Water-soluble polyfluorenes as an electron injecting layer in PLEDs for extremely high quantum efficiency

A cationic water-soluble polyfluorene containing ion-transporting side groups and mobile metal ions is synthesized. The material is used as an electron injection layer in polymer light-emitting diodes with high-work-function Al cathodes. The devices show high quantum efficiencies (see figure), with a maximum external quantum efficiency of 4.8%, approaching the theoretical maximum external quantum efficiency of about 5%.