Preparation Of Component Gradient Perovskite Film And Adjustment Of Optical Properties

With its excellent optical and electrical properties,perovskite has become one of the most eye-catching materials in the world after only a few years of development.The chemical structure of perovskite is ABX₃,where A is usually a monovalent cation,B is a divalent metal ion,and X is a halide.Therefore,the composition of perovskite materials is diverse,and their properties also change accordingly.At present,many reports have indicated that continuously changing its band gap over a large range to achieve the effect of adjusting the luminescence spectrum,improving stability,or extending the carrier diffusion length,etc.,by adjusting the composition of the perovskite,thereby,the performance of perovskite solar cells and light-emitting devices is significantly improved.It is also possible to control the properties of the material in a wide range by adjusting the composition of the perovskite,which provides a huge development space for future development.In addition,the simple preparation process and low cost of perovskite materials make it have important advantages in photovoltaic materials,luminescent materials,lasers and so on.At present,the research on adjusting the composition of perovskite materials is mainly to prepare a single component perovskite film with a specific halogen ratio by spin coating.However,this method has shortcomings such as stoichiometric errors,and more importantly,the film prepared by this method cannot be further adjusted for its composition and performance,so the perovskite prepared by this method cannot meet the actual needs.Therefore,it is of great significance to develop a method for continuously adjusting components in situ.In addition,the performance of white light-emitting diodes that have been commercialized so far cannot have a continuous light-emitting band like sunlight or incandescent lamps,and at the same time,it cannot meet the market demand for broadband white light-emitting diodes.Since the luminescence wavelength of perovskite can be continuously adjusted in the visible light band,it is of great significance to carry out the research of perovskite broadband white light-emitting diodes.In this paper,several anion exchange methods with simple preparation process and strong controllability are developed.A series of graded perovskite MAPb I_3-xBr_xthin films were prepared,and the in situ continuous adjustment of the composition,band gap and spectrum of the perovskite film was achieved.And a perovskite film with continuous gradation of composition and continuous change of luminescence wavelength was prepared on the same substrate.By characterizing the phase and optical properties of the material,the composition,band gap,luminescence and other properties of the perovskite film were studied in depth.The main work of this article is as follows:(1)A simple and controllable gas/solid phase anion exchange method is designed in this paper.This method realizes in-situ and continuous regulation of the composition and band gap of perovskite materials.In this method,due to the low concentration of reactants,the anion exchange can be carried out slowly,and the composition of the perovskite film can be continuously and finely adjusted within180 min.Specifically,the band gap of the perovskite film can be continuously adjusted from 1.58 e V to 2.25 e V only by controlling the reaction time,and the photoluminescence(PL)spectrum peak is also blue-shifted from 771.1 nm to 540.5nm.The morphology of the prepared sample is similar to that of the precursor MAPb I3 film.This chapter explains the control mechanism of this method through theoretical calculation of the anion exchange process.This work not only provides an important reference for the application of dense perovskite solar cells,but also for the preparation of large-area perovskite solar cells and perovskite white LEDs,and even provides a reference for the realization of white lasers.(2)A liquid-phase anion exchange method is also designed in this paper,and a macro-scale perovskite film with continuous graded components on the same substrate is prepared.With the continuous change of excitation position,the peak position of the photoluminescence spectrum showed continuous blue shift(from691.3 nm to 548.9 nm).Scanning electron microscopy(SEM)characterization of the morphology of the material shows that the morphology of the film at different locations also changes continuously,and it is confirmed that isopropanol has a huge influence on the morphology of the perovskite film.This work can provide a reference for the study of the influence of isopropanol on the morphology of perovskite films under different action times in the future.At the same time,in order to realize micron-scale broadband white LEDs,a film with a gradient composition of20?m in length is also prepared in this paper,and the continuous change of the emission wavelength is realized,which has the characteristics of broadband emission.Therefore,this work provides a research basis for the future development of perovskite broadband white LEDs.