  Surface states are ubiquitous to semiconductors and significantly impact the
physical properties and consequently the performance of optoelectronic devices.
Moreover, surface effects are strongly amplified in lower dimensional systems
such as quantum wells and nanostructures. Layered halide perovskites (LHPs) are
2D solution-processed natural quantum wells, where optoelectronic properties
can be tuned by varying the perovskite layer thickness. They are efficient
semiconductors with technologically relevant stability. Here, a generic elastic
model and electronic structure modelling are applied to LHPs heterostructures
with various layer thickness. We show that the relaxation of the interface
strain is triggered by perovskite layers above a critical thickness. This leads
to the release of the mechanical energy arising from the lattice mismatch,
which nucleates the surface reorganization and consequently the formation of
lower energy edge states. These states, which are absent in 3D perovskites,
dominate the optoelectronic properties of LHPs and are anticipated to play a
crucial role in the design of LHPs for optoelectronics devices.
