用于染料敏化太陽能電池的D5同類物分子設計

1、1408用于染料敏化太陽能電池的D5同類物分子設計詹衛(wèi)伸潘石*李源作陳茂篤116023)(大連理工大學物理與光電工程學院,近場光學與納米技術(shù)研究所,遼寧大連摘要：使用密度泛函理論(DFT)和含時密度泛函理論(TDDFT)以及自然鍵軌道(NBO)分析,設計比有機染料D5(OH,NH2,OCH3),既可以使分子的最低未占據(jù)分子軌道(LUMO)能級提高,又可以使吸收光譜紅移,從而分子的骨架上,對稱地引入受電子基(CF3,F,CN),可以使染料分子的吸收光譜強烈地紅移,從而更有效地利用太陽能.由LUMO能級的提高和吸收光譜的紅移來考慮,所設計的D516,D536,D537分子是比D5優(yōu)秀的同類物分子,

2、其中D516是最好的.單從吸收光譜紅移來考慮,所設計的D565,D567,D568分子是比D5優(yōu)秀的DA(電子給體共軛橋電子受體)結(jié)構(gòu).這幾種分子的光激發(fā)引起的最高占據(jù)分子軌道(HOMOs)到LUMOs成為比D5更優(yōu)秀的用于DSSC的非金屬有機染料分子.關(guān)鍵詞：密度泛函理論;中圖分類號：O641染料敏化太陽能電池;染料D5;分子設計MolecularDesignofD5AnaloguesforDye鄄SensitizedSolarCells(InstituteofNearFieldOpticsandNanotechnology,SchoolofPhysicsandOptoelectronicT

3、echnology,DalianUniversityofTechnology,Dalian116023,LiaoningProvince,P.R.China)Abstract：Usingdensityfunctionaltheory,timedependentdensityfunctionaltheoryandnaturalbondorbitalanalysis,wedesignedD5analoguemolecules,whicharesuperiortotheorganicdyeD5foruseindyesensitizedsolarcells.Thesymmetricintroducti

4、onoftheelectrondonatingsubstituents(OH,NH2,OCH3)totheelectrondonatinggroupsoftheD5skeletonraisestheenergylevelofthelowestunoccupiedmolecularorbital(LUMO)andcausesaredshiftintheabsorptionspectra.Thesechangesenhancetheabilityofthedyemoleculestocapturephotonsfromsolarradiationaswellimprovingthedrivingf

5、orceforelectroninjectionfromthedyemoleculesexcitedstatetotheTiO2electrode.Thesymmetricintroductionofelectronacceptors(CF3,F,CN)totheskeletonofD5moleculesredshiftstheabsorptionspectraofthedyemoleculesgreatly,allowingformoreefficientuseofsolarenergy.ConsideringtheincreaseintheLUMOenergylevelandthereds

6、hiftintheabsorptionspectra,thedesignedmoleculesD516,D536andD537aresuperioranaloguemoleculesofD5,ofwhichD516isthebest.Byonlyconsideringtheabsorptionspectraredshift,thedesignedmoleculesD565,D567andD568aresuperioranaloguemoleculesofD5.Amongthese,theabsorptionspectrumofD565isexpectedtobettermatchthesola

7、rradiationspectrum.ThesixselectedD5analoguesallhaveDA(donorconjugatebridgeacceptor)structures.Forthesemolecules,thetransitionsfromthehighestoccupiedmolecularorbitaltotheLUMOarisingfromopticalexcitationareall-*intramolecularchargetransfertransitions.Theirelectronicabsorptionspectralieinthenearultravi

8、oletvisiblelightzone.ComparedwithD5,D516andD565aremoreapplicableforuseinDSSCasmetalfreeorganicdyemolecules.KeyWords：Densityfunctionaltheory;ZHANWeiShenPANShi*LIYuanZuoCHENMaoDuDyesensitizedsolarcell;DyeD5;MoleculardesignReceived:November24,2009;Revised:February2,2010;PublishedonWeb:March30,2010.Corr

