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The Effect of α‐Branched Side Chains on the Structural and Opto‐Electronic Properties of Poly(Diketopyrrolopyrrole‐ alt ‐Terthiophene)
Author(s) -
Saes Bart W. H.,
Wienk Martijn M.,
Janssen René A. J.
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202001722
Subject(s) - terthiophene , alkyl , substituent , stacking , materials science , side chain , acceptor , photochemistry , polymer , band gap , crystallography , polymer chemistry , chemistry , stereochemistry , organic chemistry , optoelectronics , physics , composite material , condensed matter physics
Introducing solubilizing α‐branched alkyl chains on a poly(diketopyrrolopyrrole‐ alt ‐terthiophene) results in a dramatic change of the structural, optical, and electronic properties compared to the isomeric polymer carrying β‐branched alkyl side chains. When branched at the α‐position the alkyl substituent creates a steric hindrance that reduces the tendency of the polymer to π–π stack and endows the material with a much higher solubility in common organic solvents. The wider π–π stacking and reduced tendency to crystallize, evidenced from grazing‐incidence wide‐angle X‐ray scattering, result in a wider optical band gap in the solid state. In solar cells with a fullerene acceptor, the α‐branched isomer affords a higher open‐circuit voltage, but an overall lower power conversion efficiency as a result of a too well‐mixed nanomorphology. Due its reduced π–π stacking, the α‐branched isomer fluoresces and affords near‐infrared light‐emitting diodes emitting at 820 nm.