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Inkjet printing is a promising technology providing cost-effective method for processing various materials on deformable substrates. In this work, linear and serpentine inkjet printed interconnects on two different substrates were fabricated and electromechanically characterized. A particular attention was given to the optimization of the process parameters; high quality can be achieved only printing slowly in vertical direction and optimizing the drop spacing to the specific pattern. The electromechanical results showed that the geometrical layout and printing direction strongly affect the printing quality and the electromechanical response; serpentine shapes should be preferred to straight interconnects as better gauge factors are obtained.

The development of portable and wearable sensors is of high importance in several fields such as point-of-care medical applications and environmental monitoring. Here we design, synthesize and exploit a new composite material based on Ag/AgCl nanoparticles and PEDOT:PSS (poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate)) to fabricate a novel kind of sensor inspired by the organic electrochemical transistor (OECT). We are able to integrate an Ag/AgCl gate electrode into the semiconducting polymer in the form of NPs. As a consequence, our sensor combines an intrinsically amplified response with a simple two terminal electrical connection. Electrostatic Force Microscopy and Electrochemical Impedance Spectroscopy demonstrate the electronic coupling between the electrochemically active nanoparticles and the ionic charge gated semiconducting polymer, allowing to explain the sensor amplified transduction. The analytical signal is the current that flows in the composite polymer and its variation is directly proportional to the logarithm of Cl− concentration in the range 10−4 to 1 M, with a limit of detection of 0.5 10−4 M. Moreover, the device exhibits a shorter response time than the one of a conventional OECT endowed with an Ag/AgCl gate electrode. The sensor was used for in-situ detection of salinity in water and a textile device was obtained by depositing the composite material directly onto a cotton yarn for real-time sweat monitoring.

An efficient nanoscale semiconducting optoelectronic system is reported, which is optimized for neuronal stimulation: the organic electrolytic photocapacitor. The devices comprise a thin (80 nm) trilayer of metal and p-n semiconducting organic nanocrystals. When illuminated in physiological solution, these metal-semiconductor devices charge up, transducing light pulses into localized displacement currents that are strong enough to electrically stimulate neurons with safe light intensities. The devices are freestanding, requiring no wiring or external bias, and are stable in physiological conditions. The semiconductor layers are made using ubiquitous and nontoxic commercial pigments via simple and scalable deposition techniques. It is described how, in physiological media, photovoltage and charging behavior depend on device geometry. To test cell viability and capability of neural stimulation, photostimulation of primary neurons cultured for three weeks on photocapacitor films is shown. Finally, the efficacy of the device is demonstrated by achieving direct optoelectronic stimulation of light-insensitive retinas, proving the potential of this device platform for retinal implant technologies and for stimulation of electrogenic tissues in general. These results substantiate the conclusion that these devices are the first non-Si optoelectronic platform capable of sufficiently large photovoltages and displacement currents to enable true capacitive stimulation of excitable cells.

Organic semiconducting single crystals (OSSCs) are very promising for low cost electronics, being the highest performers among organic semiconductors in terms of charge transport, with carrier mobilities exceeding 10 cm2 V s−1. Here, it is demonstrated how it is possible to obtain millimeter-long single crystals of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) onto gold interdigitated electrodes patterned onto flexible plastic substrates, via direct inkjet printing of precursor solutions. This result is enabled by a novel chemical confinement strategy that exploits fluorinated thiols as solvophobic “chemical fences”, able to avoid the printed solution spreading, thus promoting the formation of single crystals even on highly heterogeneous surfaces, without changing the chemical nature of the surface underlying the grown crystals. Electrical measurements demonstrate a good electrical contact with the electrodes. Moreover, their response UV-vis (Ultraviolet-visible) is among the highest up to now reported for organic UV–vis photodetectors, and their performance as direct X-ray detectors is satisfactory, confirming that the printed crystals have an effective electrical contact with the underlying electrodes. Since both the solvophobic fence and the TIPS crystals precursor solution are inkjet printed on flexible substrates, this work opens novel perspectives for the practical use of OSSCs in low cost, yet performing, flexible electronics.

