Blue-green light-emitting diodes and electrochemical cells based on a copolymer derived from fluorene

A copolymer derived from fluorene has been synthesised using a fluorene monomer functionalised with poly(ethylene oxide) (PEO)-like segments as comonomer in a poly(dihexylfluorene) main chain. Efficient blue-green polymer light-emitting diodes (LEDs) based on this material and working under ambient atmosphere are reported. When using ITO as anode and aluminium as cathode, operating voltage at around 25 V are required to obtain emission intensity of 1 μW cm−2. By decreasing the film thickness from 250 to 110 nm and using calcium instead of aluminium, the corresponding operating voltage can be reduced by approximately 50% without significant loss of luminescence efficiency. Light-emitting electrochemical cells (LECs) are also demonstrated, leading to threshold operating voltages close to the electrochemical gap of poly(fluorene).