Photoluminescence Properties Of Epitaxial Quantum Dots Heterojunction In Organic Small Molecule Solutions

Due to the high quantum yield,high fluorescence purity and coverage of the entire visible spectrum,excitation range and excellent optical properties,all-inorganic perovskite cesium lead halide quantum dots?QDs?cause widespread concern.However,the perovskite QDs have smaller self-exciton binding energies and many defects which leading to the low quantum efficiency of light emission.In addition,the QDs are extremely unstable and easily quenched under the conditions of water,light and hot oxygen.So the application in the fields of light emission was limited extremely.For the cesium lead halide QDs film by solution method,the preparation of a composite system based on cesium lead halide QDs is one of the important ideas to solve the bottleneck of small absorption cross section of QDs and extreme instability in light,water,heat and oxygen environments.At present,the application of composite system not only enhances the photoluminescence intensity and the quantum yield of the QDs film,but also improves the environmental stability of the QDs.The main research of this paper is to design and construct a composite system based on all-inorganic perovskite CsPbBr₃ QDs.The CsPbBr₃/C8-BTBT composite films are prepared by the composite small molecule 2,7-dioctyl-dibenzothiophene?C8-BTBT?.In this framework,we found that the photoluminescence intensity of the composite film has been significantly improved.In addition,water and light stability of films has been improved.Further,we studied the fluorescence mechanism of the composite film,and determined the reason for the fluorescence enhancement of the film.The main contents are as follows:?1?CsPbBr₃ QDs with uniform size and excellent optical performance are synthesized by high temperature hot injection.And composite films are prepared by dip-coating process.The optical properties such as the fluorescence intensity of the thin films are studied with the change of the degree of complexing with small molecules.In the ultraviolet?361nm?,small molecule C8-BTBT has a strong absorption peak,which provides an effective solution to the problem of the weak light energy absorption as the results of small absorption cross section of QDs.Since the host material CsPbBr₃ QDs and guest material C8-BTBT similar lattice size in a,b axis as well as the energy level distribution which could form Type?heterojunction,it is conducive to enhancing the efficiency of excited state molecules injected into the host quantum dots from guest small molecules and the compound of excited state molecules release photons.We found that fluorescence intensity of composite films increases to 4 times the pure QDs film and the fluorescence quantum yield increases by nearly 38.9%when the small molecules in the high recombination ratio.Through the corresponding X-ray diffraction patterns,it is proved that the high molecular ratio of C8-BTBT lattice in the high recombination rate produces epitaxial growth on the surface of the quantum dot,resulting in eutectic.The interaction between the host and host material lattices enhances the optical properties of the film.Further research can be applied to the composite thin film electroluminescent devices.?2?We applied the inkjet printing technology to the CsPbBr₃/C8-BTBT composite system to prepare regular and well-formed composite films.Inkjet printing process has the features of high precision,direct patterning and low cost,but the traditional organic QD ink is not suitable for printing.In this thesis,the regular composite quantum dot lattice and single-line thin film are printed through substrate selection and processing and program parameter regulation.?3?Furthermore,the stability of CsPbBr₃/C8-BTBT composite film in light and water environment is further explored.The thesis explores the changes of optical parameters such as photoluminescence intensity of composite films under different processing time in light and water environment respectively.It is found that due to the orientation induced by the interaction between the CsPbBr₃QDs and the small C8-BTBT lattice,small molecules form a coating on the surface of quantum dots,effectively preventing the influence of light and water on the quantum dot films.Compared with the pure CsPbBr₃ quantum dot film,the stability of the composite film has been improved.