This report demonstrates an exciting new paradigm for thermoelectric energy conversion with both n- and p-type organic materials that possess mechanical flexibility, simple fabrication processes, and stability in air. In order to synthesize n-type samples with membranes and papers, carbon nanotubes were doped with both polyethyleneimine (PEI) and sodium borohydride (NaBH₄), showing excellent n-type characteristics with thermopower values as large as −80 μV K⁻¹. Thermoelectric modules made of both n- and p-type composites were fabricated to demonstrate thermoelectric voltage and power generation with one, two, and three p–n couples connected in series. The testing modules produced ∼6 mV thermoelectric voltage, with ∼25 nW generated power upon application of ∼22 °C temperature gradients. These promising results show that further work with many junctions connected in series would result in scalable organic p–n couple modules, which can generate power from temperature gradients or provide cooling for various electronic devices.

Carbon nanotubes (CNTs) were functionalized with polyethyleneimine (PEI) and made into composites with polyvinyl acetate (PVAc). CNTs were dispersed with different amounts of sodium dodecylbenzenesulfonate (SDBS) prior to the PEI functionalization. The resulting samples exhibit air-stable n-type characteristics with electrical conductivities as great as 1500 S/m and thermopowers as large as −100 µV/K. Electrical conductivity and thermopower were strongly affected by CNT dispersion, improving the properties with better dispersion with high concentrations of SDBS. This improvement is believed to be due to the increase in the number of tubes that are evenly coated with PEI in a better-dispersed sample. Increasing the amount of PEI relative to the other constituents positively affects thermopower but not conductivity. Air exposure reduces both thermopower and conductivity presumably due to oxygen doping (which makes CNTs p-type), but stable values were reached within seven days following sample fabrication.