The application of organic electronic materials for the detection of ionizing radiations is very appealing thanks to their mechanical flexibility, low-cost and simple processing in comparison to their inorganic counterpart. In this work we investigate the direct X-ray photoconversion process in organic thin film photoconductors. The devices are realized by drop casting solution-processed bis-(triisopropylsilylethynyl)pentacene (TIPS-pentacene) onto flexible plastic substrates patterned with metal electrodes; they exhibit a strong sensitivity to X-rays despite the low X-ray photon absorption typical of low-Z organic materials. We propose a model, based on the accumulation of photogenerated charges and photoconductive gain, able to describe the magnitude as well as the dynamics of the X-ray-induced photocurrent. This finding allows us to fabricate and test a flexible 2 × 2 pixelated X-ray detector operating at 0.2 V, with gain and sensitivity up to 4.7 × 104 and 77,000 nC mGy−1 cm−3, respectively., Organic electronics show advantages in easy processing, mechanical flexibility and low costs compared to their inorganic counterparts, yet there are not many proofs for the sake of X-ray detection. Here, Basiricò et al. build a flexible X-ray detector operated at sub-1 V using pentacene-based thin films.

The development of new materials and devices for flexible electronics depends crucially on the understanding of how strain affects electronic material properties at the nano-scale. Scanning Kelvin-Probe Microscopy (SKPM) is a unique technique for nanoelectronic investigations as it combines non-invasive measurement of surface topography and surface electrical potential. Here we show that SKPM in non-contact mode is feasible on deformed flexible samples and allows to identify strain induced electronic defects. As an example we apply the technique to investigate the strain response of organic thin film transistors containing TIPS-pentacene patterned on polymer foils. Controlled surface strain is induced in the semiconducting layer by bending the transistor substrate. The amount of local strain is quantified by a mathematical model describing the bending mechanics. We find that the step-wise reduction of device performance at critical bending radii is caused by the formation of nano-cracks in the microcrystal morphology of the TIPS-pentacene film. The cracks are easily identified due to the abrupt variation in SKPM surface potential caused by a local increase in resistance. Importantly, the strong surface adhesion of microcrystals to the elastic dielectric allows to maintain a conductive path also after fracture thus providing the opportunity to attenuate strain effects.

Large-area electronics for applications in environments with radioactive contamination or medical X-ray detectors require materials and devices resistant to continuous ionizing radiation exposure. Here the superior X-ray radiation hardness of oxide thin fi lm transistors (TFTs) based on galliumindium-zinc oxide is demonstrated, when compared to organic ones. In the experiments both TFTs are subjected to X-ray radiation and their performances are monitored as a function of total ionizing dose. Flexible oxide TFTs maintain a constant mobility of 10 cm 2 V −1 s −1 even after exposure to doses of 410 krad(SiO 2 ), whereas organic TFTs lose 55% of their transport performance. The exceptional resistance of oxide semiconductors ionization damage is attributed to their intrinsic properties such as independence of transport on long-range order and large heat of formation.

A robust and efficient interconnection layer (ICL) based on low conductive poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) and ZnO nanoparticles is implemented in a solution-air-processed, blade coated inverted polymer tandem solar cell. The commercial PEDOT:PSS (Heraeus Clevios P VP Al 4083) is modified with a fluorosurfactant to allow its deposi- tion onto any hydrophobic active layer surface. However, this method alters the electrical and energetic properties of the PEDOT:PSS thus affecting the interface with the ZnO layer, responsible for an inefficient ICL and poorly performing tandem devices. The ohmic contact at the PEDOT:PSS/ZnO interface is successfully optimized through a simple solvent treatment of the PEDOT:PSS film surface, leading to tandem devices with power conversion efficiencies (PCEs) improved by more than 50% compared to the untreated reference system. The reported method is an easy and versatile approach to optimize the functionality of the PEDOT:PSS/ZnO ICL of inverted multijunc- tion devices, applicable onto any organic active layer and compatible with a roll-to-roll production line.

