1,721,070 research outputs found
Multi-length-scale relationships between the polymer molecular structure and charge transport: the case of poly-naphthalene diimide bithiophene
No full textCharge transport in organic polymer semiconductors is a complex phenomenon affected by structural and electronic properties ranging over different length scales, from the molecular one up to the macro-scale. Charge carriers show markers of spatial localization (polarons), and drift for distances from a few to 100 mm in typical field-effect devices. Being sensitive to such different length scales, field-effect mobility is evidently a figure of merit that averages local properties at the molecular scale, over distances orders of magnitude larger. Understanding charge transfer processes at each length scale is consequently of paramount importance. To fulfill this aim, a multi-length-scale approach, encompassing experimental and theoretical modeling investigations, has to be built. Here we critically revise a series of experimental and theoretical tools that can contribute to develop a consistent multi-scale investigation methodology. We consider them within the study of an exemplary, good electron transporting naphthalene-diimide bi-thiophene copolymer, which has represented a breakthrough for the class of n-type polymers since its disclosure in 2009
Quantum-Chemical Insights into the Prediction of Charge Transport Parameters for a Naphthalenetetracarboxydiimide-Based Copolymer with Enhanced Electron Mobility
No full textTheoretical modeling has been applied to study the charge transport (CT) parameters of a high-electron-mobility (n-type) naphthalenetetracarboxydiimide copolymer that was recently synthesized and tested for organic field-effect transistor applications. To understand the physicochemical characteristics of such a material, the intra- and intermolecular CT properties of holes and electrons were investigated using different DFT functionals, evidencing the need of range-separated hybrid functionals to predict key parameters such as the hole and electron reorganization energies. Our calculations revealed clear differences between hole- and electron-charging processes, providing fundamental elements for the rationalization of their transport
Ultraflexible all-organic complementary transistors and inverters based on printed polymers
Full text linkOrganic electronics has been steadily evolving, with improving performances, including unrivaled mechanical properties. One of the main technological trends aims at thinner and lighter form factors, toward the realization of ultraflexible and conformable large-area electronic devices, capable of withstanding harsh mechanical stresses and therefore finding applications where rigid or brittle technologies would fail. Pursuing this objective, a critical role is known to be played by the substrate, whose thickness needs to be reduced as much as possible while maintaining its processability. Ultrathin substrates and a neutral plane strategy have therefore been exploited to realize ultrathin organic devices; however, ultraflexible complementary circuits based on printed organic semiconductors, realized by means of high-throughput and large-area techniques, have not been realized so far. In this work, all-polymer organic field effect transistors and complementary inverters have been printed onto a micrometer-thin parylene substrate, subsequently also used as a top isolation layer in order to place the active components in the neutral plane of stresses. These devices show appropriate low voltage operation, with supply voltages as low as 2 V, and retain stable and uniform performances upon the application of harsh mechanical stresses, such as rolling and crumpling. These results represent the first demonstration of semi-transparent and fully organic crumpable printed electronics, and pave the way toward the realization of more complex complementary logic circuits, laying the foundation for their widespread and cost-effective integration into consumer products
Atomistic Simulations of P(NDI2OD-T2) Morphologies: From Single Chain to Condensed Phases
Full text linkWe investigate theoretically the structure, crystallinity, and solubility of a high-mobility n-type semiconducting copolymer, P(NDI2OD-T2), and we propose a set of new force field parameters. The force field is reparametrized against density functional theory (DFT) calculations, with the aim to reproduce the correct torsional angles that govern the polymer chain flexibility and morphology. We simulate P(NDI2OD-T2) oligomers in different environments, namely, in vacuo, in the bulk phase, and in liquid toluene and chloronaphthalene solution. The choice of these solvents is motivated by the fact that they induce different kinds of molecular preaggregates during the casting procedures, resulting in variable device performances. Our results are in good agreement with the available experimental data; the polymer bulk structure, in which the chains are quite planar, is correcly reproduced, yet the isolated chains are flexible enough to fold in vacuo. We also calculate the solubility of P(NDI2OD-T2) in toluene and chloronaphthalene, predicting a much better solubility of the polymer in the latter, also in accordance to experimental observations. Different morphologies and dynamics of the oligomers in the two solvents have been observed. The proposed parameters make it possible to obtain the description of P(NDI2OD-T2) in different environments and can serve as a basis for extensive studies of this polymer semiconductor, such as, for example, the dynamics of aggregation in solvent
Nature of Charge Carriers in a High Electron Mobility Naphthalenediimide Based Semiconducting Copolymer
