1 research outputs found
Structure Influence on Charge Transport in Naphthalenediimide–Thiophene Copolymers
Reported here is a characterization
of a series of NDI–thiophene
copolymers with one, two, three, and four thiophene units synthesized
using Stille polycondensation of dibromo-naphthalene diimide and the
trimethylstannylthiophene monomers. The effect of extension of the
thiophene donor group is studied in terms of structure-charge transport
correlation. The influence of side chains located on the thiophene
units of copolymers with two and four thiophene units per monomer
is also investigated. Charge transport of both signs is studied experimentally
in field-effect transistors. Microstructural data obtained by near-edge
X-ray absorption fine structure (NEXAFS) and grazing incidence wide-angle
X-ray scattering (GIWAXS) is supported by AFM topography scans. Ultraviolet
photoelectron spectroscopy (UPS) and UV–vis spectroscopy data
are employed in the measurement of energy levels, and changes with
annealing temperature are also discussed. Most of the polymers reach
excellent electron and hole mobility with one copolymer (NDI-T4) exhibiting
an especially balanced ambipolar charge transport of 0.03 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>. An odd–even
effect in hole mobility is observed with higher values for polymers
with an even number of thiophene units. The reported findings indicate
that the final charge transport properties are a result of the interplay
of many factors, including crystallinity, planarity and linearity
of chain, spacing between acceptor units and packing of solubilizing branched side
chains