First-Principles Study On The Structures And Physical Properties Of Novel Two-Dimensional Energy Materials

Energy is an essential material foundation for human survival and development.Energy is also an important strategic resource for national economic and social devel-opment.The economy,energy and environment in today's society have become an in-divisible organic whole.The sustainable development of economy,energy and environ-ment is an important prerequisite for achieving China's modernization goals.The es-sence of the energy problem is the relationship between economy,energy and environ-ment.Energy has restricted the development of human society in varying degrees.On the other hand,the use of energy has damaged the environment of the earth to varying degrees,and has even threatened the survival of mankind.Since the beginning of the 21st century,mankind has been facing increasingly serious energy problems.The in-creasing depletion of petroleum resources has forced people to switch to new available resources after experiencing biomass(mainly wood),coal and petroleum energy.En-ergy must not only meet the growing economic development needs of mankind,but also meet the sustainable development of mankind and nature.The successful preparation of two-dimensional(2D) materials has broadened the academic horizons in materials research.Because electrons are limited to two-dimen-sional space,2D materials have acquired unprecedented physical,electronic,and chem-ical properties.The ability to prepare ultra-thin 2D nanomaterials with the desired com-position,size,thickness,crystal phase,defects and surface properties is particularly important for further improving their physical,chemical,optical,electronic and optical properties,as well as exploring potential applications for different properties.So far,a large number of ultra-thin 2D nanomaterials have been prepared by various synthetic methods.At the same time,with the rapid development of nanotechnology,some pow-erful characterization techniques have been developed to characterize ultra-thin 2D na-nomaterials to reveal their composition,size,thickness,crystallinity,crystal phase,de-fects,oxidation state,and electronic state.In view of the broad application prospects and advantages of 2D materials in the energy field,this thesis mainly discusses the piezoelectric effect of 2D materials(con-verting mechanical energy into electrical energy and vice versa)and light absorption(converting solar energy into electrical energy).The piezoelectric effect of the novel type of 2D materials is mainly studied from three aspects:property research,property control and structural design of 2D piezoelectric materials.The piezoelectric properties of the newly prepared 2D group IV-V MX₂ compounds are studied and it is found that they have unusual huge negative piezoelectric coefficients.The effects of adsorption of atoms on 2D piezoelectric group III-V compounds to regulate its piezoelectric proper-ties are also studied.It is found that atomic adsorption can effectively increase the sta-bility of the structure and increase the piezoelectric coefficient of the 2D material,and especially,it is able to introduce or increase the out-of-plane piezoelectric coefficient,which is very important for the practical application of piezoelectric materials.We also introduce novel 2D piezoelectric phosphene through structural reorganization,and show that single-element materials can have piezoelectric effects.For the light absorp-tion of 2D materials,a novel 2D b-Sn Se with ultra-high carrier and energy conversion efficiency is predicted by calculating the light absorption,energy conversion efficiency and carrier mobility of the 2D material.Considering the importance of structural pre-diction and design in the study of 2D materials,our research group has developed a structural search software RG²to search for possible 2D energy materials.The power of RG² is verified in our study,and preliminary results are presented.The novel 2D group IV-V structures with ultra-high carrier mobility is predicted.Our studies indicate that 2D materials have great research value in the field of energy.