Thermally Stimulated Luminescence of Naphthylsubstituted Benzidine Derivative and Tris-8-(Hydroxyquinoline) Aluminum With and Without Metal Layers

Abstract

AbstractMultilayer organic light emitting devices based on tris-8-(hydroxyquinoline) aluminum (Alq3) and a naphthyl-substituted benzidine derivative (NPB) have demonstrated practical electroluminescence with a wide range of color. Trap states in these materials play an important role in the carrier transport as well as the light emission process. We report the first observation of thermally stimulated luminescence (TSL) from Alq3 and NPB. The TSL spectra from 8 K to 300 K were used to determine the trap states in Alq3 and NPB. The results for Alq3 show a significant trap distribution at 156 K, which corresponds to a mean trap depth ranging from 0.18 to 0.12 eV, whereas the trap states in NPB are centered from 0.15 eV to 0.01 eV. We have used TSL to study the trap state properties of thin metal layers in the Alq3 films. In addition, we report photoluminescence as a function of temperature for Alq3. TSL spectroscopy provides a technique to study the trap states in a specific layer of the device structure.