Highly Integrated and Flexible Thermoelectric Module Fabricated by Brush-Cast Doping of a Highly Aligned Carbon Nanotube Web

With increasing attention on flexible or wearable power-conversion devices, intensive research efforts have been devoted to flexible organic thermoelectric (TE) modules to replace the brittle inorganic ones. In this study, a highly integrated and flexible TE module with a novel device architecture based on a carbon nanotube (CNT) web is proposed. The pristine CNT web shows great electrical conductivity of 998.3 S cm–1 with the highly aligned structure, owing to the increased carrier mobility in the longitudinal direction. To realize optimal TE property, the pristine CNT web is alternately doped with p- and n-type carriers using FeCl3 and benzyl viologen, respectively, via a brush-casting method. Brush-casting is the simple doping process that enables large-area and continuous fabrication of flexible TE modules by allowing precise doping of the localized area without a shadow mask. Flexible TE modules were then fabricated by repeated brushing and folding of the CNT webs. Owing to the synergic effect of the highly integrated high-performance TE material (highly aligned CNT web) and the facile doping process (brush-casting), flexible TE modules consisting of 120 p–n couples over an area of 8 cm2 show a maximum power output of 5.3 μW for a temperature difference of 11.7 K.