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Encyclopedia > Organic light emitting diode

An organic light-emitting diode (OLED) is a thin-film light-emitting diode (LED) in which the emissive layer is an organic compound. These devices promise to be much cheaper to fabricate than traditional LEDs. When the emissive layer is polymeric, varying amounts of OLEDs can be deposited in arrays on a screen using simple "printing" methods to create a graphical colour display, for use as television screens, computer displays, portable system screens, and in advertising and information board applications. OLED may also be used in lighting devices. OLEDs are available as distributed sources while the inorganic LEDs are point sources of light. Prior to standardization, OLED technology was also referred to as OEL or Organic Electro-Luminescence. Red, pure green, and blue LEDs. ... The word emission generally means sending something out. ... An organic compound is any member of a large class of chemical compounds whose molecules contain carbon, with exception of carbides, carbonates and carbon oxides. ... A polymer is a generic term used to describe a substantially long molecule. ... Nineteen inch (48 cm) CRT computer monitor A computer display, monitor or screen is a computer peripheral device capable of showing still or moving images generated by a computer and processed by a graphics card. ... Architect lamps Dark lighting in a concert hall allow laser effects to be visible In the 2005 Classical Spectacular performance, a state-of-the-art lighting system was used to accompany the music Lighting refers to the devices or techniques used for illumination, usually referring to artificial light sources such...


One of the great benefits of an OLED display over the traditional LCD displays found in computer displays is that OLED displays do not require a backlight to function. This means that they draw far less power and they can be used with small portable devices which have mostly been using monochrome low-resolution displays to conserve power. This will also mean that they will be able to last for long periods of time with the same amount of battery charge. Reflective twisted nematic liquid crystal display. ...


The world's first digital camera with an OLED display was the Kodak LS633 model revealed at the Photo Marketing Association (PMA) trade show in March 2003. A SiPix digital camera next to a matchbox to show scale. ... Eastman Kodak Company (NYSE: EK) is a large multinational public company producing photographic equipment. ... The Photo Marketing Association International (PMAI) is an association of photographic dealers in the continously expanding photo/imaging industry. ... 2003(MMIII) is a common year starting on Wednesday of the Gregorian calendar. ...

Contents


Two main directions

An OLED display from Samsung.
An OLED display from Samsung.
The largest OLED display prototype as of May 2005, at 40 inches. Compare with above.
The largest OLED display prototype as of May 2005, at 40 inches. Compare with above.

There are two main directions in OLED: small molecules and polymers. Samsung OLED display File links The following pages link to this file: Organic light-emitting diode ... Samsung OLED display File links The following pages link to this file: Organic light-emitting diode ... Taken from http://www. ... Taken from http://www. ...


The first technology was developed by Eastman-Kodak and is usually referred to as "small-molecule" OLED. The production of small-molecule displays requires vacuum deposition which makes the production process expensive and not so flexible. The term OLED traditionally refers to this type of device, though some are using the term SM-OLED. Eastman Kodak Company (NYSE: EK) is a large multinational public company producing photographic equipment. ...


A second technology, developed by Cambridge Display Technologies or CDT, is called LEP or Light-Emitting Polymer, though these devices are better known as Polymer Light Emitting Diodes (PLEDs). Although this technology lags the small-molecule development by several years (primarily in efficiency and lifetime), it is more promising because of an easier production technique. No vacuum is required, and the emissive materials can be applied on the substrate by a technique derived from commercial inkjet printing. This means that PLED displays can be made in a very flexible and cheap way. A polymer is a generic term used to describe a substantially long molecule. ... The word substrate can mean the following: In biochemistry, a substrate is a molecule which is acted upon by an enzyme. ... Ink jet printers are the most common type of computer printer; and industry and commerce also use them extensively for special-purpose applications. ...


Recently a third hybrid light emitting layer has been developed that uses nonconductive polymers doped with light-emitting, conductive molecules. The polymer is used for its production and mechanical advantages without worrying about optical properties. The small molecules then emit the light and have the same longevity that they have in the SM-OLEDs.


