Preparation of organic/inorganic hybrid nanocomposites by ultraviolet irradiation and their packaging applications for organic optoelectronic devices

Applied

Surface

Science

j o ur na l ho me p age :w w w . e l s e v i e r . c o m / l o c a t e / a p s u s c

Preparation

of

organic/inorganic

hybrid

nanocomposites

by

ultraviolet

irradiation

and

their

packaging

applications

for

organic

optoelectronic

devices

Ming-Hua

Chung

_,

_Jian-Shian

_Lin

_,

_Tsung-Eong

_Hsieh

_,

_Nien-Po

_Chen

_,

_Fuh-Shyang

_Juang

_,

Chen-Ming

Chen

_,

_Lung-Chang

_Liu

a_{DepartmentofMaterialsScienceandEngineering,NationalChiao-TungUniversity,Hsinchu300,Taiwan,ROC} b_{DepartmentofElectro-OpticalEngineering,YuanzeUniversity,Taoyuan320,Taiwan,ROC}

c_{InstituteofElectro-OpticalandMaterialsScience,NationalFormosaUniversity,Huwei,Yunlin63208,Taiwan,ROC} d_{MaterialandChemicalResearchLaboratories,IndustrialTechnologyResearchInstitute,Hsinchu30011,Taiwan,ROC}

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received13April2011

Receivedinrevisedform27May2011 Accepted28May2011

Available online 21 June 2011 Keywords:

Organiclightemittingdiode Lifetime

Package Organicsolarcell Optoelectronicdevice

a

b

s

t

r

a

c

t

Byultraviolet(UV)-assisted syntheticprocedure,we havesuccessfullypreparedseveralUVcurable organic/inorganichybridnanocompositeswithexcellentgasbarriercapabilities,moderatehardness,and goodadhesivestrength.Theexperimentalresultsrevealthatthephysicalpropertiesofnanocomposites dependontheirchemicalstructures.Therefore,introductionofsiliconeandpolyurethane(PU)intothe Acrylicsbackbonedramaticallyraisestheadhesivestrengthaswellasrefractiveindexandlowersthe gaspenetration.Furthermore,wehavealsoappliedlab-madenanocompositegfortheencapsulationof organicoptoelectronicdevicessuchasOLEDs,flexibleOLEDs,andorganicsolarcells.Withthepackage oflab-madenanocompositeg,theorganicoptoelectronicdeviceseffectivelyresisttheentryofmoisture andoxygenintheair,extendingthelifetimes.

© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Organic/inorganichybridnanocomposites,composedoforganic polymermatrices(e.g.acrylics,epoxy,andsilicone)andinorganic nano-fillers (e.g.silica (SiO2), titaniumoxide (TiO2), zinc oxide

(ZnO), and alumina (Al2O3)) [1], have recently attracted much

attentionbecauseoftheirmiscellaneousapplicationssuchasfuel cells[2],nonlinearoptics[3],lithiumbatteries[4],gassensors[5], flameretarding[6],photochromism[7],andsoon.Sincetheycan resisttheentryofmoistureandoxygenintheair,theyhavealso utilizedinthepreservationofbeveragesandfood[8].Althoughthe literaturesaboutthepromotionoflifetimesfortheencapsulation ofelectronicdeviceswithmetalsorglasscanshavebeenreported [9–11],theprocessofpackageisexpensiveandcomplicated. Nowa-days,mostoptoelectronicdevicesareencapsulatedwithinorganic materials(e.g.SiO2,Al2O3,etc.)[12],polymers(e.g.polyacrylics,

PET, poly(p-xylylene), etc.) [13,14]and theircombinations (i.e. organic/inorganichybridcomposites)[15]owingtotheadvantage ofsmallerformfactors,lowcost,andimprovedmanufacturability [16].Withthegasresistanceoforganic/inorganichybrid nanocom-posites,thelifetimesofoptoelectronicdevicescanbeeffectively

∗ Correspondingauthor.Tel.:+88635732475;fax:+88635732347. E-mailaddress:[email protected](M.-H.Chung).

prolongedbecauseoxygenandmoistureintheatmospherecause thecorrosionfororganiclayers,metalelectrodes,andother mate-rialsofdevices[17,18].However,theconventionalprocessesfor thesynthesesoforganic/inorganichybridnanocompositesaretime andenergy-consuming.

