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Roll-to-roll gravure printing is considered as potential leading manufacturing technology for flexible, low cost and large area optoelectronics. However, solution processed multilayer organic electronics are still challenging to be produced, especially in the case of electrodes. In this work, the gravure printing technique was successfully employed to realize the highly conductive poly(3,4ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) polymeric anode and tested for the first time in flexible ITO-free (Indium Thin Oxide) organic light emitting diodes (OLEDs). The device performances were found to be similar to those of a reference device containing a spin-coated polymeric anode. A gravure printed dimethyl sulfoxide (DMSO) post-treatment was successfully tried to improve the printed anode characteristics. The obtained results show the way for future development for processing flexible ITO-free devices using the most attractive printing technology for roll-to-roll large area manufacturing. © BME-PT.

This work shows a method to fabricate interdigital capacitors having tunable sensitivity to temperature and stable behavior pointing to the application of ionic liquids (ILs) as fundamental building blocks in capacitive devices for temperature sensing in proximity conditions. Polyvinylidene fluoride (PVDF) in blend with 1-Butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) has been deposited by drop-casting from a N,N-dimethylformamide solution to be utilized as dielectric material in screen-printed interdigitated capacitors. Capacitance and conductance trends versus temperature have been analyzed and compared to bare PVDF dielectrics. The inclusion of [BMIM][PF6] in PVDF-IL blends increases the AC capacitance of the device and its sensitivity to the temperature in the examined range (+20 °C to +110 °C). AC measurements performed at 100 kHz have shown good electrical stability for PVDF-IL blends also when measured in ambient atmosphere. As a drawback, an increase in [BMIM][PF6] concentration resulted also in an increase in AC conductance which exhibits an Arrhenius activation with temperature. Such behavior has been attributed to the increase in ion concentration and ionic mobility with temperature. The work also shows the presence of a limit value for the activation energy of AC conductance for higher concentrations of the ionic liquid.

In this work, the introduction of small variations in the electrical impedance ofHF (High Frequency) RFID (Radio Frequency Identification) tags has been exploited in the proximity sensing of temperature by applying Polyvinylidene Fluoride (PVDF) interdigital capacitive sensors as a modification of the transponder’s circuitry. The adopted electrical parasitic sensing load introduces a shift in the primary resonance peakof the tag. Theimpedance spectra have been acquired by a dedicated laboratory setup allowing to apply simultaneously thermal forcing and RF signals to the transponder itself. Thesensitivity of the modified taghas been assessed after taking into account the thermal response of the transponder chipwhich is relevant in the formulation of thermal-sensing transponders.

In this work, Vapor Annealing Sintering (VAS) process was introduced for low-cost pressureless producing dense Zinc Oxide (ZnO) thin films deposited from nanoparticles at near-room temperature (50 °C). Spontaneous densification evolution from nanoparticulate to a dense film via a dissolution-diffusion-reprecipitation mechanism was observed exposing ZnO layers to the vapor of an acetic acid aqueous solution at isothermal condition. The influence of the annealing on the optical properties of the treated films was investigated in order to study the structural changes. The proposed method can allow new opportunities for simple and low-cost ceramics thin film manufacturing also involving pressure and temperature-sensitive materials.

Carbon nanotubes-grafted-carbon fibers have been tested to improve composite performances; in particular in aerospace this substrate was tested as conductive light material in substitution of metallic foils. In this work, hierarchical growth of carbon nanotubes (CNTs) has been achieved on recovered carbon fiber (rCF). The process has been performed by thermal catalytic chemical vapour deposition (CCVD) starting from liquid precursor (such as ethanol); different combinations of process parameters were tested and the growth was verified by Scanning Electron Microscopy (SEM) and Raman Spectroscopy. The electrical characterization of the samples shows an increase of conductivity in presence of CNTs. © 2018 Author(s).

Poly(L-lactide) (PLLA) is a semicrystalline, biocompatible and biodegradable polymer widely employed in many applications (food packaging, biomedical devices, drug delivery systems). This work deals with nanocomposites of PLLA and tungsten disulfide (WS2) nanotubes (NTs) as a novel material to obtain thinner and stronger bioresorbable vascular scaffolds. We studied the influence of WS2 NTs on the mechanical properties of PLLA-WS2 films. Polarized optical microscopy reveals a high degree of orientation of the polymer molecules in stretched films that further increases with a post-stretching annealing treatment. At the same time, X-ray diffraction (XRD) and Raman spectroscopy confirm enhancement of the crystallinity induced by the WS2 NTs. © 2018 Author(s).

In this work, n-type organic thin film transistors (OTFTs) were fabricated in the bottom-gate bottom-contact configuration, depositing a fullerene-derived semiconductor (PC70BM) by drop-casting technique on SiO2 substrates treated with a self-assembled monolayer, namely the HMDS. The influence of the deposition temperature of the HMDS on the device performance was investigated, using three different temperatures. The relationship between the properties of the resulting semiconductor films and the electrical characteristics of the transistors was evaluated through admittance measurements. The frequency response of the devices vs. the bias was interpreted applying an electrical equivalent circuit to model the properties of the semiconductor and of the transistor conductive channel. The proposed model shows the critical role played by the quality of the insulator-semiconductor interface on the traps density in the semiconductor, and therefore on the increase of the mobility and on the reduction of the threshold voltage of the transistors. © 2017 Elsevier Ltd.

