It is difficult to imagine the further development of countries without increasing the rate of energy consumption. Today, specialists count hundreds of different discoveries and inventions that are tested and modernized every day. They, in turn, contribute to improving the quality of the transmitted energy and improving the accompanying factors. One such example is OLED (organic light-emitting diode) lighting. It is much more efficient than traditional light sources, and is a priority for development.
Over the past few years, there has been a significant breakthrough in organic light-emitting diodes and OLED lighting. This is due to public recognition that OLED lighting technology is the future of the industry. Nowadays, more than a hundred companies, both small and large, are engaged in the research, development and production of OLED devices (Fig. 1), and the market turnover is estimated at billions of dollars (mainly due to OLED displays). The emergence of a new market, the market for organic light-emitting diode devices for lighting purposes, was made possible by significant advances in OLED and related technologies.
In order to clearly understand all the advantages and prospects of such an invention as OLED, it is necessary to understand what a light-emitting diode (LED) is. It is also important to understand the difference between an organic and a conventional diode, what it consists of, what OLED is and why the use of this innovative development can be better than traditional lighting.
First of all, let’s define the concept of a light-emitting diode. It is a semiconductor optical radiation, the principle of which is based on the phenomenon of electroluminescence with the phenomenon of injection of minority charge carriers through a homo- or hetero-p-n junction .
Figure 1. An illustrative example of the use of OLED lighting.
However, it is necessary to distinguish between an ordinary LED and an organic LED. An organic LED is a semiconductor device made from organic compounds that effectively emit light when an electric current passes through them. Traditional (inorganic) light-emitting diodes are based on complex crystal structures. In contrast, OLED devices are flat light sources that use organic semiconductors to generate light. The use of the word «organic» in the name can be misleading, so it is worth clarifying right away that this technology has nothing in common with plant or animal origin.
OLEDs consist of a transparent plate, a transparent electrode, one or two thin organic layers and an auxiliary electrode, which can also be transparent. (Fig. 2) A combination of all these components is placed in a sealed enclosure to protect the components from oxidation and moisture. The materials used to make organic light-emitting diodes are sensitive to water and oxygen, so another coat is needed to protect them. This final layer is sometimes referred to as insulation or sealant. Ideally, the insulation should be flexible, cheap, not time consuming, transparent and strong enough to provide reliable protection.
Figure 2. Structure of an organic light-emitting diode.
To create organic light-emitting diodes, thin-film multilayer structures are used, consisting of layers of several polymers. When a positive voltage is applied to the anode, the flow of electrons flows through the device from the cathode to the anode. Thus, the cathode gives up to the emission layer, and the anode collects electrons from the conducting layer. The emission layer gets a negative charge and the conductive layer gets a positive charge. Under the influence of electrical forces electrons and holes move towards each other and recombine when they meet. This happens closer to the emission layer, because holes in organic semiconductors have a higher mobility than electrons. During recombination a decrease in the electron energy occurs, which is accompanied by the emission (emission) of electromagnetic radiation in the region of visible light. Therefore, the layer is called emission. OLED works on the same principle as inorganic light-emitting diodes: light is emitted in a semiconductor. The structure of the semiconductor molecules determines the color of the organic light emitting diode .
As for the merits of organic development, one can say that the ultra-low weight and the ultra-thin OLED panels which are 1.8 mm for the ready-to-use product, distinguish them from all other artificial light technologies. And even these figures can be further reduced by using thinner materials for sealing. Since displays and lighting lamps do not require external illumination and have the ability to regulate the voltage, they are energy efficient. Very thin layers significantly reduce size and weight. The contrast ratio of OLED displays reaches 1,000,000: 1, and the picture on the display remains bright and saturated from any viewing angle and does not suffer from direct sunlight. The brightness of OLED systems can be fully adjusted and set at any desired level by changing the operating current. Unlike neon tubes and fluorescent lamps, OLEDs give their full glow immediately after being switched on. Also, one of the most important advantages of this development is the perfect black color , as, for example, in OLED TVs, self-illuminating pixels can be completely turned off, and the user will be able to feel the very deep black color that manufacturers are so praised for . Fig. 3
Figure 3. OLED technology.
OLED lighting applications are revolutionizing the way. Nowadays, when 20% of the energy produced in the world goes to lighting, and air pollution from the production of these 20% of energy is approximately equal to 70% of the exhaust gases of all cars on the planet, supporters of the «green planet» have decided to seriously tackle organic lighting. And it does not happen without reason: after all, an OLED lamp has an efficiency of 100 lm/W (slightly better than fluorescent ones) and is twice as energy efficient. This means that with the massive distribution of OLED lamps, emissions into the atmosphere are significantly reduced. In addition, these lamps can be adjusted to the desired energy consumption. But so far, unfortunately, such lighting is expensive and people prefer to use traditional lamps. According to forecasts of scientists and specialists, OLED lamps are expected to be available at an affordable price by 2022 .
