Influence of Energetic Disorder in Doped Conjugated Polymers on Doping Efficiency and Charge Transport

Doping in conjugated polymers has recently gained attention because of its ability to freely control electrical conductivity and energy levels. Sophisticated engineering approaches and state-of-the-art doping techniques aimed at improving performance have enabled both <i>p</i>-type and <i>n</i>-type doped conjugated polymers to achieve conductivities of over 1000 S/cm. Despite the progress in the electrical conductivity, the influence of the fundamental physical quantities in conjugated polymers on the doping process has not yet been sufficiently investigated. Conjugated polymers exhibit high degree of structural disorder (including crystallinity, chain conformation, chain configuration, orientation, and impurities), which leads to substantial energetic disorder, manifesting as a widened distribution of the density of states. Moreover, structural disorder induced by the incorporation of a significant amount of dopants and Coulomb interactions between charged particles have a potential to further increase energetic disorder in doped polymer films. In this talk, I will present research findings on the conflicting effects of the energetic disorder in conjugated polymers on the charge generation and charge transport processes during doping. In the first part, I will discuss the effect of energetic disorder in conjugated polymers on the generation of free charges and doping efficiency during the doping process. Specifically, I will present that increased energetic disorder can activate bound charges into free charges and enhance doping efficiency, which were observed in poly(3-hexylthiophene-2,5-diyl) (P3HT) films of exhibiting different energetic disorder by modulating crystallinity. In the second part, I will discuss the excellent transport properties that can arise from the extremely suppressed energetic disorder in chemically doped systems, facilitated by the torsion-free main chain structure of indacenodithiophene-co-benzothiadiazole (IDTBT). Our results suggest that adequate consideration of conflicting perspectives on energetic disorder, and finding a balance between them, can be critical to enhance the final electrical properties of doped conjugated polymers.