Blue Light-emitting Properties Of Inorganic Perovskites And Their Device Applications

All inorganic metal halide perovskite materials are widely used in lighting and display fields due to their adjustable luminous color,high carrier mobility,high photoluminescence quantum yield（PLQY）and high color saturation.The development of blue light-emitting perovskite is very slow compared with the high fluorescence quantum yield of red and green light-emitting perovskite and the high external quantum efficiency of the device.Blue emission of light is an essential color in LED tri-color luminescence,so it is very important to improve the luminescence efficiency of blue light-emitting perovskite.In this thesis,we mainly study the improvement of quantum yield of blue light-emitting perovskite and the application of blue light-emitting perovskite in devices from two aspects.The main contents are as follows:（1）The quantum yield of blue light-emitting perovskite can be improved by the combination of AgNPs and inorganic perovskite CsPb（Br/Cl）₃.Spherical AgNPs were prepared by reduction method,and proved that AgNPs can resonate with CsPb（Br/Cl）₃nanocrystals by testing the surface plasmon resonance peak of silver nanoparticles.Ag@CsPb（Br/Cl）₃perovskite nanocrystals were synthesized by high temperature injection from silver solution and CsPb（Br/Cl）₃perovskite.The quantum yield of composite perovskite increased from 43%to 77%by adding the proper amount of nano-silver solution.Through the characterization of time-resolved photoemission spectroscopy（TRPL）,it is further proved that the addition of AgNPs increases the radiative decay rate of CsPb（Br/Cl）₃nanocrystals,shortens the lifetime of excited states,and thus improves the quantum yield of the composites.The optical constants measured by the elliptic polarization method and the finite difference time domain method are used for theoretical simulation.The results show that the maximum electric field intensity increases with the increase of the size and number of AgNPs.However,excessive AgNPs will reduce the quantum yield of perovskite,which is mainly due to the reduction of electric field intensity and a large number of surface defects caused by the combination of too many AgNPs and perovskite.These results indicate that Ag@CsPb（Br/Cl）₃nanocrystals have a lot of potential for development of efficient blue ray devices.Perovskite LEDs were fabricated with an ITO/PEDOT:PSS/Poly-TPD/perovskite/TPBi/Al structure.The as-prepared LEDs with Ag@CsPb（Br/Cl）₃nanocrystals emit bright blue light,and their brightness is significantly higher than that of pure perovskite,but the stability and brightness of the electroluminescence devices still need to be improved.However,the improvement of blue brightness also lays a good foundation for the follow-up work of light-emitting devices.（2）The quantum yield of the blue emission is improved by doping Sb³⁺in the inorganic double perovskite Cs₂NaInCl₆.Commercial application of CsPb X₃perovskite is limited due to its lead toxicity.In this thesis,the stable and non-toxic blue emission of double perovskite Cs₂NaInCl₆:Sb crystal has been studied.The non-luminescent Cs₂NaInCl₆crystals were prepared by the hydrothermal method,and the blue emission of Cs₂NaInCl₆:Sb double perovskite was successfully prepared by self-trapping exciton（STE）of Sb³⁺,the quantum yield is 60%.The first principle calculation shows that the doping of Sb³⁺breaks the parity-forbidden transition of the Cs₂NaInCl₆double perovskite and effectively modulates the density of states（DOS）,thereby greatly increasing the PLQY of blue STE emission.The quantum yield decreased by only 3%after 45 days of exposure to air,further illustrating the stability of the dual perovskite in air.In order to realize the application of Cs₂NaInCl₆:Sb double perovskite in white light-emitting diodes（WLED）,the cold white and positive white LEDs were successfully prepared by mixing blue,red,and green light-emitting phosphors based on the principle of three primary colors.The white emission of the double perovskite was directly prepared by using the principle of double peak modulation.The Cs₂NaInCl₆:Sb crystal was further doped with Mn²⁺,and the double peak appeared at 460 nm and 620 nm.By adjusting the content of Mn²⁺,the double peak was regulated,and the cold white light emission of double perovskite was systematically studied.