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.

多轴分子铁电体（multiaxial molecular ferroelectrics）凭借自发极化的多方向切换可产生多样性质，展现出诸多引人关注的优势，成为传统无机氧化物不可或缺的补充材料。尽管近年来该领域取得了蓬勃发展，但具备体光伏效应的多轴分子铁电体仍存在巨大研究空白。本工作报道了一种双轴卤化铅铁电体EA₄Pb₃Br₁₀（编号1，其中EA为乙胺（ethylammonium）），其具有独特的三层钙钛矿结构基元，居里温度高达约384 K。尤为特别的是，该材料的对称破缺过程属于4/mmm→Fmm2空间群转变，使得铁电相中共存在4个等价的极化方向。依托其双轴特性，可通过电场极化手段便捷地在多个极化方向之间调控该材料的体光伏效应。据我们所知，这是首例兼具方向可调光伏活性的双轴杂化钙钛矿铁电体的相关报道。本工作为调控多轴分子铁电体的宏观物理性质提供了可行途径，同时凸显了其在智能器件领域的进一步应用潜力。