DEPARTMENT OF ELECTRONICS ENGINEERING SCHOOL OF ENGINEERING AND TECHNOLOGY PONDICHERRY UNIVERSITY PUDUCHERRY 605014

CREDIT SEMINAR

TOPIC: OLED DISPLAY TECHNOLOGY

SUBMITTED BY : SUBMITTED TO: NAME: ANIL KUMAR YADAV DR. T.SHANMUGANTHAM

COURSE: M.TECH( ELECTRONICS) (ASSOCIATE PROFESSOR)

REG. NO: 13304025

Table of content

1. Introduction :

2. Working principle:

3. Types of OLEDs:

4. Material used for oled

5. Foldable or flexible oled

6. Advantage & disadvantage

7. Global Market news

8. Conclusion

9. References

AbstractOLED Flexible displays are an exciting development because of their physical and performance attributes and their capability to enable new products requiring displays with unique form factors that the current rigid glass substrate based displays cannot support. Flexible displays can be very thin, light weight, have unique form factors and be highly rugged and not prone to breakage on impact unlike rigid and flat glass substrate based displays. The flexible form factors such as having an arbitrary shape, ability to be curved, conformal, bendable, and rollable can enable a variety of new applications and products. In this chapter, we will discuss the various attributes of the flexible displays, their potential applications, and the display media appropriate for flexible displays. Like many electronic devices, the majority of today's smartphones aren't made to survive abuse. With new display technologies that are currently in development however, smartphones of the future may be more durable. These new display technologies enable flexible displays that can be rolled, dropped, squished, and stepped on without damage.Although the dream of having a smartphone that can withstand such abuse may seem far-off, flexible display technology has been in development for a while now. We've seen prototypes at gadget shows, heard and seen demonstrations on various sites, and dreamed of the day when we can have our own flexible smartphone. New rumors suggest our dream may not be too far from reality. In fact, it's possible we could see the launch of the first flexible phone sometime next year.

Introduction :An exciting technology has been available in many small devices such as cell phones and digital camera displays for the last 13 years. Soon it may available for use in larger standard office and home entertainment displays. The technology is organic light emitting diode (OLED). It is possible that in the next 2-3 years you may see an 80” OLED in your living room or board room that only requires 10 or less volts of power to operate. OLED display devices use organic carbon-based films, sandwiched together between two charged electrodes. One is a metallic cathode and the other a transparent anode, which is usually glass. Online encyclopedia, Wikipedia, defines an organic compound as “any member of a large class of chemical compounds whose molecules contain carbon, with the exception of carbides, carbonates, carbon oxides and gases containing carbon.”

An OLED (organic light-emitting diode) is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compoundwhich emits light in response to an electric current. This layer of organic semiconductor is situated between

two electrodes. Generally, at least one of these electrodes is transparent. OLEDs are used to create digital displays in devices such as television screens, computer monitors, portable systems such as mobile phones, handheld games consoles and PDAs. A major area of research is the development of white OLED devices for use in solid-state lighting applications

The basic components of an OLED are:

1. Substrate-This is support for the OLED.

2. Anode-The anode removes electrons when a current flow through the device.

3. Organic layers-These layers are made of organic molecules or polymers.

4. Conducting layer -This layer is made of organic plastic molecules that send

electrons out from the anode.

5. Emissive layer. This layer is made of organic plastic molecules(different ones

from the conducting layer) that transport electrons from the cathode; this is where

light is made.

6. Cathode (may or may not be transparent depending on the type of OLED). The

cathode injects electrons when a current flows through the device.

Applying the organic layers to the substrate can be accomplished in three ways:

1. Vacuum Deposition or Vacuum Thermal Evaporation (VTE).In a vacuum chamber, the organic molecules are evaporated through a slow heat process and then allowed to condense as thin films onto a cooled substrate. This is a very inefficient and expensive process.

2. Organic Vapor Phase Deposition (OVPD). This process employs an inert carrier gas (such as nitrogen) to precisely transfer films of organic material onto a cooled substrate in a hot-walled,low-pressure chamber. The precise transfer and ability to better control film thickness translates to lower material cost and higher production throughput.

