First-principles insights into the electronic, excitonic, and photocatalytic properties of APX 3 (A = Zn, Cd; X = S, Se) monolayers: a DFT and G 0 W 0 -BSE study

Abstract Metal phosphorus trichalcogenides (APX 3 ; A = Zn, Cd; X = S, Se) are emerging two-dimensional (2D) semiconductors with tunable properties promising for optoelectronic applications. Using first-principles density functional theory (DFT) and many-body perturbation theory (G 0 W 0 approximation and Bethe-Salpeter equation, BSE), we systematically investigate the structural, electronic, optical, excitonic, and photocatalytic properties of ZnPS 3 , ZnPSe 3 , CdPS 3 , and CdPSe 3 monolayers. Our results show that all four monolayers have indirect band gaps in the range of 3.30 eV for CdPSe 3 to 4.62 eV for ZnPS 3 . Solving the BSE highlights strong excitonic effects, with optical gaps between 3.34 eV for ZnPSe 3 to 4.56 eV for CdPS 3 . The exciton binding energies of the monolayers are also noticeable, ranging from 0.18 eV to 0.36 eV, highlighting the importance of electron–hole interactions in these 2D compounds. ZnPS 3 and CdPS 3 monolayers meet the band-edge requirements for overall water splitting, with ZnPS 3 remaining suitable even at neutral pH. These results deepen our understanding of excitonic behavior in APX 3 monolayers and provide useful direction for designing next-generation 2D optoelectronic devices.