72 research outputs found
Tuning crystal ordering, electronic structure, and morphology in organic semiconductors: Tetrathiafulvalenes as a model case
Tetrathiafulvalenes (TTFs) are an appealing class of organic small molecules giving rise to some of the highest performing active materials reported for organic field effect transistors (OFETs). Because they can be easily chemically modified, TTF-derivatives are ideal candidates to perform molecule-property correlation studies and, especially, to elucidate the impact of molecular and crystal engineering on device performance. A brief introduction into the state-of-the-art of the field-effect mobility values achieved with TTF derivatives employing different fabrication techniques is provided. Following, structure-performance relationships are discussed, including polymorphism, a phenomenon which is crucial to control for ensuring device reproducibility. It is also shown that chemical modification of TTFs has a strong influence on the electronic structure of these materials, affecting their stability as well as the nature of the generated charge carriers, leading to devices with p-channel, n-channel, or even ambipolar behaviour. TTFs have also shown promise in other applications, such as phototransistors, sensors, or as dopants or components of organic metal charge transfer salts used as source-drain contacts. Overall, TTFs are appealing building blocks in organic electronics, not only because they can be tailored to perform fundamental studies, but also because they offer a wide spectrum of potential applications. Tetrathiafulvalenes are promising active materials in organic field-effect transistors (OFETs), in which they exhibit high performances. An overview is provided of the use of this family of materials as a model building block for OFETs to highlight general concepts of organic semiconductors and their use in devices.The authors thank the ERC StG 2012-306826 e-GAMES project, the Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), the DGI (Spain) with projects BE-WELL CTQ2013-40480-R and MAT2012-30924, and the Generalitat de Catalunya (2014-SGR-17, 2014SGR97 and XRQTC).Peer Reviewe
Tuning Crystal Ordering, Electronic Structure, and Morphology in Organic Semiconductors: Tetrathiafulvalenes as a Model Case
Tetrathiafulvalenes (TTFs) are an appealing class of organic small molecules giving rise to some of the highest performing active materials reported for organic field effect transistors (OFETs). Because they can be easily chemically modified, TTF-derivatives are ideal candidates to perform molecule-property correlation studies and, especially, to elucidate the impact of molecular and crystal engineering on device performance. A brief introduction into the state-of-the-art of the field-effect mobility values achieved with TTF derivatives employing different fabrication techniques is provided. Following, structure-performance relationships are discussed, including polymorphism, a phenomenon which is crucial to control for ensuring device reproducibility. It is also shown that chemical modification of TTFs has a strong influence on the electronic structure of these materials, affecting their stability as well as the nature of the generated charge carriers, leading to devices with p-channel, n-channel, or even ambipolar behaviour. TTFs have also shown promise in other applications, such as phototransistors, sensors, or as dopants or components of organic metal charge transfer salts used as source-drain contacts. Overall, TTFs are appealing building blocks in organic electronics, not only because they can be tailored to perform fundamental studies, but also because they offer a wide spectrum of potential applications
Deposition of composite materials using a wire-bar coater for achieving processability and air-stability in Organic Field-Effect Transistors (OFETs)
Organic thin films based on composite materials of semiconducting dibenzo-tetrathiafulvalene (DB-TTF) and insulating
styrenic matrices (Polystyrene (PS10k) and Poly-alpha methylstyrene (PAMS10k) ) have been fabricated by the wire-bar
coating technique in ambient conditions (air, light, humidity) and contrasted with the ones prepared by thermally
evaporating the organic semiconductor. The transistors fabricated with DB-TTF:PS10k composites show a clear fieldeffect
behavior with p-type characteristics, exhibiting charge carriers mobilities in the range of 0.01 cm2/Vs, fully
comparable with the films obtained by thermal evaporation. However, while the thermally evaporated films show poor
stability in air, the wire-bar coated composites films and devices are highly reproducible and exhibit lower threshold
voltage values. Thus, we demonstrate the suitability of the wire-bar technique for manufacturing large area devices.The authors thank the ERC StG 2012-306826 e-GAMES project, the Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), the DGI (Spain) with project BE-WELL CTQ2013-40480-R, and the Generalitat de Catalunya (2014-SGR-17). F. G. D. P. thanks Universidad Técnica de Ambato and Secretaría de Educación Superior, Ciencia, Tecnología e Innovación for funding through a doctoral scholarship “Convocatoria abierta 2010”.Peer Reviewe
Single Crystal-Like Performance in Solution-Coated Thin-Film Organic Field-Effect Transistors
In electronics, the fi eld-effect transistor (FET) is a crucial cornerstone and
successful integration of this semiconductor device into circuit applications
requires stable and ideal electrical characteristics over a wide range of temperatures
and environments. Solution processing, using printing or coating
techniques, has been explored to manufacture organic fi eld-effect transistors
(OFET) on fl exible carriers, enabling radically novel electronics applications.