3. Inkjet Printing. OLEDs are sprayed onto the substrate the same way our desktop inkjet printer sprays ink onto paper. This greatly reduces the cost of manufacturing OLEDs and allows for printing on very large films. This allows for a much lower cost and larger home displays and PIPD products.One of the major benefits of OLEDs is their low power consumption when compared to traditional LEDs or LCDs. OLEDs also do not require backlighting to function, which in addition to using less power, also lowers manufacturing costs. Even with all the layers that make up an OLED, this is an emissive technology – meaning it generates its own light. An OLED display is very thin and compact, typically has a viewing angle of 160 degrees and will operate on as little as 2 volts. Imagine today’s typical 60” flat-screen display, but instead of an 8-in. thick, 250-lb. plasma display or a 65-lb. LCD, your 60” OLED display is only 1/2” thick and weighs roughly 30 lbs.!

Other OLED advantages over traditional LCDs include:• Increased brightness• Faster response time (fast action, live events)• Greater durability• Thinner and lighter weight product• Higher contrast

How do OLEDs work?

• OLED do not have a backlight unlike liquid crystal display (LCD). OLED create light by the following process: A battery or power supply sends a voltage through the OLED. An electrical current flows from the cathode to the organic layer and anode. As explained earlier, the anode removes electrons and adds electron holes in the conductive layer. Between the organic layers is where electrons fill the holes and give off energy in the form of photon light.

Working principle:

A typical OLED is composed of a layer of organic materials situated between two electrodes, the anode and cathode, all deposited on a substrate. The organic molecules are electrically conductive as a result of delocalization of pi electronscaused by conjugation over all or part of the molecule. These materials have conductivity levels ranging from insulators to conductors, and therefore are considered organic semiconductors. The highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of organic semiconductors are analogous to the valence and conduction bands of inorganic semiconductors.

Originally, the most basic polymer OLEDs consisted of a single organic layer. One example was the first light-emitting device synthesised by J. H. Burroughes et al., which involved a single layer of poly(p-phenylene vinylene). However multilayer OLEDs can be fabricated with two or more layers in order to improve device efficiency. As well as conductive properties, different materials may be chosen to aid charge injection at electrodes by providing a more gradual electronic profile, or block a charge from reaching the opposite electrode and being wasted.]

 Many modern OLEDs incorporate a simple bilayer structure, consisting of a conductive layer and an emissive layer. More recent developments in OLED architecture improves quantum efficiency (up to 19%) by using a graded heterojunction.

 In the graded heterojunction architecture, the composition of hole and electron-transport materials varies continuously within the emissive layer with a dopant emitter. The graded heterojunction architecture combines the benefits of both conventional architectures by improving charge injection while simultaneously balancing charge transport within the emissive region.

During operation, a voltage is applied across the OLED such that the anode is positive with respect to the cathode. Anodes are picked based upon the quality of their optical transparency, electrical conductivity, and chemical stability.]A current of electrons flows through the device from cathode to anode, as electrons are injected into the LUMO of the organic layer at the cathode and withdrawn from the HOMO at the anode. This latter process may also be described as the injection of electron holes into the HOMO.

Electrostatic forces bring the electrons and the holes towards each other and they recombine forming an exciton, a bound state of the electron and hole. This happens closer to the emissive layer, because in organic semiconductors holes are generally more mobile than electrons. The decay of this excited state results in a relaxation of the energy levels of the electron, accompanied by emission of radiation whose frequency is in thevisible region. The frequency of this radiation depends on the band gap of the material, in this case the difference in energy between the HOMO and LUMO.

As electrons and holes are fermions with half integer spin, an exciton may either be in a singlet state or a triplet state depending on how the spins of the electron and hole have been combined. Statistically three triplet excitons will be formed for each singlet exciton. Decay from triplet states (phosphorescence) is spin forbidden, increasing the timescale of the transition and limiting the internal efficiency of fluorescent devices. Phosphorescent organic light-emitting diodes make use of spin–orbit interactions to facilitate intersystem crossing between singlet and triplet states, thus obtaining emission from both singlet and triplet states and improving the internal efficiency.

