Preparation, Optical Properties Regulation And LED Device Research Based On Ion-doped Lead-free Cs₃Cu₂X₅ (X=Cl, Br) Perovskite Material

Perovskite photoluminescence materials are commonly used in the development of light-emitting diodes due to their high photoluminescence quantum yiled,tunable light emission wavelengths,and high color rendering index of light-emitting diode devices.However,the toxicity associated with lead-based perovskite materials has hindered their commercial applications.Therefore,in this study,we replaced lead with a low-toxicity copper element.Unfortunately,copper-based metal halide perovskite powders or nanocrystals,or even single crystals exposed to the environment for a long time will cause structural changes due to ion migration and lattice decomposition,directly affecting the luminous intensity.Additionally,while the emission peak width of copper-based calcium titanium oxide materials is wide,it does not cover the entire visible spectrum.Consequently,copper-based perovskite materials present a significant challenge for their application in the field of LED technology.To enhance the stability of copper-based metal halide perovskite materials,this study utilized a low-temperature anti-solvent method to prepare non-toxic Cs₃Cu₂Cl₅ single crystals,and subsequently analyzed their structure and fluorescence properties.The study revealed that the single crystal material was unstable in air due to ion migration and lattice decomposition.Na⁺doping was employed to address the lattice defects caused by chlorine vacancies in the Cs₃Cu₂Cl₅ lattice.This approach formed stronger chemical interactions between Cu⁺and Cl^-ions,avoiding ion migration and lattice decomposition,to increase non-radiative recombination and enhance the PL intensity by 18%.Even after90 days,the PL intensity remained above 48.5%of the undoped PL intensity.Finally,white LED devices were prepared using 10%Na⁺-doped Cs₃Cu₂Cl₅ crystal powder,which showed exceptional performance at high temperatures.To broaden the visible light spectrum of copper-based metal halide perovskite materials,the energy level structure was broadened by ion doping.Mn²⁺was used to adjust the conduction band（CB）and valence band（VB）of Cs₃Cu₂Br₅,further broadening the emission spectrum of Cs₃Cu₂Br₅,showing 460 nm self-trapped exciton（STE）emission and 550 nm Mn²⁺emission.Due to the high-energy absorption of Mn²⁺,the exciton energy was transferred to the Mn²⁺d orbital,reducing the blue light intensity at460 nm.When applied to LEDs,the blue emission band（380-480 nm）in Mn²⁺-doped LEDs was reduced by 71.45%compared to undoped Mn²⁺LEDs,indicating better photobiological safety performance.Finally,recognizing the current challenge of growing large crystals using the solvent method and the instability of the crystals in the environment,the study introduced the synthesis methods and properties of two new types of crystals,Mn-based CsMnCl₃·2H₂O and Cs₂MnCl₄·2H₂O.Using an improved method,9mm*3mm*2mm CsMnCl₃·2H₂O and14mm*3mm*1mm Cs₂MnCl₄·2H₂O single crystals were grown.Testing and analysis demonstrated that CsMnCl₃·2H₂O displayed red fluorescence at 620 nm when excited at a wavelength of 417 nm.CsMnCl₃·2H₂O single crystals were stable in the atmosphere,and the structure remained essentially unchanged after 120 days,with only a 24%decrease in fluorescence intensity compared to the initial luminescence intensity.This material is easily synthesized and highly stable,making it expected to have broader applications in the field of optoelectronics.