Seminar Report_2003

8/7/2019 Seminar Report_2003

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Light Emitting Polymer

Seminar

Report

Electronics And Communication Engineering Page 1

OnLIGHT EMITTINGPOLYMER

By

Rinku Kumar MauryaElectronics and CommuncationEngg.

Sec-3G2/3rd YearUniversity Roll no-0806331085


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ACKNOWLEDGEMENT

I rejoice in expressing my prodigious gratification to Mr. Manish Kashyup ,Department of Electronics & Communication Engineering, G.L.A. University,

Mathura for his indispensable guidance, generous help, perpetualencouragement, constant attention offered throughout in preparing theseminar.

I take this opportunity to pay my sincere thanks to Mr Akhil Ranjan Sir,seminar in charge, G.L.A. University, Mathura, for giving me the goldenopportunity to present the seminar.

And at last I would like to express my regards to my beloved parents, friendsand Electronics Departmental Librarian for their unlimited support and bestwishes in completion of this seminar.

Rinku Kumar Maurya (0806331085)



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DEPARTMENT OF

ELECTRONICS & COMMUNICATION ENGINNERINGCERTIFICATE

TO WHOMSOEVER IT MAY CONCERN

This is to certify that the work which is being successfully presented inthe seminar report entitled Light emitting Polymer by me in the partialfulfillment of the requirement for the award of Bachelor Of TechnologyDegree in Electronics & Communication Engineering Department at G.L.A.University, Mathura from Uttar Pradesh Technical University, Lucknow.

I appreciate his hard work & wish him success in his future

endeavour.

DATED:. 1st March,2011



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This is to certify that the above statement made by the candidate is correct tothe best of my knowledge.

SUBMITTED BYRinku Kumar MauryaB.TECH. IIIrd YEAR (EC) (MR.Akhilesh Ranjan)ROLL NO.: 0806331085 SEMINAR INCHARGE

ABSTRACT

The seminar is about polymers that can emit light when a voltage is applied toit. The structure comprises of a thin film of semiconducting polymersandwiched between two electrodes (cathode and anode).When electrons and

holes are injected from the electrodes, the recombination of these chargecarriers takes place, which leads to emission of light .The band gap, ie. Theenergy difference between valence band and conduction band determines thewavelength (colour) of the emitted light.

They are usually made by ink jet printing process. In this method redgreen and blue polymer solutions are jetted into well defined areas on thesubstrate. This is because, PLEDs are soluble in common organic solvents liketoluene and xylene .The film thickness uniformity is obtained by multi-passing

(slow) is by heads with drive per nozzle technology .The pixels are controlledby using active or passive matrix.

The advantages include low cost, small size, no viewing anglerestrictions, low power requirement, biodegradability etc. They are poised toreplace LCDs used in laptops and CRTs used in desktop computers today.

Their future applications include flexible displays which can be folded,wearable displays with interactive features, camouflage etc.



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INDEX

Topic Page

0.History 61. INTRODUCTION 8

2. SUBJECT DETAILING 9

2.1 CONSTRUCTION OF LEP 102.1.1 INK JET PRINTING 11

2.1.2 ACTIVE AND PASSIVE MATRIX 13

2.2 BASIC PRINCIPLE AND TECHNOLOGY 15

2.3 LIGHT EMISSION 16

2.4 COMPARISON TABLE 21

3. ADVANTAGES AND DISADVANTAGES 24



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3.1 ADVANTAGES 24

3.2 DISADVANTAGES 25

4. APPLICATIONS AND FUTURE DEVELOPMENTS 29

4.1 APPLICATIONS 294.2 FUTURE DEVELOPMENTS 35

5. CONCLUSION 38

REFERENCES 39

CHAPTER 0.History

The first observations ofelectroluminescence in organic materials were in theearly 1950s by A. Bernanose and co-workers at the Nancy-Universit, France.They applied high-voltage alternating current (AC) fields in air to materials

such as acridine orange, either deposited on or dissolved in cellulose orcellophane thin films. The proposed mechanism was either direct excitation ofthe dye molecules or excitation of electrons.

In 1960, Martin Pope and co-workers at New York University developedohmic dark-injecting electrode contacts to organic crystals. They furtherdescribed the necessary energetic requirements (work functions) for hole andelectron injecting electrode contacts. These contacts are the basis of charge

injection in all modern OLED devices. Pope's group also first observed directcurrent (DC) electroluminescence under vacuum on a pure single crystal ofanthracene and on anthracene crystals doped with tetracene in 1963 using asmall area silver electrode at 400V. The proposed mechanism was field-accelerated electron excitation of molecular fluorescence.

http://en.wikipedia.org/wiki/Electroluminescencehttp://en.wikipedia.org/wiki/Nancy-Universit%C3%A9http://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Acridine_orangehttp://en.wikipedia.org/wiki/Martin_Popehttp://en.wikipedia.org/wiki/New_York_Universityhttp://en.wikipedia.org/wiki/Work_functionhttp://en.wikipedia.org/wiki/Anthracenehttp://en.wikipedia.org/wiki/Nancy-Universit%C3%A9http://en.wikipedia.org/wiki/Alternating_currenthttp://en.wikipedia.org/wiki/Acridine_orangehttp://en.wikipedia.org/wiki/Martin_Popehttp://en.wikipedia.org/wiki/New_York_Universityhttp://en.wikipedia.org/wiki/Work_functionhttp://en.wikipedia.org/wiki/Anthracenehttp://en.wikipedia.org/wiki/Electroluminescence


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Pope's group reported in 1965 that in the absence of an external electric field,the electroluminescence in anthracene crystals is caused by the recombinationof a thermalized electron and hole, and that the conducting level of anthraceneis higher in energy than the exciton energy level. Also in 1965, W. Helfrich

and W. G. Schneider of the National Research Council in Canada produceddouble injection recombination electroluminescence for the first time in ananthracene single crystal using hole and electron injecting electrodes,[ theforerunner of modern double injection devices. In the same year, DowChemical researchers patented a method of preparing electroluminescent cellsusing high voltage (5001500 V) AC-driven (1003000 Hz) electrically-insulated one millimetre thin layers of a melted phosphor consisting of groundanthracene powder, tetracene, and graphite powder. Their proposed

mechanism involved electronic excitation at the contacts between the graphiteparticles and the anthracene molecules.

