Abstract
Backbone rigidity of conjugated polymers is suggested to play an essential role in realizing high-mobility transistors through the efficient interconnection of crystalline domains by tie molecules as discussed for the recently-developed donor-acceptor (DA)-type copolymers. However, no studies have directly observed interdomain hopping in these DA copolymers. Here, highly-efficient interdomain charge transport is observed in two typical high-mobility DA copolymers from the microscopic observation of charge carriers using field-induced electron spin resonance (ESR) spectroscopy. The in-plane ESR signal exhibits a clear motional narrowing effect associated with the carrier motion across the boundaries. The activation energy of the interdomain charge motion is as low as that of intradomain motion (~10 meV), both of which are clearly lower than those observed in the conventional semicrystalline polymer. The structural origin of this efficient interdomain electrical connection is the rigid, nearly torsion-free backbone conformation of the tie molecule, as demonstrated from density functional theory calculations.
Highlights
Backbone rigidity of conjugated polymers is suggested to play an essential role in realizing high-mobility transistors through the efficient interconnection of crystalline domains by tie molecules as discussed for the recently-developed donor-acceptor (DA)-type copolymers
We demonstrate that diketopyrrolo-pyrrole (DPP)-based DA copolymers shown in Fig. 1a, with a thiophenevinylene-thiophene (TVT) donor unit (DPP-TVT)[32,34,35] and with thiophene (T)-thieno[3,2-b]thiophene (TT) donor units (DPPT-TT)[28,29,30,31], exhibit highly efficient charge carrier motions, as indicated by observing the temperature dependence of the FI-electron spin resonance (ESR) linewidths
Here, we compare the microscopic carrier dynamics clarified by the Field-induced electron spin resonance (FI-ESR) measurements to the macroscopic charge transport observed in the same devices
Summary
Backbone rigidity of conjugated polymers is suggested to play an essential role in realizing high-mobility transistors through the efficient interconnection of crystalline domains by tie molecules as discussed for the recently-developed donor-acceptor (DA)-type copolymers. Through various structure–property studies, some key characteristics that enable charge transport that is resilient against structural disorders have been revealed for these DA copolymers Among these characteristics, a rigid and nearly torsion-free backbone structure plays a crucial role in high mobilities; a long, highly planar polymer backbone without folding enables both nearly trap-free charge transport along the chain[36,37,38] and efficient interchain charge transfer through the strong π–π interaction between adjacent D–A subunits[23,24,36], improving the intrinsic charge transport within the ordered domains. This efficient interdomain electrical connection should be realized by the rigid, nearly torsion-free backbone conformation, as demonstrated by the structural modeling with the DFT calculation
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