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Organic Light Emitting Diode Devices Require Pure Form Of Semiconducting Polymers

Blaze Display Technology Co., Ltd. | Updated: Oct 21, 2015

Semiconducting polymers generally have double bonds and aromatic rings. Aromatic rings are also known as conjugated pi-electron systems. These semi conducting polymers are used for organic light emitting diode (OLED) devices. OLEDs are optoelectronic devices based on small molecules or polymers that emit light when an electric current flows through them. Simple OLED consists of a fluorescent organic layer sandwiched between two metal electrodes. Under application of an electric field, electrons and holes are injected from the two electrodes into the organic layer, where they meet and recombine to produce light. OLEDs are light weight, durable, power efficient and ideal for portable applications. They have fewer process steps and also use both fewer and low-cost materials than LCD displays. OLEDs can replace the current technology in many applications due to following performance advantages over LCDs, such as greater brightness, faster response time for full motion video, fuller viewing angles, lighter weight, greater environmental durability, more power efficiency, broader operating temperature ranges, greater cost-effectiveness. Performance of organic LEDs depends upon many parameters such as electron and whole mobility, magnitude of applied field, nature of hole and electron transport layers and excited life-times. OLEDs are evolving as the next generation of light sources. Presently researchers have been going on to develop a 1.5 emitting device. This wavelength is of special interest for telecommunications as it is the low-loss wavelength for optical fibre communications. Fraunhofer IAP is concentrating on producing ultra-pure, defect free materials. Purity is very important to ensure that the basic polymeric materials exhibit the desired brilliance in red, green and blue colours for a very long time. The team is working to adapt their process to serve an industrial scale by developing low content displays with polymer materials, and finding ways to effectively encapsulate the devices. The simplest design comprises three layers. A glass plate or foil is coated with an indium tin oxide electrode. Next, an organic layer that is one ten thousandth of a mm thick is deposited on top of the first layer, and is then covered with a second electrode layer of metal. Above the electrodes, charge carriers such as electrons are injected into the thin plastic layer. As a result, electrons inside the plastic’s molecules are put into a high-energy state. When this excited state decays, the energy supplied is emitted in the form of light, which illuminates the plastic.


Organic light-emitting diodes (OLEDs), based on organic and/or polymer semiconductor materials, are promising candidates for general lighting applications, as they can cover large-area displays or panels using low-cost processing techniques. Single-color OLED displays are already available commercially. A mix of red-, green- and blue-emitting materials can be used to generate white light, but these bands of color often interact with one another, degrading device performance and reducing color quality. Using polymer nanoparticles to house light-emitting ‘inks’, scientists at the Molecular Foundry, a US Department of Energy Nanoscience Center located at Berkeley Lab, and the University of California, Berkeley, have made a thin film OLED using iridium-based guest molecules to emit various colors of visible light. The polymer nanoparticle surrounding a guest light-emitter serves as a ‘do not disturb’ sign, isolating guest molecules from one another. Each guest can then emit light without pesky interactions with neighboring nanoparticles, resulting in white luminescence. This simple and bright approach to achieving nanoscale site isolation of phosphors opens a new door for facile processing of white OLEDs for solid state lighting. With this proof-of-concept device under their belts, the team plans to vary the ratio of each color nanoparticle in the OLED to enhance efficiency and brightness. White light from OLEDs can be adjusted from cooler to warmer whites, making these materials easy to use in office or home environments. Buildings account for more than 40% of carbon emissions in the United States, so replacing even a fraction of conventional lighting with OLEDs could result in a significant reduction in electricity use. 


Organic LED televisions are finding application in home electronics market, while carmakers are considering the technology. General Motors and Hyundai Motor Co. have debuted concept cars which use OLED technology to replace the standard instrument cluster on the dashboard. However, much needs to be done to aid organics establish a foothold in the display market as challenges of achieving higher efficiencies, lower operating voltages, and lower device life times are still to be met. But, given the aggressive global efforts in this area, emissive organic thin films have an excellent chance of becoming the technology of choice for the next generation of high-resolution, high-efficiency flat panel displays. Developments in organic electronic technology may soon find commercial outlets in display black planes and other low-cost electronics. Organic materials are poised to transform the world of circuit and display technology as they hold tremendous opportunity for the low cost and sometimes surprisingly high performance.


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