  Using density functional theory, the structural and electronic-structure
properties of a recently discovered, zero-dimensional antimony halide
perovskite are studied. It is found that the herein considered material
EtPySbBr$_\mathrm{6}$ exhibits very promising electronic-structure properties:
a direct band gap close to the peak of the solar spectrum and effective masses
allowing for efficient carrier transport of electrons in particular. These
results are rationalized by analysis of the electronic structure, which reveals
the formation of intermediate bands due to orbital-hybridization effects of the
Sb s-states. This study shows that the formation of intermediate bands can lead
to highly favorable electronic-structure properties of zero-dimensional
perovskites and discusses the possibility of fabricating lead-free HaPs with
promising optoelectronic properties by targeted substitution of ions and
emergence of intermediate bands. These insights are important when
understanding and further enhancing the capabilities of antimony and other
promising lead-free compounds.
