Study Of Interface Electronic Properties Of Halide Perovskite/2D Material Heterostructures Based On Density Functional Theory

The halide perovskite materials have attracted extensive attention in photovoltaic and catalyst fields due to their excellent optoelectric properties including tunable energy band gap,high absorption coefficient,long-range carrier diffusion length,low-cost solution process.In the past decade,the power conversion efficiency?PCE?of the perovskite solar cells?PSCs?has boomed from initial 3.8%to latest 25.2%,which is in comparison with the commercialized crystalline silicon solar cells.Attributed to the unique geometry and outstanding physicochemical property,two-dimensional?2D?materials,such as graphene,have the potential to be generally applied in photoelectric devices,catalyst,energy storage,spintronics and so on.It is a very meaningful topic of research that 2D materials are integrated into the PSCs to enhance the performance of the PSCs.Thus,in this dissertation,the heterostructures of perovskite and 2D materials were studied by using the first-principles method based on density functional theory?DFT?.Furthermore,we investigated the interface effect on the electronic and optical properties of the perovskite/2D material heterostructure.The research content of this dissertation are summarily introduced as follows:???The heterostructure composed by the CH₃NH₃PbI₃ slab and monolayer graphene was investigated,which included two interfaces of PbI₂/graphene and CH₃NH₃I/graphene.The carriers transport shows different directions at the two interfaces.For the PbI₂/graphene interface,holes are extracted from the perovskite slab to the monolayer graphene,which leads to the graphene p-type doped.Nevertheless,for the CH₃NH₃I/graphene interface,electrons are injected into the graphene from the perovskite slab and then the graphene is n-type doped.The calculation shows that at the equilibrium separation,the work function of isolated graphene monolayer should be corrected by adding a value in order to assess the charge transfer in the interfaces.An interface dipole model is introduced to calculate the corrected value of the work functions.Therefore,the charge transport can be well elucidated based on the corrected work function of the monolayer graphene.A p-i-n solar cell with graphene/CH₃NH₃PbI₃/graphene configuration can be obtained by integrating the graphene to the perovskite film with CH₃NH₃I-and PbI₂-surface.The electronic filed between the both-side functional graphene layers facilitats the separation and transport of the photo-generated carries.???The all inorganic CsPbI₃/SnS heterostructures with the PbI₂/SnS and CsI/SnS interfaces were investigated by employing first-principles method.The calculation showed that the biaxial strains deriving from the interface mismatch reduce the energy level of the monolayer SnS to the low-energy level,and lead to the monolayer SnS an indirect-to-direct band gap transition.The charge transfer directions of the PbI₂/SnS and CsI/SnS interfaces are different,that is,eletrons transfer from the monolayer SnS to the perovskite for the PbI₂/SnS interface and move from the perovskite to the monolayer SnS for the CsI/SnS interface.However,the electron tunneling probabilities of the PbI₂/SnS and CsI/SnS interface are approximately equal.Both the PbI₂/SnS and CsI/SnS interfaces represent the Type-II band alignments which can facilitate the separation and transfer of the photogenerated carriers.What is more,the interface effect slightly reduces the band gap of the CsPbI₃ slab and enhances in turn the absorption ability of the CsPbI₃/SnS heterostructures.???The heterostructures were constructed by using monolayer black phosphorus?BP?to contact with the PbI₂-and CI-surface of all inorganic perovskite CsPbI₃.We investigated the electronic and optical properties of the CsPbI₃/BP heterostructure with the GGA-1/2+SOC?spin-obital coupling?method,which can reproduce the band structure of the CsPbI₃ slab and monolayer BP with the experimental accuracy.Our results showed both the PbI₂/BP and CsI/BP interfaces are indirect band gap semiconductors with the Type-II band alignment,which is different with the previous GGA calculations.We found that the CsI/BP interface represents excellent charge transfer behavior,although its tunneling probability is lower than that of the PbI₂/BP heterostructure.Moreover,due to the interface effect,the absorption abilities of the CsPbI₃/BP heterostructure in the visible and ultraviolet light region are enhanced.