Preparation Of High Efficiency Quasi-two-dimensional Perovskite Light-emitting Diodes Through Organic Molecule Passivation

Quasi-two-dimensional（quasi-2D）perovskite light-emitting diodes（Pe LED）are considered as one of the most promising candidates in the field of electroluminescence due to their unique quantum confined effect and excellent photothermal stability.However,due to the uneven distribution of the energy domain,serious non-radiative recombination occurs in the energy transfer process,which greatly hinders the performance and applications of Pe LED.This thesis detailly perform characterization of the transient absorption characteristic of the perovskite thin films,and the energy transfer process of carriers and combination dynamics are studied in depth.The radiation recombination characteristics of perovskite films were optimized from two aspects of adjusting the low-dimensional phase distribution and defect passivation.Thus,the perovskite films with uniform phase distribution and low defect density were prepared,which suppressed the non-radiation recombination of carriers and greatly improved the photoluminescence characteristics of the films.In addition,we prepared the optimized quasi-two-dimensional film into perovskite LED devices,and achieved the electroluminescence of green and blue perovskite LED respectively.With the help of organic additives,the device performance has been greatly improved,as follows:1.Research on green quasi-2D perovskite LEDs,we propose to introduce 5-aminovaleric acid（5AVA）to perovskite precursor solution prior to one-step spin casting.Hydrogen ions spontaneously dissociate from the carboxylic acid in 5AVA and bind to the amino group.The negatively charged-COO^-and positively charged-NH₃⁺strongly coordinate with dissociative Pb²⁺ions and halogen atoms,respectively.These interactions manipulate the formation of low-dimensional phases,leading to greatly concentrated distribution of low-dimensional phases towards large n values,favoring the exciton energy transfer to the radiative regions.Besides,the O atom from-COO^-group acts as a Lewis base and well passivates the surface halogen-vacancies at grain boundaries due to its electron-rich property.As a result,our champion Pe LEDs yield a maximum EQE of 19.3%with high brightness of 11782.22 cd m^-2 as well as current efficiency of 61.8 cd A^-1.We also prepared the large-area perovskite LEDs based on the5AVA passivation;the active area is 0.9 cm².The maximum EQE of 9.78%with brightness of6157.6 cd/m² was achieved.2.Research on blue perovskite film and LEDs.Two types of large organic cations（Phenethylammonium bromide and 2-Thiophenethylammonium bromide）were used to prepare quasi-two-dimensional perovskite films,and the effect of gradient doping on the luminescence peaks was investigated respectively.It is found that the optical properties of perovskite films can be significantly improved by doping large cations,and the quantum fluorescence yield of the films is significantly increased.In addition,atomic force microscopy（AFM）showed that the film surface morphology was greatly improved and the average roughness decreased significantly.These characteristics are conducive to the preparation of efficient blue light devices.Furthermore,double cationic doping was used to improve the photoluminescence and electroluminescence properties of perovskite,and the external quantum efficiency of blue quasi-two-dimensional LED prepared by us reached 6.6%.