Polymer electrophosphorescent light-emitting diode using aluminum bis(2-methyl-8-quinolinato) 4-phenylphenolate as an electron-transport layer

The characteristics of organic light-emitting diodes depend critically on the arrangement and choice of the constituent organic layers. Diodes constructed using poly(vinylcarbazole) doped with phosphorescent fac tris(2-phenylpyridine) iridium (III) [Ir(ppy)/sub 3/] as the polymer hole-transport layers and aluminum (III) bis(2-methyl-8-quinolinato) 4-phenylphenolate as hole-blocking and electron-transport layers were investigated. The peak efficiencies of the diodes were sensitive to the concentration of Ir(ppy)/sub 3/. With an optimal 2 wt% concentration, an effective external quantum efficiency of 10% photons/electron, a luminance power efficiency of 7.3 lm/W, and a low turn-on voltage of 6 V were obtained.

I. Introduction

Recently, nearly 100% [1] [2] [3] internal emission quantum efficiency has been obtained by harvesting both singlet and triplet excitons in organic light-emitting diodes (OLEDs) doped with phosphorescent emitters containing heavy metals. The strong spin-orbit coupling of a heavy metal enhances intersystem crossing and mixes the singlet and triplet states. Effective external quantum efficiency of 19% photons/electron and luminance power efficiency of 70 lm/W have been demonstrated in OLEDs based on small molecures [2], [3]. An important advantage of OLEDs based on polymers [4] over those based on small molecules is their compatibility with solution processing. This potentially allows a lower cost of production using room temperature spin-coating, screen-printing, or ink-jet printing techniques.