Harnessing thermoelectric efficiency in Germanium-Based Janus monolayers: A theoretical perspective

With rapid industrialization and increasing energy demand, thermoelectric materials emerge as key players in transforming waste heat into clean, renewable energy, offering a sustainable solution to the global energy crisis. Despite several serious attempts in the last few decades, the full potential of thermoelectric technology has not yet been exploited because of menial thermoelectric performances from conventional materials. This study uses a combination of quantum and semi-classical computational approaches to investigate the electronic and thermoelectric behavior of Germanium-based (Ge₂AB (A/B=S, Se, Te)) Janus monolayers. Due to the broken inversion symmetry (compared to the trivial transition metal dichalcogenides), the investigated monolayers comprise unique E-k dispersion and phonon transport characteristics. These characteristics significantly enhance the thermoelectric performance by promoting multi-valleys and staggered band effects in the E-k dispersion and coupling acoustic and optical phonons in the phonon spectra. Phonon dispersion analyses show non-imaginary frequencies, confirming the investigated monolayers’ structural and dynamic stability. The study focuses on critical thermoelectric parameters such as the Seebeck coefficient, electrical/thermal conductivity, thermo-power, and thermoelectric figure of merit for the proposed set of Janus monolayers. It reveals that these Janus monolayers exhibit ultra-low lattice thermal conductivity (due to the combined effect of softening of phonon modes and large-scattering due to heavier atoms) and high power factors (due to the large number of charge carriers available for the transport in the multi-valleys present near the Fermi level). The calculated results estimate the highest thermoelectric figure of merit (up to 3.52) and significantly low-lattice thermal conductivity 0.03 W m⁻¹ K⁻¹ for Janus monolayer Ge₂SeTe. The significant findings demonstrate the potential of Ge₂AB (A/B=S, Se, Te) monolayers in highly efficient energy harvesting technologies. They emphasize their potential in next-generation thermoelectric devices, which significantly affect energy conversion technologies.