Organic semiconductors are excellent candidates for X‐ray detectors that can adapt to new applications, with unique properties including mechanical flexibility and the ability to cover large surfaces. Their chemical composition, primarily carbon and hydrogen, makes them human tissue equivalent in terms of radiation absorption. This is a highly desirable property for a radiation dosimeter to be employed in medical diagnostics and therapy, however a low‐Z composition limits the absorption of ionizing radiation. The detection efficiency can be enhanced by considering the photoconductive gain (PG) effect, a significant contributor to the ionizing radiation detection mechanism in this class of materials. In this work, a process of controlled solution deposition by nozzle printing and crystallization of an organic semiconductor thin film is demonstrated whereby a flexible, arrayed thin‐film X‐ray detector with record X‐ray sensitivities among flexible radiation detectors (S = (9.0 ± 0.4) × 107 µC Gy−1cm−3) is developed. The excitonic peaks responsible for the activation of the PG effect are investigated and identified using a novel technique called photocurrent spectroscopy optical quenching, and the analysis of the changes in trap states is further demonstrated.
The attention focused on the application of organic electronics for the detection of ionizing radiation is rapidly growing among the international scientific community, due to the great potential of organic technology to enable large‐area conformable sensor panels. However, high‐energy photon absorption is challenging as organic materials are constituted of atoms with low atomic numbers. Here it is reported how, by synthesizing new solution‐processable organic molecules derived from 6,13‐bis(triisopropylsilylethynyl)pentacene (TIPS‐pentacene) and 2,8‐difluoro‐5,11‐bis(triethylsilylethynyl)anthradithiophene, with Ge‐substitution in place of the Si atoms to increase the material atomic number, it is possible to boost the X‐ray detection performance of organic thin films on flexible plastic substrates. Bis(triisopropylgermylethynyl)‐pentacene based flexible organic thin film transistors show high electrical performance with higher mobility (0.4 cm2V−1s−1) and enhanced X‐ray sensitivity, up to 9.0 × 105µC Gy−1cm−3, with respect to TIPS‐pentacene‐based detectors. Moreover, similar results are obtained for 5,11‐bis(triethylgermylethynyl)anthradithiophene devices, confirming that the proposed strategy, that is, increasing the atomic number of organic molecules by chemical tailoring to improve X‐ray sensitivity, can be generalized to organic thin film detectors, combining high X‐ray absorption, mechanical flexibility, and large‐area processing.
more » « less- NSF-PAR ID:
- 10460939
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Functional Materials
- Volume:
- 29
- Issue:
- 21
- ISSN:
- 1616-301X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Optoelectronic properties of anisotropic crystals vary with direction requiring that the orientation of molecular organic semiconductor crystals is controlled in optoelectronic device active layers to achieve optimal performance. Here, a generalizable strategy to introduce periodic variations in the out‐of‐plane orientations of 5,11‐bis(triisopropylsilylethynyl)anthradithiophene (TIPS ADT) crystals is presented. TIPS ADT crystallized from the melt in the presence of 16 wt.% polyethylene (PE) forms banded spherulites of crystalline fibrils that twist in concert about the radial growth direction. These spherulites exhibit band‐dependent light absorption, photoluminescence, and Raman scattering depending on the local orientation of crystals. Mueller matrix imaging reveals strong circular extinction (CE), with TIPS ADT banded spherulites exhibiting domains of positive or negative CE signal depending on the crystal twisting sense. Furthermore, orientation‐dependent enhancement in charge injection and extraction in films of twisted TIPS ADT crystals compared to films of straight crystals is visualized in local conductive atomic force microscopy maps. This enhancement leads to 3.3‐ and 6.2‐times larger photocurrents and external quantum efficiencies, respectively, in photodetectors comprising twisted crystals than those comprising straight crystals.
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Abstract Polymer ferroelectrics are playing an increasingly active role in flexible memory application and wearable electronics. The relaxor ferroelectric dielectric, poly(vinylidene fluoride trifluorethylene (PVDF‐TrFE), although vastly used in organic field‐effect transistors (FETs), has issues with gate leakage current especially when the film thickness is below 500 nm. This work demonstrates a novel method of selective poling the dielectric layer. By using solution‐processed 6,13‐bis(triisopropylsilylethynyl)pentacene (TIPS‐pentacene) as the organic semiconductor, it is shown that textured poling of the PVDF‐TrFE layer dramatically improves FET properties compared to unpoled or uniformly poled ferroelectric films. The texturing is achieved by first vertically poling the PVDF‐TrFE film and then laterally poling the dielectric layer close to the gate electrode. TIPS‐pentacene FETs show on/off ratios of 105and hole mobilities of 1 cm2Vs−1under ambient conditions with operating voltages well below −5 V. The electric field distribution in the dielectric layer is simulated by using finite difference time domain methods.
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Organic semiconducting small molecules have attracted increasing interest over the last decades because of their versatile, tunable optoelectronic properties and, e.g. , the ease they can be purified compared to polymeric systems. Hence, over the past few decades, a large number of small molecules, such as acenes and thiophenes, have been explored for use in semiconducting devices such as thin-film transistors. However, many of these materials can adopt various molecular arrangements, producing polymorphic structures. As a result, the same material can display vastly different optoelectronic properties. This can, in many cases, lead to a large spread of device performances. Hence, it is critical to establish knowledge- and characterization libraries towards relevant structure/processing/performance interrelations to further advance this interesting class of materials and to open new application platforms. Here, we discuss processing strategies and methodologies that allow the control and assessment of polymorph formation in semiconducting small molecules using 5,11-bis(triethylsilylethynyl)anthradithiophene (TES ADT) as a model material system. We revise how a window into the complex phase behavior of semiconducting small molecules can be obtained, how specific polymorphs can be induced, and how post-deposition treatments can be exploited. Moreover, we illustrate pathways towards patterned structures as needed to fully exploit the touted potential of this interesting class of semiconductors.more » « less
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Abstract Charge transport in organic semiconductors is highly sensitive to film heterogeneity and intermolecular interactions, but probing these properties on the length scales of disorder is often difficult. Here we use micro-Raman spectroscopy to assign vibrational modes of isomerically pure
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