From Starting Formation To The Saturation Content Of The Beta-Phase In Poly(9,9-Dioctylfluorene) Toluene Solutions

In this research, the relationship between chain aggregation and poly(9,9-dioctylfluorene) (PFO) beta-phase content with a change of the PFO solution concentration is investigated. Photoluminescence and UV vis absorption spectra are used to explore the PFO beta-phase and its content. Chain aggregation is explored by dynamic light scattering (DLS). It is found that the chain aggregation size of the starting to form PFO beta-phase is approximately 100 nm. The beta-phase content increases with the chain aggregation degree. When the beta-phase content is in the range of 44% 2%, the maximum value of the content (saturation content) of the beta-phase is reached and cannot be changed by any external field that could induce fi-phase formation. Therefore, the concept of the saturation content of the PFO beta-phase is first proposed. The mechanism from PFO beta-phase formation to saturation content is explored by DLS and atomic force microscopy. This research is significant to understand and control the molecular chain condensed-state process as well as phase transition from solution to film to achieve a photoelectric device with high charge carrier mobility, stability, and efficiency.