  The rapid growth of the solar energy industry has produced a strong demand
for high performance, efficient photoelectric materials. Many ferroelectrics,
composed of earth-abundant elements, are useful for solar cell applications due
to their large internal polarization. However, their wide band gaps prevent
them from absorbing light in the visible to mid-infrared range. Here, we
address the band gap issue by investigating, in particular, the substitution of
sulphur for oxygen in the perovskite structure ZnSnO3 . Using evolutionary
methods we identify the stable and metastable structures of ZnSnS3 and compare
them to those previously characterized for ZnSnO3 . Our results suggest that
ZnSnS3 forms a monoclinic structure followed by metastable ilmenite and
lithium-niobate structures. The latter structure is highly polarized and it
possesses a significantly reduced band gap of 1.28 eV. These desirable
characteristics make it a prime candidate for solar cell applications.