Indium tin oxide (ITO) is commonly used as the anode material. It is transparent to visible light and has a high work function which promotes injection of holes into the HOMO level of the organic layer. A typical conductive layer may consist of PEDOT:PSS as the HOMO level of this material generally lies between the workfunction of ITO and the HOMO of other commonly used polymers, reducing the energy barriers for hole injection. Metals such as barium and calcium are often used for the cathode as they have low work functions which promote injection of electrons into the LUMO of the organic layer.[28] Such metals are reactive, so they require a capping layer of aluminium to avoid degradation.

Experimental research has proven that the properties of the anode, specifically the anode/hole transport layer (HTL) interface topography plays a major role in the efficiency, performance, and lifetime of organic light emitting diodes. Imperfections in the surface of the anode decrease anode-organic film interface adhesion, increase electrical resistance, and allow for more frequent formation of non-emissive dark spots in the OLED material adversely affecting lifetime. Mechanisms to decrease anode roughness for ITO/glass substrates include the use of thin films and self-assembled monolayers. Also, alternative substrates and anode materials are being considered to increase OLED performance and lifetime. Possible examples include single crystal sapphire substrates treated with gold (Au) film anodes yielding lower work functions, operating voltages, electrical resistance values, and increasing lifetime of OLEDs.

Single carrier devices are typically used to study the kinetics and charge transport mechanisms of an organic material and can be useful when trying to study energy transfer processes. As current through the device is composed of only one type of charge carrier, either electrons or holes, recombination does not occur and no light is emitted. For example, electron only devices can be obtained by replacing ITO with a lower work function metal which increases the energy barrier of hole injection. Similarly, hole only devices can be made by using a cathode made solely of aluminium, resulting in an energy barrier too large for efficient electron injection.

Types of OLEDs:

There currently are six types of OLED screens, each designed fora different type of use. The types are:

1. Passive Matrix OLEDs (PMOLEDs) -PMOLEDs have strips of cathode, organic layers and strips of anode. The anode strips are arranged perpendicular to the cathode strips. The intersections of the cathode and anode make up the pixels where light is emitted. External circuitry applies current to selected strips of anode and cathode, determining which pixels get turned on and which pixelsremain off. Again, the brightness of each pixel is proportional to the amount of applied current.

PMOLEDs are easy to make, but they consume more power than other types of OLED, mainly due to the power needed for the external circuitry.

PMOLEDs are most efficient for text and icons and are best suited for small screens (2- to 3-inch diagonal) such as those you find in cell phones, PDAs and MP3 players. Evenwith the external circuitry, PMOLEDs consume less battery power than the LCDs that are currently used in these devices.A PMOLED display uses a simple control scheme in which you control each row (or line) in the display sequentially (one at a time). PMOLED electronics do not contain a storage capacitor and so the pixels in each line are actually off most of the time. To compensate for this you need to use more voltage to make them brighter. If you have 10 lines, for example, you have to make the one line that is on 10 times as bright (the real number is less then 10, but that's the general idea).

So while PMOLEDs are easy (and cheap) to fabricate, they are not efficient and the OLED materials suffer from lower lifetime (due to the high voltage needed). PMOLED

displays are also restricted in resolution and size (the more lines you have, the more voltage you have to use). PMOLED displays are usually small (up to 3" typically) and are used to display character data or small icons: they are being used in MP3 players, mobile phone sub displays, etc.

The first OLED products in the market used PMOLEDs - these were MP3 players, sub-displays on cellphones and radio decks for automobiles. The displays were small and usually with just one or two colors. When AMOLED panels started to emerge in 2007 and 2008 we have seen these larger displays in mobile video players, digital cameras, mobile phones main displays and even OLED TV sets.

2. Active-matrix OLEDs (AMOLEDs):-AMOLEDs have full layers of cathode, organic molecules and anode, but the anode layer overlays a thin film transistor (TFT) array that forms a matrix. The TFT array itself is the circuitry that determines which pixels get turned on to form an image.

AMOLEDs consume less power than PMOLEDs because the TFTarray requires less power than external circuitry, so they are efficient for large displays. AMOLEDs also have faster refresh rates suitable for video. The best uses for AMOLEDs are computermonitors, large-screen TVs and electronic signs or billboards.

