Preparation And Impedance Characteristics Of Perovskite Solar Cells

People pay more and more attention to the new energy resources due to the limited reserves of the fossil energy resource and environment pollution.The solar energy resource is the most promising new energy resource and the solar cells are the important device for energy transform.The solar cells have developed rapidly,especially perovskites solar cells.Perovskite solar cells have attracted attention of many scientific researchers because of their simple preparation process,wide material range and wide spectral response range.The highest power conversion efficiency for perovskite solar cells has exceeded 22.7%,and they have enormous potential for development.The perovskite material commonly used in perovskite solar cells is CH₃NH₃PbI₃,with poor stability.CH₃NH₃Pb I₃ is easily decomposed in a humid or high-temperature environment,resulting in serious degradation of solar cells.In this paper,the perovskite solar cells with triple cation material was prepared,which greatly increased the stability of the device.And we further investigated the impedance characteristics of the perovskite solar cell through electrochemical impedance spectroscopy measurement.It has a great positive effect on subsequent work.The specific study is summarized as follows:Firstly,the perovskite solar cells based on traditional mesoporous structure was prepared.The structure of the perovskite solar cell is?F doped SnO₂?/?TiO₂ compact layer?/?Li-doped TiO₂ mesoporous layer?/perovskite)/?hole transport layer?/Au.We added CH?NH₂?₂⁺and Cs⁺cations into the traditional perovskite material to form a tri-cation mixed perovskite material.The optical absorption of perovskite film increased.The efficiency of the champion perovskite solar cell increased from 16.2%to 18.2%,and the average efficiency also increased from 14.0%to 16.84%with a improved average open circuit voltage,improved average short-circuit current and improved average fill factor.The stability of the solar cells has also been greatly improved.The two kinds of devices are placed under a room-temperature air condition,a high humidity condition,and a high temperature condition,respectively.The triple-cation devices show better stability than CH₃NH₃PbI₃ based devices.We calculated the mean time to failures?MTTF?of the two kinds of devices.When the acceptable minimum efficiency P_limit was set to 70%of the initial efficiency P₀,the MTTF of the CH₃NH₃PbI₃ based perovskite solar cell was 516 h,and the MTTF of the tri-cation perovskite solar cell was 4425.8 h,which was 8 times more than the lifetime of the single cation device.These tests confirm that the performance of the tri-cation device is improved compared with the CH₃NH₃PbI₃ based device.A series of experiments were conducted to investage and analyze the impedance characteristics of perovskite solar cells.Electrochemical impedance spectra of completed devices based on different structurre was measured.According to the Nyquist plots,we established an equivalent circuit to analyze the impedance model.The high frequency part in Nyquist plot is determinded by the carrier transport process inside the solar cell system and the low frequency part is determinded by the carrier recombination process.In order to understand the functions of the layers that make up the solar cells,we have separately prepared various structures of cells for testing and analysis.The mesoporous layer is conductive to electron transport,but it has a certain role in promoting the recombination of electrons and holes.The dense layer increases the transmission resistance,but it can effectively block the holes.The hole transport layer can enhance the ability of the solar cells to extract holes and transport holes to the electrodes.We also doped the dense layer.We found that the transmission resistance of the device is slightly reduced,and the recombination resistance is greatly increased after doping the dense layer.Therefore,it can be seen that doping has a promoting effect on the solar cell performance.The impedance spectra of the CH₃NH₃PbI₃ based and tri-cation devices were characterized.The transmission resistance of the tri-cation devices was significantly lower than that of the CH₃NH₃PbI₃ based devices,which also indicated the excellent performance of the tri-cation perovskite devices.