Molecular-weight dependence of interchain polaron delocalization and exciton bandwidth in high-mobility conjugated polymers
Chang, Jui-Fen; Clark, Jenny; Zhao, Ni; Sirringhaus, Henning; Breiby, Dag W.; Andreasen, Jens W.; Nielsen, Martin M.; Giles, Mark; Heeney, Martin; McCulloch, Iain
PHYSICAL REVIEW B
2006
Interchain interactions have a profound effect on the optical as well as charge transport properties of conjugated polymer thin films. In contrast to oligomeric model systems in solution-deposited polymer thin films the study of such effects is complicated by the complex microstructure. We present here a detailed study of interchain interaction effects on both charged polarons as well as neutral excitons in highly crystalline, high-mobility poly-3-hexylthiophene (P3HT) as a function of molecular weight. We find experimental evidence for reduced exciton bandwidth and increased polaron delocalization with increasing conjugation length and crystalline quality. From comparative studies of field-effect transistor characteristics, film morphology, and optical properties our study provides a microscopic understanding of the factors which limit the charge transport in P3HT to field-effect mobilities around 0.1 cm2 V s, and which will need to be addressed to improve mobility further. © 2006 The American Physical Society.