Design And Simulation Of Perovskite Solar Cell Charge Transport Materials

In recent years,perovskite-type solar cells have developed rapidly,and the photoelectric conversion efficiency has increased rapidly.It has increased from 9.7%to 23.3%in just six years,becoming the most promising new thin-film solar cell.Many researchers have studied different kinds of perovskite materials,and have developed a variety of A/B/X combination perovskite materials.However,these different combinations of perovskite materials result in differences in their conduction band energy and valence band energy.As the important part in the provskite solar cell,the alignment of the appropriate energy levels between the HOMO level of the hole transport material and the valence band top of the perovskite material contributes to achieving a high open circuit voltage in the perovskite solar cell,resulting in higher photoelectric conversion efficiency.Therefore,hole transporting materials of different HOMO energy levels are required to be used in combination with the novel perovskite materials.At present,the research of hole transport materials is mainly used to match simple perovskites such as MAPbI3(-5.45 eV),and the research on hole transport materials matching the novel perovskite materials with lower valence band energy is still scarce.In this paper,a total of 60 designed molecules based on spiro-OMeTAD with spirobifluorene(SBF),spiro[fluorene-9,9'-xanthene](SFX)and spirobixanthene(SBX)as the spiro-core structure were studied by quantum mechanical calculation method.The heteroatoms,methoxy and diphenylamine substitutions at different positions were systematically studied.The influence of the frontier orbitals,UV-Vis absorption spectra and molecular recombination energies of all design molecules are intended to provide theoretical guidance for the design of hole transport materials capable of matching various new perovskite materials with lower valence band energy in the future.It was found that a strong oxidizing hetero atom introduced into the spiro-core structure,the four-quadrant diphenylamine structure was substituted at the 3,3',6,6' position of the spiro structure,and the methoxy group on the outermost aromatic ring substituted in the meta position can reduce the HOMO level of the molecule.The molecular stacking mode was related to the recombination energy.For SBFs and SFXs,most of the 3,3',6,6' diphenylamine substituted derivatives are packed closely and have smaller recombined energy.But for SBXs,most of the 2,2',7,7' diphenylamine substituted derivatives are packed closely.The UV-Vis absorption spectra of the three spiro-core derivatives shows that 3,3',6,6'-diphenylamine-substituted molecule is blue-shifted compared to the 2,2',7,7'-diphenylamine-substituted molecule.The SBF,SFX and SBX series of molecules with lower HOMO energy levels designed in this paper enable better matching with new perovskite materials,enabling higher open circuit voltages for perovskite solar cells.When perovskite material is used as the light absorbing layer,the blue shift absorption spectrum of the above studied molecules is expected to be complementary to the absorption layer spectrum,so that the perovskite solar cell can exert greater efficiency.