Quantitative luminous efficiency determination for large-area light-emitting devices

Abstract

During recent decades organic light-emitting devices became of increasing interest in many fields of applications. A broad spectrum of available organic molecules can be used to fabricate organic light-emitting diodes (OLEDs) emitting at various photon energies. One of the commonly used quality criteria to specify the light output of OLEDs is the luminous efficiency. The standard measurements are based on the assumption of a point source, which is not applicable in the case of large-area devices, or can be achieved only approximately by long distances between emitter and detector. Therefore, we developed a data evaluation procedure, taking into account the extended area of the emitter as well as the geometry of the detector and its spectral sensitivity. This mathematical model delivers correction factors for the luminous efficiency as a function of the distance between a large-area emitter and a detector. The model was tested experimentally for rectangular-shaped OLED structures and delivered accurate results for three different standard types of detectors.