Research On The Light Emission Of Two-dimensional Hybrid Perovskite Monocrystalline Films

Organic-inorganic hybrid perovskites have superior optoelectronic properties and show broad application prospects in high-performance functional devices,such as solar cells,light-emitting diodes(LEDs),and photodetectors.Due to the unique quantum well structure,compared to three-dimensional(3D)perovskites,the two-dimensional(2D)organic-inorganic hybrid perovskites possess many outstanding properies,such as greater exciton binding energy,higher adjustability and better stability,and have become potential candidates for the next-generation optoelectronics.In addition,the novel photophysical phenomena of the 2D organic-inorganic hybrid perovskites have also attracted widespread attention,such as spin-selective Stark effect and laser cooling.Although the 2D perovskites have great advantages,the serious trap states still greatly limit the practical application of the 2D perovskites in optoelectronic devices.Besides,the optical emission and the dynamics of the2D perovskites still need to be further studied.In this thesis,large-size,high-quality 2D organic-inorganic hybrid perovskite monocrystalline films are prepared by the anti-solvent vapor-assisted crystallization method.Then,we perform systematic studies on the optical emission and the related ultrafast dynamics of the prepared 2D perovskite monocrystalline films by optical platforms.The main contents are as follows:(1)We study the effects of the lighting environment on the crystal quality and photoelectric properties of the 2D organic-inorganic hybrid perovskite.We prepare(PEA)₂PbI₄ monocrystalline films under three different illumination conditions(with no light illumination,white-light illumination,and UV-light illumination),and then study the effects of light illumination on the crystal quality and optoelectronic properties of them.Compared to the(PEA)₂PbI₄ monocrystalline films grown in the dark condition,the intensity of the PL emission of those grown under UV-light illumination is increased by?3.1 times,and the proportion of the defect-assisted recombination is greatly reduced.Besides,the optoelectronic response(I-V curve),spectral responsivity,optical switch characteristics,transient photocurrent response,frequency response,detectivity and noise power density of the photoelectric detector based on the(PEA)₂PbI₄ monocrystalline films are greatly optimized by UV light.It indicates that UV light can conveniently and effectively improve the crystal quality of the(PEA)₂PbI₄ monocrystalline films,and optimize the photoelectric performances of the devices based on them.This work shows that using appropriate light irradiation is expected to be a novel and convenient method for optimizing the quality of 2D organic-inorganic hybrid perovskite,which is beneficial for the development of 2D perovskite multifunctional devices.(2)We explore the light-matter interaction of 2D organic-inorganic hybrid perovskite under laser irradiation.We find that under continuous two-photon excitation,the intensity of the two-photon-absorption induced PL(TPPL)of the(PEA)₂PbI₄ flake increases with time and gradually becomes?3.7 times of the initial intensity,and the PL lifetime is also extended from the initial 2.17 ns to 2.93 ns.These phenomena indicate that the defects in the(PEA)₂PbI₄ flake are gradually reduced under laser irradiation.By testing the distributions of the elements and monitoring the PL emission evolution traces of the(PEA)₂PbI₄ flakes in different atmospheres,we prove that the TPPL enhancement of the(PEA)₂PbI₄ flakes is caused by the oxygen in the air.Then,through further study and analysis,we propose a photo-induced oxygen-diffuesd trap-passivation model to reveal the ultrafast dynamics and the physical mechanism for the light-matter interaction of the 2D organic-inorganic hybrid perovskite under laser irradiation.In addition,we also prove that the trap-passivation process in 2D perovskite can diffuse to more than 10?m in the plane and has a good reversibility.The photo-induced oxygen-diffuesd trap-passivation model proposed in this work is universally applicable to 2D organic-inorganic hybrid perovskites.This work has an important guiding role in revealing the light-matter interaction of the 2D perovskites,and shows great promise for improving the performances of the 2D perovskite functional devices.(3)We investigate the energy exchange process in the perovskite heterostructure.We prepared high-quality(PEA)₂PbI₄/MAPbBr₃ perovskite heterostructure by the directional transfer method.Under two-photon excitation,the PL emission of the heterojunction region almost comes from the MAPbBr₃ microplate,and its PL intensity is?6.5 time of the PL intensity of the pure MAPbBr₃ microplate.While,the PL from the(PEA)₂PbI₄ flake is almost completely quenched in the the heterojunction region.We prove that these phenomena are due to the large amount of overlap between the absorption spectrum of the MAPbBr₃microplate and the emission spectrum of the(PEA)₂PbI₄ flakes,which induces energy transfer.Through further research,we demonsrate that the energy transfer process in the(PEA)₂PbI₄/MAPbBr₃ perovskite heterostructure occurs on an ultra-fast time scale(?50 ps),and the energy transfer efficiency is close to 100%.In addition,the energy transfer process in the(PEA)₂PbI₄/MAPbBr₃ heterostructure is strongly dependent on the thickness of the samples and the wavelength of the excitation light.This work reveals the interlayer interaction in the perovskite heterostructure,and the ultra-fast and efficient energy transfer in the perovskite heterostructure will have great potential in the field of high-performance optoelectronic devices.