How OLEDs work

OLEDs work on the principle of electroluminescence. The key to the operation of an OLED is an organic luminophore. Excitons, which consist of a bound, excited electron and hole pairs, are generated inside the emissive layer. When the exciton's electron and hole combine, a photon can be emitted. A major challenge in OLEDs is tuning the devices such that holes and electrons meet in the emissive layer in equal quantities. This is difficult because the mobilities of holes are much lower than that of electrons in organic compounds. Light emission can only occur when singlet excitons form in the emissive because the materials currently employed are typically fluorophors and cannot emit light from a triplet state. This is a problem because only one in four excitons is a singlet. By incorporating transition metals into small-molecule OLEDs, the triplet and singlet states can be mixed by spin-orbit coupling, which leads to emission from the triplet state. This emission is always red-shifted, making blue light more difficult to achieve from a triplet excited state. It is pointed out that triplet emitters can have a four times higher OLED efficiency (see ref. 1). Electroluminescence is an optical phenomenon and electrical phenomenon where a material such as a natural blue diamond emits light when an electric current is passed through it. ... A luminophore is an atom or atomic grouping in an organic compound that manifests luminescence (chemoluminescence). ... An exciton is a bound state of an electron and a hole in an insulator (or semiconductor), or in other words, a Coulomb correlated electron/hole pair. ... Properties The electron is a fundamental subatomic particle which carries a negative electric charge. ... In solid state physics, an electron hole (usually referred to simply as a hole) is the absence of an electron from the otherwise full valence band. ... For the Science Fiction weapon, as seen in Star Trek, see Photon torpedo. ... Mobility is the ability and willingness to move or change; this can depend on motor skills, special tools such as a walking stick, Zimmer Frame or wheelchair, vehicles, uncongested roads, public transport; mobility with regard to ones home depends on availability of houses and being bound to an area... A fluorophor is a compound that emits light via fluorescence. ...


To create the excitons, a thin film of the luminophore is sandwiched between electrodes of differing work functions. Electrons are injected into one side from a metal cathode, while holes are injected in the other from an anode (think of the anode as sucking electrons out). These electrons and holes move into the emissive layer and can meet to form excitons. (Mechanisms and details of exciton formation are discussed in ref.s 1 and 2) An electrode is a conductor used to make contact with a nonmetallic part of a circuit (e. ... The work function is the minimum energy (usually measured in electron volts) needed to remove an electron from the Fermi level in a metal to a point at infinite distance away outside the surface. ... Diagram of a copper cathode in a Daniells cell. ... Diagram of a zinc anode An anode (from the Greek άνοδος = going up) is the positive electrode in an electrolytic system or circuit. ...


Derivatives of PPV, poly(p-phenylene vinylene) and poly(fluorene), are commonly used as polymer luminophores in OLEDs. Indium tin oxide is a common transparent anode, while aluminium or calcium are common cathode materials. Other materials are added between the cathode/anode and the emissive layer to enhance the efficiency by facilitating or hindering hole or electron injection. You may find more materials for this technology. Poly(p-phenylene vinylene) (PPV) is conducting polymer of the rigid-rod polymer host family. ... A polymer is a generic term used to describe a substantially long molecule. ... Indium tin oxide (ITO) is a mixture of indium(III) oxide (In2O3) and tin(IV) oxide (SnO2), typically 90% In2O3, 10% SnO2 by weight. ... General Name, Symbol, Number aluminium, Al, 13 Chemical series poor metals Group, Period, Block 13, 3, p Appearance silvery Atomic mass 26. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Atomic mass 40. ...


