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Organic Light Emitting Diodes

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Uploaded on Nov 30, 2010

Organic Light Emitting DiodesOrganic Light-Emitting Diode technology, also abbreviated OLED, is relatively new but very promising, especially what concerns design of data display devices. OLEDs' main difference from other LEDs is that they are made of organic compounds which emit light in response to an electric current. This feature determines their main properties.OLEDs are made of special thin-film multilayer structures. These layers are special polymers. There is anode and cathode. Electrons can flow between them. When positive voltage is applied to the anode then electrons from the cathode start moving towards it. That means that the cathode emits them into the emissive layer while the anode gets them from a conductive layer. As the result of the flow of charged particles the layers acquire different charges. The emissive layer is charged negatively while holes appear in the conductive layer which charges positively. Under the influence of static electricity electrons and holes meet, and recombination occurs. A peculiar feature of organic matter is that the holes have greater mobility as compared with electrons. Thus recombination occurs closer to the emissive layer. Electrons' energy is decreasing which is accompanied by the emission of electromagnetic radiation into space in the form of a visible light.To improve the technology several of its aspects may be researched further. This can be the chemical composition of layers, enriching additive agents, and new studies in the field of organics. For each region of RGB spectrum experts look for necessary organic substances and formulas which may improve lifespan of LEDs. They also study operating temperature range and main properties of OLED displays.OLED display is a matrix which consists of combinations of main RGB colours, that is red, green, and blue. When regulating the voltage applied to the cell its glow colour changes. By mixing three colours we get a necessary tint.There are passive and active matrices. For passive matrices we see a set of dots where lines and columns intersect. Each intersection is an OLED. Voltage is supplied to the necessary dot, and the corresponding diode lights up with brightness proportional to the applied voltage. This type of matrix is obsolete. It cannot be used in modern devices which produce big and high-quality image.In such case we use an active matrix. Each intersection of this matrix is connected with a control thin-film transistor. A signal is sent to it. It executes the command and maintains the specified level of glow till it receives new commands. This helps to save electricity. We also see that the screen has a higher response speed to the image change.OLED displays already have many advantages over regular LCD displays. They have lower energy consumption parameters, an improved colour rendition, immediate response time and no minimum visual angle. The image can be read from any angle. They also do not require any bias lighting and have a wide range of operating temperatures.The only disadvantage is their limited life span and expensive big matrices. That is why OLEDs are becoming more and more popular today as they are used in mobile phones, photo cameras, GPS navigators, and other electronic appliances which require a high-quality colourful display of data on average-size screens that do not require continuous work.Besides, there are technologies which are based on OLED and allow to make transparent displays (TOLED technology) or even flexible displays (FOLED).Thus organic light-emitting diodes have a very promising future. There are numerous studies being conducted now, and no doubt that OLED display properties will be improving. And we can expect new high-tech devices soon.

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