1 research outputs found
Morphology Control of Nanofibril Donor–Acceptor Heterojunction To Achieve High Photoconductivity: Exploration of New Molecular Design Rule
Donor–acceptor
nanofibril composites have been fabricated,
and the dependence of their photocurrent response on the structure
and morphology of the donor part has been systematically investigated.
The nanofibril composites were composed of template nanofibers, assembled
from an electron acceptor molecule, perylene tetracarboxylic diimide
(PTCDI), onto which (through drop-casting) various electron donor
molecules (<b>D1</b>–<b>D4</b>) were coated. The
donor molecules have the same π-conjugated core, but different
side groups. Due to the different side groups, the four donor molecules
showed distinctly different propensity for intermolecular aggregation,
with <b>D1</b>–<b>D3</b> forming segregated phases,
while <b>D4</b> prefers homogeneous molecular distribution within
the film. It was found that the nanofibril composites with <b>D4</b> exhibit the highest photocurrent, whereas those with aggregation-prone <b>D1</b>–<b>D3</b> exhibited much lower photocurrent
under the same illumination condition. Solvent annealing is found
to further enhance the aggregation of <b>D1</b>–<b>D3</b> but facilitate more uniform molecular distribution of <b>D4</b> molecules. As a result, the photocurrent response of PTCDI
fibers coated with <b>D1</b>–<b>D3</b> decreased
after vapor annealing, whereas those coated with <b>D4</b> further
increased. The detrimental effect of the aggregation of donor molecules
on the PTCDI fiber is likely due to the enhanced local electrical
field built up by the high charge density around the aggregate–nanofiber
interface, which hinders the charge separation of the photogenerated
electron–hole pair. The results reported in this study give
further insight into the molecular structural effect on photoconductivity
of hybrid materials, particularly those based on donor–acceptor
composites or interfaces, and provide new molecular design rules and
material processing guidelines to achieve high photoconductivity