Exotic ferroelectricity in strained BaZrS3 chalcogenide perovskite for photovoltaics

Ferroelectricity in solar cells is credited with a multitude of benefits, including improved charge carrier separation and higher than band gap device voltages, however most ferroelectrics are wide-gap materials that generate very little photocurrent. Some halide perovskites are ferroelectric, but they suffer from degradation, despite their otherwise excellent performance. Recently, BaZrS3, a chalcogenide perovskite has received attention due to its optimal band gap, non-toxicity, and superior stability. The ground state of BaZrS3 is reportedly a GdFeO3-type distorted perovskite (space group Pnma). Here, using first-principle calculations, we show that the polar Pna21 is thermodynamically as stable as Pnma. This new phase is weakly ferroelectric, exhibiting a net polarization of 0.27 µC/cm2 and a d33 piezoelectric coefficient of only ~1 pm/V. Under strain, the interplay between out-of-plane and in-plane octahedral tilts amplifies spontaneous polarization, spin splitting, and large polaron radii. These exotic traits are comparable to those of the popular halide perovskites. Ferroelectricity in solar cells can improve charge carrier separation and provide higher than bandgap device voltages. Here, first-principles calculations in strained BaZrS3 reveal ferroelectricity and exotic properties akin to halide perovskites for photovoltaics applications.