Insights Into Ferroelectric Phase Transition Mechanism for One-Dimensional Halide Perovskites to Attain Record-Performance Self-Powered X-Ray Detection

The spontaneous polarization in ferroelectric perovskites offers a promising route toward self-powered X-ray detection, yet the microscopic link between ferroelectric phase transition and detector-relevant carrier dynamics remains largely unexplored. Here, using 1D [3-(aminomethyl)piperidinium]BiI₅ single crystals (3AMP SCs) as a model system, we uncover how a specific first-order ferroelectric–paraelectric transition mechanism directly governs polarization-driven carrier transport and photovoltaic behavior. Structural analyses reveal that room-temperature ferroelectricity originates from the non-centrosymmetric ordering of 3AMP²⁺ cations and strong organic–inorganic interfacial coupling, while the transition at 364 K is driven by highly anharmonic hydrogen-bond dynamics and stabilized by the rigidity of the Bi–I framework. This cooperative mechanism generates a robust polarization field along the c-axis, which reduces exciton binding energy, suppresses trap-assisted recombination, and enables efficient carrier separation through the bulk and anomalous photovoltaic effects. As a direct consequence of this phase-transition-controlled transport behavior, the 3AMP SC-based detector achieves record-performance self-powered X-ray detection, with a sensitivity of 566.79 µC Gy_air⁻¹ cm⁻², an ultra-low detection limit of 5.24 nGy_air s⁻¹, and excellent long-term stability. This work establishes a clear structure–phase transition–polarization–transport–performance relationship in Bi-based halide perovskites, providing a new framework for designing ferroelectric materials for self-powered optoelectronic devices.