Abstract
The application of organic electronic materials for the detection of ionizing radiations is very appealing thanks to their mechanical flexibility, low-cost and simple processing in comparison to their inorganic counterpart. In this work we investigate the direct X-ray photoconversion process in organic thin film photoconductors. The devices are realized by drop casting solution-processed bis-(triisopropylsilylethynyl)pentacene (TIPS-pentacene) onto flexible plastic substrates patterned with metal electrodes; they exhibit a strong sensitivity to X-rays despite the low X-ray photon absorption typical of low-Z organic materials. We propose a model, based on the accumulation of photogenerated charges and photoconductive gain, able to describe the magnitude as well as the dynamics of the X-ray-induced photocurrent. This finding allows us to fabricate and test a flexible 2 × 2 pixelated X-ray detector operating at 0.2 V, with gain and sensitivity up to 4.7 × 104 and 77,000 nC mGy−1 cm−3, respectively.
Highlights
The application of organic electronic materials for the detection of ionizing radiations is very appealing thanks to their mechanical flexibility, low-cost and simple processing in comparison to their inorganic counterpart
We investigate direct X-ray photo-conversion in micro-crystalline thin films of bis-(triisopropylsilylethynyl) pentacene (TIPS-pentacene) deposited by drop casting onto flexible poly(ethyleneterephthalate) (PET) substrates
The detectors consist of a 100 nm thick TIPS-pentacene organic active layer deposited by drop-casting onto interdigitated gold electrodes fabricated on 125 mm thick PET film
Summary
The application of organic electronic materials for the detection of ionizing radiations is very appealing thanks to their mechanical flexibility, low-cost and simple processing in comparison to their inorganic counterpart. We investigate direct X-ray photo-conversion in micro-crystalline thin films of bis-(triisopropylsilylethynyl) pentacene (TIPS-pentacene) (a standard material for the fabrication of organic devices onto flexible plastic substrates22) deposited by drop casting onto flexible poly(ethyleneterephthalate) (PET) substrates We find that these devices are characterized by an unexpected high X-ray sensitivity that we justify by interpreting the detection mechanism as a photo-modulation of the semiconductor conductivity due to charge accumulation during X-ray exposure, resulting in a photoconductive gain effect. From such findings, we develop a kinetic model that gives an important insight into the physical process that leads to highly sensitive response to ionizing radiation by such low-Z organic materials. The ultra-low voltage operation paves the way towards battery-operated wearable detectors
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