物理化学学报2018，Vol.34Issue(11)：1197-1201,5.DOI:10.3866/PKU.WHXB201804097
钙钛矿CH3NH3Pbl3晶体的电化学
Electrochemistry of Perovskite CH3NH3Pbl3 Crystals
摘要
Abstract
Perovskite CH3NH3Pbl3 is an ionic crystal with suitable band gap and conductivity for optoelectronic applications.The sensitivity of the CH3NH3Pbl3 crystal and its derivatives to chemical composition,film-forming process,and even moisture lead to difficulties in evaluating its electronic structure and redox behavior using electrochemical techniques.Nevertheless,full understanding of the electrochemical behavior of the perovskite crystal is certainly beneficial for tuning its redox properties and chemical stability,especially for device fabrication.We show that the band structure of CH3NH3Pbl3 can be successfully evaluated based on electrochemical square wave voltammetry.The energy level of the bottom of the conduction band of the perovskite crystal was determined directly from the onset reduction potential with reference to the onset oxidation potential of ferrocene,and estimated to be-3.56 eV;the top of the valence band,at-5.07 eV,was determined indirectly after taking into consideration the bandgap,because the oxidation current of the iodide ions shields that corresponding to the valence band of the CH3NH3Pbl3 crystal.The overlap of the oxidation currents from the iodide ions and the valence band of the crystal suggests that there are excess iodide ions in CH3NH3Pbl3 not involved in the development of the valence band.In addition,the alternating current (AC) impedance spectra of CH3NH3Pbl3 indicate that the iodide ions are not completely immobilized.These imply that the defects in the crystal are related to the iodide ions to a large extent.The electrochemistry of CH3NH3Pbl3 in an organic electrolyte reveals its coupling degradation during the redox processes in square wave and cyclic voltammetry.The degradation reactions result from the reduction of lead ions and oxidation of iodide ions in the perovskite crystal.In electrochemical reduction,along with the reduction that occurs in the conduction band,the lead ions in the crystal are reduced to metallic lead,which introduces a phase change in the crystal,as revealed in cyclic voltammetry;the metallic lead can be re-oxidized electrochemically.In the case of electrochemical oxidation,the iodide ions,as well as the valence band of CH3NH3Pbl3,lose electrons.The electrochemically generated iodine diffuses into the organic electrolyte gradually,which results in the loss of iodide ions in the crystal.Such loss of iodide ions continues during the cyclic redox reaction.Apparently,the electrochemical investigations on perovskite CH3NH3Pbl3 show that the crystal is extremely reactive during the redox process;attention should be paid on controlling the excess iodide ions and the irreversible phase change resulting from the oxidation of lead ions.关键词
钙钛矿/太阳能电池/电化学/能带/氧化还原反应Key words
Perovskite/Solar cell/Electrochemistry/Band gap/Redox reaction分类
化学化工引用本文复制引用
杨春和,唐爱伟,滕枫,蒋克健..钙钛矿CH3NH3Pbl3晶体的电化学[J].物理化学学报,2018,34(11):1197-1201,5.基金项目
北京交通大学科技基金(KSRC12006536)及国家自然科学基金(61674011,61735004)资助项目 The project was supported by the Scientific Research Fund of Beijing Jiaotong University (KSRC12006536) and the National Natural Science Foundation of China (61674011,61735004). （KSRC12006536）
