11 results on '"Hamna F. Iqbal"'
Search Results
2. Organic Field‐Effect Transistors as Flexible, Tissue‐Equivalent Radiation Dosimeters in Medical Applications
- Author
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Andrew M. Zeidell, Tong Ren, David S. Filston, Hamna F. Iqbal, Emma Holland, J. Daniel Bourland, John E. Anthony, and Oana D. Jurchescu
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dosimetry ,flexible electronics ,organic field effect transistors ,radiation detection ,X‐ray detection ,Science - Abstract
Abstract Radiation therapy is one of the most prevalent procedures for cancer treatment, but the risks of malignancies induced by peripheral beam in healthy tissues surrounding the target is high. Therefore, being able to accurately measure the exposure dose is a critical aspect of patient care. Here a radiation detector based on an organic field‐effect transistor (RAD‐OFET) is introduced, an in vivo dosimeter that can be placed directly on a patient's skin to validate in real time the dose being delivered and ensure that for nearby regions an acceptable level of low dose is being received. This device reduces the errors faced by current technologies in approximating the dose profile in a patient's body, is sensitive for doses relevant to radiation treatment procedures, and robust when incorporated into conformal large‐area electronics. A model is proposed to describe the operation of RAD‐OFETs, based on the interplay between charge photogeneration and trapping.
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- 2020
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3. Importance of Electric-Field-Independent Mobilities in Thick-Film Organic Solar Cells
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Carr Hoi Yi Ho, Yusen Pei, Yunpeng Qin, Chujun Zhang, Zhengxing Peng, Indunil Angunawela, Austin L. Jones, Hang Yin, Hamna F. Iqbal, John R. Reynolds, Kenan Gundogdu, Harald Ade, Shu Kong So, and Franky So
- Subjects
General Materials Science - Abstract
In organic solar cells (OSCs), a thick active layer usually yields a higher photocurrent with broader optical absorption than a thin active layer. In fact, a ∼300 nm thick active layer is more compatible with large-area processing methods and theoretically should be a better spot for efficiency optimization. However, the bottleneck of developing high-efficiency thick-film OSCs is the loss in fill factor (FF). The origin of the FF loss is not clearly understood, and there a direct method to identify photoactive materials for high-efficiency thick-film OSCs is lacking. Here, we demonstrate that the mobility field-dependent coefficient is an important parameter directly determining the FF loss in thick-film OSCs. Simulation results based on the drift-diffusion model reveal that a mobility field-dependent coefficient smaller than 10
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- 2022
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4. Crystal engineering of alkylethynyl fluoroanthradithiophenes
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Karl J. Thorley, Derek Dremann, Hamna F. Iqbal, Sean R. Parkin, Oana D. Jurchescu, and John E. Anthony
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Chemistry (miscellaneous) ,Process Chemistry and Technology ,Materials Chemistry ,Biomedical Engineering ,Energy Engineering and Power Technology ,Chemical Engineering (miscellaneous) ,Industrial and Manufacturing Engineering - Abstract
2-Dimensional brickwork packing is desirable for high mobility organic semiconductors. We synthesised acene derivatives that adopt this packing without using heavier group 14 elements to investigate substituent effects on bulk transport properties.
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- 2022
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5. Real-time monitoring of trap dynamics reveals the electronic states that limit charge transport in crystalline organic semiconductors
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John E. Anthony, Hamna F. Iqbal, Oana D. Jurchescu, and Emma Holland
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Materials science ,business.industry ,Band gap ,Process Chemistry and Technology ,Transistor ,Charge (physics) ,Trapping ,Microstructure ,law.invention ,Organic semiconductor ,Mechanics of Materials ,law ,Optoelectronics ,General Materials Science ,Charge carrier ,Electronics ,Electrical and Electronic Engineering ,business - Abstract
Organic semiconductors (OSCs) have the potential to become ubiquitous in our lives as part of various optoelectronic devices given their low-cost processing, light weight, and the opportunities that they offer for designing new materials with “on demand” properties. Many OSCs have achieved remarkable performances, however, a complete understanding of the fundamental processes that govern their properties is still lacking. One such process is charge carrier trapping, a phenomenon that profoundly impacts the performance and stability of devices. Here we report on a comprehensive study on the physics of traps resulting from microstructure changes by monitoring the generation/annihilation of traps in 2,8-difluoro-5,11-bis(triethylsilylethynyl)anthradithiophene (diF-TES ADT), a high-mobility small molecule OSC. The variations in charge carrier mobility measured in organic field-effect transistors (OFETs) deliberately exposed to solvent vapor are correlated with the density and energetic distribution of the electronic states in the band gap of the OSC in all intermediate states of the microstructural transformations. Given the strong dependence of the electrical properties on the film microstructure, such information is instrumental in identifying performance-limiting processes in devices and subsequently guiding material processing to achieve intrinsic limits. The discovery of defect-tolerant intermediate crystalline motifs may provide new pathways for fabricating stable, high-performance devices for next-generation low-cost electronics.
