| In recent years,van der Waals heterostructures（vd WHs）have attracted extensive attention as an effective method to improve the properties and extend the application range of optoelectronic materials.It is well-known that heterojunctions can be classified according to different band arrangement,and different types of heterojunctions have different properties and application fields:straddling Type-I heterojunctions are more suitable for luminescent applications;staggered Type-II heterojunctions are commonly used for photocatalysis,photoelectrics,and photoelectric detection;broken gap Type-III heterojunctions are mainly used in tunneling field effect transistors（FETs）.Therefore,the dynamic modulation of band arrangement is a significant and challenging aspect of designing devices with multifunctional applications.Generally,applying strain,electric field,defect engineering,and doping are the common methods to regulate the band type.However,it is worth noting that large external electric field and stress engineering may have adverse effects on the stability and performance of the structures,and the accuracy of the defect engineering is difficult to control;therefore,doping may be a better choice.On this basis,3D all-inorganic perovskite CsSnBr3and 2D monolayer material WS2were used to construct the heterojunction in this paper.By replacing S atom in monolayer WS2with Se atom,we explore the change of energy band type of heterojunction and its photoelectric properties.The following are the main research content and results of this thesis:1.According to the octahedral structure of the perovskite CsSnBr3,we obtained two structures with different terminated surfaces,and two initial heterojunctions Sn Br2/WS2and Cs Br/WS2with fewer atoms and the mismatch less than 5%were obtained by combining them with monolayer WS2respectively.We doped monolayer WS2with 0%,50%and 100%Se atoms in the two initial heterojunctions respectively,and selected the most stable interlayer distance and heterojunction model as the research object by calculating their binding energy.Based on the first principle,the energy band,density of states,optical absorption,interfacial charge transfer and effective mass of each monomer and heterojunction are calculated and analyzed.2.The calculation results show that:with the increase of doping ratio of Se atom,the electronic energy band provided by WS2（1-x）Se2xmonolayer gradually shifted up,the band gap value of heterojunction gradually increases,the contribution of VBM and CBM changes,and the band alignment transform from type-II to type-I and type-III to type-II for Sn Br2/WS2and Cs Br/WS2heterojunctions,respectively.3.Meanwhile,building CsSnBr3/WS2（1-x）Se2xvd WHs improves the optical absorption range and intensity,and the optical absorption intensity can reach the order of 105.In addition,the effective mass of electrons values decrease with the doping ratio of Se atom x=100%to x=0 because of the transition of the CBM from smooth to steep,which will improve the carrier migration rate.The research results in this thesis provide a theoretical method for regulating the band types of vd WHs and improving the photoelectric properties of materials,and have some enlightenment on photoelectric application and photoelectric detection technology. |
