Preparation And Exciton Luminescence Mechanism Study Of Two Dimensional Perovskite Materials

In recent years,perovskite materials have made significant research progress in many fields such as solar cells,light emitting diodes,photodetectors,and lasers and so on.Among them,two-dimensional(2D)perovskite has great scientific significance and application value in structure control and spectral transformation because of its good stability,strong luminescence,intrinsic quantum well structure and strong exciton luminescence.Therefore,an in-depth understanding of the exciton luminescence characteristics of 2D perovskites is the basis for the application of perovskite materials.In this paper,we choose 2D perovskite nanosheets as the experimental object to explore the exciton luminescence characteristics.The main research contents include the following three parts:(1)Aiming at the problem that the exciton luminescence behavior of 2D perovskite materials with ultra-high exciton binding energy is still unclear,the thermal injection method is used to prepare PEA₂Pb Br₄2D perovskite materials.Elliott linear analysis and self-trapped exciton induced by Cd doping broadband emission strategy are used to study the exciton behavior mechanism.Firstly,the surface morphology,crystal structure and optical properties of the as prepared material are characterized.We find that 2D material has a strong exciton absorption peak and a small Stokes shift,exciton binding energy is 310 me V by using Elliott formula to fit the absorption spectrum.The carrier recombination type is confirmed by variable power excitation test,and the free exciton luminescence exciton is further studied.The lattice distortion model shows that the strong exciton phonon coupling is the main reason for the Cd doped self-trapped excitons.Through the linear analysis,the synergistic effect of free excitons and self-trapped excitons in the absorption and recombination process is confirmed.(2)Single layer PEA₂PbI₄2D perovskite is synthesized and the origin of band tail luminescence is studied.Firstly,the basic morphology and optical properties of 2D perovskite of PEA₂Pb I₄is characterized.We find that the perovskite semiconductors exhibit the exciton binding energy-band gap dependence similar to those of the?-?group semiconductors,indicating that the perovskite semiconductors have similar structural properties to those of the?-?group semiconductors.Gaussian single peak fitting find that it shows a strong band-tail luminescence peak in the long wave direction.Fitting the exciton lifetime of different wavelengths,we find that it conformed to the exciton local state physical model,revealing the origin of band-tail luminescence.In addition,the halogen mixture is used to adjust the wavelength of luminescence in single-layer two-dimensional perovskite.(3)The optical stability and optical properties of the two-dimensional perovskite OTAM₂Pb I₄are studied by the organic ligand octamine,which is convenient for the preparation of high-quality films.Firstly,the basic morphology and optical properties of the system are characterized,and the optimum conditions of the preparation are explored.The results show that annealing can lead to the recombination of interlayer ligands,which leads to the increase of exciton coupling and the decrease of exciton life.However,the exciton binding energy of single layer two-dimensional perovskite is much greater than that of interlayer coupling energy,Exciton dissociation is still carried out in the form of resonant energy transfer,and there is no tunneling between layers.