  Polar heterogeneous photocatalysts were shown to lead to enhanced
charge-carrier separation that results in superior activity for example for
photocatalytic water splitting. Promising photocatalyst materials such as
oxynitrides can be rendered polar by epitaxial strain, which however also
increases their band gap, making them unsuitable for visible light absorption.
This suggests a trade-off between small band gaps and polar distortions - both
being crucial for the catalyst's efficiency. In this paper we investigate,
using density functional theory calculations, the suitability of strained
AB(O$_x$S$_{1-x}$)$_{3}$ perovskites for photocatalytic water splitting. These
materials normally have band gaps too small for water splitting but inducing
polar distortions via epitaxial strain can increase the band gap to the
suitable range. We find perovskite BaZr$_y$Ti$_{1-y}$O$_2$S compounds to be
highly promising for photocatalytic water splitting due to large polar
distortions and suitable band gaps.
