Theoretical Exploration of Si7X (X = Ge, Sn): Bridging Structural and Energy-Related Applications

A comprehensive study is conducted on the structural, mechanical, dynamical, electronic, optical, and thermoelectric properties of Si₇X (X = Ge and Sn) using first-principles calculations. Structural analysis confirms the stability of both compounds, while the elastic and mechanical properties reveal their ductile nature. Dynamical stability is verified through phonon dispersion spectra, ensuring the robustness of the predicted phases. Electronic band structure calculations indicate that both Si₇Ge and Si₇Sn are semiconductors with direct band gaps of 1.03 and 0.75 eV, respectively. These materials also exhibit excellent optical absorption, with coefficients reaching 10⁵ cm⁻¹, making them ideal for optoelectronic applications. The maximum photoconversion efficiency, determined using the spectroscopic limited maximum efficiency (SLME) method, is calculated to be 30.3% for Si₇Ge and 23.2% for Si₇Sn at 300 K. Furthermore, thermoelectric performance is evaluated, with the average figure of merit (ZT) found to be 0.76 for Si₇Ge and 0.78 for Si₇Sn, highlighting their potential for renewable energy applications. These results underscore the promise of Si₇Ge and Si₇Sn as multifunctional materials for photovoltaic, optoelectronic, and thermoelectric technologies.