The Synthesis and Characterization of Bisisoindigo Polymers with Electron-Deficient Comonomers for Applications in Organic Electronics

Abstract

Organic electronic materials can be used to make low cost, lightweight, and flexible electronic devices that are not possible with traditional inorganic semiconductors. New semiconductors with improved properties will be required to commercialize these devices. This thesis describes the synthesis of new conjugated polymers using the bisisoindigo structure coupled with electron-deficient thiophene dioxide or benzothiadiazole comonomers. These materials combine a core-expanded isoindigo structure with a polymer design that uses all electron-deficient comonomers. The synthesis of thiophene dioxide-containing polymers was attempted through both the synthesis of thiophene dioxide monomers and through post-polymerization modification. Bisisoindigo polymers with a benzothiadiazole comonomer were synthesized using the Stille reaction. The optoelectronic and physical properties of these polymers were characterised, and the materials were applied in organic field effect transistors (OFETs). Ambipolar device performance was observed in OFETs with hole and electron mobilities up to 4.0 x 10-3 cm2 V-1 s-1 and 1.4 x 10-3 cm2 V-1 s-1 respectively. Additionally, proper selection of OFET source and drain electrodes produced devices with improved threshold voltages by improving energy alignment between the polymer frontier molecular orbital energies and the contact metal.