Strained MoSi2N4 Monolayers with Excellent Solar Energy Absorption and Carrier Transport Properties

Abstract

The recently synthesized two-dimensional (2D) MoSi2N4 material with a proper band gap and excellent environmental stability promises potential optoelectronic applications. On the basis of first-principles calculations and electron–phonon interaction theory, we systematically analyze the structural, optical, carrier distribution and transport, and photocatalytic water-splitting properties of pristine and strained MoSi2N4 monolayers. They are all found to be dynamically stable. Their optical absorption efficiencies are very high for photon energy larger than the respective band gap. Surprisingly, the optical absorption coefficient of tensile MoSi2N4 is as large as 106 cm–1 across 300–880 nm. To the best of our knowledge, this is the best among optoelectronic materials in the visible region. In addition, compressive strain results in spatial separation of photogenerated electrons and holes, which is beneficial for increasing their separation rates. Transport properties indicate that the lifetime and mean free path (MFP) of photogenerated electrons and holes are, respectively, on the scale of several femtoseconds and within 1.5 nm. Tensile strain notably increases them, becoming comparable to conventional semiconductor Si. Finally, pristine and strained MoSi2N4 monolayers are predicated to be able to photooxidize and photoreduce H2O with proper band edges and H2O adsorption capacities. These systematic characterizations not only deepen understanding of the physical and optoelectronic properties of MoSi2N4 but also indicate promising applications of MoSi2N4 in electronics, optoelectronics, and photocatalytic water splitting.