Tuning Short Contacts between Polymer Chains To Enhance Charge Transport in Amorphous Donor-Acceptor Polymers

The design of semiconducting polymers with optimal charge transport characteristics has been at the crux of scientific research during the recent decades. While increase in crystalline order and planar conjugated backbones were demonstrated to be the key to success, they are not always mandatory. Sometimes, the charge carrier mobility can be enhanced by selecting conjugated backbones that are resilient to thermal fluctuations, despite leading to poor structural order. Herein, by coupling all-atom molecular dynamics simulations, electronic structure calculations, and kinetic Monte Carlo charge transport simulations, we demonstrate that the charge carrier mobility in amorphous donor-acceptor conjugated polymers is controlled by the density and quality of close-contact points between the chains and that the latter varies with the size of the donor block and the resulting alkyl side-chain density. We show an application of this strategy to the high-mobility poly(indacenodithiophene-alt-benzothiadiazole) (IDTBT) and poly(dithiopheneindenofluorene-alt-benzothiadiazole) (TIFBT) copolymers.