Regulating The Growth Of Two-dimensional Perovskite Films Through Cation Doping And Interface Engineering

In the past ten years,people have carried out in-depth research on three-dimensional（3D）structure organic-inorganic hybrid perovskite materials,and achieved fruitful results.The highest photoelectric conversion efficiency of 3D perovskite solar cell（PVSC）has exceeded 24%,which can compete with commercial thin film solar cells and silicon solar cells.However,the instability of 3D perovskite is still the main obstacle to the industrialization of PVSC technology.In order to improve the stability of perovskite materials and its battery devices,researchers have done a lot of research work by means of precursor engineering,interface engineering,and optimizing device structure and packaging technology.Among them,the introduction of large volume organic amine cations into the three-dimensional structure of perovskite materials as spacer cations to prepare two-dimensional（2D）structure hybrid perovskite,using the hydrophobic properties of organic chain segments on spacer cations to form a protective layer inside the perovskite materials to prevent the erosion of external water on the perovskite structure,is an effective way to improve the moisture resistance and stability of hybrid perovskite materials.However,the introduction of large volume organic amine cations has a negative impact on the performance of the battery.The insulating spacer cation layer will block the transport of carriers along the direction perpendicular to the substrate,resulting in the decrease of short-circuit current and photoelectric conversion efficiency of the battery devices.Therefore,how to improve the efficiency of 2D perovskite solar cells has become a new hotspot of hybrid perovskite solar cells.The chemical composition of the hybrid perovskite material and the properties of its substrate have an important influence on the quality of the perovskite crystal film.Based on this,we take two-dimensional perovskite PEA₂MA_n-1Pb_n I_3n+1（n=5）as the research object to explore the influence of chemical composition and substrate properties on the film quality and battery performance.Firstly,the two-dimensional perovskite PEA₂MA_3.5FA_0.5Pb₅I₁₆ thin film with large grain and good crystal orientation was obtained by FA⁺cation doping.The photoelectric conversion efficiency of the cell device was increased from 8.25%to 10.43%.Then,we use the interface engineering method to realize the interface modification by depositing ultra-thin PFN layer（<5nm）on PTAA,and further regulate the growth of two-dimensional perovskite PEA₂MA_3.5FA_0.5Pb₅I₁₆ film.The introduction of PFN layer has many benefits:Firstly,the surface wettability of PTAA is improved,and a complete 2D perovskite film covering the substrate is obtained;Secondly,the formation of n=1phase in 2D perovskite film is reduced,enhancing the absorption of light and improving the short-circuit current of battery devices;Thirdly,it reduces the defect density in perovskite film,which is conducive to reducing the non radiative recombination in the carrier transport process.Finally,the cell device with high quality PEA₂MA_3.5FA_0.5Pb₅I₁₆ film as the light absorption layer was obtained.The PCE was 12.78%,the current density（Jsc）was 15.59 mA cm^-2,and the open circuit voltage（Voc）was 1.13 V.In addition,the stability（wet stability,light stability,thermal stability）and the repeatability of the preparation of the battery are also significantly improved.The above research process is of great significance to promote the development of two-dimensional perovskite solar cells.