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

We report the synthesis of novel fluorene-based pi-conjugated polymers and the investigation of their electroluminescent properties in organic light-e mitting devices. We also report on the photo- and electroluminescence of ma terials of the same class whose synthesis was recently published. The alter nated incorporation of phenylene or thiophene moieties in fluorene-based pi -conjugated polymers leads to the tunability of the electroluminescent prop erties. The spectral emission varies from blue to green or yellow, dependin g 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 cha rge injection layer such as LiF and a hole transport layer such as N,N'-dip henyl-N,N'-bis(3-methylphenyl)-1,1-biphenyl-4,4'-diamine significantly impr oves the electroluminescence efficiency of the diode from 4.5 to 125 cd/m(2 ).