In this paper, we have rapidly synthesized several organic/inorganichybrid nanocompositeswithultraviolet (UV)-assisted polymerization and then investigated their physical properties. Because they possess excellent adhesive strength, moderatehardness,andgoodtransparencies,wehavealsoapplied them forthepackage of organicoptoelectronicdevices suchas organiclightemittingdiodes(OLEDs),flexibleOLEDs,andorganic solarcells.Theexperimentalresultsmanifestthatthelifetimesof organicoptoelectronic devices dramatically raise and lab-made organic/inorganic hybrid nanocomposites exhibit excellent gas barriercapability.

2. Experimental

2.1. Materials

Allofmonomers(Fig.1),photoinitiators(Fig.2),organic mate-rials for electronic devices (Fig. 3), solvents, and fillers (silica; 30–100nm)usedintheexperimentwerepurchasedfromAldrich Co.andusedwithoutfurtherpurification.

0169-4332/$–seefrontmatter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2011.05.117

Fig.1. Monomersforlab-madeorganic/inorganichybridnanocomposites.

2.2. PreparationofUV-curableorganic/inorganichybrid nanocomposites

2.2.1. Preparationofnanocompositea(Scheme1)

Benzyl methacrylate (BZMA; 117g), methyl methacrylate (MAA;86g),2-hydroxyethylmethacrylate(2-HEMA;130g),silica (39g),andI-184(6g)weremechanicallystirredandirradiatedbya UVlamp(EntelaUVP;100W)atroomtemperaturefor20min.Then nanocompositeawasobtained.Thedataforweight-average molec-ularweight(Mw),number-averagemolecularweight(Mn),Mw/Mn

ratio,andviscosityofnanocompositeaweretabulatedinTable1. 2.2.2. Preparationofnanocompositeb,c,andd(Schemes2–4)

PU/Acrylicsa(333g),silica(39g),I-184(2g),andI-369(4g) weremechanicallystirred and irradiatedbya UV lamp(Entela

Fig.2.Photoinitiatorsforlab-madeorganic/inorganichybridnanocomposites.

UVP;100W)atroomtemperaturefor20min.Then nanocompos-itebwasobtained.Withthesameamountsofmonomers,fillers, andphotoinitiators,nanocompositecanddweresynthesizedby thesimilarprocedure.Inaddition,theirviscositiesandmolecular weightsweretabulatedinTable1.

2.2.3. Preparationofnanocompositee(Scheme5)

Siliconea (333g), silica (39g), I-184 (3g), I-369 (1.5g), and I-ITX (1.5g) were mechanically stirred and irradiated by a UV lamp(EntelaUVP;100W)atroomtemperaturefor20min.Then nanocompositeewasobtained.AsshowninTable1,itsviscosity andmolecularweightweredescribed.

2.2.4. Preparationofnanocompositef(Scheme6)

Siliconea(166.5g),2-HEMA(166.5g),silica(39g),I-184(3g), I-369(1.5g),andI-ITX(1.5g)weremechanicallystirredand irra-diatedbyaUVlamp(EntelaUVP;100W)atroomtemperaturefor 20min.Thennanocompositefwasobtained.Moreover,itsviscosity andmolecularweightwerelistedinTable1.

2.2.5. Preparationofnanocompositeg(Scheme7)

Siliconea(166.5g),PU/Acrylicsb(166.5g),silica(39g),I-184 (2.7g),I-369(1.35g),I-ITX(1.35g),andI-127(0.6g)were mechan-icallystirredandirradiatedbyaUVlamp(EntelaUVP;100W)at roomtemperaturefor20min.Thennanocompositegwasobtained. AsmanifestedinTable1,itsmolecularweightandviscositywere described.