POC polymer is an oxadiazole-carbazole copolymer we have previously synthetized and established as light emitting material in Organic Light Emitting Devices (OLEDs), although POC quantum yield emission efficiency and color purity still need to be enhanced. On the other hand, tris[2-phenylpyridinato-C2,N]iridium(III) (Ir(ppy)3) complexes, namely Ir(ppy)3 are among the brightest luminophores employed in green light emitting devices. Our aim, in this work, is to take advantage of Ir(ppy)3 bright emission by combining the Ir complex with blue emitting POC to obtain tunable light emitting composites over a wide range of the visible spectrum. Here we have investigated the optical proprieties POC based nanocomposites with different concentrations of Ir(ppy)3, ranging from 1 to 10 wt%. Both spectral and time resolved fluorescence measurements show an efficient energy transfer from the polymer to the dopants, resulting in white-emitting composites. The most intense and stable emission has been found when POC was doped with about 5 wt% concentration of Ir(ppy)3. © 2016 Elsevier B.V.

The variations in physical parameters of an organic field-effect transistor having dioctylbenzothieno[2,3-b]benzothiophene (C8BTBT) as the channel semiconductor were investigated under different light irradiation conditions at wavelengths of 350 nm, 370 nm, 400 nm and by increasing exposure doses. The progress of the electro-optical history of the transistor was evaluated by repeating I–V scan cycles both in the dark and under light exposure. The information recorded upon different exposure times was used to detect the photoactivated charge-trapping effects. The device showed a stable I–V response in the dark bias ( V DS = −10 V, −10 V ≤ V GS ≤ +10 V) conditions and a persistent threshold voltage ( V T ) shift under illumination at all irradiation wavelengths. We suggested that the observed dose-dependent V T drifts were due to charge retention in trap sites within the organic semiconductor. The threshold voltage was recognized as the main parameter affected by charge retention. V T variations were modelled versus time through a single exponential revealing a maximum in charge relaxation times for irradiations at wavelengths of 370 nm, in proximity of the C8BTBT bandgap energy. Furthermore, bias-stress effects and persistent photoinduced V T drifts were found to depend on comparable characteristic times. Therefore, a common nature for both the bias-stress decay and relaxation from photoexcitation mechanisms is likely.

To date, highly conductive PEDOT:PSS is the most promising transparent electrode for printing-based flexible organic electronics. Spin-coating and slot-die coating have been commonly used for printing this material. Among the roll-to-roll printing processes, gravure is the most promising for manufacturing large area electronics offering the advantages of high speed and high printing definition. However, gravure printing highly conductive PEDOT encounters some technological limitations such as low thickness, layer inhomogeneity and high surface roughness resulting in a layer not suitable as electrode in electronic devices. In order to realize an electrode of highly conductive PEDOT by gravure printing, a multilayer approach with variable ink concentration was tried using IPA as process solvent. Variable solvent amount of overlapped printed layers was found to play an important role in the spreading of the PEDOT ink onto the pre-printed layers and in the smoothing of its existent peaks. In particular, adopting increasing ink dilution with increasing of the overlapped layers, multi-layer gravure-printed highly conductive PEDOT was successfully realized with characteristics suitable as transparent electrode for organic electronic devices (sheet resistance lower than 130 Ω/sq, conductivity higher than 450 S/cm and optical transmittance over 80%). This is the first time that such results were reached by gravure printing technique thanks to the easy proposed approach. © 2015 Elsevier B.V.

The performances and the stability of a polymer solar cell (PSC) mainly depend on the architecture of the device and the materials used for the fabrication (photoactive and interface layers and contacts). In this work we made a comparative study between standard and inverted PSCs having an identical pair of hole and electron transport layers: molybdenum trioxide (MoO3) and poly[(9,9-bis(3'-(N,Ndimethylamino) propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN), respectively. We realized devices using a blend film of poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b;4,5-b']dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiopene)-2,6-diyl]/[6,6]-phenyl C71 butyric acid methyl ester (PBDTTT-C:[70]PCBM). The standard and inverted cells sequences were ITO/MoO3/PBDTTT-C:[70]PCBM/PFN/Ag and ITO/PFN/PBDTTT-C:[70]PCBM/MoO3/Ag, respectively. We studied the performances of both kinds of devices in order to investigate the influence of the architecture (standard vs inverted) on the performance of the solar cells. All the devices were characterized by IV light, IV dark and quantum efficiency measurements. The best device reached a power conversion efficiency of 6%. The inverted device has an improved current output compared to the standard one. In order to elucidate the absorption of photons inside the blend, we performed the optical modeling of the devices using the transfer matrix formalism and we simulated the effective absorption in the photoactive layer and the optical electric field inside the devices.