The field of application of organic light-emitting diodes is very wide, OLED technology has become the basis for displays, lighting panels, luminous furniture, and is also unique in the manufacture of flexible screens. The world’s leading companies in the field of electronics, electrical engineering and lighting are already offering a number of innovative products based on OLED technology, both for industrial use and for the end consumer.
Verbatim offers color-adjustable organic polymer light panels (made by Mitsubishi and Pioneer) under the Velve brand. These panels have an efficiency of 28 lm/W, a service life of 8,000 hours, and a brightness of 2,000 cd/m2. They are available in two sizes (although Verbatim can customize any panel size): 131 x 44 mm and 65 x 72 mm. Its depth is only 5 mm. Their main component is small OLED molecules and stripes of three colors (red, yellow, blue), with which color adjustment is achieved.
Philips can offer freeform structured OLED lighting devices that can contain text or images. According to Philips, the consumer response to these panels has been very good — people are glad they have access to this latest technology. Of course, it is obvious that Philips OLED lighting installations are not yet profitable: they are needed in order to show the world how high-tech the company is and how intensive the development in the field of organic polymers is.
In collaboration with Audi and Philips, art designer Michael Hammers has designed 15 OLED lamps to decorate a rather unusual conference room: a winter garden at the Audi Forum Center in Ingolstadt. This room is located in immediate proximity of the car delivery point and the company museum and is used by the Monitoring Centre. The light rays emanating from the lamps are so thin that they can hardly be distinguished from the side — this is a feature of organic elements. It seems that the light really dissolves in the air, and only the power cord indicates that there is a light source somewhere nearby. Each lamp has an aluminum frame and a stainless steel front panel, under which are located 36 Lumiblade GL350 OLEDs. Each lamp contains 3900 lumens of light, so that the room is illuminated with approximately 58 thousand lumens. This is the first conference room in the world to be exclusively illuminated with OLEDs, which proves how quickly this new technology has matured .
The «Victory» table lamp from Novaled combines the latest development in OLED technology with the highest quality materials to create a unique lighting experience. Lumiblade organic light-emitting diodes are mounted in ultra-thin light holders, forming a V-shape, the world-famous victory sign, approved by British Prime Minister Winston Churchill. The main material from which the lamp is made is high quality carbon fiber, a material that is not only very durable but also very malleable .
QD-OLED is a kind of symbiosis of OLED technology and the actively promoted by Samsung QLED technology. In other words, these are hybrid screens in which Samsung has combined quantum dots (QLED) with organic light-emitting diodes. In fact, Samsung wants to launch panels with blue OLED emitters with a layer of quantum dots on top of them. They will engage in converting blue light to red and green. Both technologies have found their application in modern TVs of the upper and premium market segments (QLED TVs are sold and even produced in Russia), and both are characterized primarily by high color reproduction quality. According to Samsung representatives, their combination will allow the company to increase significantly the level of purity and color depth, as well as improve brightness and contrast while reducing power consumption .
It is worth noting that OLED development is not perfect: numerous competitors to OLED technology have been talking about its weak points. Some of them state that exactly the reason for pixels burn-in  is enough not to buy this product. In fact, the problem is exaggerated. For example, it quite often happens that OLED pixels have the so-called afterglow or afterimage effect for some time after changing the picture, as if the OLED screen remembers the previous picture. An average consumer considers this to be burn-in. Gerald Strӧmer, the product marketing manager for LG Electronics in Germany, explains that the possible afterglow is related to the technical characteristics of the OLED panels. It is short-lived and does not affect pixel performance. Hence, this is not a functional error or burn-in. Moreover, various protective mechanisms in LG OLED TVs minimize effectively the risk of afterimages and even can actively remove them if necessary .
The efforts of scientists who are engaged in researching new areas of application of OLED technology are now aimed at introducing it into the field of energy. According to them, this technology is able to reduce energy consumption and carry out its transmission virtually with no loss over long distances with an efficiency much greater than by existing methods. This, in turn, will contribute to greater environmental protection, minimization of emissions, and, ultimately, will have a positive effect on the existence of man and the entire planet as a whole.
Based on the foregoing, one can say with certainty that the new technology is gaining momentum and it will take a leading position in the world market very soon. The production of such technologies is expanding and becoming more competitive. Experts are working to ensure that more and more developers and sponsors are involved in the implementation of these projects. Scientists predict that no obstacles will prevent the implementation of plans for the introduction of organic light-emitting diodes in the energy sector in the near future.
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