Theoretical Investigation of High-Performance MXY (M = Mo/W, X = S/Se, and Y = Se/Te) Janus Monolayers for Photovoltaic and Optoelectronic Applications

Abstract

Herein, MXY (M = Mo/W, X = S/Se, and Y = Se/Te) Janus monolayers (JMLs) are theoretically investigated to explore their numerous photovoltaic/optoelectronic (PV/OE) features. It is predicted that the MoSSe/MoSeT/WSSe/WSeTe JMLs are semiconductors having a direct energy band gap (E g ) of 1.71/1.43/1.71/1.35 eV. In contrast, the MoSTe/WSTe possesses an indirect E g of 1.15/0.89 eV. The MoSSe/MoSeTe JMLs manifest the red shift as the peak for its real/imaginary part of the dielectric constant (ε 1 (ω))/(ε 2 (ω)), while the absorption coefficient (α(ω)) demonstrates a blue shift. Strikingly, the MoSeTe/WSeTe JMLs are showing the highest spectroscopic limited maximum efficiency (SLME) of 32.75/32.05% at a 6.28/5.72 µm thickness, which makes it highly effective for photo absorbers. Alongside, the MoSSe/WSSe JMLs are also showing a high SLME of 28.15% for a critical thickness of 6.89/7.56 µm. Furthermore, the MoSeTe/WSeTe JMLs contain low reverse saturation current density, open-circuit voltage, fill-factor, and high short circuit current, while MoSSe/WSSe exhibit high values of these parameters. Alongside, the MoSeTe demonstrates a large transport asymmetry, having large effective masses (m * ) for holes ( m * h m 0 = 0.319). In contrast, the WSeTe exhibits preferable transport aspects with low m * for electrons ( m * e m 0 = 0.117) and holes ( m * h m 0 = 0.0.149). Hence, it is our strong belief that the above mentioned direct Eg JMLs with sufficiently large SLME, make them the best candidates for PV and OE devices.