CARBON NANOTUBE/GRAPHENE COMPOSITE SEMICONDUCTORS FOR HIGH PERFORMANCE POLYTHIOPHENE ORGANIC THIN FILM TRANSISTORS

Abstract

<p>Incorporating nanoparticles within a polymer to improve the mobility of the filmis one promising way of creating organic thin film transistors (OTFTs) with large mobilities that could be applicable in real world applications. Carbon nanotubes (CNTs)and graphene nanoplatelets (GNPs) are extensively studied for this application. In order to overcome their tendency to aggregate, a method for creating a stable dispersion within both the solution phase and the film is needed. Here an easy method is established for creating a stable dispersion of CNTs or GNPs within a polymer solution which results in excellent OTFT mobility.A non-percolating network of non-covalently functionalized single walled carbon nanotubes was embedded within poly[5,5’-bis(3-dodecyl-2-thienyl)-2,2’bithiophene](PQT-12) thin films for the purpose of enhancing field effect mobility in thin film transistors. The host polymer was used to stabilize the nanotubes in suspension by π orbital overlap caused by simple application of ultrasonication. The stable nanotube suspension was cast into two different device architectures both with excellent mobilities and on/off ratios. The effect of nanotube content on polymer interaction within suspension, film morphology and electrical properties are discussed. A CNT nanocomposite OTFT with enhanced mobility was also tested for applications in vapour sensing. A method is also presented for the creation of graphene nano-platelets (GNPs) for implementation in nano-composite films. Heat treatment of expandable graphite within a vacuum evaporation chamber yielded chemically pure GNPs of a few nanometer thickness. Exfoliating expandable graphite without heat treatment resulted in even higher concentrations but chemically impure GNPs. The material was non-covalently stabilizedwith PQT-12 in a similar method to CNTs and used to create OTFTs with enhanced mobility. The effect of heat treatment parameters and exfoliation conditions on GNP thickness, size and chemical purity are discussed, as well as effect of GNP content on mobility and on/off ratio.</p>