OLEDs

OLED stands for organic light-emitting diode, a self-emissive display and lighting technology built from organic compounds that emit light when an electric current is applied. An OLED device generally consists of a substrate with an anode, a cathode, and multiple thin organic layers, including an emissive layer and charge-transport layers. Injected electrons and holes meet in the emissive layer and form photons.

Principle: Light comes from recombination of electrons and holes in the emissive layer. The emitted color is set by the energy gap of the emitting material. Phosphorescent emitters can harvest both singlet and triplet excitons, reaching high efficiency; blue emitters, historically, have posed lifetime and efficiency challenges. Devices can be stacked (tandem) to improve brightness and lifetime.

History and variants: First practical OLEDs were demonstrated in the late 1980s by Ching Tang and Steven VanSlyke at Kodak. The dominant consumer formats are passive-matrix OLEDs (PMOLED) and active-matrix OLEDs (AMOLED), with AMOLEDs common in smartphones and TVs. White OLEDs are used for lighting or with color filters for displays.

Advantages include high contrast, wide viewing angles, fast response, and the potential for thin, flexible, or transparent panels. Limits include higher fabrication costs, sensitivity to moisture requiring robust encapsulation, and ongoing blue-emitter stability challenges, along with risks of image persistence in static content.

Applications span display panels for mobile and TV devices, wearables, and general lighting. Research focuses on improving blue lifetimes, efficiency, and durability, as well as on flexible, rollable, and transparent OLED technologies.