Theoretical Study On Thermoelectric Properties Of New Type Of Two-dimensional Layered Phosphorene Derivatives

Nowadays,the global energy crisis and environmental pollution are becoming increasingly serious.Electrical energy directly transformed from thermal energy through thermoelectric device which is a promising way to increase energy efficiency and alleviate environmental pollution,has great application value.A great deal of work has been done to improve the thermoelectric properties of materials for decades.It has been found that the thermoelectric conversion performance of materials can be effectively improved after nanometerization due to the quantum size effects.The great success of graphene provides a natural platform and opens up a new opportunity for two-dimensional thermoelectric devices.After this,two-dimensional materials have become a hot spot in thermoelectric materials.As an emerging two-dimensional material,phosphorene has a good thermoelectric figure of merit,but its practical application is limited by its chemical instability.Owing to its excellent electronic properties and stable crystal structure,the two-dimensional single-layer phosphide has received widespread attention from researchers.In this paper,we carried out the following work around phosphorene derivatives:1. Byusing first-principles calculations combined with the semi-classical Boltzmann transport theory,we systematically investigate the thermoelectric properties of monolayer Si P and Ge P.High anisotropy is observed in both phonon and electron transport of monolayer Si P and Ge P where the thermal and electrical conductivity along the xx crystal direction are smaller than those along the yy crystal direction.The lattice thermal conductivity?room temperature?along the xx crystal direction is about 11.05 W/m K for monolayer Si P and 9.48 W/m K for monolayer Ge P.However,monolayer Si P and Ge P possess almost isotropic Seebeck coefficient,and the room temperature values with both n-and p-type doping approach 2.9 m V/K and2.5 m V/K,respectively.Based on the electron relaxation time estimated from the deformation potential theory,the maximum thermoelectric figure of merit of monolayer Si P and Ge P with n-type doping approach 0.76 and 0.78 at 700 K,respectively.The results presented in this work shed light upon the thermoelectric performance of monolayer Si P and Ge P,and provide theoretical guidance for future practical applications.2. We also systematically investigate the thermal and thermoelectric properties of monolayer In P₃through combining first-principles calculations and semi-classical Boltzmann transport theory.Our calculations show that the average lattice thermal conductivity of monolayer In P₃is about 0.63 W/m K at room temperature,which is comparable to that of classical thermoelectric materials.Such a poor phonon transport property mainly originates from its smaller group velocity and stronger phonon–phonon scattering?including both scattering magnitude and channels?.Unlike the isotopic phonon transport property,the electronic conductivity and electronic thermal conductivity of monolayer In P₃present obvious anisotropic behavior.Meanwhile,a high Seebeck coefficient is also predicted in monolayer In P₃with both n-and p-type doping due to the large electronic band gap and sharp increase in electronic conductivity.Based on the electron relaxation time estimated from deformation potential theory,the room temperature thermoelectric figure of merit of monolayer In P₃is found to be as high as 2.06?with p-type doping?and 0.61?with n-type doping?along the armchair and zigzag directions.The results presented in this work shed light on the thermoelectric performance of monolayer In P₃and qualify its potential application in a multifunction device that contains both photovoltaic and thermoelectric technologies.