Study On The Preparation Of Metal Halide Perovskites And The Light Emitting Devices

In recent years,metal halide perovskite materials have become one of the star materials in optoelectronics field due to their excellent photoelectric properties,such as direct adjustable bandgap,good carrier transport characteristics,and high conversion efficiency.Perovskite based light emitting devices have advantages of high luminous color purity,low cost,and simple manufacturing processes over other light emitting devices,which meet the market demand.However,with various preparation methods of perovskites,such basic and systematic research reports like the effect of preparation parameters on properties of the materials,are relatively rare.Moreover,perovskite light-emitting devices generally contain organic components,resulting in poor stability,which has seriously hampered the application of devices.In view of the hot and difficult issues on the perovskite research,based on the organic and the inorganic metal halide perovskite materials,this article intensively studied the one-step and two-step preparation,revealed the effect of process parameters on the surface morphology,crystalline quality and optical properties of the perovskite and studied the photoelectric properties using temperature-dependent PL technology.Then the preparation and optimization of the transport layer materials in perovskite devices were studied in detail.Finally,based on the emitting layers and structures,three types of perovskite LEDs were prepared,which the device luminescence characteristics were studied,the working mechanism of the device was described,and the continuous working stability was analyzed in depth.The specific research contents are as follows:1.One step and two step methods were used to prepare CH₃NH₃PbBr₃respectively.In the one-step method,factors such as spin coating speed,annealing time,and annealing temperature,in the spin-soaking method,factors such as spin coating speed,soaking temperature and time of the lead bromide layer,in the spin-spin method,spin coating speed and annealing time were changed.the effect of process conditions on the surface morphology,optical and crystalline properties of CH₃NH₃PbBr₃ was investigated.2.CsPbBr₃ was prepared by evaporation-soaking and evaporation-evaporation methods.In evaporation-immersion method,the evaporation rate and soaking time of lead bromide were changed.In evaporation-evaporation method,the order of evaporation of lead bromide and bismuth bromide,annealing atmosphere and temperature were changed.The surface morphology,optical and crystalline properties of CsPbBr3 was studied under different process.3.CH₃NH₃PbI3-XCl_X material was prepared by evaporation-soaking on the ZnO nanorod substrates by MOCVD.The surface morphology and optical properties at RT of the perovskite layer were studied.The T-dependent PL was used to characterize its photoelectric properties.The corresponding exciton binding energy was calculated to be 77.6±10.9 meV,and the energy of the optical phonon was 38.8.±2.5 meV with a temperature coefficient of 0.25±0.005 meV/K.4.Preparation and optimization of perovskite LED transport layers ZnO,NiO and Al₂O₃.In magnetron sputtering technique,we changed the power,pressure and argon-oxygen ratio to optimize the material properties.The results show that the film morphologies can be effected by high-energy particle bombardment and collisions between particles.The electrical properties are mainly affected by how much the sputtering process affects the incorporation of nickel vacancies and lithium.5.Based on the device’s emitting layer and structure,three types of perovskite LEDs were prepared.（1）ZnO/CH₃NH₃PbBr₃/PEDOT:PSS.The device’s turn-on voltage is about 3.5 V.The color purity is relatively high.However,the stability of the device is poor and the luminous intensity is also weak.（2）ITO/Al₂O₃/CsPbBr₃.The MIS perovskite LED with inorganic perovskite film was proposed for the first time.The device’s turn-on voltage is 6 V.The color purity is very high.The EL peak intensity begins to decay after 4.89 mA.The stability of the device is significantly better than previous device.Only 20 minutes of continuous 10 V operation in the air without encapsulation,it begins to attenuate significantly.（3）ZnO/CsPbBr3/NiO.For the first time,a fully functional inorganic perovskite LED based on thin film working in the air is prepared.The device’s turn-on voltage is 3 V.During continuous 7 V operation in the air for approximately 30 min without encapsulation,the EL spectrum fluctuates less,and the FWHMs are maintained between 21.4-23.5 nm.The stability of the device is superb.