Transparent metal oxides became an important class of low-temperature solution-processed electron transport layers (ETLs) for inverted polymer solar cells (PSCs) due to their high optical transparency in the visible range, relatively good electrical conductivity and tunable work function. In this work we made a comparative study between the electrical performances of devices realized with various metal oxides as ETLs: ZnO, ZnO:Al and TiOx. These oxides were prepared by low-temperature solution process techniques and used in PSCs with the configuration glass/Indium tin oxide (ITO)/ETL/photoactive layer/MoO3/Ag. The photoactive layer was a blend of poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b;4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)] and [6,6]-phenyl C71 butyric acid methyl ester. The best power conversion efficiency (9.1%) under simulated AM1.5G illumination of 100 mW/cm2, was achieved for the PSC fabricated using a ZnO:Al interlayer. In order to elucidate the electrical processes at the interfaces between the ETL and the blend, impedance spectroscopy analysis was carried out. The ZnO:Al PSC shows better charge transfer properties between the active layer and the ITO and longer charge carrier lifetime. These factors contribute to improve the fill factor and increase the current output leading to an higher power conversion efficiency.

We demonstrated the suitability of polymer composites filled with silicon carbide (SiC) powders derived from a recycling process for applications in electronic devices manufacturing. SiC powders have been synthesized from the process byproducts and used as fillers in the formulation of polystyrene (PS)/SiC composites, which have been used in the preparation of substrates using the solution-casting technique. Different substrates have been prepared by changing the concentration of SiC in the composite in the range from 6.7 to 67 wt % and used in simple electronic devices by performing gold contacts in both planar and stacked configurations. The electrical behaviors of both stacked and planar devices were investigated in direct current (DC) and alternate current (AC) regimes. The experimental results showed that charge percolation could be considered an explanation for the abrupt change in the differential conductivity observed around 30 wt %. Fowler-Nordheim tunneling at high fields has been found to be compatible with static characteristics and with high-frequency AC measurements and, therefore, charge tunneling between SiC islands has been proposed as the physical mechanism provoking the changes in charge transport in the substrates investigated. From this first experimental analysis, it appears that SiC/PS composites could suit their use in tunneling-gate dielectrics (i.e., in transistors suitable for their applications in nonvolatile random-access memory) for low concentrations or as a continuous semiconducting media when SiC is dispersed in high-concentration composites. © 2016 American Chemical Society.

Thick-film alternating current powder-based electroluminescent (ACPEL) succeeds on the market as mature technology for large-area light sources. An additional boost for its development may come from the radiation curing technology. Since it is totally compatible with high-speed roll-to-roll processing, radiation curing can offer multiple advantages to further lower costs and make easier the fabrication process of ACPEL devices. In this paper, the application of the electron beam (EB) curing technology to produce flexible ACPEL devices was explored for the first time. In particular, devices with emitting layer made by EB irradiation were successfully fabricated on poly(ethylene terephthalate) (PET) substrate. Device properties were evaluated and compared with those obtained using the conventional ultraviolet curing process. Smaller driving voltages and higher luminous output were observed for the EB treated samples as a consequence of a more cross-linked polymeric binder of the emitting layer generated. In addition, possible effects of EB overdose were also investigated; experiments revealed that excessively high doses can induce the degradation of both polymeric binder and emitting particles. Therefore, the feasibility of using the EB curing was proven to fabricate ACPEL devices, launching it as the next future technology for more sustainable, very fast, and one-step manufacturing of powder-based alternating current EL devices. © 2016 IEEE.

A novel, easy, and cost-effective synthetic procedure is reported for the production of very highly regioregular poly[3-(4-alkoxyphenyl)thiophene]s by means of oxidative coupling. Four copper complexes were synthesized and used as catalysts to obtain polymers with higher regioregularity compared to the previous oxidative coupling methodologies reported in the literature and similar to that obtained by McCullough and Rieke methods in the synthesis of poly-3-alkylthiophenes. The regioregularity of the synthesized polymers was investigated by UV–Visible characterization on polymer thin films and 1H NMR analysis. The remarkable potentialities of these polymers have emerged from field-effect transistor mobility measurements operated on devices with bottom-contact configuration and hexamethyldisilazane-treated SiO2 gate dielectric, showing a well-defined p-type field-effect response and maximum mobility values in air higher than 10−4 cm2 V−1 s−1. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4351–4360

The oxidative polymerization of 5,6-dihydroxyindoles and related hydroxyindoles at pH

The pyro-electrohydrodynamic (EHD) manipulation of liquids has been discovered and demonstrated recently as a high resolution printing technique avoiding the use of nozzles and external electrodes. The activation of the pyro-electric effect is usually achieved on ferroelectric crystals by an external heating source or by an infrared laser. Here, we show an original modality for triggering the pyro-EHD process through a light-absorbing polymer nanocomposite thin layer deposited on the ferroelectric substrate, thus overcoming some limitations of the previous configuration. Significant simplification and compactness of the set-up is achieved thanks to the nanocomposite coating, since a commercial low-cost white-light halogen lamp can be adopted to trigger the pyro-jetting process from a liquid reservoir. Remarkably, high resolution is achieved in dispensing very high viscous liquids. Practical demonstrations in polymer optical microlenses direct printing using polydimethylsiloxane and poly(methyl methacrylate) are finally reported to validate the approach in handling high-viscous polymers for practical applications. © 2015 AIP Publishing LLC.

