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3/11/2012
English202C|DandanShe
OLEDs:ANewEraInScreen
OLEDs: A New Era In Screen
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AudienceandScopeThepurposeofthisdocumentistoinformElectricalEngineeringmajorstudentsfocusondisplays
andlightingoranyoneinterestedindisplaysandlightingaboutOrganicLight-emittingDiode
(OLED)sources.Afterreadingthisdocument,theaudiencewillbeabletoidentifythekey
componentsofOLEDs,howOLEDsworkandtheirbasicapplications.ThisdocumentmayarousetheaudienceinterestinOLEDsfieldandmakethemexploremoreaboutthisfield.Thistypeof
documentdescribingOLEDswouldbefoundintextbooksormagazinesdealingwithhigh
technologies.
Introduction
Canyouimagineacellphone,whichisthin,lightandbendable?SamsunghasinventedaconceptphoneusingOLEDtechnology,makingthisideacometrue(AsshowninFigure1).
Figure1.SamsungsOLEDbendableconceptphone
OLEDsaresolid-statedevicescomposedofthinfilmsoforganicmoleculesthatcreatelightwith
theapplicationofelectricity.OLEDscanprovidebrighter,crisperdisplaysonelectronicdevices
anduselesspowerthanconventionallight-emittingdiodes(LEDs)orliquidcrystaldisplays
(LCDs)usedtoday.OLEDsareuniquebecausetheyarethin,flexible(evencanberolled)and
transparent.OLEDscanhaveeithertwolayersorthreelayers.Thisdocumentwillfocusonthe
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two-layerdesign.OLEDisanewtechnology,soevennowwecannotbuyaTVwithOLEDscreen.
However,thisisanewdirectionfordisplays.Soitisimportanttounderstandhowtheywork,
whattheadvantagestheyhaveanditsfuture.Thedocumentwillfocusonthecomponentsof
OLEDs,howtheywork,theadvantagesofOLEDsandtheirapplications.
Figure2.Aflexible,bendable,transparentOLEDscreen
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OLEDsComponentsOLEDisaflatlightemittingtechnology,madebyplacingaseriesoforganicthinfilmsbetween
twoconductors.Whenelectricalcurrentisapplied,abrightlightisemitted.OLEDscanbeused
tomakedisplaysandlighting.BecauseOLEDsemitlight,theydonotrequireabacklightandso
arethinnerandmoreefficientthanLCDdisplays(whichdorequireawhitebacklight).OLEDsarenotjustthinandefficient,theycanalsobemadeflexibleandtransparent.
LikeanLED,anOLEDisasolid-statesemiconductordevicethatis100to500nanometersthick,or
about200timessmallerthanahumanhair.OLEDscanhaveeithertwolayersorthreelayersof
organicmaterial;inthelatterdesign,thethirdlayerhelpstransportelectronsfromthecathodeto
theemissivelayer.
AnOLEDconsistsofthefollowingparts:substrate,anode,conductivelayer,emissivelayer
andcathode(AsshowninFigure3).
Figure3.OLEDstructure
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OLEDconsistsofthefollowingparts:
Substrate(clearplastic,glass,foil)-ThesubstratesupportstheOLED.Anode(transparent)-Theanoderemoveselectrons(addselectron"holes")whenacurrentflowsthroughthedevice.Organiclayers-Theselayersaremadeoforganicmoleculesorpolymers.Conductinglayer-Thislayerismadeoforganicplasticmoleculesthattransport"holes"fromtheanode.OneconductingpolymerusedinOLEDsispolyaniline.
Emissivelayer-Thislayerismadeoforganicplasticmolecules(differentonesfromtheconductinglayer)thattransportelectronsfromthecathode;thisiswherelightismade.Onepolymerusedin
theemissivelayerispolyfluorene.
Cathode(mayormaynotbetransparentdependingonthetypeofOLED)-Thecathodeinjectselectronswhenacurrentflowsthroughthedevice.
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HowdoOLEDsEmitLight?
Theprocessisasfollows(Asshown
infigure4):1.Thebatteryorpowersupplyof
thedevicecontainingthe
OLEDappliesavoltageacrosstheOLED.
2.Anelectricalcurrentflowsfromthecathodetotheanodethrough
theorganiclayers(an
electricalcurrentisaflowof
electrons).Thecathodegives
electronstotheemissivelayer
oforganicmolecules.
3.Theanoderemoveselectronsfromtheconductivelayeroforganic
molecules.
4.Attheboundarybetweenthe
emissiveandtheconductivelayers,electronsfindelectron
holes.Whenanelectronfinds
anelectronhole,theelectron
fillsthehole(itfallsintoan
energyleveloftheatomthat'smissinganelectron).When
thishappens,theelectrongives
upenergyintheformofa
photonoflight.
5.TheOLEDemitslight.
