Effect of Regioregularity on Charge Transport and Structural and Excitonic Coherence in Poly(3-hexylthiophene) Nanowires

摘要

This study explores the role of very small changes in poly(3-hexylthiophene-2,5-diyl) (P3HT) regioregularity on the physical and electronic properties of P3HT nanowires. Due to a high level of synthetic control, we are able to isolate the effects of regioregularity from those of polymer molecular weight and dispersity for the first time. A series of P3HTs with regioregularities from 96 to 99%, similar molecular weights, and low dispersities are synthesized. The charge transport properties of these polymers, along with a Soxhlet extracted 93% regioregular P3HT purchased from Rieke metals, are investigated in both thin film and nanowire transistors. The resulting structural characteristics are examined by atomic force microscopy and X-ray diffraction, and the optical characteristics are explored by UV-vis absorption. It is found that increasing the P3HT regioregularity results in improved charge transport characteristics, with an increase in mobility by a factor of 4 for the regioregularities examined. The increased mobility is shown to reflect increasing structural coherence lengths in the (010) direction, as well as improved J-aggregate characteristics due to greater planarity and reduced numbers of defect sites along the polymer nanowires. Overall, this study serves to emphasize the importance of determining and reporting even small changes in polymer regioregularity.