电化学阻抗谱简介 (EIS)

电化学阻抗谱简介(EIS)－TypicalapplicationexamplesinDSCandCISsolarcells503，StateKeyLaboratoryofCatalysis马贵军2007年11月20日Seminar2内容概要•关于EIS方法–什么是EIS方法?–EIS测量有哪些特点?–哪些体系适合进行EIS测定?–如何测量得到EIS?–EIS测量结果的有哪些表达形式?•IS在DSC和CIS电池中的应用举例什么是EIS?•EIS：ElectrochemicalImpedanceSpectroscopy•别名：交流阻抗(ACimpedance)•定义：是一种以小振幅的正弦波电位(或电流)为扰动信号的电化学测量方法。电极系统角频率为正弦波信号X电流或者电位电位或者电流角频率为正弦波信号Y在一系列下测得的一组这种频响函数值就是电极系统的EIS，即G()～曹楚南、张鉴清著，《电化学阻抗谱导论》，2002年Y=G()XG()为阻抗或者导纳EIS测量有哪些特点?•以小幅值的正弦波对称的围绕稳定电位极化，不会引起严重的瞬间浓度变化及表面变化。•由于通过交变电流是在同一电极上交替地出现阳极过程和阴极过程，即使测量信号长时间作用于电解池，也不会导致极化现象的积累性发展。（准稳态方法）•速度较快的子过程的阻抗谱出现在比较高的频率域，而速度较慢的子过程的阻抗谱则出现在比较低的频率域，可据此判断子过程的数目及其动力学特征。曹楚南、张鉴清著，《电化学阻抗谱导论》，2002年哪些体系适合进行EIS测定?•因果性条件–当用一个正弦波的电位信号对电极系统进行扰动，要求电极系统只对该电位信号进行响应。•线性条件–只有当一个状态变量的变化足够小，才能将电极过程速度的变化与该状态变量的关系近似作线性处理。•稳定性条件–电极系统在受到扰动后时，其内部结构所发生的变化不大，可以在受到小幅度扰动之后又回到原先的状态。曹楚南、张鉴清著，《电化学阻抗谱导论》，2002年如何测量得到EIS?•装置简图•相应的操作软件Potentiostat(EG&G,M273)Lock-inamplifier(EG&G,M5210).EIS测量结果的表达形式•Y=G()XG()为阻抗或者导纳，总称阻纳。它是一个随频率变化的矢量，用变量为f或其角频率为的复变函数表示，可记为：G()＝G’()＋jG’’()若G为阻抗，则有Z()＝Z’()＋jZ’’()相位角＝arctg(-Z’’/Z’)-Z’’~Z’为阻抗复平面图，也称为Nyquist图；~logf(或log)log|Z|~logf(或log)Bode图EIS测量结果典型示例NyquistRS**Bode特征频率*=1/RC时间常数＝1/*=RC表征界面电荷转移速度快慢semicirclepeakEIS测量结果的分析方法——等效电路•TypicalexampleRsRctCH+++-+---MetalElectrolyteElectrochemicalsystemNormalequivalentcircuit10100100F＋＋＋＋＋＋－－－－－－常相位角元件Constant-PhaseElement(CPE)Q弥散效应：固体电极的电双层电容的频响特性与“纯电容”并不一致，而有或大或小的偏离的现象。nQjYZ)(100n1曹楚南、张鉴清著，《电化学阻抗谱导论》，2002年•用于电导测定•过程研究•电池稳定性测试•电场分布及表面态能量分布•……在染料敏化电池（DSC）中的应用串联阻抗(RS)–Electrolyteresistance–Electroderesistance–InterfacialresistancebetweenelectrodeandTCOSchematicdiagramofDSCB.-K.Koo,etal,JElectroceram.2006,17,79-82EquivalentcircuitVariationofefficiencyofDSSCusingPtelectrodesandCNTelectrodewithtimeB.-K.Koo,etal,JElectroceram.2006,17,79-82ApplicationinthemeasurementofconductivityInitial:17ohmAfter5days:62.5ohmB.-K.Koo,etal,JElectroceram.2006,17,79-82CNTPtNosignificantchange电极过程研究FrequencyHigh(kHz)Low(mHz)Middle(10~100Hz)Charge-transferattheplatinumcounterelectrodePhotoinjectedelectronswithintheTiO2Nernstiandiffusionwithintheelectrolyte•AtypicalEISforDSC–ThreesemicirclesintheNyquistplot–ThreecharacteristicfrequencypeaksinaBodephaseanglepresentationR.Kern,etal,ElectrochimicaActa.2002,47,4213-4225过程研究示例1：Nyquist图Kuo-ChuanHoGroup,SolarEnergyMater.&SolarCells,2006,90,2398-2404Kuo-ChuanHoGroup,SolarEnergyMater.