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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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