In-Plane Thermoelectric Properties of Flexible and Room-Temperature-Doped Carbon Nanotube Films

Soft materials with high power factors (PFs) and low thermal conductivity (κ) are critically important for integration of thermoelectric (TE) modules into flexible form factors for energy harvesting or cooling applications. Here, air stable p- and n-type multiwalled carbon nanotube films with high PFs (up to 521 μW/m K2) are reported, with n-type doping carried out in a facile two-step process. The maximum figures of merit (ZTs) of p-type and n-type CNTs are obtained as 0.019 and 0.015 at 300 K, respectively, with all three transport properties—Seebeck coefficient, electrical conductivity, and κ—measured in-plane, providing a more accurate ZT. Using time-domain thermoreflectance, we report a fast and non-contact measurement of κ without complex microfabrication or material processing. Moreover, there is no material mismatch between the p- and n-type legs of the TE module. Such materials have the potential for widespread applications in inexpensive and scalable wearable energy harvesting and localized heating/cooling.