Solid-state polymer light-emitting electrochemical cells

Solid-state polymer light-emitting electrochemical cells have been developed using thin films of conjugated polymers blended with solid electrolytes. The cells contain three parts: the polymer blend films as the active medium, and two contact electrodes: indium-tin oxide and aluminum. When externally biased, the conjugated polymers are p-doped and n-doped on opposite sides of the polymer layer, and a dynamic light-emitting p-n junction is formed between the doped regions. The admired solid electrolyte provides the dopant counterions and the ionic conductivity necessary for the doping. The p-n junction is dynamic and reversible, with an internal built-in potential close to the bandgap of the redox-active conjugated polymers. Orange, green and blue lights emitted from the pn junction have been obtained with turn-on voltage less than 3 V and external quantum efficiency higher than 2% photons/electron. In addition, a two-color light-emitting electrochemical cell has also been fabricated based on a bilayer structure consisting of two different luminescent polymers. The light-emitting p-n junction can be switched from one layer to another under different bias conditions.