Nanowire‐Bundled Grain Boundaries in Thermoelectric Materials

Abstract Improving thermoelectric material performance is essential for energy harvesting and solid‐state cooling applications. This study demonstrated a novel structure of Bi₂Te₃‐based thermoelectric materials with ZnO nanowire‐bundled grain boundaries, realized via atomic layer deposition (ALD) and subsequent spark plasma sintering (SPS). The ZnO nanowires formed at the interfaces due to the rearrangement of the ALD‐grown ZnO ultrathin layer over Bi_0.4Sb_1.6Te₃ powder, driven by localized heating during the SPS process and the anisotropic nature of ZnO. The nanowire‐bundled interfaces enhanced phonon scattering, thereby reducing lattice thermal conductivity while maintaining excellent electrical transport. This structural innovation achieved a high figure‐of‐merit, zT_max = 1.69 ± 0.09 at 373 K and an average zT of 1.55 over the range of 300–473 K. A thermoelectric module fabricated with 127 p–n pairs achieved a record‐high conversion efficiency of 6.57% at a temperature difference of 163 K. These findings highlight the potential of nanowire‐bundled interfaces to enhance the thermoelectric material performance and pave the way for scalable next‐generation energy conversion technologies.