A new polyfluorene containing repeated ethylenoxy units linked to glycerol as side chains: Synthesis and application as an electron injection material in the fabrication of polymer light-emitting diodes

A new polyfluorene derivative (PF-GOH) containing repeated ethylenoxy units linked to glycerol as side chains was synthesized as an electron injection material. The polymer was not very soluble in methanol, but reasonably soluble in mixed solvents such as methanol/ethylene glycol (EG) and isopropyl alcohol (IPA)/EG. Polymer light-emitting diodes (PLEDs) were fabricated with a ITO/PEDOT:PSS/MEH-PPV/PF-GOH/Al configuration. The PLEDs exhibited significantly improved performance in the presence of the PF-GOH layer compared to the device without the electron injection polymer layer. The performance of the PLEDs was largely dependent on the solvent systems employed. Among methanol, methanol/EG (3:1), and IPA/EG (1:1), the best performance was obtained when IPA/EG (1:1) was used. The improved performance was attributed to the more uniform thickness of the electron injection layer of PF-GOH, leading to much less current leakage.