Hybrid Lead-Free Ferroelectric Solid Solutions with an Optimized Bandgap for X-ray Detection

Ferroelectric semiconductors hold promise for emerging applications in photovoltaics and photodetection. Solid ferroelectricity with a narrow bandgap has long been pursued to facilitate efficient charge generation and transport. However, their integration has been a continuous challenge as a possible leakage current can compromise ferroelectricity. Here, through the molecular modification and solid solution strategy on a series of one-dimensional (1,4-BDA)Sb x Bi 1– x Br 5 ( x = 0–1) (BDA = 1,4-butanediaminium), we have achieved robust ferroelectricity with a high Curie temperature ( T c ) of 379 K, and a reduced bandgap of 2.25 eV is realized in the composition (1,4-BDA)Sb 0.7 Bi 0.3 Br 5 . Benefiting from the promotion effect of the narrow bandgap and ferroelectric built-in electric field, compared to the parent (1,4-BDA)BiBr 5, these attributes enable (1,4-BDA)Sb 0.7 Bi 0.3 Br 5 to demonstrate X-ray detection capability with a sensitivity of up to 7479 μC Gy air –1 cm –2 and a limit of detection of 260 nGy air s –1, which is more than 21 times lower than that required for standard medical diagnostics. This study will provide insight into designing ferroelectric semiconductors for high-performance photoelectric devices.