Characterization of Organic Light-Emitting Diodes Using Impedance Spectroscopy and Equivalent Circuits

Abstract

The operational mechanisms in organic light-emitting diodes (OLEDs) based on single molecules or conjugated polymers, under different conditions have been investigated by different techniques over the years. This review discusses the studies from pioneering groups that advanced the use of impedance spectroscopy (IS) and equivalent circuit technique to investigate these mechanisms in OLEDs while emphasizing its novel applications. Section one discusses the theory behind IS and equivalent\ circuit similation by expatiating on IS as a transfer function and the modeling of equivalent circuits. Section two discusses the charge transport and accumulation in OLEDs, purposely focusing on how charges flow through each organic layer composed of an OLED device and the accumulation of these charges at respective interfaces. Section three discusses the application of this novel technique to investigate traps in OLED devices. Section four discusses the degradation mechanism in OLED devices and how the IS and equivalent circuit technique was used to investigate this mechanism. Finally, section five was devoted to the other impedance spectroscopy techniques, specifically other common measurements used in investigating the operational mechanisms in OLEDs. Overall, the technique is an excellent analytical tool for characterizations that are highly desirable in organic electronics.