Advantages

The radically different manufacturing process of OLEDs lends itself to many advantages over traditional flat panel displays. Since OLEDs can be printed onto a substrate using traditional inkjet technology they can have a significantly lower cost than LCDs or plasma displays. A more scalable manufacturing process enables the possibility of much larger displays. Unlike LCDs which employ a back-light and are incapable of showing true black, an off OLED element produces no light allowing for infinite contrast ratios. The range of colors, brightness, and viewing angle possible with OLEDs is greater than that of LCDs or plasma displays. Flat panel displays encompass a growing number of technologies enabling video displays that are lighter and much thinner than traditional television and video displays using cathode ray tubes, usually less than 10 cm (4 inches) thick. ... Ink jet printers are the most common type of computer printer; and industry and commerce also use them extensively for special-purpose applications. ... A plasma display is an emissive flat panel display where light is created by phosphors excited by a plasma discharge between two flat panels of glass. ... The contrast ratio is a metric of a video display defined as the ratio of the light intensity of the brightest possible color a display is capable of to the darkest color a display is capable of. ...


Without the need of a backlight, OLEDs use less than half the power of LCD displays and are well-suited to mobile applications such as cell phones and digital cameras. Motorola T2288 mobile phone A mobile phone is a portable electronic device which behaves as a normal telephone whilst being able to move over a wide area (compare cordless phone which acts as a telephone only within a limited range). ... A SiPix digital camera next to a matchbox to show scale. ...


The fact that OLEDs can be printed onto flexible substrates opens the door to new applications such as roll-up displays or displays embedded in clothing.


Disadvantages

The biggest technical problem left to overcome has been the limited lifetime of the devices. Red and green OLED elements already had lifetimes of well over 20,000 hours but blue OLED lifetimes had lagged significantly behind. However, in May 2005, Cambridge Display Technology announced a blue OLED with a lifetime of over 100,000 hours. Lifetime can refer to: The length of time a person is alive. ...


According to Kodak, which is developing small molecule OLED, lifetime problems are not so significant for that type of OLED, mainly as a result of doping the base material of the OLEDs, which, they claim, has led to much better device performance both electrically and optically. Universal Display for example have produced a blue OLED that has a lifetime of 10,000 hours. There are still a number of problems to overcome though. One of these is intrusion of water into displays which damages and destroys the organics. Therefore, improved sealing processes are important for practical manufacturing. Also, efficient outcoupling of waveguided light within the substrates is an area of continued research. Eastman Kodak Company (NYSE: EK) is a large multinational public company producing photographic equipment. ... In physics, optics, and telecommunication, a waveguide is a structure that confines and guides a propagating electromagnetic wave. ...


Commercial development of the technology is also restrained by patents held by Kodak and other firms, requiring other companies to acquire a license. A patent is a set of exclusive rights granted by a government to an inventor or applicant for a limited amount of time (normally maximum 20 years from the filing date, depending on extension). ... Eastman Kodak Company (NYSE: EK) is a large multinational public company producing photographic equipment. ... It has been suggested that Licensing (strategic alliance) be merged into this article or section. ...


Commercial potential

Many proponents and investors in the burgeoning field of OLED research and development are optimistic regarding the technology because it offers the potential to revolutionize the flat-panel display (FPD) industry, and therefore change how and where people can watch television or use computers.


OLED technology is already finding commercial applications as diverse as heads-up displays in aircraft, displays inside high-end sports cars, in head-mounted displays and even as a replacement for lightbulbs. More speculative uses include ideas as varied as clothing that incorporates flexible OLED screens in order to change its color at the click of a button, or high definition virtual reality rooms where OLED screens cover every surface. an HMD A head-mounted display (HMD) is a display device that a user typically wears on the head to have video information directly displayed in front of their eyes. ...


According to data compiled by the Society for Information Display: in 2003, the world OLED market was only $251 million. As of 2004, the world-wide OLED market was approximately $408 million. By 2008, experts are unsure exactly how fast it will have grown - conservative estimates are as low as $3 billion while other industry analysts feel it could reach as high as $8 billion. If such a high number of sales are reached, it will have a substantial economic impact for developers and vendors of LCD displays and CRT displays. LCD redirects here. ...


References

Scientific American is one of the oldest and most serious popular-science magazines. ...

See also

Flexible electronics is a technology for building electronic circuits by depositing electronic devices on flexible substrates such as plastic. ... A FOLED is a term used for a flexible OLED. While OLEDs might commonly be applied to sturdy panels, such as glass, a FOLED is the same thing built on a flexible substrate. ...

External links


 
 

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