posted on 2021-08-23, 16:05authored byGuangfeng Liu, Jie Liu, Andrew S. Dunn, Peter Nadazdy, Peter Siffalovic, Roland Resel, Mamatimin Abbas, Guillaume Wantz, Yves Henri Geerts
Directional crystallization
from the melt has been used as a tool
to grow parallel crystalline stripes of p- and n-type molecular semiconductors.
To start, the phase behavior of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT-C8): tetracyanoquinodimethane
(TCNQ) blends (molar ratio from 20:1 to 1:1) has been investigated
by variable-temperature X-ray diffraction, differential scanning calorimetry,
and polarized optical microscopy. The partial charge transfer between
the C8-BTBT-C8 donor and the TCNQ acceptor as a function of temperature
has been studied. Blends of 10:1 and 20:1 have been selected for directional
crystallization because they show similar thermotropic and phase behavior
comparable to that of pure C8-BTBT-C8. Directional crystallization
results suggest that moderate cooling rates (6 and 12 °C min–1) leads to a digitated growth mode that gives rise
to parallel crystalline stripes of C8-BTBT-C8 and C8-BTBT-C8-TCNQ
charge-transfer complexes (C8-BTBT-C8-TCNQ CT), as confirmed by confocal
Raman imaging. X-ray diffraction reveals high preferential orientation
and good in-plane alignment for both C8-BTBT-C8 and C8-BTBT-C8-TCNQ
CT crystallites.