Photoferroelectric, coupled with photon-generated carrier and ferroelectric spontaneous polarization, exhibits fascinating physical phenomena such as photovoltaic, photorefractive and photostriction effects. Such merits make photoferroelectric have important application prospects in the next generation of optoelectronic devices.

Recently, the most active two-dimensional (2D) multilayer hybrid perovskite provides a broad platform for the construction of a new class of photoferroelectric material. It still remains a challenge to make a subtle balance between high T_c and outstanding semiconducting properties to assemble high T_c 2D multilayered perovskite photoferroelectric.

In a study published in J. Am. Chem. Soc., the research team led by Prof. LUO Junhua from Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences developed a bromine-substitution-induced high-T_c 2D bilayered perovskite photoferroelectric.

The researchers introduced bromine atoms on n-propylamine cations through a halogen substitution strategy. For 2D hybrid perovskite ferroelectrics, the ordered-disordered dynamic motions of organic moieties behave as main driving forces to induce spontaneous polarization. Therefore, subtle molecular engineering modification on organic structural element has direct effect on the structures and properties of perovskite ferroelectric. Halogen atoms replacing hydrogen atoms of organic cations may increase in the potential energy barrier of motions of organic cations, and high-T_c 2D hybrid perovskite ferroelectric was obtained.

By using this molecular engineering strategy, the researchers constructed a new 2D bilayered hybrid perovskite (BPA)₂(FA)Pb₂Br₇. Such bilayered perovskite not only maintains the original polar structure, but also shows a high Curie phase transition temperature.

They observed the remarkable augmentation of Curie temperature ΔT = 85.4 K. Single crystal structure analysis and theoretical calculations demonstrated that the halogen interaction between the organic cations and the inorganic perovskite framework, and the heavy halogen Br atoms, lead to the increased ferroelectric phase transition energy barrier, raising the Curie temperature of 2D perovskite photoferroelectric.

Besides, the researchers investigated the interaction of light with 2D perovskite ferroelectric. Based on perovskite ferroelectric single crystal devices, they achieved the significant ferroelectric photovoltaic effect in the direction of its crystallographic polar axis, and easily tuned the bulk photovoltaic effects by inverse polarization directions under applied electric poling.

This study enhances the hybrid perovskite photoferroelectrics family and provides a reference for future optimization of perovskite photovoltaic devices.