| Over the past century,the technological revolution and industrialization have promoted tremendous progress in human civilization,and the increasing demand for energy has led to the predatory exploitation of earth resources.At present,the lack of fossil energy worldwide has attracted the attention of countries around the world.Scientists have explored the development and utilization of various renewable resources,such as wind,water,and geothermal energy.Solar energy is widely distributed,clean and renewable etc,which has been considered as one of the most promising new energy sources.The use of solar energy is mainly divided into photothermal,photovoltaic,photocatalysis,and photobiology.Among them,solar cells based on the photoelectric effect are the ones with a long research period and the most widely used.There are a variety of solar cell materials that have been developed,including early silicon-based materials and compound semiconductor materials.Among them,perovskite solar cells have attracted extensive attention in recent years because of their high efficiency,low cost and simple preparation process.The organic/inorganic halide lead-iodine compound material is the core composition structure of perovskite solar cells.Its chemical composition is CH3NH3PbI3?MAPbI3?and NH2CH=NH2PbI3?FAPbI3?.Chemical formula X is iodine?I?,chlorine?Cl?,bromine?Br?or a combination of them.The first perovskite materials were applied to solar cells in 2009,but it was only eleven years ago.By improving its chemical composition and optimizing its structure,the photoelectric conversion efficiency of perovskite solar cells has been rapid growth from the beginning of 3.8%to 25.2%.It's already comparable to the best monocrystalline silicon solar cells,which can fully reflect its great research value and potential.The organic/inorganic metal halide perovskite material serves as the light absorption layer of solar cells.The reason why it can obtain high photoelectric conversion efficiency is because it has an ideal adjustable optical band gap,a high light absorption coefficient,a wider light absorption,and range,longer carrier transmission distance,etc.Establishing the relationship between these properties and their chemical composition structure and internal physical principles can in turn predict the chemical composition and structure of materials with ideal photoelectric properties to a certain extent,which will help guide us to find more stable properties and conversion efficiency higher materials.This paper uses the first principles to calculate,analyze and study the relationship between the photoelectric properties of organic/inorganic metal halide perovskite materials and their chemical composition and structure.The software used is Materials Studio?MS?.In this paper,I study the background and working principle of perovskite solar cells,and demonstrate the first-principles?FPs?and theoretical basis of density functional theory?DFT?.Firstly,the energy band structures and optical properties of three structures of organic/inorganic metal halide perovskite?CH3NH3PbI3?are calculated by the first principle method.The results show that the square structure of perovskite CH3NH3PbI3material has better energy band structure and optical properties,and is more suitable for solar cell.At the same time,we have established organic/inorganic metal halide perovskite crystals doped with tin?Sn?and halogen elements?Cl,Br,I?,and obtained the corresponding band structure,absorption spectrum and reflection spectrum by calculation.The results show that perovskite CH3NH3PbI3doped with Sn can narrow the band gap,and doped with Cl and Br can make the band gap wider.When the doping rate of Sn is about 56%,the band gap of the cubic structure crystal is reduced to 1.330e V,which has good photoelectric performance.Then,a solar cell photosensitive material with formamidine(?NH2CH=NH2+or FA?iodolead compound?FAPbI3?structure was constructed by Material Studio software,and its energy band structure,density of states and partial density of states were calculated by density functional theory.And the reasons for the high photoelectric conversion efficiency of the perovskite solar cell materials(FA0.75Cs0.25Sn0.5Pb0.5I3)reported in Science Magazine were analyzed theoretically.On the premise of ensuring that the photoelectric conversion efficiency is not reduced,we discussed the use of non-toxic elements to replace lead in FAPbI3,and calculated the band gap width,lattice constant and light absorption efficiency of the crystal after substituting the atoms of calcium?Ca?,zinc?Zn?,germanium?Ge?,strontium?Sr?,tin?Sn?,tantalum?Ta?for lead?Pb?.Compared with the solar spectral distribution,it was found that FAGe I3,FASn I3,and FAZn I3have better absorption properities in the solar spectral range.If the bandgap width and light absorption characteristics are taken into consideration,although the performance of FAGe I3is