First-principles Study On The Electronic And Optical Properties Of Perovskite Doped By Cs And Sr

A promising light-absorbing material in emerging perovskite solar cells has attracted widespread attention from scientists at home and abroad.In recent years,the photoelectric conversion efficiency of perovskite solar cells has increased from 3.8%to over 22%.Despite the rapid development in the record of PCE,there are some issues,relating to halide perovskite materials that need to be solved before halide perovskite solar cells technology can be widely commercialized.For instance,the use of toxic Pb in the high-PCE PSCs which can pollute the environment and do harm to human health;The instability caused by the volatile organic cations,methylammonium or formamidinium in the state-of-the-art halide perovskite.So,it is a great challenge to deal with these issues without sacrificing some of the key properties,for example,band gaps,optical absorption,and defect tolerance,although previous efforts in this area have been met with some success.In this thesis,first-principles calculations based on density functional theory,is used to study electronic and optical properties of organic-inorganic hybrid perovskite materials.The results of the calculation are as follows:In MAPb_（1-x）Sr_xI₃,band gaps of 1.44 to 2.66 eV are adjustable with the incorporation of strontium,while the band gap of MAPbI₃ is 1.58 eV.The calculation of the density of states shows that the d orbital of the strontium element mainly plays a role in the conduction band,so that the conduction band moves upward.For the analysis of optical properties,the absorption peak of each component material lies within 3-4 eV with the increase of the doping proportion of strontium.The optical properties show a blue-shift tendency compared with MAPbI₃.In FAPb_（1-x）Sr_xI₃,the band gap is 1.84 eV when the strontium doping ratio is0.125,and the band gap is 2.61 eV when the strontium doping ratio is 0.5.From the analysis of the density of states,it can be seen that the d orbital of the strontium element mainly acts on the conduction band,and the contribution to the conduction band is relatively reduced when the strontium doping ratio is 0.375.when the strontium doping ratio is 0.5,strontium contributes to both the valence band and the conduction band,so that the valence band shifts downwards and the band gap upwards.Analysis of its optical properties shows that there is a general blue-shift tendency compared with the optical properties of FAPbI3.Compared with the absorption coefficient of MAPb_（1-x）Sr_xI₃,the absorption coefficient is reduced by about 25%.The band gap of Cs_yMA_（1-y）Pb_（1-x）Sr_xI₃ changed with 1.44 eV to 2.50 eV with the doping of cesium and strontium,and the band gap did not change linearly.From the analysis of the density of states,we can see that the p orbital of the cesium element mainly contributes to the valence band,and the s and p orbitals of the strontium element mainly play a role in the conduction band.As the proportion of doping increases,the contribution gradually increases.The analysis of its optical properties revealed that different proportions of the material began to respond to light at about1.5 eV,while the absorption of the components in the range of 3.5-4 eV was the strongest,indicating that the visible light and the higher energy of the ultraviolet The band has a good response.By analyzing the different optical axes of the same material,these materials exhibit anisotropic optical characteristics.