9、espondingauthor.Email:span;Tel:+8641184707863EditorialofficeofActaPhysicoChimicaSinicaNo.5ZHANWeiShenetal.：MolecularDesignofD5AnaloguesforDyeSensitizedSolarCells1409SinceGrätzeletal.1reportedthedyesensitizedsolarcells(DSSC)basedonRucomplexin1991,moreattentionhasbeenpaidtoDSSCduetoitscomparative

10、lylowcostandhighefficiency1-3.However,DSSCsensitizedbyfreemetalorganicdyehasattractedmoreinterestsfromresearchersbecauseofitsmuchlowercost4-11.Inparticular,thestructuraldiversityandthesimplesyntheticrouteoforganicdyemoleculesprovideconditionsforseekingmorecompetitiveDSSCsensitizer.Thus,themoleculard

11、esignoforganicdyescomesintodevelopmenttoimprovethefunctionofDSSC12-20.ThedyemoleculesappliedtoDSSCshouldhaveastructure5,19,21-25of“donorconjugatebridgeacceptor(DA)”,inwhichthe“electronacceptor”mustcontainthe“anchoringgroup”.Bythe“anchoringgroup”,dyemoleculescanabsorbontothesurfaceofTiO2nanocrystalli

12、ne6,13,15,20,25-26.Atpresent,the“anchoringgroup”isusuallychosenascarboxyl(COOH).MostDAdyestakedialkylaminesordiphenylaminemoietiesaselectrondonor,carboxylicacid,cyanoacrylicacidorrhodanine3aceticacidmoietiesaselectronacceptorwhichalsoactsasananchoringgroup.CarboxygroupscanhangonthesurfaceofTiO2,prov

13、idingastrongrestrictiontodyesandgoodelectronchannel.PhotoabsorptioncharacteristicofDAdyesisconnectedwithintramolecularchargetransfer(ICT)excitationfromelectrondonortoelectronacceptormoiety,whichresultsinefficientelectrontransferfromdyesexcitationstateviaelectronacceptormoiety(carboxygroups)toTiO2con

14、ductionbandedge(CB).ChargetransferorseparationbetweenelectrondonorsandacceptorsintheexcitationstatecanfacilitatetheelectroninjectionfromdyestoTiO2CB,thusitcanseparatethecationicchargefromsurfaceandeffectivelypreventthephotoelectron(theinjectedelectron)fromcompoundingwithoxidizeddyes12,25.Thelowestun

15、occupiedmolecularorbital(LUMO)energylevelpositionsofdyemoleculesandtheirabsorptionspectraarethemostkeyfactorsfortheapplicationofdyestoDSSC27.LUMOenergylevelofdyemustbehigherthanTiO2conductionbandedge,andthehigheritis,thelargerthedrivingforceforelectroninjectionfromdyesexcitationstatetoTiO2willbe,whi

16、chismorebeneficialtotheimprovementofDSSC10,17-18,22,26,28-31.Nowadays,thegoodmatchbetweenUVVisabsorptionspectraofsyntheticalsensitizedDSSCdyesandthatofthesolarradiationspectrahasnotbeenachieved,whichisoneoftheurgenttasks.Itisreportedthat,thelengtheningofconjugatedbridgeofdyemolecularstructurecouldle

17、adtoredshiftinmolecularabsorptionspectra16,20,32.Butthelengthshouldbeproper,asoverlongconjugatedbridgewillcausetheaccumulationofdyemoleculesonthesurfaceofTiO2,affectingthepropertiesofDSSC4,8,25.Generally,theabilitiesofelectrondonorgroup(D)donatingelectrons,electronacceptorgroup(A)acceptingelectronsa

18、ndtheelectricpropertiesofconjugatebridgehavegreatinfluenceonthephotophysical,electrochemicalandintramolecularchargetransferpropertiesofDAdyes.TheneedofhighefficiencyDSSCcanbemetbythechangeofchemicalstructureofeveryelement(D,A,orconjugatebridge).Absorptionspectraofdyemoleculesshouldmatchsolarradiatio

