Organic light-emitting diodes: current status and prospects of development in the technique of lighting


It is interesting history of the emergence and development of organic light emitting diodes (OLED = Organic Light Emitting Diode).

The foundation was laid in 1953, when Andrè Bernanose (1912-2002) was the glow of organic materials (acridin orange and quinacidrin), placing them in a strong alternating electric field. These materials by themselves do not possess any meaningful electrical conductivity.
The fundamental basis for the future of OLED was founded in 1977 with the discovery of conductive polymers. (For research in this field to three scientists - Alan J. Heeger, Alan MacDiarmid and Hideki Shirakawa in 2000 was awarded the Nobel Prize in Chemistry).
The next step was taken in 1979 when a chemist Chin W. Tang in the research laboratory of Eastman Kodak Company discovered the phenomenon of electroluminescence of organic materials under the influence of constant voltage ≤ 10 V. In the experiments with solar panels, he saw a blue glow.
In 1987, Chin W. Tang and Steve Van Slyke demonstrated they created the first LED of thin organic layers.
In principle, the layered structure with a separate layer for the transport of electrons, holes and their recombination in the organic layer of modern OLED remains unchanged. It provides a good chance to improve the OLED.
In the future, only the Kodak and Pioneer invested in the development of these advanced technologies.
In the 1980's. appeared early fundamental patents in the field of OLED. Here, in the first place, it should be mentioned US-Patent 4356429 (1982), on which up to 2009 appeared more than 300 patents. In general, today we know more than 6000 patents.
Significant progress was made in 1989, when Richard Friend, Jeremy Burroughes and Donald Bradley, of Cambridge University have used polymeric materials for the manufacture of light, combining the two effects - light-emitting organic materials and polymers with high electrical conductivity.
Since then, interest in the promising benefits of OLED in the scientific community has been significantly increased, and during the subsequent 10 years of this led to the emergence of the first commercially available samples. Their use is limited, however, a pocket displays, information and signal display.
The first samples of OLED, suitable for lighting purposes, appeared in 1999, and from 2000 to 2009. were significantly improved their basic settings - brightness, luminous efficiency and lifetime.
Organic light emitting diodes consist of a set of very thin organic semiconductor layers, concluded between the metal cathode and the anode-based oxide alloy indium-tin (ITO - Indium-Tin-Oxid). (By means of organic materials on the basis of hydrocarbon compounds).
The total thickness of layers in the staple - less than 100 nm.
When applied to the electrodes of low DC voltage OLED begins to radiate diffusely scattered light.
Schematically, a typical OLED structure is shown in photo 1


photo 1

In OLED structures used samoprovodyaschie polymers that do not require any conductive additives (for example, aluminum particles, or soot).
Electrical conductivity samoprovodyaschih polymers lies in the range from 10-15 to 10 cm / m (cm - Siemens - unit of electrical conductivity in the SI system).
For comparison: the Teflon and quartz - 10-16 S / m, the silicon - 10.3 S / m, with silver and copper - 108 cm / m. Thus, conductive polymers on the characteristics of conduction cover the range from insulators to metallic conductors.
The conductivity of polymers based on the overlapping of the double bonds within the polymer chain and to maximize long chains. Transfer of charges occurs under the influence of external electric field - due to abrupt movement of electrons and holes along the polymer chain. Much of the resistance occurs at the transitions between the polymer chains.
Charge carriers is "defective" electrons, which are most conductive plastic formed by oxidation.
This process is called "p-activation" - similar to the classic activation of inorganic semiconductors.
Oxidation, however, creates an order of magnitude greater density of defect electrons.
Positive charges of the polymer lattice are compensated by anions so-called conductive salt.

For transparent OLED used a glass substrate (substrate). Above it is translucent ITO-anode, and then follow the usual amorphous
organic layers and a transparent cathode. To produce OLED-panel area of 1m ² requires only about 1 g of organic materials.

OLED protection against oxidation and other external influences made glass encapsulation.
Without such a hermetic protection of organic layers from the influence of oxygen and humidity can not guarantee sufficient lifetime OLED, even after storage in working order. Direct UV-radiation and high ambient temperature may lead to accelerated aging of organic layers.

Color OLED emission determined by the structure of organic molecules. Can be realized as the primary colors (red, green, blue), and a very wide range of shades of white light. (Learn more about options for generating white light, see the publication under the heading "Cvetodiody» - «OLED - the future started today?").

