Polymer-Specific Polarity Inversion in Heavily Doped Conjugated Polymers

Polarity inversion—the switching of electrical polarity with increasing doping level—is a promising route to n-type polymeric materials. Yet it has been observed in only a handful of conjugated polymers, and why it fails to occur universally has remained unclear. Here, we investigate the origin of this polymer-specific behavior through a systematic comparison of isoindigo-based conjugated polymers doped with gold(III) chloride (AuCl₃). Above a threshold AuCl₃ concentration, an n-type doping pathway involving chlorination of the conjugated backbone emerges, driving the p- to n-type transition. The critical gold atomic density for inversion is estimated at ∼0.4 atoms nm⁻³. Importantly, the dopant uptake capability of each polymer film depends on its chemical structure; this structural dependency determines whether the dopant concentration in the film can exceed the threshold required for polarity inversion, thereby accounting for the polymer-specific differences in polarity inversion behavior.