Table1

Thedataforviscosityandmolecularweightoflab-madeorganic/inorganichybrid nanocomposites. Nanocomposite Viscosity(cps) Mw Mn Mw/Mn a 15,100 233,100 113,300 2.06 b 8600 123,100 66,100 1.86 c 23,200 275,000 138,400 1.99 d 22,800 262,000 125,400 2.09 e 6900 73,700 43,200 1.71 f 8800 103,100 56,700 1.82 g 12,400 118,600 62,800 1.89 h 10,700 93,200 48,600 1.92

Al O O N O N

Alq

BCP

mCP

Firpic

Os

TAPC

DMPDI MgPc

N

N

Os

P

N

N

N

P

N

N

N

N

CF

C

F

N

Ir

N

N

F

F

F

F

O

O

N

N

N

N

N

O

O

O

O

O C O C C CH3

+

+

UV (100

W, 20 min), R.T.

I-

184

, silica

nanocomposite a

nanocomposite b

PU/Acrylics a UV (100W, 20 min), R.T.

I-184, I-369, silica

Cl NH O C O (CH2)6 (CH2)6 _Cl n O O C CH2 CH H O O C O OCN

Scheme2. Synthesisofnanocompositeb.

I-184, I-369, silica UV (100W, 20 min), R.T. PU/Acrylics b O O C (CH2)6 O CO H N_H O O C O (CH2)6 _OCN R CH CH2 C O O O C O CH CH2 m n R: NHCO O (CH2)6 NH CO O (CH2)6 nanocomposite c

OCN O C O O N H H CO O C O O R CH CH2 C O O O C O m n R: NHCO O NH CO O (CH2)6 (CH2)6 (CH2)6

I-184, I-369, silica UV (100W, 20 min), R.T.

nanocomposite d PU/Acrylics c

Scheme4. Synthesisofnanocomposited.

Si OCH3 OCH3 OCH3 (CH2)3 O C O C C CH3 H2 C CH3 CH2 C O O (CH2)3 Si OCH3 OCH3 O C H3 n UV (100W, 20 min), R.T.

I-184, I-369, I-ITX, silica

Silicone a

nanocomposite e

Scheme5.Synthesisofnanocompositee.

Si OCH3 OCH3 OCH3 (CH2)3 O C O C C CH3 H2 UV (100W, 20 min), R.T. I-184, I-369, I-ITX, silica Silicone a nanocomposite f 2-HEMA CH3 C _C O C O OH OH C O O m CH2 CH3 C n H3CO OCH3 OCH3 Si (CH2)3 O O C CH2 CH3 C +

Si OCH3 OCH3 OCH3 (CH2)3 O C O C C CH3 H2 UV (100W, 20 min), R.T. I-184, I-369, I-ITX, I-127, silica

Silicone a PU/Acrylics b + R R O O C O CO H N_H O O C O OCN n x CO OCH3 OCH3 Si (CH2)3 O O C CH2 CH3 C R CH CH2 C O O O C O CH CH2 z y R: NHCO O NH CO O (CH2)6 (CH2)6 nanocomposite g

Scheme7. Synthesisofnanocompositeg.

2.2.6. Preparationofnanocompositeh(Scheme8)

Epoxya(333g),alumina(39g),andTSHFA(6g)were mechan-icallystirredandirradiatedinaUVlamp(EntelaUVP;100W)at roomtemperaturefor20min.Thennanocompositehwasobtained. ThedataforMw,Mn,Mw/Mnratio,andviscosityofnanocomposite

hweretabulatedinTable1. 2.3. Instruments

MolecularweightsandviscositiesweremeasuredbyaWaters AllianceGPCV2000andaViscolite700,respectively.Furthermore, we examined the adhesion strength, hardness, transparencies, refractiveindices,andgaspermeationrateswithamicro-computer universaltestingmachine(HungTaCo.),apencilstypefilm hard-nesstester(ZSH2090),aHITACHIU-3300,aFilmetricsF20,andan Illinois-8501,respectively.TheUVlampsusedforsynthesesand curingwererespectivelyEntelaUVP100Wand2450W.Moreover, werecordedthephotoelectricpropertiesandlifetimesofOLEDsby Keithley2400andSpectrascanPR650,respectively.Thefilm

thick-O O R: O R O C CH2OH R CH2OH C x y z TSHFA, silica UV (100W, 20 min), R.T. nanocomposite h Epoxy a

