Strong-Confined Blue-Emitting Cesium Lead Bromine Perovskite Quantum-Dots And Their Light-Emitting Diodes

Perovskite quantum dots(QDs)light emitting diodes(LEDs)with wide color gamut and high color-purity are considered to be the most ideal light-emitting component for the next-generation high-definition display.Compared to red and green perovskite QDs LEDs,the efficiency and stability of blue perovskite QDs LEDs are still insufficient.Research has shown that stable blue light emission can be achieved by reducing the crystal size of CsPbBr3 QDs.However,strongly confined CsPbBr3 QDs are prone to form a wide size distribution during the synthesis process,resulting in low color purity,high defect states density,and poor optical performance.Therefore,this paper systematically studied the formation process and mechanism of strongly confined CsPbBr3 QDs,developed a new synthesis process for narrow size distribution and high color purity cesium lead bromide QDs,designed a dual functional ZnMgO electron transport layer,and obtained high color purity and high efficiency pure blue light CsPbBr3 QDs LED.The main research work is as follows:In this paper,a stepwise synthesis method was developed to explore the formation process of perovskite QDs.The first step is to mix and dissolve lead trihydrate acetate,cesium carbonate and benzoyl bromide to form a crude solution.Then the crude solution is transformed into perovskite QDs by adding polar alcohol.The formation rate of the perovskite QDs can be adjusted by the amount of added polar alcohol.Research found that the synthesis of perovskite QDs undergone three formation steps:PbBr3-complexes.PbBr64 octahedrons and perovskite crystals.The clear formation process lays the foundation for the controllable synthesis of perovskite QDs.Based on the formation process of perovskite QDs and LaMer nucleation theory,a strong-confined bromine-based perovskite QDs with narrow size distribution was synthesized.An in-situ PL system was constructed to monitor the nucleation and growth of perovskite QDs with different Br/Pb ratios.For a high Br/Pb ratio precursor,the monomer supply rate and nucleation speed are accelerated and the Ostwald ripening process is suppressed.As a result,a uniform(relative standard deviation of 9.6%)and strong-confined monodispersed CsPbBr3 QDs was achieved.Due to narrow size-distribution,the strong-confined monodispersed CsPbBr3 QDs presented a pure-blue emission(460 nm)with full-width at half-maximun(FWHM)of 20 nm.Besides,a high Br/Pb ratio reduces the halide vacancy defects of perovskite QDs,and the PLQY is increased to 97%.This article uses the strongly confined blue emission QDs mentioned above to prepare LEDs.Before preparing LEDs,QDs must be cleaned to remove excess organic ligands and byproducts from the QDs solution,ensuring high carrier mobility of the QDs film.This article used dodecylamine(DDAM)and phenylethylamine(PEA)to exchange with the long-chain oleylamine ligands,achieving pure-blue perovskite QDs with high luminous efficiency and high carrier mobility.Based on these QDs,a LEDs with configuration of ITO/PEDOT:PSS/PVK/perovskite QDs/ZnMgO/Ag was prepared by all solution process.Optimizing the parameters of various functional layers,the pure-blue perovskite LEDs with EQE of 4.9%and an emission peak was 470 nm were realized.Further,the LEDs present a narrow EL FWHM of 20 nm and color-purity of 97.3%.Although the blue-emission LEDs has achieved,there are still some obvious problems to be solved.For example,the surface ligands of QDs were taken away by polar solvent when ZnMgO is spin-coated onto QDs films,resulting in serious luminescence quenching of QDs films.Further,ZnMgO with high oxygen vacancy(Ov)defect density will cause carrier non-radiation recombination at the interface between ZnMgO and QDs.Therefore,a difunctional ZnMgO(D-ZnMgO)nanocrystal was synthesized by adding PEABr to modify the ZnMgO surface.On the one hand,the Ov defect of ZnMgO was reduced by adding the PEABr ligand,resulting in weakened nonradiation recombination at the interface between QDs and ZnMgO films.Besides,the ligand loss and halide vacancy induced by the polar solvent of ZnMgO can be filled by added PEABr ligands,resulting in perovskite QDs maintaining high luminous performance.On the other hand,reduced Ov defect lead to the reduction of conduction band minimum and electron mobility of ZnMgO.which improve the balanced electron and hole injection into QDs.Finally.The LED presented pure-blue emitting at 470 nm wavelength,a maximum luminance of 11.134 cd m-2,and EQE of 10.1%,which is the record efficiency for pure-blue emission perovskite LEDs.The device also showed a continuous operation half-lifetime of 35 hours at luminance of 100 cd m-2.