Organic semiconducting polymers represent cost effective, solution processable materials that have proven valuable for a variety of photovoltaic and optoelectronic applications. However, the inherent morphological heterogeneity of these materials complicates traditional spectroscopic characterization resulting in an incomplete understanding of the excited state dynamics. We use transient absorption microscopy (TAM), which couples femtosecond temporal and sub-micron spatial resolution to directly measure excited state diffusion in polymer thin films while reducing the effects of microscale morphological heterogeneity. Using TAM, we observe unprecedented rates of diffusivity in poly[N-9’’-hepta-decanyl-2,7-carbazole-alt-5,5-(4’,7’-di-2-thienyl-2’,1’,3’-benzothiadiazole)] (PCDTBT) averaging 0.53 cm<sup>2</sup>/s. Orientation of the polymers using microscopically grooved substrates results in highly anisotropic transport with exciton diffusion in the direction of alignment increased by a factor of 10 relative to the drop-cast films. We show that due to polymer orientation exciton diffusion can be as high as 7.0 cm<sup>2</sup>/s. Further understanding of how polymer orientation effects exciton diffusion on length scales relevant to charge transfer will advance the development of next generation organic optoelectronic and photovoltaic devices.

Direct imaging of ultrafast exciton transport in PCDTBT thin films by transient absorption microscopy

255th National Meeting (2018)

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