Large Enhancement of Polarization in a Layered Hybrid Perovskite Ferroelectric Semiconductor via Molecular Engineering

Switchable spontaneous polarization is the vital property of ferroelectrics, which leads to other key physical properties such as piezoelectricity, pyroelectricity, and nonlinear optical effects, etc. Recently, organic-inorganic hybrid perovskites with 2D layered structure have become an emerging branch of ferroelectric materials. However, most of the 2D hybrid ferroelectrics own relatively low polarizations (<15 µC cm^-2 ). Here, a strategy to enhance the polarization of these hybrid perovskites by using ortho-, meta-, para-halogen substitution is developed. Based on (benzylammonium)₂ PbCl₄ (BZACL), the para-chlorine substituted (4-chlorobenzylammonium)₂ PbCl₄ (4-CBZACL) ferroelectric semiconductor shows a large spontaneous polarization (23.3 µC cm^-2 ), which is 79% larger than the polarization of BZACL. This large enhancement of polarization is successfully explained via ab initio calculations. The study provides a convenient and efficient strategy to promote the ferroelectric property in the hybrid perovskite family.