2, Politecnico Di Milano, Milan, , Italy
3, University of Groningen, Groningen, , Netherlands
Solution-processable high mobility semiconductors, such as polymers and single walled carbon nanotubes (s-SWCNTs), offer a concrete opportunity to develop high-performance flexible electronics. The possibility to formulate stable dispersions of carbon nanotubes by non-covalent functionalization through conjugated polymers in a wide range of solvents allows the adoption of cheap solution-based deposition techniques like inkjet printing, suitable for low-cost and scalable fabrication processes. A deep knowledge of the charge transport mechanism in the printed networks is crucial in order to address an efficient processing and realize high-performance field-effect transistors. Unfortunately, it is still unclear how the polydispersity of the semiconducting nanotubes and their interaction with the functionalizing polymer affect charge injection and transport in random or semialigned networks.
In this work, we study High Pressure Carbon Monoxide (HiPCO) CNT networks wrapped by PCPDTBT (Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4 b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)]), demonstrating the possibility to tune the ambipolar behaviour in field-effect devices by varying the number of printing passes, yielding to effective charge mobilities as high as 20 cm2V −1s−1 for holes and 8 cm2V −1s−1 for electrons.
The different temperature dependence of mobility observed with variable printing passes - ranging from a bandlike to a thermally activated transport - denotes a not trivial interplay between polymer and nanotubes in defining the charge transport in the FET channel.
Such mutual interplay is further investigated via Charge Modulation Spectroscopy (CMS) measurements, providing a mean to singularly probe the charge transport properties of the different components in an operating device.