Boosting thermoelectric performance of carbon nanotube-based materials and devices by radical-containing molecules

Abstract

Organic thermoelectric materials are attracting growing research interests as they are seen as environmentally friendly functional materials with tremendous potential for use in waste heat recovery. The absence of low electrical conductivity has somewhat slowed down the development of most organic thermoelectric materials. Blending the organic semiconductor materials with single walled carbon nanotube (SWCNT) has become an extremely important strategy to boost the conductivity and thermoelectric performance of organic materials. Therefore, in this paper, novel arylimide compounds NDI-2 T and PDI-2 T with radical substituents of TEMPO are designed from molecular engineering, complexing with SWCNT as organic thermoelectric composites. Compared with the non-radical compounds of NDI-2TP and PDI-2TP, the introduction of radicals in NDI-2 T and PDI-2 T can significantly improve the performance of the thermoelectric composites. Radical-containing composite films exhibit outstanding thermoelectric performance compared to the film based on non-radical molecules. The best power factor reaching 278.2 ± 8.2 μW m−1 K−2 for p-type films, while n-type films can attain 64.6 ± 13.5 μW m−1 K−2. The NDI-2 T/SWCNT devices can obtain a maximum output power of 0.94 μW when the temperature gradient is around 60 K, which is 5 times higher of NDI-2TP/SWCNT device. The significantly enhanced thermoelectric performance of the composite film based on organic radical compounds is resulted from the increased interactions between the radical compounds and SWCNTs and modulated carrier concentrations in the composite films. This work provides a new direction for the design of high-performance thermoelectric materials and devices.