The modeling of dynamical degradation process for operating organic light emitting diode

Abstract

The dynamical degradation process of operating organic light-emitting diode (OLED) was proposed and investigated by non-destructive reflectivity measurements using a p-polarized He-Ne laser as probing tool. The intrinsic OLED degradation mechanism mainly depends on intermediate layers at organic/electrode interfaces. The optical behavior of these interfacial dielectric layers and corresponding optical parameters may be capable of representing OLED degradation in macroscopic aspect. Optical parameters defined as optical constants (n, k) and thickness (d) were obtained from fitting our experimental data to a theoretical model including interfacial dielectric layers with (n, k, d) as adjustable parameters. Our experimental results revealed that the change of the reflectivity spectra obtained from static and operated OLED was observable. The tendency of change in reflectivity spectra can be used as qualitative and dynamical aspect of degradation of operating OLED. The dynamical degradation process can be quantitatively modeled by inspecting the variation of optical parameters. This dynamical aspect may also include time-dependent information of degradation as operating OLED. Our data-fitting results indicated that optical constants of intermediate layers have a trend to increase as OLED from static to turn-on status. The thickness of intermediate layers obtained from data-fitting ranged from 0.2 to 14nm, satisfying our expectation. The reflective spectra obtained from basic OLED with ITO/Alq 3 /LiF/Al structure revealed a clear dip located around 61.5 o incident angle from ITO glass side as OLED in turn-on status. It indicated that surface plasma resonance may occur even in OLED layer structure.