Theoretical Study Of Carrier Mobility And Photocatalytic Properties Of Novel Two-Dimensional Materials

With the development of modern society,environmental pollution and energy shortage have become the focus of world attention.Nowadays,fossil fuel is still the the main source of global energy,which gives rise to environmental pollution and climate change.Therefore,optimizing the energy structure to improve the utilization rate of energy and the development of clean and renewable energy are important approaches to meet the increasing global energy requirement and to resolve the environmental problems caused by the overuse of large amounts of fossil fuels.In the past few decades,the limitations of traditional material properties have been making the development of low-energy devices and the clean and renewable energy into a bottleneck period.In 2004,with the successful preparation and widespread application of monolayer graphene,which has the unique physical optoelectronic properties,a new way to exploring and utilizing the novel materials has been pointed out.Inspired by the discovery of graphene,a large number of new two-dimensional materials with atomic thickness,such as trasition metal dichalcogenides,hexagonal boron nitride,black phosphoenene,silicene,and transition metal carbides or carbonitrides,have constantly beening discovered and widely applied in photovoltaic devices,photocatalysis,sensors,energy storage materials and other fields.Therefore,we have systematically investigated the characteristics of the electronic properties and their strain responses,absorption and utilization of solar energy,carrier transport properties,as well as the potential for photocatalystic water splitting to produce hydrogen of several novel two-dimensional materials such as monolayer and bilayer SnP₃semiconductors,Penta-X₂Y?X=P,As,Sb;Y=C,Si?using the first-principles calculations based on density functional theory.We hope that the theoretical results can provide meaningful guidance for the future experiments of developing low-power photovoltaic devices or photocatalytic water splitting to generate hydrogen.The main contents and conclusions are summarized as follows:1.Using the first-principles calculations based on density functional theory,we firstly proposed and systematically investigated the structural stability,electronic,optical and carrier transport properties of novel monolayer and bilayer SnP₃ semiconductor.The results show that monolayer and bilayer SnP₃ semiconductors not only exhibit exercellent kinetics and thermodynamic stability,but also have cleavage energy of 0.57 and 0.38 J/m²,respectively,which imply the possibility of their exfoliation from layered bulk SnP₃ experimentally.Monolayer and bilayer SnP₃ semiconductors are indirect semiconductors with band gaps of0.72 eV and 1.02 eV,respectively.Tunable bandgaps can be achieved by applying biaxial strain.Meanwhile,when the tensile strain is greater than 12%and the compressive strain is less than 4%,monolayer and bilayer SnP₃ transform from indirect semiconductors into quasi-direct and direct semiconductors,respectively,which greatly increases the efficiency of photoexcitation.In addition,the carrier mobility of monolayer SnP₃ semiconductor was several times higher than the previously reported monlayer GeP₃.In addition,the bilayer SnP₃semiconductor has an ultrahigh hole mobility of up to 10⁴ cm²V^-1s^-1.These results qualify monolayer and bilayer SnP₃ semiconductor as promising novel 2D materials for applications in microelectronics,optoelectronics and field-effect transistors.2.Using the first-principles calculations based on density functional theory,the properties of mechanical,electronic,optical and carrier transport properties of the kinetically and thermodynamically stable Penta-X₂C?X=P,As,Sb?family was firstly and systematically investigated to determine whether it can be used as a photocatalyst for water splitting to generate hydrogen.The results indicate that the Penta-X₂C are indirect semiconductors with band gaps of 2.64 eV,2.09 eV and 1.35 eV,respectively,which are favorable for the utilization of visible-ultraviolet light.More importantly,the band edge positions of Penta-P₂C and Penta-As₂C could perfectly meet the requirements of redox potential in the process of photocatalytic water splitting for hydrogen production.The photogenerated electrons and holes of Penta-X₂C family possesses anisotropic and ultrahigh mobility up to 10³¹0⁵ cm²V^-1s^-1,which are favourable to reduce the recombination rate of photogenerated electron-hole pairs and thus improving the efficiency of photocatalysis.Moreover,the Penta-X₂C family shows exercellent mechanical properties,such as relatively smaller young's modulus,large critical strain and interestingly,negative poisson's ratio.Therefore,the Penta-X₂C family has potential applications not only in photocatalytic water splitting to generate hydrogen,but also in designing microelectronics,optoelectronic devices,and nanomechanics.3.Using the first-principles calculations based on density functional theory,we have firstly investigated the potential of the Penta-X₂Si?X=P,As,Sb?family as a photocatalyst for water splitting to generate hydrogen.The results show that all of the Penta-X₂Si family are suitable as a candidate photocatalyst for water splitting to generate hydrogen because of the proper band gaps of 2.69 eV,2.37 eV and 2.03 eV,and the band edge positions of the Penta-X₂Si family can perfectly satisfy the redox reaction potential requirements of photocatalytic water splitting.Meanwhile,the Penta-X₂Si family exhibits excellent light absorption in visible-ultraviolet region,which can reach 10⁵ cm^-1.More importantly,the photogenerated electron and hole of Penta-X₂Si family possess strongly anisotropic and ultrahigh mobility up to 10⁵ cm²V^-1s^-1,which promotes the separation and migration of the photogenerated electrons and holes.Therefore,the Penta-X₂Si family can not only be used as a candidate photocatalyst for photocatalytic water splitting to produce hydrogen,but also has great application prospects in the fields of optoelectronic devices,sensors and nanomechanics.