Recent Progress in White Light-Emitting Electrochemical Cells

Solid-state white light-emitting electrochemical cells (LECs) exhibit the following advantages: simple device structures, low operation voltage, and compatibility with inert metal electrodes. LECs have been studied extensively since the first demonstration of white LECs in 1997, due to their potential application in solid-state lighting. This review provides an overview of recent developments in white LECs, specifically three major aspects thereof, namely, host-guest white LECs, nondoped white LECs, and device engineering of white LECs. Host-guest strategy is widely used in white LECs. Host materials are classified into ionic transition metal complexes, conjugated polymers, and small molecules. Nondoped white LECs are based on intra- or intermolecular interactions of emissive and multichromophore materials. New device engineering techniques, such as modifying carrier balance, color downconversion, optical filtering based on microcavity effect and localized surface plasmon resonance, light extraction enhancement, adjusting correlated color temperature of the output electroluminescence spectrum, tandem and/or hybrid devices combining LECs with organic light-emitting diodes, and quantum-dot light-emitting diodes improve the device performance of white LECs by ways other than material-oriented approaches. Considering the results of the reviewed studies, white LECs have a bright outlook.