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Polarization Dependence of Charge Conduction in Conjugated Polymer Films Investigated with Time- Resolved Terahertz Spectroscopy



Timothy J. Magnanelli, Sebastian Engmann, Jared K. Wahlstrand, John C. Stephenson, Lee J. Richter, Edwin J. Heilweil


We interrogate polarization anisotropy associated with charge conduction in films of the block co polymer PCDTPT, consisting of alternating cyclopenta dithiophene (donor) and thiadiazolo pyridine (acceptor) units with respect to sample morphology. Film preparation techniques facilitate alignment to heterogeneously etched substrates and are contrasted with randomized films and a liquid toluene dispersion. Room temperature Time-Domain Terahertz (TDS) and Time- Resolved Terahertz (TRTS) spectroscopic methods are employed to measure excitation-probe polarization dependencies on extracted carrier mobilities and generation efficiencies. Comparisons are made among films of different ordering, to the traditional photoconductive polymer poly-3-hexylthiophene (P3HT), isolated charge carriers, and between conduction signatures and metrics of their populations, i.e. transient absorption signals. Polarization anisotropy is observed from charge conduction predominantly along the backbone propagation direction of PCDTPT, supporting intramolecular charge transfer and significantly higher mobility than P3HT. PCDTPT is found to be unique for its strong conductivity when isolated in toluene dispersion. Quantitative comparisons yield a better understanding of polaron/free- charge relaxation and transfer mechanisms and illustrate dynamics among photoexcited charge carriers and their diffusion within different material morphologies.
Journal of Physical Chemistry C


ultrafast spectroscopy, terahertz, anisotropy, conjugated polymer, conductance
Created March 6, 2020, Updated June 10, 2020