Formation of parallel aligned nano-fibrils of a donor–acceptor conjugated copolymer via controlling J-aggregates and post treatment

Abstract

We increased the content of J-aggregates in poly[2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-alt-2,2′ : 5′,2′′ : 5′′,2′′′-quaterthiophene](PDQT) solution by choosing appropriate solvents. It was found that the higher content of J-aggregates in solution in good solvents (i.e. CF) led to the formation of parallel aligned nano-fibrils. This morphological transition from the disordered domains to ordered ones could also occur after thermal treatment or solvent vapor annealing. Parallel aligned fibrils of PDQT formed in films via annealing at 200 °C for 20 min or solvent vapor annealing in a CF atmosphere with a relatively low vapor pressure for 24 hours. In the films filled with parallel aligned fibrils, the PDQT molecules adopted an edge-on orientation and the π–π stacking direction of molecules was perpendicular to the growth direction of fibrils. PDQT chains preferred to adopt the extended conformations without chain-folding due to the extremely rigid backbones. The intact conjugation planes of rigid PDQT chains with extended conformations allow the further growth of parallel aligned fibrils, which enhanced the connectivity between crystalline domains. The results in this work are thought to be helpful to improve the charge-carrier transport in PDQT films.