Influence of layer thickness to the emission spectra in microcavity organic light emitting diodes

Abstract

Microcavity organic light emitting diodes (OLEDs) have attracted great attention because they can reduce the width of emission spectra from organic materials, enhance brightness and achieve multipeak emission from the same material. In this work, we have fabricated microcavity OLEDs with widely used organic materials, such as N,N′-di(naphthalene-1-yl)-N,N′- diphenylbenzidine (NPB) as a hole transport layer and tris (8-hydroxyquinoline) (Alq) as emitting and electron transporting layer. These organic materials are sandwiched either between two thick silver mirrors or one thin copper and one thick silver mirrors. The influence of total cavity length (from 164 nm to 243nm) and the cavity Q-factor to the emission behavior has been investigated. In all cases, an OLED without bottom mirror, i.e. with the organic materials sandwiched between indium tin oxide and a thick silver mirror, has been fabricated for comparison. We have characterized the devices with photoluminescence, electroluminescence, and reflectance measurements. Multiple peaks have been observed for some devices at larger viewing angles. © 2005 IEEE.