First-principles study of optoelectronic and thermoelectronic properties of the ScAgC half-Heusler compound

Abstract

Here, we present a theoretical study in the context of photovoltaic (PV) and thermoelectric (TE) applications of ScAgC. The electronic, optical, and thermoelectric properties have been investigated systematically using density functional theory (DFT) and semi-classical Boltzmann transport theory. DFT calculates a direct band gap of 0.47 eV, whereas the $G_0{W}_0$ method estimates a band gap of 1.01 eV. We used parabola fitting to estimate the effective mass values for bands B1 to B4 at $\Gamma$-point, which are -0.087 (-0.075), -0.17 (-0.27), -0.17 (-0.27), and 0.049 (0.058) along the $\Gamma$-$X$ ($\Gamma$-$L$) direction, respectively. Furthermore, the optoelectronic properties are calculated and analyzed over an energy range of 0 to 10 eV. The optical conductivity, refractive index, and dielectric function show strong optical transitions in the visible region. The lowest calculated reflectivity is 0.24 at 4.7 eV, and the highest calculated value of the absorption coefficient is $1.7\times 10^6$ cm${}^{-1}$ at $8.5$ eV. At 300 K, we expect a maximum solar efficiency (SLME) of 33\% at a thickness of $1\mu$m. The lattice part of the thermal conductivity shows a maximum value of 3.8 Wm${}^{-1}$K${}^{-1}$ at $1200$ K. At 1200 K, for electron doping of $3.9\times 10^{21}$ cm${}^{-3}$, the maximum value of $S^2\sigma /\tau$ is $145\times 10^{14}$ $\mu$WK${}^{-2}$cm${}^{-1}$s${}^{-1}$, while for hole doping of $1.5\times 10^{21}$ cm${}^{-3}$, it is $123\times 10^{14}$ $\mu$WK${}^{-2}$cm${}^{-1}$s${}^{-1}$. The highest $ZT$ at $1200$ K is expected to be $0.53$, whereas the optimal efficiency is predicted to be $8.5\%$ for cold and hot temperatures of $300$ K and $1200$ K, respectively. The collected results suggest that the ScAgC compound is a potential candidate for renewable energy sources such as solar cell and TE applications

14 pages, 11 figures (To appear in Phys. Scr.)

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• Band gap renormalization, carrier mobility, and transport in Mg${}_2$Si and Ca${}_2$Si: \textit{Ab initio} scattering and Boltzmann transport equation study
• Significant first-principles electron-phonon coupling effects in the LiZnAs and ScAgC half-Heusler thermoelectrics