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A novel study about the synthesis of zirconia and calcia-stabilized zirconia powders were carried out by DC thermal plasma starting from cheap precursors as the carbonates. Different operational parameters were investigated to explore the effects of the process conditions, such as the plasma torch power and the gas flow rate on the composition and the morphology of the powders. The products phase changes from a metastable tetragonal to monoclinic/tetragonal mixture. Basically a main tetragonal phase was obtained at low torch power (7 kW) while the amount of monoclinic phase linearly rises with the power, up to 66 wt% at 26 kW of plasma power and high gas flow rate. The gas flow rate also affects the shape and the size of the powder, where high values reduce powder aggregation and enhance the spherical shape. The best results were achieved at 22 kW of plasma power and high gas flow rate, with powders of roundness about 79% and a wide particle size distribution. Adding the calcium carbonate to the zirconium carbonate (corresponding to 8 wt% CaO in the final mixture), the plasma treatment mainly produces a tetragonal phase zirconia, that at 1400 °C in furnace changes in a stable cubic phase. These powders could be made suitable for further industrial applications after proper treatments.

The present work proposes a method and an apparatus that allows the in vitro diagnostic analysis of biological samples to be carried out by analyzing the light radiation transmitted through the sample. An OLED (Organic LED) source, with broad emission spectrum for white light, was used; the optical path of the light radiation emitted by the source has been adapted to the specific wavelengths of the system (405 nm, 450 nm, 492 nm, 550 nm, 620 nm) and the detection of the signal was carried out through the use of an OPD (organic photodiode) with the appropriate photoresponse. To suitably select the analysis signal, a series of photonic crystals have been used, with the aim to also obtain a bandwidth of less than 10 nm as required by the solutions already present on the market. The proposed system gives the opportunity to reduce the overall dimensions of the analyzer compared to the systems existing on the market, avoiding the use of supplementary optical fibers and interference filters.

Printing technologies can offer high potential for the thin film deposition of functional materials. Among the printing techniques, the gravure is considered one of the most promising, although to date it is still little employed, especially for the inorganic functional materials. In this work, the study of the gravure printing process for the metal oxides thin film production on flexible polymer substrate is reported. For this purpose, zinc oxide (ZnO) was chosen due to its versatile properties and nanosize effects, which make it suitable for many high technology areas. The gravure printing was made using low viscosity inks of ZnO nanoparticles. The characteristics of the printed thin films were examined and discussed. Thanks to the understanding of the physics underlying the film forming during the printing process combined to the knowledge on such specific material, uniform, compact, very transparent and smooth films were obtained in different nanometric thicknesses. Moreover, the possibility of fabricating ceramic nanocomposite films directly through this printing technique is also presented. Thanks to its scientific approach, this work makes available to the world of ceramics an industrial versatile and low-cost production technique which can allow to study and develop high-quality thin film ceramics with technologically interesting properties as well as nanoparticles behavior and their treatments in order to develop and use their fascinating nanosize properties.

The poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is one of the most attractive conducting polymers proposed as electrode for flexible electronics. Promising methods for enhancing its low conductivity, main limit for its use, are based on post-treatment. However, most of them are not suitable for mass production. In this study, the gravure printing technique was tried for the post-treatment of the PEDOT layer using dimethylsulfoxide (DMSO), as practical, safe and cost effective process for improving the printed electrode. An increase of the conductivity of the printed PEDOT:PSS layer was found and attributed to the rearrangement of the polymeric chains that leads to the formation of PEDOT-rich regions improving the conducting pathways. In addition, smoother film surface and improved stability to the humidity were obtained, representing further advantages for its employment in plastic electronics. Therefore, the feasibility and the efficacy of the DMSO post-treatment of the PEDOT:PSS films by gravure printing were demonstrated, showing the way for the low cost all in-line industrial production of large area PEDOT:PSS electrodes.

