The Synthesis and Optoelectronic Properties of Crosslinkable Polyfluorene

In this work, we have successfully synthesized polyfluorene derivatives, poly(9,9’-dihexylfluorene-co-N-(4-butylphenyl)diphenylamine) (PFA) and poly(9,9’-dihexylfluorene-co-benzothiadizole) (F6BT) with and without containing the oxetane crosslinkable group. They degraded at temperature up to 410℃.DSC results indicated that the Tg of PFAO and F6BTO was reduced by incorporating the oxetane group into the side chain. From the solvent resistibility test, we knew that PFAO and F6BTO could be crossinked partially. The fluorescent microscopy of their blend revealed that the domain size resulted from phase separation was reduced by crosslinking. As they were fabricated into polymer light emitting diodes (PLED), they also showed that the blend system had lower trun-on voltage compared to their individual components due to the formation of ”type-II” heterojuction. After crosslinking, the highest brightness of the PLED is up to 2518cd/m2 and the EL efficiency is up to 1.26cd/A.. Apparently, crosslinking could increase the number of exciplexes formed in the region of ”type-II” heterojuction.