Visible and near infra-red ultrafast transient absorption (TA) spectroscopy shows that excited state coupling (both inter- and intra-chain) and exciton/polaron diffusion in poly(3-hexylthiophene) (P3HT) crystalline nanofibers (NF) is significantly altered upon the transition from suspension in a marginal solvent to solid state, and also by the solvent in which the crystallization takes place. Specific absorption features in the NF samples previously assigned to delocalized polaron and interchain exciton transitions allow direct assessment of charge-separation and mobility as a function of different solvent processing conditions. Comparison of TA spectral and kinetic features in nanofiber samples show that the primary mode of polaron (charge carrier) recombination switches from geminate to non-geminate on a power-dependent basis, reflecting the turn-on of exciton annihilation. Species-specific decay kinetics extracted by global and local analysis show distinct power law behavior in nanofibers, where the power law decay exponent is suggested as a metric for excited state mobility.

VIS/NIR transient absorption spectroscopy of conjugated polymer crystals

246th National Meeting (2013)

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