Preparation And Optical Properties Of Novel Lead-free Perovskite Nanomaterials

The photoelectric conversion efficiency of 3D Pb-based perovskite solar cells has developed from the initial 14.9%to the current 22.1%in just a few years.Its outstanding photoelectric performance and application prospect have become a hot research topic.Perovskite nanomaterials have attracted extensive attention due to their high quantum yield,and the fact that they can regulate fluorescence emission in the whole range of ultraviolet and visible light.However,the toxicity of lead will do great harm to human body and environment,and perovskite nanocrystals are also very unstable in the air,which is not conducive to their practical application.Therefore,it is very important to develop lead-free perovskite nanomaterials with low toxicity and high stability.Three lead-free perovskite quantum dots?NH₄?₃Sb₂X₉,organic-inorganic hybrid MA₂CuBr₄ and pure inorganic Cs₂CuX₄ were prepared by ligand-assisted reprecipitation?LARP?method in this thesis.Its basic properties and optical properties were studied by a series of characterization methods.?1??NH₄?₃Sb₂X₉ quantum dots were prepared at room temperature,with ammonium halide and antimony halide as raw materials.By analyzing its morphology,structure and optical properties,it is found that the synthesized?NH₄?₃Sb₂Br₉ quantum dot is quasi-spherical with regular morphology and uniform size.The UV absorption peak was 310 nm and the fluorescence emission peak was 410 nm,showing weak self-absorption and high quantum yield and stability.The synthesized?NH₄?₃Sb₂I₉quantum dot has a weak fluorescence emission peak at 525 nm.Through anion exchange reaction,the fluorescence emission peak of?NH₄?₃Sb₂X₉ quantum dots can be tuned in the blue light range from 384 nm to 435 nm.?2?MA₂CuBr₄ quantum dots were prepared from methylamine bromide and copper bromide at room temperature.The morphology,structure and optical properties of the synthesized quantum dots were analyzed,and it was found that the synthesized quantum dots were quasi-spherical with regular morphology and an average diameter of 2.7±0.1 nm.Moreover,it also has excellent optical properties.The UV absorption peak is at 280 nm,and the fluorescence emission peak is at 397nm.The fluorescence intensity is very strong,and the quantum yield is as high as32.7%.?3?Cs₂CuX₄ quantum dots were prepared with cesium bromide and copper bromide,cesium chloride and copper chloride as raw materials under open environmental conditions at room temperature.By analyzing its morphology,structure and optical properties,it is found that the synthesized quantum dots are quasi-spherical with regular morphology and uniform size.Compared with organic-inorganic hybrid cupric perovskite quantum dots,these pure inorganic cupric quantum dots show better optical properties and stability.The quantum yield of Cs₂CuBr₄ quantum dots is 37.5%,while that of Cs₂CuCl₄ quantum dots is as high as51.8%,which is nearly 10 times higher than that of other lead-free chlorine-based perovskite quantum dots.In addition,the particle size and fluorescence emission peak of quantum dots can be tuned by adjusting the molar ratio of raw materials,so that it can be adjusted within the range of blue-green light.