Ideal electrical characteristics, in organic materials, are typically only found in
single crystals. Tiresome growth and manipulation of these hamper practical
production of fl exible OFETs circuits. To date, neither devices nor any circuits,
based on solution-processed OFETs, has exhibited an ideal set of characteristics
similar or better than today’s FET technology based on amorphous
silicon. Here, bar-assisted meniscus shearing of dibenzo-tetrathiafulvalene
to coat-process self-organized crystalline organic semiconducting domains
with high reproducibility is reported. Including these coatings as the channel
in OFETs, electric fi eld and temperature-independent charge carrier mobility
and no bias stress effects are observed. Furthermore, record-high gain in
OFET inverters and exceptional operational stability in both air and water are
measured.The authors thank the ERC StG 2012-306826 e-GAMES project, the
Networking Research Center on Bioengineering, Biomaterials, and
Nanomedicine (CIBER-BBN), the DGI (Spain) project BE-WELL
CTQ2013-40480-R, and the Generalitat de Catalunya (2014-SGR-
17). Research in Sweden was fi nancially supported by the Advanced
Functional Materials Center at Linköping University, the Önnesjö
Foundation, the Knut and Alice Wallenberg Foundation (Power Paper
project, scholars), the Swedish Foundation for Strategic Research (SSF,
Synergi project). F.G.D.P. thanks Universidad Técnica de Ambato and
Secretaría de Educación Superior, Ciencia, Tecnología e Innovación for
funding through a doctoral scholarship “Convocatoria abierta 2010.”
The authors also thank Witold Tatkiewicz for his help with the ImageJ
software.Peer reviewe
Synergistic Effect of Solvent Vapor Annealing and Chemical Doping for Achieving High-Performance Organic Field-Effect Transistors with Ideal Electrical Characteristics
Contact resistance and charge trapping are two key obstacles, often intertwined, that negatively impact on the performance of organic field-effect transistors (OFETs) by reducing the overall device mobility and provoking a nonideal behavior. Here, we expose organic semiconductor (OSC) thin films based on blends of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT-C8) with polystyrene (PS) to (i) a CH3CN vapor annealing process, (ii) a doping I2/water procedure, and (iii) vapors of I2/CH3CN to simultaneously dope and anneal the films. After careful analysis of the OFET electrical characteristics and by performing local Kelvin probe force microscopy studies, we found that the vapor annealing process predominantly reduces interfacial shallow traps, while the chemical doping of the OSC film is responsible for the diminishment of deeper traps and promoting a significant reduction of the contact resistance. Remarkably, the devices treated with I2/CH3CN reveal ideal electrical characteristics with a low level of shallow/deep traps and a very high and almost gate-independent mobility. Hence, this work demonstrates the promising synergistic effects of performing simultaneously a solvent vapor annealing and doping procedure, which can lead to trap-free OSC films with negligible contact resistance problems
Tetramethylbenzidine-TetrafluoroTCNQ: A narrow-gap semiconducting salt with room temperature relaxor ferroelectric behavior
We present an extension and revision of the spectroscopic and structural data
of the mixed stack charge transfer (CT) crystal
3,3,5,5-tetramethylbenzidine--tetrafluoro-tetracyanoquinodimethane
(TMB-TCNQF4), associated with new electric and dielectric measurements.
Refinement of syncrotron structural data at low temperature has led to revise
the previously reported [Phys. Rev. Mat. 2, 024602 (2018)] structure.
