Cellulose Fiber-Based Hierarchical Porous Bismuth Telluride for High-Performance Flexible and Tailorable Thermoelectrics

Porous modification is a general approach to endowing the rigid inorganic thermoelectric (TE) materials with considerable flexibility, however, by which the TE performances are severely sacrificed. Thus, there remains an ongoing struggle against the trade-off between TE properties and flexibility. Herein, we develop a novel strategy to combine Bi₂Te₃ thick film with ubiquitous cellulose fibers (CFs) via an unbalanced magnetron sputtering technique. Owing to the nano-micro hierarchical porous structures and the excellent resistance to crack propagation of the Bi₂Te₃/CF architectures, the obtained sample with a nominal Bi₂Te₃ deposition thickness of tens of micrometers exhibits excellent mechanically reliable flexibility, of which the bending deformation radius could be as small as a few millimeters. Furthermore, the Bi₂Te₃/CF with rational internal resistance and tailorable shapes and dimensions are successfully fabricated for practical use in TE devices. Enhanced Seebeck coefficients are observed in the Bi₂Te₃/CF as compared to the dense Bi₂Te₃ films, and the lattice thermal conductivity is remarkably reduced due to the strong phonon scattering effect. As a result, the TE figure of merit, ZT, is achieved as high as ∼0.38 at 473 K, which competes with the best flexible TEs and can be further improved by optimizing the carrier concentrations. We believe this developed technique not only opens up a new window to engineer flexible TE materials for practical applications but also promotes the robust development of the fields, such as paper-based flexible electronics and thin-film electronics.