slightly lower than FAPbI3,it can be an ideal material to replace FAPbI3.Another perovskite material(FA0.75Cs0.25Sn0.5Ge0.5I3)does not contain toxic element lead?Pb?,which has photovoltaic performance close to FA0.75Cs0.25Sn0.5Pb0.5I3.The above results lay the foundation for further research on the application of these materials in related technologies.Third,the carrier transport rate of the electron transport layer in the flat perovskite solar cell was explored.In this paper,six major electron transport materials TiO2,Zn O,WO3,Zr O2,Sn O2,Zn O2in current perovskite solar cells and doped formamidine lead compounds(FA0.75Cs0.25Sn0.5Pb0.5I3)perovskite solar cell transmission models are constructed,which are obtained through optimized structure and theoretical calculation.Their effective electron mass and carrier transmission rate are determined.It was found that the mobility of electrons in TiO2crystal was slightly higher than the carrier mobility of FA0.75Cs0.25Sn0.5Pb0.5I3,which could reasonably explain the reason why titanium dioxide is widely used in perovskite solar cells.In addition,we explored eight new semiconductor materials that have not yet been used as electron transport layers in perovskite solar cells.The calculation results show that the order of the electron mobility from large to small along the x direction is:Ta2O5>Nb2O5>Bi2O3>Sb2O3>Nb2O5>Zn S2>In2S3>V2O5,the order along the y direction is:Ta2O5>Bi2O3>Sb2O3>Nb2O5>Pr2O3>In2S3>Zn S2>V2O5.It can be seen that Ta2O5and Bi2O3have good heat resistance and relatively good electron transport rate.Fourth,the properties of new hole-transporting layer materials in perovskite solar cells were explored.Hole transport materials need to have a sufficiently high hole mobility and hole conductivity to ensure that holes are effectively transported after the hole transport layer is separated from the perovskite layer interface.Using the Visualizer module of MS software,copper phthalocyanine Cu Pc,2',7'-bis?bis?4-meth oxyphenyl?amino?spiro[cyclopenta[2,1-b:3,4-b']dithiophene-4,9'-fluorene]FDT,Poly-triarylamine PTAA,poly?3,4-ethylenediox ythiophene?/poly?styrene sulfonate?PEDOT/PSS poly?3–hexylthiophene?P3HT organic hole transport material molecules and Cu CSN,Cu I,In Cu S2,Cu O,Cu2O,Ni O crystal structure are constructed.The electronic density of states?DOS?,HOMO/LUMO energy levels,and light absorption properities were obtained after optimization and calculation.The electron cloud distribution map was analyzed in detail using FDT molecules as an example.It was found that with the increase of the equipotential surface,the electron cloud is closer to the nucleus.The absorption of most inorganic hole transport materials is mainly concentrated at shorter wavelengths,while the organic hole transport materials are distributed at longer wavelengths,most of which are above 2000 nm.Only PTAA,Spiro-OMetad and Cu Pc have absorption spectra in the range of the solar spectrum.The HOMO energy levels of the seven organic hole transport material molecules are in good agreement with the valence bands of CH3NH3PbI3and NH2CH=NH2PbI3,which is conducive to carrier transport.Inorganic hole transport material Cu I has a wide band gap,and the effective electron masses of Ni O,Cu O and Cu2O are small.Fifth,the stability of perovskite solar cell materials was explored based on first principles.The poor stability of organic/inorganic perovskite solar cells is an important factor that limits their commercial production.Firstly,the formation energy,phonon scattering spectrum,density of state and the thermodynamic properties of the perovskite solar cell material?MAPbI3,FAPbI3?are calculated and analyzed,which determine its chemical stability.In order to better clarify and understand the structural stability of perovskite materials,their lattice parameters and tolerance factor t were calculated.It was found that their tolerance factor t value was 0.81<t<1.11,which was consistent with the structure of perovskite.Then,the elastic modulus of(FA0.75Cs0.25Sn0.5Pb0.5I3)and three crystal structures of?MAPbI3,FAPbI3?were studied.The elastic properties such as bulk modulus,shear modulus,Young's modulus and Poisson's ratio of the material were calculated by Voigt-Reuss-Hill approximation.From the point of view of the elastic modulus Cij,except for the MAPbI3of the orthogonal structure,the other structures are relatively stable.The ductility and brittle toughness of the material were discussed using B/G and Poisson's ratio.It is found that MAPbI3with cubic structure is the hardest,but its toughness is poor.Furthermore,based on the young's modulus,the three-dimensional surface graph can be drawn,which can directly reflect the stability degree of crystal structure along different directions.This can provide some guidance for the preparation of high stability perovskite materials in the laboratory. |
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