In-situ Preparation Of Perovskite Nanocrystal Films And Their Application In Light-emitting Diodes

Metal halide perovskites have been regarded a promising candidate for the next generation of lighting and display technology,owing to the advantage of easily tunable spectra,high photoluminescence quantum yield（PLQY）,narrow full width at half maximum of photoluminescence spectra,solution processing at low temperature.For the fabrication of perovskite light-emitting diodes（Pe LED）,the complex and unstable post-treatment process of colloidal nanocrystal can be avoided through the in-situ preparation method,which has great value of application.This paper is focused on the in-situ preparation of perovskite nanocrystals and their application in light-emitting devices.Starting with the perovskite precursor solution,by adjusting the organic ammonium salt ligands,perovskite components（mixed cations and mixed anion）and additive,the bandgap and grain sizes are tuned.The defects are passivated,low-dimensional（n=1 and n=2）perovskite phases are suppressed,and consequently the PLQY and carrier mobility of the perovskite nanocrystalline film are imporved and efficient green and blue Pe LEDs are fabricated.The specific contents are as follows:（1）In order to improve the PLQY of perovskite film,FAPb Br₃ nanocrystalline thin films are in-situ prepared through dual ligands of phenethylamine hydrobromide（PEABr）and diisopropylamine hydrobromide（DIPABr）.The Coulomb force between PEA⁺and Br^-in[Pb Br₆]^4-octahedron could limit the grains size of FAPb Br₃ and passivate the surface defects.Meanwhile,low dimensional layered（n=1 and n=2）perovskite phases are formed,which result in significant non-radiative recombination.DIPABr can promote the formation of perovskite phases with larger n value and cooperatively passivate the surface defects.The maximum PLQY of the nanocrystalline film is increased to 70.5%,and the maximum external quantum efficiency（EQE）of the corresponding green light Pe LED reaches 7.5%.The dual-ligand strategy can also improve fluorescence quantum yield in Cs Pb Br₃ and MAPb Br₃ nanocrystalline films,and the maximum PLQY can reach 80.3%.（2）By adjusting the molar ratio of Rb/Cs,three-dimensional mixed cationic Rb_xCs_1-xPb Br₃ polycrystalline film with blue light emission was prepared.Mixed cationic perovskite nanocrystalline film was in-situ prepared by introduction of PEABr ligand.The results show that mixed cationic perovskite nanocrystals suffer phase separation during crystallization process.Hence,it is necessary to control the anti-solvent dripping time to optimize the crystallization and optical properties of Rb_xCs_1-xPb Br₃ mixed cationic perovskite nanocrystalline film.With the addition of tetraphenylphosphorous chloride（TPPCl）,the homogeneous precursor solution was obtained.Consequently,the separation of mixed cationic perovskite nanocrystals during crystallization and the formation of low-dimensional layered perovskite phase were inhibited,and the PLQY of the film was increased to 47.3%.The maximum EQE of blue Pe LED reaches 2.8%and the emission wavelength is 480 nm.（3）Mixed halide blue perovskite(Cs Pb Br_3-xCl_x)nanocrystals films were in-situ prepared by incorporation of PEABr ligand.The optical and electrical properties of the nanocrystal films were regulated by formamidine acetate（FAOAc）additive.Acetate ions（OAc^-）could promote the dissolution of organic ammonium cations in the antisolvent ethyl acetate and then be in favor of washing away more organic ammonium salts.According to DFT calculation,the thermodynamic stability of layered（n=2）perovskite phase was reduced by incorporation of formamidine ions（FA⁺）,and then the formation of n=2 phase was suppressed.The PLQY and carrier mobility of perovskite nanocrystal film was increased to 59.9%and 47.3 cm² V^-1 s^-1,respectively.The target device exhibits a maximum efficiency of 8.8%at 477 nm.