Device performance was limited by the poor electrical conductivity ofcontemporary organic materials. This was overcome by the discovery anddevelopment of highly conductive polymers.

Electroluminescence from polymer films was first observed by RogerPartridge at the National Physical Laboratory in the United Kingdom. The

device consisted of a film of poly(n-vinylcarbazole) up to 2.2 micrometresthick located between two charge injecting electrodes. The results of theproject were patented in 1975 and published in 1983. The first diode devicewas reported at Eastman Kodak by Ching W. Tang and Steven Van Slyke in1987. This device used a novel two-layer structure with separate holetransporting and electron transporting layers such that recombination and lightemission occurred in the middle of the organic layer. This resulted in areduction in operating voltage and improvements in efficiency and led to the

current era of OLED research and device production.

http://en.wikipedia.org/wiki/National_Research_Council_(Canada)http://en.wikipedia.org/wiki/Organic_light-emitting_diode#cite_note-10http://en.wikipedia.org/wiki/Dow_Chemicalhttp://en.wikipedia.org/wiki/Dow_Chemicalhttp://en.wikipedia.org/wiki/National_Physical_Laboratory_(United_Kingdom)http://en.wikipedia.org/wiki/N-Vinylcarbazolehttp://en.wikipedia.org/wiki/Ching_W._Tanghttp://en.wikipedia.org/wiki/Steven_Van_Slykehttp://en.wikipedia.org/wiki/National_Research_Council_(Canada)http://en.wikipedia.org/wiki/Organic_light-emitting_diode#cite_note-10http://en.wikipedia.org/wiki/Dow_Chemicalhttp://en.wikipedia.org/wiki/Dow_Chemicalhttp://en.wikipedia.org/wiki/National_Physical_Laboratory_(United_Kingdom)http://en.wikipedia.org/wiki/N-Vinylcarbazolehttp://en.wikipedia.org/wiki/Ching_W._Tanghttp://en.wikipedia.org/wiki/Steven_Van_Slyke


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CHAPTER1.Introduction-Imagine these scenarios

- After watching the breakfast news on TV, you roll up the set like a largehandkerchief, and stuff it into your briefcase. On the bus or train journey toyour office, you can pull it out and catch up with the latest stock marketquotes on CNBC.- Somewhere in the Kargil sector, a platoon commander of the Indian Armyreadies for the regular satellite updates that will give him the latest terrainpictures of the border in his sector. He unrolls a plastic-like map and hooksit to the unit's satellite telephone. In seconds, the map is refreshed with thelatest high resolution camera images grabbed by an Indian satellite whichpassed over the region just minutes ago.

Dont imagine these scenarios at least not for too long.The current 40billion-dollar display market, dominated by LCDs (standard in laptops)and cathode ray tubes (CRTs, standard in televisions), is seeing theintroduction of full-color LEP-driven displays that are more efficient,brighter, and easier to manufacture. It is possible that organic light-emitting materials will replace older display technologies much likecompact discs have relegated cassette tapes to storage bins.



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CHAPTER 2-SUBJECT DETAILING2. LIGHT EMITTING POLYMER

It is a polymer that emits light when a voltage is applied to it. Thestructure comprises a thin-film of semiconducting polymer sandwichedbetween two electrodes (anode and cathode) as shown in fig.1. Whenelectrons and holes are injected from the electrodes, the recombination ofthese charge carriers takes place, which leads to emission of light thatescapes through glass substrate. The bandgap, i.e. energy differencebetween valence band and conduction band of the semiconducting polymerdetermines the wavelength (colour) of the emitted light.



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2.1 CONSTRUCTION

Light-emitting devices consist of active/emitting layers sandwichedbetween a cathode and an anode. Indium-tin oxides typically used for theanode and aluminum or calcium for the cathode. Fig.2.1(a) shows the

structure of a simple single layer device with electrodes and an active layer.

Single-layer devices typically work only under a forward DCbias. Fig.2.1(b) shows a symmetrically configured alternating current light-emitting (SCALE) device that works under AC as well as forward andreverse DC bias.

In order to manufacture the polymer, a spin-coating machine is used thathas a plate spinning at the speed of a few thousand rotations per minute. Therobot pours the plastic over the rotating plate, which, in turn, evenly spreadsthe polymer on the plate. This results in an extremely fine layer of the polymerhaving a thickness of 100 nanometers. Once the polymer is evenly spread, it isbaked in an oven to evaporate any remnant liquid. The same technology isused to coat the CDs.



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2.1.1 INK JET PRINTING

Although inkjet printing is well established in printing graphic images,

only now are applications emerging in printing electronics materials.Approximately a dozen companies have demonstrated the use of inkjetprinting for PLED displays and this technique is now at the forefront ofdevelopments in digital electronic materials deposition. However, turninginkjet printing into a manufacturing process for PLED displays hasrequired significant developments of the inkjet print head, the inks and thesubstrates (see Fig.2.1.1).Creating a full colour, inkjet printed displayrequires the precise metering of volumes in the order of pico liters. Red,

green and blue polymer solutions are jetted into well defined areas with anangle of flight deviation of less than 5. To ensure the displays haveuniform emission, the film thickness has to be very uniform

