Preparation and Synthesis of Conjugated Polymer Nanoparticles in Aqueous Dispersion Via Miniemulsion Polymerisation for Organic Field Effect Transistors

Abstract

Conjugated polymer semiconductors are a promising class of material for future electronic devices due to the easy tunability of their chemical properties through molecular design enabling charge transport, optical properties, mechanical flexibility, and solution-processability into thin films. These materials are excellent candidates for a variety of emerging organic electronic applications such as organic field-effect transistors (OFETs), organic photovoltaic cells (OPV) and organic light-emitting diodes (OLEDs). Conventional methods to obtain functional thin films for devices are highly dependent on halogenated solvents that are commonly highly volatile and harmful to health. In order to realize its full commercial potential, it is crucial to develop a solution-processing method that is environmentally friendly. Synthetic approaches to tune the molecular structure of the polymer can improve solubility and processability with "greener" solvents, but additional synthetic steps introduce further complexity to the overall device fabrication procedure. The most recent approach to minimise the use of organic solvents in device fabrication is the use of colloidal systems (organic phase dispersed in aqueous media). Conjugated polymer nanoparticles (CPNs) can be prepared from preformed polymers or from a mixture of monomers that would react after the particle formation to synthesise the desired polymer via microemulsion or miniemulsion. However, the fabrication of electronic devices using CPNs from preformed polymers led to low performance OPVs and OFETs due to the nature of the surfactant used to prepare the CPNs, which can act as charge-carrier trap. The first OFET with high mobility using CPNs prepared by miniemulsion was reported in 2015. In this thesis, a novel approach that combines the synthesis of the polymer in the core of the nanoparticles (miniemulsion polymerisation) to obtain semiconductor polymers in high loadings dispersed in aqueous media, and the processability of CPNs to obtain thin film into substrates to fabricate OFETs, is described. P3HT has been widely studied as reference material in organic electronics. The synthesis and characterisation of P3HT CPNs for its application into low-voltage devices using a recently reported thienyl MIDA boronate ester will be discussed in the third chapter. In further chapters will be discussed the synthesis and characterisation of IDT-BT and DPPT-BT CPNs. The surfactant removal will be also discussed, towards the improvement of the CPNs in electronic devices. Finally in the fifth chapter will be discussed the challenge of depositing the CPNs onto substrates and the post-deposition treatments to remove the remaining surfactant in the semiconductor layer for OFETs fabrication.

Date of Award	1 Aug 2020
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michael Turner (Supervisor) & Michael Ingleson (Supervisor)