Interface Manipulation Of Two-dimensional Ⅲ-Ⅵ Materials For Applications Of Solar Energy Conversion

With the increasing global energy demand and increasingly serious environmental issues,solar energy conversion applications（including solar cells and photocatalytic technology）have become the focus and hotspot of researches in the area of materials science and energy.Two-dimensional（2D）materials are ideal candidates for solar cells and photocatalytic decomposition due to their atomic thickness,good mechanical properties,large specific surface area,high carrier mobility and easily tuned band gap properties.The physical and chemical properties of the surface and interface for 2D materials are often related to the electronic and photoelectric properties of materials.Therefore,appropriate means of interface engineering would be the key to improve the conversion efficiency of 2D materials solar cells and photocatalytic technology for water splitting.The highly exposed surface atoms and abundant interface characteristics of 2D materials provide more possibilities for interface engineering to tune the properties of 2D materials.However,the structure and formation mechanism for interface are complicated,involving varies interfacial interractions of van der Waals forces,covalent bonds,charge transfer and interfacial dipole.Therefore in-depth understanding of the formation mechanism of different interfaces and exploring the chemical and physical properties of different interface structures based on this,and according to different applications（solar cells and photocatalytics for water splitting）,choosing appropriate means of interface engineering to reasonable tune and optimize the surface and interface of 2D materials and finally improve the the conversion efficiency of solar cell and photocatalytic technology for water splitting would be the important research topics.In this dissertation,based on molecule-2D materials organic interfaces and 2D material heterostructure interfaces,the density functional theory coupled the van der Waals force correction were carried out to study the physical and chemical adsorption state structures of molecules on the 2D materials surface and van der Waals vertical 2D heterostructures in depth.Aimed at the key scientific issues for solar cells and photocatalytics for water splitting,the involved interface egineering means and interfacial interactions were systematically investigated to reveal the mechanism of adsorption for different molecules and interface engineering of 2D materials heterostructures.We further discussed the influence of different interface engineering means on the properties for 2D materials,proposed effective methods to optimize the interfacical structures and properties,and finally an efficient,stable and reliable solar cell and photocatalyst for water splitting were designed.The main research contents are as follows:（1）Since conventional doping methods would reduce the mobility of 2D materials and make it difficult to achieve effective doping without destructions,a non-destructive remote doping method is proposed by using interface charge transfer,that is,molecular physical adsorption combined with strain engineering to control the conductive properties of two-dimensional materials.We investigated the physical adsorption of varies organic molecules on the surface of the 2D In Se.The influence of the interfacial charge transfer for organic molecules on the conductive properties of 2D In Se,including the carrier type,carrier concentration and carrier mobility were discussed.The effects of the strain on the stability of interfacial structure,carrier concentration and mobility for 2D In Se were analysed and the synergistic effect of organic molecular physical adsorption and strain engineering on improving the conductivity of2D In Se was clarified.Finally,by remote doping with TTF molecules,an effective N-type doping of 2D In Se was achieved,and the 2D In Se with improved carrier concentration and mobility was obtained,and its conductivity was as high as 1.85×10⁵ S/m at room temperature.In addition,the strain applied to the adsorption structure can also solve the problems of molecular physical adsorption at room temperature,such as unstable structure,small charge transfer and unsatisfactory doping effect.We also extend this method to other III-VI materials,and the calculation results proved that this method is universal to improve the doping effect of other two-dimensional materials.（2）To solve the stability problem of performance for the flexible solar cell,a stable molecule/2D material interface structure with chemical adsorption were builded,via the interface charge transfer and interfacial dipole role between molecules and 2D materials.An interface engineering method which can make 2D In Se always maintain the property of direct band gap during the mechanical deformation process was proposed and a flexible P-N junction solar cell based on Mo O₃ partially doped In Se monolayer was designed.A large amount of charge transfer caused by the large difference of the work function between the molecule with high work function and 2D In Se,as well as the dipole effect caused by the deformation of the molecular structure due to the chemisorption,significantly reduced the work function of 2D In Se and realized the effective P-type doping.In addition,chemisorption destroys the weak In-Inπ-πbond of In Se,making the corresponding energy level become less sensitive to external strains,so that the 2D In Se with chemisorption can always maintain the direct band gap property under large mechanical deformation.By partially adsorbing Mo O₃ on In Se monolayer,the doped part of In Se acts as the donor and the undoped part of In Se acts as the receptor.Drived by the work function difference between Mo O₃-In Se and In Se,the charge spontaneously transfers from the undoped In Se part to the Mo O₃-doped In Se part,thus forming a strong built-in electric field at the interface of the P-N junction to promote the separation of photogenerated carriers.The final calculation results show that the solar cell can maintain an energy conversion efficiency of more than 5%under large mechanical deformation,and the maximum efficiency can reach up to 20.7%.（3）To improve the efficiency of Z-scheme photocatalyts for water splitting,utilizing the polarity of Janus materials,an efficient Z-scheme heterostructure photocatalyt for water splitting with spatially separated redox sites was designed.The intrinsic dipole moment of single-layer Janus material can not only shift the H⁺/H₂ and H₂O/O₂ redox potential on both sides of the material to break the band gap limit（1.23 e V）of photocatalyts for water splitting,but also separate the redox sites in space.Moreover,the built-in electric field caused by dipole moment can accelerate the separation of photogenerated carriers and greatly inhibit the recombination of photogenerated carriers.When stacking heterostructures based on the Janus materials,due to the intrinsic dipole moment,different stacking orders would lead to different directions of the built-in electric field at the interface,thus determining different charge transfer modes（Z-Scheme or Type-Ⅱheterojunction）.For Z-scheme heterostructures,only when the direction of the intrinsic dipole moment of the polar material is consistent with the direction of the interfacial built-in electric field,the redox abilities of the heterostructure can be enhanced,and vice versa.Finally,the In₂Se₃/Sn P₃ heterostructure Z-scheme photocatalyst was constructed.The photocatalyst has strong redox abilities and well-separated photocarriers,and the photocatalytic hydrolysis efficiency of STH can reach 19.26%.