6.Thecolorofthelightdependsonthetypeoforganicmoleculeintheemissivelayer.ManufacturersplaceseveraltypesoforganicfilmsonthesameOLEDtomake
colordisplays.
7.Theintensityorbrightnessofthelightdependsontheamountofelectricalcurrentapplied:
themorecurrent,thebrighterthelight.
Figure4.HowOLEDswork
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TheAdvantagesofOLEDs
OLEDsoffermanyadvantagesoverbothLCDsandLEDs:
Thinnerandlighter.
Flexible.Becausethelight-emittinglayersofanOLEDarelighter,thesubstrateofanOLEDcanbeflexibleinsteadofrigid.OLEDsubstratescanbe
plasticratherthantheglassusedforLEDsandLCDs.
Brighter.BecausetheorganiclayersofanOLEDaremuchthinnerthanthecorrespondinginorganic
crystallayersofanLED,theconductiveandemissive
layersofanOLEDcanbemulti-layered.Also,LEDs
andLCDsrequireglassforsupport,andglassabsorbs
somelight.OLEDsdonotrequireglass.
LessPower.LCDsworkbyselectivelyblockingareasof
thebacklighttomaketheimagesthatyousee,while
OLEDsgeneratelightthemselves.BecauseOLEDsdonotrequirebacklighting,theyconsumemuchlesspowerthanLCDs(mostoftheLCDpowergoestothebacklighting).Thisisespecially
importantforbattery-operateddevicessuchascellphones.
Easiertoproducelargersize.BecauseOLEDsareessentiallyplastics,theycanbemadeinto large, thin sheets. It is much more difficult to grow and lay down so many liquidcrystals.
Large fields of view.OLEDs can offer about 170 degrees view. Because LCDs work byblockinglight,theyhaveaninherentviewingobstaclefromcertainangles.OLEDsproduce
theirownlight,sotheyhavea
muchwiderviewingrange.
Figure5.BendableOLEDcansupplysharperimages.
Figure6.OLEDiseasytobemade
intolargesize,andstillhashigh
qualityofimages.
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ApplicationsofOLEDs
SamsungSuperOLEDTVsInJanuary2012SamsungunveiledtheirfirstOLEDTVproduct,theKN55ES900055"Super
OLEDTV.Thisamazingtelevisionoffersunparalleledcolorgamut,contrastandrefreshrate,andalsofeaturesSamsung'slatest3D,SmartandControltechnologies.
ASUSPadfone
ASUSpadfoneisanAndroid(v4,ICS)mobilephonethathasanexternaltabletdockingstation
accessory.Thephoneitselfhasa4.3"qHD(800x600)OLEDdisplay,adual-coreCPU,8mp
cameraand64GBofinternalmemoryandamicroSDslot.
Figure7.SamsungSuperOLEDTV
Figure8.ASUSPadphone
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CowonD3Plenue
CowonsD3isanAndroidrunningPMPwitha3.7AMOLEDdisplay,fullHDsupport,WIFI,
HDMIout,BluetoothandaT-DMBTVtuner.Itsgot8/16/32GBofonboardstorageanda
microSDslot.
Conclusion
ItturnsoutthatbecauseOLEDsarethinandsimple,theycanbeusedtocreateflexibleandeventransparentdisplays.Theyharnessorganicmaterialsinordertomoreefficientlyproducelight.This
isprettyexcitingasitopenedupawholeworldofpossibilities.EventhoughOLEDsarestillfacing
manyproblemssuchastheyarerelativelyexpensivetoproducemassively,theyarestillthenewdirectionofthedisplayscango.Sinceallthecomputerandcellphonecompaniesarecompetingnew
screentechnology,knowinganddevelopingOLEDsdisplayswillhelpthemwinthegame.OLEDstechnologyismaturingrapidly,soOLEDswillundeniablyplayimportantrolesindisplayandlighting
fields.
Figure9.CowonD3Plenue
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References:
Informationnotalreadyknownsummarizedfromthefollowingwebsites:
http://www.oled--info.com/introduction
http://en.wikipedia.org/wiki/OLED
http://electronics.howstuffworks.com/oled1.htmhttp://www.oled---a.org/
http://www.forbes.com/sites/michaelkanellos/2012/01/12/seven---reasons---why---oled---tvs---
could---really---be---real/
http://www2.dupont.com/OLED/en_US/index.html
Imagesretrievedfrom:
http://www.oled---info.com/toray---samsung---flexible---oled---photo
http://www.engadget.com/2007/05/24/sonys---worlds---first---16---7---million---color---flexible---
oled/http://www.solarfeeds.com/in---focus---oled---displays/http://quanta.hanyang.ac.kr/Education/Education_OLED_Principles.htm
http://static.ddmcdn.com/gif/oled---cell.gif
http://static.ddmcdn.com/gif/oled---process.gifhttp://www.oledw.com/oled---
news/200907/1496.shtmlhttp://www.oledw.com/oled---news/201009/2631.shtml
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