Field-induced dissociation
Abstract
The efficiency of organic light-emitting diodes (OLEDs) relies heavily on optimizing charge carrier transport, which is determined by the energy levels of the material, specifically the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). However, determining the LUMO energy level accurately remains a challenge. This work focuses on indirectly calculating the LUMO level by studying the exciton binding energies of phosphorescent OLED emitters. By carrying out field-induced dissociation measurements in which the photoluminescence efficiency of phosphorescent materials is measured as a function of the applied electric field in reverse bias, in combination with kinetic Monte Carlo (KMC) simulations, the binding energy of triplet exciton of the phosphorescent emitters can be estimated. The binding energy of triplet excitons in Ir-based phosphorescent emitters is found to lie in the range of 1.1-1.4 eV.