Probing molecular arrangements of the organic semiconductor 2,7-Dioctyl[1]benzothieno[3,2- b][1]benzothiophene thin film at the interface by UV Resonant Raman scattering

Raman spectroscopy was employed to investigate nanometric thick films of the organic semiconductor 2,7-Dioctyl[1]benzothieno[3,2-b][1]benzothiophene, following a comprehensive vibrational characterization of the compound condensed phases at various excitation wavelengths. UV Raman excitation enabled the characterization of the thin films, revealing that the molecular orientation at the film/air interface is characterized by a different organization and/or a high degree of disorder compared to the bulk phase. The low penetration depth of the UV Raman excitation allows for the retrieval of this information, unlike the XRD data

Chemical Doping of the Organic Semiconductor C8-BTBT-C8 Using an Aqueous Iodine Solution for Device Mobility Enhancement

The performance of organic field-effect transistors is still severely limited by factors such as contact resistance and charge trapping. Chemical doping is considered to be a promising key enabler for improving device performance, although there is a limited number of established doping protocols as well as a lack of understanding of the doping mechanisms. Here, a very simple doping methodology based on exposing an organic semiconductor thin film to an aqueous iodine solution is reported. The doped devices exhibit enhanced device mobility, which becomes channel-length independent, a decreased threshold voltage and a reduction in the density of interfacial traps. The device OFF current is not altered, which is in agreement with the spectroscopic data that points out that no charge transfer processes are occurring. Kelvin probe force microscopy characterization of the devices under operando conditions unambiguously proves that an important reduction of the contact resistance takes place after their exposition to the iodine solution, reaching almost ohmic contact

Inkjet-printed stretchable and low voltage synaptic transistor array.

Wearable and skin electronics benefit from mechanically soft and stretchable materials to conform to curved and dynamic surfaces, thereby enabling seamless integration with the human body. However, such materials are challenging to process using traditional microelectronics techniques. Here, stretchable transistor arrays are patterned exclusively from solution by inkjet printing of polymers and carbon nanotubes. The additive, non-contact and maskless nature of inkjet printing provides a simple, inexpensive and scalable route for stacking and patterning these chemically-sensitive materials over large areas. The transistors, which are stable at ambient conditions, display mobilities as high as 30 cm2 V-1 s-1 and currents per channel width of 0.2 mA cm-1 at operation voltages as low as 1 V, owing to the ionic character of their printed gate dielectric. Furthermore, these transistors with double-layer capacitive dielectric can mimic the synaptic behavior of neurons, making them interesting for conformal brain-machine interfaces and other wearable bioelectronics

Role of geometry, substrate and atmosphere on performance of OFETs based on TTF derivatives

Abstract We report a comparative study of OFET devices based on zone-cast layers of three tetrathiafulvalene (TTF) derivatives in three configurations of electrodes in order to determine the best performing geometry. The first testing experiments were performed using SiO 2 /Si substrates. Then the optimum geometry was employed for the preparation of flexible OFETs using Parylene C as both substrate and dielectric layer yielding, in the best case, to devices with μ FET = 0.1 cm 2 /Vs. With the performed bending tests we determined the limit of curvature radius for which the performance of the OFETs is not deteriorated irreversibly. The investigated OFETs are sensitive to ambient atmosphere, showing reversible increase of the source to drain current upon exposition to air, what can be explained as doping of TTF derivative by oxygen or moisture

Highly piezoresistive textiles based on a soft conducting charge transfer salt

The integration of smart materials into human wearable interfaces is a current topic of interest. This paper reports the integration into a polyester textile of a bi-layer (BL) film based on a polymeric matrix containing a top-layer of a microcrystalline network of an organic conductor. The resulting textiles, in addition to be conducting, exhibit the excellent strain sensing properties of BL films maintaining at the same time their flexibility.This work was funded by CETEMMSA, the EU EC FP7 ONE-P large-scale collaborative project no. 212311, Marie Curie Est FuMaSSEC, the DGI (Spain) with project EMOCIONa (CTQ2006-06333/BQU), and Generalitat de Catalunya 2009SGR-00516. Authors also thank the Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), an initiative of ISCIII.Peer Reviewe

Dual-Gate Organic Field-Effect Transistor for pH Sensors with Tunable Sensitivity

Dual‐gate field‐effect transistors (FETs) based on organic semiconductor polymer and SiOx as the topmost active sensing layer permit monitoring of pH in physiologically relevant conditions in a fast and reversible fashion. Beyond that, due to the bottom gate‐induced field effect, such sensors exhibit tunable sensitivity and provide faster continuous measurements compared to conventional bulky glass bulb pH sensors. pH response of bare SiOx is evaluated independently by means of voltmeter measurements. When assembled in dual‐gate architecture, the pH response of FET devices scales in agreement with the theoretical model, which assumes capacitive coupling, exhibiting an amplification of up to 10. This opens up the possibility for reversible and reliable sensing based on organic semiconductors well beyond pH sensors.R.P. and A.M.F. contributed equally to this work. R.P. acknowledges support from the Marie Curie Cofund, Beatriu de Pinós Fellowship (AGAUR 2014 BP‐A 00094). A.M.F. acknowledges a postdoctoral fellowship support from the Natural Sciences and Engineering Research Council (NSERC) of Canada. This project was supported by the Stanford Catalyst for Collaborative Solutions Program and the Beijing Institute of Collaborative Innovation (BICI).Peer reviewe

Photo-induced intramolecular charge transfer in an ambipolar field-effect transistor based on a pi-conjugated donor-acceptor dyad

A pi-conjugated tetrathiafulvalene-fused perylenediimide (TTF-PDI) molecular dyad is successfully used as a solution-processed active material for light sensitive ambipolar field-effect transistors with balanced hole and electron mobilities. The photo-response of the TTF-PDI dyad resembles its absorption profile. Wavelength-dependent photoconductivity measurements reveal an important photo-response at an energy corresponding to a PDI-localized electronic pi-pi* transition and also a more moderate effect due to an intramolecular charge transfer from the HOMO localized on the TTF unit to the LUMO localized on the PDI moiety. This work clearly elucidates the interplay between intra- and intermolecular electronic processes in organic devices

Tetramethylbenzidine-TetrafluoroTCNQ (TMB-TCNQF4): 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-tetrafluorotetracyanoquinodimethane (TMB-TCNQF4), associated with new electric and dielectric measurements. Refinement of synchrotron structural data at low temperature has led to revise the previously reported C2/m structure. The revised structure is P21/m, with two dimerized stacks per unit cell, and is consistent with the low-temperature 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 P21/m-no phase transitions-but did not allow substantiating the presence of disorder. On the other hand, dielectric measurements have evidenced a typical relaxor ferroelectric behavior already at room temperature, with a peak in the real part of dielectric constant ϵ′(T,ν) 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 (Ea ∼0.3 eV) with a room-temperature conductivity of ∼10-4 ω-1 cm-1