In 2008, using new metal-organic complexes company Osram Opto Semiconductor (Regensburg), a sample of white OLED c radiation, which, with the average luminance of 1000 cd / m ² provides a light output 63 lm / W, a continuous emission spectrum, and good color reproduction.
In the laboratory of semiconductor technology Dresden University received a sample of white OLED with a luminous efficacy 90 lm / watt.
Color OLED characterized more bǒlshimi values luminous efficiency - up to 210 lm / W, with a number of prototypes green LED brightness reached 1500 cd / m ².

If the OLED used in signs emergency evacuation routes, it is sufficient luminous brightness of the panel is equal to 100 cd / m ².
For the purposes of illumination brightness white OLED light must be at least 1500-2000 cd / m ².

For luminous efficiency OLED today already exceed the compact fluorescent lamps. Certain progress has been made in increasing the life of OLED. If the red and green samples with a brightness of 1000 cd / m ² is achievable lifespan from 50 000 to 250 000 hours, then the blue OLED - yet only ≤ 20 000 hours.
For inorganic LEDs life often measured by 50 -%-Term decline of brightness from the original value.
For OLED, which will be used in general lighting systems, life should be measured as the time of use, after which the brightness drops by 30%.

Producers of the first prototypes of organic light-emitting diodes believe that in the next 5 years have all predosylki to start mass production of these innovative light sources.
Concern Philips Lighting assumes "to launch" mass production of OLED-modules even in 2010. (Source: www.displaysearch.com).
Today OLED for general lighting can not yet be considered cost-effective: a module with a luminous flux of 1000 lumens is more than 1000 €, while the price of an inorganic light-emitting diode with the same stream - 40 €.
The first samples of OLED for lighting purposes cost 500 € / m ².

Given the technological progress achieved widespread commercial availability of OLED white light is projected in 2014, but provided the price is not above 50 € / m ².


The prospect of development of mass production of organic light-emitting diodes

Manufacturing Company Research and manufacture of prototypes OLED Anticipated start mass production
Osram 2008-2012 gg. 2012
Philips 2008-2010 gg. 2010
Lumiotec 2009-2011 gg. 2011
GE (General Electric Lighting) 2010-2011 gg. 2012
Konica Minolta 2010-2011 gg. 2012
Other firms 2011-2012. 2013

The graph (Photo 2) illustrate the dynamics of change in luminous efficiency OLED and inorganic LEDs in comparison with the main sources of the world wide use (1995-2009 gg. And forecast to 2015)


Great interest OLED, which in the "off" state, or almost totally reflect light or create the effect of a flat mirror.

An impressive example is shown in photo 3, which shows kompyuternaya 3D-model of the interior of the future in the fading light: luminous panels - is OLED, which made a constant voltage; "window" through which contact with the outside world - is dead OLED.

photo 3

Photo 4 - square sample OLED (170h170 mm) with white radiation, manufactured by Osram Opto Semiconductor - represented in the on and off states.

At the fair "Euroluce 2009" in Milan the company Philips has demonstrated the world's first collection of lighting fixtures based on OLED. In this series, called "OH ... LED", including table, floor, wall and hanging lamps (photo 5).
photo 4 photo 5

Scientific and practical work in the field of OLED, despite the economic problems continue in both Europe and the United States.
In Germany, invested more than € 500 million on two basic projects ( "OPAL" and "TOPAS"), which should be completed in 2011-2012.

Possible applications of OLED lighting technology in the application:
• Functional and decorative lighting.
• Orientation lighting in car interiors, aircraft, facilities and passenger ships in the interiors of public buildings.
• Illuminated advertising panels, emergency lighting fixtures with icons - signs for emergency evacuation routes.
• Transparent model - to be embedded in the windows and shelves in museums and shopping halls
• Luminous details overalls personnel Rescue Services

Long-term prognosis of promising applications of OLED:
• Large luminous panels on the ceilings and walls - neslepyaschee diffusely scattered light facilities.
• luminous windows that after sunset replace daylight (photo 3).
• Luminous curtains and blinds.
• Illuminated interior rear wall in domestic refrigerators.

For complete information please review the previous publications under the heading "Interesting about the light - Lighting Equipment - LEDs:
• «OLED-organic light-emitting diodes: the future started today?"
• «OLED - new designs"
• «New organic LED with a record life - 60tys. o'clock
• «Philips Lighting: the first models based on OLED lighting for residential interior"