No full textThe nature of charge carriers in recently developed high mobility semiconducting donor-acceptor polymers is debated. Here, localization due to charge relaxation is investigated in a prototypal system, a good electron transporting naphthalenediimide based copolymer, by means of current-voltage I-V electrical characteristics and charge modulation spectroscopy (CMS) in top-gate field-effect transistors (FETs), combined with density functional theory (DFT) and time dependent DFT (TDDFT) calculations. In particular, pristine copolymer films are compared with films that underwent a melt-annealing process, the latter leading to a drastic change of the microstructure. Despite the packing modification, which involves also the channel region, both the electron mobility and the energy of polaronic transitions are substantially unchanged upon melt-annealing. The polaron absorption features can be rationalized and reproduced by TDDFT calculations for isolated charged oligomers. Therefore, it is concluded that in such a high electron mobility copolymer the charge transport process involves polaronic species which are intramolecular in nature and, from a more general point of view, that interchain delocalization of the polaron is not necessary to sustain charge mobilities in the 0.1 to 1 cm(2) V-1 s(-1) range. These findings contribute to the rationalization of the charge transport process in the recently developed class of donor-acceptor pi-conjugated copolymers featuring high charge mobilities and complex morphologies
Organic Electronics Picks Up the Pace: Mask-Less, Solution Processed Organic Transistors Operating at 160 MHz
Full text linkOrganic printed electronics has proven its potential as an essential enabler for applications related to healthcare, entertainment, energy, and distributed intelligent objects. The possibility of exploiting solution-based and direct-writing production schemes further boosts the benefits offered by such technology, facilitating the implementation of cheap, conformable, bio-compatible electronic applications. The result shown in this work challenges the widespread assumption that such class of electronic devices is relegated to low-frequency operation, owing to the limited charge mobility of the materials and to the low spatial resolution achievable with conventional printing techniques. Here, it is shown that solution-processed and direct-written organic field-effect transistors can be carefully designed and fabricated so to achieve a maximum transition frequency of 160 MHz, unlocking an operational range that was not available before for organics. Such range was believed to be only accessible with more performing classes of semiconductor materials and/or more expensive fabrication schemes. The present achievement opens a route for cost- and energy-efficient manufacturability of flexible and conformable electronics with wireless-communication capabilities
Monitoring of Drug Release via Intra Body Communication with an Edible Pill
No full textOral drug administration provides a convenient and patient-compliant way for drug delivery, especially for chronic diseases and prolonged pharmacological treatments. However, due to the repetitiveness of such therapeutic approach, the patients are led to neglect/forget the therapy affecting the healthcare delivery. Indeed, the non-adherence to pharmacological prescriptions and the unknown amount of real-time drug release result in a non-compliant therapeutic drug level over the protracted therapies. The proposed technology will enable the monitoring of both pharmacological adherence and real-time drug release. The approach exploits a passive intrabody communication (IBC) activation in order to enable an edible pill, realized starting from food additives and food-grade materials, to monitor pharmacological adherence. Following activation, the signal is modulated by IBC coupling switching triggered by pill degradation in a gastrointestinal tract, resulting in a monitored drug release. The proof-of-concept is designed for a targeted release and monitoring of Metformin in the intestine. The system shows an in vitro limit of cumulative drug release detection of 18 μg mL−1 and a limit of real-time drug release detection of 2 μg mL−1 min−1. This platform represents the first solution to monitor passive drug release in real-time, from intake to complete absorption, enabling unique and long-sought healthcare therapy and treatment opportunity
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Reproducible, High Performance Fully Printed Photodiodes on Flexible Substrates through the Use of a Polyethylenimine Interlayer
No full textThis paper investigates with a statistical analysis the issue of performance reproducibility and optimization in fully inkjet-printed organic photodetectors on flexible substrates. The most crucial process step to obtain reproducible, well performing devices with a high process yield turns out to be the printing of the thin polyethylenimine interlayer used as a surface modifier for the bottom electrode. Controlling solution composition and deposition parameters for this layer, a 57 nA cm-2mean reverse dark current was achieved, with an outstanding standard deviation as low as 15 nA cm-2, with dramatic improvements in process yield (from less than 20% to over 90%). Device performance in terms of dark currents, EQE (from 50% up to 90% at 525 nm, depending on process), and rectification (ratio between forward current and reverse current over 104and reaching 105in the best cases) is among the best for fully printed detectors. Furthermore, the importance of relative humidity control in the deposition environment during the interlayer printing on device characteristics is reported, indicating the processing conditions optimal for scaling to mass manufacturing. The overall interlayer optimization approach was applied to a process using widely adopted materials in the organic optoelectronics field, and thus retains relevance on a broad range
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