The revised structure is , with two dimerized stacks per unit cell, and
is consistent with the vibrational data. However, polarized Raman data in the
low-frequency region also indicate that by increasing temperature above 200 K
the structure presents an increasing degree of disorder mainly along the stack
axis. X-ray diffraction data at room temperature have confirmed that the
correct structure is -- no phase transitions -- but did not allow to
definitely substantiate the presence of disorder. On the other hand, dielectric
measurement have evidenced a typical relaxor ferroelectric behavior already at
room temperature, with a peak in real part of dielectric constant
around 200 K and 0.1 Hz. The relaxor behavior is explained
in terms of the presence of spin solitons separating domains of opposite
polarity that yield to ferroelectric nanodomains. TMB-TCNQF4 is confirmed to be
a narrow gap band semiconductor ( eV) with room temperature
conductivity of cm.Comment: 21 pages, including the Supporting Information in the same file.
Version 3 updates the x-ray structural data at room temperatur
Synthesis of 2D porous crystalline materials in simulated microgravity
Altres ajuts: the ICN2 is funded by the CERCA programme/Generalitat de Catalunya. The GIWAXS experiments were conducted on the NCD-SWEET beamline of the ALBA synchrotron, Spain. GIWAXS experiments of Ni(HITP) and COF-TAPB-BTCA were performed at the NCD-SWEET beamline at ALBA Synchrotron with the collaboration of ALBA staff.To date, crystallization studies conducted in space laboratories, which are prohibitively costly and unsuitable to most research laboratories, have shown the valuable effects of microgravity during crystal growth and morphogenesis. Herein, an easy and highly efficient method is shown to achieve space-like experimentation conditions on Earth employing custom-made microfluidic devices to fabricate 2D porous crystalline molecular frameworks. It is confirmed that experimentation under these simulated microgravity conditions has unprecedented effects on the orientation, compactness and crack-free generation of 2D porous crystalline molecular frameworks as well as in their integration and crystal morphogenesis. It is believed that this work will provide a new "playground" to chemists, physicists, and materials scientists that desire to process unprecedented 2D functional materials and devices
Microfluidic pneumatic cages : A novel approach for in-chip crystal trapping, manipulation and controlled chemical treatment
The precise localization and controlled chemical treatment of structures on a surface are significant challenges for common laboratory technologies. Herein, we introduce a microfluidic-based technology, employing a double-layer microfluidic device, which can trap and localize in situ and ex situ synthesized structures on microfluidic channel surfaces. Crucially, we show how such a device can be used to conduct controlled chemical reactions onto on-chip trapped structures and we demonstrate how the synthetic pathway of a crystalline molecular material and its positioning inside a microfluidic channel can be precisely modified with this technology. This approach provides new opportunities for the controlled assembly of structures on surface and for their subsequent treatment
Organic metal engineering for enhanced field-effect transistor performance
Advance Article.A key device component in organic field-effect transistors (OFETs) is the organic semiconductor/metal
interface since it has to ensure efficient charge injection. Traditionally, inorganic metals have been
employed in these devices using conventional lithographic fabrication techniques. Metals with low or
high work-functions have been selected depending on the type of semiconductor measured and,
in some cases, the metal has been covered with molecular self-assembled monolayers to tune the work
function, improve the molecular order at the interface and reduce the contact resistance. However,
in the last few years, some approaches have been focused on utilizing organic metals in these devices,
which have been fabricated by means of both evaporation and solution-processed techniques. Higher
device performances have often been observed, which have been attributed to a range of factors, such
as a more favourable organic/organic interface, a better matching of energy levels or/and to a reduction
of the contact resistance. Further, in contrast to their inorganic counterparts, organic metals allow their
chemical modification and thus the tuning of the Fermi level. In this perspective paper, an overview of the
recent work devoted to the fabrication of OFETs with organic metals as electrodes will be carried out. It will
be shown that in these devices not only is the matching of the HOMO or LUMO of the semiconductor with
the metal work-function important, but other aspects such as the interface morphology can also play a
critical role. Also, recent approaches in which the use of organic charge transfer salts as buffer layers at the
metal contacts or on the dielectric or as doping agents of the organic semiconductors that have been used
to improve the device performance will be briefly described.The authors thank the ERC StG 2012-306826 e-GAMES project,
the Networking Research Center on Bioengineering, Biomaterials
and Nanomedicine (CIBER-BBN), the DGI (Spain) for the project
BE-WELL CTQ2013-40480-R and the Generalitat de Catalunya for
the project 2014-SGR-17. We acknowledge CSIC for the publication
as Open Access in the RSC.Peer reviewe
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