Fig Systematic of inkjet printing for PLED Screens



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For some materials anddisplay applications the film thickness uniformity may have to be betterthan 2 per cent. A conventional inkjet head may have volume variationsof up to 20 per cent from the hundred or so nozzles that comprise the head

and, in the worst case, a nozzle may be blocked. For graphic art thisvariation can be averaged out by multi-passing with the quality to the printdependent on the number of passes. Although multi-passing could be usedfor PLEDs the process would be unacceptably slow. Recently, Spectra, theworlds largest supplier of industrial inkjet heads, has started tomanufacture heads where the drive conditions for each nozzle can beadjusted individually so called drive-per-nozzle (DPN). Litrex in theUSA, a subsidiary of CDT, has developed software to allow DPN to be

used in its printers. Volume variations across the head of 2 per cent can beachieved using DPN. In addition to very good volume control, the head hasbeen designed to give drops of ink with a very small angle-of-flightvariation. A 200 dots per inch (dpi) display has colour pixels only 40microns wide; the latest print heads have a deviation of less than 5microns when placed 0.5 mm from the substrate. In addition to theprecision of the print head, the formulation of the ink is key to makingeffective and attractive display devices. The formulation of a dry polymer

material into an ink suitable for PLED displays requires that the inkjetsreliably at high frequency and that on reaching the surface of the substrate,forms a wet film in the correct location and dries to a uniformly flat film.The film then has to perform as a useful electro-optical material. Recentprogress in ink formulation and printer technology has allowed 400 mmpanels to be colour printed in under a minute.



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2.1.2 ACTIVE MATRIX AND PASSIVE MATRIX

Many displays consist of a matrix of pixels, formed at theintersection of rows and columns deposited on a substrate. Each pixel is alight emitting diode such as a PLED, capable of emitting light by being

turned on or off, or any state in between. Coloured displays are formed bypositioning matrices of red, green and blue pixels very close together. Tocontrol the pixels, and so form the image required, either 'passive' or'active' matrix driver methods are used. Pixel displays caneither by active or passive matrix. Fig. 2.1.2 shows the differences betweenthe two matrix types, active displays have transistors so that when aparticular pixel is turned on it remains on until it is turned off.The matrix pixels are accessed sequentially. As a result passive displays are

prone to flickering since each pixel only emits light for such a small lengthof time. Active displays are preferred, however it is technically challengingto incorporate so many transistors into such small a compact area.

Fig 2.1.2 Active and passive matrices



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In passive matrix systems, each row and each column of the display has itsown driver, and to create an image, the matrix is rapidly scanned to enableevery pixel to be switched on or off as required. As the current required tobrighten a pixel increases (for higher brightness displays), and as the display

gets larger, this process becomes more difficult since higher currents have toflow down the control lines. Also, the controlling current has to be presentwhenever the pixel is required to light up. As a result, passive matrix displaystend to be used mainly where cheap, simple displays are required.

Active matrix displays solve the problem ofefficiently addressing each pixel by incorporating a transistor (TFT) in serieswith each pixel which provides control over the current and hence thebrightness of individual pixels. Lower currents can now flow down the control

wires since these have only to program the TFT driver, and the wires can befiner as a result. Also, the transistor is able to hold the current setting, keepingthe pixel at the required brightness, until it receives another control signal.Future demands on displays will in part require larger area displays so theactive matrix market segment will grow faster.PLED devices are especially suitable for incorporating into active matrixdisplays, as they are processable in solution and can be manufactured usingink jet printing over larger areas.



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2.2 BASIC PRINCIPLE AND TECHNOLOGY

Polymer properties are dominated by the covalent nature of carbon bondsmaking up the organic molecules backbone. The immobility of electronsthat form the covalent bonds explain why plastics were classified almostexclusively insulators until the 1970s.

A single carbon-carbon bond is composed of two electrons being shared inoverlapping wave functions. For each carbon, the four electrons in thevalence bond form tetrahedral oriented hybridized sp3 orbitals from the s &

p orbitals described quantum mechanically as geometrical wave functions.The properties of the spherical s orbital and bimodal p orbitals combineinto four equal , unsymmetrical , tetrahedral oriented hybridized sp3

orbitals. The bond formed by the overlap of these hybridized orbitals fromtwo carbon atoms is referred to as a sigma bond. A conjugated pi bondrefers to a carbon chain or ring whose bonds alternate between single anddouble (or triple) bonds. The bonding system tend to form stronger bondsthan might be first indicated by a structure with single bonds. The single

bond formed between two double bonds inherits the characteristics of thedouble bonds since the single bond is formed by two sp2 hybrid orbitals.The p orbitals of the single bonded carbons form an effective pi bondultimately leading to the significant consequence of pi electron de-localization. Unlike the sigma bond electrons, which are trapped betweenthe carbons, the pi bond electrons have relative mobility. All that isrequired to provide an effective conducting band is the oxidation orreduction of carbons in the backbone. Then the electrons have mobility, as

do the holes generated by the absence of electrons through oxidation with adopant like iodine



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2.3 LIGHT EMISSION

The production of photons from the energy gap of a material is very similarfor organic and ceramic semiconductors. Hence a brief description of the

process of electroluminescence is in order.Electroluminescence is the process in which electromagnetic(EM) radiationis emitted from a material by passing an electrical current through it. Thefrequency of the EM radiation is directly related to the energy of separationbetween electrons in the conduction band and electrons in the valenceband. These bands form the periodic arrangement of atoms in the crystalstructure of the semiconductor. In a ceramic semiconductor like GaAs orZnS, the energy is released when an electron from the conduction band

falls into a hole in the valence band. The electronic device thataccomplishes this electron-hole interaction is that of a diode, whichconsists of an n-type material (electron rich) interfaced with p-type material(hole rich). When the diode is forward biased (electrons across interfacefrom n to p by an applied voltage) the electrons cross a neutralized zone atthe interface to fill holes and thus emit energy.

The situation is very similar for organic semiconductors with two notableexceptions. The first exception stems from the nature of the conduction

band in an organic system while the second exception is the recognition ofhow conduction occurs between two organic molecules.



