Research On Fabrication Of Phase-Pure FAPbI₃-Based Perovskite Films And Corresponding High Performance Solar Cells

In the past few years,organic-inorganic perovskite solar cells(PSCs)have made their mark in the field of energy conversion materials with a rapid boost in power conversion efficiency(PCE)from 3.8%to 24.2%over the last ten years.Formamidine(FA)lead halide(FAPbI3)perovskite is more suitable for photovoltaic applications because of its good light capture performance,long carrier diffusion length and superior thermal stability.In view of this,this article has adopted three different methods to prepare high-quality,high-performance FAPbI3-based perovskite solar cells.Firstly,the method of "template-assisted perovskite structure" is used to prepare ultra phase-pure and high-quality ?-FAPbI3 perovskite solar cells.The method lies in post-treating colloidal film(MAI-PbI2-DMSO)with FAI/IPA solution so as to build a perovskite template-assisted structure,MAPbI3-FAI-PbI2-DMSO,which is helpful for preparation of completely purified ?-FAPbI3 perovskite film with avoiding the formation of ?-FAPbI3.After detailed investigation,prooving and systematic analysis of the reaction mechanism of this method and according to the testified mechanism,this article first determined the necessary preparation conditions of the phase-pure ?-FAPbI3 thin films,and then studied the preparation results in depth from both qualitative and quantitative analysis.The high-quality FAPbI3 perovskite thin film prepared by this method greatly improved the short-circuit current density(Jsc)of the device,(Jsc)24.99 mA/cm2 and the open-circuit voltage(Voc)1.09 V.The final photoelectric conversion efficiency(PCE)was 21.24%,which was the highest efficiency of the pure-phase FAPbI3 perovskite cell at that time.In a nitrogen environment,the FAPbI3 perovskite device achieved the thermal aging of 800 hours and the light aging of 500 hours,respectively.On the premise of achieving high-efficiency,pure-phase FAPbI3 perovskite solar cells,in order to improve the stability of the FAPbI3 solar cells,this article uses a "partial pre-nucleation method" to prepare high FA content mixed cations(FAMA)perovskite solar cells.Partial pre-nucleation method uses FAI/MAI solution to treat mesophase FAI-PbI2-DMSO,and the molecular exchange between FAI and DMSO due to their similar molecular structure reduces the Gibbs free energy during perovskite nucleation;it also promotes the nucleation of perovskite and inhibits the phase separation during nucleation.The trap states in the final FA0.92MA0.08PbI3 perovskite film is greatly reduced,and a high-quality mixed cationic perovskite film is realized.The device prepared by this method has stable repeatability with a maximum efficiency of 20.80%,and the stability was improved.In order to further improve the stability of FAPbI3 solar cells and promote the commercialization of perovskite,this paper stabilizes the alpha phase of FAPbI3 by constructing a "phase stabilizer"(FAIxRbI1-x-PbI2-DMSO).The construction of the stabilizer solves the problem of instability of the ?-phase,reduces the defect states in the film.The final prepared perovskite film has an excellent surface morphology.The perovskite solar cell prepared by this method finally achieved a photovoltaic efficiency of 20.36%and the stability was better improved.