| In this thesis,the photoelectric conversion properties and physical mechanism of MAPbI3-based organic-inorganic hybrid perovskite solar materials are systematically studied by density functional theory.The main research contents are as follows:Effect of iodine vacancies on the photoelectric properties of MAPbI3.Effect of X-site substitution on the photoelectric properties of FAPbX3(X=I,Br,Cl,F).Effect of hydrostatic pressure on photoelectric materials of FAPbI3.Effect of Pb-site doping on the Photoelectric Properties of MAPb1-XSnXI3(X=0,0.25,0.5,0.75,1)and MAGeXPb1-xI3(X=0,1/3,2/3,1).The following conclusions were obtained.Tetragonal and orthogonal phases of intrinsic MAPbI3,the calculated lattice parameters,band gaps and optical absorption coefficients are consistent with the experimental values.The high optical absorption coefficients results from the electrons jumping from the valence band I 5p orbits to the Pb 6p orbits.There are two different kinds of iodine vacancies in both phases,and their chemical stability is similar.The two different kinds of iodine vacancy result in the doping energy band appearing in the band gap,and the doping energy band is from Pb 6p electrons mainly,which is below the Fermi level.The iodine vacancy result in the red shift of optical absorption coefficients,which result in the optical absorption of MAPbI3 with the iodine vacancy locating in the range from 0.5 eV to 1.47 eV,which locate at the infrared ray part occupying 51%of radiant energy of sunlight.Therefore,the photoelectric conversion efficiency of the perovskite solar cell is improved.The effect of X on the crystal structure,electronic arrangement and optical absorption properties of FAPbX3(X=I,Br,Cl,F).The calculated lattice constants and band gap values of the intrinsic FAPbI3 are consistent with the experimental values.When X goes from I to F,the Pb-X bond lengths and Pb-X-Pb bond angles of FAPbX3 are decreased.As the decrease in Pb-X-Pb bond angles,the Pb s and X p orbital coupling is reduced.This result in the band gaps are increased,the electron and holes effective mass are increased,and the absorption spectra blue shifted.This is not benifical to the absorption of sunlight by materials.The effect of hydrostatic pressure on the crystal structure,electronic arrangement and optical absorption coefficient of FAPbI3.In the range of 0～7GPa,the lattice constant and Pb-I bond lengths of FAPbI3 are decreased,and multiple structural phase transitions occur.As the decrease in Pb-I bond lengths,the Pb s and X p orbital coupling is enhanced.This result in the band gaps are decreased,the dispersion of the band edge are increaseed,the role of hydrogen bonding are increased,optical absorption coefficient red shifted and the absorption intensity are enhanced.Therefore,when FAPbI3 is subjected to a pressure of less than 7 GPa,the power conversion efficiency of the perovskite solar cell can be further improvedThe effect of Pb-site doping on the crystal structure,electronic arrangement and optical absorption coefficient of the material.With the increase of Sn content,the band gap value of MAPb1-XSnXI3(X=0,0.25,0.5,0.75,1)gradually decreases,and the dispersion behavior gradually increases at the top of the valence bands.Sn-I bond lengths are smaller than the Pb-I bond lengths,which rise the valence band and enhance the band dispersion behavior.After doping the Sn element,the optical absorption coefficient of the material gradually red shift,which is beneficial to improve the power conversion efficiency of solar cell.As the content of Pb increases,the band gap value of each component of MAGexPb1-xI3(X=0,1/3,2/3,1)gradually increases.From the optical absorption coefficients of each component,the MAGeo.67Pbo.33I3 material with less lead can be used as the light absorbing layer of solar cell,which is beneficial to improve the power conversion efficiency of the perovskite solar cell. |
