma sintering. Density functional theory, optical absorption spectroscopy, femtosecond transient absorption and local-structure analyses revealed that Bi doping introduced resonant features near the band edge, narrowed the optical bandgap from 0.21 to 0.11 eV, accelerated carrier relaxation and reorganized the Pb-Te/Bi coordination environment. In the optimized Pb_0.98Bi_0.02Te, the carrier concentration reached 1.2 × 10¹⁹ cm^-3 while the Hall mobility remained as high as 905 cm² V^-1 s^-1 at 300 K, yielding a peak power factor of 30.2 μW cm^-1 K^-2 at 373 K. Meanwhile, ordered grain boundaries and coherent nanodomains reduce the lattice thermal conductivity to 0.75 W m^-1 K^-1 at 823 K. Consequently, Pb_0.98Bi_0.02Te achieved a peak thermoelectric figure of merit (zT) of approximately 1.3 at 723 K, maintained zT > 1 from 500 to 823 K, and delivered an average zT of 0.59 over 300-623 K. This band-interface co-design strategy provides a generalizable route for coupled optimization in n-type PbTe and offers a solution-processable platform for mid-temperature waste-heat recovery.