Synthesis and characterization of polyfluorene electrolytes as green and red light-emitting layers for high-efficiency PLEDs

A series of ammonium-ended alkyl-substituted polyfluorene copolymer with narrow band-gap comonomer benzothiadiazole (BTDZ) and 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DBT) were synthesized of by Suzuki polycondensation. The resulting polymers can be processed as an RGB active layer in polymer light emitting devices from environment friendly solvents such as alcohols. It is found out that devices from such polymers show equal or higher external quantum efficiencies (QE) with the high work-function metal cathode such as Al than by using the low work-function (Ca or Ba) cathode. The added BTDZ and DBT units not only change the polymers' emission color, but also greatly improved the device performances of the polymers, as a result of the suppression of excimer formation which is common to rigid polyelectrolyte chains.