Halide Perovskite Direct X-Ray Detector with an Extremely Low Dark Current via Interfacial Engineering

X-ray detection technology has been developed and frequently used for medical imaging diagnostics, security inspection and scientific research areas. In a scintillator-type detector, a semiconducting material is excited by a probing X-ray and emits ultraviolet-visible (UV-Vis) light into a photodetector, which in-turn outputs an electrical signal and, ultimately, forms an image. However, this technology suffers from strong self-absorption and afterglow emission leading to a blurred image.¹<br/>In contrast, X-ray direct detectors which convert X-ray photons into electric charges have a superior resolution than scintillators and are more efficient since they don’t suffer from optical losses. However, current commercial solutions (e.g. amorphous Se) are not suitable for high-energy X-ray applications such as computed tomography (CT) for cancer detection because of their low atomic number (Z). Recent innovations based on Cadmium Telluride (CdTe) or Cadmium Zinc Telluride (CZT) semiconductors with high Z are promising for high-energy CT relevant X-rays. However substantial challenges in the fabrication and deployment of the active layer material have limited their widespread adoption. For instance, high-quality CdTe crystals take 3 months of high-temperature growth to fabricate at a cost in excess of $1500 per cm³.<br/>Recently, halide perovskite (PVK) materials have emerged as promising materials for direct X-ray detection, already demonstrating excellent mobility-lifetime products (µτ) comparable to CZT and CdTe, detector-grade bulk resistivity, and high stopping power at high-energy X-rays.² To date, high sensitivity up to 10⁶ μC Gy_aircm⁻² and a very impressive lowest detectable dose rate (LoD) of &lt;10 nGy s⁻¹ have been achieved.³ However, the dark current is still large &gt;1 nA cm⁻² which is one of the main obstacles to commercialising PVK X-ray direct detection technology. One of the origins of the large dark current is related to the interface defects at the PVK material and charge transport layers in the device stack.<br/>In this talk, we present a high-performing, direct X-ray detector with a device structure based on an alloyed perovskite single crystals synthesized via a state-of-the-art inverse temperature crystallisation (ITC) method. We introduce the use of a fluoride-based buffer layer to attain control over the device’s dark current to reach an impressive low dark current of ~10 pA cm⁻². This value establishes a new record, 10x lower than conventional CZT and CdTe direct detectors. Furthermore, the detector showed a clear X-ray-induced current and the LoD of 167 nGy s⁻¹. This study will open a new direction for PVK X-ray detectors with extremely low dark current towards integration with application-specific integrated circuit (ASIC) chips/backplanes for multi-pixel detection.<br/><br/>References<br/>(1) Moseley, O. D. I.; Doherty, T. A. S.; Parmee, R.; Anaya, M.; Stranks, S. D. Halide Perovskites Scintillators: Unique Promise and Current Limitations. <i>J. Mater. Chem. C</i> <b>2021</b>, <i>9</i> (35), 11588–11604. https://doi.org/10.1039/D1TC01595H.<br/>(2) Li, Z.; Zhou, F.; Yao, H.; Ci, Z.; Yang, Z.; Jin, Z. Halide Perovskites for High-Performance X-Ray Detector. <i>Mater. Today</i> <b>2021</b>, <i>48</i>, 155–175. https://doi.org/10.1016/j.mattod.2021.01.028.<br/>(3) Jiang, J.; Xiong, M.; Fan, K.; Bao, C.; Xin, D.; Pan, Z.; Fei, L.; Huang, H.; Zhou, L.; Yao, K.; Zheng, X.; Shen, L.; Gao, F. Synergistic Strain Engineering of Perovskite Single Crystals for Highly Stable and Sensitive X-Ray Detectors with Low-Bias Imaging and Monitoring. <i>Nat. Photonics</i> <b>2022</b>, <i>16</i> (8), 575–581. https://doi.org/10.1038/s41566-022-01024-9.