Nanoscale Interfaces of Janus Monolayers of Transition Metal Dichalcogenides for 2D Photovoltaic and Piezoelectric Applications

摘要

Using first-principles calculations, we demonstrate a combination of two emergent fields, type II van der Waals heterostructures and Janus structures, for the purpose of optimizing the harvesting of solar and nano-electromechanical energy. The most stable stacking order in these nanoscale heterobilayers comprising Janus monolayers of transition metal dichalcogenides has been ascertained based on the interlayer binding energies. The binding energies in WSeTe/WSTe and MoSeTe/WSTe heterobilayers are found to be -27.93 and -25.67 meV/angstrom(2) at an equilibrium interlayer layer distance of 3.25 and 3.32 angstrom, respectively, indicating the exothermicity in the process of heterobilayer formation, and hence, its experimental feasibility. The mechanical and dynamical stabilities have also been confirmed for these heterobilayers using the Born Huang stability criteria and phonon dispersion calculations. Our results unveil the mechanism underlying the electronic, piezoelectric, photocatalytic properties, and carrier mobility in these Janus heterobilayers. The power conversion efficiency in the 2D ultrathin excitonic solar cells constituted by some of the heterobilayers studied in this work has been found to lie in the range of 15-20%. Moreover, a very high carrier mobility (>200 cm(2)/V.s) together with a large visible-light absorption coefficient (alpha approximate to 10(5 )cm(-1)) has been observed in these heterobilayers. The piezoelectric coefficients in these ultrathin heterobilayers (d(33) = 13.91 pm/V) is found to reach close to the values obtained in multilayer/bulk structures built from Janus monolayers of Mo-based dichalcogenides. Our findings highlight the promising applications of these heterobilayers in ultrathin excitonic solar cells, nanoelectronics, and nanopiezotronics.