Flexible thermoelectrics have attracted rapid growing interest for sustainable energy harvesting technology to power flexible electronics, such as wearable devices. The inorganic TE semiconductors are still the most competitive candidates for this technique due to their best efficiencies, although the pristine materials cannot be directly used as their intrinsic brittleness and rigidity. Therefore, great efforts from various interdisciplinary fields have been dedicated to searching solutions to improve the flexibility of conventional inorganic TE materials. However, there remains a struggling against the trade-off between the TE performance and flexibility.
Herein, we present a novel strategy to craft flexible thermoelectric nanocomposites through depositing M2C3 (M=Bi, Sb; C=Te, Se) alloys on the freestanding transparent single-walled carbon nanotubes (SWCNTs) scaffold. The nanocomposite reveals highly-ordered and nanoporous characteristics, which consists of (000l)-textured M2C3 nanograins grown on SWCNTs with good adhesion and perfect alignment along the M2C3<[endif]-->2[endif]-->0> and SWCNTs axis. The freestanding M2C3 nanocomposite exhibits remarkable mechanically reliable flexibility over hundreds bending circles, of which the bending deformation diameter could be as high as a few millimeters. Besides low-dimension and porosity effects, the highly-ordered microstructures give vital contributions to the excellent flexibility, especially at large bending curvatures. Large power factors of ~1600 to 1100 μW/mK2 are obtained for the Bi2Te3/SWCNTs nanocomposite from room temperature (RT) to 473 K. Owing to the high density of defects, such as Bi2Te3/SWCNTs interfaces, stacking faults and nanopores, the in-plane thermal conductivity is as low as 0.5 W/mK. Such high power factor and low thermal conductivity give rise to a TE figure of merit (ZT) of ~ 0.9 at room temperature (RT). Our approach opens up a new avenue to fabricate flexible TE materials with high performance, which could have promising applications in flexible electronics.