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With non-organic semiconductors there is a band gap associated withBrillouin zones that discrete electron energies based on the periodic orderof the crystalline lattice. The free electrons mobility from lattice site tolattice site is clearly sensitive to the long-term order of the material. This isnot so for the organic semiconductor. The energy gap of the polymer ismore a function of the individual backbone, and the mobility of electronsand holes are limited to the linear or branched directions of the moleculethey statistically inhabit. The efficiency of electron/hole transport betweenpolymer molecules is also unique to polymers. Electron andhole mobility occurs as a hopping mechanism which is significant to thepractical development of organic emitting devices.

PPV has a fully conjugated backbone (figure 2.2.1), as a consequence theHOMO (exp link remember 6th form!) of the macromolecule stretchesacross the entire chain, this kind of situation is ideal for the transport ofcharge; in simple terms, electrons can simply "hop" from one orbital tothe next since they are all linked.

Figure 2.2.1 Ademonstration ofthe fullconjugation of

electrons in PPV.The delocalized electron clouds are coloured yellow.PPV is a semiconductor. Semiconductors are so called because they haveconductivity that is midway between that of a conductor and an insulator.While conductors such as copper conduct electricity with little to no energy (inthis case potential difference or voltage) required to "kick-start" a current,insulators such as glass require huge amounts of energy to conduct a current.Semi-conductors require modest amounts of energy in order to carry a current,and are used in technologies such as transistors, microchips and LEDs.



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Band theory is used to explain the semi-conductance of PPV, see figure 5. In adiatomic molecule, a molecular orbital (MO) diagram can be drawn showing asingle HOMO and LUMO, corresponding to a low energy orbital and a highenergy * orbital. This is simple enough, however, every time an atom is

added to the molecule a further MO is added to the MO diagram. Thus for aPPV chain which consists of ~1300 atoms involved in conjugation, theLUMOs and HOMOs will be so numerous as to be effectively continuous, thisresults in two bands, a valence band (HOMOs, orbitals) and a conductionband (LUMOs, * orbitals). They are separated by a band gap which istypically 0-10eV (check) and depends on the type of material. PPV has a bandgap of 2.2eV (exp eV). The valence band is filled with

Figure 2.2.2 Aseries of orbital

diagrams.



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all the electrons in the chain, and thus is entirelyfilled, while the conduction band, being made up of empty * orbitals (theLUMOs) is entirely empty).

In order for PPV to carry a charge, the charge carriers (e.g. electrons) must begiven enough energy to "jump" this barrier - to proceed from the valence bandto the conduction band where they are free to ride the PPV chains emptyLUMOs.(Fig. 2.2.2)

A diatomic molecule has a bonding and an anti-bonding orbital, twoatomic orbitals gives two molecular orbitals. The electrons arrange

themselves following, Auf Bau and the Pauli Principle. A single atom has one atomic obital

A triatomic molecule has three molecular orbitals, as before one bonding,one anti-bonding, and in addition one non-bonding orbital.

Four atomic orbitals give four molecular orbitals.

Many atoms results in so many closely spaced orbitals that they areeffectively continuous and non-quantum. The orbital sets are called

bands. In this case the bands are separated by a band gap, and thus thesubstance is either an insulator or a semi-conductor.



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It is already apparent that conduction in polymers is not similar to that ofmetals and inorganic conductors , however there is more to this story! Firstwe need to imagine a conventional diode system, i.e. PPV sandwichedbetween an electron injector (or cathode), and an anode. The electroninjector needs to inject electrons of sufficient energy to exceed the bandgap, the anode operates by removing electrons from the polymer andconsequently leaving regions of positive charge called holes. The anode isconsequently referred to as the hole injector.

In this model, holes and electrons are referred to as charge carriers, both arefree to traverse the PPV chains and as a result will come into contact. It islogical for an electron to fill a hole when the opportunity is presented andthey are said to capture one another. The capture of oppositely chargedcarriers is referred to as recombination. When captured, an electron and ahole form neutral-bound excited states (termed excitons) that quickly decayand produce a photon up to 25% of the time, 75% of the time, decayproduces only heat, this is due to the the possible multiplicities of theexciton. The frequency of the photon is tied to the band-gap of thepolymer; PPV has a band-gap of 2.2eV, which corresponds to yellow-greenlight.

Not all conducting polymers fluoresce, polyacetylene, one of the firstconducting-polymers to be discovered was found to fluoresce at extremely lowlevels of intensity. Excitons are still captured and still decay, however theymostly decay to release heat. This is what you may have expected sinceelectrical resistance in most conductors causes the conductor to become hot.

Capture is essential for a current to be sustained. Without capture thecharge densities of holes and electrons would build up, quickly preventingany injection of charge carriers. In effect no current would flow.



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2.4 COMPARISON TABLE

This tablecompares themainelectronicdisplaystechnologies.Each displaytype is

describedbriefly, andthe relativeadvantagesanddisadvantages arereviewed.Display

Type

Acronym Emissive orReflective

Technology Advantages Disadvantages

CathodeRay Tube

CRT Emissive The CRT isa vacuumtube using ahot filamentto generatethermo-electrons,

electrostaticand/ormagneticfields to

Very bright

Wideviewingangle

No mask, sono pixel size

limitation formono

Minimumpixel size

High (5kVto 20kV+)drivevoltages

Not a flatpanel (rare

exceptions)Can befragile,particularly



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focus theelectronsinto a beamattracted to

the highvoltageanode whichis thephosphorcoatedscreen.Electrons

collidingwith thephosphoremitluminousradiation.Color CRTstypically use

3 electronsources(guns) totarget red,green, andblue patternson phosphorthe screen.

