Surface Passivation Of Perovskite Solar Cells Prepared By Two-Step Gas Phase Method

Amazing progress has been achieved in perovskite solar cells（PSCs）in the past decade.In the perovskite prepared by sequential deposition,methylaminium iodide（MAI）/formamidinium iodide（FAI）will remain on the surface of the perovskite film,making the perovskite have a strong p-type surface.In inverted devices,however,the p-type surface is not conducive to the transfer of electrons from the perovskite to the adjacent electron transport layers（ETLs）.To improve device efficiency and stability,three-dimensional（3D）structured perovskite films are usually passivated with two-dimensional（2D）structured perovskite.However,some 2D phases have poor carrier mobility and sometimes cannot passivate perovskite;and in the inverted structure,it is very important to control the thickness of the 2D layer.To address this problem,a rapid organic amine fumigation strategy was adopted in this thesis to conformally generate2D structured alternating cationic interlayer（ACI）phases on 3D structured perovskites prepared by two-step vapor-phase method.The ACI phase passivates the surface defects of the 3D phase perovskite film,further inhibiting the non-radiative recombination.Finally,high-efficiency PSCs with different components were fabricated.This paper conducts research from the following aspects:First,this article tried to use O₃ gas to treat the perovskite film,and found that it would destroy the perovskite structure and reduce the efficiency of PSC.Then we fumigated the surface of the perovskite film with ammonia gas,and found that a small amount of ammonia gas can increase the current of PSC,but reduce the stability of PSC.Subsequently,organic amines with different saturated vapor pressures were used for fumigation,and it was found that the passivation effect was related to the saturated vapor pressure.According to the characterization results of device performance and photoluminescence intensity after fumigation,we selected benzylamine（PMA）with moderate saturated vapor pressure for fumigation passivation.Then this article optimized the process of PMA fumigation to passivate perovskite films.Firstly,we optimized the fumigation temperature.Then the fumigation time and humidity were changed to get the best fumigation process.We finally fabricated a small-area（0.1125 cm²）device with an efficiency of 21.10%.Simultaneously,we successfully passivated device with a total area of 145 cm² in a batch.Finally,this article characterized the fumigated film structure by synchrotron radiation grazing incidence wide-angle X-ray scattering（GIWAXS）and high-resolution transmission microscopy（HRTEM）.It was found that the ACI phase perovskite conformally formed on the surface of the 3D film with a layer spacing of 1.2nm.We precisely controlled the 2D perovskite thickness and structure by varying the fumigation time.Then,the surface properties of the film were tested,and it was found that the surface of the film changed from p-type to n-type after fumigation with PMA;after 10 s of fumigation,a type-I heterojunction was formed,which blocked the recombination of holes and electrons at the interface;after 35 s of fumigation,a type-II heterojunction was formed.type heterojunction,which may form a recombination center for electrons and holes.The thermodynamic stability of the ACI phase perovskite with a lattice spacing of 1.2 nm is higher than that of the RP phase with a lattice spacing of 1.4 nm,calculated by DFT.The 2D perovskite layer produced by PMA fumigation suppresses defect-related non-radiative recombination,reduces excitonic defect states,and increases the average carrier lifetime of the film,which is subsequently confirmed using fluorescence confocal microscopy.Deep level transient energy spectrum（DLTS）demonstrated that the surface of the control film usually has interstitial defects I_i,vacancy defects V_Pb,and antisite defects I_MA or I_Pb with deeper energy levels.After fumigation,the interaction of PMA⁺with the[Pb I₆]^4-unit not only annihilates the shallower defects but also annihilates the deeper antisite defects.Finally,through the stability test,it was found that the 2D perovskite produced after fumigation can hinder the light/heat-induced interfacial ion migration and improve the photothermal stability of PSC.In conclusion,in this thesis,2D perovskite was conformally formed on the surface of 3D perovskite through rapid organic amine fumigation passivation strategy,which reduced the defect density in the 3D film and improved the power conversion efficiency and stability of the device.In addition,this strategy can also be operated in the air,has universal applicability,and can be applied to the preparation of ultra-large-area PSC modules,providing a new strategy for the industrialization of PSCs in the future.