LAUSR

High‐performance thermoelectric (TE) materials with great flexibility and stability are urgently needed to efficiently convert heat energy into electrical power. Recently, intrinsically crystalline, mechanically stable, and flexible inorganic TE fibers that show TE properties comparable to their bulk counterparts have been of interest to researchers. Despite remarkable progress in moving TE fibers toward room‐temperature TE conversion, the figure‐of‐merit value (ZT) and bending stability still need enhancement. Herein, interfacial‐engineering‐enhanced TE properties of micro–nano polycrystalline TE fibers fabricated by thermally drawing Bi2Te3‐based bulks in a glass‐fiber template are reported. The interfacial engineering effect comes from generating stress‐induced oriented nanocrystals to increase electrical conductivity and producing strain‐distorted interfaces to decrease thermal conductivity. The 4 µm‐diameter fibers achieve a 40% higher ZT (≈1.4 at 300 K) than their bulk counterparts and show a reversible bending radius of 50 µm, approaching the theoretical elastic limit. This fabrication strategy works for a wide range of inorganic TE materials and benefits the development of fiber‐based micro‐TE devices.