19、nspectra,andtheirLUMOandHOMOenergylevelsmustmatchtheconductionbandedgeenergylevelofTiO2electrodeandtheredoxpotentialofI-/I3-electrolyte.Forstudyonthepropertiesofmoleculeinphotophysicsandphotochemistry,themolecularnonadiabaticprocesshasattractedmuchattentioninrecentyears.Hanetal.33-35hasinvestigatedt

20、henonadiabaticphenomenonofsmallmoleculesindetail.Forlargermoecules,however,nowadayswecannotcarryoutaccurateresearchonnonadiabaticprocessandwedonotdiscussthisissueparticularlyinthispaper.Recently,anorganicdyecalledD5(Fig.1)attractsmoreattentionbecauseitcansensitizeDSSCtoenhanceitssolarenergyconversio

21、nefficiencyby5%,andareexpectedtobeappliedinsolidDSSC7,15,23,26,36-40.ButthewavelengthofD5atmaximumabsorbanceis476nm,andthemaximumwavelengthofD5absorbedonthesurfaceofTiO2blueshiftsto444nm41,whichseFig.1MolecularstructuresofdyeD5anditsanalogues(D5xy)xandyinD5xydenotedifferentsubstituentsandpositionsba

22、sedonD5.Forexample,D536,x=3,y=6,usingOCH3toreplaceHinthepositionsofR1andR6.1410ActaPhys.鄄Chim.Sin.,2010riouslydyetomolecules.findD5affectsaisbetternotconsideredtheabilityofdyetoabsorbsolarenergy.Organicphotosencitizerastheusedbestphotosencitizer.forDSSCbymodifyingItispossibleD5(DFT)Beforetryingtimea

23、nydependentsynthesis,DFTthe(TDDFT)densityfunctionaltheory42-43and44-47wereadoptedtoteringprovideasoundtheoreticalfoundationfortheandabsorptionofanaloguesspectraaccordingtotheirmoleculardesignenergyandlevelsfil9,14,16,29-30,36,48-51thelation.designofmoreefficientdyemolecules.BasedonwasD5,anattemptons

24、implerDuringmoleculesdyethedesign,theprincipleofdesigningmadeviaacalcumuchismoleculetointroducewassubstitutentinsistedon.groupThemethodtoD5skeleton.ofmodifying1ComputationalmethodsGaussianDFTandof03softwareTDDFTpackagecalculationswereperformedusingthe52.TheanyD5symmetryanditsanaloguesconstraintswere

25、atthefullyB3LYPoptimizedgroundlevelinstateofvacuumgeometriestheorywithwithoutthe6figurations31G(d)basissorptiontoeachset.TheelectroniccontributiontransitionofsinglyandtheexcitedstatecontronictationsabsorptionspectraoftheD5analogueswerecalculated.simulatedTheelecaboutusingandTDDFToscillatorspectrawit

26、hstrengths.requirethesameThesecalculationbasiscalculationsoftheallowedsetandexchangewerecarriedexcicorrelationculationfunctionaloncontaininginthevacuumsolvationandeffectsolution.inethanolTheTDwasB3LYPcalB3LYPthegeometriesexperimentfunctionaloptimizedcalculationsinvacuum.qualitativelyDFTperformedcoin

27、cideandTDDFTwithmodelcomputation(CPCM)resultsTheconductorpolarizablecontinuumwiththe30,40-41,53-55.24,56methodsissuggestedconductedbyusingKlamtparametersanditerative57-58tocontainthesolvationmedloguesineffect.ordertoNaturalanalyzebondtheorbitalcharge(NBO)populationsanalysisofthewasD5perforana40,59.2

28、ResultsanddiscussionandForproperties.LUMOthedyeofsensitizedDSSC,theenergylevelsofHOMOdyeToandobtainitsabsorptionefficientelectronspectraareinjectionthemostfromimportantexcitedergytobandleveltheconductionofbandoftheTiO2electrode,theLUMOencanprocessesinjectenergyelectronsleveldyemoleculeoftotheTiOTiOm