&SolarCells,2006,90,2391-2397MichaelGrätzelGroup,JACS,2006,128,4146-4154R.Kern,etal,ElectrochimicaActa.2002,47,4213-4225过程研究示例2：Bode图JianbaoLiGroup,Electrochem.Commun.2006,8,946-950WarburgimpedanceFinitediffusionimpedance过程研究示例3：Nyquist图在CuInS2太阳电池中的应用Backgroundandexperimental•TypetransformationinCuInSe2andCuInS2solarcellsisanimportantissuewithfarreachingconsequences.p-type(Cu-rich)n-type(Cu-poor)•Inthepresentstudy,thepresenceofap-nhomojunctioninsideCuInS2inaTiO2/CuInS2deviceisrevealedwithadetailedimpedancespectroscopyandcapacitancestudy.n-TiO2140nmp-CuInS2130nmTCO40nmn-CuInS2Carbonspot(graphiteconductiveadhesive,2.3mm)Spraypyrolysisn-n-psystemTechniquesforthemeasurementofhomojunctioninCIS•Electron-beam-inducedcurrent(EBIC)–onlythicktype-convertedCuInSe2layersseveralmicrometers•Secondaryionmassspectroscopy(SIMS).–onlythicktype-convertedCuInSe2layersseveralmicrometers•Impedancespectroscopy(IS)–Monitorthepresenceofan-typeregioninCuInS2withunprecedentedaccuracy.–Determinethethickness,aswellastheeffectivedonorandacceptordensities.–Findouttheenergypositionsoftheinvolveddeepacceptorstateanddeepholetrapbymeasuringthetemperaturedependenceoftheinterfacecapacitance.ResultsandDiscussion•I-VcurvesofTiO2/CuInS2devicesatdifferenttemperaturesinthedarkGooddiodebehavioratalltemperatures.ISofTiO2/CuInS2devicesatdifferentpotentialsandtemperaturesForfrequenciesabove100kHz,theR1C1branchdominatesovertheothers.Accordingly,at1MHzC1,beingthespace-chargecapacitance,canbecalculateddirectlyfromtheimaginarypartoftheimpedanceZ”.f=100Hz~1MHzC−2-VplotsofaTCO/TiO2/CuInS2/carbondeviceatdifferenttemperatures.JunctionModelsT340K340KT400K340KT400KT400KFullDepletionRegion(FDR)FDRFDRFDRFDRp-n-nsystemBanddiagramsofp-CuInS2/n-CuInS2/n-TiO2asafunctionoftemperatureatzeroappliedbiasvoltage.C−2-VequationsdeducedbythesupposedmodelsModelIModelII-AModelII-BModelIIIT340K340KT400KT400KUponfittingtheaboveexpressionstotheexperimentaldata,usingrelativedielectricconstantsof55foranataseTiO2and10forbothp-andn-CuInS2.ParametersobtainedfromtheC−2-VequationsModelParametersn-CuInS2p-CuInS2II-AThickness(nm)10030ND&NA(cm-3)4×10162×1017II-BThickness(nm)4090ND&NA(cm-3)2×10174×1016Note:T=400KBecausep-CuInS2isfirstlydeposited,modelII-Bismorereasonable.Summary•EISisapowerfultoolforidentifyingelectronicandionictransportprocessesinDSC.•ISisatechnologyversatileandsensitivetotheinterfaceandstructureofjunctions.MichaelGrätzelGroup,JACS,2006,128,4146-4154致谢感谢施晶莹博士在报告材料方面给予的大力帮助感谢504组同学给予的有益讨论谢谢大家!ND&NA~1/Tn-CuInS2p-CuInS2Bothacceptoranddonordensitiesdecreasewithincreasingtemperature,oppositetoourexpectations.ThisisexplainedbytheactivationofaCu”Inacceptors