Solvent effect induced charge polarity switching from p- to n-type in polyaniline and carbon nanotube hybrid films with a high thermoelectric power factor

Understanding and controlling the polarity of organic materials is essential for a broad range of organic electronic applications. It is commonly assumed that the charge carrier type of organic hybrid materials is dominated by the charge carrier type of the two components, either holes or electrons. Here, through the Seebeck coefficient, we show that unusual mobile electrons contribute substantially to charge-carrier transport in hybrid films made of traditional p-type emeraldine base polyaniline (PANI) and p-type single-walled carbon nanotubes (SWCNTs). To the best of our knowledge, n-type PANI/SWCNT hybrid films with no dopants have never been reported yet. Ultraviolet-visible (UV-vis) and Fourier transform infrared (FTIR) spectra suggest that the ground-state electron-transfer from PANI to SWCNTs is mainly responsible for the n-type properties. The obtained n-type PANI-SWCNT hybrid films exhibit a high n-type thermoelectric power factor of 1031 μW m⁻¹ K⁻², which is among the highest values for PANI/SWCNT hybrid films reported in the literature. The results demonstrate a promising way for high-performance n-type thermoelectric materials, which may light the enthusiasm for understanding and controlling the charge polarity of organic materials.