Robust, Flexible Thermoelectric Film for Energy Harvesting by a Simple and Eco-Friendly Method.

As for the self-supporting composite films, it is significant to develop a structural design that allows for excellent flexibility while reducing the negative effect on thermoelectric (TE) properties. Herein, a robust, flexible TE film was fabricated by in situ chemical transformation and vacuum-assisted filtration without any organic solvents involved. The performance of the films was further optimized by adjusting the Ag/Te ratio and post-treatment methods. Owing to the semi-interpenetrating nanonetwork structure formed by AgxTe nanowires and bacterial cellulose, the obtained TE film displayed a high tensile strength of ∼78.4 MPa and a high power factor of 48.9 µW m-1 K-2 at room temperature. A slight electrical conductivity decrement of the TE film in flexible test (∼2% after 1000 bending cycles) indicates an excellent flexibility. Finally, a TE bracelet was assembled to harvest body heat energy, and a steady current of ∼2.7 µA was generated when worn on the wrist indoors. This work provides a reference for the structural design and practical application of flexible TE films.

Ultrahigh Power Factor of Ternary Composites with Abundant Se Nanowires for Thermoelectric Application.

In this work, ultrahigh-performance single-walled carbon nanotube (SWCNT)/Se nanowire (NW)/poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) ternary thermoelectric (TE) nanocomposite films are successfully designed by rational design of CNT/Se/PEDOT:PSS ternary nanocomposites. The addition of CNTs apparently improves the electrical conductivity of composite films, resulting in a relatively huge growth of the power factor. The PEDOT:PSS interface layers uniformly attach on both sides of the Se NWs and CNTs effectively, forming a tightly interleaving and interconnected three-dimensional network. As a consequence, a maximum power factor of 863.83 µW/(m·K2) has been achieved for the sample containing 26 wt % CNTs at 434 K. Ultimately, a flexible TE generator prototype consisting of 5-unit freestanding composite film strips is fabricated using the optimized composite films, which can generate a maximum output power of 206.8 nW at a temperature gradient of 44.7 K. Therefore, the present work has a further potential to be used for the flexible polymer/carbon TE nanocomposite films and devices.

Flexible Thermoelectric Films Based on Bi2Te3 Nanosheets and Carbon Nanotube Network with High n-Type Performance.

Flexible thermoelectric materials and devices have gained wide attention due to their capability to stably and directly convert body heat or industrial waste heat into electric energy. Many research and synthetic methods of flexible high-performance p-type thermoelectric materials have made great progress. However, their counterpart flexible n-type organic thermoelectric materials are seldom studied due to the complex synthesis of conductive polymer and poor stability of n-type materials. In this work, bismuth tellurium (Bi2Te3) nanosheets are in situ grown on single-walled carbon nanotubes (SWCNTs) assisted by poly(vinylpyrrolidone) (PVP). A series of flexible SWCNTs@Bi2Te3 composite films on poly(vinylidene fluoride) (PVDF) membranes are obtained by vacuum-assisted filtration. The high electrical conductivity of 253.9 S/cm, and a corresponding power factor (PF) of 57.8 µW/m·K2 is obtained at 386 K for SWCNTs@Bi2Te3-0.8 film. Moreover, high electrical conductivity retention of 90% can be maintained after a 300-cycle bending test and no obvious attenuation can be detected after being stored in an Ar atmosphere for 9 months, which exhibits good flexibility and excellent stability of the SWCNTs@Bi2Te3 composite films. This work shows a convenient method to fabricate n-type and flexible thermoelectric composite film and further promotes the practical application of n-type flexible thermoelectric materials.