Tuning Orientational Order of Highly Aggregating P(NDI2OD‑T2) by Solvent Vapor Annealing and Blade Coating
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posted on 2018-12-17, 15:49 authored by Daniel Trefz, Yannic M. Gross, Carsten Dingler, Roman Tkachov, Amer Hamidi-Sakr, Anton Kiriy, Christopher R. McNeill, Martin Brinkmann, Sabine LudwigsIts
inherent strong tendency to aggregate in solution is used in
the following study to prepare highly anisotropic films of the n-type
copolymer poly{[N,N′-bis(2-octyldodecyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)). Solvent vapor annealing (SVA) allows to tune the size
of oriented domains in spherulite-like superstructures with alignment
up to several hundreds of micrometers. Blade coating (BC), on the
other hand, yields square centimeter large perfectly oriented films
with dichroic ratios of 18 and charge transport anisotropies up to
14. On the nanometer scale highly oriented fibers of form I are visible
in the oriented areas with the fiber long axis parallel to the chain
direction. We give experimental evidence that structure formation
does involve liquid crystal (LC) mesophases at high solution concentrations
which are frozen upon solvent removal. Temperature post-treatment
of the oriented films gives, on the other hand, evidence for a classical
semicrystalline nature of this polymer with spherulites consisting
of crystalline and amorphous domains. These findings point to a different
growth behavior than previously discussed for the well-studied p-type
polymer poly(3-hexylthiophene) and suggests that the definition and
distinction between liquid-crystalline and semicrystalline nature
might need to be reassessed.