Scheme8.Synthesisofnanocompositeh.

nesswasmeasuredbyasurfaceprofiler(TENCORP-10).Inaddition, thecurrent–voltage(I–V)curvesfororganicsolarcellswere mea-suredintheairbyaninstrument(Keithley238),whoseaccuracy canreachpicoampere,underilluminationofwhitelight froma 300Whalogenlamp(SaturnCo.)whoseintensitywasrecordedon aradiometer(IL-1700).ThelifetimesforOLEDs,flexibleOLEDs,and organicsolarcellswereexaminedinreal-timeconditions. 2.4. FabricationofOLEDsandflexibleOLEDs

The fabrication of OLEDs wasexecuted in a glove box. The indiumtinoxide(ITO)glass(5/square)wasultrasonicallywashed with the acetone, methanol, and de-ionized water for 5min. Afterdried witha streamof nitrogen as wellas theoven and treatmentof O2 plasmafor90s, wedeposited1,1-bis(4-bis(4

-menthylphenyl)aminophenyl)cyclohexane(TAPC;holetransport layer;40nm),9H-carbazole-9,9-(1,3-phenylene)-bis-(9C1)(mCP; green emitting material)/Osmium(II) bis(3-(trifluoromethyl)-5-(4-tert-butylpyridyl)-1,2,4-triazolate) diphenylmethylphosphine (Os; red emitting material)/bis(3,5-difluoro-2-(2-pyridyl)phenyl -(2-carboxypyridyl)iridiumIII(Firpic;blueemittingmaterial) mix-ture(25nm;weightratio=82/17/1), 2,9-dimethyl-4,7-dimethyl-phenanthroline (BCP; electron transport layer; 15nm), tris-[8-hydroxyquinoline]aluminium(Alq3; electron transport layer;

30nm), lithium fluoride (LiF; electron injection layer; 0.5nm), andaluminium(Al;cathode;150nm)layerbylayerontotheITO glassbyvacuumevaporation.Finally,lab-madenanocompositeg

(100␮m)wasdepositedontheAlelectrodebyspin-coating tech-nique(stageI:1500r.p.m.for20s;stageII:3500r.p.m.for30s)and curedbyUVilluminationfor10s.(Fig.4(a)).Thesimilarprocess wasexecutedinthefabricationofflexibleOLEDsexcepttheITO glasswasreplacedwiththeITOPET(poly(ethyleneterephthalate)) (Fig.4(b)).

2.5. Fabricationoforganicsolarcells

Thefabrication oforganicsolarcells wasalso executedin a glovebox.TheITOglass(5/square)wasultrasonicallywashed

Fig.4. Structuresoflab-made(a)OLEDs,(b)flexibleOLEDs,and(c)organicsolarcells.

withtheacetone,methanol,andde-ionizedwaterfor5min,dried withastreamofnitrogenaswellastheoven,and treatedwith O2plasmafor90s.Thenwedepositedmagnesiumphthalocyanine

(MgPc; p-type semiconductor; 30nm), N,N -bis(1,5-dimethyl)-3,4:9,10-perylenebis(dicarboximide)(DMPDI;n-type

semiconduc-tor;50nm),2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline(BCP; electrontransportlayer;15nm),andaluminium(Al;anode;90nm) layerbylayerontotheITOglasswithvacuumevaporation.Finally, lab-made nanocomposite g (100␮m) was deposited on the Al electrodebyspin-coatingtechnique(stageI:1500r.p.m.for20s; stageII:3500r.p.m.for30s)andcuredbyUVilluminationfor10s (Fig.4(c)).

