Flexible radiation dosimeters incorporating semiconducting polymer thick films

Abstract

Flexible radiation dosimeters have been produced incorporating thick films (>1 μm) of the semiconducting polymer poly([9,9-dioctylfluorenyl-2,7-diyl]-co-bithiophene). Diode structures produced on aluminium-metallised poly(imide) substrates, and with gold top contacts, have been examined with respect to their electrical properties. The results suggest that a Schottky conduction mechanism occurs in the reverse biased diode, with a barrier to charge injection at the aluminium electrode. Optical absorption/emission spectra reveal a band gap of 2.48 eV for the polymer. The diodes have been used for direct charge detection of 17 keV X-rays, generated by a molybdenum source. Using operating voltages of -10 and -50 V respectively, sensitivities of 54 and 158 nC/mGy/cm 3 have been achieved. Increasing the operating voltage shows that the diodes are stable up to approximately -200 V without significant increase in the dark current of the device (<0.2 nA).

Enhanced x-ray detection sensitivity in semiconducting polymer diodes containing metallic nanoparticles

“…[12] Although these organic materials can be susceptible to radiation damage, [13] they have some advantages for their use as X-ray detectors, such as mechanical flexibility, tissue equivalence, and an ability to be coated over large areas. [13,14] We have previously produced X-ray induced photocurrents (on the order of ten nA) in several micrometer thick semiconducting polymer films exposed to incident 17.5 keV Xray doses of up to 70 mGy.s -1 . [11,14] As the dark current produced by these devices is approximately 0.1 nA, the X-ray induced photocurrent can be detected in laboratory applications using sensitive ammeters and electrical amplifiers.…”

Heavy metallic oxide nanoparticles for enhanced sensitivity in semiconducting polymer x-ray detectors

“…Previously, direct detection of electron [13] and alpha (α) particles [14,15] has been achieved using polymers as the active layer. We have recently shown that direct X-ray induced photocurrents can be observed in metal/semiconducting polymer/metal diode structures [7,8,16,17] indicating the feasibility of using conjugated polymers in direct real-time radiation detection applications. The addition of small organic semiconducting molecules to Published in Nanotechnology 23 (2012) 235502 4 the polymer increased the charge-carrier mobility, which resulted in increased X-ray sensitivities [18].…”

High charge-carrier mobilities in blends of poly(triarylamine) and TIPS-pentacene leading to better performing X-ray sensors

“…Numerous electronic devices, including field effect transistors [1], light-emitting diodes [2], photovoltaic cells [3], and radiation sensors [4,5], have in recent years employed organic materials as the active component. These devices share one common feature in that their efficiency depends strongly on the transport of charge carriers.…”

“…The use of polymers -in the place of conventional inorganic semiconductors -opens up the possibility for large-area fabrication of sensors using low-cost, wet processing techniques, Published in Organic Electronics (2011) 12, 1903-1908 3 such as spin-casting, spray-casting, ink-jet or roll-to-roll printing [17]. Radiation sensors made from polymers exhibit greater mechanical flexibility in comparison to inorganic solids [5]. Furthermore, the elemental composition of most polymers (C, H, N and O) makes them an ideal candidate for dosimeters in medical applications, in which the detector requires a "human tissue-equivalent" interaction with radiation.…”