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, we compared the photovoltaic performance of standard and inverted polymer solar cells with the aim to elucidate the origin of the different current output. We realized devices with both architectures 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 cell sequence is ITO/PEDOT:PSS/PBDTTT-C:[70]PCBM/Ca/Al and the inverted one is ITO/ZnO/PBDTTT-C:[70]PCBM/MoO3/Ag. The inverted architecture shows better performances compared to the standard one mainly in terms of current output. The optical modeling has revealed that this architecture allows more photons to be absorbed in the blend film, giving rise to an higher current output, although the observed improvement cannot be completely attributed to the calculated higher absorption of the incoming light. By using the impedance spectroscopy analysis, we found that the inverted device architecture has higher values for the interface trap time constant and the density of interface states. Both parameters contribute to retain the charge collection efficient, compared to the standard configuration, despite the increased charge carrier density and to further improve the current output. © 2016 Elsevier B.V. All rights reserved.

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.

Melanin denotes a variety of mammalian pigments, including the dark electrically conductive eumelanin and the reddish, sulfur-containing, pheomelanin. Organic (bio)electronics is showing increasing interests in eumelanin exploitation, e.g., for bio-interfaces, but the low conductivity of the material is limiting the development of eumelanin-based devices. Here, for the first time, we report an abrupt increase of the eumelanin electrical conductivity, revealing the highest value presented to date of 318 S/cm. This result, obtained via simple thermal annealing in vacuum of the material, designed on the base of the knowledge of the eumelanin chemical properties, also discloses the actual electronic nature of this material's conduction.

This study investigates the influence of the deposition temperature of hexamethyldisilazane (HMDS) on the performances of organic thin film transistors (OTFTs) using the [6,6]-phenyl-C71-butyric acid methyl ester (PC70BM) as semiconductor. N-type OTFTs have been fabricated using this fullerene derivative, deposited from solution by drop casting technique on HMDS self-assembled monolayer (SAM) deposited at three different temperatures, 7 °C, 25 °C and 60 °C, in order to evaluate the influence of these deposition conditions on the morphology of PC70BM films and on the electrical responses of fullerene derivative-based OTFTs.The effect of the treatments of the surfaces was observed through contact angle measurements. AFM imaging of the deposited material has been used to analyse its structure and morphology. The transistors performances have been evaluated through I vs. V static characterization and parameters extraction.Contact angle vs. HMDS deposition temperature shows the minimum value at 60 °C, instead here field effect mobility presents a maximum. It has been observed that the lower hydrophobicity of the surface of the SAM induces the formation of more homogeneous surface of the PC70BM film, resulting in an increase of the OTFTs performances. © 2016 Elsevier Ltd.

We report our work about OLED devices where the emissive layer is based on CdSe/ZnS quantum dots (QDs) combined with poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT) in two different ways: blends at various QDs concentrations and sequential deposition of QDs and F8BT layers. The fluorescence of the blends presents a wide emission in the range (500-700) nm due to the combination of fluorescence by the polymer (maximum at 540 nm) and QDs (maximum at 634 nm). Among the layered structures, the fluorescence emission by the QDs substantially contributes to the spectrum only for the F8BT/QDs bilayer. The OLEDs devices realized with the blend at 15 wt% of QDs show the highest luminance respect to all the devices, and threshold voltage values similar to the neat polymer device. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work, FETs are used as a research tool to study charge carrier mobilities in PbS nanocrystals (NCs) thin-films employed as semiconducting layer in bottom-gate bottom-contact (BGBC) field-effect transistors (FETs). The as-synthesised NCs are surrounded by long alkyl chain ligands which act as electrical insulators. Therefore, a ligand exchange process with shorter molecules is necessary to enhance the free charges generation and transport. We used two different ligands: 1,2 ethandithiol (EDT) and 1,2,3,4-tetrabutylammonium iodide (TBAI) and studied the charge mobility of PbS NCs comparing the electrical characteristics of FETs made by exchanged NCs. We analysed also the contemporary presence of both exchanged nanocrystals on the device. All the transistors showed p-type transport behaviour, enhanced by an annealing process at 100 °C for 10 min. After this, only the TBAI-treated NCs devices showed a n-type transport, resulting in an ambipolar behaviour. Inkjet printing deposition techniques was also successfully used to deposit PbS-(TBAI) NCs and ambipolar devices were obtained. In addition, for printed devices it was found that it is possible to modulate the charge transport properties by applying surface treatment to the substrate with a pentafluorothiophenol (PFTP). Indeed in this case, the p-type transport was suppressed while n-type behaviour was induced.

