Excitonic\nand Environmental Screening Effects in Two-Dimensional\nJanus MSO (M = Ga, In)

In this work, we investigate Janus monolayer MSO (M =\nGa, In) systems\nusing the state-of-the-art GW method within the framework of the many-body\nperturbation theory. Ground-state density functional theory calculations\nreveal that both the substitution of S atoms with O atoms and the\nchemisorption of the O atoms on a single side of the MS layer narrow\nthe band gaps and reduce the carrier mobilities. Notably, one-shot\nGW calculations demonstrate that the GaSO-2 and InSO-1 systems exhibit\noptimal band gaps for visible light absorption. Based on the Bethe–Salpeter\nequation, the exciton binding energies of isolated Janus monolayer\nGaSO-2 and InSO-1 systems are lower than those of their prototype\nGaS and InS by 0.37 and 0.17 eV, respectively. Further calculations\nshow that the exciton binding energies of the Janus GaSO-2 and InSO-1\nsystems can be precisely tuned by adjusting their thicknesses and\nthe thicknesses of their substrates. A deep understanding of the mechanisms\nfor tuning the exciton binding energies in Janus GaSO-2 and InSO-1\nsystems is crucial for the future design of advanced photovoltaic\ndevices.