Evaluating Origin of Electron Traps in Tris(8-hydroxyquinoline) Aluminum Thin Films using Thermally Stimulated Current Technique

Abstract

We measured the energy distributions and concentrations of electron traps in O2-unexposed and O2-exposed tris(8-hydroxyquinoline) aluminum (Alq3) films using a thermally stimulated current (TSC) technique to investigate how doping O2 molecules in Alq3 films affect the films' electron trap and electron transport characteristics. The results of our TSC studies revealed that Alq3 films have an electron trap distribution with peak depths ranging from 0.075 to 0.1 eV and peak widths ranging from 0.06 and 0.07 eV. Exposing the Alq3 films to O2 atmosphere induced a marked increase in electron trap concentration, indicating that electron traps with an energy distribution originate from O2 molecules absorbed in Alq3 films. We measured the current density-voltage characteristics of these films. The driving and turn-on voltages of the O2-exposed Alq3 film became higher than those of the O2-unexposed Alq3 film owing to the increase in electron trap concentration caused by the O2 doping of the Alq3 films.