Mixed Halogen Perovskite Sky-blue Light-emitting Devices Based On Quasi-two-dimensional Structure

Metal halide perovskite materials have many advantages,such as high fluorescence quantum yield,adjustable band gap,solution processing,high carrier mobility and unique defect tolerance,etc.,which have shown a wide range of research and application prospects in perovskite light-emitting devices,solar cells,lasers and photodetectors.At present,perovskite materials show good external quantum efficiency in near-infrared,green and red light devices,all of which have exceeded 20%.As an indispensable part of display devices,the relatively poor performance of blue light emitting devices limits the application of perovskite luminescent materials in display and lighting.Therefore,the research of perovskite blue light emitting devices has attracted extensive attention.Generally,blue light-emitting devices are prepared in the following two ways:1)High band-gap mixed halide perovskite luminescent material MAPbBr_xCl_1-xis used as the luminescent layer of the device(the luminescent wavelength is between 450-490 nm).2)The low-dimensional perovskite material is used as the luminescent layer.The two-dimensional layered perovskite material has a natural multi-quantum well structure,which can realize effective energy transfer between wells,improve the excited state density in the low-band gap luminescent phase,and suppress the non-radiation composite loss.In this paper,long chain butylamine cation and polymer additive polyethylene oxide were introduced into the halogen perovskite luminescent layer MAPbBr₂Cl.The quasi two-dimensional layered perovskite formed by long chain butylamine cation(BA⁺)can effectively improve the morphology and reduce the defect density of the film.The introduction of polymer additive polyethylene oxide(PEO)further reduces the grain size,passivates the defect state of the film,and inhibits ion migration and non-radiation composite loss.Thanks to the efforts of many researchers,perovskite light-emitting devices,solar cells and photodetectors made of perovskite materials have all made excellent achievements.However,the metallic lead contained in perovskite materials is a toxic substance,and perovskite materials are easily soluble in water.If the metallic lead is released into the natural environment and then flows into the human body and other organisms,it will cause significant harm to the health of the human body and other organisms.Therefore,the use of non-toxic metal lead ions is the future direction of the development of perovskite materials,which is also a very challenging task.Based on the stability and toxicity problems of blue perovskite light-emitting devices,the following work has been done in this paper:(1)The morphology,crystal structure and photophysical properties of three-dimensional halogen perovskite material MAPbBr₂Cl were studied by introducing different proportion of long chain butylamine cations.The results of scanning electron microscopy(SEM)show that adding long-chain butylamine cations can improve the morphology of the film.Compared with three-dimensional perovskite film,the grain size of the film decreases first and then increases with the increase of long-chain butylamine cations proportion.The photoluminescence(PL) and electroluminescence(EL)of the device showed blue shift.Through X-ray diffraction(XRD)analysis,the diffraction peak of(100)gradually moves to a small angle until the diffraction peak appears at a low Angle(<10°).This result indicates that the introduction of long chain butylamine cation leads to the increase of lattice constant,forming a quasi-two-dimensional perovskite structure.(2)The introduction of the polymer additive polyethylene oxide into the quasi-two-dimensional perovskite material has been studied.On the basis of the optimized BA 0.75,mixed solutions of BA 0.75 and PEO with different concentrations were prepared.The morphology,crystal structure and photophysical properties of films prepared by different solutions were analyzed by means of SEM,XRD,PL and EL.With the increase of polymer PEO content,the surface of the film is smooth without avity,and the grain size decreases obviously.The photoluminescence(PL)and lectroluminescence(EL)of the device show a slight blue shift phenomenon.The introduction of polymers further improves the efficiency of blue light perovskite devices.The introduction of long chain butylamine cation and polymer additive polyethylene oxide into the halogen perovskite luminescent layer MAPbBr₂Cl can inhibit ion migration and non-radiative recombination by reducing grain size and passivating defects.A sky-blue perovskite light-emitting device with a maximum wavelength of 484 nm,a maximum luminance of 2876 cd/m²and a maximum current efficiency of 3.7 Cd/A has been fabricated by this method,which is nearly 15 times higher than that of MAPbBr₂Cl.(3)Different concentrations of Ba²⁺were introduced into the mixed halide and organic spacer cationic quasi-two-dimensional perovskite precursor solution(BA₂Cs_n-1Pb_n (Br/Cl)_3n+1,which was expressed as BA 1,to prepare mixed solutions of BA 1 and BaCl₂at different concentrations.Through experiments,we found that the introduction of Ba²⁺can adjust the phase distribution of quasi-two-dimensional perovskite materials,improve the charge transfer capacity and luminous efficiency of the device.The maximum luminance and luminescence efficiency of the sky-blue light-emitting device is 1444 cd/m²and 4.6 Cd/A,which is 1.6 times of that of the device without adding Ba²⁺.This paper presents a method for the preparation of low toxic light emitting devices.