Preparation Of All-inorganic Perovskite Quantum Dots And Their Applications In Optoelectronic Device

Wide varieties of quantum dots?QDs?luminescent materials have been found.Traditional quantum dots are mainly composed of elements?-?race such as CdSe and elements?-?race such as InP.Compared with traditional quantum dots,perovskite quantum dots?PQDs?do not require a core/shell structure,which not only reduce the costs,but also exhibit superior optical properties?such as higher photoluminescence quantum yield?PL QY?,wider excitation spectrum,narrower emission spectrum,tunable emission spectrum,etc.?.These characteristics also make PQDs one of the most promising optoelectronic materials at present,and thus these emerging nanomaterials have been widely used in light-emitting diodes?LEDs?,solar cells,photodetectors and other fields.Nevertheless,the development of perovskite nanomaterials has been constrained by their poor stability,which means PQDs are particularly sensitive to the environmental factors such as water,light,and heat.Therefore,in this paper,the research on improving the stability of perovskite quantum dots has been carried out,and the prepared efficient and stable perovskite quantum dots also show tremendous potential in photovoltaic devices,which will further promote the development of perovskite nanomaterials as good candidates for the photoelectric devices in the future.In this dissertation,all-inorganic perovskite quantum dots CsPbX₃?X=Cl,Br,I?are taken as the research object.Stepping from the synthetic route of all-inorganic perovskite quantum dots,the optimization of the synthesis strategy through the regulation of ligand,temperature,reaction time and composition has been put to achieve the precise regulation of perovskite quantum dots.Not only does it improve the stability of the perovskite quantum dots,but also it maintains a high fluorescence quantum efficiency without any attenuation.On the basis of this work,the high-efficiency perovskite quantum dots are applied to optoelectronic devices.The detailed research contents and consequences are as follows:1.The controllable and efficient mixed halide CsPbX₃ PQDs were prepared by hot injection method.In summary,the single-and mixed-halide CsPbX₃ PQDs were synthesized via the hot injection technique.The surface ligands were strongly coordinated onto the surface of the PQDs,hence optimizing the optical properties and improving the stability of the resulting CsPbX₃ PQDs.The friendly double ligands OA/OAm were used instead of the traditional OA/OAm/TOP mixture to synthesize the PQDs.As compared with the previous strict synthesis processes which needed vacuumization or/the glovebox equipment,our method is rather simple to prepare high-quality PQDs through accurately controlling the ratio of different halide atoms and the hot injection technique.The resulting PQDs have high PL QY?40-95%?,narrow FWHM?the narrowest FWHM<10 nm?,tunable band gap?408-694 nm?in the entire-visible-light window,and most importantly they show strong photostability,which will bring wide applications for PQDs in photoelectric devices,such as LEDs and solar cells.2.CsPbBr₃ quantum dots were doped into a blend of poly?3-hexylthiophene?and indene-C60 bisadduct to fabricate bulk heterojunction polymer photodetectors. The addition of the QDs significantly increased the shunt resistance of the device, thereby suppressing the reverse leakage current and improving both the signal-to-noise ratio and the specific detectivity.The photoresponse and recovery time both decreased because of the enhanced built-in electric field and the improved charge carrier mobility.3.Based on the original hot injection method,the gradual transformation process from CsPbBr₃ PQDs to Cs₄PbBr₆ PNCs was achieved by adding ZnBr₂ as a revulsive and reducing the amount of Pb at the same time.During the transformation process from CsPbBr₃ PQDs to Cs₄PbBr₆ PNCs,the QY of the remaining CsPbBr₃ PQDs still maintains higher almost up to 99%owing to the process of“Survival of the fittest”that occurred in the CsPbBr₃ PQDs and the decrease of the nonradiation process.Interestingly,when the revulsive content was increased to 95%,we obtained approximately single phase 416-structure Cs₄PbBr₆ PNCs.By monitoring their absorption and emission spectra,we obtained an absoption peak at 313 nm and an emission peak at 336 nm,which is consistent with previous theoretical studies,thus obtaining the precise luminous peak position of the 416-structure Cs₄PbBr₆ PNCs.It is further directly clarified that the green emission peak previously seen in the hybrid structures of the416-structure and the 113-structure exclusively comes from the luminescence of the 113-structure rather than from the 416-structure.As a result,we firstly succeeded in preparing the green light LEDs based on the remaining optimized CsPbBr₃ PQDs.The maximum value of the luminance is up to 1941.6 cd m^-2 and the maximum EQE is about 1.21%,which opens up a new avenue for acquiring high efficiency fluorescent CsPbBr₃ PQDs and the corresponding fruitful photoelectric devices in the future.