Performance Of Two-dimensional Perovskite Solar Cells Based On Aromatic Cyclic Organic Amines

Perovskite solar cells（PSCs）with three-dimensional crystal structure based on organic-inorganic perovskite have achieved rapid development in recent years,which is demonstrated by the rapid improvement of their photoelectric conversion efficiency（PCE）.However,the instability of three-dimensional perovskite materials has not been solved.Inert large volume organic cations can not only enhance their structural stability through the strong interaction between the covering organic cations and[Pb I₆]^4-element,but also prevent water molecules from penetrating and corroding the internal inorganic layer.However,the decrease of the conductivity of the organic layer impedes the transport of charge carriers between the perovskite quantum well.Therefore,compared with three-dimensional perovskite,two-dimensional perovskite（RPPs）exhibits a wider band gap and higher exciton binding energy（E_b）,resulting in a lower photoelectric conversion efficiency.In low dimension（n<3）under these conditions,the device efficiency can be improved by optimizing the phase purity,phase distribution and crystal orientation of RPP films.On the one hand,effective methods to promote the vertical orientation of RPPs are through the introduction of additives or deposition of2D perovskite films at high temperatures.However,most of these studies rely on special additives to obtain high PCE,and 2D perovskite films treated with additives usually require additional annealing,which is extremely detrimental to the process repeatability.On the other hand,effective control of the phase distribution in RPPS is extremely difficult by stoichiometric mixing of precursor components dissolved in polar solvents such as dimethylformamide（DMF）,dimethylsulfoxide（DMSO）,and dimethylacetamide（DMAC）.Previous studies have highlighted the presence of distinct phases（from n=1-∞）in vertically aligned 2D perovskites during spin coating of stoichiometric precursors.In principle,this ordered n-value phase distribution provides an energy cascade process that facilitates the transfer of charge through the RPP device.However,low n phases（n=1 and 2）act as defect centers in RPPs resulting in recombination of charge carriers,and the accumulation of 3D phases on the surface will seriously affect the long-term stability of the device.Because of two-dimensional perovskite charge separation and transfer of solar cells that formed in the process of perovskite processing quantum potential barrier,the influence of management by stoichiometric mixture preparation of precursor solution of two-dimensional perovskite phase distribution becomes very difficult,at this point,we developed a method of generality,by introducing a nonpolar solvent,The influence of phase distribution of 2-D perovskite films formed by single crystal precursors is greatly reduced.For specific thiophenethylamine-based two-dimensional perovskite films prepared using the mixed solvent ratio of dimethylacetamide and toluene,optical spectrometric measurements clearly verified the narrow phase distribution in the vertically ordered arrangement,and the GIWAXS results showed a preferred vertical orientation with high crystallinity.The efficiency of thiophenethylamine 2-D perovskite solar cells prepared by collaborative engineering technology can reach 14.68%,which is 50%higher than that of conventional stoichiometric precursor systems.In addition,the unpackaged device demonstrated superior operating stability,retaining 93%of the original PCE under constant illumination in ambient air.In the process of optimizing the vertical phase distribution,we selected a two-step method as the research object,and investigated the effects of different aromatic ring halides and their added locations on the quality of perovskite film and the performance of solar cell devices.By comparison,it is found that adding organic cationic salt into the solution of the first step is conducive to the crystallization of perovskite film and the formation of larger grains.Meanwhile,this method can control the vertical orientation distribution of two-dimensional perovskite in the three-dimensional film,which is conducive to the transmission and collection of electric charges.The efficiency of the perovskite solar cell devices prepared by this method is more than 18.5%,and the stability of the perovskite solar cell devices is obviously improved compared with the three-dimensional devices without adding organic cationic salts.