Optical Techniques for Light-Emitting Electrochemical Cells

The concept of solid-state light-emitting electrochemical cells (LECs), proposed in 1995, opened a new field in display and lighting technologies. The key advantage of this technology derives from a single emissive layer containing an emissive material and an ionic salt. Mobile ions in the emissive layer induce electrochemical doping at electrodes and thus the operation voltage can be reduced even if using air-stable electrodes. Since the first demonstration of LECs, many materials-oriented efforts have been made in improving device performance of LECs. However, some difficulties arising from material properties limit further optimizing the device characteristics of LECs. Recently, optical techniques have been shown to achieve better device properties without using new materials. Light extraction techniques recycle the light trapped in layered device structure and thus enhance the light output and efficiency of LECs. Recombination zone probing techniques offer direct evidence of carrier balance in LECs and is helpful in optimizing device performance. Spectral filtering based on microcavity effects and localized surface plasmon resonance from metal nanoparticles have the advantages of easy fabrication and compatibility with device processing of LECs. This Minireview provides an overview of the three categories of recent advances in optical techniques for LECs.