Optical functions of tris (8-hydroxyquinoline) aluminum (Alq3)

Abstract

In this work we report spectroscopic ellipsometry study of the optical functions of tris (8-hydroxyquinoline) aluminum (Alq3) thin films on glass substrates in the spectral range from 1.55 eV to 5 eV. Optical functions of Alq3 deposited on unheated substrates and on substrates kept at 100°C have been determined. The influence of atmosphere exposure to the optical properties has been investigated. Studies on degradation of OLEDs usually focus on changes due to crystallization of Alq3 or cathode degradation during operation (in atmosphere or encapsulated). In this work we show that exposure to atmosphere of an Alq3 layer even without deposition of metal cathode results in change of the optical properties of the layer. It has been found that deposition at higher substrate temperature yields improvement in environmental stability of the films, i.e. less decrease of the PL intensity over time with atmosphere exposure, as well as increased PL intensity. Evolution of the optical functions obtained by spectroscopic ellipsometry, absorption, and photoluminescence spectra are presented and discussed.