Naphthalene-diimide (NDI) based copolymers for organic field effect transistors (OFETS)

In the last decades, organic electronics have become a focus of intense research field. Recent studies have shown tremendous advantage of organic materials, among which the access to solution deposition strategies to produce flexible, low cost, electronic devices. Increasingly high mobility values were demonstrated for polymeric semiconductors; nevertheless, the development of new high mobility polymers, especially n-type, is still a primary task. Among n-type, copolymers incorporating naphthalene-diimide (NDI) acceptor unit represent a breakthrough, for its high mobility and stable operation. This thesis project focuses on the electrical characterization of NDI based copolymers with different donor and solubilizing side chains. In the first part of this work, backbone planarization through furan units is evaluated, in straight comparison with standard bithiophene units. In the second part, the effect of the insertion of fluorine atoms in an NDI-thiophene-phenyl-thiophene copolymer is investigated. It is shown that ink formulations and solution processing have a remarkable effect on charge transport: higher mobility values were achieved by inducing aggregation in solution, assisting self-assembling and leading to long-range ordered films where backbone orientation is controlled using directional deposition methods. Finally, a not trivial structure-properties correlation is observed in case of Furan based copolymers, pointing at the role of charge localization in the charge transport mechanism; differently, improved self-assembling properties of the fluorine substituted copolymer were found to assist the transport within the channel of a Field Effect Transistor. This thesis work, lasted nine months and was performed at the Center for Nano Science and Technology (CNST), of the Istituto Italiano di Tecnologia (IIT) under the supervision of Mario Caironi and Alessandro Luzio, respectively Team-Leader and PostDoc at IIT, and Professor Guglielmo Lanzani of Politecnico di Milano. The investigated polymers and related supported information were provided from the group of Michael Sommer (Freiburg, Germany).