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Aggregation in a High-Mobility n‑Type Low-Bandgap Copolymer with Implications on Semicrystalline Morphology
journal contribution
posted on 2012-11-07, 00:00 authored by Robert Steyrleuthner, Marcel Schubert, Ian Howard, Bastian Klaumünzer, Kristian Schilling, Zhihua Chen, Peter Saalfrank, Frédéric Laquai, Antonio Facchetti, Dieter NeherWe explore the photophysics of P(NDI2OD-T2), a high-mobility
and
air-stable n-type donor/acceptor polymer. Detailed steady-state UV–vis
and photoluminescence (PL) measurements on solutions of P(NDI2OD-T2)
reveal distinct signatures of aggregation. By performing quantum chemical
calculations, we can assign these spectral features to unaggregated
and stacked polymer chains. NMR measurements independently confirm
the aggregation phenomena of P(NDI2OD-T2) in solution. The detailed
analysis of the optical spectra shows that aggregation is a two-step
process with different types of aggregates, which we confirm by time-dependent
PL measurements. Analytical ultracentrifugation measurements suggest
that aggregation takes place within the single polymer chain upon
coiling. By transferring these results to thin P(NDI2OD-T2) films,
we can conclude that film formation is mainly governed by the chain
collapse, leading in general to a high aggregate content of ∼45%.
This process also inhibits the formation of amorphous and disordered
P(NDI2OD-T2) films.