AMOLED (active-matrix organic light-emitting diode) is a display technology for use in mobile devices and televisions. OLED describes a specific type of thin-film-display technology in which organic compounds form the electroluminescent material, and active matrix refers to the technology behind the addressing of pixels.

As of 2012, AMOLED technology is used in mobile phones, media players and digital cameras, and continues to make progress toward low-power, low-cost and large-size (for example, 40-inch) applications

An AMOLED display consists of an active matrix of OLED pixels that generate light (luminescence) upon electrical activation that have been deposited or integrated onto a thin-film-transistor (TFT) array, which functions as a series of switches to control the current flowing to each individual pixel. Typically, this continuous current flow is controlled by at least two TFTs at each pixel (to trigger the luminescence), with one TFT to start and stop the charging of a storage capacitor and the second to provide a voltage source at the level needed to create a constant current to the pixel, thereby eliminating the need for the very high currents required for passive-matrix OLED operation.

TFT backplane technology is crucial in the fabrication of AMOLED displays. The two primary TFT backplane technologies, namely polycrystalline silicon (poly-Si) and amorphous silicon (a-Si), are used today in AMOLEDs. These technologies offer the potential for fabricating the active-matrix backplanes at low temperatures (below 150°C) directly onto flexible plastic substrates for producing flexible AMOLED displays

3. Transparent OLEDs have only transparent components (substrate, cathode and anode) and, when turned off, are up to 85% as transparent as their substrate. When a transparent OLED display is turned on, it allows light to pass in both directions. A transparent OLED display can be either active- or passive-matrix.

4. Top-emitting OLEDs have a substrate that is either opaque orreflective. They are best suited to active-matrix design. Manufacturersmay use top-emitting OLED displays in smart cards.

5. White OLEDs emit white light that is brighter, more uniform and more energy efficient than that emitted by fluorescent lights. White OLEDs also have the true-color qualities of incandescent lighting. Because OLEDs can be made in large sheets, they can replace fluorescent lights that are currently used in homes and buildings. Their use could potentially reduce energy costs for lighting

Foldable or flexible OLEDsFlexible OLED is an emerging display technology that enables beautiful and efficient displays and lighting panels. Thin OLEDs are already being used in many mobile devices and TVs, and the next generation of these panels will be flexible and bendable

Different kinds of flexibility

When we talk about flexible OLEDs, it's important to understand what that means exactly. A flexible OLED is based on a flexible substrate which can be either plastic, metal or flexible glass. The plastic and metal panels will be light, thin and very durable - in fact they will be virtually shatter-proof.

Flexible oleds have substrates made of very flexible metallic foils or plastics. Foldable OLEDs are very lightweight and durable. Their use in devices such as cell phones and PDAs can reduce breakage, a major cause for return or repair. Potentially, foldableOLED displays can be sewn into fabrics for “smart” clothing, such as outdoor survival clothing with an integrated computer chip, cell phone, GPS receiver and OLED display sewn into it.

Second generation flexible OLED devices may indeed be flexible to the final user. Finally, when the technology is ready, we may see OLED panels that you can fold, bend or stretch. This may create all sorts of exciting designs that will enable large displays to be placed in a mobile device and only be opened when required.

Flexible OLED products

After years of research, in October 2013, Samsung announced the world's first product to use a flexible OLED display - the Galaxy Round curved smartphone. This is an Android 4.3 smartphone similar to the Galaxy Note 3, with the major feature being the 5.7" Full-HD curved (400 mm curvature radius) flexible display (samsung simply refers to it as a flexible Super AMOLED, strangely they are not using the YOUM brand)

LG is producing flexible OLED panels, 6" in size. It is expected that LG will also unveil their own smartphone (called the G Flex) with a flexible OLED towrads the end of 2013.

Initial capacity in both companies is low (a few hundreds of thousands of panels per month). Samsung's capacity is higher (they are using a Gen-5.5 line and LG is using a Gen-4.5 line) but this too will not be enough even for a single mass market phone. The company are probably waiting to see how consumers react to those new panels before they commit to increase capacity.

Samsung launched their YOUM flexible OLED panels in January 2013, showing some cool prototypes of curved and flexible OLED displays.

