电化学阻抗谱简介

1、电化学阻抗谱简介第一页，共30页。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电池中的应用举例第二页，共30页。什么是EIS?EIS：Electrochemical Impedance Spectroscopy别名：交流阻抗(AC impedance)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

2、化学阻抗谱导论，2002年Y = G()XG()为阻抗或者导纳第三页，共30页。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年第四页，共30页。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

3、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年第五页，共30页。如何测量得到EIS?装置简图相应的操作软件Potentiostat (EG&G, M273)Lock-in amplifier (EG&G, M5210).第六页，共30页。EIS测量结果的表达形式Y = G()X G()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

4、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) -ZZ为阻抗复平面图，也称为Nyquist图； log f (或log ) log|Z| log f (或log )Bode 图第七页，共30页。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semicirclepeak第八页，共30页。EIS测量结果的分析方法等效电路Typical exampleRsRctCH+-+-MetalElectrolyteElectrochemical systemNormal

5、 equivalent circuit10100100 F第九页，共30页。常相位角元件Constant-Phase Element (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。0 n 1曹楚南、张鉴清著，电化学阻抗谱导论，2002年第十页，共30页。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）中的应用第十一页，共30页。串联阻抗 (RS)Electrolyte resistanceElectrode resistanceInterfacial resistance between electr

6、ode and TCOSchematic diagram of DSCB.-K. Koo,et al, J Electroceram. 2006,17 ,79-82Equivalent circuit第十二页，共30页。Variation of efficiency of DSSC using Pt electrodes and CNT electrode with timeB.-K. Koo,et al, J Electroceram. 2006,17 ,79-82第十三页，共30页。Application in the measurement of conductivityInitial

7、: 17 ohmAfter 5 days: 62.5 ohmB.-K. Koo,et al, J Electroceram. 2006,17 ,79-82CNTPtNo significant change第十四页，共30页。电极过程研究FrequencyHigh (kHz)Low (mHz)Middle(10100 Hz )Charge-transfer at the platinum counter electrodePhotoinjected electrons within the TiO2Nernstian diffusion within the electrolyteA typi

8、cal EIS for DSCThree semicircles in the Nyquist plot Three characteristic frequency peaks in a Bode phase angle presentationR.Kern,et al, Electrochimica Acta. 2002,47,4213-4225第十五页，共30页。过程研究示例 1： Nyquist 图 Kuo-Chuan Ho Group, Solar Energy Mater. & Solar Cells, 2006,90,2398-2404第十六页，共30页。Kuo-Chuan Ho

9、 Group, Solar Energy Mater. & Solar Cells, 2006,90,2391-2397Michael Grtzel Group, JACS, 2006,128,4146-4154R.Kern,et al, Electrochimica Acta. 2002,47,4213-4225过程研究示例 2： Bode 图 第十七页，共30页。Jianbao Li Group, Electrochem. Commun.2006,8 ,946-950Warburg impedanceFinite diffusion impedance过程研究示例 3： Nyquist 图

10、 第十八页，共30页。在 CuInS2太阳电池中的应用 第十九页，共30页。Background and experimentalType transformation in CuInSe2 and CuInS2 solar cells is an important issue with far reaching consequences. p-type (Cu-rich) n-type (Cu-poor)In the present study, the presence of a p-n homojunction inside CuInS2 in a TiO2 /CuInS2 devic

11、e is revealed with a detailed impedance spectroscopy and capacitance study. n-TiO2140 nmp-CuInS2130 nmTCO 40 nm n-CuInS2Carbon spot(graphite conductive adhesive, 2.3 mm)Spray pyrolysis n-n-p system第二十页，共30页。Techniques for the measurement of homojunction in CISElectron-beam-induced current (EBIC)only

12、 thick type-converted CuInSe2 layers several micrometersSecondary ion mass spectroscopy (SIMS). only thick type-converted CuInSe2 layers several micrometers Impedance spectroscopy (IS)Monitor the presence of a n-type region in CuInS2 with unprecedented accuracy. Determine the thickness, as well as t

13、he effective donor and acceptor densities.Find out the energy positions of the involved deep acceptor state and deep hole trap by measuring the temperature dependence of the interface capacitance.第二十一页，共30页。Results and DiscussionI-V curves of TiO2/CuInS2 devices at different temperatures in the dark

14、Good diode behavior at all temperatures.第二十二页，共30页。 IS of TiO2/CuInS2 devices at different potentials and temperaturesFor frequencies above 100 kHz, the R1C1 branch dominates over the others. Accordingly, at 1 MHz C1, being the space-charge capacitance, can be calculated directly from theimaginary p

15、art of the impedance Z”.f = 100Hz 1MHz第二十三页，共30页。 C2-V plots of a TCO/TiO2 /CuInS2/carbon device at different temperatures.第二十四页，共30页。Junction ModelsT340 K340KT400 K340KT400 KFull Depletion Region(FDR)FDRFDRFDRFDR p-n-n system Band diagrams of p-CuInS2 /n-CuInS2 /n-TiO2 as a function of temperature

16、at zero applied bias voltage.第二十五页，共30页。C2-V equations deduced by the supposed modelsModel IModel II-AModel II-BModel IIIT340 K340KT400 K Upon fitting the above expressions to the experimental data, using relative dielectric constants of 55 for anataseTiO2 and 10 for both p- and n-CuInS2.第二十六页，共30页。

17、Parameters obtained from the C2-V equations ModelParametersn-CuInS2p-CuInS2II-AThickness (nm)10030ND&NA (cm-3)4101621017II-BThickness (nm)4090ND&NA (cm-3)2101741016Note: T = 400 KBecause p-CuInS2 is firstly deposited, model II-B is more reasonable.第二十七页，共30页。SummaryEIS is a powerful tool for identifying electronic and ionic transport processes in DSC.IS is a technology versatile and sensitive to the interface and structure of junctions.Michael Grtzel Group, JACS, 2006,128,4146-4154第二十八页，共30页。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 !