Light extraction and optical loss mechanisms in organiclight-emitting diodes

摘要

The internal quantum efficiency of organic light-emitting diodes (OLEDs) can reach values close to 100% if phosphorescent emitters to harvest triplet excitons are used, however the fraction of light that is actually leaving the device is considerably less. Loss mechanisms are for example waveguiding in the organic layers and the substrate as well as the excitation of surface plasmon polaritons at metallic electrodes. In this work we use numerical simulations to identify and quantify different loss mechanisms. Changing various simulation parameters, for example layer thicknesses, enables us to study their influence on the fraction of light leaving the OLED. With these simulations we therefore can enhance the light output of the OLED stack.We present simulations of bottom-emitting OLEDs based on the green emitter tris-(8-hydroxyquinoline) aluminum (Alq_3) with transparent indium tin oxide anode and a metallic cathode, as well as microcavity devices with two metallic electrodes. The results of the simulations are compared with experimental data on the angular dependent emission spectra and published efficiency data.