On the Origin of Polymer‐Specific Polarity Inversion in Heavily Doped Conjugated Polymers

ABSTRACT Polarity inversion of conjugated polymers, the switching of electrical polarity with increasing doping level, is considered a promising approach for achieving n ‐type polymeric materials. Previous studies have attempted to explain this phenomenon, particularly in terms of changes in the band structure at different doping levels. However, polarity inversion has only been observed in a limited number of conjugated polymers, and the reasons why it does not occur universally remain unclear. Herein, the origin of the polymer‐specific occurrence of polarity inversion is investigated through a systematic comparative analysis of a series of isoindigo‐based conjugated polymers doped with gold(III) chloride (AuCl 3 ). When the concentration of AuCl 3 in the polymer film exceeds a certain threshold, an n ‐type doping pathway involving chlorination of the conjugated backbone emerges, contributing to a transition from p ‐ to n ‐type behavior. The critical gold atomic density at which inversion occurs is estimated to be ∼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.