Ultrasonically induced liquid-phase exfoliation boosts excellent performance of Bi0.5Sb1.5Te3/PVDF thermoelectric films

Abstract

The morphology and surface state of Bi₂Te₃-based powders are vital for the performance of flexible printed Bi₂Te₃-based thermoelectric (TE) films. However, up to now, Bi₂Te₃-based powders used for preparing flexible printed Bi₂Te₃-based films are mostly prepared by the ball milling (BM) method, which easily introduces oxide layers on the surface, and then deteriorates the TE performance of the films. Herein, we have developed an ultrasonically induced liquid-phase exfoliation (UILPE) technology to prepare flaky Bi_0.5Sb_1.5Te₃ (BST) powders with a thinner surface oxide layer and a weak donor-like effect, which facilitates BST grain growth during the sintering process in the BST/polyvinylidene fluoride (PVDF) films, leading to an increase in the (000l) preferential orientation of BST grains and microstructure densification, thus enhancing electrical transport properties. The room-temperature power factor of the UILPE-BST/PVDF film reaches 2.27 mW m⁻¹ K⁻², 57% higher than that of the BM-BST/PVDF film. The cooling temperature difference of the single-leg device fabricated with the UILPE-BST/PVDF films is about 1.6 K, which is twice that of the device fabricated with the BM-BST/PVDF films. The large-scale planar device fabricated with UILPE-BST/PVDF films has generated a cooling zone which is 2.4 K below the ambient temperature, exhibiting excellent in-plane heat dissipation capability. This work demonstrates that UILPE is an effective method for the preparation of Bi₂Te₃-based powders with flake-like morphology and weak surface oxidation, providing an efficient approach for the fabrication of high-performance large-scale flexible TE film cooling devices.