Synthesis of semiconducting polymers for use in organic electronics

A series of novel semiconducting co-polymers based on known, fused aromatic monomers (dibenzosilole, dithienosilole and dithienopyrrole) were synthesized for use in organic field effect transistor (OFET) devices. The fused monomers were copolymerized with triarylamine and thienothiophene units to give a series of six donor polymers. Their electronic energy levels were probed by UV-Vis and photoelectron spectroscopy, and predictions regarding their performance were drawn from this information. Two polymers were tested in OFETs and conclusions were made concerning the relationship between structure and performance. Four donor-acceptor type polymers were synthesized using dithienopyrrole as the electron rich unit. This monomer was copolymerized with benzothiadiazole, difluorobenzothiadiazole, thienopyrrolodione and 1,1’-bithienopyrrolodione. These low band gap polymers were tested as the donor polymer in polymer:fullerene BHJ devices. A novel monomer with long branched alkyl substituents, based on the extended fused-ring system indacenodithiophene (IDT), was synthesized. The nitrogen analogue of this monomer (NIDT) was of interest as its performance could be compared to the carbon and silicon versions of IDT. A route to NIDT was devised and then it was polymerized with four electron poor monomers. The energy levels were estimated by UV-Vis and photoelectron spectroscopy, followed by testing of the materials in OFET and OPV devices. Those with the lowest lying HOMO levels performed best in OPVs. Another series of NIDT containing polymers were synthesized, designed specifically for use in OFET devices. The aim was to produce polymers with highly planar backbones which would form ordered domains and enhance hole transport. An NIDT monomer was synthesized with linear hexadecyl substituents in order to improve π-stacking. The linear NIDT monomer was then copolymerized with thiophene, thienothiophene, thienopyrrolodione and diketopyrrolopyrrole. It was found that the diketopyrrolopyrrole containing polymer, performed best in OFETs and the molecular weight played a large role in how a polymer performed.