In this work, highly conductive and transparent films based on poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) doped with dimethyl sulfoxide (DMSO) were printed onto a flexible substrate, the polyethylene naphthalate (PEN), using the gravure printing method. Gravure-printed DMSO-PEDOT:PSS ink suitably modified with isopropanol was developed and used as anode in flexible solar cells replacing the commonly used anode, that is, Indium Tin Oxide (ITO). Several inks were prepared and characterized in terms of viscosity and surface energy and tested by gravure printing. The wettability of the PEN substrate was investigated through contact angle measurements. For comparison, the anodic conductive polymer was also spin coated on the PEN substrate using an ink suitable for this technique. The films produced with both the techniques, gravure printing and spin coating, each using a proper ink, were characterized in terms of structure and physical–chemical properties. The printed layers were employed as anodes into ITO free-polymer solar cells based on a bulk heterojunction of Poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno [3,4-b]thiophenediyl}) (PTB7) and [6,6]-phenyl C70-butyric acid methyl ester ([70]PCBM). The performances of the devices with printed and spin coated polymeric anode were compared. The cell with the spin-coated anode reached a power conversion efficiency of 3% while the corresponding device with the printed anode a value around 2%. POLYM. COMPOS., 36:1104–1109, 2015. © 2015 Society of Plastics Engineers

In this work, we report the application of a sol–gel derived ZnO thin film as a buffer layer for high efficiency inverted polymer solar cells. ZnO films are widely used in such devices because they have a relatively high electron mobility, high transparency and environmental stability. The ZnO precursor was prepared by dissolving zinc acetate and ethanolamine in the 2-methoxyethanol. ZnO thin films were then deposited on indium tin oxide (ITO)/glass substrates by spin coating the above solution. Inverted polymer solar cells with the configuration ITO/ZnO/photoactive layer/MoOx/Ag were realized in order to investigate the performance of ZnO thin film. The photoactive layer is a blend of poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b;4,5-b′]dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiophene)-2,6-diyl] (PBDTTT-C) and [6,6]-phenyl C71 butyric acid methyl ester ([70]PCBM) (1:1.5 w/w). We made a comparative study of the photovoltaic behavior of devices with ZnO films deposited using different sol–gel recipes. In particular, we varied the zinc acetate/ethanolamine molar ratio to have ZnO films with different trace amounts of starting materials. In addition we also prepared ZnO films annealed at 200 °C for different times (from 5′ to 60′) in order to evaluate this effect on the trace amount removal. © 2014, Springer Science+Business Media New York.

In this work we studied the influence of the annealing treatments of a sol-gel derived ZnO electron transport layer deposited on ITO substrate, on the performances of inverted bulk heterojunction polymer solar cells using a blend of poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b;4,5-b′]dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiopene)-2,6-diyl] and [6,6]-phenyl C71 butyric acid methyl ester. Since the annealing treatments needed to complete the formation of the solution-processed ZnO film can modify the underlying ITO electrode, we analyzed the performance of the fabricated cells in terms of the properties of ITO and ZnO films. We found a linear relationship between the sheet resistance of the ITO layer and the series resistance of the corresponding device, which strongly influences the fill factor. The best power conversion efficiency (7%) under simulated AM 1.5G illumination of 100 mW/cm2 was achieved for the polymer solar cell fabricated using a ZnO film annealed at 150 °C for only 5 min. Higher annealing temperatures and times increase the sheet resistance of the ITO worsening the device performances. © 2015 Elsevier B.V. All ights reserved.

Organic light emitting diodes (OLEDs) are nowadays the most attractive technology for displays and lighting applications. However, their short lifetime remains the most important limit for their broad commercialization. In particular, blue OLEDs generally present the worst stability respect to the other colors. While the extrinsic degradation can be easily controlled by proper encapsulation, understanding the origins of the intrinsic degradation remains a challenge: up to now, the proposed mechanisms have not considered possible phenomena that can occur during OFF-time periods. In this study, intrinsic degradation phenomena have been studied through shelf life experiments performed at different storage conditions on two types of blue OLEDs. Experiments revealed that physical aging occurs for both types of devices, leading to irreversible time-dependent luminance loss.