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- 2020
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6. Organic single crystals of charge-transfer complexes: model systems for the study of donor/acceptor interactions
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Katelyn P. Goetz, Emily G. Bittle, Christina A. Hacker, Sujitra J. Pookpanratana, Oana D. Jurchescu, and Hamna F. Iqbal
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Materials science ,Photoemission spectroscopy ,Process Chemistry and Technology ,Charge (physics) ,Electronic structure ,Microstructure ,Electron transport chain ,Acceptor ,Organic semiconductor ,Mechanics of Materials ,Chemical physics ,General Materials Science ,Electrical and Electronic Engineering ,HOMO/LUMO - Abstract
The charge-transfer (CT) state arising as a hybrid electronic state at the interface between charge donor and charge acceptor molecular units is important to a wide variety of physical processes in organic semiconductor devices. The exact nature of this state depends heavily on the nature and co-facial overlap between the donor and acceptor; however, altering this overlap is usually accompanied by extensive confounding variations in properties due to extrinsic factors, such as microstructure. As a consequence, establishing reliable relationships between donor/acceptor molecular structures, their molecular overlap, degree of charge transfer and physical properties, is challenging. Herein, we examine the electronic structure of a polymorphic system based on the donor dibenzotetrathiafulvalene (DBTTF) and the acceptor 7,7,8,8-tetracyanoquinodimethane (TCNQ) in the form of high-quality single crystals varying in the donor–acceptor overlap. Using angle-resolved photoemission spectroscopy, we resolve the highest occupied molecular orbital states of the CT crystals. Analysis based on field-effect transistors allows us to probe the sub-gap states impacting hole and electron transport. Our results expand the understanding on the impact of donor and acceptor interactions on electronic structure and charge transport.
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- 2021
7. Suppressing bias stress degradation in high performance solution processed organic transistors operating in air
- Author
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John E. Anthony, Hu Chen, Chad Risko, Oana D. Jurchescu, Karl J. Thorley, Iain McCulloch, Qianxiang Ai, and Hamna F. Iqbal
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Materials science ,Fabrication ,Science ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Article ,General Biochemistry, Genetics and Molecular Biology ,Bias stress ,law.invention ,Trap (computing) ,law ,Electronic devices ,Multidisciplinary ,business.industry ,Transistor ,General Chemistry ,021001 nanoscience & nanotechnology ,Electrical and electronic engineering ,0104 chemical sciences ,Threshold voltage ,Solution processed ,Optoelectronics ,Degradation (geology) ,Field-effect transistor ,0210 nano-technology ,business - Abstract
Solution processed organic field effect transistors can become ubiquitous in flexible optoelectronics. While progress in material and device design has been astonishing, low environmental and operational stabilities remain longstanding problems obstructing their immediate deployment in real world applications. Here, we introduce a strategy to identify the most probable and severe degradation pathways in organic transistors and then implement a method to eliminate the main sources of instabilities. Real time monitoring of the energetic distribution and transformation of electronic trap states during device operation, in conjunction with simulations, revealed the nature of traps responsible for performance degradation. With this information, we designed the most efficient encapsulation strategy for each device type, which resulted in fabrication of high performance, environmentally and operationally stable small molecule and polymeric transistors with consistent mobility and unparalleled threshold voltage shifts as low as 0.1 V under the application of high bias stress in air., Electrical instability of organic field-effect transistors (OFETs) during operation remains a challenge that limits the device’s real-world technological viability. Here, the authors report a method for diagnosing and suppressing bias stress in solution-processed OFETs operated in air.
