Modification And Research Of Hole Transport Layer Of PIN Type Perovskite Solar Cell

The organic-inorganic hybrid perovskite material is an ideal solar cell material because of its high carrier mobility,long electron/hole diffusion length,suitable band gap,and wide light absorption range.It is widely used in the preparation of solar cells.In just over a decade,the efficiency of perovskite solar cells has rapidly increased from3.8%to 23.2%,demonstrating the great potential of perovskites as solar cell materials.The speed of efficiency improvement is not only related to the excellent semiconductor properties of perovskite itself,but also the hard work of researchers.However,the perovskite material itself is sensitive to water and oxygen,and the crystal structure is easily destroyed by polar solvents,which places high demands on the preparation conditions of the device.In order to improve the efficiency and stability of perovskite solar cells,researchers have optimized the perovskite solar cells from different aspects,such as controlling the elemental composition of perovskite,optimizing the crystallization process of perovskite film,optimizing the electron transport layer and to regulate the interface and optimize the device structure.In the common PIN-type perovskite solar cell with PEDOT:PSS as the hole transport layer,the strong acidity and strong hygroscopicity of PEDOT:PSS will have a great influence on the perovskite layer and affects the efficiency and stability of the entire device.Without good stability,perovskite solar cells have no commercial value.This paper focuses on the impact of the modification of the hole transport layer PEDOT:PSS on the performance of perovskite solar cells.The main contents include the following three aspects:1、Select the material of the light absorbing layer.Among the materials widely used in the preparation of perovskite solar cells are CH₃NH₃PbI_3-xCl_x and CH₃NH₃PbI₃.Due to the difference in bandgap and film-forming properties of the two materials,the properties of the fabricated devices may vary.We used two materials to prepare perovskite solar cells under the same conditions,and analyzed the two types of cells by electrochemical impedance analysis to select a perovskite material which is more suitable for our device structure.Electrochemical impedance is one of the commonly used methods for analyzing the state of carrier transport inside a device.The impedance and the device performance made of the two types of perovskite materials(CH₃NH₃PbI_3-xCl_x and CH₃NH₃PbI₃)were compared under the same fabrication condition.The device performance shows almost the same values.However,after analysis,we found that the device with CH₃NH₃PbI₃ as the light absorbing layer generally has carrier accumulation at the interface,and the cell with CH₃NH₃PbI_3-xCl_x film formed on PEDOT:PSS substrate is better than that of CH₃NH₃PbI₃.Thus,we selected the chlorinated perovskite material CH₃NH₃PbI_3-xCl_x as the light absorbing layer for our next experimental study.2、PEDOT:PSS doped with sodium citrate is used as the hole transport layer,and PCBM is used as the electron transport layer to improve the open circuit voltage and efficiency of the solar cell.The doping was realized by adding different concentrations of sodium citrate solution into PEDOT:PSS raw solution.The open circuit voltage of the device was increased from 1.057 V to 1.134 V,and the device efficiency was increased from 15.05%to 18.39%.Using various measurement methods for analysis,we found that the increase in voltage is mainly due to the addition of sodium citrate to increase the PEDOT:PSS work function,which makes the valence band more closely match the valence band of perovskite.Moreover,the perovskite forms a good film on the modified PEDOT:PSS,and the electron and hole transport is smoother,which makes the short-circuit current and the filling factor of the device increase slightly,and finally the overall efficiency of the device is greatly improved.At the same time,the addition of sodium citrate reduces the acidity of the PEDOT:PSS solution,reduces the corrosion of the perovskite by acidity,and greatly improves the stability of the device.3、The LiF thin layer was inserted into the ITO/PEDOT:PSS structure to modify the PEDOT:PSS to explore its effect on device performance.The thickness of the inserted LiF thin layer was explored,and various analytical tests were performed on the device.It was found that although the device performance was only slightly improved,the PEDOT:PSS film had a dipole effect due to the LiF thin layer polarization,which made PEDOT:PSS film ohmic contact reduced.