| With the development of social industrialization,the energy crisis and environmental pollution are becoming more and more serious.As a means to effectively use solar energy to generate clean energy,photocatalysis is expected to solve these two problems.Traditional three-dimensional photocatalysts have low specific surface area,weak light absorption capacity,and high carrier recombination rate,making it difficult to meet the design requirements of high-efficiency photocatalysts.Two-dimensional materials have great application prospects in the field of photocatalysis due to their large specific surface area,numerous catalytic reaction sites and good light absorption capacity.Two-dimensional transition metal chalcogenides(2D TMDCs)are stable in the atmospheric environment and have a suitable light absorption band gap.They are a good choice as photocatalysts,but the symmetry of their structure along the out-of-plane direction leads to the failure of effective separation of photogenerated carriers,which limits the photocatalytic efficiency.Twodimensional asymmetric transition metal chalcogenides(2D Janus TMDCs)synthesized in recent years have inherited the excellent properties of 2D TMDCs,and intrinsic dipoles help separate photogenerated carriers,which are more effective than 2D TMDCs,improving the light conversion efficiency.However,due to the spatial confinement effect of the singlelayer Janus TMDCs,the carriers are always confined in the same layer of material,resulting in unsatisfactory improvement in the carrier separation effect.Therefore,the design of heterojunctions that can efficiently separate carriers has become the hot spots in the field of photocatalysis.Designing new heterostructures to improve catalytic efficiency is the current focus and difficulty in the field of photocatalysis.This paper uses first-principles density functional theory to carry out the following research work:(1)The photocatalytic properties of single-layer 2D Janus TMDCs and single-layer 2D TMDCs were systematically studied.The light conversion efficiency of the single-layer catalyst material is obtained by calculating the band gap,band edge position,intrinsic dipole,and overpotential of the material,and the influence of various factors on the light conversion efficiency is analyzed.Through comparison,it is found that the intrinsic dipole of 2D Janus TMDCs can reduce the redox potential of water,so that the band gap breaks through the 1.23 eV limit;it is concluded that the small band gap and the large intrinsic dipole can improve the monolayer catalyst;finally screened out the most suitable 2D Janus TMDCs material CrSTe as a single-layer catalyst,and its light conversion efficiency is as high as 43%.(2)In order to better separate the carriers,we screened the direct Z-type heterojunction based on work function matching,band gap size,and band edge position design.Through a series of studies,it is found that the small band-gap and large band-order heterojunctions composed of two 2D Janus TMDCs with large work functions are conducive to the formation of Z-type charge transfer paths,thereby improving the redox capability of carriers;The superposition of intrinsic dipole and interface dipole in the same direction can increase the potential difference between the two sides of the heterojunction,and the direction of the potential difference falling from the side where the oxidation reaction occurs to the side where the reduction reaction occurs can reduce the redox potential difference of water,thereby improving carrier utilization.After designing and screening,we obtained highefficiency 2D Janus TMDCs direct Z-type heterojunction CrSSe-CrSeTe(S-Se),its light conversion efficiency reached 23.5%.At the same time,a reasonable design criterion for high-efficiency direct Z-type heterojunction is proposed. |
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