Classifying the Electronic and Optical Properties of Janus Monolayers

Inspired by the recent synthesis of monolayer MoSSe we conduct a first-principles high-throughput investigation of 216 MXY Janus monolayers consisting of a middle layer of metal atoms (M) sandwiched between different types of chalcogen, halogen, or pnictogen atoms (X,Y). Using density functional theory and many-body perturbation theory we perform an exhaustive computational characterization of the 70 most stable semiconducting monolayers. These are found to exhibit diverse and fascinating properties including finite out-of-plane dipoles, giant Rashba-splittings, direct and indirect band gaps ranging from 0.7 to 3.0 eV, large exciton binding energies, and very strong light matter interactions. The data has been generated using the workflow behind the Computational 2D Materials Database (C2DB) and is freely available online. Our work expands the class of known Janus monolayers and points to several potentially synthesisable structures, which could be interesting candidates for valley- or opto-electronic app...