High-efficiency polymer light-emitting devices using organic salts: A multilayer structure to improve light-emitting electrochemical cells

Balanced charge injection in polymer light-emitting devices is very important for high brightness and quantum efficiency. To improve the well-known light-emitting electrochemical cells (LECs), we fabricated multilayer electroluminescent devices employing an ammonium salt-containing poly(ethylene oxide) blend as hole- or electron-injecting materials. The charge injection can be greatly promoted due to the ionic space charges near both electrodes. The current-voltage-optical output characteristics of the triple-layer device using both the hole- and the electron-injecting layers are very similar to the well-known LEC devices. We obtained high quantum efficiencies of 0.9% and 1.5% photons/electron in forward- and reverse-bias field of the triple-layer device, respectively. (C) 2002 American Institute of Physics.