Regulation And Optimization Of CsPbBr₃ And Electron Transport Layer For The All-inorganic PeLED

In the last few years,lead halide perovskite materials have attracted global attention for their great prospects in low-cost lighting and high resolution display fields,owing to their high photoluminescence(PL)emission efficiency,adjustable color characteristics,narrow-band emission,and easy solution preparation.However,the instability of perovskite materials is still a major obstacle for their practical applications.In this circumstance,inorganic cesium lead halide(CsPbX3,X=C1,Br,I)has begun to receive much attention for their higher thermal stability(-500 ?)and moisture resistance than those of organic-inorganic hybrid lead halideperovskite.As a consequence,PeLEDs based on CsPbX3 QDs have triggered a recent research hotspot.In order to achieve a highly efficient and stable PeLED,it is necessary not only to ensurethe luminescence properties of the perovskite material,but also to match the interface levels between the functional layers.Among them,particular concern is the charge transport layer,which plays an important role in energy level matching,charge transport,and protection of the perovskite emitting layer.On the one hand,due to that the inorganic metal oxide semiconductor has good chemical stability and can effectively block moisture,it canbe used as a charge transport layer to replace the conventional organic semiconductor material.On the other hand,magnetron sputtering is a well known low-cost and large-scale manufacturing technology for the film fabrication,and the film thickness can be finely controlled by the deposition rate and time.Moreover,the method can avoid any organic solvents and organic materials completely.In this thesis,we concentrated on how to use CsPbX3 QDs as an emissive layer and how to design and prepare sputtered inorganic metal-oxide semiconductors as charge transport layersto fabricate the PeLEDs.The main contents of each chapter of the thesis are as follows:In chapter one,we first overviewed the crystal structure,photoelectric properties and preparation of halide perovskite materials;and then described briefly the device structure,working principle,performance character and development historyof PeLED;we also introduced the controllablepreparation of CsPbBr3 NPs as well as the related PeLEDs,and discussed the influence of charge transport layer on the performance of the device.Finally,we presented the main research contents and results of this work.In chapter two,we focused on the synthesis and the cleaning of CsPbBr3 QDs.Based on the results of TEM and steady-state PL spectra,we identified the effects of synthesis temperature on the morphologies andoptical properties of the quantum dots.Additionally,with SEM and steady-state PL characterization,we studied the effects of cleaning times on the removal of coating agents from the quantum dot surface and the morphology of spin-coating film.It was found that the CsPbBr3 QDs obtained by hot injection synthesis at 180 ? and washed twice,which dispersed in mixed solution of ethyl acetate and hexane,is used suitably as the emissive layer for the PeLED device.In chapter three,we prepared the all-inorganic PeLED device with CsPbBr3 QDs as the emissive layer and sputtered NiO and ZnO as the charge transport layers.We characterized the device and found that both of the luminescence intensity and efficiency were low.The underlying possible reason was the poor electron injection,leading to the much unbalanced carrier injections between electrons and holes.To overcome the shortage,the ZnO/AZO composite electron transport layer was used to replace the only ZnO layer.After the systematical investigation of different thickness ratios of ZnO and AZO films on the luminescence performance of the PeLED device,it was found that,when the ZnO(15 nm)/AZO(15 nm)composite film wasused as the electron transport layer,the balance of electron and hole injection was optimizedand the luminescence performance of the device got greatly improved.The operation stability of the unpacked PeLED was also evaluated under air atmosphere by repeated bias scans.The current density-voltage curves of the device remains almost unchanged,while the luminance-voltage curves have only a slight drop,indicating that the PeLEDs prepared by magnetron sputtering have good operational stability and test repeatability.In chapter four,we discussed the current problems and challenges of perovskite LED devices,and proposed possible research directions in future.