0.2mm(color)

Low cost

standardsizes

Low costhigh-rescolor

Wideoperatingtemperature

rangeModerate(20khrs+)life

neck-end

Heavy

Source of X-

rays unlessscreened

Affected bymagneticfields

Difficult torecycle ordispose of

Liquid

CrystalDisplay

LCD Reflective An LCD

uses theproperties ofliquidcrystals in an

Small,static, monopanels canbe very lowcost

Backlightadds cost,and oftenlimits theuseful life



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electric fieldto guidelight fromoppositely

polarizedfront andback displayplates. Theliquid crystalworks as ahelicaldirector

(when thedriverpresents thecorrectelectricfield) toguide thelight through

90 from oneplate

Both monoand colorpanelswidelyavailable

Requires ACdrivewaveform

Fragileunless



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CHAPTER 3-ADVANTAGES AND

DISADVANTAGES

3.1Advantages

Demonstration of a 4.1" prototype flexible display from Sony

The different manufacturing process of OLEDs lends itself to severaladvantages over flat-panel displays made with LCD technology.

Lower cost in the future: OLEDs can be printed onto any suitablesubstrate by an inkjet printer or even by screen printing, theoreticallymaking them cheaper to produce than LCD orplasma displays.However, fabrication of the OLED substrate is more costly than that ofa TFT LCD, until mass production methods lower cost throughscalability. Roll-roll vapour-deposition methods for organic devices doallow mass production of thousands of devices per minute for minimalcost, although this technique also induces problems in that multi-layerdevices can be challenging to make.

Light weight & flexible plastic substrates: OLED displays can befabricated on flexible plastic substrates leading to the possibility offlexible organic light-emitting diodes being fabricated or other newapplications such as roll-up displays embedded in fabrics or clothing.

As the substrate used can be flexible such as PET , the displays maybe produced inexpensively.

Wider viewing angles & improved brightness: OLEDs can enable agreater artificial contrast ratio (both dynamic range and static,

http://en.wikipedia.org/wiki/Flexible_organic_light-emitting_diodehttp://en.wikipedia.org/wiki/Substrate_(printing)http://en.wikipedia.org/wiki/Plasma_displayhttp://en.wikipedia.org/wiki/Flexible_organic_light-emitting_diodehttp://en.wikipedia.org/wiki/Rollable_displayhttp://en.wikipedia.org/wiki/Flexible_substratehttp://en.wikipedia.org/wiki/Polyethylene_terephthalatehttp://en.wikipedia.org/wiki/File:Ecran_oled_flexible.jpghttp://en.wikipedia.org/wiki/Flexible_organic_light-emitting_diodehttp://en.wikipedia.org/wiki/Substrate_(printing)http://en.wikipedia.org/wiki/Plasma_displayhttp://en.wikipedia.org/wiki/Flexible_organic_light-emitting_diodehttp://en.wikipedia.org/wiki/Rollable_displayhttp://en.wikipedia.org/wiki/Flexible_substratehttp://en.wikipedia.org/wiki/Polyethylene_terephthalate


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measured in purely dark conditions) and viewing angle compared toLCDs because OLED pixels directly emit light. OLED pixel coloursappear correct and unshifted, even as the viewing angle approaches90 from normal.

Better power efficiency: LCDs filter the light emitted from abacklight, allowing a small fraction of light through so they cannotshow true black, while an inactive OLED element does not producelight or consume power.

Response time: OLEDs can also have a faster response time thanstandard LCD screens. Whereas LCD displays are capable of between2 and 8 ms response time offering a frame rate of +/-200 Hz, an OLEDcan theoretically have less than 0.01 ms response time enabling

100,000 Hz refresh rates.

3.2Disadvantages

LEP display showing partial failure

http://en.wikipedia.org/wiki/Surface_normalhttp://en.wikipedia.org/wiki/Backlighthttp://en.wikipedia.org/wiki/Refresh_ratehttp://en.wikipedia.org/wiki/File:Oled_display_alterung.jpghttp://en.wikipedia.org/wiki/File:Light_Emitting_Polymer_display_partially_failed.jpghttp://en.wikipedia.org/wiki/Surface_normalhttp://en.wikipedia.org/wiki/Backlighthttp://en.wikipedia.org/wiki/Refresh_rate


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An old OLED display showing wear

Lifespan: The biggest technical problem for OLEDs was the limitedlifetime of the organic materials .In particular, blue OLEDs

historically have had a lifetime of around 14,000 hours to half originalbrightness (five years at 8 hours a day) when used for flat-paneldisplays. This is lower than the typical lifetime of LCD, LED orPDPtechnologyeach currently rated for about 25,000 40,000 hours tohalf brightness, depending on manufacturer and model. However,some manufacturers' displays aim to increase the lifespan of OLEDdisplays, pushing their expected life past that of LCD displays byimproving light outcoupling, thus achieving the same brightness at a

lower drive current. In 2007, experimental OLEDs were created whichcan sustain 400 cd/m2 ofluminance for over 198,000 hours for greenOLEDs and 62,000 hours for blue OLEDs.

Color balance issues: Additionally, as the OLED material used toproduce blue light degrades significantly more rapidly than thematerials that produce other colors, blue light output will decreaserelative to the other colors of light. This differential color outputchange will change the color balance of the display and is much morenoticeable than a decrease in overall luminance. This can be partiallyavoided by adjusting colour balance but this may require advancedcontrol circuits and interaction with the user, which is unacceptable forsome users. In order to delay the problem, manufacturers bias thecolour balance towards blue so that the display initially has anartificially blue tint, leading to complaints of artificial-looking, over-saturated colors. More commonly, though, manufacturers optimize thesize of the R, G and B subpixels to reduce the current density throughthe subpixel 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 OLEDs: Improvements to the efficiency andlifetime of blue OLEDs is vital to the success of OLEDs as

http://en.wikipedia.org/wiki/Plasma_displayhttp://en.wikipedia.org/wiki/Luminancehttp://en.wikipedia.org/wiki/Plasma_displayhttp://en.wikipedia.org/wiki/Luminance


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replacements for LCD technology. Considerable research has beeninvested in developing blue OLEDs with high external quantumefficiency as well as a deeper blue color. External quantum efficiencyvalues of 20% and 19% have been reported for red (625 nm) and green

(530 nm) diodes, respectively. However, blue diodes (430 nm) haveonly been able to achieve maximum external quantum efficiencies inthe range between 4% to 6%.

