Preparation And Controlling Of CsPbBr₃ Perovskite Film

Perovskite is a semiconductor material with low cost,high carrier mobility and high optical absorption coefficient.It has great potential in the fields of solar cells,electroluminescence,lasers and displays.At present,the efficiency of organic-inorganic hybrid perovskite solar cels has reached 21%.However,it should not be neglected that organic-inorganic hybrid perovskite has poor stability and decomposes rapidly in humid air or at high temperature.All inorganic perovskite nanocrystalline materials CsPbX₃?X=Cl,Br,I?with similar structures have attracted wide attention.Their excellent photoelectric properties,including high quantum yield and short radiation lifetime,are attributed to nanoscale effects,such as quantum confinement effect.In the paper,perovskite thin films with CsPbBr₃ quantum dots were prepared by centrifugal deposition,and their morphology and optical properties were studied.By comparing with the traditional method,the centrifugal deposition method is determined to prepare the film and we repair the film later.Finally,compact and stable CsPbX₃ thin films were obtained,with high quantum yield and strong absorption performance.The main results of the paper are as follows:?1?CsPbBr₃ quantum dots are synthesized by crystallization at room temperature.By determining the ligand ratio,the quantum dots formed are cubic perovskite structure with good crystallinity.They have excellent optical properties.The peak wavelength is 520 nm and the half-peak width is 20 nm.By comparing the effects of different filtration methods on the solution of quantum dots,it is determined that uniform and compact CsPbBr₃ quantum dot films are prepared by centrifugal deposition directly.Perovskite quantum dots with different luminescence wavelengths are synthesized by doping halogen group elements in different proportions.The quantum dots have high fluorescence efficiency at room temperature.By changing the concentration of nanocrystals and multi-centrifugal deposition,the thickness of nanocrystals can be adjusted from 10 nm to micron level.The PL strength of quantum dot films decreases rapidly and irreversibly under air environment for a long time,and the wavelength redshift occurs at the same time.In vacuum drying environment,the PL strength of quantum dot films is stable and almost unchanged.At the same time,the characteristics of thermal stability,humidity stability and light stability of quantum dot films prepared by centrifugation are studied by changing different conditions.Finally,by annealing 810 nm thick film with toluene/alcohol mixed solvent,the root mean square roughness?Rms?of the film surface is reduced from 37.8 to 32 nm,which makes the film prepared by centrifugation more uniform and smooth.?2?By measuring the transmittance of the dielectric film,the optical parameters of the film can be obtained.The propagation process of light through thin films and substrates is studied,and the background of asymmetric Fabry-Perot?FP?with absorbance of film is described.The functional relationship between transmittance and optical constants n,?,d is deduced in detail.An effective calculation method,local ergodic method,is selected to calculate the optical constants of thin films.The transmission spectra of dielectric films with different thickness can be measured by ultraviolet-visible spectrophotometer,and then the related transmission spectra data can be input to the computer.The optical constants of the films can be calculated without choosing the initial values and requiring the extreme points on the spectral lines,only by defining the convergence interval.The interference dominant region and absorption dominant region are discussed carefully,and the possible errors of thin films are analyzed.?3?We study the stimulated radiation in CsPbBr₃ thin films prepared by centrifugal deposition.When the excitation intensity increases,the spectrum emitted from the edge of the sample has gain narrowing and obvious threshold characteristics.We find that the laser characteristics can be improved by changing the film thickness and then controlling the guided mode in the waveguide.With the increase of the film thickness,the threshold of CsPbBr₃ thin films decreases,and the gain coefficient increases.The maximum net gain coefficient is 112.7cm^-1 and the minimum threshold is 16.2 J cm^-2 at 810 nm thickness,which is caused by the variation of absorption coefficient and waveguide effect.Finally,the effect of solvent annealing on stimulated radiation of C_SPbBr₃ thin films is studied.By annealing 810 nm thick films with toluene/alcohol mixed solvent,the gain coefficient reaches 132.8 cm^-1,and the threshold is reduced to 14.2 J cm^-2.This is due to the improvement of the morphology and quality of the film,which reduced the scattering of the film surface.Our research results show that CsPbBr₃ thin film has high gain and low threshold,and is an excellent laser material.