Construction of Flexible, Self-Supporting, and In-Plane Anisotropic PEDOT:PSS Thermoelectric Films via the Wet-Winding Approach

In-plane anisotropic thermoelectric (TE) films with TE properties optimized in preferred orientation can establish a good match between the direction with optimal property for materials and the direction of temperature difference. Based on the highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) fibers previously produced via wet-spinning, in this work, we further developed flexible and self-supporting PEDOT:PSS thick films with evident TE property anisotropy by a wet-winding approach. The as-obtained films were mainly composed of orderly tiled PEDOT:PSS fibers, thus possessing intrinsically highly oriented and ordered PEDOT:PSS chain packing. On the basis of their Raman spectra, a large portion of expanded chain conformation of quinoids was also evidenced, which thereby greatly facilitated intra-chain charge transport along the PEDOT-conjugated backbones. As a result, the as-obtained anisotropic films delivered a power factor of up to 35.8 mu W m-1 K-2, which was 2.4 times that of the isotropic counterpart prepared via drop-casting and also superior over that of many binary inorganic-organic TE composite films reported previously. Besides, the fiber-wound PEDOT:PSS films also showed high mechanical strength and excellent stability upon cyclic bending. With five stripes of the anisotropic films, a prototype TE generator was further assembled, for which a good match between the optimal property direction and temperature difference direction was achieved. This work may pave the way for the development of anisotropic TE materials and devices that can be of interest for the design of next-generation wearable electronics and energy harvesters.