Dopant-Induced Energetic Disorder in Conjugated Polymers: Determinant Roles of Polymer–Dopant Distance and Composite Electronic Structures

Dopants induce energetic disorder in conjugated polymers and can adversely impact charge transport. In this work, we studied the dopant's impact on the density of states (DOS) of crystalline and amorphous domains in poly(3-hexylthiophene) (P3HT). We measured Seebeck coefficient–conductivity curves in films of doped regioregular and regiorandom P3HT and their blends. These curves were simulated by using a generalized Gaussian disorder model. We also characterized the undoped and doped films using X-ray scattering and near-infrared spectroscopy. Based on our studies, we conclude that the separation distance between the carriers on the polymer and the dopant anion is a crucial parameter that impacts dopant-induced disorder and depends on the morphology of the material. We also show that DOS distributions for both crystalline and amorphous regions are needed to understand charge transport over a broad range of doping levels. Our studies show that amorphous domains suffer a larger dopant-induced disorder but still contribute to charge transport. Thus, it is important to design dopants that minimize the dopant-induced disorder in both the crystalline and amorphous domains.