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- 2021
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8. Organic Field‐Effect Transistors as Flexible, Tissue‐Equivalent Radiation Dosimeters in Medical Applications
- Author
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John E. Anthony, Emma Holland, J. Daniel Bourland, David S. Filston, Andrew M. Zeidell, Hamna F. Iqbal, Oana D. Jurchescu, and Tong Ren
- Subjects
Materials science ,General Chemical Engineering ,medicine.medical_treatment ,General Physics and Astronomy ,Medicine (miscellaneous) ,Dose profile ,Radiation ,radiation detection ,Biochemistry, Genetics and Molecular Biology (miscellaneous) ,flexible electronics ,Particle detector ,law.invention ,law ,medicine ,Dosimetry ,General Materials Science ,lcsh:Science ,Dosimeter ,dosimetry ,organic field effect transistors ,Communication ,Transistor ,General Engineering ,X‐ray detection ,Communications ,Radiation therapy ,Field-effect transistor ,lcsh:Q ,Biomedical engineering - Abstract
Radiation therapy is one of the most prevalent procedures for cancer treatment, but the risks of malignancies induced by peripheral beam in healthy tissues surrounding the target is high. Therefore, being able to accurately measure the exposure dose is a critical aspect of patient care. Here a radiation detector based on an organic field‐effect transistor (RAD‐OFET) is introduced, an in vivo dosimeter that can be placed directly on a patient's skin to validate in real time the dose being delivered and ensure that for nearby regions an acceptable level of low dose is being received. This device reduces the errors faced by current technologies in approximating the dose profile in a patient's body, is sensitive for doses relevant to radiation treatment procedures, and robust when incorporated into conformal large‐area electronics. A model is proposed to describe the operation of RAD‐OFETs, based on the interplay between charge photogeneration and trapping., A radiation detector based on an organic field‐effect transistor (RAD‐OFET) is introduced for passive radiation dosimetry. RAD‐OFETs are tissue‐equivalent devices that can be placed directly on a patient's skin to directly measure radiation dose delivery and are sensitive for doses relevant to many radiation treatment procedures.
- Published
- 2020
9. Elucidating the Role of Water‐Related Traps in the Operation of Polymer Field‐Effect Transistors
- Author
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Matthew Waldrip, Oana D. Jurchescu, Hu Chen, Hamna F. Iqbal, and Iain McCulloch
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Materials science ,Work (electrical) ,Foundation (engineering) ,Field-effect transistor ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,0210 nano-technology ,01 natural sciences ,Engineering physics ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials - Abstract
The work at Wake Forest University was supported by the National Science Foundation through Grants No. DMR-1627925 and ECCS-1810273. I.M. acknowledges funding from KAUST Office of Sponsored Research (OSR) under awards no. OSR-2018-CARF/CCF-3079, no. OSR-2015-CRG4-2572 and OSR -4106 CPF2019, as well as EC FP7 Project SC2 (610115), EC H2020 (643791), and EPSRC EP/M005143/1.
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- 2021
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10. Large‐Area Uniform Polymer Transistor Arrays on Flexible Substrates: Towards High‐Throughput Sensor Fabrication
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Matthew Waldrip, Iain McCulloch, Oana D. Jurchescu, David S. Filston, Andrew M. Zeidell, Hamna F. Iqbal, and Hu Chen
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chemistry.chemical_classification ,Materials science ,Fabrication ,business.industry ,Foundation (engineering) ,Spray coating ,Transistor array ,Nanotechnology ,02 engineering and technology ,Polymer ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Industrial and Manufacturing Engineering ,Flexible electronics ,0104 chemical sciences ,Semiconductor ,chemistry ,Mechanics of Materials ,General Materials Science ,0210 nano-technology ,business ,Throughput (business) - Abstract
This work was partially supported by National Science Foundation through grants DMR-1627925 and ECCS-1810273.
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- 2020
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11. Organic thin-film transistors with flame-annealed contacts
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Andrew Wadsworth, Matthew Waldrip, Oana D. Jurchescu, Iain McCulloch, and Hamna F. Iqbal
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Materials science ,Dopant ,business.industry ,Annealing (metallurgy) ,Contact resistance ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Semiconductor ,Thin-film transistor ,Electrode ,Surface roughness ,Work function ,Electrical and Electronic Engineering ,Composite material ,0210 nano-technology ,business - Abstract
Reducing contact resistance is critical to developing high-performance organic field-effect transistors (OFETs) since it impacts both the device mobility and switching speed. Charge injection and collection has been optimized by applying chemical treatments to the contacts, such as self-assembled monolayers (SAMs), oxide interlayers, or dopants. Here, we tested how flame annealing the surface of the electrodes impacts the interface and bulk components of the contact resistance, as well as the overall device performance. A butane micro torch was used to flash-anneal the gold electrodes, which allowed gold grains to crystallize into larger domains. We found that, along with the grain size, the surface roughness of the contacts was also increased. SAM treatment created a lower work function shift on a flame annealed electrode than when deposited on an untreated surface, due to the greater surface roughness. This resulted in a larger interface contact resistance. However, flame annealing also produced an order of magnitude reduction in the density of trap states in the semiconductor layer, which reduced the bulk contact resistance and channel resistance. These competing effects yielded OFETs with similar performance as untreated devices.
- Published
- 2020
- Full Text
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