Density Functional Theory Studies The Optoelectronic Properties Of α-CsPbI₃ Perovskite Materials Doped With Elements Of The Fourth Main Group

All inorganicα-Cs Pb I₃ perovskite material with its high light absorption rate,appropriate band gap and good stability in the field of solar cells,light-emitting diodes and other photodetectors has been widely concerned by people.However,due to the Pb element inα-Cs Pb I₃ perovskite materials,it will pollute the environment and affect the industrial production,so the photoelectric performance of solar cells can be guaranteed it is very important to reduce the Pb content at the same time.In this paper,Ge,Sn,Si elements with the same main group as Pb are used to replace or partially replace Pb in perovskite materials.As the tolerance factor of Cs Si I₃ is greater than 1,it does not conform to the standard of perovskite materials,so it is not considered in all substitutions.In this paper,density functional theory（DFT）,CASTEP module in Materials Studio software,and the crystal model established by GGA and PBE functional optimization are used to calculate the first principles.The results show that the tolerance factors of Cs Ge I₃ and Cs Sn I₃ are 0.934 and0.874,respectively,when Pb is replaced by Ge and Sn,and the structural stability of Cs Ge I₃ and Cs Sn I₃ is improved.The band gap values of Cs Ge I₃ and Cs Sn I₃ are 0.622e V and 0.444e V,respectively.Comparing the UV Vis spectra and the imaginary of the dielectric function of the three materials,it can be seen that the absorption spectra of Cs Ge I₃ and Cs Sn I₃ are red shifted with the substitution of Ge and Sn in the visible light range of 400nm～760nm.Therefore,the effect of substituting Ge for Pb inα-Cs Pb I₃ is the most obvious,which not only improves the light absorption capacity but also enhances the stability of the structure.One of the most important points of this research is that it completely replaced the toxic lead,which not only reduced the environmental pollution,but also laid the foundation for the development of lead-free batteries.After that,in order to find out the most suitable concentration in the fourth main group,we use different concentrations of Ge,Sn,Si to studyα-Cs Pb I₃ perovskite materials,and simulate the optical and electrical properties of the doped Cs Pb_1-xM_xI₃（x=0.125,0.25;M=Ge,Sn,Si）.The results show that the most suitable band gap is1.234e V when the concentration of Ge is 0.25,and Ge doping can improve the optical absorption ability of the material,and improve the stability of the material while reducing the Pb concentration.Therefore,Cs Pb_0.875Ge_0.125I₃ perovskite material can be used as a suitable optical absorber for perovskite solar cells.