Feature: LEDs


OLEDs create high-quality, power-efficient displays By Duncan Clark, Operations Director, NextGen Nano


T


he market for organic light emitting diode (OLED) technology is worth an estimated annual $18bn today. It all started in the


1950s, when André Bernanose and his co-workers at the Nancy-Université, France, made the first discovery of electroluminescence in organic materials, when the team applied alternating current to acridine orange die dissolved in and deposited on cellulose. In 1987, Ching Wan Tang of Eastman


Kodak made a number of innovations in high-definition OLEDs, which resulted in the commercialisation of new flat-panel technology.


OLED structure OLEDs consist of a thin film of organic semiconductor sandwiched between an


26 April 2021 www.electronicsworld.co.uk


anode and a cathode. When a voltage is applied to the semiconductor, a diffused- area luminance arises. While traditional light-emitting diodes (LEDs) produce a small-point light source, OLED emissions are comparatively soſter, producing less glare. Tis is one of the many reasons they are well suited to televisions. One of the biggest selling points for


OLEDs is their ability to render a state of true black, which means they produce higher contrast displays. In a practical example, liquid-crystal display (LCD) televisions require LED backlighting to produce light, which is then filtered by the LCD. As a result, these devices cannot achieve true black and power will be consumed even by black image areas. OLEDs do not have this problem.


Inactive OLEDs do not emit light or consume power, allowing for higher contrast ratios and a better overall viewing


experience. Removing the need for a backlight also makes OLED devices lighter in weight and thinner in thickness, and gives them wider viewing angles. It is because of these properties that companies like Sony and LG have used OLEDs to produce sleeker, thinner flatscreen displays. As with any light source, increasing


the electrical current through the OLED semiconductor will result in brighter displays. However, problems have arisen in the past with conventional OLEDs and fast degradation rates, particularly for OLEDs that emit blue light.


Blue OLEDs To generate white light, three colours of organic material are patterned together to form the emissive semiconductor layers: red, green and blue. Blue OLED semiconductor materials are traditionally less efficient and degrade faster than their red and green


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