An Unprecedented Biaxial Trilayered Hybrid Perovskite Ferroelectric with Directionally Tunable Photovoltaic Effects

Multiaxial molecular
ferroelectrics, in which multiple-directional
switching of spontaneous polarization creates diverse properties,
have shown many intriguing advantages, making them indispensable complements
to conventional inorganic oxides. Despite recent blooming advances,
multi­axial molecular ferro­electric with bulk photo­voltaic
effects still remains a huge blank. Herein, we report a biaxial lead
halide ferro­electric, EA4Pb3Br10 (1, EA = ethyl­ammonium), which adopts the unique
trilayered perovskite motif with a high Curie temperature of ∼384
K. Particularly, for 1, the distinct symmetry breaking
with 4/mmm­Fmm2 species leads
to the emergence of four equivalent polarization directions in the
ferroelectric phase. Based on its biaxial nature, the bulk photo­voltaic
effect of 1 can be facilely tuned between such multiple
directions through electric poling. As far as we know, this is the
first report on biaxial hybrid perovskite ferro­electric showing
directionally tunable photo­voltaic activity. This work provides
an avenue to control the bulk physical properties of multi­axial
molecular ferro­electrics, and highlights their potential for
further applications in the field of smart devices.