German scientists have developed a new type of organic light-emitting diode (OLED) that produces white light that rivals incandescent bulbs and is even more energy efficient than fluorescent lamps. The research leader, Sebastian Reneco of the German Institute of Applied Optics, said the OLED prototype may be an ultra-efficient source of light for displays and general illumination, and their long-term goal is to take advantage of traditional Low cost tape and tape printing to assemble these devices.
In recent years, many countries have sought to convert incandescent lighting into compact fluorescent lamps because the latter can save more energy. For the same reason, the use of light-emitting diodes (LEDs) in displays and general lighting has also gained popularity. However, whether it is fluorescent or LED lighting, the quality of white light produced by it has to be improved. Fluorescent lamps can be uncomfortable because of the lack of red light, and most white LEDs currently on the market will have some blue color, which makes people feel a bit cold.
In contrast, OLEDs are made from a wide variety of materials and it is relatively easy to obtain high quality white light. As far as OLEDs are concerned, the problem they face has not always been white light quality, but their energy efficiency. The energy efficiency of fluorescent lamps is about 60 lumens to 70 lumens per watt. The energy efficiency of incandescent lamps is about 10 lumens to 17 lumens per watt. So far, the maximum reported energy efficiency of OLEDs is 44 lumens per watt.
In the latest issue of Nature, Reneco and colleagues report an OLED structure design with an energy efficiency of up to 90 lumens per watt, with a maximum energy efficiency of up to 124 lumens per watt.
Researchers have improved and improved the OLED design process. On the one hand, they dope the organic material that connects the luminescent material to its metal contacts, thereby reducing its operating voltage. On the other hand, they use glass that is more optically compatible with the device substrate to make the outer surface of the device. In a conventional structure, approximately 80% of the light is lost.
The most novel aspect of this OLED is the organization of different luminescent materials inside the device. Three materials were used to emit blue, green, and red light, respectively, with a host matrix material in between.è¯€çª is the choice of a matrix material with a high "spin state" that matches the blue light and is interposed between the green and red materials as part of the separated host matrix material. This means that any electron-hole pair (exciton) that escapes from a red or green material will pass through the blue light material, increasing the chance of conversion to photons.
However, the main drawback of this new type of OLED is still its lifetime. Although companies such as Philips have been able to produce OLEDs with the same lifetime as fluorescent lamps (more than 10,000 hours), materials with higher performance often do not last as long. At present, the lifetime of Reneco's OLED devices can only be as short as a few hours.
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