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.