Optoelectronic Properties Of Two-dimensional SnSe/GeTe Heterostructures:First-principles Calculations

Since the discovery of graphene in the early 21st century,two-dimensional materials(2D)have rapidly become a research hotspot in the field of low-dimensional nanomaterials due to their excellent physical properties,and many novel 2D materials have been fabricated experimentally after graphene,such as h-BN,Mo S₂,phosphonene and so on.The 2D group-?/?monochalcogenides MX(M=Sn,Ge;X=S,Se and Te)as the phosphorus-like material with similar structure to black phosphorene,has attracted more and more attention in the application of solar cell and photoelectric converter because of their suitable band gaps,high carrier mobility and abundant earth reserves.At present,the research on 2D group-?/?monochalcogenides is mainly focused on its single intrinsic two-dimensional materials,and the research on the construction of heterojunction between them is still very lacking.In this paper,based on the research on the lattice characteristics and experimental progress of the layered group-IV/VI monochalcogenides MX,we propose the lateral and vertical Sn Se/Ge Te heterostructures with high photovoltaic performance based on layered Sn Se and Ge Te,and using first-principles calculations based on density functional theory to systematically study their structure,electronic and optical properties.We found that these heterostructures not only have excellent optical properties,but also have type-II band alignments,which have extraordinary application potential in the field of optoelectronics.(1)First,we study the lateral Sn Se/Ge Te heterostructures.Our results show that the lateral Sn Se/Ge Te heterostructures can exist stably when the one-dimensional splicing interface is along the armchair direction and the zigzag direction.Their lattice mismatch and formation energy are very small,and the vicinity of the interface is connected by covalent bonds,which has good stability,which is very beneficial to the epitaxial growth of heterostructures.According to their electronic properties,it is found these heterostructures are semiconductors with type-II band alignments,and their electronic properties can be effectively tuned by changing the size and composition ratio of the heterostructures.More importantly,these heterostructures process higher absorption capacity and higher power conversion efficiency(19.4%?22.3%)in the visible light range.As an ideal environment-friendly energy source to solve the problem of world energy shortage,solar energy still lacks the efficient conversion material to convert solar energy into electric energy.These exotic electronic and optical properties of the lateral Sn Se/Ge Te heterostructures make them a promising candidate materials for photovoltaic applications.(2)Considering the different stacking modes of 2D materials,we also stacked layered Sn Se and Ge Te in the vertical direction to construct the vertical Sn Se/Ge Te heterostructure(Van der Waals heterostructure).Compared with lateral heterostructure,vertical heterostructure has lower requirements for lattice mismatch,and often has unique properties under the action of van der Waals force between layers.We also calculated the photoelectric properties of the Sn Se/Ge Te vertical heterostructure,including the energy band structure,band alignment,and light absorption coefficient,and found that its light absorption ability in the visible light range is very good.In order to realize the regulation of the optoelectronic properties of the vertical heterostructure,we applied stress to it,and the results showed that the energy band structure of the vertical Sn Se/Ge Te heterostructure changed greatly under the condition of applying biaxial stress,but the optical properties are very stable,and its photoelectric conversion efficiency has been significantly improved,which shows that the vertical Sn Se/Ge Te heterostructure also has potential photovoltaic applications.