Red Phosphorescent Dopant/Polymeric Host System as an Emitting Layer: Effect of Hole Blocking Materials

Abstract

Phosphorescent OLEDs with the configuration of ITO/PEDOT/EML/HBL/Alq3/LiF/ Al were fabricated and their electroluminescent performance was investigated. Synthesized red phosphorescent iridium (III) bis(2-phenyl-isoquinoine) (2-acetyl-cyclohexane) (Ir-PIQCH) dopant and p{[N-(2-ethylhexyl)-3,6-bis(styryl) carbazole]-alt-[2,5-(4-biphenyl)-1,3,4-oxadiazole]} [P(CZ-OXD)] host were used as emitting layer in OLEDs. The devices showed red emission (max.EL about 660nm), similar with PL emission of Ir-PIQCH dopant. EL properties of the phosphorescent OLEDs were measured to investigate the effect of hole blocking layers such as 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), bathocuproine (BCP), and bis(2-methyl-8-quinolinate)-4-phenylphenolate (BAlq) on luminescence and color purity of the devices. It was found that Device 3 using BCP as HBL showed pure red emission with CIE coordinates value as (x=0.6673, y=0.3231), due to higher energy barrier (1.03eV) between P(CZ-OXD) host polymer and hole blocking BCP.