posted on 2020-03-18, 18:06authored byRaj Pandya, Richard Y. S. Chen, Qifei Gu, Jeffrey Gorman, Florian Auras, Jooyoung Sung, Richard Friend, Philipp Kukura, Christoph Schnedermann, Akshay Rao
We present a statistical
analysis of femtosecond transient absorption
microscopy applied to four different organic semiconductor thin films
based on perylene-diimide (PDI). By achieving a temporal resolution
of 12 fs with simultaneous sub-10 nm spatial precision, we directly
probe the underlying exciton transport characteristics within 3 ps
after photoexcitation free of model assumptions. Our study reveals
sub-picosecond coherent exciton transport (12–45 cm2 s–1) followed by a diffusive phase of exciton
transport (3–17 cm2 s–1). A comparison
between the different films suggests that the exciton transport in
the studied materials is intricately linked to their nanoscale morphology,
with PDI films that form large crystalline domains exhibiting the
largest diffusion coefficients and transport lengths. Our study demonstrates
the advantages of directly studying ultrafast transport properties
at the nanometer length scale and highlights the need to examine nanoscale
morphology when investigating exciton transport in organic as well
as inorganic semiconductors.