Preparation And Properties Of CH₃NH₃PbI₃ Perovskite

The CH₃NH₃PbI₃ perovskite is a new optoelectronic material formed at the molecular level of organic and inorganic components.It has the advantages of low production cost,simple preparation process,low recombination rate of electron-hole pair and excellent light absorption and so on.In recent years,The solar cell based on CH₃NH₃PbI₃ material is developing rapidly,which has been a new generation of photovoltaic material.It is of great research significance to study on the relationship between CH₃NH₃PbI₃ perovskite composition,synthesis process and crystal characteristics,which provide theoretical help for the applications in solar cells,the specific performance of micro devices and even molecular devices.In this work,CH₃NH₃PbI₃ perovskite was prepared by solution evaporation.The effects of temperature,halogen element?Cl,Br?doping and 1,8-diiodooctane addition on the properties of CH₃NH₃PbI₃ perovskite were systematically studied.The microstructures,thermal stability and optical properties of the perovskite materials were investigated by means of infrared spectroscopy,thermal analysis,X-ray diffraction and UV-vis absorption spectroscopy.The main results are as follows:?a?CH₃NH₃PbI₃ was prepared by solution evaporation method,and the effect of evaporation temperature on the properties of CH₃NH₃PbI₃ perovskite was studied.The results show that CH₃NH₃PbI₃ can obtain excellent crystallization performance at the temperature of 85oC,and the grain size of the crystal is in the best condition?The largest size?.At the same time,the CH₃NH₃PbI₃ material has a strong absorbance at this temperature,and the band gap energy of CH₃NH₃PbI₃ is 1.62 eV.?b?The effect of additive DIO on the properties of the material was studied after obtaining the optimum evaporation temperature process.The results show that the peak intensity of the diffraction characteristic of the sample containing additive DIO is higher than that of the original CH₃NH₃PbI₃.The layer spacing d values of the sample containing additive DIO and the original CH₃NH₃PbI₃ are 6.23? and 6.34?,respectively,using the Bragg formula according to the first order diffraction peak data.The additive does not change the crystal structure of the material.The UV-vis absorption boundary of CH₃NH₃PbI₃ added with DIO shift to the long-wave direction compared to the original CH₃NH₃PbI₃,and the band gap decreases.?c?CH₃NH₃PbI₃ was doped into Cl,Br element.The results show that the diffraction characteristic peaks intensity of CH3NH3PbI2 Cl and CH3NH3PbI2 Br are slightly lower than that of CH₃NH₃PbI₃.The diffraction pattern does not reflect the diffraction peaks of the precursor PbI2,indicating that the materials are completely crystallized.The interlayer spacing d values for CH₃NH₃PbI₃,CH3NH3PbI2 Br and CH3NH3PbI2 Cl are 6.35?,6.37? and 6.40?,respectively.?d?In the TG-DTA analysis,CH₃NH₃PbI₃,CH3NH3PbI2 Br and CH3NH3PbI2 Cl show two weight loss platforms at room temperature to 600°C.The initial temperature of the first weight loss platforms of the three materials appeare at 265.7°C,248.3°C and255.2oC,respectively.The initial temperature of CH₃NH₃PbI₃ perovskite weight loss platform is higher than that of CH3NH3PbI2 Br and CH3NH3PbI2 Cl,and the weight loss rate of the three materials are 25.74%,13.11% and 19.67%,respectively,which correspond to the molecular weight ratio of CH3NH3 I,CH3NH3Br and CH3NH3 Cl.The temperature of weight loss platform of PbI2 is from 480°C to 600°C.When the first weight loss platform appearing,PbI2 is in a stable state.The weight loss is due to the decomposition of precursor organic compounds CH3NH3 I,CH3NH3Br and CH3NH3 Cl.And the second weight loss platform is caused by the decomposition of PbI2.?e?In the wavelength range of 200⁸00nm,the positions of the absorption peaks of the three materials appeare at 460 nm,446nm and 425 nm,respectively.It is shown that they have a strong optical absorption at this wavelength.Compared to the absorption peaks of CH3NH3PbI2 Cl and CH3NH3PbI2 Br doped perovskite,The absorption peak of CH₃NH₃PbI₃ peroskite extends to the long wave direction.The band gap energy levels of CH₃NH₃PbI₃,CH3NH3PbI2 Cl and CH3NH3PbI2 Br perovskite materials are 1.62 eV,1.70 eV and 1.78 eV,respectively.