Organic Light-Emitting Diodes

OLEDs provide high-contrast and low-energy displays, rapidly becoming the dominant technology for advanced electronic screens. Here is a brief Discussion about OLED.

LED to OLED

• We all know that the conventional LEDs are made from a variety of inorganic semiconductor materials.
• Organic Electro Luminescence (OEL), is any Light Emitting Diode (LED) whose emissive electroluminescent layer is composed of a film of organic compounds.
• The layer usually contains a polymer substance that allows suitable organic compounds to be deposited. They are deposited in rows and columns onto a flat carrier by a simple printing process.
• The resulting matrix of pixels can emit light of different colours.
• The organic material is electrically conductive due to the delocalization of pi-electrons caused by conjugation over all or part of the molecule, and the material therefore functions as an organic semiconductor. The organic materials can be small organic molecules in a crystalline phase, or polymers. In case of Polymers they can also be called Polymer Diodes.

Uses

• OLEDs have advantages such as they include thin, low cost displays with a low driving voltage, wide viewing angle and high contrast and color gamut.
• Polymer LEDs have the added benefit of printable and flexible displays. OLEDs have been used to make visual displays for portable electronic devices such as cellphones, digital cameras, and MP3 players while possible future uses include lighting and televisions.

Types of OLEDS

• Broadly OLEDs are of two types viz. those based on small molecules and those using polymers. OLED displays can use either passive-matrix (PMOLED) or active-matrix addressing schemes. Active-matrix OLEDs (AMOLED) require a thin-film transistor backplane to switch each individual pixel on or off, but allow for higher resolution and larger display sizes.

General Structure

• OLED is composed of a layer of organic materials situated between two electrodes, the anode and cathode, all deposited on a substrate.
• The organic molecules are electrically conductive as a result of delocalization of pi electrons caused by conjugation over all or part of the molecule.
• These materials have conductivity levels ranging from insulators to conductors, and therefore are considered organic semiconductors.
• The highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of organic semiconductors are analogous to the valence and conduction bands of inorganic semiconductors. The most basic polymer OLEDs consisted of a single organic layer. Today, the multilayer OLEDs are fabricated with two or more layers in order to improve device efficiency.