29、ustNotbeeveryhigherexcitedthanthedyeconduction2.molecule2electrode,becauseofmanyotheraButstrongthewithimpactcausinghigherenergyonthethedeexcitationofdyemolecule,whichhaslevelelectronoftheinjectionLUMO,tothetheTiO2electrode.becomeelectronofDSSC.stronger,injectionfromdyemoleculetoTiOdrivingforcefor2el

30、ectrodewillInorderwhichtomakeresultstheoxidizedinthehigher(loseelectrons)transferefficiencydyemoleculeefficientlyrecover(gainelectrons)fromI-/I-3redoxcoupleintheelectrolyte,theHOMOenergylevelofdyemoleculehastoharvestingbelowerefficiency,thantheredoxdyepotentialmoleculeofmustI-/I-3have.Togaingreaterh

31、ighermolarlightabsorptionationcoefficientinthewideareaofsolarabsorptionspectraednow,inthisregion,spectraattheareaof500-600nmisthespectra.strongest.SolarIfraditheitofwillsensitizedbeaperfectDSSCsensibilizer.dyemoleculeHowever,areincludDSSC,theresolarwhoseisnotabsorptionanykindspectraoforganicdyemolec

32、ulesuitedupfortomoleculeradiationparedonTiOspectra.Especially,canthematchabsorptionperfectlyspectrawithofdyethe2electrodesorptionwiththatinthevacuumexhibitsandpolarsignificantsolvent.blueSofar,shift,thecomzoneredofnearspectraultravioletofdyeregionmoleculeandarevisiblemainlyintheshortwaveabjudgeshift

33、theofqualityabsorptionofsensitizedspectraDSSCisstilldyetheregion.molecule.primaryTherefore,ThestandardtheD5typetodyeandmoleculeforDSSCwillbedesignedaccordingtotheHOMOwavelengthLUMOenergylevelscalculatedbyDFTandtheisaTheoftheabsorptionspectracalculatedbyTDDFT.maximumbetterresultsfreeofmetalexperiment

34、organicanddyecalculationforDSSCdemonstrate.BecausethatD523,26,36,38,40-41,60anicvarietydyeoforganicsuperiormolecularstructure,itispossibletodetoergyD5BasedonourprevioustoD5investigationforDSSCbymodifyingD527,themodificationthanlevel,shouldI,onmakesothattheconditionthenewthedrivi

35、ngthatD5forceitsmoleculeHOMOmaximizeforelectronenergyLUMOeninjectionlevelisoflower-/I-3thedyemoleculefromtheexcitationstatetoTiOBesides,greater,whichcanraiseconversion2electrodecouldbecomeasdiationmuchdyeaspossible,molecularinorderabsorptiontomakespectratheabsorptionshouldefficiencybeofredofsolarDSS

36、C.shiftedratureTheandextensionphotonsmoretheintroductionofconjugateefficient.ofthebridgeelectronindyedonatingmolecularsubstituentstrucandboneelectronwithdrawingsubstituentmoleculescouldwhichandmovealsotheHOMOandLUMOtotheenergychromophorelevelsofbackdyechemicalprovideapossibilitycausetheforredtheshif

37、tadjustmentsinabsorptionofthespectrum,photonoticedthatandtheelectrochemicalexpansionofconjugatedpropertiesofbridgedyes.inItDshouldAdyebemoleculesonmoleculesTiOcaneasilyleadtotheaccumulationofdyemolecules2surface,reducingenergytotheTiOelectroninjectionyieldsfromthedye2conductionbandbecauseofintermole

38、cularanaloguetransferconjugatedyebridge.molecules,betweenmolecules.Inaddition,wedidthenotIngeometryextendthemodificationofthethelengthofdyemoleculeofD5theshouldontonotbetoolarge;otherwise,thedyeciencyTiOmoleculesadsorbedAsshownof2DSSCsurfaceperunitareaaswellastheconversioneffiinperFig.1,unitareataki

