Synergistic Effects of External Electric Field and Solvent Vapor Annealing with Different Polarities to Enhance β-Phase and Carrier Mobility of the Poly(9,9-dioctylfluorene)Films

In this work,the synergistice efects of external electric field(EEF)and solvent vapor annealing to enhanceβ-phase and carrier mobility of poly(9,9-dioctylfuorene)(PFO)films were investigated.It is found that EEF can promote the PFOβ-phase conformation transition and orientate the PFO chains along the EEF direction with the as-sistance of polar solvent vapor annealing.PFO chain orderness is closely related to the solvent polarity.In particular,the B-phase content in the annealed film of strong polar chloroform vapor increases from 18.7%to 34.9%after EEF treatment.Meanwhile a characteristic needle-like crystal is formed in the flm,as a result,the hole mobility is en-hanced by an order of magnitude.The mechanism can be attributed to the fast polarization of solvent dipole under the action of EEF,thus forming a driving force that greatly facilitates the orientation of PFO dipole unit.Research also reveals that EEF driving of the PFO chains does not occur with an insoluble solvent vapor since the solvent molecules cannot swell the film,thus there is insufficient free volume for PFO chains to adjust their conformation.This research enriches the understanding of the relationship between solvent vapor annealing and EEF in orientation polymers,and this method is simple and controlled,and capable of integrating into large-area thin film process,which provides new insights to manufacture low-cost and highly ordered polymer films,and is of great significance to enhance carrier mobility and efficiency of photoelectric devices based on polymer condensed matter physics.