Material technologies

Small molecules

Alq3, commonly used in small molecule OLEDs Efficient OLEDs using small molecules were

first developed by Dr. Ching W. Tang et al  at Eastman Kodak. The term OLED traditionally

refers specifically to this type of device, though the term SM-OLED is also in use.

Molecules commonly used in OLEDs include organometallic chelates (for example Alq3, used in the organic light-emitting device reported by Tang et al.), fluorescent and phosphorescent dyes and conjugated dendrimers. A number of materials are used for their charge transport properties, for example triphenylamine and derivatives are commonly used as materials for hole transport layers.[33] Fluorescent dyes can be chosen to obtain light emission at different wavelengths, and compounds such as perylene, rubrene and quinacridone derivatives are often used.[34] Alq3 has been used as a green emitter, electron transport material and as a host for yellow and red emitting dyes.

The production of small molecule devices and displays usually involves thermal evaporation in a vacuum. This makes the production process more expensive and of limited use for large-area devices than other processing techniques. However, contrary to polymer-based devices, the vacuum deposition process enables the formation of well controlled, homogeneous films, and the construction of very complex multi-layer structures. This high flexibility in layer design, enabling distinct charge transport and charge blocking layers to be formed, is the main reason for the high efficiencies of the small molecule OLEDs.

Coherent emission from a laser dye-doped tandem SM-OLED device, excited in the pulsed regime, has been demonstrated. The emission is nearly diffraction limited with a spectral width similar to that of broadband dye lasers.

Researchers report luminescence from a single polymer molecule, representing the smallest possible organic light-emitting diode (OLED) device.Scientists will be able to optimize substances to produce more powerful light emissions. Finally, this work is a

first step towards making molecule-sized components that combine electronic and optical properties. Similar components could form the basis of a molecular computer.

Polymer light-emitting diodes

poly( p -phenylene vinylene) , used in the first PLED. Polymer light-emitting diodes (PLED),

also light-emitting polymers (LEP), involve an electroluminescent conductive polymer that

emits light when connected to an external voltage. They are used as a thin film for full-

spectrum colour displays. Polymer OLEDs are quite efficient and require a relatively small

amount of power for the amount of light produced.

Vacuum deposition is not a suitable method for forming thin films of polymers. However, polymers can be processed in solution, and spin coating is a common method of depositing thin polymer films. This method is more suited to forming large-area films than thermal evaporation. No vacuum is required, and the emissive materials can also be applied on the substrate by a technique derived from commercial inkjet printing.However, as the application of subsequent layers tends to dissolve those already present, formation of multilayer structures is difficult with these methods. The metal cathode may still need to be deposited by thermal evaporation in vacuum. An alternative method to vacuum deposition is to deposit a Langmuir-Blodgett film

Typical polymers used in PLED displays include derivatives of poly( p -phenylene vinylene) and polyfluorene. Substitution of side chains onto the polymer backbone may determine the colour of emitted light or the stability and solubility of the polymer for performance and ease of processing. While unsubstituted poly(p-phenylene vinylene) (PPV) is typically insoluble, a number of PPVs and related poly(naphthalene vinylene)s (PNVs) that are soluble in organic solvents or water have been prepared via ring opening metathesis polymerization.

Phosphorescent materials

Ir(mppy)3, a phosphorescent dopant which emits green light.

Phosphorescent organic light emitting diodes use the principle of electrophosphorescence to

convert electrical energy in an OLED into light in a highly efficient manner, with the internal

quantum efficiencies of such devices approaching 100%.Typically, a polymer such as poly(n-

vinylcarbazole) is used as a host material to which an organometallic complex is added as a

dopant. Iridium complexes [48]  such as Ir(mppy)3 are currently the focus of research, although

complexes based on other heavy metals such as platinum have also been used.

The heavy metal atom at the centre of these complexes exhibits strong spin-orbit coupling, facilitating intersystem crossing between singlet and triplet states. By using these phosphorescent materials, both singlet and triplet excitons will be able to decay radiatively, hence improving the internal quantum efficiency of the device compared to a standard PLED where only the singlet states will contribute to emission of light.

