The effect of surfactants on electrohydrodynamic jet printing and the performance of organic field-effect transistors

In this article, we report on the direct writing of multi-walled carbon nanotube (MWCNT) composite inks based on three different surfactants via the electrohydrodynamic (EHD) jet printing technique. All three surfactants, including two types of polymeric surfactants and an ionic surfactant, successfully dispersed the MWCNTs in the ink medium. Although the MWCNT composite with the ionic surfactant could not be printed by the EHD process, the MWCNT composites with polymeric surfactants could be successfully printed using this technique. Furthermore, the printed lines exhibited different electrical and electronic characteristics, depending on the type of surfactant. A large amount of the poly(4-styrenesulfonic acid) (PSS) surfactant was required to disperse the MWCNTs in ethanol, whereas a smaller amount of polymeric Triton X-100 (TX100) was required to obtain a MWCNT composite suspension in distilled water, and therefore, the printed lines of the latter provided higher conductivities. In addition, the surface potential and charge carrier injection properties of the EHD-printed MWCNT lines depended on the type of surfactant in the MWCNT composite. Finally, organic field-effect transistors (OFETs) employing source/drain electrodes based on MWCNT/surfactant composites exhibited opposing electrical characteristics depending on the type of surfactant. The MWCNT/PSS lines showed excellent electrical performance when used as electrodes in p-type OFETs, whereas the MWCNT/TX100 lines exhibited excellent performance when used as electrodes in n-type OFETs.