Regulation Of Energy Band And Luminescence Properties In Blue Quasi-2D Lead Bromide Perovskite Via Lattice Strain

Metal halide perovskite materials have the advantages of low cost,solution preparation,and continuously tunable color,which can be used in display,lighting,and optical communication fields.In perovskite light-emitting devices,quasi-two-dimensional perovskites have apparent advantages,such as better device stability and lower heat loss of devices.However,the research on blue-light perovskite light-emitting diodes still has a considerable challenge.The development of blue quasi-two-dimensional lead halide light-emitting devices is the key to perovskite-based full-color displays and white-light illumination.Therefore,the research of perovskite blue light-emitting devices has become a research hotspot of scholars in recent years.Lattice strain is closely related to the energy band,luminescence properties,and thermal properties of blue quasi-2D lead bromide perovskites.This thesis mainly focuses on regulating and optimizing blue quasi-two-dimensional perovskite via lattice strain.This thesis is divided into the following two parts:（1）By introducing the A-site（PEABr）organic large cation,the size of the perovskite is controlled to realize the quasi-2D perovskite.The composition of 2D perovskite is then adjusted by adjusting the lattice strain by changing the concentration of three cations of different sizes:Cs⁺,CH₃CH₂NH²⁺（EA⁺）,and Rb⁺to fine-tune the lattice strain to achieve global lattice expansion and lattice contraction.A new ternary quasi-two-dimensional bromide perovskite material,PEA₂(Cs_xEA_yRb_1-x-yPb Br₃)₂Pb Br₄,was specially designed.First-principles calculations to study crystal structure and energy bands using density functional theory（DFT）methods.The luminescence properties of blue quasi-2D lead bromide perovskite materials were analyzed,with spectra tuned to photoluminescence from 508 nm to 464 nm and electroluminescence from 510 nm to 470 nm.Heat treatment is used to accelerate the release of residual strains due to lattice mismatch and disorder,which can lead to defect degradation.（2）A series of optimizations have been carried out on the quasi-2D perovskite device.The optimization is carried out from three aspects,namely,precursor concentration,the hole transport layer,and solvent engineering,respectively.First,the attention of the precursor is regulated,and the precursors with the concentration of 0.2 M,0.3 M,and 0.4M are used,respectively.It can be found that the most suitable precursor solution is the concentration of 0.2 M.Then,the vacancy transport layer was tuned by doping poly（4-styrene sodium sulfonate）（PSS-Na）into PEDOT:PSS solution to increase the work function of HTL,thereby lowering the potential barrier of the perovskite layer and promoting Hole transport.The perovskite films deposited on the modified PEDOT exhibited uniformly covered surface morphology without any defects,increasing the PL intensity.In particular,perovskite films coated on dopant-modified HTL exhibited better crystallinity and reduced emission quenching.The luminescence peak is PEDOT:PSS+PSS-Na HTL PELED device,the maximum brightness is 3633 cd/m² at 498 nm,and the maximum current efficiency is 11.7 cd/A.When preparing the perovskite light-emitting layer,chlorobenzene（CB）and ethyl acetate（EA）were used as anti-solvents to analyze the perovskite thin films.It was found that the film using ethyl acetate as the anti-solvent had better crystallization and morphology than the perovskite film,resulting in improved carrier transport and crystalline properties,and obtained dense perovskite film and small perovskite film.Finally,a high-brightness quasi-two-dimensional perovskite light-emitting diode device was obtained.Compared with the standard device,the device obtained by anti-solvent engineering showed a significant improvement in maximum brightness.The study of lattice strain relaxation in blue quasi-2D lead bromide perovskite could open avenues for high-performance and stable blue quasi-2D perovskite LEDs.