Electrolyte-gated organic field-effect transistors (EGOFETs), based on ultrathin pentacene films on quartz, were operated with electrolyte solutions whose pH was systematically changed. Transistor parameters exhibit nonmonotonic variation versus pH, which cannot be accounted for by capacitive coupling through the Debye–Helmholtz layer. The data were fitted with an analytical model of the accumulated charge in the EGOFET, where Langmuir adsorption was introduced to describe the pH-dependent charge buildup at the quartz surface. The model provides an excellent fit to the threshold voltage and transfer characteristics as a function of the pH, which demonstrates that quartz acts as a second gate controlled by pH and is mostly effective from neutral to alkaline pH. The effective capacitance of the device is always greater than the capacitance of the electrolyte, thus highlighting the role of the substrate as an important active element for amplification of the transistor response.

Made available in DSpace on 2018-12-11T17:30:44Z (GMT). No. of bitstreams: 0 Previous issue date: 2016-06-01 Water-gated organic transistors have been successfully exploited as potentiometric transducers in a variety of sensing applications. The device response does not depend exclusively on the intrinsic properties of the active materials, as the substrate and the device interfaces play a central role. It is therefore important to fine-tune the choice of materials and layout in order to optimize the final device performance. Here, polyethylene naphthalate (PEN) has been chosen as the reference substrate to fabricate and test flexible transistors as bioelectronic transducers in liquid. PEN is a biocompatible substrate that fulfills the requirements for both bio-applications and micro-fabrication technology. Three different semiconducting or conducting polymer thin films employing pentacene, poly(3-hexylthiophene) or poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) were compared in terms of transconductance, potentiometric sensitivity and response time. The different results allow us to identify material properties crucial for the optimization of organic transistor-based transducers operating in water. Dipartimento di Scienze della Vita Università di Modena and Reggio Emilia (UNIMORE), Via Campi 103 Programa de Pós-graduação em Ciência e Tecnologia de Materiais (POSMAT) Universidade Estadual Paulista (UNESP) Istituto per Lo Studio Dei Materiali Nanostrutturati (ISMN) Consiglio Nazionale Delle Ricerche (CNR), Via Gobetti n.101 Departamento de Física Química e Matemática (DFQM) Universidade Federal de São Carlos (UFSCar) ST Microelectronics Analog and MEMS Group (AMG), Str. Primosole 50 ST Microelectronics Analog and MEMS Group (AMG), Via Remo de Feo 1 Faculdade de Ciências e Tecnologia (FCT) Universidade Estadual Paulista (UNESP) Laboratório Nacional de Nanotecnologia (LNNano) Centro Nacional de Pesquisa em Energia e Materiais (CNPEM) Institut de Ciéncia de Materials de Barcelona (ICMAB) Consejo Superior de Investigaciones Cientifica (CSIC) University of Cambridge Electrical Engineering Division, 9 JJ Thomson Avenue Programa de Pós-graduação em Ciência e Tecnologia de Materiais (POSMAT) Universidade Estadual Paulista (UNESP) Faculdade de Ciências e Tecnologia (FCT) Universidade Estadual Paulista (UNESP)

The nanomechanical properties of ultrathin and nanostructured films of rigid electronic materials on soft substrates are of crucial relevance to realize materials and devices for stretchable electronics. Of particular interest are bending deformations in buckled nanometer-thick films or patterned networks of rigid materials as they can be exploited to compensate for the missing tensile elasticity. Here, we perform atomic force microscopy indentation experiments and electrical measurements to characterize the nanomechanics of ultrathin gold films on a polydimethylsiloxane (PDMS) elastomer. The measured force-indentation data can be analyzed in terms of a simple analytical model describing a bending plate on a semi-infinite soft substrate. The resulting method enables us to quantify the local Young’s modulus of elasticity of the nanometer-thick film. Systematic variation of the gold layer thickness reveals the presence of a diffuse interface between the metal film and the elastomer substrate that does not contribute to the bending stiffness. The effect is associated with gold clusters that penetrate the silicone and are not directly connected to the ultrathin film. Only above a critical layer thickness, percolation of the metallic thin film happens, causing a linear increase in bending stiffness and electrical conductivity.