Tailoring optical and ferroelectric properties in Sb1-xBixSI towards solar absorber applications

A new paper by the von Rohr group reports how substituting bismuth for antimony in the van der Waals chalcohalide SbSI allows continuous tuning of both optical and ferroelectric properties. The study shows that the bandgap decreases to about 1.5 eV with increasing Bi content — an energy well suited for solar absorption — while ferroelectricity is progressively suppressed, as revealed by the disappearance of soft-phonon modes and second-harmonic generation signals. First-principles calculations attribute this behavior to a reduced lone-pair activity on the Sb/Bi site, which destabilizes the polar ground state.

These results highlight Sb₁₋ₓBiₓSI as a promising model system for understanding structure–property relationships in layered chalcohalides and for developing new materials for photovoltaic applications.