Key Takeaways & Executive Findings
- •• • The HBES-PDBiI5 film achieves a hole mobility of 2.16 cm2 V−1 s−1 and a mobility-lifetime product of 9.1 × 10−4 cm2 V−1, surpassing conventional thick-film detectors and rivaling single-crystal performance, which is critical for high-sensitivity X-ray detection. • • The X-ray detector exhibits a record sensitivity of 19,009 μC Gyair−1 cm−2 and an ultralow detection limit of 3.35 nGyair s−1, enabling low-dose imaging and reducing radiation exposure in medical and industrial applications. • • The flexible imager retains 85% of its X-ray response after 1000 bending cycles, demonstrating mechanical durability essential for wearable and conformal electronics. • • The flexible imager achieves 85% edge photocurrent retention compared to 58% for rigid detectors, effectively eliminating vignetting and geometric distortion, which is vital for accurate imaging of curved objects in nondestructive testing.
Abstract
Flexible X-ray detectors are constrained by the difficulty of producing semiconductor films that simultaneously exhibit uniform morphology, high crystallinity, and mechanical robustness. Here, we introduce a hydrogen-bond engineered supramolecular (HBES) strategy to overcome these limitations in supramolecular bismuth halide clusters (PDBiI5). By incorporating polyacrylic acid (PAA), a dynamic supramolecular network is formed that suppresses the coffee-ring effect during ultrasonic spray-coating via increased solution viscosity and controlled kinetic balance between solvent evaporation and solute diffusion. The HBES approach also modulates crystallization kinetics, extending crystal growth time from 23 to 41 s, yielding densely packed films with enhanced crystallinity and reduced defect states. These improvements lead to superior charge transport: a hole mobility of 2.16 cm2 V−1 s−1 and a mobility-lifetime product of 9.1 × 10−4 cm2 V−1. The resulting X-ray detectors achieve a record sensitivity of 19,009 μC Gyair−1 cm−2 and an ultralow detection limit of 3.35 nGyair s−1, with excellent operational and environmental stability. Leveraging the mechanical robustness from the supramolecular network, we demonstrate the first direct-type flexible X-ray imager, retaining 85% performance after 1000 bending cycles. This imager overcomes geometric distortion and vignetting, maintaining 85% edge photocurrent versus 58% for rigid detectors, enabling clear imaging of curved objects. This work establishes a versatile supramolecular engineering paradigm for high-performance flexible X-ray detection and imaging.
1. Introduction
Direct X-ray detection semiconductors such as amorphous selenium (a-Se) and cadmium telluride (CdTe) have long been used in medical and industrial imaging, yet they suffer from fundamental limitations: a-Se exhibits poor absorption for high-energy X-rays and requires high operating voltages, while CdTe is costly and toxic. Metal halide perovskites have emerged as promising alternatives due to their high atomic numbers and excellent charge transport, but lead toxicity remains a significant barrier. Bismuth-based halides offer comparable X-ray attenuation (Bi Z=83) with reduced toxicity, yet their polycrystalline films often suffer from poor morphology and low crystallinity, limiting device performance.
This work addresses these bottlenecks by introducing a hydrogen-bond engineered supramolecular (HBES) strategy using polyacrylic acid (PAA) to create a dynamic network that suppresses the coffee-ring effect and modulates crystallization kinetics. This approach yields uniform, highly crystalline films with reduced defect states, enabling record sensitivity and ultralow detection limits. Furthermore, the supramolecular network imparts mechanical flexibility, allowing the first direct-type flexible X-ray imager that overcomes geometric distortion and vignetting, critical for conformal imaging applications.
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ZHANG Shiwei, WANG Xu, SUN Jiayi, WANG Lixia, CHANG Yamin, WANG Junfang, PAN Yongle, WANG Hao, YUAN Ziquan, MENG Xiangyue (2026). Hydrogen-bond engineered supramolecular bismuth halides for flexible X-ray imaging without geometric distortion. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-026-4126-0
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Frequently Asked Questions
What is the mechanism by which PAA suppresses the coffee-ring effect and improves film uniformity?
PAA increases solution viscosity and modulates the kinetic balance between solvent evaporation and solute diffusion, preventing the outward capillary flow that causes coffee-ring patterns. This results in uniform film morphology, as evidenced by the extended crystal growth time from 23 to 41 s and the formation of densely packed films with enhanced crystallinity.
How does the HBES strategy affect the trap-state density and charge transport properties?
The HBES approach reduces trap-state density to 1.18 × 10^12 cm−3, which is significantly lower than conventional films. This reduction in defects leads to enhanced carrier mobility (2.16 cm2 V−1 s−1) and a high mobility-lifetime product (9.1 × 10−4 cm2 V−1), rivaling single-crystal performance.
What are the key performance metrics of the HBES-PDBiI5 X-ray detector, and how do they compare to existing bismuth-based detectors?
The detector achieves a sensitivity of 19,009 μC Gyair−1 cm−2 and a detection limit of 3.35 nGyair s−1, which are among the best reported for bismuth halide detectors. For comparison, earlier MA3Bi2I9 single crystals achieved sensitivities up to 1.06 × 10^4 μC Gyair−1 cm−2 and detection limits as low as 55 nGyair s−1, indicating a substantial improvement.
How does the flexible imager maintain performance under bending, and what is the impact on imaging quality?
The flexible imager retains 85% of its X-ray response after 1000 bending cycles, demonstrating excellent mechanical robustness. This durability, combined with the suppression of vignetting (85% edge photocurrent retention vs. 58% for rigid detectors), enables clear imaging of curved objects without geometric distortion, which is critical for industrial nondestructive testing and medical imaging on non-planar surfaces.
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