Improved Performance of Polymer Light-Emitting Diodes with an Electron Transport Emitter by Post-Annealing

The enhancement of electroluminescent (EL) performance of polymer light emitting diodes (PLEDs) with electron transport emitter poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) through thermal annealing treatment is investigated. Post-annealing of the PLEDs at temperature 120°C over the glass transition temperature of F8BT (99°C) could bring about an improvement of EL efficiency to more than twice that of the untreated devices, up to 6.02cd/A. The improvement of the EL efficiency is due to the balance of electron and hole carriers in the exciton recombination zone, because the dominative electron current in the PLEDs could be reduced by post-annealing in terms of both issues of electron transport limited in the F8BT film and electron injection decreased by the interface between F8BT/cathode.