In this work we made a comparative study between the electrical performances of three different electron transport layers (ETLs), used to build inverted polymer solar cells (PSCs). Two different metal oxides are prepared with a solution process: the first one is zinc oxide, prepared by a solgel procedure dissolving zinc acetate and ethanolamine in the 2-methoxyethanol, the second one is titanium oxide, prepared by spin coating a solution of commercial Titanium(IV)-isoproxide in 2-methoxyethanol. The last ETL is an alcohol soluble conjugated polymer: poly[(9,9-bis(3′-(N, N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)](PFN). Inverted PSCs with the configuration glass/ITO/ETL/photoactive layer/MoO3/Ag were realized in order to investigate the performance of different ETL thin films. The photoactive layer was a blend of poly[(4,8-bis-(2-ethylhexyloxy)-benzo[1,2-b;4,5-b′] dithiophene)-2,6-diyl-alt-(4-(2-ethylhexanoyl)-thieno[3,4-b]thiopene)-2,6-diyl] and [6,6]-phenyl C71 butyric acid methyl ester. The best power conversion efficiency (6.4%) under simulated AM1.5G illumination of 100 mW/cm2, was achieved for the PSCs fabricated using a ZnO and PFN films.

In this paper we present the synthesis and characterization of two novel copolymers obtained from a bithiophene unit carrying octylsulfanyl side chains and thienothiophene units substituted with keto (PK) or ester (PE) groups. Their structural, electrochemical and photophysical properties were investigated by gel permeation chromatography (GPC), thermogravimetric analysis (TGA), NMR, UV-visible-NIR spectroscopy, cyclic voltammetry (CV) and atomic force microscopy (AFM). They possess good solubility in common organic solvents, filmability, proneness to form π-stacks, moderate solvatochromism, good thermal stability and low band gap energy. They were tested as donor materials in combination with [70]PCBM (electron acceptor) in bulk-heterojunction polymer solar cells. The geometry of the devices is: glass/ITO/PEDOT:PSS/copolymer:[70]PCBM/Ca/Al. The external quantum efficiency curve of the best device, realized using a blend of PK : [70]PCBM, 1 : 2 weight ratio, shows a broad response from 350 to 1000 nm. The power conversion efficiency under 100 mW cm-2 AM 1.5G illumination is greater than 1%. © 2014 The Royal Society of Chemistry.

In this paper we realized different PQCs polymeric anodes PEDOT:PSS based (octagonal, dodecagonal and Thue-Morse patterns) using a high-resolution electron beam lithography (EBL) technique. We characterized and selected photonic quasi crystal structures that could enhance the efficiency of a polymeric based White Organic Light Emitting Diode (WOLED) device onto the nanostructured highly conductive PEDOT:PSS polymer electrode. © 2014 AEIT.

Hybrid heterojunctions of conjugated polymers and inorganic nanomaterials are a promising combination for obtaining high performance solar cells (SC). In this work we have explored new possible uses of the WS2 nanotubes (NTs) both as the only acceptor material blended with a polymer and in ternary systems mixed with a polymer and quantum dots (QDs). In particular we have spectroscopically investigated binary blends of poly(3-hexylthiophene) (P3HT) and WS2 NTs, P3HT and CdSe QDs, and ternary blends of P3HT, CdSe QDs and WS2 NTs. We report fluorescence quenching effects of the QD signal in the P3HT-CdSe-WS2 system with the increase of NT concentration. Static and time-resolved fluorescence studies reveal efficient resonant energy transfer from the QDs to the NTs upon photoexcitation. The evidence of energetic interaction between WS2 NTs and QDs opens new fields of application of WS2 NTs and holds very promising potential for improving charge transfer phenomena in the active layer of hybrid solar cells. This journal is © the Partner Organisations 2014.

In this work, highly conductive anode based on PEDOT:PSS is proposed as substitute of Indio-Tin Oxide (ITO) in flexible solar cells. The anodic conductive polymer was spin coated on a 125 μm thick polyethylene naphthalate (PEN) substrate. The obtained film was characterized in terms of structure and physical- chemical proprieties. The obtained results are very promising and the conductive film will be investigated in future as electrode in a complete polymeric solar cell. © 2014 AIP Publishing LLC.

Silicon carbide powders have been synthesized from tires utilizing a patented recycling process. Dynamic light scattering, Raman spectroscopy, SEM microscopy, and X-ray diffraction have been carried out to gather knowledge about powders and the final composite structure. The obtained powder has been proven to induce resistive switching in a PMMA polymer-based composite device. Memory effect has been detected in two-terminal devices having coplanar contacts and quantified by read-write-erase measurements in terms of level separation and persistence.

In this work we present a direct printing of microlenses using high viscous polymer materials. In particular the pyro-electric effect activated onto a Lithium Niobate crystal is exploited for the fabrication on demand of microlens array. © 2014 AEIT.

