First-principles investigation of electronic and thermoelectric properties of monolayer pentagonal nanostructures of C2B4 and C4B2

In this study, we investigate the electronic and thermoelectric properties of monolayer nanostructures of C2B4 and C4B2 by first principles calculations. At the first, we calculated the electronic band structure and density of states based on density functional theory (DFT) and using the QUANTUM ESPRESSO computational package. The band gap values were obtained as 0.43 eV (direct band) and 1.45 eV (indirect band) for C4B2 and C2B4, respectively. Then, based on the calculated electronic energy, we obtain the thermoelectric transport coefficients such as the Seebeck coefficient, electrical conductivity, electrical thermal conductivity, and dimensionless figure of merit by solving the semiclassical Boltzmann transport equation in relaxation time approximation and within Boltztrap computational package. The calculated results show almost isotropic transport properties for both nanostructures. In particular, the C2B4 nanostructure exhibit comparative thermoelectric performance compared to C4B2. Also, the Seebeck coefficient and figure of merit of C2B4 is even larger than that of C4B2 under the studied carrier concentration and temperature region, so that, the Seebeck coefficient and figure of merit for p-type doping at room temperature were obtained as 1765 µV/K and 1.02 for C2B4, and 216 µV/K and 0.81 for C4B2, respectively.