The Mn Doping Mechanism And Heterophase Interface With SnO₂ Properties Of All-inorganic Perovskite Solar Cell Material CsPbI₂Brby First-principles Calculations

The All-inorganic perovskite material CsPbX3?X=I,Br,Cl?has attracted the attention of researcher society of thin-film solar cells due to its excellent thermal stability and photoelectric properties.In particular,the CsPbI₂Br,because of its relatively suitable band gap?1.91 eV?and excellent stability,makes it the most potential all-inorganic perovskite solar cell absorption layer material.At present,researchers at home and on abroad have conducted extensive experimental research on the elements doping and interfacial properties of CsPbI₂Br,but the manner and modification mechanism of CsPbI₂Br doped with certain elements?for example,Mn?are still controversial.At the same time,the microstructure and properties of the heterogeneous interface related to the absorption layer need to be further explored.Therefore,this dissertation based on the first-principles calculations of density functional theory,the Mn doping micro-mechanism and the absorption layer CsPbI₂Br/electron transport layer SnO₂ heterogeneous interfacial local lattice and electronic properties are deeply studied at the atomic and electron level.It is expected to provide theoretical basis and help for the composition-structure design of CsPbI₂Br battery materials.The main results obtained are as follows:?1?The calculated results of the electronic properties of CsPbI₂Br show that CsPbI₂Br is a direct band gap semiconductor material.The valence band maximum?VBM?is mainly composed of I-5p and Br-4p orbitals,while the conduction band minimum?CBM?is mainly from the contribution of Pb-6p orbital.The bonding between Pb and I or Br atoms is a mix of ionic and covalent characteristics.The calculation for optical properties shows that the imaginary part of the dielectric function for CsPbI₂Br has three significant peaks,of which the peak at 2.84 eV is mainly the contribution of electron transitions from the VBM to the CBM,the static dielectric constant is 4.97;In the absorption spectrum,When the photon energy is greater than 1.36 eV,the absorption coefficient of CsPbI₂Br gradually increases.?2?The total energy and binding energy of the Mn substitutional and interstitial doping were calculated.It was found that the binding energy of the doping system are negative,which indicates that both Mn substitutional and interstitial doping CsPbI₂Br should be stable,with interstitial doping being the most stable.The most stable substitutional and interstitial doping model was selected for the calculation of electronic structure.The results show that when Mn substitutional doping CsPbI₂Br,the Mn-3d orbital is strongly localized at the Fermi level to form the intermediate bands,which means that Mn substitutional doped CsPbI₂Br will form an intermediate band semiconductor,widen the photon absorption range,and improve the utilization rate of photons.For Mn interstitial doped CsPbI₂Br,the Fermi level passes through the conduction band minimum and the impurity level introduced by Mn doping is above the band gap near the conduction band minimum.The conductive carriers are mainly contributed by conduction band electrons;this system exhibits the characteristics of an n-type doped semiconductor.In addition,both Mn substitutional and interstitial doping CsPbI₂Br will cause the static dielectric constant increase significantly,the light absorption capacity to be significantly enhanced,and the reflectance to be reduced.Moreover,Mn interstitial doping exhibits excellent optical performance in the low energy region.?3?CsPbI₂Br?100?/SnO₂?110?heterogeneous interface show that the interface lattice mismatch is 6.4%and the interface binding energy is-0.79 J/m²,which indicates that the interface orientation and bonding modes can exist stably;the differential charge density shows that there are electrons transfer exists at the interface,which promotes atomic bonding on the interface.The density of states calculations finds that the CsPbI₂Br?100?/SnO₂?110?interface has an interface state caused by I-5p orbital and O-2p orbital at the Fermi level,which is one of the reasons for the low conversion efficiency of solar cells.