Organic light-emitting device dark spot growth behavior analysis by diffusion reaction theory

Dark spot growth rate tracing experiments performed on an organic light-emi tting device show that moisture entering into the device is relatively prop erly fitted by Fick's diffusion equation in the substrate/indium tin oxide (ITO)hole transport layer (HTL)/silver (Ag) structure. It is believed that the moisture is dissolved into the polymer layer, which results in a decrea se in the diffusion coefficient in the device with the substrate/ITO/HTL/el ectroluminescent (EL) polymer/Ag structure. The diffusion and chemical reac tion occurring in the cathode layer further decreases the diffusion coeffic ient in the device with the substrate/ITO/HTL/EL polymer/calcium/Ag structu re. Useful parameters, such as diffusion and solubility constants, describi ng possible mechanisms happening during dark spot growth on organic light-e mitting diode devices are extracted. (C) 2001 John Wiley & Sons, Inc.