Illuminating the electrolyte in light-emitting electrochemical cells

Light-emitting electrochemical cells (LECs) convert electric current to light within an active material comprising an electroluminescent organic semiconductor and an electrolyte. It is well established that it is the presence of this electrolyte that enabled the recent development of low-cost fabrication methods of functional LECs as well as the realisation of unique device architectures. At the same time, it should be acknowledged that the current lower performance of LECs in comparison to the more commonplace organic light-emitting diode, at least in part, is intimately linked to the utilisation of non-ideal electrolytes. In this review, we present the tasks that the electrolyte should fulfil during the various stages of LEC operation, and how the characteristics of the electrolyte can affect the LEC performance, specifically the turn-on time, the efficiency and the operational stability. We thereafter introduce the different classes of electrolytes that have been implemented in LEC devices up to date, and discuss how these electrolytes have been able to meet the specific requirements of the LEC technology.