The synthesis and the microstructural characterization of isotactic poly (N-pentenyl-carbazole) (i-PPK) are reported. The achieved polymer is semicrystalline, the melting temperature is 138°C. i-PPK Fourier transform infrared spectroscopy (FTIR) spectrum and X-ray diffraction pattern are compared with those of polyvinylcarbazole. The observed differences are tentatively associated to higher flexibility of the i-PPK chains due to the alkylene group connecting the carbazole group to the main chain. The presence of intrachain and interchain interactions between carbazole units, which bring these groups to stack each other, is assumed. i-PPK optical properties are investigated and an electroluminescent behaviour of polymer is observed. Organic light emitting diodes based on i-PPK layers are founded to emit white light. POLYM. COMPOS., 36:1110–1117, 2015. © 2015 Society of Plastics Engineers

In the present work, we report the influence of the solvents on the morphology and the uniformity of inkjet printed n-type (electron-transporting) perylene diimide (PDI-8CN2) semiconductor films on SiO 2 substrates. In particular, a solvent mixture composed by o-dichlorobenzene and chloroform was employed and the semiconductor crystalline structure was investigated as a function of the mixing ratio of the component solvents. For each mixture composition, the printing parameters such as substrate temperature and drop overlapping degree, were optimized to improve the reproducibility of the deposition process and the structural quality of the final films. Organic thin film transistors were fabricated and electrically characterized. The electrical measurements suggest that for the devices with larger active areas, the solvent mixture approach improves the performances of OTFTs in comparison with the use of pure o-dichlorobenzene solution.

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).

A polymeric PEDOT:PSS film nanostructured with Photonic Quasi Crystals that opens the path towards more efficient white OLEDs is presented. For the first time three different quasi crystal families were fabricated (octagonal, dodecagonal and Thue-Morse) onto a conductive polymeric film combining high-resolution electron beam lithography (EBL) and plasma etching techniques to improve light extraction and to control spectral tunability. The efficiency gain obtained in light extraction holds great promise for the use of quasi crystals as functional components in polymeric based White Organic Light Emitting Diode (WOLED) devices. © 2015 The Royal Society of Chemistry.

Many research efforts are focused toward significant improvements of polymeric solar cells efficiency, energy harvesting range, time, and environmental stability. Particular attention is given to hybrid organic/inorganic composites constituted of polymer/lead chalcogenides (PbS and PbSe) nanocrystals (NCs) to extend the spectral sensitivity of cells to near-infrared wavelengths. In this work we report the synthesis and characterization of PbS nanocrystals with absorption edge at 984 nm. The nanocrystals have a cubic crystal structure and size of about 2 nm as found by X-ray diffraction analysis. They were combined with poly(3-hexylthiophene) (P3HT) polymer to obtain P3HT:PbS blends with different PbS loadings. A post-deposition ligand exchange on PbS NCs by 1,2-ethanedithiol (EDT) allowed a better interaction between polymer and nanocrystals as showed by fluorescence measurements. The P3HT:PbS blends were deposited and treated by a layer by layer spin coating process and used as active layer in solar cells having structure glass/ITO/PEDOT:PSS/blend/Al. The major result obtained for this hybrid system is an increase of PCE by about two orders of magnitude with respect to analogous reported cells where a post-deposition ligand exchange was performed.

