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Dynamics in Electronically Excited States of Diketopyrrolopyrrole–Thiophene Conjugated Polymer Thin Films
journal contribution
posted on 2021-03-09, 01:13 authored by Tobias Reiker, Zitong Liu, Carsten Winter, Nils Fabian Kleimeier, Deqing Zhang, Helmut ZachariasConjugated polymers
based on diketopyrrolopyrrole (DPP) are a versatile
basis for a variety of high-performance organic semiconductors. Two
conjugated polymers with DPP as an electron acceptor were prepared.
The DPP-based polymers were completed with quaterthiophene (PDPP4T)
as a donor in the first case; for the second donor–acceptor
conjugated polymer, two thiophenes have been replaced by thieno-thiophene
(PDPPTTT). Time-resolved two-photon photoemission spectroscopy is
employed to study the lifetimes of electronically excited states.
On the basis of the 2PPE spectra, we propose four unoccupied states
between the determined valence band maximum and LUMO of the thin films.
Electron kinetic energy resolved lifetimes range from a few 100 fs
up to 1.4 ps and show also a slower component around 10 ps. After
annealing, the ultrafast decay of the lowest-energy electrons in the
upper polaron state terminated after about 20 ps. This happens in
PDPPTTT for the high-energy level as well. We suggest that it is connected
with improved charge transport properties of the film.