3. Resultsanddiscussion

3.1. Preparationoforganic/inorganichybridnanocompositesby UV-assistedpolymerization

UV, which is the electromagnetic radiation of 180–400nm, exhibitshighenergytocausethedissociationofphotoinitiators, consequently producing free radical or cationic polymerization [19].Inthisstudy,allthesyntheticreactionswithUVprocedure takeonly20minandproceedwithoutsolventsasmanifestedin Schemes1–8whilethosewithconventionalthermalmethodstake 8–24handproceedwithsolvents.Inaddition,thecuringtimefor

Table2

Thephysicalpropertiesoflab-madeorganic/inorganichybridnanocomposites.

Nanocomposite Adhesive

strength(kg/cm)

Hardness Transparency(%) Permeationratefor oxygen(g/m2_day)

Permeationratefor moisture(g/m2_day) a 0.3 2H 90 0.25 0.21 b 0.8 2H 87 0.20 0.17 c 1.4 3H 90 0.10 0.08 d 1.3 H 91 0.14 0.11 e 1.6 3B 95 0.08 0.06 f 1.7 2B 93 0.07 0.05 g 2.1 B 92 0.05 0.03 h 1.5 3H 46 0.17 0.13

Fig.5.TEMsoflab-madenanocomposite(a)a,(b)b,(c)c,(d)d,(e)e,(f)f,(g)gand(h)h.

lab-madeorganic/inorganichybridnanocompositesunderUV

irra-diationisonly10swhilethatwithconventionalthermalmethodis

severalhours.WithUVprocedure,thewholeproductionefficiency

canbeincreasedandtheproductisimmediatelyreadyfor

test-ing,shipment,andstorageratherthanamulti-stepthermaldrying

process.Furthermore,UVprocesshaslowerenergyconsumption

andisalsoanenvironmentallyfriendlytechnologywithout

emis-sionsofvolatileorganiccompounds(VOCs)andflammability.These

meritsfitthedemandsforthecleanandlow-costpreparationof

organic/inorganichybridnanocomposites.

3.2. Physicalpropertiesoflab-madeorganic/inorganichybrid

nanocomposites

As shown in Table 2, the physical properties of lab-made

organic/inorganichybridnanocompositesdeeply dependonthe chemical structures of organic polymers since the amounts of fillers,initiators,andphotoinitiatorsutilizedforthepreparation of organicpolymer/filler hybrids arethe same. In case of sim-pleacrylics nanocomposite (i.e. nanocomposite a), its adhesive strength,hardness,transparencies,permeationrateforoxygen,and

Fig.6.Lifetimesoflab-made(a)OLEDsactuatedat6Vand(b)flexibleOLEDsactuatedat6V.

permeationratefor moistureare 0.3kg/cm, 2H, 90%, 0.25g/m2

day, and 0.21g/m2 _{day, respectively. When PU and silicone}

are introduced into the backbone of organic/inorganic hybrid nanocomposite,nevertheless,itsadhesivestrengthandrefractive indexdramaticallyraiseandthegaspenetrationdrops.Thisresult comesfromthatPUandsiliconeexhibithighersurfaceenergythan acrylics[20].Therefore,introductionofPUandsiliconecausesthe increaseofadhesivestrengthtotheglass,alsoenhancinggas block-ingcapability.

AmongPU/Acrylics nanocomposites(i.e.nanocompositeb, c,

and d), nanocompositec exhibitsthe largestadhesive strength (1.4kg/cm)and lowestgaspenetration (oxygen:0.10g/m2 _day;

moisture:0.08g/m2 _{day).Accordingtotheexperimentalresults,}

wealsofindthatthehardnessofPU/Acrylicsnanocompositeswith phenylrings(i.e.nanocompositebandc)ishigherthanthatwith cycloalkylrings(i.e.nanocomposited),revealingthehardnessof PU/Acrylicsnanocompositesextremelydependsontheirchemical structures.Moreover,thehardnessofPU/Acrylicsnanocomposites withtwofunctionalgroups(i.e.nanocompositec)ishigherthan thatwithonefunctionalgroup(i.e.nanocompositeb).

