Research On Quasi-2D Perovskite Blue Light-Emitting Diodes Using Mixed Organic Ligands

Perovskite materials have many advantages,such as simple preparation process,high color purity and high fluorescence quantum yield,which make perovskite materials have excellent application prospects for electroluminescent devices.The highest EQE of near-infrared,red and green perovskite LED is more than 20%.The EQE of perovskite LED is close to that of commercial LED.However,blue perovskite LED also has some problems,such as low efficiency,spectral instability,short life and so on.How to prepare efficient and stable of blue perovskite LED becomes the key to realize the application of perovskite LED in the field of panchromatic display.With the deepening of the research on blue perovskite LED,quasi two-dimensional perovskite materials show their unique advantages in high efficiency blue perovskite LED.This paper mainly studies the blue perovskite devices from the aspect of mixed organic ligands.This paper is divided into the following parts:(1)Quasi two dimensional perovskite LED was fabricated by all-solution method,and the device luminescence was realized successfully.The all-solution method is a solution to spin coating the transport layer and the light-emitting layer.This method is simple to operate and can reduce the complex steps,but compared with the traditional evaporation method,the performance of the device is lower.Two organic ligands,ethylammonium bromide(EABr)and phenylethylammonium bromide(PEABr),were added to the three-dimensional perovskite Cs Pb Cl_0.9Br_2.1with mixed halogen to form quasi two dimensional perovskite.Excellent fluorescence properties of quasi two dimensional perovskite is based on PEABr and EABr inhibites the formation of high n phase.By adjusting the ratio of the two ligands,it is found that the ratio of the two ligands affects the n phase distribution.It can be seen from the photoluminescence spectrum that the emission peak shifts to a shorter wavelength.The electroluminescence peak of the device changes from 478 nm with 0%EABR to 466 nm with 50%EABR,and the brightness of the device is almost unchanged.Finally,a pure blue perovskite device with maximum brightness of 20 cd/m² and maximum EQE of 0.2%and emission peak below470 nm is obtained.(2)The blue perovskite devices prepared by mixed halogen have the problem of red shift of emission peak.In order to solve this problem,pure brominated perovskite Cs Pb Br₃ was selected as the research object.In addition to the organic ligand PEABr,1,3-propyldiammonium bromide(PDADBr),was added to form the quasi two dimensional perovskite with pure bromine.The feasibility of the new ligand PDADBr was proved by the characterization of the film.This organic ligand can not only adjust the n phase distribution,realize the blue shift of luminescence peak,but also improve the surface morphology of the film,passivate the defects of the film and improve the fluorescence performance of the film.When the concentration of PDADBr is 10%,the fluorescence intensity of the film is the highest,and the fluorescence decay lifetime increases from 2ns to 13 ns,and the surface roughness decreases to 1.7 nm.The electroluminescence peak of the device moves from 508 nm(green light)to 480 nm(blue light).The maximum brightness of the device can reach 100 cd/m²z and the maximum EQE is nearly 1%.