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Excellent properties of type-II van der Waals Janus-XM2X’/MX heterojunctions toward solar cell utilization

Constructing van der Waals (vdW) heterojunctions is an effective strategy for band engineering of two dimensional (2D) materials. The XM2X’/MX (M = Al, Ga, In; X = S, Se, Te) heterostructures are investigated by first-principles calculation. Five XM2X’/MX with less than 3% of lattice mismatch are found to be direct-band-gap type-II band structures with moderate band gap from 1.08 to 1.73 eV in HSE06 method, high optical absorption coefficient (∼105 cm−1) and broad absorption spectrum, which facilitates effective utilization of the solar visible light and separation of photo-generated electron-hole pairs. Intriguingly, the band gap and band offsets are tunable to achieve high power conversion efficiency by external electric field and vertical strain. These results indicate potential applications of the XM2X’/MX in solar energy conversion.