Ionic Materials to Improve Charge Injection in Polymer Electroluminescent Devices

Balanced charge injection and recombination in polymer light-emitting devices are very important for high brightness and quantum efficiency. Ionic materials such as ionomers, single-ion conductors, and bi-ionic ionic blend materials were employed as charge injection layers (hole injecting layer, electron injecting layer, or both of them) in polymer electroluminescent (EL) devices. The charge injection can be greatly promoted due to dipole moments or the ionic space charges near both electrodes. Theses multi-layer approaches using ionic materials highly improve the EL quantum efficiencies. When we fabricated kinds of energy-well devices by incorporating hole- and electron-injecting layers simultaneously, the EL efficiency was highly enhanced and the current-voltage-luminescence characteristics are very similar to the light-emitting electrochemical cells.