Simple, low-cost, water-processable n-type thermoelectric composite films from multiwall carbon nanotubes in polyvinylpyrrolidone

A significant challenge facing the advancement of organic thermoelectric devices is developing low-cost, solution-processable, air-stable, high performance n-type materials. In this work, we fabricate multiwall carbon nanotube (MWCNT)/polyvinylpyrrolidone (PVP) composite films by simply dispersing MWCNTs and PVP in water and spraying the resulting ink onto a substrate. We report a switch in the Seebeck coefficient of the MWCNTs from p-type to n-type behavior, even when the concentration of MWCNTs is as high as 90 wt.% in PVP. Additionally, we observe a great enhancement of the thermoelectric properties of the material when low quantities of polyethyleneimine (PEI) are added, reaching an n-type power factor of 1.98 μW m⁻¹ K⁻² for a composite film containing 30 wt.% MWCNTs in PVP and 0.05 PEI/MWCNT wt. ratio. Furthermore, the material shows good air and thermal stability. We believe that the low-cost of the components, the air-stability and the simplicity of the water-processable system make PVP/MWCNTs a potential n-type organic material for future thermoelectric applications.