39、ngwillbeHreduced.fromtheskeletonofD5moleculeindifferentpositions,wemodifiedtheD5moleculeswiththeelectrondonatingsubstituent(OH,NHandtheelectronwithdrawingsubstituent(CF2,OCHCN),re3)3,F,spectively.Xiaetal.30haveusedthismethodtomodifythecouZHANWeiShenetal.：MolecularDesignofD5AnaloguesforDyeSensitizedS

40、olarCells1411marinmolecule.Tofacilitatediscussion,wenumberedthemodifiedmolecules,organicmolecules(Fig.1).WehavedesignedfailedByinDFT/TDDFTthe6DFTofwhichoptimization.(D521,D526,D529,D531,D544,54kindsD545)ofcalculation(seeSections2.3and2.4),itisshownabsorptionthatlevelspectrumD516,D536relativeandtoD53

41、7,D5,butnotalsoonlymakeinduceLUMOredshiftenergyintypesbecientlyofgreatertheTiOandorganicthanenlargemoleculesthatofthedrivingmakeD5.TheDSSCsensitizedbytheseforceuseofforsolarelectronenergyinjectionmoreeffiinto2electrode.Moreover,itsHOMOenergylevelislowerthanthepositionoftheredoxI-/I3-.Therefore,theco

42、nversionefficiencyasoftheDSSCadoptingthesethatsensitizersshouldbegreaterthanthattypesofD5.oforganicItshouldmoleculesbenotedacteristics:thesetypessubstituent,firstly,oforganicthesubstituentsmoleculesareshareallsomecommoncharsubstituentssymmetricallyarelocatedinthebeingelectronreplacedthedonatinginpai

43、r;electrongroupsecondly,donatingorinthetheconjugateenergybridgeneartheelectrondonatinggroup.TheLUMOforgreatest.electronlevelpositioninjectionoffromD516excitedisthehighest,stateintosothethedrivingTiOforce2istheshowDFT/TDDFTthattheLUMOcalculationenergyresults(seelevelsofD565,SectionsD5672.3andandD5682

44、.4)arelowerTiOthanofthedrivingthatofD5force(muchforelectronhigherthaninjectionconductionfrombandexcitededgestateof2),leadsthesetheirD5,makingabsorptiontomoleculesthelowerintotheTiO2islowerthanthatofD5,whichfullspectraelectronuseofaretransfersolarredenergy.shiftedrateAndintenselycomparedtheirHOMOcomp

45、aredwithD5,butenergywithlevelssionefficiencyarelowerofthan-thethatDSSCofredoxadoptingI-/I3these.Therefore,typesofthemoleculesconverasmoleculessensitizersishigherthanthatofD5.Thesetypesoforganicstituentsstituentsarealsoallsharetheelectronsomecommonwithdrawingcharacteristics:substituent;thesubelectron

46、introductionacceptingmaybelocatedintheelectrondonatinggroup,thesubtheofthegroupelectronorwithdrawingtheconjugatesubstituentbridge.Therefore,intoD5dyethemoleculesofmaycausestrongredshiftintheabsorptionspectraindicateDFT/TDDFTorganicmolecules.levels.electronTheconjugatebridgeofnonplaneistrontransition

47、fromtheelectrondonatingnotconductivegrouptototheICTelecofstructuresacceptingofD5group11,14-16andsome.Fig.2ofshowsitsanalogues.theoptimizedThemolecularconjugatebridgeswhichofalltheD5analoguesexceptforD537areallplane,ByanalysisisjusttheofsameNBO,asweD5.findthatthechargepopulationsofOptimizedgeometrica

48、lstructuresofdyeD5anditsanaloguesdonorgroup,conjugatedbridge,andacceptorgroupofD5are0.061-0.184Amoleculare,0.114e,structure.and-0.174Fore,D536,respectively,theyarewhich0.057ise,a0.126typicalDD565,e0.184and-0.105e,they;for-0.094areD537,e.Alle,0.097theyare0.057e,0.130e,and-0.184ee,;andforandof-0.092e,

49、0.184thesemoleculese;efor,andD568,-0.281havetheye;forD567,theyaresimilarare0.130De,-0.021Astruce,tures.0.043ThechargepopulationsofthreegroupsofD516are0.154e,electrone,and-0.197e,respectively.Thepositivechargesoftheacceptingdonatingchargesfore,thisofgroupofgroupD516andaremuchthenegativemorethancharge

