| The excellent performance of perovskite cells,such as balanced charge transfer characteristics and high light-absorption coefficient,has consolidated its development direction in solar cell applications.The preparation process of perovskite solar cells is relatively easy to implement,the raw material cost is low and the device conversion efficiency has been continuously improved in recent years,so it is considered as a promising photovoltaic alternative technology.The efficient photovoltaic conversion efficiency of perovskite solar cells is a goal constantly pursued by the new energy industry.Its realization is affected by multiple factors such as the e lectronic and optical properties related to the electron transport layer,the photosensitive layer,and the hole layer materials,and the defect states on the various(interface)surfaces of the devices.The surface(interface)formed by the CH3NH3PbI3(MAPbI3)light-absorbing material and the fullerene derivative(PCBM)electron transport layer has a large effect on the stability and carrier mobility of the perovskite solar cells.Based on this,the first-principles calculation method is used to study the stability,adsorption energy,electronic and optical absorption properties of clean MAPbI3(100)and PCBM-adsorbed surface of MAPbI3(100)at the micro-atomic and electronic level.Due to the asymmetry of the PCBM molecule structure,the effect of different molecular orientations on the stability of the adsorption structure was studied.We found that when the adsorption energy is-0.87 eV(the energy of PCBM molecule adsorbing on the surface MA~+cations),the adsorption system tends to be the most stable state.The density of states shows that the clean MAPbI3 surface and the PCBM-adsorbed MAPbI3 surface do not produce new electronic states at the Fermi level.The calculation of optical properties found that the absorption of PCBM enhanced the light absorption coefficient of MAPbI3.These results help to explain the experimental phenomenon that the solar cell with MAPbI 3 absorber layer|PCBM electron transport layer has higher photovoltaic efficiency.Judging from the differential charge and Bader charge,most of the atoms on the adsorption surface have significant charge transfer,which also shows that there is a strong interaction between the atoms between the MAPbI3 absorption layer and the PCBM electron transport layer.The(110)surface of MAPbI3 has a low indices of crystal face as a stable and highly compatible photosensitive surface.Since the electronic state on the surface can negatively affect the photovoltaic efficiency of the device,it should be passivated.Phenylethylamine(PEA~+),as a molecular ligand,has been actively engaged in experiments such as continuous degradation and interfacial charge recombination,and also has satisfactory performance in improving surface defects.Therefore,by constructing an adsorption model of MAPbI3 and small molecules,the lattice structure and electrical properties of PEA~+-adsorbed MAPbI3(110)surface are calculated.The change of bond length,bond angle and density of system states between atoms showed that the electronic state of the clean MAPbI3(110)surface was mainly contributed by 5p orbits of I atoms near the first layer of the surface and 6s and 6p orbitals of Pb atoms.When the adsorption distance is 3.393?,PEA~+has an obvious passivation effect on the MAPbI3(110)surface state.The adsorption of PEA~+greatly improves the surface harmful effects of MAPbI3,which provides more interaction between the surface and other transport layer materials. |
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