Photo- and electroluminescence of five bithiophene disubstituted 1,3,4-thiadiazoles, constituting a new class of solution processable materials for organic opto-electronics, were studied. It was found that the introduction of alkyl solubilizing substituents bathochromically shifted the photo- and electroluminescence bands. The most pronounced effect was observed for the substitution at the Cα position which changed the emitting light color from bluish to green. All five derivatives were tested in host/guest type organic light emitting diodes (OLEDs) with either poly(N-vinylcarbazole) (PVK) or poly(N-vinylcarbazole) + 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PVK + PBD) matrices. The latter matrix turned out especially well suited for these guest molecules yielding devices of varying color coordinates. The best luminance (750 cd/m2) was measured for 2,5-bis(5'-octyl-2,2'-bithiophene-5-yl)-1,3,4-thiadiazole with the luminous efficiency exceeding 0.4 cd/A. © 2014 Elsevier B.V. All rights reserved.

The most exploited active material for photovoltaic devices is the regioregular poly(3-hexylthiophene) (P3HT), p-type conjugated polymer, blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), n-type material. The deposition methods and the induced morphology strongly influence the functionality of the active material and in turn the final charge generation performances of a photoactive layer. In the present work, we studied the influence of PCBM concentration on the morphological and spectroscopic properties of the inkjet printed P3HT:PCBM blends through atomic force microscopy (AFM), Raman spectroscopy and transient absorption spectroscopy. The aim is to value the charge formation yield in the blends, prepared by inkjet technology, as function of the acceptor concentrations in correlation with morphology and intermixing of the two components. For the inkjet printed samples the blends composition that corresponds to the best intermixing between P3HT and PCBM and the higher charges formation yield should be between 20% and 45% in weight (wt)., differently for what has been found previously for spin-coated samples. Indeed, for inkjet prepared film, the 45 wt.% blend ratio leads to much bigger domains with respect to the spin-coated samples as shown from the AFM measurements. © 2013 Elsevier B.V. All rights reserved.

This study addresses the issue of poor intercomparability of measurements of organic photovoltaic (OPV) devices among different laboratories. We present a round robin performance testing of novel OPV devices among 16 laboratories, organized within the framework of European Research Infrastructure Project (SOPHIA) and European Energy Research Alliance (EERA). Three types of OPVs with different structures, dimensions and encapsulations are studied and compared with reference Si solar cells certified by accredited laboratories. The agreement of the measurements of these among different laboratories is analyzed by focusing on testing procedures, testing equipment and sample designs. A number of deviations and pitfalls are revealed and based on the analyses, a set of recommendations are suggested for improving the agreement among the measurements of such OPV technologies. European Commission's FP7 programme; European Energy Research Alliance (EERA); EUDP; UK Department for Business, Innovation and Skills

Zinc oxide nanoparticles (ZnONPs) and stearic acid are herein used for the preparation of hydrophobic coatings with good moisture barrier property on flexible plastic substrates. Fast, high throughput, mild and easy-to-run processing techniques, like airbrushing and gravure printing, are applied for thin films deposition of these materials. The results of this study indicated that the best hydrophobic coating in terms of water contact angle (115&deg, ) is obtained through a two-steps printing deposition of a ZnONPs layer followed by a stearic acid layer. All the deposition procedures proved to be effective in terms of water vapor barrier properties, reaching values of 0.89 g/m2/day, with a 45% reduction with respect to the bare substrate. These preliminary data are very encouraging in the perspective of a low cost and green approach for the realization of functional coatings for packaging applications.

Organic thin film phototransistor (OPTs) devices in bottom-gate/top-contact configuration were fabricated and used as analytic system to study the electrical and optical properties of pentacene. The channel of the OTFT devices was illuminated by laser radiation of wavelength 670 nm and the effect of irradiation on the electrical responses of the devices was investigated at different temperatures and incident optical powers. The photoresponse and the electrical parameters of the devices (mobility, threshold voltages and on/off ratios – ION/IOFF) were evaluated in order to investigate the relationship between the light sensing behavior of the phototransistors and their electrical performances. Moreover, the OPT's time-resolved electrical response to light irradiation was modelled to decouple the fast-varying photoexcitation effects from slow bias stress decays in order to investigate the reversibility properties, the time stability of electrical responses and the photocurrent.

