Random copolymerization of regiorandom polythiophene to improve planarity, aggregation and hole-transport

Charge transport in semiconducting conjugated polymers mainly devolves on the solid-state ordering of polymer chains with respect to its packing and orientation. Therefore, controlling the inter- and intra-molecular interactions of polymer chains is vital for achieving high performance conjugated polymers for electronic applications. Herein, by a macromolecular design scheme, we optimized the microstructure of a regiorandom poly (thiophene) copolymer for efficient charge transport. By introducing side chain-free phenyl and pyridyl units into the backbone, we achieved regiorandom polymers possessing improved inter- and intra-molecular interactions with a much closer π-π molecular stacking and a larger size of crystallites. Improved charge carrier motion and transport in both vertical and horizontal directions were revealed when the resulting phenyl and pyridyl substituted polymers were applied as hole-transporting materials in organic field-effect transistors, diode-like space-charge-limited current devices, and perovskite solar cells. Particularly, the pyridyl substituted polymer exhibited more than two times higher charge carrier mobilities in the above mentioned device configurations compared with the pristine regiorandom poly (thiophene).