Understanding the influence of polymer molecular weight on the morphology, photophysics, and photovoltaic properties of polymer solar cells is central to further advances in the design, processing, performance and optimization...
An easy and novel synthetic concept for building intrinsically stretchable and elastic semiconducting polymers is designed in this study, in which a conjugated rod−coil block copolymer with a rigid poly(9,9-di-n-octyl-2,7-fluorene) (PFO)conjugated rod and soft poly(isoprene) (PI) coils were utilized as model compounds for demonstration. By combining a coupling reaction for a conjugated block and reversible addition− fragmentation chain transfer for a functional soft block, a simplified synthetic procedure for semiconducting polymers incorporating different lengths of the PI moiety, PF-b-(PI) x (x = 0.9, 1.2, and 1.8), was thus developed. Upon intense mechanical stress, both their stretching and rubbery properties associated with highly stable luminescence were demonstrated because of the molecular-level rigid island structure of self-assembly nanostructured PF domains bridged by PI segments. In particular, the PF-b-PI 1.8 thin film could not only be stretched by up to 150% without forming any cracks but also be employed for the fabrication of free-standing films with both excellent elasticity and tough mechanical strength after cross-linking, showing high stability in quantum yield over 1000 stretching cycles at 150% strain.
Electron transport is critical to the use of n-type semiconducting
polymers in diverse electronic and optoelectronic devices. Herein,
we combine measurements of field-effect electron mobility and bulk
electron mobility with thin-film microstructure characterization to
elucidate the polymer chain length dependence of electron transport
in n-type semiconducting polymers, exemplified by a naphthalene diimide-biselenophene
copolymer, PNDIBS. Both bulk electron mobility measured by the space–charge
limited current method and field-effect electron mobility of PNDIBS
and other n-type semiconducting copolymers exhibit a peak at a critical
degree of polymerization (DPc) of 45–60 repeat units.
The decreased electron mobility below DPc is shown to originate
from reduced intercrystallite connectivity while above DPc, intrachain twisting/folding, interchain entanglements, and intracrystallite
limitations dominate electron transport. These findings provide a
unified picture of the effects of polymer molecular weight on electron
transport in naphthalene diimide-based polymers and offer a more quantitative
design rule for high-mobility n-type polymers with donor–acceptor
architecture.
A new approach to improve charge transport and solid-state morphology in a semiconducting polymer was developed through metal coordination without disruption of the π-conjugation.
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