Abstract
Organic semiconductor materials exhibit a great potential for the realization of large-area solution-processed devices able to directly detect high-energy radiation. However, only few works investigated on the mechanism of ionizing radiation detection in this class of materials, so far. In this work we investigate the physical processes behind X-ray photoconversion employing bis-(triisopropylsilylethynyl)-pentacene thin-films deposited by bar-assisted meniscus shearing. The thin film coating speed and the use of bis-(triisopropylsilylethynyl)-pentacene:polystyrene blends are explored as tools to control and enhance the detection capability of the devices, by tuning the thin-film morphology and the carrier mobility. The so-obtained detectors reach a record sensitivity of 1.3 · 104 µC/Gy·cm2, the highest value reported for organic-based direct X-ray detectors and a very low minimum detectable dose rate of 35 µGy/s. Thus, the employment of organic large-area direct detectors for X-ray radiation in real-life applications can be foreseen.
Highlights
Organic semiconductor materials exhibit a great potential for the realization of large-area solution-processed devices able to directly detect high-energy radiation
The efforts spent by the scientific research community to conceive and realize innovative X- and gamma-ray detectors based on organic molecules and polymers originate from the exceptional properties of these materials, above all the possibility to deposit them from solution onto nonconventional substrates and over large areas by means of easy low-cost processing techniques[13,14]
Bottom-gate bottom-contact organic field-effect transistors (OFETs) based on TIPS-pentacene were fabricated by solution depositing TIPS-pentacene thin films (≈80 nm thick) by bar-assisted meniscus shearing (BAMS) technique on Si/SiO2 substrates with interdigitated gold electrodes at a speed of 10 mm/s
Summary
Organic semiconductor materials exhibit a great potential for the realization of large-area solution-processed devices able to directly detect high-energy radiation. A wide range of strategies were recently suggested to enhance the absorbance of the organic layer, such as introducing in the active layer high-Z elements as nanoparticles[2] or quantum dots[5], coupling the added high-Z elements with organic bulk heterojunctions[5,6], inserting carbon nanotubes in the active layer[10], and, more recently, by adding high-Z atoms directly into the molecule structure[15] Such peculiarities of organic materials open the way for several innovative applications, spanning from medical diagnostics to public safety, space, cultural heritage, and environmental monitoring, since large-area, light-weight, low-cost, and flexible devices could overcome the limitations of traditional inorganic semiconductor X-ray detectors (e.g., amorphous-Si, amorphousSe, poly-CZT, diamond)[16,17,18,19,20]. In our previous work[21] we attributed the direct X-ray photoconversion observed in microcrystalline thin films of bis-(triisopropylsilylethynyl) pentacene (TIPS-pentacene) to an electron traps assisted photoconductive gain mechanism, where the magnitude and the dynamics of the response together with the high sensitivity to the X-rays of the organic thin-film devices could be rationalized, thanks to a developed kinetic model
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