Inorganic Halide Perovskite Materials And Their Application In Light Emitting Diode

In this thesis,we mainly investigate the optoelectronic properties of cesium(Cs)based perovskite materials and their application in the light emitting diode(LED).Compared to the organic-inorganic hybrid perovskites,Cs based perovskite displays improved thermal stability.However,the Cs based perovskite as active layers of a LED requires further improvements of film quality and luminescent properties,and the microstructure mechanism of perovskites is also worth exploring.By controlling the film morphology,improving the photoelectric properties and the crystal structure of CsPbBr3 system,we fabricated high efficient and stable LED devices.Firstly,we analyzed photoelectric properties and film morphologies of CsPbBr3 system in detail by using scanning electron microscopy(SEM),atomic force microscopy(AFM),fluorescence microscopy,fluorescence spectroscopy(PL),ultraviolet–visible(UV-vis)absorption spectroscopy,X-ray diffraction(XRD),LED testing system and other methods.Traditional lead perovskites have environmental pollution.To solve this problem,we explored environmentally friendly lead-free perovskite Cs3Bi2Br9.The lead-free perovskite Cs3Bi2Br9 was characterized and analyzed by PL,UV-vis,XRD and scanning electron microscopy(TEM).Our work mainly consists of following three parts:1.Organic–inorganic hybrid perovskites have attracted wide scientific attentions in the field of solution-processed LED.However,in spite of their remarkable characteristics,the intrinsic thermal and environmental instability of their organic components still remains an obstacle toward long term device applications.So all-inorganic halide perovskites employing inorganic cations,such as three dimensional(3D)CsPbBr3 has been studied in our research.The performances of perovskite films were improved by introducing polyethylene oxide(PEO)as a heterogeneous dielectric material in CsPbBr3 system,and perovskite films were further improved by anti-solvent steam process.The exciton binding energy(Eb)of CsPbBr3 film was significantly improved after the introduction of PEO and anti-solvent chloroform(CF)fumigation(CsPbBr3-PEO-CF),so that the fluorescent performance of CsPbBr3 film was significantly enhanced.Based on the above method,the LED device based on CsPbBr3-PEO-CF thin film obtained the highest EQE of 4.76%.2.Two-dimensional(2D)perovskites have attracted wide attentions in the field of perovskite research.However,the presence of insulating organic long-chain spacer cation dramatically deteriorates the charge transport properties along the out-of-plane nanoplatelet direction and limit the LED device performance.In order to overcome this issue,we successfully incorporate small alkaline ions such as sodium(Na+)to replace long organic molecule as spacer to fabricate 2D Na2Csn-1Pbn Br3n+1 for the first time.Grazing incident X-ray diffraction(GIXRD)measurements verify the 2D layered formation with preferential crystalline orientation.A new 2D-3D mixed perovskite was fabricated.Meanwhile,in order to further improve the quality of the film to obtain high efficiency LEDs device,a small amount of ethylene oxide compound 18-crown-6(crown)was introduced in perovskite.Therefore,a 2D-3D Na2Csn-1Pbn Br3n+1-CsPbBr3 LED achieves a remarkably high EQE of 15.9% with good operational stability.3.In order to reduce the toxic metal such as Pb in perovskite and fabricate environmentally friendly Pb-free perovskite material,Bi was used to replace Pb in preparation of Pb-free perovskite.The films and quantum dots based on Cs3Bi2Br9 were fabricated.Luminescent properties and band-gap structure of Cs3Bi2Br9 were compared in detail.Our work paves a way to develop environmentally-friendly Pb-free perovskite for future applications.