Ecomaterials in Solar Cell Design 2018 Verónica González.pdf

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EcomaterialsinSolarCellDesign
VerónicaGonzálezandIsraelLópez
Contents
CurrentProblemswithSolarCells...............................................................1
ClassifyingEcomaterialsinSolarCells..........................................................2
MaterialswithGreenerEnvironmentalProfiles..............................................2
MaterialswithLessHazardousSubstances..................................................5
MaterialsofHigherRecyclability............................................................11
MaterialsofHigherResourceProductivity...................................................15
ConclusionsandFurtherOutlook................................................................21
References........................................................................................23
CurrentProblemswithSolarCells
Inthelastyears,thegreenscienceshavefocusedtheirattentioninsearchofnew
energysources,whichcansupplythehigh-energydemandinafriendlyenviron-
,theuseofoilenergyrepresentsthe33%oftheglobal
energyconsumption,followedbycoalandgas,beingsolarenergytheleastused

usein2014[1].
Solarenergyhasgainedspecialattentionforbeingthemostabundantavailable
,
beingthesiliconsolarcellsthemostpopularbyitshigh-powerconversionefficiency
(PCE)reachingupto20%[2].Despiteitshighperformance,siliconsolarcellsare
restrictedforamassiveuseduetoitshighfabricationcosts,whichhasled
researcherstosearchanddevelopnewmaterialsthatcaneffectivelyreplacesilicon.
However,someofthesematerials,farfrombeinghelpful,arehighlycontaminating
ález•ópez(*)
UniversidadAutónomadeNuevoLeón,UANL,FacultaddeCienciasQuímicas,Laboratoriode
MaterialesI,,,SanNicolásdelosGarza,NuevoLeón,Mexico
e-mail:adela.******@;israel.******@
#SpringerInternationalPublishingAG20181
ínezetal.(eds.),HandbookofEcomaterials,
/978-3-319-48281-1_23-2:.
áópez

energyconsumptionin2014
(Datacollectedfrom[1])
,itisneces-
sarytodevelopedhuman-friendlyandenvironment-consciousmaterials,without
-
materialscouldhelptoestablishagreentechnologicalsociety.
Theuseofenvironmentallyfriendlymaterialsasanalternativetoreplacepollut-
,ithas
notbeenpossibletomatchthehighefficienciesofcommercialsolarcellswiththe
useofecomaterials;however,someofthefourmainparametersofsolarcellshave

cellareshort-circuitcurrent(Jsc),open-circuitvoltage(VOC),efficiency(η),andfill
factor(FF).
ClassifyingEcomaterialsinSolarCells
MaterialswithGreenerEnvironmentalProfiles
Materialsfromwasteandrenewableresourcesandwasteareprocessedinamore
,fruits,andvegetablesas
photosensitizers.
Dye-SensitizedSolarCells(DSSCs)
Innature,awidevarietyofcolorscanbefound,fromviolettored,completely
,flowers,
andleavesofplants,withtheaimofbeingusedaspossiblephotosensitizers.
Comparedtoorganicsemiconductors,adyehasnoabilitytotransportexcitons;
thatiswhy,theDSSCsnormallyincludeanadditionalorganicmaterial:ahole
:.
EcomaterialsinSolarCellDesign3

theDSSCwithacompact
TiO2layer(Reproducedfrom
[4].Copyright(2009)
Elsevier)
Lightabsorptionisthefirststepofthemechanismofenergyconversioninasolar
,alltheefficientsolarcellsabsorbinthevisiblewavelength
range,becauseinthisarea,thenumberofphotonsandtheirenergyismaximum.
Ahighbandgapsemiconductor,suchasTiO2,whichonlyabsorbsintheultraviolet
region,canbedyedtoabsorbinthevisibleregion[3].
Aswasmentionedbefore,aDSSCiscomposedofasemiconductoroxide,
achargetransferdye,
processinitiateswhendyesabsorbphotons,andthenexcitonisformedatthe
,anelectrontravelsthroughthe
semiconductoroxide,
correspondstothedifferencebetweenFermilevelandredoxpotentialoftheelectron
inthesemiconductorandtheelectrolyte,,thedyecanbe
regeneratedbyacceptinganelectronfromtheelectrolyte;inthisprocess,the
reductionagentisregeneratedbyreductionofoxideagentatthecounterelectrode;
then,thecircuitiscompletebymigrationofanelectronthroughanexternalload
[4].Figure2showsthephotovoltaicprocessinaDSSC.
Anthocyanindyes,themostprimitivepigment,areresponsibleformostofthe
cyaniccolorsoscillatingbetweenred,violet,anddarkblueofmostfruits,flowers,
-
ductors,thankstocarbonylandhydroxylgroupspresentintheanthocyanin

moleculetotheconductionbandoftheinorganicsemiconductor,whichiswhythey:.
áópez
-voltage(J-V)curvesoffabricatedDSSCsbasedonthenaturaldyes
extractedfrom(a)fruitsofivygourdand(b)flowersofredfrangipaniasthesensitizerunderthe
illuminationof100mW/-VcurveofstandardN3dyeshownasinsetforcomparison
(Reproducedfrom[6].Copyright(2013)Elsevier)
-
poundsisduetoalcoholicboundprotonswhichcondensewithhydroxylgroups
presentatTiO2surfaceandexhibitawidebandinUV-visibleregionduetocharge
transfertransitions[5].
Anotherexampleofpigmentsutilizedassensitizersisβ-carotene,whichisthe

