Efficient red-light-emitting diodes based on novel amino-alkyl containing electrophosphorescent polyfluorenes with Al or Au as cathode

Novel amino-alkyl containing polyfluorenes with Ir complex in pendant chain were synthesized by Suzuki polycondensation and efficient red-light-emitting devices based on the polymers that were fabricated using high work-function metal (Al or Au) as cathode. It was found that the prepared polyfluorenes exhibit good device performances, and the best device efficiency was achieved based on PFN-Irpiq1 that showed a maximal quantum efficiency (QEmax) of 3.7% and 1.6% for Al and Au as cathode, respectively, which was comparable to that of 5.5% for low work-function metals Ba as cathode. The efficiencies of devices from the aforementioned polymers showed a reduced roll-off upon the increase of current density, which is beneficial for the highly efficient phosphorescent dye/host-doped systems. The obtained high efficiencies with air-stable metals as cathode reflect that the copolymers have dual functions of being efficient light-emitting and electron injection ability. The results indicated that the incorporation of Ir complex into amino-alkyl containing polyfluorenes side chain is a potential approach to achieve efficient light-emitting devices with air-stable high work-function metal as the cathode.