Flexible Polymer X-ray Detectors with Non-fullerene Acceptors for Enhanced Stability: Toward Printable Tissue Equivalent Devices for Medical Applications

Abstract

There is growing interest in the development of novel materials and devices capable of ionizing radiation detection for medical applications. Organic semiconductors are promising candidates to meet the demands of modern detectors, such as low manufacturing costs, mechanical flexibility, and a response to radiation equivalent to human tissue. However, organic semiconductors have typically been employed in applications that convert low energy photons into high current densities, for example, solar cells and LEDs, and thus existing design rules must be re-explored for ionizing radiation detection where high energy photons are converted into typically much lower current densities. In this work, we report the optoelectronic and X-ray dosimetric response of a tissue equivalent organic photodetector fabricated with solution-based inks prepared from polymer donor poly­(3-hexylthiophene) (P3HT) blended with either a non-fullerene acceptor (5Z,5′Z)-5,5′-((7,7′-(4,4,9,9-tetraoctyl-4,9-dihydro-s-indaceno­[1,2-b:5,6-b′]­dithiophene-2,7-diyl)­bis­(benzo­[c]­[1,2,5]­thiadiazole-7,4-diyl))­bis­(methanylylidene))­bis­(3-ethyl-2-thioxothiazolidin-4-one) (o-IDTBR) or a fullerene acceptor, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Indirect detection of X-rays was achieved via coupling of organic photodiodes with a plastic scintillator. Both detectors displayed an excellent response linearity with dose, with sensitivities to 6 MV photons of 263.4 ± 0.6 and 114.2 ± 0.7 pC/cGy recorded for P3HT:PCBM and P3HT:o-IDTBR detectors, respectively. Both detectors also exhibited a fast temporal response, able to resolve individual 3.6 μs pulses from the linear accelerator. Energy dependence measurements highlighted that the photodetectors were highly tissue equivalent, though an under-response in devices compared to water by up to a factor of 2.3 was found for photon energies of 30–200 keV due to the response of the plastic scintillator. The P3HT:o-IDTBR device exhibited a higher stability to radiation, showing just an 18.4% reduction in performance when exposed to radiation doses of up to 10 kGy. The reported devices provide a successful demonstration of stable, printable, flexible, and tissue-equivalent radiation detectors with energy dependence similar to other scintillator-based detectors used in radiotherapy.

Highly Stable Oxide Thin-Film Transistor-Based Complementary Logic Circuits under X-ray Irradiation

“…X-ray radiography has been widely used for a broad range of applications such as nondestructive inspection in industry and disease diagnosis in hospitals. − In X-ray diagnosis systems, many efforts have been made to achieve high-performance digital X-ray detectors with high resolution and stability to generate optimized image quality for accurate diagnosis. − A thin-film transistor (TFT) panel, which is one of the components of a digital X-ray detector, plays an important role in implementing high-quality images from the incoming electric signal produced by photodiodes and scintillators. Thus, developing highly stable TFT devices that can sustain their electrical performance under X-ray irradiation is crucial. ,,, In previous reports, several groups utilized TFTs with various channel materials, such as amorphous silicon (a-Si) TFTs ,− and low-temperature polycrystalline silicon (LTPS) TFTs, − for backplane pixels of digital X-ray detectors.…”

Design Parameters and Human Biocompatibility Assessment Protocols for Organic Semiconducting Neural Interfaces: Toward a Printed Artificial Retina with Color Vision

“…The substrate was changed from glass to Kapton, a flexible polymer material previously shown to be suited for wearable electronic device fabrication. [ 56 ] This change substantially reduces the surface energy of the substrate such that the semiconductor material spread is contained during printing as the deposited ink prefers to interact with itself rather than the substrate. This surface energy gradient produces a thermodynamic driving force that counteracts the coffee ring spreading of material, resulting in deposited pixels with a much more uniform spherical shape and less pronounced lateral thickness variation (Figure 5C).…”

Advances in Flexible Organic Photodetectors: Materials and Applications

“…This radiation-induced fluorescence produces a strong non-linearity in the R of the OPDs due to their high sensitivity to optical photons and prevents the full realization of tissue-equivalent printed polymer dosimeters. M.J. Large et al, in 2021, provided the first study of a non-fullerene acceptor (o-IDTBR) in combination with a donor polymer fabricated onto polyimide (Kapton) as a mechanically flexible substrate that is known to exhibit high transmission to X-rays and negligible radiation-induced fluorescence; the structure is shown in Figure 13 b [ 42 ]. To enhance the sensitivity of the organic detectors, they utilized a plastic scintillator with a spectral window where the organic semiconductors have a much higher absorption coefficient.…”

“… ( a ) Prototype of curved image sensor, Reprinted with permission from [ 38 ] ©2020 Nature Portfolio and ( b ) layered device architecture employed in the fabricated organic photodetector devices of this study. The scintillator is employed to facilitate indirect X-ray detection for dosimetry characterizations Reprinted with permission from [ 42 ] ©2021 ACS Publications. …”