Applications of OLEDs in solid state lighting require the achievement of high brightness with good CIE coordinates (for white emission). The use of macromolecular species like polyhedral oligomeric silsesquioxanes (POSS) in conjunction with the use of phosphorescent species such as Ir for printed OLEDs have exhibited brightnesses as high as 10,000 cd/m2.

OLED AdvantagesThe LCD is currently the display of choice in small devices and is also popular in large-screen TVs. Regular LEDs often form the digits on digital clocks and other electronic devices. OLEDs offer many advantages over both LCDs and LEDs, including:• The plastic, organic layers of an OLED are thinner, lighter and more flexible than the crystalline layers in an LED or LCD.• Because the light-emitting layers of an OLED are lighter, the substrate of an OLED can be flexible instead of rigid. OLED substrates can be plastic rather than the glass used for LEDs and LCDs.• OLEDs are brighter than LEDs. Because the organic layers of an OLED are much thinner than the corresponding inorganic crystal layers of an LED, the conductive and emissive layers of an OLED can be multi-layered. Also, LEDs and LCDsrequire glass for support, and glass absorbs some light. OLEDs do not require glass.• OLEDs do not require backlighting like LCDs. LCDs work by selectively blocking areas of the backlight to make the images that you see, while OLEDs generate light themselves. Because OLEDs do not require backlighting, they consume much less power than LCDs (most of the LCD power goes to the backlighting). This is especially important for battery-operated devices such as cell phones.• OLEDs are easier to produce and can be made to larger sizes. Because OLEDs are essentially plastics, they can be made into large, thin sheets. It is much more difficult to grow and lay down so many liquid crystals.• OLEDs have large fields of view, about 170 degrees. Because LCDs work by blocking light, they have an inherent viewing obstacle from certain angles. OLEDs produce their own light, so they have a much wider viewing range.Lower cost in the future

OLEDs can be printed onto any suitable substrate by an inkjet printer or even by screen printing, theoretically making them cheaper to produce than LCD or plasma displays. However, fabrication of the OLED substrate is more costly

than that of a TFT LCD, until mass production methods lower cost through scalability. Roll-to-roll vapour-deposition methods for organic devices do allow mass production of thousands of devices per minute for minimal cost, although this technique also induces problems in that devices with multiple layers can be challenging to make because of registration, lining up the different printed layers to the required degree of accuracy.

Lightweight and flexible plastic substrates

OLED displays can be fabricated on flexible plastic substrates leading to the possible fabrication of flexible organic light-emitting diodes for other new applications, such as roll-up displaysembedded in fabrics or clothing. As the substrate used can be flexible such as polyethylene terephthalate (PET),the displays may be produced inexpensively.

Wider viewing angles and improved brightness

OLEDs can enable a greater artificial contrast ratio (both dynamic range and static, measured in purely dark conditions) and a wider viewing angle compared to LCDs because OLED pixels emit light directly. OLED pixel colors appear correct and unshifted, even as the viewing angle approaches 90° from normal.

Better power efficiency and thickness

LCDs filter the light emitted from a backlight, allowing a small fraction of light through. So, they cannot show true black. However, an inactive OLED element does not produce light or consume power, thus allowing true blacks. Dismissing the backlight also makes OLEDs lighter because some substrates are not needed. This allows electronics potentially to be manufactured more cheaply, but, first, a larger production scale is needed, because OLEDs still somewhat are niche products.When looking at top-emitting OLEDs, thickness also plays a role when talking about index match layers (IMLs). Emission intensity is enhanced when the IML thickness is 1.3–2.5 nm. The refractive value and the matching of the optical IMLs property, including the device structure parameters, also enhance the emission intensity at these thicknesses.

