Study On Organic/Inorganic Hybrid Perovskite Light Emitting Diode Based On Dion-Jacobson Structure

Solution-processable organic–inorganic lead halide perovskites are promising for the light-emitting applications due to their excellent properties such as narrow emission linewidths,tunable bandgaps,high luminescence efficiencies,and large charge carrier mobility.So far,the development prospects for the external quantum efficiency of three-dimensional（3D）perovskite light-emitting devices are considerable,but commercial applications of 3D halide perovskites is inhibited by their poor stability.Compared with 3D perovskites,low-dimensional perovskites have attracted widespread attention due to their large structural diversity and the ability to improve environmental stability.In addition,the quantum and dielectric confinement effects not only expand the exciton binding energy of the quasi-two-dimensional（quasi-2D）perovskites,but also enhance the charge confinement.So far,most of the quasi-two-dimensional perovskites materials studied in perovskite light-emitting devices are based on large-sized monoamine cations that form a double-layered organic spacer between the perovskites sheets,also known as Ruddlesdenpopper（RP）structures.Research on the structure of RP materials has been relatively mature,widely used in perovskite solar cells and perovskite light-emitting diodes and achieved high efficiency.It is particularly important that the hydrophobic large-size amine hinders the interaction between water and the perovskites material and improves the stability of the material.However,since there is only one connection between the monoamine cation and the perovskite layer,there is a van der Waals effect between the bimolecular organic spacer layers.However,the organic spacer between the perovskite tablets can also be a layer of large size diamine cations,due to the direct connection of diamine cations,does not have a lower strength of the van der Waals effect,and the stability is further improved.The quasi-two-dimensional perovskite material based on this structure is called Dion-Jacobson（DJ）structure.So far,there are relatively few studies on quasi-two-dimensional perovskite LEDs based on DJ structure.In this paper,we mainly study the luminescence characteristics,surface morphology,crystal structure and stability of organic-inorganic perovskites light-emitting diodes based on 1,4-butanediamine hydrobromide（BDADBr）with quasi-two-dimensional DJ structure.At the same time,we added appropriate amount of polyethylene oxide（PEO）to passivate the defects in the film,and improve the photoluminescence quantum efficiency and stability of perovskite.Specific work contents are as follows:（1）To study the effect of adding BDADBr DJ materials containing diamine cations to the 3D perovskites on the morphology,crystallinity,photophysical and electroluminescence properties of the device.According to the experimental results,the molar ratio of Pb Br₂:（MABr+BDADBr）is 1:1.2,and the perovskite precursor solution with the molar ratio of MABr:BDADBr of 1:0 and 8:1 is configured.Here,1:0 is essentially 3D perovskites（MAPb Br₃）,8:1 refers to the DJ structure of the long-chain amine BDA introduced.According to the analysis of the experimental results,compared with the 3D perovskites film,because of the 8:1 sample introduction of long chain amine to form the quasi-2D perovskite,the grain size is reduced,the film morphology coverage is complete,and the leakage current phenomenon is reduced.8:1 sample is a green light-emitting device with an electroluminescence spectrum（EL）of 516 nm and a maximum external quantum efficiency of 1.1%.（2）The light stability and environmental stability of the 3D perovskites and the quasi-2D perovskites light-emitting device based on the DJ structure are compared.The8:1 sample of 3D perovskites（MAPb Br₃）and DJ structure were irradiated with a laser with a wavelength of 405 nm for 5 minutes,and the photoluminescence（PL）intensity of the 8:1 sample was reduced to 86%of the initial value.The MAPb Br₃ is reduced to80%of the initial value.In addition,the MAPb Br₃ and 8:1 samples were placed at a temperature of 20℃and a relative humidity of 60%-70%without being packaged.After two weeks,it was found that the PL intensity of the 8:1 sample is decreased to ca.56%of its initial intensity,while the PL intensity of the MAPb Br₃ sample and the absorption value at 450 nm are greatly reduced.According to the measured data,they have dropped by 4 times and 6 times,respectively,revealing that serious degradation has occurred.Through the analysis of experimental results,it is concluded that the addition of BDADBr can enhance light stability and environmental stability.This provides a new idea for improving the stability of perovskites light-emitting diodes.（3）In order to further improve the luminous efficiency of the device,we added polymer PEO to the perovskite precursor solution containing DJ material to prepare green perovskite light-emitting diodes.And explore the introduction of different concentrations of PEO into the（BDA）（MA）_n-1Pb_nBr_3n+1 perovskites luminescent layer,which will affect the device efficiency,perovskite film morphology（SEM）,X-ray diffraction（XRD）,ultraviolet absorption and visible spectroscopy（UV-vis）,photoluminescence spectroscopy（PL）and electroluminescence spectroscopy（EL）.The experimental results show that adding an appropriate amount of polymer PEO makes the perovskite film dense and continuous,passivates the defect state in the film,and improves the photoluminescence quantum efficiency and stability of the perovskite.In addition,it was also found that the emission spectrum was red-shifted after adding PEO,indicating that PEO inhibited the formation of small n-phases in the perovskite film.After adding an appropriate amount of polymer PEO,the luminous brightness of the perovskite light-emitting diode based on the DJ structure is 6800 cd m^-2,and the external quantum efficiency of the device is increased by 2-3 times.