The prospect of exploiting quantum dots (QDs) properties (tunable absorption spectrum, multiple exciton generation) while maintaining the flexible structure of polymer systems opens new possibilities in the photovoltaic field. Although charge transport dynamics in pristine polymer and QDs systems have been quite well established lately, a complete understanding of the charge transfer process between QDs and polymers when they are in blends is still lacking. In this work we used static and ultrafast fluorescence spectroscopy together with Atomic force Microscopy (AFM) to study the exciton dynamics in polymer/QDs films. Specifically we used poly(3-hexylthiophene) (P3HT) as the hole conducting donor material and the core shell CdSe(ZnS) QDs as the electron acceptor material. The QDs surface has been treated with two different capping ligands treatments: one based on the use of pyridine and the other one on hexanoic acid. The influence of the two different methods on the exciton dynamics and on the morphology will also be discussed. Blends containing differently treated P3HT/CdSe(ZnS) wt% ratios have been prepared producing films having uniform morphology and good intermixing, as proved by AFM measurements. Ultrafast fluorescence decays allowed us to compare the exciton dynamics in the polymer pristine respect to the treated P3HT/CdSe(ZnS) films. Efficient fluorescence quenching has been shown by both kind of blends respect to the pure polymer. © 2014 The Authors.

In this work we improved the performance of ITO-free polymer solar cells (PSCs) by incorporating silver nanoparticles (AgNPs) in the highly conductive (HC) PEDOT:PSS anode. The AgNPs were synthetized in-situ in the PEDOT:PSS water dispersion. This anode was used to realize PSCs with the following geometry: glass/HC-PEDOT:PSS/PEDOT:PSS/PBDTTT-C:[70]PCBM/Ca/Al. All the devices were characterized by UV-VIS spectroscopy, impedance spectroscopy, IV light, IV dark and quantum efficiency measurements. The presence of AgNPs in the HC-PEDOT:PSS anode contributes to improve the absorption of the photoactive layer and to lower the resistivity of the anode.

In this work, the photophysical proprieties of 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) dye in the poly-vinylcarbazole (PVK) matrix are analyzed with a particular attention to the energy transfer processes between the matrix and the dye. PVK films doped with weight percent varying from 1 to 8 wt% of DCM have been fabricated. The emission spectra are dominated by the presence of DCM and a strong red shift in the emission spectra of the blend has been observed as function of dye concentration. A quenching effect in the excitons lifetime increasing the concentration of the dopants has been observed. These two phenomena have been studied in terms of energy processes inside the blends. POLYM. COMPOS., 34:1500–1505, 2013. © 2013 Society of Plastics Engineers

In this article, we describe the development of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)-based ink for the fabrication of indium tin oxide (ITO)-free polymer solar cells (PSCs). The ink consisted of PEDOT:PSS, suitably doped with dimethyl sulfoxide (DMSO) in solution. The printed PEDOT:PSS showed electrical conductivity of 1000 S/cm and transparency around 85% in the visible range. Then, they were employed as anodes in ITO-free polymer PSCs based on a bulk heterojunction of poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester. The effects of surface treatments (O2 plasma, UV ozone) of glass substrates on the quality and morphology of the printed layer were investigated in order to improve the anode quality. The performances of the devices with printed polymeric anode were compared to the one realized depositing DMSO-PEDOT:PSS by spin coating technique. The best cells performances were obtained by UV ozone treatment reaching a power conversion efficiency of 1.5%. POLYM. COMPOS., 34:1493–1499, 2013. © 2013 Society of Plastics Engineers

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.