Water damage: Water can damage the organic materials of thedisplays. Therefore, improved sealing processes are important forpractical manufacturing. Water damage may especially limit thelongevity of more flexible displays.

Outdoor performance: As an emissive display technology, OLEDsrely completely upon converting electricity to light, unlike most LCDswhich are to some extent reflective; e-inkleads the way in efficiencywith ~ 33% ambient light reflectivity, enabling the display to be usedwithout any internal light source. The metallic cathode in an OLEDacts as a mirror, with reflectance approaching 80%, leading to poorreadability in bright ambient light such as outdoors. However, with theproper application of a circular polarizer and anti-reflective coatings,the diffuse reflectance can be reduced to less than 0.1%. With 10,000fc incident illumination (typical test condition for simulating outdoorillumination), that yields an approximate photopic contrast of 5:1.

Power consumption: While an OLED will consume around 40% ofthe power of an LCD displaying an image which is primarily black,for the majority of images it will consume 6080% of the power of anLCD however it can use over three times as much power to displayan image with a white backgroundsuch as a document or website. This

can lead to disappointing real-world battery life in mobile devices.You may balance this however, by setting your background to black,and your characters to any actual color.

http://en.wikipedia.org/wiki/E-inkhttp://en.wikipedia.org/wiki/Foot-candlehttp://en.wikipedia.org/wiki/E-inkhttp://en.wikipedia.org/wiki/Foot-candle


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Screen burn-in: Unlike displays with a common light source, thebrightness of each OLED pixel fades depending on the contentdisplayed. The varied lifespan of the organic dyes can cause adiscrepancy between red, green, and blue intensity. This leads to

image persistence, also known as burn-in.

UV sensitivity: OLED displays can be damaged by prolongedexposure to UV light. The most pronounced example of this can beseen with a near UV laser (such as a Bluray pointer) and can damagethe display almost instantly with more than 20mW leading to dim ordead spots where the beam is focused. This is usually avoided byinstalling a UV blocking filter over the panel and this can easily be

seen as a clear plastic layer on the glass. Removal of this filter canlead to severe damage and an unusable display after only a few monthsof room light exposure.

http://en.wikipedia.org/wiki/Screen_burn-inhttp://en.wikipedia.org/wiki/Laser_pointer#Blue_and_violet_laser_pointershttp://en.wikipedia.org/wiki/Screen_burn-inhttp://en.wikipedia.org/wiki/Laser_pointer#Blue_and_violet_laser_pointers


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CHAPTER 4- Applications And Future

Developments4. APPLICATIONS

Polymer light-emitting diodes (PLED) can easily be processed into large-areathin films using simple and inexpensive technology. They also promise tochallenge LCD's as the premiere display technology for wireless phones,pagers, and PDA's with brighter, thinner, lighter, and faster features than thecurrent display.

4.1 PHOTOVOLTAICS

CDTs PLED technology can be used in reverse, to convert light intoelectricity. Devices which convert light into electricity are called photovoltaic(PV) devices, and are at the heart of solar cells and light detectors. CDT has anactive program to develop efficient solar cells and light detectors using itspolymer semiconductor know-how and experience, and has filed severalpatents in the area.

Digital clocks powered by CDT's polymer solar cells.

4.2 POLY LED TV

Philips will demonstrate its first 13-inch PolyLED TV prototype based onpolymer OLED (organic light-emitting diode) technology Taking as itsreference application the wide-screen 30-inch diagonal display with WXGA(1365x768) resolution, Philips has produced a prototype 13-inch carve-out of



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this display (resolution 576x324) to demonstrate the feasibility ofmanufacturing large-screen polymer OLED displays using high-accuracymulti-nozzle, multi-head inkjet printers. The excellent and sparkling imagequality of Philips' PolyLED TV prototype illustrates the great potential of this

new display technology for TV applications. According to current predictions,a polymer OLED-based TV could be a reality in the next five years.

4.3 BABY MOBILE

This award winning baby mobile uses light weight organic light emittingdiodes to realize images and sounds in response to gestures and speech of theinfant.



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4.4 MP3 PLAYER DISPLAY

Another product on the market taking advantage of a thin form-factor, light-emitting polymer display is the new, compact, MP3 audio player, marketed byGoDot Technology. The unit employs a polymeric light-emitting diode(pLED) display supplied by Delta Optoelectronics, Taiwan, which is madewith green Lumation light-emitting polymers furnished by Dow Chemical Co.,Midland, Mich.

Samsung applications

By 2004 Samsung, South Korea's largest conglomerate, was the world's largestOLED manufacturer, producing 40% of the OLED displays made in the world,and as of 2010 has a 98% share of the global AMOLED market.The company

http://en.wikipedia.org/wiki/Samsunghttp://en.wikipedia.org/wiki/South_Koreahttp://en.wikipedia.org/wiki/Conglomerate_(company)http://en.wikipedia.org/wiki/AMOLEDhttp://en.wikipedia.org/wiki/Samsunghttp://en.wikipedia.org/wiki/South_Koreahttp://en.wikipedia.org/wiki/Conglomerate_(company)http://en.wikipedia.org/wiki/AMOLED


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is leading the world OLED industry, generating $100.2 million out of the total$475 million revenues in the global OLED market in 2006. As of 2006, it heldmore than 600 American patents and more than 2800 international patents,making it the largest owner ofAMOLED technology patents.

Samsung SDI announced in 2005 the world's largest OLED TV at the time, at21 inches (53 cm). This OLED featured the highest resolution at the time, of6.22 million pixels. In addition, the company adopted active matrix basedtechnology for its low power consumption and high-resolution qualities. Thiswas exceeded in January 2008, when Samsung showcased the world's largestand thinnest OLED TV at the time, at 31 inches and 4.3 mm.