Two red emitters InP/ZnS quantum dots (QDs) (absorption 570 nm/emission 605 nm and absorption 597/emission 624) were inserted at different concentrations in the blue emitting polymer poly(9,9'- dioctylfluorene) (PFO). Nanocomposites were obtained by mixing the QDs as purchased and the polymer dissolved in the appropriate solvent and deposited by spin coating to give homogeneous films. The morphological properties were characterized by scanning electron microscopy (SEM), that showed a good level of dispersion of the QDs within the polymer. The study of the optical and electrooptical properties of the nanocomposites layer inserted in OLED devices (glass/ITO/PEDOT:PSS/PFO-QD/Ca/Al) is reported and compared to pure polymer based device. Photoluminescence and electroluminescence spectra show an energy transfer from the polymer to QDs in presence of the nanocomposites containing InP/ZnS quantum dots that absorb at 570 nm. © 2013 American Scientific Publishers.

In this article, the electrical and optical properties of organic light emitting diodes (OLEDs) are analyzed, deriving the devices limits at high applied electric fields and at different temperatures. The temperature failures zones have been evaluated, studying the temperature-dependent electrical properties of the OLEDs by means of barrier parameter evaluation, and observing the charge carrier injection at metal/organic interfaces. In particular, for different device thicknesses, it is possible to detect both the surface glass transition point and the complete bulk glass transition of the amorphous organic material employed eventually correlating such mechanisms to device limitations at high applied field. POLYM. COMPOS., 34:1477–1482, 2013. © 2013 Society of Plastics Engineers

In this work, we studied energetic and optical proprieties of a polyester-containing oxadiazole and carbazole units that we will indicate as POC. This polymer is characterized by high photoluminescence activity in the blue region of the visible spectrum, making it suitable for the development of efficient white-emitting organic light emission devices. Moreover, POC polymer has been combined with two red emitters InP/ZnS quantum dots (QDs) to obtain nanocomposites with wide emission spectra. The two types of QDs have different absorption wavelengths: 570 nm [InP/ZnS(570)] and 627 nm [InP/ZnS(627)] and were inserted in the polymer at different concentrations. The optical properties of the nanocomposites have been investigated and compared to the ones of the pure polymer. Both spectral and time resolved fluorescence measurements show an efficient energy transfer from the polymer to QDs, resulting in white-emitting nanocomposites. © Springer Science+Business Media Dordrecht 2013.

This paper presents a novel strategy to fabricate two-dimensional poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) photonic crystals (PCs) combining electron beam lithography (EBL) and plasma etching (PE) processes. The surface morphology of PEDOT:PSS PCs after mild oxygen plasma treatment was investigated by scanning electron microscopy. The effects on light extraction are studied experimentally. Vertical extraction of light was found to be strongly dependent on the geometric parameters of the PCs. By changing the lattice type from triangular to square and the geometrical parameters of the photonic structures, the resonance peak could be tuned from a narrow blue emission at 445 nm up to a green emission at 525 nm with a full width at half-maximum of 20 nm, which is in good agreement with Bragg's diffraction theory and free photon band structure. Both finite-difference time-domain and plane wave expansion methods are used to calculate the resonant frequencies and the photonic band structures in the two-dimensional photonic crystals showing a very good agreement with the experiment results. A 2D nanopatterned transparent anode was also fabricated onto a flexible polyethylene terephthalate (PET) substrate and it was integrated into an organic light-emitting diode (OLED). The obtained results fully confirm the feasibility of the developed process of micro/nano patterning PEDOT:PSS. Engineered polymer electrodes prepared by this unique method are useful in a wide variety of high-performance flexible organic optoelectronics. © 2013 American Chemical Society.

A new blue emitter oxadiazole/carbazole copolymer has been synthesized and combined with CdSe/ZnS quantum dots (QDs). Surface passivation of the QDs by ionic liquids was crucial to improve their compatibility with the polymer allowing the deposition of homogeneous nanocomposites films. The nanocomposites have been characterized by thermogravimetric analysis, infrared, UV–visible absorption, and photoluminescence spectroscopy. The emission spectra of nanocomposites show a wide spectrum from blue to orange wavelengths due to the combination of colors emitted by the polymer and QDs, respectively. POLYM. COMPOS., 34:1471–1476, 2013. © 2013 Society of Plastics Engineers

In this work we demonstrate the possibility to realize a novel unconventional ITO-free organic light emitting diode (OLED) utilizing a photonic polymeric electrode. Combining electron beam lithography and a plasma etching process to partially structure the highly conductive poly(3,4 ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) it is possible to realize an embedded photonic crystal (PC) structure. The realized PC-anode drastically reduces the light trapped in the OLED, demonstrating the possibility to eliminate further process stages and making it easier to use this technology even on rollable and flexible substrates. © 2013 IOP Publishing Ltd.

