First-principles Study Of The Photoelectronic Properties Of Two-dimensional Sc₂CCl₂/AB₂（A=Si,W;B=S,Se,Te） And HfSe₂/InSe Heterostructures

Based on the current environmental and energy issues and the requirement of"double carbon"target,society needs low-carbon sustainable development.One of the effective ways to achieve an efficient and low-carbon transition of energy is through the use of solar energy conversion methods.Solar energy conversion technologies are currently used in the photovoltaic and photochemistry field.Among them,two-dimensional van der Waals heterostructure semiconductors for solar cells or driving photocatalytic overall water splitting have become popular because of zero carbon emission and no additional products in the reaction process.But still not solving the problem of low solar energy conversion efficiency,so it is urgent to screen efficient photovoltaic and photocatalytic materials.The main focus of this paper is to investigate the mechanism and feasibility study of two-dimensional Sc₂CCl₂/Si S₂van der Waals heterostructure for solar cells and two-dimensional Sc₂CCl₂/WX₂（X=Se,Te）and Hf Se₂/In Se van der Waals heterostructure for photocatalytic hydrogen evolution reaction based on first principles.1.The geometries of nine configurations of two-dimensional Sc₂CCl₂/Si S₂heterostructure was constructed and optimized,and the four most stable configurations were identified for further study based on the calculated values of binding energy.Their thermodynamic stability was confirmed based on ab initio molecular dynamics simulations.Their electronic structure properties,light absorption,and power conversion efficiency（PCE）were calculated,and the effect of strain engineering was investigated.The results based on the hybridization density generalization HSE06calculations show that all four configurations exhibit similar type-II energy band arrangement and direct band gap,and the heterostructure projects to two monolayers with interleaved energy bands,whose built-in electric field directions promote electron transfer from the Sc₂CCl₂monolayer to the Si S₂monolayer exactly.In addition,the YY configuration has good light absorption in the visible and UV range with a PCE value of up to 23.20%due to its near-zero conduction band shift and a sizing band gap of 1.49 e V.These findings provide theoretical support for the development of high-efficiency solar cells and photodetectors using Sc₂CCl₂/Si S₂heterostructures.2.The Sc₂CCl₂/WX₂（X=Se,Te）van der Waals heterostructures were constructed using Sc₂CCl₂,WSe₂,and WTe₂monolayer.The feasibility of the heterostructure for photocatalytic hydrogen generation was investigated based on first principles calculations of electronic structure properties,light absorption,and carrier mobility,and the differences in hydrogen generation performance of the two heterostructures were compared.It is found that the Sc₂CCl₂/WSe₂and Sc₂CCl₂/WTe₂heterostructures are confirmed to drive the photocatalytic hydrogen and oxygen precipitation reactions in a direct Z-scheme,although the conduction band bottom（CBM）of the Sc₂CCl₂monolayer and the valence band top of the WX₂（X=Se,Te）monolayer do not meet the redox potential conditions for water splitting.In addition,the strongest light absorption of the monolayer in the heterostructure can reach5.34×10⁴cm^-1in the visible range.Meanwhile,the solar-to-hydrogen（STH）conversion efficiency(_STH)was calculated based on the overpotential and the band gap projected on the monolayer in the heterostructure.The_STHof the Sc₂CCl₂/WTe₂and Sc₂CCl₂/WSe₂heterostructure can reach 20.70%and 7.35%.The calculated results show a significant effect of strain engineering on the_STHof the Sc₂CCl₂/WX₂（X=Se,Te）heterostructure.The_STHof the Sc₂CCl₂/WSe₂heterostructure can be increased from 20.70%to 23.00%at a 6%tensile strain.In addition,the Gibbs free energy change（?G）for the hydrogen evolution reaction（HER）ranges from 1.66 e V to 1.95e V,and the rate-limiting step of?G for the oxygen evolution reaction（OER）ranges from 1.66 e V to 1.95 e V,where the overpotential of the two heterostructures are thermodynamically feasible for driving hydrogen and oxygen generation.Although both heterostructures can achieve efficient photocatalytic water splitting,Sc₂CCl₂/WTe₂has a better photocatalytic performance.3.Nine configurations of Hf Se₂/In Se heterostructure with type-II band alignment were designed.And four configurations with large binding energies were selected,and their mechanism and thermodynamic feasibility of photocatalytic total water splitting was investigated.The electronic structure properties,optical absorption,and carrier mobility of the four conformations were calculated using the HSE06.Among them,the monolayer band edge projections and the built-in electric fields of the HIx and HIy configurations indicate that both configurations are type-II heterostructures and can satisfy the conditions for water splitting,while the band edges of the other two configurations do not satisfy the conditions for hydrogen generation.Based on the obtained overpotentials and band gaps,the corrected STH efficiencies(,_STH)were calculated to be 25.24%and 25.07%,respectively.The effect of strain effect on,_STHwas also investigated in this chapter,but the results were not significant.The?G for HER ranges from 0.92 e V to 1.13 e V,and the rate-limiting step of?G for OER range from 1.69 e V to 2.07 e V,show the two configurations are thermodynamically feasible for driving hydrogen and oxygen generation.Therefore,Hf Se₂/In Se heterostructures are potential candidates for the development of efficient photocatalysts with high STH.