Chemical vapor deposition of high charge carrier mobility benzothiadiazole-based conjugated polymer thin films

Abstract

Low band gap benzothiadiazole–oligothiophene conjugated polymer thin films are prepared using oxidative chemical vapor deposition (oCVD). The synthesis and deposition occur simultaneously from the gas phase in oCVD; no solubilizing groups are attached to the benzothiadiazole or thienyl moieties, which allows molecular packing and charge carrier mobility to increase. Moreover, oCVD, which is a solventless, scalable and substrate independent approach, readily leads to the formation of dense and low surface roughness benzothiadiazole–oligothiophene conjugated polymer thin films. Polymerization yield, doping and conductivity of the benzothiadiazole–oligothiophene conjugated polymers are shown to be strongly influenced by the oxidant-to-monomer ratio. Interestingly, benzothiadiazole–oligothiophene conjugated polymer thin films synthesized by oCVD exhibit hole mobilities up to 4.0 cm² V⁻¹ s⁻¹, surpassing those of previously reported benzothiadiazole–oligothiophene conjugated polymers prepared by spin-coating, dip-coating and drop casting.