Response time

OLEDs also can have a faster response time than standard LCD screens. Whereas LCD displays are capable of between 1 and 16 ms response time offering a refresh rate of 60 to 480 Hz, an OLED theoretically can have a response time less than 0.01 ms, enabling a refresh rate up to 100,000 Hz.. OLEDs also can be run as a flicker display, similar to a CRT, in order to eliminate the sample-and-hold effect that creates motion blur on OLEDs

OLED Disadvsantages

OLED seem to be the perfect technology for all types of displays,

however, they do have some problems, including:

OLED manufacture currently requires process steps that make it extremely expensive. Specifically, it requires the use of low-temperature polysilicon backplanes; LTPS backplanes, in turn, require laser annealing from an amorphous silicon start, so this part of the manufacturing process for AMOLEDs starts with the process costs of standard LCD, and then adds an expensive, time-consuming process that cannot currently be used on large-area glass substrates.Lifespan

The biggest technical problem for OLEDs was the limited lifetime of the organic materials. One 2008 technical report on an OLED TV panel found that "After 1,000 hours the blue luminance degraded by 12%, the red by 7% and the green by 8%."In particular, blue OLEDs historically have had a lifetime of around 14,000 hours to half original brightness (five years at 8 hours a day) when used for flat-panel displays. This is lower than the typical lifetime of LCD, LED or PDP technology. Each currently is rated for about 25,000–40,000 hours to half brightness, depending on manufacturer and model.Degradation occurs because of the accumulation of nonradiative recombination centers and luminescence quenchers in the emissive zone. It is said that the chemical breakdown in the semiconductors occurs in four steps: 1) recombination of charge carriers through the absorption of UV light, 2) hemolytic dissociation, 3)subsequent radical addition reactions that form π radicals, and 4) disproportionation between two radicals resulting in hydrogen-atom transfer reactions.However, some manufacturers' displays aim to increase the lifespan of OLED displays, pushing their expected life past that of LCD displays by improving light outcoupling, thus achieving the same brightness at a lower drive current. In 2007, experimental OLEDs were created which can sustain 400 cd/m2 of luminance for over 198,000 hours for green OLEDs and 62,000 hours for blue OLEDs.

Color balance issuesAdditionally, as the OLED material used to produce blue light degrades significantly more rapidly than the materials that produce other colors, blue light output will decrease relative to the other colors of light. This variation in the differential color output will change the color balance of the display and is much more noticeable than a decrease in overall luminance. This can be avoided partially by adjusting color balance, but this may require advanced control circuits and interaction with the user, which is unacceptable for some users. More commonly, though, manufacturers optimize the size of the R, G and B subpixels to reduce the current density through the sub pixel in order to equalize lifetime at

full luminance. For example, a blue subpixel may be 100% larger than the green subpixel. The red subpixel may be 10% smaller than the green.

Efficiency of blue OLEDsImprovements to the efficiency and lifetime of blue OLEDs is vital to the success of OLEDs as replacements for LCD technology. Considerable research has been invested in developing blue OLEDs with high external quantum efficiency as well as a deeper blue color. External quantum efficiency values of 20% and 19% have been reported for red (625 nm) and green (530 nm) diodes, respectively.

However, blue diodes (430 nm) have only been able to achieve maximum external quantum efficiencies in the range of 4% to 6%.

OLED market reports News:Flexible and Curved Display Technologies and Market Forecast ReportCompany: Touch Display Research

Report publishing date:  10/2013

Press Release––Flexible and curved displays will account for 16% of market by 2023

Santa Clara, October 1, 2013—Touch Display Research announces the publication of “Flexible and Curved Display Technologies and Market Forecast Report.” This report profiles over 260 companies and research institutes working on flexible and curved displays. Touch Display Research forecasts that the flexible and curved display market will grow from less than 1% market share in 2013 to $27 Billion and 16% market share of global display revenue by 2023.

Figure. Flexible and curved display market forecast to 2023

OLED Displays Market - Global Industry Analysis, Market Size, Share, Growth And Forecast, 2012 - 2018Company: Transparency Market Research

Report publishing date: 01/2013

The research report on the OLED displays market is analyzed based on major applications such as mobile phones, TV, notebooks, tablets, digital cameras, and automotives. The global OLED displays market is expected to reach $25.9 billion by 2018 from $4.9 billion in 2012 growing at a CAGR of 31.7% from 2012 to 2018. Mobile phones are the largest end use application and accounted for 71% of the total OLED displays market in 2012, but the share of OLED TV displays are expected to surpass the shares of mobile phone displays by 2015

.

