A fast meniscus-guided coating for ultrahighly oriented
thin films
of a typical donor–acceptor π-conjugated polymer, poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno[3,2-b]thiophene)](PDPP-DTT) was realized. A coating speed higher than
100 mm/s, which was regarded as a Landau–Levich regime, was
applicable. The 2D order parameter (S
2) of the thin films changed by selecting the solvent and adjusting
the initial concentration of the solution, and the large elongated
rodlike preaggregates formed particularly in chlorobenzene contributed
to the high orientation in the solid film state, resulting in the
highest value of S
2 = 0.87. Focused on
the PDPP-DTT preaggregate formation in the solution, the SAXS analysis
was carried out to investigate the shape and size of the preaggregates.
The mechanism of the molecular orientation was discussed by taking
the preaggregates and the solution flow under the coating process
into account.