IncaseofSilicone/Acrylicsnanocomposites(i.e. nanocompos-iteeand f), theiradhesive strength,refractive indices, andgas penetration are obviously superior to those of simple acrylics nanocomposite(i.e.nanocompositea).Amongthem,theadhesive strengthofnanocompositefcanreach1.7kg/cmanditspermeation ratesforoxygenandmoistureare0.07and0.05g/m2_day,

respec-tively.Nonetheless,introductionofsiliconedrasticallydecreases thehardnessofnanocompositessothatthehardnessof nanocom-positeseandfbecomes3Band2B,respectively.

In order to further improve the physical properties of lab-madeorganic/inorganichybridnanocomposites,wehavetriedto addbothPUandsiliconeintothebackbonesofacrylicstoform nanocompositeg,whoseadhesivestrength,hardness,permeation rateforoxygen,andpermeationrateformoistureare2.1kg/cm,B, 0.05g/m2_{day,and0.03g/m}2 _{day,respectively.Theexperimental}

resultsmanifestthatintroductionofPUandailiconesubstantially improvestheadhesivestrengthandgaspenetration.

Although we have also successfully synthesized epoxy nanocomposite(i.e.nanocompositeh)withgoodadhesivestrength (1.5kg/cm)andlowgaspenetration(oxygen:0.17g/m2_day;

mois-ture:0.13g/m2_{day),colorstaintakesplaceduringUVsyntheticand}

curingprocess,leadingtotheirpoortransparencies(46%). More-over,nano-fillers(i.e.silica)werehomogeneouslydispersedinthe polymermatricesasshowninFig.5(a)–(h),indicatingthatthe pre-paredmaterialswerenanocomposites.

Amongallthelab-madenanocomposites,nanocompositeg pos-sessesthebestphysicalpropertiescomparedwithothermaterial groupsbecausetheirpolymermatrices(i.e.Silicone/PU/Acrylics) mayhavelargestsurfaceenergy[20],causingtheraiseof adhe-sivestrengthtotheglassandtheincreaseofgasresistance.Since nanocomposite g exhibits fast curingduration (10s), excellent adhesivestrength(2.1kg/cm),moderatehardness(H),andlowgas penetration(oxygen:0.05g/m2_{day;moisture:0.03g/m}2_day),we

haveexecutedtheencapsulationoforganicoptoelectronicdevices (i.e.OLEDs,flexibleOLEDs,andorganicsolarcells)withthemto evaluatetheirgasbarriercapabilityandtopromotethelifetimes oforganicoptoelectronicdevices.

3.3. PackageofOLEDsandflexibleOLEDs

AsshowninFig.6(a),theluminanceofOLEDswithout encap-sulationsharplydropswhilethedeviceisactuatedat6Vandtheir half-lifetimes,definedasthedurationwhentheluminancedecays from theoriginal amount to itshalf, are only 10h. Thisresult revealsthattheoxygenandmoistureintheatmosphereinducesthe erosionofmetalelectrodeandorganiclayers.However,the half-lifetimesdrasticallyriseto95hwhilenanocompositegispackaged inthedevice.Thisresultmanifeststhatlab-madeorganic/inorganic hybridnanocompositescanblocktheentryofmoistureand oxy-genintheairintotheOLEDs,thereforequenchingthedegradation Table3

Thephotoelectricconversionpropertiesoflab-madeorganicsolarcells.

