Molecularly doped liquid crystalline polymer as a hole transport layer in organic electroluminescence device

Abstract

Organic thin film electroluminescence devices were fabricated by molecularly doped method with N,N'-Diphenyl-N,N'-bis(3-methylphenyl)-11,-biphenyl-4,4'-diamine (TPD) as a hole transport agent, tris(8-quinolinolato) aluminium(III) (Alq(3)) as an emitting and electron transport agent, and poly(methyl methacrylate) (PMMA), polycarbonate (PC), side chain liquid crystal polymers (SCLCP) and copolymer as matrix for TPD. The effect of polymer matrix and hole transport layer fabrication method on the electroluminescence characteristics were examined. The highest intensity and stability of EL device was obtained by film casting method using dichloroethane as a solvent at a polymer/TPD concentration of 0.005 wt% and evaporation temperature of 30 degrees C. The electroluminescence intensity increased in the order of PMMA<PC<SCLCP as polymer matrix. The luminance started at voltage as low as 3 V and reached the maximum luminance of 756 cd/m(2) at 11 V in the EL device consisted of ITO/SCLCP:TPD/Alq(3)/Mg(SCLCP/TPD=30/70 by wt)