Non-toxic molecular ferroelectrics have attracted significant interest due to their unique flexibility, low costs, and environmental friendliness. However, such materials with narrow bandgaps and ferroelectricity above room temperature (RT) are still scarce. Herein, we present a brand-new lead-free molecular ferroelectric [C₈N₂H₂₂]_1.5[Bi₂I₉] synthesized hydrothermally. [C₈N₂H₂₂]_1.5[Bi₂I₉] features a zero-dimensional (0D) structure with a polar space group of Pc, as confirmed by single-crystal X-ray diffraction and second-harmonic generation (SHG) analyses. The RT hysteresis loop reveals the intrinsic ferroelectricity of [C₈N₂H₂₂]_1.5[Bi₂I₉] with a spontaneous polarization (P_s) of 1.3 μC cm⁻². A visible-light optical bandgap has been confirmed by UV-vis spectroscopy and theoretical calculations. A notable ferroelectric photovoltaic (PV) effect has been revealed in [C₈N₂H₂₂]_1.5[Bi₂I₉]-based photoelectric devices with an open-circuit voltage (V_oc) of 0.39 V and a short-circuit current density (J_sc) of 2.3 μA cm⁻² under AM 1.5G illumination. The PV performance can be significantly enhanced by tuning the ferroelectric polarization, achieving a maximum Voc of 0.47 V and Jsc of about 50 μA cm⁻². This study offers a novel member of the 0D lead-free hybrid organic–inorganic molecular ferroelectric family possessing great promise for optoelectronic devices.

中文翻译：

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零维室温分子铁电体中的体光伏效应 [C8N2H22]1.5[Bi2I9]


无毒的分子铁电体因其独特的柔韧性、低成本和环境友好性而引起了人们的极大兴趣。然而，这种具有窄带隙和室温 （RT） 以上铁电性的材料仍然稀缺。在此，我们提出了一种全新的水热合成的无铅分子铁电 [C₈N₂H₂₂] _1.5[Bi₂I₉]。[C₈N₂H₂₂]_1.5[Bi₂I₉] 具有零维 （0D） 结构，极空间群为 Pc，单晶 X 射线衍射和二次谐波产生 （SHG） 分析证实了这一点。RT 磁滞回线揭示了 [C₈N₂H₂₂] _1.5[Bi₂I₉] 的本征铁电性，自发极化 （P_s） 为 1.3 μC ^cm-2。可见光光学带隙已通过 UV-vis 光谱和理论计算得到证实。在 AM 1.5G 照明下，基于 [C₈N₂H₂₂]_1.5[Bi₂I₉] 的光电器件具有显着的开路电压 （V_oc） 和 2.3 μA ^cm-2 的短路电流密度 （J_sc） 的光电器件中揭示了显着的光伏 （PV） 效应。 通过调整铁电极化可以显著提高 PV 性能，实现最大 Voc 为 0.47 V，Jsc 约为 50 μA cm⁻²。本研究提供了 0D 无铅混合有机-无机分子铁电家族的新成员，在光电器件方面具有很大的前景。