Highly Enhanced Light Extraction from Surface Plasmonic Loss Minimized Organic Light-Emitting Diodes

摘要

Light extraction of organic light emitting diodes (OLEDs) has been an important issue in order to increase the external quantum efficiency (EQE) of the devices for displays and solid-state lighting, because 70%～80% of the emitted light is confined in the substrate (substrate mode), in the organic layer and in the transparent electrode (waveguide mode), or lost by absorption and surface plasmon polaritons of the metal electrode (absorption and SP mode). Various methods have been proposed to extract the substrate mode and/or the waveguide modes, including the use of a micro lens array (MLA) on the glass substrate, the insertion of a photonic crystal structure, diffusive particles, silica aero gel, and the use of a low refractive index grid between the transparent conducting electrode and the glass substrate. The use of a patterned high refractive index substrate, a fully buckled device system or using a plastic substrate with a multifunctional anode stacks has also been suggested for effective light extraction methods. However, the absorption and SP losses by the metal electrode(s) in bottom and top emission OLEDs cannot be avoided; therefore, we need to minimize them in OLEDs to increase the EQE.