Inkjet printed bilayer light-emitting electrochemical cells for display and lighting applications

A new bilayer light-emitting electrochemical cell (LEC) device, which allows well-defined patterned light emission through an easily adjustable, mask-free, and additive fabrication process, is reported. The bilayer stack comprises an inkjet-printed lattice of micrometer-sized electrolyte droplets, in a "filled" or "patterned" lattice configuration. On top of this, a thin layer of light-emitting compound is deposited from solution. The light emission is demonstrated to originate from regions proximate to the interfaces between the inkjetted electrolyte, the light-emitting compound, and one electrode, where bipolar electron/hole injection and electrochemical doping are facilitated by ion motion. By employing KCF3 SO3 in poly(ethylene glycol) as the electrolyte, Super Yellow as the light-emitting compound, and two air-stabile electrodes, it is possible to realize filled lattice devices that feature uniform yellow-green light emission to the naked eye, and patterned lattice devices that deliver well-defined and high-contrast static messages with a pixel density of 170 PPI.