Encapsulatingmaterial Actuatingtime(h) Voca_{(V) Isc}b_(mA/cm2_{) FillFactor(%) Efficiency(%) Decayratio(DR)}c_(%)

Noencapsulation 0 0.48 2.46 40.2 0.487 – 24 0.48 1.15 36.2 0.198 59.3 48 0.48 0.48 36.9 0.092 81.1 Nanocompositeg 0 0.48 2.48 41.3 0.491 – 24 0.48 1.75 42.6 0.377 23.2 48 0.48 1.28 40.3 0.251 48.9

a_{Opencircuitvoltage.} b_{Shortcircuitcurrent.}

c _{DecayratioisdefinedasDR=((Eff}

o−Effe)/Effo)×100%whereEffoandEfferepresenttheefficiencyoforganicsolarcellfororiginalstate(actuatingtime=0h)and

Fig.7.I–Vcurvesoflab-madeorganicsolarcells((a):withoutencapsulationand (b):withlab-madenanocompositeg).

ofmetalelectrodeaswellasorganicmaterialsandextendingthe lifetimes.ComparedwithcommercialUVcurable encapsulating adhesives(EPO-TEKH20S;EpoxytechnologyInc.),thedeviceswith nanocompositeghave longerlifetimesand shorter curingtime becausethecuringtimeandhalf-lifetimesofOLEDswithEPO-TEK H20Sare3minand38h,respectively.

ThesimilarresultcanbeobservedincaseofflexibleOLEDsas showninFig.6(b).Thehalf-lifetimesofflexibleOLEDswiththe encapsulationof nanocompositeg are30h,which are 4.3- and 2.2-foldslongerthanthosewithoutencapsulationandwith EPO-TEKH20S,respectively,provingthatlab-madeorganic/inorganic hybridnanocompositesexhibitexcellentgasbarriercapabilityand aregoodencapsulatingmaterialsforflexibleOLEDs.

3.4. Packageoforganicsolarcells

Theconversionofsunlightintoelectricalenergyhasbeen cur-rentlyanessentialissuebecausesunlightisaninexhaustible,clean, and environmentally friendly energy source. Although silicon-basedsolarcellsexhibitgoodefficiencies,theircostsareveryhigh sincepurifiedsiliconisexpensiveandthemanufacturing proce-dureiscomplicated.Consequently,organicsolarcellshavebeen

alternativecandidatesforphotoelectricconversionduetolowcost andhighprocessability.However,thelifetimesoforganicsolarcells havebeenavitalobstacleforthecommercializationbecause oxy-genandmoistureintheaircorrodetheorganicmaterialsandmetal electrodesofdevices,highlyreducingthelifetimes.Furthermore, mostresearchesfocusontheimprovementoftheefficienciesfor solarcellsbutthestudiesaboutthepromotionoflifetimesareless reported.

AsshowninFig.7(a)andTable3,lab-madeorganicsolarcell withoutencapsulationexhibits rectifyingeffectunder darkand photoelectricconversionpropertiesunderilluminationofwhite light(conversionefficiency=0.487%)becauseMgPcandDMPDIare respectivelyp-typeandn-typesemiconductorsandthusp/n het-erojunctiongenerates.Whiletheactuatingtimeprolongs,however, thephotoelectricconversioncapabilitygraduallydropssincethe moistureandoxygenintheatmospherepenetrateintothedevice, causingtheerosionoforganicmaterialsandmetalelectrodes.After actuatedfor48h,theefficiencyonlyremainstobe0.092%(decay ratio=81.1%).

Inordertofurtherincreasethelifetimesoforganicsolarcells,we haveutilizednanocompositegfortheencapsulationofthedevices. Withnanocompositeg,asmanifestedinFig.7(b)andTable3,the decayratiodramaticallyreducesandcanbeonlyrespectively23.2 and48.9%whentheactuatingtimearerespectively24and48h. Thisresultdemonstratesthat nanocompositegcanpreventthe entryofoxygenandmoistureintheatmosphereintothedevice, successfullyimprovingthelifetimesoforganicsolarcells.

4. Conclusions

We conclude that UV curable organic/inorganic hybrid nanocompositeswithgoodadhesionstrength,fastcuringspeed, moderatehardness,andexcellentgasbarriercapabilityhavebeen successfullysynthesizedunderUVirradiation.Withthe encapsu-lationofnanocompositeg,thelifetimesofOLEDs,flexibleOLEDs, andorganicsolarcellscanbeincreaseddrasticallyowingtotheir gasblockingeffect.

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