Surface Ligand Modification Of Halide Perovskite Nanocrystals And Study Of Their Photophysical Propertie

The solution processability,easy preparation and excellent photophysical properties of halide perovskite nanocrystals(NCs)have made remarkable application achievements in optoelectronic devices such as solar cells,light emitting diodes(LEDs)and lasers in the past few years,showing broad application prospects.The quantum confinement effect closely related to its luminescence characteristics,the abundant surface states as well as the strong interaction between surface ligands and surface atoms caused by crystal ionic properties are important sources of excellent optical properties of halide perovskite NCs.Therefore,improving their optical properties and structural design principles attract a lot of research interest.Although the synthesis process of halide perovskite NCs is simple,too fast crystal formation process makes it difficult to monitor the growth dynamics of NCs formation.Therefore,it is difficult to comprehensively understand the evolution process of halide perovskite NCs.In addition,the influence of strong quantum confinement on the exciton state and exciton recombination process of halide perovskite NCs are not clear enough.The influence of the electronic state of surface ligands on the photophysical process of halide perovskite NCs is to be determined.Therefore,in this thesis,ligand and coordination are used to systematically study the growth,morphology,exciton state and exciton dynamics of NCs related to the quantum confinement effect and surface effect mentioned above.The main contents are as follows:(1)A simple one-step one-pot method for the synthesis of CsPbX3 NCs was proposed without the process of precursor preparation and injection.The formation and growth process of NCs was discussed by monitoring the spectrum of the reaction process.Compared to classical synthesis method,this non-injection synthesis method has relatively slow nucleation and growth kinetics.At the same time,without the temperature gradient and injection speed diversity bring less intrinsic variables to the reaction,which improves controllability and predictability.By preparing NCs with a variety of morphological characteristics and halogen components,the universality and usability of the synthesis method are proved,and the applicability of this method in basic photophysical research of NCs is highlighted.In addition,primary growth mechanism study of such CsPbX3 nanostructures reveals that the ionization state of H2O mediates the CsPbX3 NCs shapes.(2)Blue emission CsPbBr3 NCs with extremely small crystal size(1-2 nm)but high photoluminescence quantum yield(PLQY,72.4%)are synthesized with a new surface ligand,single(6-amino-6-deoxy)beta cyclodextrin(6A-βCD),which is also acting as the confined growth templates for such small QDs.The intrinsic photophysical mechanism of multiple photoluminescence(PL)peaks in ultra-small CsPbBr3 NCs are revealed by PL spectrum,time-resolved photoluminescence(TRPL)spectrum and transient absorption spectrum(TAs).Strong quantum confinement effect caused by the ultra-small size increases the exciton binding energy(113.8 MeV).The enhancement coupling of exciton and lattice lead to the energy transfer,and the emergence of self-trapped excitons as well as PL2,PL3 and PL4 with long wavelength emission.The bright blue emission origins from the recombination process of excitons(free excitons and self-trapped excitons)enhanced by higher exciton binding energy.(3)The size and emission of inorganic perovskite CsPbBr3 NCs are simply and effectively controlled by using different different proportions of electronegative ligands 2-acrylamide-2-methylpropionic sulfonic acid(AMPS)and oleic acid(OA),and abnormal PL shifts different from the classical quantum confinement effect are observed.AMPS has stronger electronegativity than OA and can absorb more CS+ and Pb2+ions in the precursor.With the increase of AMPS,the size of NCs increased,but the PL emission exhibited blue shift.TRPL and TAS further confirmed that the binding of ligands to excited hot electrons is the physical origin for such abnormal photoluminescence behavior of CsPbBr3 NCs,exhibiting anomalous quantum size effects.