Control on β conformation of poly(9,9-di-n-octylfluorene) via solvent annealing

Films of poly(9,9-dioctylfluorene) (PFO) are of great importance in fabricating light emitting diodes. In practice, the β-phase of PFO is expected due to its high efficiency in the transport of charge carrier. To promote the formation of β-phase, PFO films are immersed and annealed in the mixture of solvent/nonsolvent. The effects of temperature, solvent/nonsolvent ratio, and annealing time are examined systematically. It is found that the fraction of β-phase can be highly improved by increasing the ratio of solvent/nonsolvent. The reconfiguration of PFO molecules for β-phase in annealing is generally finished in 10 min. The finding in this study demonstrates that solvent-assisted annealing offers a fast and economic approach for mass annealing.