Energetic Disorder in Doped P3HT: A Crucial Factor in Overcoming Coulomb Binding for Free Charge Generation

Doping of conjugated polymers, which offers precise control over energy levels and electrical conductivity, has faced setbacks because of its low doping efficiency. The majority of generated charge carriers become bound to dopant counterions through Coulomb interaction, leaving only a small fraction of free charges. Although the inherent energetic disorder in polymers may reduce the theoretically predicted Coulomb potential barrier and facilitate the release of bound charges to become mobile, this hypothesis has not been thoroughly quantified. In the present study, we investigate how the energetic disorder of conjugated polymers influences the release of free charges by reducing the activation energy, thus quantitatively assessing the effect of disorder on doping efficiency. Specifically, we examine the relationship between energetic disorder resulting from modifications of the crystallinity of poly(3-hexylthiophene-2,5-diyl) (P3HT) films, a model conjugated polymer, and the quantity of free charge and doping efficiency. A regiorandom P3HT film, characterized by low crystallinity and high static energetic disorder, exhibits an increased concentration of free charges. Consequently, its doping efficiency─defined as the ratio of free charges to total charges─is enhanced. We expect our findings to guide molecular design strategies and materials selection for the development of highly conductive doped-polymer materials.