Two-dimensional Thermoelectric Materials From High-throughput Screening

Thermoelectric materials can convert heat to electricity,and have the advantages of all solid state,small volume,high reliability,and noise/pollution free.With the increase of environment and energy issues,the potential application of thermoelectric materials in automobile exhaust waste heat power generation and thermoelectric-photovoltaic composite solar cells etc.has received wide attention from researchers in the world.Searching for high performance thermoelectric material is a hot topic in this field.In the 1990s,Hicks and Dresselhaus proposed that the quantum confinement effect can effectively enhance the thermoelectric properties of superlattice.This work provided theoretical support for finding low dimensional systems with good thermoelectric properties.With the successful fabrication of graphene in the beginning of this century,two dimensional(2D)materials have recently attracted much attention.In 2D materials,electrons are confined within a plane,so they may have better thermoelectric properties compared with their counterpart bulk materials due to quantum confinement effect.Meanwhile,with the development of material modeling and simulation technology and the high-throughput computing concept under the "material genome initiative" framework,a powerful tool for finding new 2D thermoelectric materials becomes available.In this work,we first identified all possible 2D materials by high-throughput screening of the inorganic crystal structure database(ICSD).Then,based on the high-throughput first principles calculations,band structures of 2D materials were calculated and the effect of strain on band structures were analyzed.Finally,based on Boltzmann transport equation calculations,2D materials with good thermoelectric properties were virtual screened and identified.First,89 layered compounds with Van der Waals interaction were identified from ICSD by high-throughput screening.Their 2D counterparts were classified based on space groups.Then their magnetic moment and energy structures were calculated respectively.From the calculation results,it was found that 22 bulk layered compounds are magnetic.After exfoliation into 2D materials,nine compounds have unchanged magnetic moment,while eight decrease and other five increase.By calculating the band structures,it was found that ten 2D materials have indirect-to-direct bandgap transition when exfoliated to two-dimensional materials,while other six have direct-to-indirect bandgap ransition with exfoliation.Under in-plane strain,thriteen 2D materials have indirect-direct band gap transition,among them eight are under tensile strain while five under compress strain.Finally,power factors of 2D materials as a function of carrier concentration were calculated.It was found that p-type monolayer Bi2Te3 has the highest power factor,and its maximum power factor is three times higher than the bulk material.These results indicate that,after exfoliation into 2D materials,dimension reduction can change the magnetic moment and band structure of some materials,and then improve thermoelectric performance.In-plane strain can tune the band structures of 2D materials effectively.Our research will help to understand of 2D materials physics,help to design of new 2D thermoelectric materials,and help to expand 2D materials application in semiconductor nano-devices.