Preparation Of Lead-free Metal Halide Perovskite Nanocrystals And Their Optoelectronic Applications

As a new type of optoelectronic material,metal halide perovskite has shown great application potential in the field of new generation lighting and display.Perovskite represented by lead-based halide after more than ten years of development,its optoelectronic device performance gradually meets the requirements of commercialization,but the toxicity and stability of lead itself and other problems,researchers are constantly exploring the solution path,on the one hand,by encapsulating organic polymers to construct hydrophobic structure or prepare lead-based halide perovskite nanocrystals（Nanocrystals,NCs）to reduce the dimension to improve its stability,on the other hand,in order to fundamentally solve the above problems,develop lead-free metal halide perovskites with low toxicity,expected good stability and excellent optical properties.This paper mainly focuses on the low-toxicity,low-cost copper element,using its own unique self-trapping emission excitons（STEs）to explore its application in optoelectronic devices:（1）In order to develop new white light-emitting diodes（WLEDs）with low toxic,low cost and high color rendering index（CRI）,a new one-dimensional（1D）copper mixed halogen blue emission Cs₅Cu₃Cl₆I₂ NCs were prepared by hot injection method,and the influence of temperature on its nucleation growth was explored,nanocrystals of uniform size were obtained,and yellow-green emission 1D CsCu₂I₃ nanorods were obtained by ligand-assisted anti-solvent precipitation.The organic copper halide crystals emitted with orange-yellow light were further mixed with above to prepare new WLEDs of warm white（3896 K）,white（5603 K）and cold white（9819 K）,corresponding to color coordinates of（0.39,0.40）,（0.33,0.33）,（0.29,0.27）,and their white light CRI exceeded 95,showing the application potential of copper halide perovskites in the field of environmentally friendly and low-cost solid-state WLEDs.（2）In order to solve the problem of low yield and uneven size of zero-dimensional（0D）Cs₃Cu₂Cl₅ NCs,InCl₃ was introduced into the precursor by hot injection method to regulate its nucleation and growth,improve the yield,reduce the nanocrystals with an average particle size of 41 nm to 23 nm,obtain a uniformly dispersed nanocrystalline solution.For the first time,we prepared electroluminescent device ITO/ZnO/NCs/NPB/MoO₃/Al with Cs₃Cu₂Cl₅ NCs,and a green light-emitting diode with a brightness of 100 cd·m^-2 was obtained,and the preparation of a new copper-based halide NCs electroluminescent diode was realized.（3）Focusing on the unique luminescence phenomenon of 1D CsCu₂Br₃,CsCu₂Br₃ films were prepared by in-situ spin-coating,and the internal electron-phonon coupling intensity was quantified by the Huang-Rees equation,and the fluorescence quenching phenomenon at temperatures higher than 220 K was explained.It was found that its broadband fluorescence emission with a full width at half maximum（FWHM）of 116 nm originated from its own unique STEs emission.Furthermore,by introducing excess CsBr into the precursor,a film with smaller surface roughness and more dense and smooth was obtained,a light-emitting device with Cs-Cu-Br as the light-emitting layer was prepared,and an electro-yellow light-emitting diode with a brightness of 60 cd·m^-2 was obtained,and the preparation of a new lead-free electroyellow light-emitting diode was realized.