High-quality quasi-2D perovskite crystalline layers integrated in detectors for X-ray imaging

-

-

Schematic illustration of a perovskite X-ray imager made by coating the perovskite layer on pixelated substrates from solution. A typical perovskite structure is shown in the square on the right. 

-

Digital X-ray panels, employing semiconductor-based flat screens instead of a phosphor film, represent a next-generation technique for medical imaging, security screening and threat detection. Classical semiconductors are expensive to scale up to meet demand for applications. A large panel with high detection efficiency enables high resolution medical imaging with a low X-ray dosage that may be significantly safer for patients. X-ray imaging also offers a non-destructive tool to visualize the internal structure of an object, or to probe the scattering patterns when an X-ray is scattered from a crystal – useful in understanding a material’s structures and dynamics. Researchers at the Center for Integrated Nanotechnologies at Los Alamos National Laboratory, writing in the journal Advanced Materials, have integrated quasi-2D perovskite materials, a low-cost nano-structured semiconductor, in digital X-ray panels.

The conventional method for building high performance detectors often yields a porous, micro-crystalline structure that kills the detection efficiency and operational stability. The team has discovered that high efficiency X-ray sensors can be achieved with the hot-casting method, suitable for depositing thick crystalline layers that are the key element for building high performance detectors.

The research team introduced n-butylamine iodide into a methylammonium lead iodide precursor, leading to a “quasi-2D” perovskite structure. It is found the addition of the n-butylamine iodide in the precursor reduces the nucleation sites, which promotes large crystalline grain formation. Coating at elevated temperatures, on both rigid and flexible substrates, produced 10-µm-thick quasi-2D perovskite layers with near single crystalline quality.

Photodiodes built with the quasi-2D layers exhibit a low noise and stable operation under constant electrical field over 96 hours in dark conditions, and over 15 hours under X-ray irradiation. The team found that the detector responds sensitively under X-ray, delivering a high sensitivity of 1214 µCGyair-1cm-2, and a sensitivity gain was observed when operated under higher fields. The sensor developed by the team exhibits 100 times better detection sensitivity than the state-of-the-art selenium panel. Finally, the work demonstrated high resolution images using a single pixel device that can resolve features in the order of magnitude of 80 to 200 µm. The work paves the path for printable direct conversion X-ray imager development.

The solution-based method, combining cation engineering and hot-casting, can be adapted for coating over a large, meter-scale area or can be applied on curved surface for 3D imaging to support radiation detection from all directions. Los Alamos National Laboratory first discovered the hot-casting method to produce highly crystalline perovskite layers for photovoltaics and radiation detections. The method is particularly useful for thick crystalline layer fabrication – free of solvent or voids – that enables ultra-sensitive X-ray imaging. The approach is also compatible with other coating methods like ink-jet printing and blade coating where a thicker layer on a larger area can be expected for upscaled hard X-ray sensing.

The hotcasting method is LANL IP No. US10770239B1 and provisional IP No. S133859.000.

Funding and Mission

The work was supported by the Laboratory Directed Research and Development program office, the J. Robert Oppenheimer Distinguished Postdoc Fellowship, the U.S. Department of Energy Office of Science, and the U.S. Department of Defense Defense Threat Reduction Agency. The work supports the Energy Security mission area and the Materials for the Future capability Pillar.

Reference

“Quasi-2D Perovskite Crystalline Layers for Printable Direct Conversion X-Ray Imaging,” Advanced Materials (2022). DOI: https://doi.org/10.1002/adma.202106498. Authors: Hsinhan Tsai, Shreetu Shrestha, Darrick Williams, Wanyi Nie (Los Alamos National Laboratory); Lei Pan, Lei R. Cao (The Ohio State University); Hsin-Hsiang Huang, Leeyih Wang (National Taiwan University); and Joseph Strzalka (Argonne National Laboratory).

Technical Contact: Wanyi Nie