Promising photovoltaic performance in ternary chalcogenides ASbS2 (A=Na, K): Atomistic insights from <i>ab initio</i> calculations

Ternary chalcogenides (TCGs) are drawing significant attention as a promising light absorber for thin-film solar cells but their material properties are not yet well understood. Here, we report a study of lattice dynamics and optoelectronic properties of TCGs ASbS2 (A=Na, K) using advanced first-principles techniques, including self-consistent phonon (SCP) theory, the many-body perturbation GW approach, and momentum relaxation time approximation. By performing phonon calculations with SCP theory, we prove dynamical stabilities of their monoclinic phases, yielding low lattice thermal conductivities below 1.3 W/m K caused by the Sb atomic rattling vibrations. Moreover, our calculations of quasi-direct bandgap, exciton binding energy, absorption coefficient, and charge carrier mobilities demonstrate their superior optoelectronic properties for thin-film solar cells with relatively high values of spectroscopically limited maximum efficiency. This work provides a useful guide for the design of advanced light absorbers based on TCGs.