Green polarized electroluminescence from poly （9, 9-dioctylfluorene-alt- benzothiadiazole）

Abstract

Polarized green electroluminescence has been achieved at the peak wavelength of 550 nm from alternate copolymer poly （9, 9-dioctylfluorene-alt- benzothiadiazole） （PFBT）, which was synthesized by polycondensation. The liquid crystalline state of this copolymer under certain thermal treatment results in the uniaxial orientation of the conjugated backbones on an alignment layer. A rubbed-hole injection layer poly（3,4-ethylenedioxythiophene）:polystyrenesulfonate （PEDOT:PSS） was utilized as the alignment layer. Polarized absorption and photoluminescence spectra indicate the good alignment of the copolymer films with an ordering parameter of 075. Polarized polymer light-emitting diodes were fabricated with the structure of ITO/PEDOT:PSS/PFBT/LiF/Al. An electroluminescence polarization ratio of about 4 was achieved at a voltage of 15 V, with the luminance of 450 cd/m2 and luminous efficiency of 021 cd/A.