In May 2008, Samsung unveiled an ultra-thin 12.1 inch laptop OLED displayconcept, with a 1,280768 resolution with infinite contrast ratio. According toWoo Jong Lee, Vice President of the Mobile Display Marketing Team atSamsung SDI, the company expected OLED displays to be used in notebookPCs as soon as 2010.

In October 2008, Samsung showcased the world's thinnest OLED display, alsothe first to be 'flappable' and bendable.[90] It measures just 0.05 mm (thinnerthan paper), yet a Samsung staff member said that it is "technically possible to

make the panel thinner".To achieve this thickness, Samsung etched an OLEDpanel that uses a normal glass substrate. The drive circuit was formed by low-temperature polysilicon TFTs. Also, low-molecular organic EL materials wereemployed. The pixel count of the display is 480 272. The contrast ratio is100,000:1, and the luminance is 200 cd/m. The colour reproduction range is100% of the NTSC standard.

In the same month, Samsung unveiled what was then the world's largestOLED Television at 40-inch with a Full HD resolution of 19201080 pixel. Inthe FPD International, Samsung stated that its 40-inch OLED Panel is thelargest size currently possible. The panel has a contrast ratio of 1,000,000:1, acolour gamut of 107% NTSC, and a luminance of 200 cd/m (peak luminanceof 600 cd/m).

http://en.wikipedia.org/wiki/AMOLEDhttp://en.wiktionary.org/wiki/flappablehttp://en.wiktionary.org/wiki/bendablehttp://en.wikipedia.org/wiki/Organic_light-emitting_diode#cite_note-flapping-89http://en.wikipedia.org/wiki/Full_HDhttp://en.wikipedia.org/wiki/AMOLEDhttp://en.wiktionary.org/wiki/flappablehttp://en.wiktionary.org/wiki/bendablehttp://en.wikipedia.org/wiki/Organic_light-emitting_diode#cite_note-flapping-89http://en.wikipedia.org/wiki/Full_HD


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At the Consumer Electronics Show (CES) in January 2010, Samsungdemonstrated a laptop computer with a large, transparent OLED displayfeaturing up to 40% transparency and an animated OLED display in a photoID card.[

Samsung's latest AMOLED smartphones use theirSuper AMOLEDtrademark, with the Samsung Wave S8500 and Samsung i9000 Galaxy Sbeing launched in June 2010. In January 2011 Samsung announced their SuperAMOLED Plus displays- which offer several advances over the olderSuperAMOLED displays - real stripe matrix (50% more sub pixels), thinner formfactor, brighter image and a 18% reduction in energy consumption.

Sony applications

Sony XEL-1, the world's first OLED TV. (front)

Sony XEL-1 (side)

http://en.wikipedia.org/wiki/Consumer_Electronics_Showhttp://en.wikipedia.org/wiki/Organic_light-emitting_diode#cite_note-photoid-92http://en.wikipedia.org/wiki/AMOLEDhttp://en.wikipedia.org/wiki/Super_AMOLEDhttp://en.wikipedia.org/wiki/Samsung_Wave_S8500http://en.wikipedia.org/wiki/Samsung_i9000_Galaxy_Shttp://en.wikipedia.org/wiki/Super_AMOLEDhttp://en.wikipedia.org/wiki/Super_AMOLEDhttp://en.wikipedia.org/wiki/Sony_XEL-1http://en.wikipedia.org/wiki/File:Sony_XEL-1.jpghttp://en.wikipedia.org/wiki/File:Sony_oled.jpghttp://en.wikipedia.org/wiki/Consumer_Electronics_Showhttp://en.wikipedia.org/wiki/Organic_light-emitting_diode#cite_note-photoid-92http://en.wikipedia.org/wiki/AMOLEDhttp://en.wikipedia.org/wiki/Super_AMOLEDhttp://en.wikipedia.org/wiki/Samsung_Wave_S8500http://en.wikipedia.org/wiki/Samsung_i9000_Galaxy_Shttp://en.wikipedia.org/wiki/Super_AMOLEDhttp://en.wikipedia.org/wiki/Super_AMOLEDhttp://en.wikipedia.org/wiki/Sony_XEL-1


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The Sony CLI PEG-VZ90 was released in 2004, being the first PDA tofeature an OLED screen. Other Sony products to feature OLED screensinclude the MZ-RH1 portable minidisc recorder, released in 2006 and theWalkman X Series.

At the Las VegasCES 2007, Sony showcased 11-inch (28 cm, resolution960540) and 27-inch (68.5 cm, full HD resolution at 19201080) OLED TVmodels Both claimed 1,000,000:1 contrast ratios and total thicknesses(including bezels) of 5 mm. In April 2007, Sony announced it wouldmanufacture 1000 11-inch OLED TVs per month for market testing purposes.On October 1, 2007, Sony announced that the 11-inch model, now called theXEL-1, would be released commercially; the XEL-1 was first released in

Japan in December 2007.In May 2007, Sony publicly unveiled a video of a 2.5-inch flexible OLEDscreen which is only 0.3 millimeters thick. At the Display 2008 exhibition,Sony demonstrated a 0.2 mm thick 3.5 inch display with a resolution of320200 pixels and a 0.3 mm thick 11 inch display with 960540 pixelsresolution, one-tenth the thickness of the XEL-1.

In July 2008, a Japanese government body said it would fund a joint project of

leading firms, which is to develop a key technology to produce large, energy-saving organic displays. The project involves one laboratory and 10 companiesincluding Sony Corp. NEDO said the project was aimed at developing a coretechnology to mass-produce 40 inch or larger OLED displays in the late2010s.

