Counter-ion exchange as a tool to modulate polaron delocalization and temperature stability of doped polymeric semiconductors

The design of high-performance doped semiconductors requires an understanding of the coupling between ionic and electronic carriers. We utilize a method of counter-ion exchange using the polymeric semiconductor PBTTT-C₁₄ to deconvolute the effects of ionic/polaronic interactions with the electrical properties of doped semiconducting polymers. Here, the dopant NOPF₆ is used followed by the exchange of counter-ions ranging from 5 to 11 Å in diameter. The long-range order of the polymeric crystallites is not affected with this exchange process while effectively modifying the counter-ion distance to the charge carrier. Doped films achieve electrical conductivity of 320 S/cm and is not sensitive to an increased ion-polaron distance. We posit that other factors dominate the electrical properties at a device scale, such as the morphology and presence of domain boundaries. Interestingly, the temperature stability of the doped film can be drastically improved with the use of counter-ions containing less labile bonds. This platform serves as a unique way to retain the morphology of polymeric thin films while studying charge interactions at the local scale.