photosensitizedperformanceofthispigmenthasbeencomparedwithanthocyanin,
,
β-caroteneandanthocyaninwereextractedfromfruitsofivygourdandflowersof
redfrangipani,
frangipaniexhibitshigherphotosensitizedperformancecomparedtothefruitsof
ivygourdandthisisduetoabetterchargetransferbetweenthedyesofflowersofred
-
voltage(J-V)curvesofthetwoDSSCs,anditcanbeobservedthatthecellfabricated
withflowersofredfrangipanishowsanotablehighperformanceofshort-circuit
current;generationofthisvaluemainlydependsonthequantityofdyeabsorbedon
thesemiconductorsurface,lightharvestingefficiency,andelectroninjectionability.
Anthocyanincontainsalcoholicgroups,whichmayhelpformaximumbindingon
thesurfaceofsemiconductoroxide[6].:.
EcomaterialsinSolarCellDesign5
Table1Photoelectrochemicalpropertiesoffruitjuiceandnaturalextractsolarcells(Reproduced
from[7].Copyright(2008)Elsevier)
JscVocPmaxFFCathode(catalyst
Dye(mA/cm2)(V)(mW/cm2)(%)type)

“Moro”










Alotofcolorantsfromfruits,vegetables,flowers,andplantshavebeenstudiedto


natural,itisnotpossibletomakeadirectcomparisononwhichisthemostefficient

sensitizersareobtainedbysolventextraction(skinofjaboticaba);someothersare
extractedanddopedwithorganicacidstostabilizecolorants(redcabbage);chemical
manipulationisusedtoobtainedmodifieddyes,suchaschlorophyll,andthemost
eco-friendlyarepreparedonlybysqueezing,as,forexample,redSicilianorange[7].
AnotherimportantparametertoconsiderinthesynthesisofaDSSC,asiswell
known,

cross-sectionalSEMimageofaDSSCandtheenergyleveldiagramofitscompo-
nentmaterials[8].Inthisstudy,SnO2andP3HTwereutilizedashighmobility
alternativetoconventionalDSSC.
MaterialswithLessHazardousSubstances
OrganicSolarCells(OSC)
Organicsolarcellsuseorganicsemiconductorsduetotheirhighabsorptioncoeffi-
cientsanditsabilitytotransportthelightexcitationenergyintheformofexciton
(electron-holepair).Organicmaterialsarestilllagged,comparedtoinorganicmate-
rials,duetotheirreducedlifetime;however,theyarepresentedasanalternativefor
low-costsolarcells.
Inanorganicsolarcell,photovoltaicenergyconversionprocessstartswiththe
formationofanexcitonattheinterfaceofholetransportinglayer(HTL)andelectron:.
áópez
(a)ChemicalstructureofID504dyeandP3HTandapproximateenergyleveldiagramfor
thematerialsusedinthisstudy,alongwithindicationofthecriticalstepsinphotovoltaicconver-
sion.(b)Cross-sectionalSEMimageoftheoptimizedSnO2-dye-P3HTSDSC(Reproducedfrom
[8].Copyright(2013)RoyalSocietyofChemistry)
transportinglayer(ETL).Both,electronsandholes,travelthroughETLandHTL,
respectively,untilreachingtheelectrodesandgeneratecharge.
Powerconversionefficiencyofsolarcellsisdeterminedbybothabsorptiondepth

withsemiconductormaterialsthatexhibitlargediffusionlengthandsmallabsorption
depth;therefore,amorphousandcrystallinesiliconarepreferredtosynthesizethis

lengthsmallerthantheabsorptiondepth,thiswillexhibitlowconversionefficiency
:.
EcomaterialsinSolarCellDesign7

energymaterialsasafunction
oftheabsorptiondepthand
diffusionlength(Reproduced
from[9].Copyright(2017)
Elsevier)
low-chargecarriermobilityanddiffusionlength;therefore,toachieveefficient
chargeextraction,thethicknessoftheactiveregionmustbeclosetothediffusion
,typicalvaluesofabsorptiondepthanddiffusionlengthfordifferent
materialsutilizedinsolarcellsaresummarized[9].
Dependingontheirconfiguration,OSCcanbeclassifiedasconventionaland
,conductorglass(normallyFTOorITOglass)is
coatedwithathinfilmofPEDOT:PSS,andthentheactivelayerisplacedonitstop
tofinallyclosethecircuitwithametallicnegativeelectrode;underthisconfigura-
tion,holestravelthroughPEDOT:PSS,whileelectronstraveltowardthemetal
electrode.
Ontheopposite,inaninvertedsolarcell,conductorglassiscoatedwithathin
filmofasemiconductoroxide,
PEDOT:PSSisplacedattheinterfaceoftheactivelayerandametallicpositive
electrode;thus,electronstravelthroughthesemiconductoroxide,whileholestravel
towardPEDOT:
[10].
Normally,organicsolarcellsarecomposedoftwotypesofsemiconductors:
-work-
functionelectrode(tocollectelectrons)andahigh-work-functionelectrode
(tocollectholes).Duringtheexcitation,anelectronispromotedfromthehighest
occupiedmolecularorbital(HOMO)tothelowestunoccupiedmolecularorbital
(LUMO),andthen,freechargecarriersareproducedwhenanexcit