In the present work, the pyro-electrohydrodynamic technique was used for the realization of tunable-size microlens arrays. Poly(methyl methacrylate) dissolved in different solvent mixtures was used as the polymeric material for the realization of the microstructures. By controlling the experimental parameters and in particular, the volume of the drop reservoir, graded-size square arrays of tens of microlenses with focal length in the range 1.5-3 mm were produced. Moreover, the optical quality and geometrical features were investigated by profilometric and interferometric analysis. (C) 2013 Optical Society of America

Actually the most promising polymer solar cell architecture utilizes ITO as transparent conductve anodic electrode. The limited flexibility of ITO and the increasing cost of indium make this kind of electrode not desirable for realizations of low-cost and flexible solar cells. For this reason, it is necessary to develop low-cost, highly flexible and transparent electrodes that can replace the widely used ITO. In this paper, we investigated a new commercial dispersion of PEDOT:PSS suitably modified with dimethyl sulfoxide in solution in order to obtain a highly transparent and conductive manufactured film (HC-PEDOT:PSS) by inkjet printing.

In this work, experimental measurements on polystyrene-ZnO nanocomposite scattering films and on organic light-emitting device with and without the scattering layers are presented. The results are also compared with Henyey-Greenstein radiative-transfer model to narrow down the parameters that can be important in the identification of more suitable scattering layers. As a result, an increase of efficiency of about 30% has been obtained that it can be translated in 60% of outcoupled light in respect to the total generated amount.

New luminescent polymer nanocomposites were synthesized combining carbazole/oxadiazole copolymer (POC) and CdSe/ZnS quantum dots (QDs) surface passivated by ionic liquids. Ionic liquid ligands improve the photostability of QDs and their compatibility with polymer allowing the deposition of homogeneous nanocomposites films. The nanocomposites were characterized by UV and photoluminescence spectroscopy.

We report on the employ of several kinds of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) dispersions as a hole injection layer to increase the stability and the charge injection in organic light emitting diodes (OLEDs). The PEDOT:PSS dispersions have been characterized in solution and thin film by means of dynamic viscosity, Dynamic Light Scattering, profilometer, contact angle measurement, UV–Vis–NIR transmittance and current–voltage characteristics. Then, the dispersions have been employed to manufacture OLEDs with structure: indium tin oxide (ITO)–PEDOT:PSS–poly(9,9-dihexyl-9H-fluorene-2,7-diyl – Tris (8-hydroxy)quinoline aluminium – Al . Device electrical and optical properties have been extensively investigated and discussed in function of PEDOT:PSS ratio. We have found that the hole barrier at the ITO–PEDOT:PSS interface plays a key role in electrical transport and in setting the external quantum efficiency.

Summary: studies on the influence of chemical and physical treatments on thepropertiesofindium–tin oxide(ITO) thinfilms arereported.The ITOfilms areutilizedas transparent anodes of organic light-emitting diodes (OLEDs) incorporatingpoly(9,9-dihexyl-9H-fluorene-2,7-diyl) (PF6) as the hole transporter material and8-hydroxyquinoline aluminum salt (Alq3) as emitter material. Chemical (HCl, piranhasolutions), thermal (vacuum annealing), physical treatments (oxygen plasma, UVozone) and combined treatments are studied. First, ITO layers with differenttreatments are characterized by using four point probe method, contact anglemeasurement, X-Ray diffraction (XRD), surface profilometer, scanning electronmicroscopy (SEM), UV-Vis-IR transmittance. Later, electrical and optical propertiesof OLEDs with treated ITO as anode are extensively investigated. Keywords: contact angle; electrical properties and measurements; electroluminescence; ITOsurface treatments; OLED Introduction The performance of organic devices hasmotivated a vast research activity in thefield of solid-state physics and in that of thetechnology of organic molecules. Althougha large variety of transparent conductingoxides (TCO) are known, the anode oforganic light emitting diodes (OLEDs) is,in the most of the cases, a thin layer of amixed indium–tin oxide (ITO). ITO is byfar the common choice, due to the com-mercial availability, its good transparencyin the visible range and low resistivity.Therefore, the relationship between theproperties of ITO modified by varioussurface treatments and the device perfor-mancehas beenwidely studied.

The relation between the electrical, chemical, and morphological properties of indium−tin oxide (ITO) thin films and organic light-emitting diode (OLED) performance is studied. We report on chemical (HCl, piranha solutions), thermal (vacuum annealing), physical (oxygen plasma, UV ozone), and combined treatments on ITO layers. The effects of these different treatments have been studied using the four-point probe resistivity measurement method, contact angle measurement, X-ray diffraction, surface profilometry, and UV−vis−IR transmittance. Double-layer OLEDs with treated ITO as the anode and poly(9,9-dihexyl-9H-fluorene-2,7-diyl) and 8-hydroxyquinoline aluminum salt as the hole transporter and emitting material, respectively, have been realized. The electrical and optical properties of OLEDs have been extensively investigated, and it is shown that UV ozone−HCl combined treatment yields the highest hole injection efficiency and luminance and the lowest drive voltage. For each OLED with treated ITO, the anode...

