Modulation Of Optoelectronic Properties Of Quasi-Two-Dimensional Perovskite Films And Fabrication Of Efficient Light-Emitting Diodes

As a direct bandgap semiconductor material,metal halide perovskite exhibits excellent optical and electrical properties,making it great potential in light-emitting diodes(LEDs).In recent years,with the in-depth study on perovskite,quasi-two-dimensional perovskite with larger exciton binding energy and faster exciton recombination rate have received extensive attention.This thesis focuses on the study of quasi-two-dimensional perovskite materials and LED devices.By optimizing the phase distribution to modulate optoelectronic properties of the film,the perovskite films with high photoluminescence quantum efficiency are prepared,and the resulting LEDs with optimization of interface engineering show high performance.The main work includes the following:1.The phase distribution in quasi-two-dimensional perovskite is of great importance for the emission efficiency of the films.The effects of methanesulfonate(MeS)additive on the interaction of organic ligands during the crystallization of perovskite films and the phase distribution of the resulting film were investigated.Through density functional theory calculations,we found that the organic ligand BA prefers to bind with MeS through hydrogen bonding rather than Br anion of the inorganic perovskite framework,which provides us with the theoretical guidance for the control of the phase distribution in the quasi-two-dimensional perovskite film.Transient dynamics result indicates that the ratio of energy acceptor-to-donor is increased after the introduction of MeS,which enhances the energy transfer in perovskite films.Fourier transform infrared absorption and X-ray photoelectron spectroscopy analysis show that MeS can eliminate uncoordinated Pb²⁺,thereby reducing exciton loss in energy transfer process.By smoothing energy transfer pathways,we had obtained perovskite films with photoluminescence quantum yield of73%,which is 1.5 times higher than that of original films.2.The organic polymers with high hole mobility and matched energy level alignment have been widely used as a hole transport layer in perovskite light-emitting diodes.However,the perovskite precursor shows strong hydrophobicity on such materials,which makes it difficult to deposit a dense film on the substrate.Here,the hole transport layer was modified by polyvinylpyrrolidone(PVP)which has a strong hydrophilic group(pyrrolidone group)and hydrophobic group(alkyl),greatly reducing the contact angle of the perovskite precursor on it.The films deposited on the strongly hydrophobic HTL show reduced roughness and full coverage.Besides,the C=O group of PVP can passivate uncoordinated Pb²⁺of the perovskite,which effectively decreases the interfacial defect served as non-radiative recombination sites.Therefore,we had fabricated perovskite LEDs with a maximum external quantum efficiency of20.5%,which is the record value of quasi-two-dimensional perovskite LEDs to date.3.Tandem LEDs provide a strategy for achieving high brightness,high efficiency and long operational lifetime at low current density.In this paper,an efficient charge generation unit(Bphen:Cs₂CO₃/Al/HAT-CN/Mo O₃)was designed and a new tandem perovskite-organic LED device was fabricated.The charge generation layer Bphen:Cs₂CO₃/Al/HAT-CN has a large energy barrier with the adjacent transport layer,resulting in weak charge generation,separation and injection capabilities.The charge generation unit composed of a charge generation layer and a hole injection layer Mo O₃(1 nm)has strong charge generation,separation and injection capabilities due to the gradient energy level,which makes the tandem device obtain high performance.Consequently,we had fabricated a green tandem LED with external quantum efficiency>34%,brightness>200,000 cd m^-2,power efficiency>47 lm W^-1,and T₅₀ lifetime>2230 h.