Characterization of organic light-emitting diodes using impedance spectroscopy and equivalent circuits

Abstract

Operational mechanisms in organic light-emitting diodes (OLEDs) based on single molecules or conjugated polymers, under different conditions, have been extensively investigated using a variety of techniques. This review discusses the studies from pioneering groups that advanced the use of impedance spectroscopy (IS) and equivalent circuit techniques to investigate these mechanisms in OLEDs. Emphasis is placed on foundational and contemporary studies that have advanced the use of IS and equivalent circuit simulation techniques to analyze charge transport, accumulation, and interfacial dynamics within OLED structures. The theoretical basis of IS as a transfer function, along with the principles of equivalent circuit simulation, is discussed in detail. Special attention is given to the application of these techniques in identifying trap states and assessing device degradation. Additionally, this review examines alternative representations and complementary measurements used in conjunction with IS for probing OLED behavior. Collectively, the findings underscore IS and equivalent circuit simulation as robust analytical methods, offering critical insights into the performance and stability of organic electronic devices.