Oxygen diffusion dynamics in organic semiconductor films

Abstract

Transient absorption spectroscopy is commonly used to probe the yield and kinetics of excited states of materials. We present a transient absorption spectroscopic assay of oxygen diffusion in a series of solution-processed polymer films. The films were partially encapsulated with an epoxy/glass top barrier as a simple model system for organic photovoltaic and light emitting devices with metal top contacts. The results presented herein show that this spectroscopic approach can be a versatile and quantitative in situ assay of local oxygen concentrations in such organic semiconductor films. With our current apparatus, the approach has a time resolution of 5 seconds, thereby enabling direct measurement of oxygen diffusion kinetics into a semiconductor film. The versatility of this approach suggests it could be widely applicable to measurement of oxygen diffusion into organic optoelectronic devices, including for example oxygen diffusion through encapsulation and barrier layers. Employing this approach, we demonstrate significant differences in oxygen diffusion kinetics between different semiconducting polymers. We furthermore demonstrate the impact of an additional getter (ZnO) and light exposure upon the local oxygen concentration, providing new insights into the role of oxygen diffusion kinetics in determining the environmental stability of organic semiconductors.