Metal Halide Perovskite Light Emitting Materials:Preparation And Properties Study

Metal halide perovskites own many outstanding photoelectric properties,such as direct and tunableband gap,wide spectral absorption,large light absorption coefficient,long charge carrier diffusion distance,high photoluminescence efficiency,and narrow emission line width.In recent years,they have emerged as new kind of semiconducting materials and attracted much attention.They have been widely studied and applied to fabricate high-performance optoelectronic devices such as solar cells,light-emitting diodes(LEDs),photodetectors and lasers.So far,tremendous efforts have been made to improve the efficiency of these devices.However,metal halide perovskites are ionic crystals and show high sensitivity to the environmental factors including the humidity,light,and temperature.Presently,there are a few studies on improving the stability of metal halide perovskite light emitting materials and corresponding devices.In addition,low-cost and large-scale synthesis is particularly important for the popularization and application of metal halide perovskites.It is greatly significant and meaningful to develop simple and controllable synthetic route to obtain stable metal halide perovskites.This dissertation focuses on two core issues,one is about facile,large-scaled and controllable preparation of metal-halide perovskites,and the other one is about improving the stability of metal halide perovskite and corresponding devices to the humidity,air,and temperature.This dissertation is composed of four chapters.The main contents of each chapter are as follows:In the first chapter,we firstly introduce the crystal structure,basic properties and classification of perovskite materials.Then,the newly emerged metal halide perovskites are introduced in details,including the synthesis methods,device applications,strategies to stabilize these materials and corresponding devices.Based on these background,the basic research ideas and contents of this dissertation are proposed.In the second chapter,the organic-inorganic hybrid perovskite(C4H9NH3)2PbBr4 microplatelets and nanobelts were rapidly synthesized in large scale by simple ligand assisted re-precipitation method.The growth mechanism and structure of the nanobelts are further studied.It is found that nanobelts can be obtained under the regulation of potassium ions.It is for the first time to report one-dimensional(C4H9NH3)2PbBr4 nanobelts synthesized by such simple solution precipitation method.The prepared nanobelt powder is stable in air for one month,and exhibits bright purple-blue light under ultraviolet light irradiation.The photoluminescence quantum yield is as high as 16%.(C4H9NH3)2PbBr4 nanobelts are used to fabricate photodetector on a flexible substrate electrode and its performance is tested.It is found that the photodetector based on(C4H9NH3)2PbBr4 nanobelts exhibits higher response current and larger switching ratio than the photodetector based on(C4H9NH3)2PbBr4 microplatelets.The interconnected network structure with many pores in the nanoble device increases the light scattering and enhance the light harvesting for photodetection.At the same time,the nanobelt-based device shows better bending resistance,and the response current is only reduced by 10%after bending the flexible substrate for 1000 times.In addition,after stored in the air for one week,the response current of nanobelt-based photodetector is only reduced by 20%,indicating its good stability.In the third chapter,the stable dual-phase CsPbBr3-CsPb2Br5 nanocrystals are synthesized by simple ligand assisted re-precipitation method to improve the stability of light-emitting diode.In this synthesis process,the bromide-rich circumstance is beneficial to generate high quality dual-phase perovskite nanocrystals with PLQY as high as 92%and a narrow emission linewidth of 19 nm.More importantly,as-synthesized dual phase perovskite nanocrystals exhibit much higher thermal stability in heating tests in air with a considerable humidity of 30%?55%than the previously reported single-phase CsPbBr3 nanocrystals.Even after the treatment under 200?,high photoluminescence intensity can be still maintained in the dual phase nanocrystal film.The better thermal stability of the dual-phase CsPbBr3-CsPb2Br5 is attributed to the interfacial interaction between CsPbBr3 and CsPb2Br5.Based on the good stability,CsPbBr3-CsPb2Br5 light emitting layer is prepared in air and used to fabricat LED device.The CsPbBr3-CsPb2Br5 LED shows a turn-on voltage of 2.5 V and a maximum brightness of 8383 cd m-2.Compared to single-phase CsPbBr3 nanocrystal-based LED,the dual-phase CsPbBr3-CsPb2Br5 LED exhibits much better performance such as higher external quantum efficiency and longer operational lifetime.The last chapter gives the sumamary and perspective on the problems and opportunities for the further development of metal halide perovskite light emitting materials and corresponding LED devices.