Constructing Anti‐barrier Layers to Eliminate Grain Boundary Resistivity for Enhancing Thermoelectric Properties of Polycrystalline Mg ₃ (Sb, Bi) ₂

Abstract In heavily‐doped polycrystalline semiconductors, charge carrier transport at reduced temperatures is dominated by ionization or grain boundary scattering, which degrades carrier mobility and consequently constrains overall thermoelectric performance. The strategic implementation of anti‐barrier layers at metal‐semiconductor interfaces offers a promising solution to enhance electronic drift motion, thereby alleviating grain boundary resistivity. In this work, W nanoparticles are rationally induced in polycrystalline n ‐type Mg 3 (Sb, Bi) 2 by leveraging the electron work function principle. W serves as an efficient electron transport medium, enabling seamless charge carrier migration across interfaces, that significantly enhances electron mobility, yielding an exceptional power factor of 24 µW cm −1 K −2 in the temperature range of 473–573 K. Furthermore, the incorporation of W nanoparticles induces substantial phonon scattering, resulting in low lattice thermal conductivity of 0.58 W m −1 K −1 at 773 K. These synergistic effects lead to substantial enhancement of zT across a broad temperature spectrum, with an impressive average zT of 1.34 throughout the 323–773 K range. The exceptional zT ave values translate to a predicted single‐leg device conversion efficiency of 15.4% with Δ T = 450 K. This study presents a successful and universal composite strategy for designing metal‐semiconductor contacts with anti‐barrier potential, aiming to enhance the thermoelectric properties.