2D Janus SnSeS monolayers for solar energy conversion: insights from DFT and excitonic analysis

The growing global demand for sustainable energy solutions has driven intensive research into novel materials for solar energy conversion. In this study, we employ first-principles calculations based on density functional theory to investigate the structural, thermodynamic, electronic, optical, and excitonic properties of a two-dimensional (2D) SnSeS monolayer. Results reveal that 2D SnSeS is an indirect semiconductor, exhibiting a band gap of 0.94 eV at the PBE level and 1.63 eV at the HSE06 level. We employed a tight-binding model combined with the Bethe-Salpeter equation (TB+BSE) approach to explore the optical and excitonic behavior further, analyzing the response at independent-particle approximation and BSE levels. Excitonic effects resulting from quantum confinement yield a binding energy of 338 meV, characteristic of two-dimensional systems. Additionally, the power conversion efficiency of the SnSeS monolayer was assessed using the Shockley-Queisser limit and the spectroscopy-limited maximum efficiency framework. The estimated efficiency ranges from 20.20% to 29.27%, underscoring the potential of this material for next-generation photovoltaic applications.