In October 2008, Sony published results of research it carried out with theMax Planck Institute over the possibility of mass-market bending displays,which could replace rigid LCDs and plasma screens. Eventually, bendable,transparent OLED screens could be stacked to produce 3D images with muchgreater contrast ratios and viewing angles than existing products.

http://en.wikipedia.org/wiki/Sony_CLI%C3%89_PEG-VZ90http://en.wikipedia.org/wiki/Walkman_X_Serieshttp://en.wikipedia.org/wiki/Las_Vegas_metropolitan_areahttp://en.wikipedia.org/wiki/Consumer_Electronics_Showhttp://en.wikipedia.org/wiki/Contrast_ratiohttp://en.wikipedia.org/wiki/Sony_XEL-1http://en.wikipedia.org/wiki/New_Energy_and_Industrial_Technology_Development_Organizationhttp://en.wikipedia.org/wiki/Max_Planck_Institutehttp://en.wikipedia.org/wiki/Viewing_anglehttp://en.wikipedia.org/wiki/Sony_CLI%C3%89_PEG-VZ90http://en.wikipedia.org/wiki/Walkman_X_Serieshttp://en.wikipedia.org/wiki/Las_Vegas_metropolitan_areahttp://en.wikipedia.org/wiki/Consumer_Electronics_Showhttp://en.wikipedia.org/wiki/Contrast_ratiohttp://en.wikipedia.org/wiki/Sony_XEL-1http://en.wikipedia.org/wiki/New_Energy_and_Industrial_Technology_Development_Organizationhttp://en.wikipedia.org/wiki/Max_Planck_Institutehttp://en.wikipedia.org/wiki/Viewing_angle


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Sony exhibited a 24.5" prototype OLED 3D television during the ConsumerElectronics Show in January 2010.

In January 2011, Sony announced the NGP handheld game console (the

successor to the PSP) will feature a 5-inch OLED screen.

On 17th February 2011, Sony announced it's 25" OLED ProfessionalReference Monitor aimed at the Cinema and high end Drama Post Productionmarket.

LG applications

As of 2010 LG produces one model of OLED television, the 15 inch

15EL9500and has announced a 31" OLED 3D television for March 2011.

http://en.wikipedia.org/wiki/PlayStation_Portable_successorhttp://en.wikipedia.org/wiki/PlayStation_Portablehttp://en.wikipedia.org/wiki/LGhttp://en.wikipedia.org/wiki/PlayStation_Portable_successorhttp://en.wikipedia.org/wiki/PlayStation_Portablehttp://en.wikipedia.org/wiki/LG


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5. FUTURE DEVELOPMENTS

Here's just a few ideas which build on the versatility of light emittingmaterials.

High efficiency displays running on low power

and economical to manufacture will find many uses in the consumerelectronics field. Bright, clear screens filled with information andentertainment data of all sorts may make our lives easier, happier and safer.

Demands for information on the move could drivethe development of 'wearable' displays, with interactive features.

Eywith changing information cole woul givemany brand ownerve edge



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The ability of PLEDs to be fabricated on flexiblesubstrates opens up fascinating possibilities for formable or even fully flexibledisplays e catching packaging intent at the point of sa d s a valuablecompetition

FEW MORE DEVELOPMENTS

Because the plastics can be made in the form of thin films or sheets,they offer a huge range of applications. These include television orcomputer screens that can be rolled up and tossed in a briefcase, andcheap videophones.

Clothes made of the polymer and powered by a small battery packcould provide their own cinema show.

Camouflage, generating an image of its surroundings picked up by acamera would allow its wearer to blend perfectly into the

background A fully integrated analytical chip that contains an integrated light

source and detector could provide powerful point-of-caretechnology. This would greatly extend the tools available to a doctorand would allow on-the-spot quantitative analysis, eliminating theneed for patients to make repeat visits. This would bring forward thestart of treatment, lower treatment costs and free up clinician time.

The future is bright for products incorporating PLED displays. Ultra-light, ultra-thin displays, with low power consumption and excellentreadability allow product designers a much freer rein. Theenvironmentally conscious will warm to the absence of toxic substances



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and lower overall material requirements of PLEDs, and it would not bean exaggeration to say that all current display applications could benefitfrom the introduction of PLED technology. CDT sees PLED technologyas being first applied to mobile communications, small and low

information content instrumentation, and appliance displays. With theemergence of 3G telecommunications, high quality displays will becritical for handheld devices. PLEDs are ideal for the small displaymarket as they offer vibrant, full-colour displays in a compact,lightweight and flexible form. Within the next few years, PLEDs areexpected to make significant inroads into markets currently dominatedby the cathode ray tube and LCD display technologies, such astelevisions and computer monitors. PLEDs are anticipated as the

technology of choice for new products including virtual reality headsets;a wide range of thin, technologies, such as televisions and computermonitors. PLEDs are anticipated as the technology of choice for newproducts including virtual reality headsets; a wide range of thin,lightweight, full colour portable computing; communications andinformation management products; and conformable or flexibledisplays.



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6. CONCLUSION

Organic materials are poised as never before to trans form the world ofdisplay technology. Major electronic firms such as Philips and pioneer andsmaller companies such as Cambridge Display Technology are betting thatthe future holds tremendous opportunity for low cost and surprisingly highperformance offered by organic electronic and opto electronic devices.Using organic light emitting diodes, organic full colour displays mayeventually replace LCDs in laptop and even desktop computers. Suchdisplays can be deposited on flexible plastic coils, eliminating fragile andheavy glass substrate used in LCDs and can emit light without thedirectionality inherent in LCD viewing with efficiencies higher than that

can be obtained with incandescent light bulbs.Organic electronics are already entering commercial world. Multicolorautomobile stereo displays are now available from Pioneer Corp., of TokyoAnd Royal Philips Electronics, Amserdam is gearing up to produce PLEDbacklights to be used in LCDs and organic ICs.The first products using organic displays are already in the market. Andwhile it is always difficult to predict when and what future products will beintroduced, many manufactures are working to introduce cell phoned and

personal digital assistants with organic displays within the next few years.The ultimate goal of using high efficiency, phosphorescentflexible organic displays in laptop computers and even for home videoapplications may be no more than a few years in to the future. The portableand light weight organic displays will soon cover our walls replacing thebulky and power hungry cathode ray tubes.



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REFERENCE

www.cdtltd.co.uk www.research.philips.com www.covion.com www.lep-light.com

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