Transparent conducting graphene electrodes for ... · Compatibility of graphene based TCE with high temperature processes has been proven • Successful dye loading on G -coated electrode

Bologna Section

TransparentconductinggrapheneelectrodesforphotovoltaicapplicationsLucaOrtolani1,CaterinaSummonte1,RitaRizzoli1,Meganne Christian1,IsabellaConcina2,3,Gurpreet S.Selopal2,3,RiccardoMilan2,3,AlbertoVomiero3,4,VittorioMorandi1

1.CNR-IMM,ViaGobetti 101,40129, Bologna, Italy.2.SENSORLab,Department ofInformation Engineering, UniversityofBrescia, ViaValotti 9,25133Brescia, Italy.3.CNR-INOSENSORLab,ViaBranze 45,25123Brescia, Italy.4.Luleå UniversityofTechnology, 97198Luleå,Sweden.

2Bologna Section

2

Grapheneastransparentconductiveelectrode

[F.Bonaccorso etal.NaturePhotonics 4 (2010),611] [S.Bae etal.NatureNanotechnology 5 (2010),574]

Graphenevs.differentTCEs Graphenetypes

R□ ≈ 102 Ω/□T ≈ 90 - 95 %

Grapheneis2Dcrystalmadeofsp2hybridizedCarbonatoms.

Graphene hasremarkablephysicalandchemicalpropertiesfromflatspectrumtransparency,highelectrical andthermalconductivity.

It isanexcellent candidatetoreplaceMOfilmastransparentconductiveelectrodes(TCEs) inmanytechnological applications.

LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015

3Bologna Section

3

Graphenekeypropertiesfortechnologicalexploitation

[ L.G. de Arco et al. ACS Nano 5 (2010), 2865 ]Bendingangle(2θ)

Cond

uctance(mS)

Bendingangle(2θ)

Cond

uctance(mS)

Flexibility

[Thomas Swan Corp. – Elicarb® graphene ]

(inair)

High-temperatureresistant

ITOstructurechangesover500°C

ChemicalStability

Graphenecansustainhighinplanestrainswithoutdamaging, itcansustaintemperatureabove800Canditsstructureprovidesexcellent chemical stability overawiderangeofharshenvironments.


4Bologna Section

CVDsynthesisandcharacterization

SEM TEM Raman

CVDGrapheneGrowth

GrapheneisgrownusingCVDovereitherfoilsorfilmsofCuat1000Cusingmethane asCprecursor.

Samplesmax.dim.:30x60mm2 (60x100mm2 forfoils)P regimes:APCVD,LPCVDGaslines: Ar,N2,H2,NH3,CH4,C2H2,O2

Polycrystallinegrapheneisgrownonbothsubstratetypes,withtypicaluniformthicknessof1-4layersoverthewholesurface.Grainsizeisover10µm.

APCVDsamplesonCufilmshavesmallergrainsizeandhighernumberofdefects.

LPCVD

APCVD

4LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015

Bologna Section

Grapheneelectrodesfordye-sensitizedsolarcells.IncollaborationwithA.Vomiero group,CNR-INOBrescia(IT)&LuleaTU(SE).


6Bologna Section

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GrapheneDSSCdesign

Lightharvester Dye:usually aRucomplex (calledN719)

Photoanode: TiO2 NPs (transparent:10-15nmNPs);scattering (150-200nmNPs)

Electrolyte:iodine redoxcouple

Counter electrode:Pt (about 5nmthick)onTCOglass

Graphenecanprovidesuperioropticalpropertiesandimprovedchemicalstability

towards electrolyteetching

GrapheneTCEmustprovideadhesionduringtitaniaannealingandduringwetoperation.


7Bologna Section

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• TransparentTiO2 layer(forphotogeneration purposes)

• Depositionofonesinglelayeroftransparent20nm-sizedTiO2nanoparticles (Dyesol)atatime

• TiO2 annealed@500oCfor30mins forsinteringpurposes• Graphenehastomaintainconductivity,transparencyandadhesion

tothesubstrateafterannealing

DSSCbased ongraphene-coated frontcontact

Grapheneonglassoveralargearea(15×25mm2)

graphene

FTOITO

Graphene-glasselectrodeshowssuperioropticalpropertiesandthedyecouldbesuccessfullyloadedontheTiO2-graphenesubstrate.

Dyeband

GrapheneTCE

Graphene+TiO2

Graphene+TiO2+Dye

[G.Singh Selopal, L.O.etal. Sol.En.Mat.Sol.Cell135(2015)99–105]


8Bologna Section

DSSC cellscharacterization

J-VcharacteristicsasafunctionoftheTiO2 filmthickness under

simulatedsunlight(AM1.5G, 100mW cm-2)

OptimalTitania layerthickness isreportedtobe15µm…

rGO TCEinanallsolid-stateDSSC,PCEat0.26%(Wangetal.,Nano Lett.2008)

2%PCEfor4µmPCElinearincreaseisrelatedto

JSC linearincrease.FFandVOC playaminorroleinboostingPCE

Graphene-DSSChigherseriesresistance(420ohm)compared

toFTO(10ohm)limitstheperformancesofthefinaldevice

[G.Singh Selopal, L.O.etal. Sol.En.Mat.Sol.Cell135(2015)99–105]


Bologna Section

GrapheneasTCEinthird-generationPVcellsIncollaborationwithC.Summonte groupinCNRIMM-Bologna


10Bologna Section

Thirdgenerationphotovoltaicswithnanostructuredabsorbers

ThirdGenerationPhotovoltaics goal istoachievehigherefficiencyusingthinfilmtechnologyas inSecondGenerationPV(p-i-n a-Si:H thinfilmsolarcells):

• useofabundant andlowcostmaterial(asa-Si:H)• betteruseofthesolarspectrum

• reductionofallopticallosses

NASCEnT:SILICONNANODOTSFORSOLARCELLTANDEM

FabricationofSinanocrystalsbymeansofhigh-Tthermaltreatment ofSirichSiO2/SiC

Transparent ConductiveElectrodeshouldsustainprocessesupto1100°C


11Bologna Section

AttemptsofintroducingSi-NCswithinaPVdeviceshavebeenreportedintheliterature.

