A significant technological revolution is taking place behind the exquisite and elegant wooden doors of the Bayer House in Dresden, Germany: in the antique brick building with the observatory on the roof, the Institute of Applied Optics Physics is undergoing organic Research on light-emitting diode (OLED) production equipment. Unlike energy-saving lamps, halogen light sources, and LED lighting, OLED technology can be used to make a thin-film globe that emits daylight and emits various soft lights at night or a wallpaper that emits color and fluorescence.
As early as 1969, chemist Herbert Naarmann proposed in a scientific paper the idea of ​​using a special polymer as a semiconductor. Twenty-one years later, Jeremy Burroughes and colleagues from the Cavendish Laboratory Research Group at the University of Cambridge made LEDs for the first time using plastic polymers. The production principle is very simple. The paste plastic is applied to the substrate for hardening, and after a sufficiently strong current is applied to the substrate, the surface emits yellow-green light. The success of the experiment has evoked great interest because plastics are easier to process than ordinary semiconductor materials, and plastics are cheaper.
The gap between energy saving lamps is still big
However, over the years, OLEDs have not been able to form a strong market competitiveness in terms of luminous efficiency and service life. The industrialization of OLED technology is far from the imagination of researchers: the polymer originally planned to be replaced by a small organic molecular. Like inorganic semiconductor components, OLEDs need to be produced in clean spaces because they reduce their useful life. Even the tiniest dust falling on the semiconductor layer of the thickest 12 nanometers (sometimes only a few nanometers thick) will destroy its structure, and the structure of the OLED is more complicated. Moreover, the OLED must be stored in a completely vacuum and dry environment.
Despite the difficulties, this kind of luminescent plastic has been developed in recent years: OLEDs with an average luminous power of 20Lm/W are not as efficient as halogen light sources (24Lm/W), and are not comparable to energy-saving lamps (65-85Lm). /W), but the luminous efficiency of OLEDs has far exceeded that of incandescent lamps (14Lm/W). OLED is undoubtedly with development potential. In 2009, the Institute of Applied Optical Physics (IAPP) of the University of Dresden exhibited an OLED light-emitting panel with a luminous efficiency of 90 Lm/W. The EU's OLED100 promotion project has set a goal of achieving OLEDs with luminous efficiency of 100 Lm/W, 100,000 hours of life, 100 square centimeters, and a cost of 100 euros per square meter. But for the sake of caution, the project did not mention specific time limits.
OLED technology brings profits to enterprises
This technology has at least brought profits to companies in Dresden. Novaled was founded in 2001 by the Dresden University of Technology and the Fraunhofer Institute for Optical Microsystems (IPMS) and became active in the market in 2003. After only a few years of development, the company has been a world leader in OLED structure and material development. The company has 110 employees and plans to have sales of 20 million euros in 2011.
The company's success is mainly due to the development of lighting materials in Dresden. Unlike the simple model of the laboratory, the actual structure of the OLED is much more complicated. There are many so-called functional layers between the positive and negative electrodes and a luminescent layer incorporating dyes of various colors, sometimes even up to 10 layers.
The OLED market still needs to wait and see
The pigments incorporated in the OLED light-emitting layer are composed of a carbocyclic structure, and the color of the luminescent substance is determined by an intermediate element such as ruthenium, rhodium or platinum. Unlike inorganic LEDs, white light is produced by a mixture of basic colors, that is, even if the OLED emits white light, it contains red, blue, and green light sources.
As a pioneer in OLED technology, Novaled has hundreds of patents for innovative materials. Even so, the company still has a lot of research needs, such as the fine structure of the luminescent layer and the blue dye used. Blue is critical for white OLEDs because of the shortest life of this dye. In addition to the Dresden region, market competition in other regions has become increasingly fierce. In early 2009, Philips first announced the introduction of the company's tailor-made LumibladeOLED into the market.
But so far, these OLED products are mainly used by developers and designers, as well as attracting people's attention in exhibitions and other occasions. In early 2010, Siemens-Osram introduced the Orbeos, a light-emitting panel with a honeycomb shape of only 79 mm in diameter, which has a limited sales volume of 251 euros per product. The president of Novaled believes that it is good to have such a product into the market, which proves its feasibility, but it is probably only in the pre-industrial era.
Reinecke, a researcher at the Institute of Applied Optical Physics at the University of Dresden, believes that the OLED market still needs to wait and see. He believes that although the technology is ready-made, the cost of large-scale production is currently too high, and it may take another five years for the OLED market to mature.
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