OLED Lighting Market Forecast Q2 2012Company: Nanomarkets

Report publishing date: 03/2012

This report provides NanoMarkets' market forecasts for OLED lighting. It includes the revenue potential for the OLED lighting applications that currently interest the OLED market the most (luxury consumer lighting, decorative lighting for large buildings and showrooms, office lighting, residential lighting and automotive lighting). It also includes a detailed analysis of pricing trends in OLED lighting, including the likely roadmaps for pricing by unit, luminance and square meter.

OLED Displays and Lighting Market to 2020Company: GBI Research

Report publishing date: 10/2011

This OLED lighting and displays market report gives an in-depth analysis of the global OLED market for displays and lighting, covering four major regions – North America (USA and Canada), Europe, Asia–Pacific.

The report covers market revenue forecasts for the OLED market (displays and lighting) from 2005-2020, and it also provides market revenues breakdown for displays by application types: mobile phones, TV, IT monitors and others, and technology type; PMOLED and AMOLED.

LG Electronics expects the OLED TV market to gradually replace the LED TV marketLG Electronics reported their financial results for Q4 2013 and the Korean company doubled its operating profits compared to last year. LG reports a good quarter in its TV business, but the mobile unit reported a loss (partly blamed on marketing spending) even though they sold 13.2 million phones which is 50% higher than in Q3 2012.

Regarding OLEDs, LG says that they expect the OLED TV market to pick up from 2014, "gradually becoming the main growth driver of the display business and replacing the LED TV market". The company plans to extend the distribution network and to strengthen regionally differentiated marketing activities in order to increase sales of OLED TVs in 2014.

Samsung sold over 10 million Galaxy Note phones in South KoreaSamsung announced that they shipped over 10 million Galaxy Note smartphones in South Korea alone since launching the original Galaxy Note in 2011. A month ago the company announced that they shipped over 10 million Note 3 smartphones globally in little over 2 months, and they also shipped over 38 million Galaxy Noteand Note 2 smartphones globally since launching the original Galaxy Note in 2011.All of Samsung's Galaxy Note models use large HD Super AMOLED displays. The original Note had a 5.3" 1280x800 OLED, the Note 2 had a 5.5" OLED display (1280x720, non-Pentile) and the latest Note 3 sports a 5.7" Full-HD Super AMOLED display (386 PPI, PenTile).

LG sold over 13,000 G Flex phones, says excessive force may cause bumps on the displayAccording to a report from Korea, LG sold over 13,000 G Flex smartphones in Korea. LG wants to lead the flexible OLED smartphone market, and is now launching this phone in the US and in Europe. iSuppli: the OLED TV market is finally beginning, shipments will reach 10 million in 2018.Market research firm iSuppli expects the OLED TV market to grow quickly in coming years. 2014 will still be a slow year with only 50,000 sets sold globally (most of them will be made by LG), but this will quickly grow to 700,000 in 2015, 2.2 million in 2016 and 5.1 million in 2017.

In 2018, over iSuppli came back from CES with the conclusion that while there are still challenges, it seems that TV makers are committed to promote OLED technologies. They expect the technical issues to be overcome and high-volume production will begin soon.

Conclusion:

OLED display revenues will exceed $35B in 2018, up from $11B in 2013. AMOLED revenues passed PMOLED in 2009. AMOLED is the growth force for OLED in the future. Breakthroughs in oxide TFT and a-Si TFT backplanes and in color patterning are needed for AMOLED to move to larger sizes. More than 10 new AMOLED fabs or fab updates are expected in the next three years. OLED lighting will reach $6.3 billion by 2018. Diversify OLED lighting for different applications. Higher efficiency, longer lifetime, and high priced types are needed as well as lower efficiency, shorter lifetime and lower priced types. OLED lighting costs need to be reduced, and efficiency needs to be improved for mass adoption. OLED can be combined with other hot technologies: touch screens, e-paper displays, and 3D. OLED works in niche applications where LCD cannot compete: flexible displays transparent displays lighting.

Refrences

http://www.oled-info.com/

http://en.wikipedia.org/wiki/ OLED

http://news.oled-display.net/

http://www.engpaper.com/

http://www.gsmarena.com/lg_flexible_oled_smartphone_display_enters_mass_production-news-6921.php

http://www.raystar-optronics.com/

http://electronics.howstuffworks.com/oled1.htm