First-principle Calculations On Thermoelectric Coefficients Of Organic Carbon Nitrides

With the rapid development in economy all over the world,the consumption of fossil energy has continuously increased,leading to severer and severer energy scarcity.During the utilization of fossil energy,most of energy are wasted in the form of heat.So it is of great significance to enhance the efficiency of energy usage or to make use of waste heat.Thermoelectric(TE)technology can transform low-grade heat directly into high-grade electricity,which has wide potential for applications on waste heat recycle.The efficiency of TE conversion depends on the figure of merit of TE materials,(5(5(5(5,which is the ratio of power factor over thermal conductivity.How to enhance power factor or reduce thermal conductivity is crucial for TE application.The development of nanotechnology has brought new prospects for thermoelectrics.Low-dimensional structures can not only reduce thermal conductivity effectively,but also enhance power factor.Inorganic TE materials have excellent electrical and thermal properties.So main research work focus on lowering thermal conductivity with phonon engineering.But these strategies are complex and require much effort.By contrast,organic TE materials has low thermal conductivity and high Seebeck coefficient,and inherit advantages of organics,such as light weight,high flexibility,and low cost,thus having received wide attention gradually.In this paper,we propose to enhance the electric properties of organics with the overlap of ? orbitals.Through First-principle calculations and Boltzmann transport theory,we study the TE performance of polymeric carbon nitride.The maximum of (5(5(5(5 is 0.67 at room temperature.The most important key of large figure of merit is its one-dimensional band structure.To make advantage of the preferred electronic structure,we compare the electronic properties of three carbon nitride derivatives and A-A stacked graphite.It is found that strong overlap of ? orbitals and in-plane electronic confinement can cause the lowdimensional band structure.And discontinuous in-plane ? bonds result in the in-plane electronic confinement.Also,for the method,we improve the general constant relaxation time approximation method innovatively based on deformation potential theory.The method we use do not depend on experimental measurements,more convenient for researchers to predict TE performance of materials.Our research work provides a new idea to enhance the TE efficiency of organic materials.