Two-Dimensional Hybrid Perovskite Ferroelectric Induced by Perfluorinated Substitution

Two-dimensional (2D) hybrid organic–inorganic
perovskites
(HOIPs), which possess the merits of good material stability, structural
diversity, and ease of fabrication, are highly desirable for widespread
applications of ferroelectrics, solar cells, and electroluminescent
devices. Although some molecular design strategies toward ferroelectrics
have been proposed, however, it is still a great challenge to precisely
induce and optimize the ferroelectricity in 2D HOIPs. Here, for the
first time through perfluorinated substitution strategy, we successfully
design a high-performance 2D HOIP ferroelectric, (perfluorobenzylammonium)2PbBr4, exhibiting more obvious second harmonic
generation intensity, larger piezoelectric response, more polar axes,
larger spontaneous polarization of 4.2 μC cm–2, and higher Curie temperature of 440 K than those of parent (benzylammonium)2PbBr4. Compared to the selective effect of monofluorinated
substitution on different positions of the benzene ring, where (3-fluorobenzylammonium)2PbBr4 and (4-fluorobenzylammonium)2PbBr4 are not ferroelectrics, the pioneering perfluorinated substitution
is more universal and effective for targeted design of aromatic ferroelectrics.
This work offers an efficient strategy for precisely designing high-performance
2D HOIP ferroelectrics.