Perovskite （csPbBr₃） Nanowire Polarized Light Emitting Diodes Based On Mechanical Rubbing Process

Halide perovskite has been an active research field in recent years.The material not only has excellent photoelectric properties,such as adjustable direct bandgap,narrow emission peak,long carrier diffusion length and high light absorption coefficient,but also is easy to prepare by solution processing.Halide perovskite has a wide range of applications in photoelectric devices such as light-emitting diodes,solar cells and lasers.So far,researchers have successfully prepared zero-dimensional quantum dots,one-dimensional nanorods/nanowires,two-dimensional nanosheets,quasi-two-dimensional structures,three-dimensional bulk materials of perovskite.One-dimensional materials have anisotropic characteristics,which can be arranged in an orderly manner by external action,and thus polarized light is obtained.In traditional display technology,polarizers are added in front of the non-polarized light source to obtain polarized light.This configuration will lose about 50%of the incident light of the non-polarized light source,which is disadvantageous from the perspective of energy saving and environmental protection.If the linearly polarized electroluminescent device actively emits light,it can replace the polarizer,liquid crystal cell and even the background light source of the traditional liquid crystal display,thereby simplifying the device structure with larger viewing angle and improving the brightness of the display with less energy loss.Therefore,Cs Pb Br₃ nanowires were synthesized and then oriented by mechanical rubbing to prepare polarized perovskite light-emitting diodes.The specific research contents are as follows:1)Cs Pb Br₃ nanowires were synthesized by hot injection.The structure and morphology of Cs Pb Br₃ nanowires were characterized by X-ray diffraction（XRD）,transmission electron microscope（TEM）and scanning electron microscope（SEM）.The photophysical properties of Cs Pb Br₃ nanowires were studied by UV-vis absorption spectroscopy and fluorescence emission spectroscopy.The nanowires were surface-treated by Pb Br₂,NH₄BF₄,and NH₄SCN.The results show that the Cs Pb Br₃nanowires are dispersed in the solvent in the form of bundles,and their length can reach the micron level.The surface treatment improved the photoluminescence quantum yield（PLQY）of the nanowire dispersion and a better dispersion resulted.2)Based on the Cs Pb Br₃ nanowires synthesized,a polarized light-emitting film was successfully prepared using the rubbing orientation method.Metalloscope was used to compare the advantages and disadvantages of the solvent,temperature,and added polymer in the rubbing process.Atomic force microscope（AFM）and SEM were used to characterize the surface morphology of the film obtained by dry rubbing and wet rubbing,respectively.The results showed that the dry rubbing prepared film has fewer grooves.In this experiment,a fluorescent film with a polarization property was successfully prepared,and the fluorescence polarization degree reached 0.5.3)Based on the polarizing fluorescent film,the electroluminescence device was investigated.Using different hole transport layer（HTL）materials,such as:PEDOT:PSS（poly（3,4-ethylenedioxythiophene）:poly（styrene））,PVK（polyvinylcarbazole）,poly-TPD（poly[N,N’-bis（4-butylphenyl）-N,N’-bis（phenyl）benzidine]）,and several kinds of stacked structures.The concentration and the speed of the spin coating process of the hole transport layer were optimized as well.The device performance obtained by dry rubbing and wet rubbing was compared.The results show that device with the single-layer poly-TPD as HTL prepared by dry rubbing has the best performance.The turn-on voltage is 6.5 V and the highest luminance is 3.5 cd/m².Meantime,the external quantum efficiency（EQE）is 0.08%,and the electroluminescence polarization degree is0.14.