Polymer Photodetectors for Printable, Flexible, and Fully Tissue Equivalent X‐Ray Detection with Zero‐Bias Operation and Ultrafast Temporal Responses

Abstract

A new printable organic semiconducting material combination as a tissue equivalent photodetector for indirect X‐ray detection is demonstrated in this work. The device exhibits a higher optical‐to‐electrical conversion efficiency than any other reported printable organic systems for X‐ray photodetection while also operating efficiently with zero applied bias. Complete X‐ray detectors fabricated by coupling the photodiode with a plastic scintillator are among the first flexible and fully tissue equivalent X‐ray detectors capable of operating without external bias. The response to X‐rays is energy independent between 50 keV and 1.2 MeV, with a detection sensitivity equivalent to inorganic direct X‐ray detectors and one of the fastest temporal responses ever reported for organic X‐ray detectors. The materials can be printed into arrays with a pixel pitch of 120 μm, providing 2D spatial detection. The devices are found to be highly stable with respect to time, mechanical flexing, and large (5 kGy) radiation doses. The new materials and fully tissue equivalent X‐ray detectors reported here provide stable, printable, flexible, and tissue equivalent detectors with a high radiolucency that are ideally suited for wearable applications, where simultaneous monitoring and high transmission of the X‐ray absorbed dose into the human body is required.

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

“…This match in response between theoretical and experimental data demonstrates the energy dependence, and hence tissue-equivalence, of the organic photodetector is dominated by the energy dependence of the plastic scintillator to which it is coupled, implicitly stating the energy independence of the organic semiconducting material utilized within the photodetector. Due to the similar densities of P3HT:PCBM and P3HT:o-IDTBR solid films, energy independence can also be implied for P3HT:o-IDTBR. The response of the P3HT:PCBM photodetector coupled with the BC-430 plastic scintillator plateaus for photon energies above 200 keV.…”

“…Furthermore, the ability to temporally detect the Linac pulses is directly comparable to identical organic photodiode architectures on glass and to state-of-the-art silicon radiation detectors. 26 This result indicates that the elevated series resistance of the Kapton devices does not influence the RC time constant enough to result in a slower temporal response in the context of X-ray detection performance compared to other "fast" detector technologies, although a direct comparison of the limiting temporal response of each technology would require a faster pulsed energy source.…”

“…From a fabrication perspective, the solubility of organic semiconductors allows for materials to be blended together into functional inks with control over the density and equivalent atomic number to tune the tissue equivalency match. Furthermore, these inks can be printed over large areas onto a variety of substrates at low cost, ,, including mechanically flexible substrates. , Organic photodetectors (OPDs) fabricated on flexible poly­(ethylene terephthalate) (PET) substrates have been previously reported, , demonstrating a mechanically flexible and optically transparent substrate for radiation detection. However, the plastic substrates commonly used for printed electronics [PET and poly­(ethylene naphthalate) (PEN)] have been reported to show fluorescence under high intensity X-ray radiation, such as commonly encountered in medical applications .…”

Recent Advances in Solution‐Processable Organic Photodetectors and Applications in Flexible Electronics

“…[ 163 ] A flexible X‐ray detector, fabricated by integrating the printed OPD with a plastic scintillator, enables 2D spatial detection and self‐powered operation. [ 164 ] As shown in Figure 10b, a plastic foil‐based curved digital X‐ray image sensor was developed for approaching cone beam computed tomography X‐ray imaging. [ 165 ] The curved X‐ray image sensor has a large area of 6.0 cm × 8.0 cm size and contains 480 × 640 pixels.…”

Towards high spatial resolution tissue-equivalent dosimetry for microbeam radiation therapy using organic semiconductors

“…Organic semiconductors take advantage of all the dosimetric and mechanical benefits of film, but without their limitations in the readout technique (Griffith et al, 2020). Given their density (1 g cm À3 ) and hydrogen/carbon-based composition, organic semiconductors can mimic the dose of ionizing radiation deposited in water, reducing the need for complicated calibration factors and without perturbing the scattering conditions of the beam (Posar et al, 2021). Organic semiconductors have shown promising results during investigations for application in medical imaging (Keivanidis et al, 2008), lightemitting diodes (Hirata & Shizu, 2016) and advanced radiation dosimeters (Kingsley et al, 2009;Mills et al, 2013).…”