The effects induced by different electrical contacts, both for the anode and for the cathode, have been analyzed in Organic Light Emitting Diodes (OLEDs). The properties of anode electrode, Indium Tin Oxide (ITO), have been varied through different surface treatments allowing roughness control, carbon impurity removal, spikes decrement. These induce changes of ITO surface chemical-physical characteristics as roughness, surface energy and surface polarity. OLEDs manufactured employing treated ITO have showed an improvement of 25 times in luminance. Thermionic injection model has been used to estimate decrement in effective hole barrier at ITO-organic layer. It is shown that this effect is correlated to ITO surface energy. The second step of process optimization has concerned the cathode electrode investigation. In order to perform this task, Al, Ca/Al, Ag, Mg/Ag have been used to realize different ITO/PEDOT:PSS/PF6/Alq3/Metal OLEDs. Measurements of electrical and optical behaviour have been performed. A thermionic injection model, with and without Schottky barrier decrement, has been used to calculate the change of the cathode electrical barrier.

Laser crystallization of a-Si:H on PES, PET and AryLite™ polymer substrates is reported. For each material, the glass transition temperature T g and the coefficient of thermal expansion have been evaluated, to determine the optimum deposition and crystallization processes conditions. 1000-A thick intrinsic amorphous silicon films have been deposited on the substrates by Plasma Enhanced Chemical Vapour Deposition in the temperature range of 120–250°C. Dehydrogenation and crystallization have been obtained by high energy (10 J) XeCl pulsed excimer laser. The irradiation conditions have been varied to study their influence on the electrical and optical properties of crystallized material. Structural characterization has been performed by X-ray Diffraction. Increasing the radiation energy densities up to 220 mJ/cm 2 crystallites sizes up to 750 A have been obtained.

Laser crystallization of amorphous silicon film on polymeric substrate is reported. Intrinsic amorphous films 1000 A thick have been deposited on Polyethersulphone (PES) by PECVD technique in the deposition temperature range of 120-200 °C. Dehydrogenation and crystallization of the thin films have been obtained by high energy (10 J) XeCl pulsed excimer laser. The irradiation conditions have been varied to study their influence on dehydrogenated and crystallized material properties. Electrical and optical properties of as-deposited and crystallized films have been investigated. Structural characterization (SEM, XRD, AFM) has been performed. Average crystallite size and grain distribution have been evaluated. For the substrate, the glass transition temperature (Tg) and the coefficient of thermal expansion (CTE) have been evaluated by DSC (Differential Scanning Calorimetry) and TMA (Thermo Mechanical Analysis) measurements and the compatibility with the deposition and crystallization processes have been verified.

Hydrogenated microcrystalline silicon-carbon (μc-Si 1-x C y :H) films have been grown in a plasma enhanced chemical vapour deposition system from silane-methane gas mixtures highly diluted in hydrogen. The effects of RF power, hydrogen dilution and substrate temperature on μc-Si 1-x C y :H properties have been investigated. The increase in RF power reduces the average crystallite size of Si, enhances the carbon fraction, C/(C+Si), and causes a decrease in dark conductivity. The hydrogen dilution ratio R, [H 2 ]/([SiH 4 ]+[CH 4 ]), strongly affects the structure of the films. For R

Hydrogenated microcrystalline silicon–carbon films (μc-SiC:H) have been grown in a plasma enhanced chemical vapor deposition system in low power regime, by silane+methane gas mixtures highly diluted in hydrogen. The effects of RF power density on the film properties and on the amorphous to crystalline phase transition have been investigated. The increase of the RF power density causes the decrease of the crystallinity degree and crystallite grain size and an increment in carbon incorporation. XRD analysis shows that μc-SiC:H alloys with higher dark conductivity (>10−2 Ω−1 cm−1) contain silicon and carbon (3R graphite) crystallites, having average grain size of 200 A, embedded in an amorphous silicon–carbon matrix. In low power regime μc-SiC:H films can be grown at low substrate temperature (200 °C).

Hydrogenated microcrystalline silicon (μc-Si:H) films were prepared by Plasma Enhanced Chemical Vapor Deposition from a mixture of silane highly diluted in hydrogen. The effect of the silane concentration on the deposition rate and on the optical, electrical and structural properties were investigated. The silane concentration appears to control orientation and grain size. Highly conductive μc-Si:H films were grown with high deposition rate at silane concentration of 3%. These films show an enhancement of the optical absorption in the near infrared region. In the visible region the absorption is lower than a-Si:H, however the transient PC signal, induced by 532 nm laser pulses (6 ns time duration), shows an high amplitude and a width comparable with the optical pulse one. μc-Si:H materials can be used for fast photodetectors of pulsed visible light.

Hydrogenated microcrystalline silicon (μc-Si:H) films have been prepared by plasma-enhanced chemical vapour deposition (PECVD) from a mixture of silane highly diluted in hydrogen. The effect of the molecule dwell time on the deposition rate and on the electrical and structural properties has been investigated. The molecule dwell time appears to control orientation and grain size. Highly conductive μc-Si:H films with a rough surface have been grown at a high deposition rate at higher molecule dwell time in an appropriate silane concentration. These films show an enhancement of the optical absorption in the near-infrared region suitable for photovoltaic applications.