However,allreporteddevicesareusefulformaterialcharacterization,buttheintroducedconstraintsmake

Wu,SEMSC128(2014)435

ConibeerProgPhotov19(2011)813Perez-WulfSEMSC2012

Perez-Wulf,APL95(2009)153506

Janz28thEPVSECParis2013SongSEMSC92(2008)474

LöperAPL102(2013)033507LöperAdv.Mater24(2012)3124

TheproblemoftheTCEhasbeencircumventedbymodifyingthe

design,exposingtheTCEtolow-Tannealing

Atthemomentnoneoftheapproachessucceededin

producingaworking device

11

Issues ontheintroductionofSi-NCswithinaphotovoltaic(PV)device


12Bologna Section

Testprocesstocheckhigh-TresistanceofgrapheneTCE

Graphene

Quartz

1.Graphenetransferonquartz

Graphene

Quartz

a-Si

2.Protectivecappingofgraphene

3.Anneala1100CinN2

1100C

Graphene

Quartz

4.CappingremovalinTMAH

1. PECVDdeposition of40nma-Si:H capping2. AnnealingatdifferentTinflowingN23. Capping removalin2%diluted tetramethyl

ammonium hydroxide(TMAH)

4. Testopticalandelectricalproperties

The capping is needed to prevent graphene burning due toresidual oxygen in the annealing atmosphere during theannealing step for NPs formation

TestingofgrapheneTCEresistancetohigh-temperatureannealing


13Bologna Section

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Annealed600C2hN2

a-Siresiduesreduced transparency

Bestsamplesmaintaintheiropticalpropertiesupto1100C

Residuesfroma-Sicappingaffectfewsamplesopticalperformances.

• AspreadisobservedafterG-sheettransferonfusedsilicasubstratesduetothetransfer

procedure

• Afterdeposition andremovalofthecappinglayerandafterthermaltreatment,thespread

doesnotincrease

CompatibilityofgraphenebasedTCEwithhightemperatureprocesses(1100C)confirmed

Thermaltreatments:opticalandelectricalstability


14Bologna Section

Graphene

FusedSilica

PiN fullprocesseddevicewithgrapheneelectrode

p-aSi:HaSi:H adsorber

n-aSi:HSilvercontact

1000°C,30'annealedgraphenehasbeenintroducedasTCEwithinastandardamorphoussiliconp-i-n device(processtemperature:≤ 250°C)

Measurementundersimulatedsunlight(AM1.5G)shownicedevices.

IncreasedVOC suggestsimproved bandalignment between grapheneandp-type

selectivecontact.

[Fujii 28thEPVSECp.2694]

AmoderatedecreaseofJsc isobservedforGafter1000°C,probablyduetoincompletea-Sicappingremoval.

Highseriesresistanceobserved:bettersheetresistancerequired!

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Improvedbandalignment

HigherSheetResistance

a-Siresidues

IntroductionofannealedGinp-i-ndevices:resultsandcomparisonwithITO


15Bologna Section

IntroductionofGinanactualn-i-pstructureincluding Si-NCs: issues andopenpoints

Graphene

FusedSilica

PiN fullprocessednanostructureddevicewithgrapheneelectrode

n-a-Si:Ha-SiC:H /a-SRC

p-aSi:HSilvercontact

Processsequence:• PECVDdeposition, throughamask oftheprecursorof

theSi-nc material(400nm)• Furnaceannealing influentN2.

– 600°C4h(→hydrogenevolution– neededtoavoidexplosiveevolutionduringcrystallization)

– 900°C30’– 1100°C30’

Graphene

FusedSilica

p-a-Si:HSiNCinSiC matrix

n-aSi:HSilvercontact

1100C30min

200µm

StrainduetoHdesorptionandrecrystallizationanddelaminationofthe

multilayerfilm


16Bologna Section

Conclusions

16

GraphenecanbeappliedinoperatingDSSCsevenafterhightemperaturesintering,withaverygoodPCE(about2%)

CompatibilityofgraphenebasedTCEwithhightemperatureprocesseshasbeenproven

• SuccessfuldyeloadingonG-coatedelectrodewithoutdetachingproblemsuptohighTiO2 thicknesslayer.

• Itwillpossibletofurther increaseTiO2 layerthickenstoimprovetheopticaldensityofthefilm(knownresult:optimumthicknessabout15mm).

• MeasuredPCEisalmost8timeshigherthanpreviousachievementsincomparabledevices.

• GrapheneTCEcansustainprocessesupto1100°Cwithoutsignificantdegradation intermsofsheetresistanceandtransmittance(contrarytoITO,whichdeterioratesabove900°C).

Graphenesheet-resistanceinTCEmustbeimproved

• Dopingofgraphene,Transferofmultiplegraphenemembranes,atthecostofworseningT%,improvementofthesynthesis,withlargerdomains,reduceddefectsandimpurities.


Bologna Section

ThankyouallforyourattentionLucaOrtolani – CNRIMM-BolognaSection–


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Transparent conducting graphene electrodes for ... · Compatibility of graphene based TCE with high temperature processes has been proven • Successful dye loading on G -coated electrode