Ferroelectrically Modulated Photoresponse in a Zero-Dimensional Hybrid Perovskite [C ₄ N ₂ H ₁₄ ][BiBr ₅ ] with a High Ferroelectric Curie Temperature

Nonlead molecular ferroelectrics combining high-temperature ferroelectricity and efficient self-powered photoresponse are desirable for next-generation eco-friendly optoelectronic devices. However, the design and synthesis of such materials remain challenging. Herein, a zero-dimensional (0D) bismuth-based hybrid perovskite, [C 4 N 2 H 14 ][BiBr 5 ], was synthesized via a hydrothermal method. Single-crystal X-ray diffraction analysis reveals that this compound crystallizes in the polar space group P 2 1 . The intensity of its second harmonic generation (SHG) is 1.20 times that of potassium dihydrogen phosphate (KDP). It features a high ferroelectric Curie temperature ( T c ) of 529 K and a decomposition temperature of 597 K, indicative of good thermal stability from experimental characterization. Room-temperature (RT) ferroelectric hysteresis measurements reveal a saturation polarization ( P s ) of 0.372 μC/cm 2 . A direct bandgap of 2.75 eV has been revealed by theoretical calculations and spectral analysis. Bulk ferroelectric photovoltaic effect has been detected under AM 1.5G illumination, delivering a short-circuit current density ( J sc ) of 1.86 nA/cm 2 and an open-circuit voltage ( V oc ) of 0.031 V. Critically, ferroelectric polarization modulation enhances the photocurrent density by 62-fold, reaching 114.63 nA/cm 2 . This work demonstrates the integration of high-temperature ferroelectricity and efficient self-powered photoresponse in a 0D nonlead hybrid system, offering a feasible strategy for developing eco-friendly self-powered photodetectors.