The Efect On The Photoelectric Performance Of Cs₃Bi₂X₉(X:Cl,Br,I) With Defect Structure

As a significance part of modern energy development,solar energy has developed by leaps and bounds in recent decades.As one of the representatives of new solar cell light-absorbing materials,perovskite has caught up with the development of traditional solar materials in more than ten years.As far as lead-based perovskite materials are concerned,environmental protection is the main restricting factor for their commercial applications.Therefore,lead-free inorganic perovskite materials with stable structures have been paid attention to by researchers.Experiments have proved that Cs₃Bi₂X₉(X:Cl,Br,I)is a new lead-free perovskite material with stable structure and excellent performance.However,the basic theoretical mechanism and performance control of its optical and electrical properties is still insufficient.The factors of bulk defects and interface defects of these materials have been calculated for the adjustment and control of optoelectronic properties.The influence of different defect structures on the photoelectric properties of the material has been analyzed based on first-principles theoretical calculations,the result will provide a theoretical reference for the practical application of the material in the future.(1)By calculating the defects of different bodies in the Cs₃Bi₂X₉(X:Cl,Br,I)crystal,we found that the increase of the defects of the same element in the crystal makes the structure instability,and the optical and electrical characteristics change greatly,from Cl to Br and then to I.This kind of influence will increase,and the result of Bi atom defect and X atom defect are different and will influence each other.For the three materials,their photoelectric properties are mainly affected by the valence electron orbitals of Bi and X.The valence electron orbit of Cs atoms mainly acts in the depth of the energy band.The bulk defect of Cs and Bi will cause the valence band to move toward Fermi energy.The bulk defect of X will cause a sub-energy band at the bottom of the conduction band,where the bulk defect of Bi will inhibit the generation of sub-energy bands in the conduction band,and the bulk defect of I will significantly inhibit the valence band energy from moving to the Fermi level.This inhibitory effect is the strongest with I and the weakest with Cl.Secondly,we found that the sub-energy band generated by the conduction band will red-shift the spectral absorption peak and enhance the material's ability to absorb long-wavelength light.The movement of valence band energy will inhibit the occurrence of red-shift and the movement of valence band energy.It will affect the material's absorption of long-wavelength light,especially when Bi defects are present.(2)A stable polarization surface is selected in the(001)crystal direction of the crystal,and the different interface defect structures of the three materials are calculated.It is found that the Cs₃Bi₂X₉(X:Cl,Br,I)materials have their own one-dimensional,two-dimensional,and zero-dimensional The spatial structure will have a greater impact on the interface structure.When Cs and Cl defects appear at the interface of the one-dimensional material Cs₃Bi₂Cl₉,the continuity of the energy band in the valence band will be weakened,and the Bi defect will strengthen its continuity;the two-dimensional material Cs₃Bi₂Br₉Sub-energy bands easily appear in the spectrum,so the absorption peak in the spectrum has a large red shift.Due to its small thickness,the light absorption intensity will decrease;the electrical balance of the zero-dimensional material Cs₃Bi₂I₉is easily destroyed.When only Cs and Bi are in the When the interface is defective,the structure will be destroyed,and I can also prevent this from happening when the interface is defective.This is also related to the unique dioctahedral structure in Cs₃Bi₂I₉.The calculation also found that the interface defect of Bi and the interface defect of X have a stronger influence on the light absorption performance.Therefore,the influence of defect structure is a factor that cannot be ignored in experimental preparation and performance testing.