Light-emitting electrochemical cells: basic understanding for functional and sustainable devices

The light-emitting electrochemical cell (LEC) comprises mobile ions in the active material. It is the action of these ions that enables its attractive properties; notably, that complete LECs can be fabricated by scalable ambient-air printing and coating. The redistribution of the ions causes electrochemical doping of the emissive semiconductor (p-type at anode, n-type at cathode), which results in the formation of a p-n junction doping structure. This in-situ formed doping structure enables the printing fabrication, but also poses challenges from conceptual and performance perspectives. For instance, the doping regions comprise high concentration of mobile polarons that can cause severe exciton-polaron quenching, and the position of the emissive p-n junction for constructive interference cannot be controlled by conventional spatial design during device fabrication. Here, we present conceptual insights and rational design methods for alleviation of exciton-polaron quenching and for control of the position of the in-situ formed p-n junction for efficient emission. We also present developments towards an LEC, which is sustainable during both fabrication, operation and recycling.