Control And Research Of Halogen Precursors On Properties Of All-Inorganic Metal Halide Perovskite Nanocrystals

Metal halide perovskite materials have flourished in recent years and have been widely used in popular research fields such as solar cells,photodetectors,lasers,light-emitting diodes(LED)and photocatalysis due to their excellent optical properties and low-cost solution processability,and made a series of research progress and breakthroughs.From the perspective of the most basic material synthesis,this thesis improves the photophysical and chemical properties and structures of two important perovskite materials-lead-based and lead-free perovskite nanocrystals through the selection and optimization of a series of halogen precursors.stability,and elucidated the key principle of property improvement,and finally developed and fabricated pure blue LED devices based on this.In the field of colloidal perovskite synthesis,the most commonly used preparation method for high-quality perovskite nanocrystals is hot-injection,and the commonly used halogen sources are mostly silyl halides(TMSX,X=Cl,Br,I),benzoyl halides(Bz-X)and other long carbon chain organics.Although these halides can provide halide ions and regulate the growth of nanocrystals to a certain extent,they are toxic,highly volatile,and flammable,which are not conducive to the large-scale preparation and commercial utilization of materials.To address this issue,the first part of this work explores the feasibility of the all-inorganic germanium salt GeX4(X=Cl,Br,I)as a halogen source to synthesize lead-based metal halide perovskite nanocrystals CsPbX3.It is found that CsPbX3 nanocrystals can be successfully prepared by using GeX4 as a halogen source,and the crystal structure stability and photoluminescence quantum yield(PLQY)of the nanocrystals prepared based on GeX4 are obvious compared with the traditional TMSX and Bz-X halogen sources.improvement.At the same time,germanium halide also supports two simple ways of halide precursor mixing and post-synthesis anion exchange to synthesize halogen-mixed nanocrystals,especially CsPb(Cl0.5Br0.5)3 nanocrystal,its fluorescence peak is extremely narrow and the emission position is in the pure blue light band(～460 nm),and the PLQY also reaches more than 90%,which is one of the most efficient blue light emitting materials at present.Inspired by the work on lead-containing perovskites,the second part of the work uses GeX4 as a halogen source to synthesize all-inorganic non-lead halide perovskite nanocrystals.The study found that the use of GeX4 can not only successfully synthesize a series of all-inorganic non-lead perovskite nanocrystals such as Cs2AgInCl6,Cs4MnBi2Cl12,Cs2AgBiBr6 and Cs3Sb2I9,but also under the same synthesis conditions,by comparing with the traditional halogen source TMSX,the preparation of germanium halide The particle size distribution of the nanocrystals is smaller,the fluorescence intensity is stronger,the fluorescence lifetime is longer,the phase stability and PLQY are also significantly improved,and the Ge element is not introduced into the final perovskite lattice to change the target product.Basic structural properties.In order to further understand and elucidate the key principles and functional basis for the synthesis of high-quality perovskite nanocrystals from germanium halides,we have further investigated the chemical energies of halogen atoms in various halides with the help of theoretical calculation tools,and found that Germanium halides have stronger binding and activation energies of halogen atoms than traditional organic halides,which are beneficial to the regulation of crystal size and surface defects during nanocrystal reactions.The research results of this work show that GeX4 can be used as an ideal halogen source to replace traditional highly toxic organic halides to synthesize all-inorganic metal halide nanocrystals with higher optoelectronic properties and apply them to high-performance optoelectronic devices.