With the advent of the world community to the concept of sustainable development, which implies the greening of the entire industry and increasing the environmental awareness of consumers, products that have the designation "organic" are of great interest and increased demand. And organic LEDs are no exception. New technological solutions and new products invariably attract the attention of "advanced" consumers, keeping pace with the times. What is it - organic LEDs, what are the principles of their work and prospects for use? This is the topic of this article.
Quite a bit of history
The electroluminescent properties of organic materials were discovered in 1950 by the French physicist Andre Bernanoz. But only in 1987, this discovery acquired a technological solution in the first OLED device manufactured by Kodak. And in 2000, three chemists at once - A. MacDiarmid, H. Sirakawa and A. Heeger - were awarded the Nobel Prize for their discoveries in the field of thin-conducting polymers of organic origin. Only in 2008, the first OSRAM OLED lamp went on sale, of which only 25 copies were made at a price of 25 thousand euros. Today, several companies offer such lamps at prices starting from 500 euros, and there are already several directions in OLED technologies: PHOLED, TOLED, FOLED, and others that are understandable only to specialists.
Where is the organics?
Oddly enough, but the use of the word "organic" in this context has nothing to do with products of animal or vegetable origin. Organic light emitting diodes, or OLED (from the English Organic Light Emitting Diode), is a semiconductor made of carbon material that generates radiation when an electric current passes through it. In their manufacture, products of organic chemistry (carbon compounds) are used, which allows us to call them organic LEDs.
The device and composition
The device itself consists of four parts: the base, the anode, the cathode, the conductive and radiating layers. The base or substrate may be glass, plastic or metallized plates. The anode is tin doped indium oxide. A conducting and radiating layer are layers of polymers and low molecular weight organic compounds. The cathode is made of aluminum, calcium or other metal.
Technology is not for physicists
Organic LEDs are based on the principle of a sandwich. Several thin layers of semiconductors of organic origin are sandwiched between differently charged electrodes (positive and negative). And all this is located on the basis of a transparent material - glass or plastic (for example, flexible polyimide). When current flows through the electrodes, they form charged particles (quasiparticles and electrons). In the middle organic layer, these particles are concentrated and create high-energy excitation, which causes the emission of light of different colors by the organic layer. Thus, the active matrix on organic light-emitting diodes is precisely the luminescent or phosphorescent organic layers.
Organic LED Array Types
Matrix OLED displays are divided into active-matrix and passive-matrix. Active-matrix devices are controlled by thin-film field-effect transistors that are located under the anode film. In a passive-matrix image is formed at the intersection of perpendicularly arranged anode and cathode bands, while control is carried out from an external circuit. Based on this, there are three schemes of color OLED displays:
- With separate color emitters - three organic matrices emit three basic colors (blue, green and red), from which the image is formed.
- With three white emitters and special color filters.
- Blue emitters convert short waves to long waves of red and green.
Modern application
Nowadays, OLED technologies are mainly used in highly specialized developments. Holography and night vision devices, organic displays of car radios and digital cameras, phone screens and light sources, televisions and monitors - all these are already realities of OLED technologies.
Service life of OLED devices
All modern devices created by this technology, sooner or later, exhibit a burnout of color brightness. Even at the opening, the fragility of the emission of organic LEDs was discovered. The life of the device today is considered almost exhausted if the brightness of the display decreased by 50%. Operation is stopped at this rate of about 70%. But corporate investment in the development of these technologies is yielding results - more often the consumer changes an outdated device even before it approaches the near end of its service life.
The best
The largest panel with organic LEDs today is the product of a joint project of OSRAM, Philips, Novaled, Fraunhoter IPMS corporations. The size of the panel is 33 by 33 cm, the area of the active part is 828 square meters. cm, and aperture - 76%. At a brightness of 1 thousand candelas per square meter, the flux of light particles is 25 lumens per watt. The largest Lumiotec panel sold today has a size of 15 by 15 centimeters and a luminous flux of up to 60 lumens per watt, which is equal to one fluorescent light bulb. By 2020, Panasonic Corporation plans to launch a display on organic LEDs with a luminous flux of 128 lumens per watt. The American corporation DoE competes with it, which promises panels with a flow of up to 170 lumens per watt.
Prospects for OLED Panels
Most existing designs today are prototypes. They are expensive, made in limited quantities, do not bend and are not yet effective enough. Large corporations have focused on reducing the cost of the project, increasing size and increasing productivity. Experts predict the mass appearance of these products with affordable prices in the world market by 2020.
OLED lighting
Organic LEDs in lighting are still on the market in their infancy. Mass production of this product has not yet been launched by any corporation. The price of such lamps is still quite high for the average consumer, and the brightness and durability leave much to be desired. The turnover of 75 billion dollars in the world market, which makes up the share of OLED lighting, is a rather small amount. The consumers of these products are not individuals, but other corporations that design furniture and premises, as well as the automotive industry corporation.
Advantages and disadvantages
Organic LEDs have both advantages and disadvantages. Among the first indisputable are their low power consumption and uniform distribution of light throughout the panel, high efficiency, environmental friendliness and soft light. But the main advantage is the ability to give them flexibility and subtlety. And the shortcomings can be considered the short life of the diodes, the high cost and technological problems (the organic component is oxidized by contact with water, which requires additional sealing). But corporations continue to invest in the development of these technologies, seeing in them the future of electronics.
How ecological is it
OLED materials do not contain heavy metals and toxic elements such as mercury. They are easily processed and do not require special collection and additional technological capacity for disposal. Iridium phosphorescent lamps with organic LEDs are non-toxic, and its quantity is extremely small. Transporting thin and light OLED panels requires less resources, which reduces costs and reduces the environmental burden. For example, a TV with a 55-inch OLED monitor has a thickness of 4 mm and weighs about 4-5 kilograms.
Science fiction will become reality
Despite the skepticism of some experts, most are confident that OLED technology will be a major breakthrough in the 21st century. Fantastic projects will become real, namely:
- It is these technologies that will allow creating not an illusory, but quite real three-dimensional picture.
- Lighting everywhere will replace OLED lamps.
- Transparent solar panels will appear.
- Flexible gadget monitors can fit in your pocket.
- Incredibly light monitors with high color quality and a wide viewing angle will have instant response, minimal size and dimensions.
- The use of technology in the military industry is generally amazing.
- But luminous clothes have already appeared in designer collections.
But do not stop there - the motto of theoretical scientists and practitioners. Modern science has long been at a bifurcation point, when any discovery can turn the development of civilization into a completely unpredictable channel. There are plenty of examples of such discoveries: this is the fullness of the vacuum, and the Krasnikov pipes, and even the discovery of organic compounds in deep space. Today, the vanguard of electronic gadgets is organic LEDs, and what tomorrow - who knows?