-
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.
LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015
-
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).
5LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015
-
6Bologna Section
6
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.
LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015
-
7Bologna Section
7
• 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]
LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015
-
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]
8LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015
-
Bologna Section
GrapheneasTCEinthird-generationPVcellsIncollaborationwithC.Summonte groupinCNRIMM-Bologna
9LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015
-
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
10LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015
-
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
LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015
-
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
12LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015
-
13Bologna Section
13
Annealed600C2hN2
a-Siresiduesreduced transparency
Bestsamplesmaintaintheiropticalpropertiesupto1100C
Residuesfroma-Sicappingaffectfewsamplesopticalperformances.
• AspreadisobservedafterG-sheettransferonfusedsilicasubstratesduetothetransfer
procedure
• Afterdeposition andremovalofthecappinglayerandafterthermaltreatment,thespread
doesnotincrease
CompatibilityofgraphenebasedTCEwithhightemperatureprocesses(1100C)confirmed
Thermaltreatments:opticalandelectricalstability
LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015
-
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!
14
Improvedbandalignment
HigherSheetResistance
a-Siresidues
IntroductionofannealedGinp-i-ndevices:resultsandcomparisonwithITO
LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015
-
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
15LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015
-
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.
LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015
-
Bologna Section
ThankyouallforyourattentionLucaOrtolani – CNRIMM-BolognaSection–
17LucaORTOLANI- Nanoitaly2015- 21-23Sept.2015