Light-emitting diodes from fluorene-based π-conjugated polylmers

We report the synthesis of novel fluorene-based pi-conjugated polymers and the investigation of their electroluminescent properties in organic light-emitting devices. We also report on the photo- and electroluminescence of materials of the same class whose synthesis was recently published. The alternated incorporation of phenylene or thiophene moieties in fluorene-based pi-conjugated polymers leads to the tunability of the electroluminescent properties. The spectral emission varies from blue to green or yellow, depending on the composition of the copolymers. To enhance the luminous efficiency of the devices, the hole injection and hole transport into the polymer were improved by insertion of an insulating buffer layer and the incorporation of efficient hole transport material in the polymer. The insertion of a charge injection layer such as LiF and a hole transport layer such as N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1-biphenyl-4,4'-diamine significantly improves the electroluminescence efficiency of the diode from 4.5 to 125 cd/m(2).