SOLID-STATE POLYMER LIGHT-EMITTING ELECTROCHEMICAL-CELLS

Solid-state polymer light-emitting electrochemical cells have been dev eloped using thin films of conjugated polymers blended with solid elec trolytes. The cells contain three parts: the polymer blend films as th e active medium, and two contact electrodes: indium-tin oxide and alum inum. When externally biased, the conjugated polymers are p-doped and n-doped on opposite sides of the polymer layer, and a dynamic light-em itting p-n junction is formed between the doped regions. The admired s olid electrolyte provides the dopant counterions and the ionic conduct ivity necessary for the doping. The p-n junction is dynamic and revers ible, with an internal built-in potential close to the bandgap of the redox-active conjugated polymers. Orange, green and blue lights emitte d from the pn junction have been obtained with turn-on voltage less th an 3 V and external quantum efficiency higher than 2% photons/electron . In addition, a two-color light-emitting electrochemical cell has als o been fabricated based on a bilayer structure consisting of two diffe rent luminescent polymers. The light-emitting p-n junction can be swit ched from one layer to another under different bias conditions.