Research On Film Fabrication And Device Optimization Of All-inorganic Perovskite Light-emitting Diodes

Metal halide perovskite have shown great application potential in optoelectronic devices such as solar cells,light-emitting diodes,photodetectors,and lasers due to its excellent optoelectronic properties.Benefiting from the high fluorescence quantum yield and narrow emission spectrum of perovskite materials,the performance of perovskite light-emitting diodes(Pe LEDs)has been rapidly developed,and its external quantum efficiency(EQE)exceeded 20%in just a few years.However,there are still some key scientific and technical issues at the material and device level in order to further improve the performance of Pe LEDs for commercial applications.Although all-inorganic perovskite materials have higher thermal stability and environmental stability than organic-inorganic hybrid perovskite materials,the narrow-bandgap Cs Pb I₃ films for red light devices are prone to phase transformation at room temperature,which affects device life.And the low solubility of all-inorganic perovskites limits the further development of Pe LEDs performance based on solution method.In addition,the surface plasmon polariton(SPP)mode at the metal electrode interface of Pe LEDs leads to light loss,which seriously restricts the light extraction efficiency of the devices.In view of the above problems,this thesis focuses on all-inorganic perovskite materials and devices.For red-light perovskite materials,the optoelectronic properties of solution-processed perovskite films are improved by regulating the composition of perovskite materials.For the perovskite film prepared by vapor deposition,the defects of the vapor-deposited perovskite film are passivated by the interface layer.For the metal electrode interface loss,the light extraction efficiency of Pe LEDs is improved by introducing a grating structure,which effectively improves the electroluminescence performance of Pe LEDs.The specific research work is summarized in the following three aspects:1.In view of the poor phase stability of the narrow-bandgap Cs Pb I₃ perovskite materials at room temperature,bromide ions were introduced into the perovskite precursor solution.The bromide ions partially replace the iodide ions in the perovskite lattice and adjust the halogen atomic ratio,so the Goldschmidt tolerance factor was adjusted to the range where the cubic perovskite crystal can exist stably.Thus,phase-stable Cs Pb(Br_0.43I_0.57)₃ perovskite film was prepared.In addition,a layer of hole transport material PTAA is inserted between the anode ITO and the hole transport layer PEDOT:PSS.PTAA not only has excellent hole transport properties but also can inhibit the corrosion of the ITO electrode by the acidic PEDOT:PSS.Therefore,by optimizing the composition of perovskite films and the device structure of Pe LEDs,the electroluminescence performance of red Pe LEDs based on all-inorganic perovskite is improved,and its maximum brightness and EQE are 2765cd m^-2 and 0.8%,respectively.2.In view of the problems of many surface defects and poor crystal quality of perovskite films deposited by vacuum vapor deposition,the PEABr interface layers were introduced on both the upper and lower surfaces of perovskite films,which effectively passivated the surface defects and improved the crystal quality of perovskite films.The maximum brightness and EQE of the all-inorganic red Pe LEDs prepared by vacuum vapor deposition can reach 2338 cd m^-2 and 1.75%,respectively.3.In order to solve the problem of light loss caused by SPP mode between metal electrode and organic layer interface in flat Pe LEDs,the grating microstructure with specific period was introduced into the device,which can effectively suppress the light loss of SPP mode and improve the light extraction efficiency of the device.One-dimensional periodic grating microstructures with precise and controllable period and good morphology were fabricated on the substrate by using the laser double-beam interference technique.The perovskite film was prepared by vacuum vapor deposition,which ensured that the grating microstructure on the substrate could be more completely transferred to the interface between the top metal electrode and the electron transport layer,and effectively stimulated the light coupling output of the SPP mode.Thereby the light extraction efficiency of Pe LEDs were improved,and the current efficiency of the device was increased from 0.93 cd A^-1 to 1.69 cd A^-1.