Interfacial Performance Regulation And Defect Passivation Of Perovskite Solar Cells

The efficient utilization of solar energy is an important guideline to promote the adjustment of energy structure and to form a green and low-carbon system of production and life.Developing high-efficiency and low-cost solar cell devices is the key breakthrough to realize the application of solar energy conversion.Among them,perovskite solar cells(PSCs)have been widely studied for their excellent photoelectric properties and low-cost preparation methods.At present,the certified power conversion efficiency(PCE)of perovskite solar cells has reached 25.8%,making it the most promising solar photovoltaic technology in the new generation.However,the intrinsic properties of perovskite crystals and the contact interfaces and defects associated with the device structure are the main factors restricting the device efficiency and stability,which hinder its commercial application.From this point of view,this thesis aims to improve the photovoltaic performance and stability of devices,including contact interface regulation of perovskite films and defect passivation,focusing on the regulation of "buried interface" and crystalline terminal of perovskite film,and regulates from the perspectives of defect passivation,energy level arrangement,stress release.The effect of surface ion exchange reaction on mechanical properties of thin films and its application in flexible PSCs were also further investigated.The specific investigation carried out is as follows:(1)Premodified mesoporous TiO2 layer regulates and stabilizes the "buried interface" of perovskite solar cells.The "buried interface" between the electron transport layer(ETL)and the perovskite layer inside PSCs is hard to be observed and regulated.Besides,there are a lot of defects,which seriously affect the interface charge extraction and the stability of heterojunction.In this work,pseudohalide anion(BH4-)was used to pretreat the ETL-TiO2 layer.The BH4-ion acted with the uncoordinated Pb2+ at the interface to form a heterojunction with lower defects and higher stability.The final device performance was improved from 18.2%to 20.4%,and the environmental stability was significantly enhanced.Although this work has improved the performance of PSCs in TiO2 system,due to the low electron mobility and the complex preparation process of TiO2 layer,it is not conducive to its industrialization and promotion.SnO2-based PSCs that can be prepared by low-temperature aqueous solution method,which has been attracted attention gradually.In the future,we will conduct research on the defects of SnO2 base and related problems of the contact interface with perovskite films.(2)Surface modification engineering collaboratively regulates SnO2 surface defects and perovskite film crystallization.Based on the technological benefits of SnO2 electron transport layer,the defects of SnO2 surface and its influence on the crystallization process of perovskite thin films were regulated.The surface of SnO2 was modified with pseudohalide ammonium salt(NH4PF6),which not only deactivated the oxygen vacancy defect in SnO2,but also assisted the crystallization process of perovskite film,which inhibited the formation of halogen vacancy on the lower surface of the film and alleviated the lattice strain.The performance of the device was improved from 20.76%to 22.50%,and the stability was improved accordingly.Although this work illustrates that the regulation of the contact interface between SnO2 and perovskite is the key to improve the device performance,the defects of the crystalline terminal of the perovskite film are also the critical factors limiting its performance and stability,and the regulation of the crystalline terminal is also very necessary.We will continue to explore ways to improve the properties of crystal terminals.(3)The crystalline terminal of perovskite films with lower lattice defects and strong hydrophobicity was constructed.A large number of suspended bonds and defects are easily formed on the upper surface of perovskite films at the end of crystallization,which is the essential difficulty affecting the performance and stability of perovskite films.Based on this,pseudohalide anions(PF6-)and long-chain cations were combined to modulate the upper surface of perovskite crystals,which can effectively reduce the halogen vacancy,metal lead cluster and organic molecular vacancy on the upper surface of perovskite crystals,and obtained perfect crystal surface with low defects.In addition,contributing to the interaction between long chain cations and perovskite structure,the surface of the film is closely covered.Surface hydrophobicity of the film is greatly improved,and the comprehensive stability of the device is significantly improved.The final device realized 23.14%photoelectric conversion efficiency.This work mainly optimizes the device performance from the perspective of passivation and hydrophobic regulation of crystal end defects,but the structural defects of crystal terminal and their effects on mechanical properties are still lacking.Given view of this,we will focus on the structural defect regulation to improve the mechanical properties of the film.(4)Reconstruction of crystalline terminal to control mechanical properties of thin films and its application in flexible PSCs.Based on the premise of terminal defect regulation,surface reconstruction was adopted to repair the terminal structure of perovskite films ascribing to mechanical properties attenuation caused by structural collapse caused by element mismatch at the crystalline terminal.In this work,the adsorption reaction of perovskite crystals on three different halogen/pseudo-halogen anions was calculated and analyzed by first principles.Combined with surface morphology analysis,hydrophobicity test and kinetic characterization,pseudo-halogen(BF4-)salts with the best comprehensive performance were selected.SEM characterization exhibited that the BF4-ion salt treated films had almost no cracks after 2000 bending,while the films from control group had a large number of obvious cracks,and there were obvious signs of component decomposition around the cracks,which proved that surface ion exchange and passivation strategies could not only reduce the surface defects of the films,but also enhance the mechanical properties and improve bending resistance.We further applied it to flexible PSCs,achieving a 22.12%photoelectric conversion efficiency,and the device still has 95%of the initial performance after 2000 times bending.