50、sthatofofD5,electronbuttheanalogueconjugateshouldbridgehaveareDlowerAthanmolecularthatofstructureD5.TheresuperiorandTabletoloweritsanalogues,1D5.listspartfromofthewhichbondlengthswecanoffindchemicaltheirdifferencebondsofD5individualsthan1pmingeneral,andthegreatestdifferenceamongismolecularstabilitie

51、sislowerthanofD53pm.andTherefore,itsanaloguesitisarebelievedonthethatwholethethesame.itsTheofD5analogueselectronicareorbitals,D516structuresandofHOMOsandLUMOsofD5andwhileD565LUMOsareshownaresingleinFig.3.statesTheofHOMOs*orbiTable1Selectedbondlength(R,inpm)ofthedyeD5anditsanaloguesaFig.3Isodensitypl

52、ots(isodensitycontour=0.02a.u.)ofthefrontierorbitalsofdyeD5anditsanaloguestals.HOMOshavegroundstatecharacteristics,whileLUMOshaveexcitedstatecharacteristics.Inthegroundstate,theelectronsaremainlydistributedintheelectrondonor(diphenylanilinegroup)andconjugatedbridge(vinyleneandthiophenegroup).Intheex

53、citedstate,theelectronsaredistributedinthethiophenesandcyanoacrylicacidgroups,butmostlyintheanchoringgroup(carboxyl:COOH).ForD5analogues,HOMOs(HOMOandHOMO-1)areorbitalwhichislocatedintheelectrondonorgroups,electronacceptorgroupsandtheconjugatebridge,orthewholemolecule.AndtheLUMOs(LUMOandLUMO+1)are*o

54、rbitalwhichislocatedintheconjugatebridgeandtheelectronacceptor(anchor)group.TheelectronicorbitalsofD5analoguesarethesameasthatofD5duetotheirsimilarmolecularstructures.Underillumination,throughintramolecularchargetransfer,electronsmovefromHOMOstoLUMOs,andeventuallyreachtheanchoringgroups.Inthissystem

55、,thelightinducedelectronicdistributionchangeisconsideredasoneofthedecisivefactorsresultinginefficientchargeseparation.Thusitcanbeconcluded:theelectrontransportfromelectrondonortoelectronacceptor(anchor)occurredduringthecourseofexcitationofdyemolecules.Asdyemoleculesareadsorbedonthesemiconductorsurfa

56、ceviathecarboxylgroup,theexcitationpromotestheelectroninjectionprocess.TheelectronicstructuresofD5anditsanaloguesareverybeneficialtosolarcells.2.3EnergyleveldiagramThediagramforcalculatedfrontiermolecularorbitalenergylevelsoftheD5,D516,andD565invacuumandethanolisdepictedinFig.4.TheLUMOenergylevelpos

57、itionsofD536,D537,D565,andD567invacuumare-2.585,-2.558,-3.374,and-3.374eV(inethanol:-2.667,-2.667,-3.347,and-3.320eV),respectively.TheHOMOenergylevelpositionsofD536,D537,D565,andD567invacuumare-4.980,-5.061,-5.361,andH-1:HOMO-1,H-2:HOMO-2,L+1:LUMO+1,L+2:LUMO+2ZHANWeiShenetal.：MolecularDesignofD5Anal

58、oguesforDyeSensitizedSolarCells1413-5.551respectively.eV(inenergyWhetherethanol:in-4.898,vacuum-4.980,orinthe-5.061,and-5.306eV),-/I-3(ca-4.8eV),therefore,D5moleculethatloseselectronscouldberestoredbyallLUMOinjectionhigherthanenergythoselevelgettingpositionselectronsofD516,fromelectrolyte.D536,andD537areD537frommolecularofD5,excitationthus,thestatedrivingofforcesD516,forD536electronandgythatleveltoTiOofD5,positions2electrodebuthighero