High-Performance X-ray Detection Made of Bismuth Perovskite Single Crystal Based on Hydrogen-Bond-Free and Interlayer-Spacing Engineering Strategies

Hybrid organic-inorganic halide perovskites (HPs) show great potential for optoelectronic applications. However, their poor stability against moisture and oxygen significantly limits their practical applications. Developing hybrid perovskites with improved stability is essential yet remains a considerable challenge. Lead-free A₃Bi₂I₉ perovskites have become attractive semiconductor materials for next-generation X-ray sensing because of their elevated bulk resistivity, efficient X-ray absorption, and low ion migration. Nonetheless, the increased spacing between lamellae along the c-axis hinders carrier mobility in the vertical orientation, thereby presenting difficulty in enhancing the detection sensitivity of these materials. In this work, we present two practical approaches that offer innovative solutions to the aforementioned challenges. The first approach, termed the "hydrogen-bond elimination" strategy, focuses on improving the stability of low-dimensional (LD) HPs by preventing the organic components from establishing strong hydrogen bonds with external water molecules. The "interlayer-spacing engineering" approach focuses on improving carrier transport in the vertical direction. As a proof-of-concept application, a novel large sterically hindered A-site cation, phenyltrimethylammonium (C₉H₁₄N⁺), without hydrogen bonding, is introduced to reduce the interlayer spacing through inducing greater structural distortions. The large (C₉H₁₄N)₃Bi₂I₉ single crystals (SCs) grown exhibit reduced interlamellar spacing, resulting in a mobility-lifetime (μτ) product of 8.53 × 10^-3 cm² V^-1. This value surpasses that of the top-performing MA₃Bi₂I₉ SC by a factor of 3, which has a μτ product of 2.87 × 10^-3 cm² V^-1. As a result, X-ray detection devices using (C₉H₁₄N)₃Bi₂I₉ SCs demonstrate a remarkable sensitivity of 1373.27 μC Gy_air^-1 cm^-2 under a minimal field strength (5.71 V mm^-1) and an exceptionally low detection limit (LoD) of 4.69 nGy s^-1. These findings pave the way for creating efficient X-ray detection devices using A₃Bi₂I₉-type perovskite or perovskite-like materials, offering an alternative that avoids the use of toxic elements.