Molecular-driven lead-free halide photoferroelectric solid solution for high-temperature sensitive self-powered x-ray...

Halide double perovskite ferroelectrics have recently emerged as an environmentally friendly candidate in radiation detection, photovoltaics, and optoelectronic memory devices due to their unique spontaneous polarization and semiconductor properties. However, it is a huge challenge to achieve efficient carrier transport and high Curie temperature (T_c) in double perovskite ferroelectrics, owing to the limitations of twisted frameworks and structural construction. Here, we present a high-T_c heterovalent metal solid solution double perovskite ferroelectric, (4Br2FBZ)₂CsAgBiBr₇ (4Br2FBZ-CAB, 4Br2FBZ = 4-bromo-2-fluorobenzylammonium), through a strategy of cation-engineered symmetry regulation. The metal ions Ag and Bi transitioned from an alternating arrangement to a mixed-site solid solution pattern, effectively optimizing the electronic band structure to enhance carrier transport. Meanwhile, 4Br2FBZ-CAB exhibits a high T_c of 484 kelvin, substantially expanding the family of high-T_c lead-free ferroelectrics. Benefiting from its remarkable photoelectric and ferroelectric properties, a high self-powered x-ray detection sensitivity of 273.8 microcoulomb per gray per square centimeter (μC Gy_air^-1 cm^-2 ) was achieved at room temperature. In addition, this exceptionally high T_c enables the detector to operate self-powered at high temperatures, resulting in an excellent sensitivity of 896.9 μC Gy_air^-1 cm^-2 and a low detection limit of 13.9 nGy_air s^-1 at 425 kelvin. This work opens an avenue for expanding the family of high-T_c lead-free perovskite ferroelectrics with superior semiconducting properties.