  In an outstanding experimental advance in the field of two-dimensional
nanomaterials, cuprous iodide (CuI) and silver iodide (AgI) monolayers have
been grown via a novel graphene encapsulation synthesis approach
[Adv.Mater.2022, 34, 2106922]. Inspired by this accomplishment, we conduct
first-principles calculations to investigate the elastic, phononic thermal
transport, electronic, and optical properties of the native CuI and AgI and
Janus Cu2BrI and Ag2BrI monolayers. Electronic and excitonic optical properties
are elaborately studied using the many-body perturbation theory on the basis of
GW approximation. Our results indicate that these novel systems are stable but
with soft elastic modulus and ultralow lattice thermal conductivity. It is also
shown that the studied monolayers are wide-gap semiconductors with exciton
binding energies close to 1 eV. The effects of mechanical straining and
electric field on the resulting electronic and optical properties are also
analyzed. The presented first-principles results provide a deep understanding
of the stability, phononic transport, and tunable optoelectronic properties of
the native CuI and AgI and Janus Cu2BrI and Ag2BrI monolayers, which can serve
as a guide for the oncoming studies.
