| Perovskite solar cells have attracted widespread attention from researchers around the world due to their advantages such as the simple preparation process,low cost and rich variety.Their photoelectric conversion efficiency(PCE)has been rapidly increased from 3.8%to 27%within a few years.The photoelectric conversion performance has exceeded the dye-sensitized solar cells and thin-film solar cells.The methylamine lead iodide(CH3NH3PbI3)as a core material of organic-inorganic hybrid perovskite solar cells has the advantages of suitable band gap,high light absorption coefficient and long carrier lifetime.It can absorb photons to generate electron-hole pairs to achieve photoelectric conversion.However,the performance improvement issues such as the toxicity of Pb in the material and the stability of the solar cells have not been completely solved,thus the large-scale production and commercial use of these materials have been limited.Considering the toxic effects of lead halide perovskite,a large number of studies have been proved that doping in perovskite CH3NH3PbI3 can effectively improve the photovoltaic performance and reduce the toxicity of lead.Therefore,it becomes meaningful to explore the lead-free perovskite materials for providing the better stability and improving the photoelectric conversion efficiency without harming human health and the environment.In this paper,using the first-principles calculation method and substitute the partial lead atoms with metal atoms in the perovskite CH3NH3PbI3.The properties of doping metal elements in the cubic,tetragonal and orthogonal phases of perovskite,including the lattice constant,electronic properties,optical properties and exciton dissociation have been explored and analyzed in detail.The main work of this paper is1.Density functional theory and the CASTEP software have been used to study the electronic structures and charge transport properties of CH3NH3PbI3 perovskite for three phases,which substituted Pb with 12.5%Ag.The data of bond lengths and angles support that introducing Ag dopant induces more significant distortion of AgI6 octahedral in perovskite structures.Ag dopant shift the Fermi level to deep energy and slightly increase the band gap about 0.1eV.The tiny contribution of Ag-5s orbitals for conduction band and the deep energies of Ag-4d orbitals cause the absence of dopant states in band gap.The increased electron and hole effective masses lead to the reduced charge carrier mobilities and imbalanced charge transport properties,also result into more difficult exciton dissociation.This work provides a theoretical perspective for studying the effects of higher concentration Ag doping on the electronic structures,charge transport properties and photovoltaic properties of perovskite CH3NH3PbI3 materials.2.The problems of toxicity and stability of Pb in the perovskites need to be further improved.In this work,four alkaline earth metal atoms(Mg,Ca,Sr,Ba)have been used to replace one Pb atom for cubic and tetragonal phases,respectively.The PBE and HSE06 hybrid functional calculation method were used to simulate the geometric properties,electronic structures,optical properties and effective masses of the doping perovskite structures.The results of the geometric structure data show that the Mg dopant can cause the perovskite volume decrease,while the volumes of Ca,Sr and Ba dopant perovskite increase significantly;the electronic structures with four kinds of Mg,Ca,Sr,and Ba dopants show that the bandgap values of cubic and tetragonal perovskites are increased by about 0.2eV and the Fermi levels are all shifted to low energy;the light absorption spectrums prove that doped with alkaline-earth metals for cubic phase perovskite in the wavelength range of 400?440nm and the tetragonal phase perovskite in the wavelength range of 360?400nm all show the better light absorption performance than pure phases;the effective masses of the alkaline earth metal dopants are increasing,which would increase the exciton binding energy and cause more difficult dissociation.These results provide theoretical insights for further exploration of the electronic and optical properties of the alkaline earth metals doped in perovskite CH3NH3PbI3. |
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