Study On Hydrazinium Ion Mixed Formamidine-based Perovskite Solar Cells

In recent years,organic-inorganic hybrid perovskite solar cells have attracted widespread attention due to their simple preparation process,low production cost and rapid improvement of power conversion efficiency（PCE）.High-efficiency perovskite solar cells usually are prepared based on FAPbI₃ mixed component perovskite as light-absorbing layer.However,phase transition is easily happened in FAPbI₃ at room temperature,which leads to low stability of devices and rapid decay of PCE.It impedes commercial application of FAPbI₃-based perovskite solar cells.In this thesis,phase-stable light-absorbing materials with FAPbI₃-based structural unit and different dimension structure were designed and synthesized.The morphology and photoelectric properties of films were studied and matching device fabricating processes were explored,which were supposed to provide usable suggestions for the design of efficient and stable light absorbing layer.Novel FA/HA films can be obtained by adding hydrazinium ion（HA⁺）to FAPbI₃,which have an 1D/3D mixed structure and stableα-FAPbI₃ at room temperature.The strong hydrogen bonding of HA⁺enhances the continuity between grains and increases the grain size,which effectively coordinates the connection between iodine ions and adjacent grains.Furthermore,non-radiative recombination is effectively suppressed due to the 1D-HA-phase at grain boundary,which formed by HA⁺and[Pb X₆]^4-exposed between adjacent perovskite crystals.High-quality FA_0.7HA_0.3 films with high crystallinity,large grain size and few defects were prepared by one-step anti-solvent method.The average carriers lifetime of FA/HA film increased from 142.31 ns to385.36 ns and the defect density decreased from 1.17×10¹⁶ cm^-3 to 3.42×10¹⁵ cm^-3.Perovskite solar cells based on FA_0.7HA_0.3 achieved a PCE of 19.03%and retain 87%of initail PCE after 1080 h at room temperature in ambient environment.HA⁺ was further induced to Cs_0.05(MA_0.17FA_0.83)_0.95Pb(I_0.83Br_0.17)₃（FAMACs）.HA⁺can stabilize the structure of FAPbI₃ cooperated with MA⁺and Cs⁺.XRD,SEM,UV-visible absorption spectrum and steady-state fluorescence spectrum show that the addition of HA⁺has a significant effect on the crystallinity,surface morphology and photophysical properties of FAMACs perovskite.Meanwhile,the optimal composition is determined as（FAMACs）_0.85HA_0.15.Confocal fluorescence microscopy,time-resolved photoluminescence spectroscopy and Kelvin probe force microscope reveal that the trap state can be effectively restrained and the non-radiative recombination is largely suppressed in HA⁺mixed FAPbI₃-based perovskite film.The average carriers lifetime of FA/HA film increased from 434.6 nsto 1216.57 ns and the defect density decreased from 1.06×10¹⁶ cm^-3 to 3.10×10¹⁵ cm^-3.PSC using（FAMACs）_0.85HA_0.15achieves PCE of 21.20%which can retain 90%at room temperature in ambient environment for 2520 h.It exhibits improved environmental stability and confirms the research advantages of mixed ion perovskites.