The electroluminescence (EL) of isotactic and syndiotactic poly(N-pentenyl-carbazole) (PPK), achieved by coordination polymerization, is studied in order to investigate the interrelation between the polymer tacticity and their physical-chemical properties. The use of these polymers in organic light-emitting diode (OLED) fabrication is also explored. Thermal and x-ray diffraction analyses of PPKs show that the isotactic stereoisomer is semicrystalline, whereas the syndiotactic one is amorphous. Optical analysis of both stereoisomers, carried out on film samples, reveals the presence of two different excimers: 'sandwich-like' and 'partially overlapping'. Nevertheless, the emission intensity ratio between 'sandwich-like' and 'partially overlapping' excimers is higher in the isotactic than in the syndiotactic stereoisomer. Using the synthesized polymers as OLED emitting layers, the influence of the polymer tacticity on the EL properties of the device is highlighted. In detail, while blue OLEDs are obtained by using the syndiotactic stereoisomer, OLEDs with a multilayer structure fabricated with the isotactic stereoisomer emit white light. The contribution of three different emissions (fluorescence, phosphorescence and electromer emissions) with comparable intensities to the detected white light is discussed. © 2017 IOP Publishing 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.

Bottom-emitting organic diode devices with polymeric anode were fabricated and their performances were compared to devices with different anodes. The highly transparent (transmittance ≈ 90%) and conductive (700 S/cm) anode was poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) processed from aqueous solution and modified by addition of dimethyl sulfoxide (DMSO). The electro-optical characteristics of the DMSO-doped PEDOT:PSS based device and devices with architectures based on undoped PEDOT:PSS and/or indium tin oxide (ITO) were investigated and the effects of the different anodes were analyzed by means of electrical responses in static and dynamic regimes. The efficiency of the device with the proposed polymeric anode was comparable to that of ITO based device but reduced with respect to the device including PEDOT:PSS as hole-injection layer. These results were correlated to the film morphological properties and discussed in terms of interfacial state density modification.

In this work we studied the optical and transport properties of hybrid nanocomposites of CdS quantum dots (QDs) and poly( N -vinylcarbazole) (PVK) polymer. The CdS QDs were prepared by thermal decomposition (thermolysis) of a single source precursor, Cd bis-thiolate, in a high boiling solvent, octadecene (ODE). The optical characterization of the QDs has been carried out by UV–vis absorption and photoluminescence spectroscopy while the morphological properties have been investigated atomic force microscopy and transmission electron microscopy. The analyses have shown that CdS QDs of diameter below 6 nm can be synthesized by such route with good light emission in the UV range. The QDs have been dispersed in a poly( N -vinylcarbazole) (PVK) matrix to obtain a PVK:CdS nanocomposite layers. An increase of conductivity and a quenching of the photoluminescence have been observed when the nanocomposite layer was inserted in ITO/PVK:CdS/Al structures.

The integration of semiconductor nanoparticles (NPs) into a polymeric matrix has the potential to enhance the performance of polymer-based solar cells taking advantage of the physical properties of NPs and polymers. We synthesize a new class of CdS-NPs-based active layer employing a low-cost and low temperature route compatible with large-scale device manufacturing. Our approach is based on the controlled in situ thermal decomposition of a cadmium thiolate precursor in poly(3-hexylthiophene) (P3HT). The casted P3HT:precursor solid foils were heated up from 200 to 300 °C to allow the precursor decomposition and the CdS-NP formation within the polymer matrix. The CdS-NP growth was controlled by varying the annealing temperature. The polymer:precursor weight ratio was also varied to investigate the effects of increasing the NP volume fraction on the solar cell performances. The optical properties were studied by using UV–Vis absorption and photoluminescence (PL) spectroscopy at room temperature. To investigate the photocurrent response of P3HT:CdS nanocomposites, ITO/P3HT:CdS/Al solar cell devices were realized. We measured the external quantum efficiency (EQE) as a function of the wavelength. The photovoltaic response of the devices containing CdS-NPs showed a variation compared with the devices with P3HT only. By changing the annealing temperature the EQE is enhanced in the 400–600 nm spectral region. By increasing the NPs volume fraction remarkable changes in the EQE spectra were observed. The data are discussed also in relation to morphological features of the interfaces studied by Focused Ion Beam technique.

We developed and characterized inks based on dispersions of N-doped titanium dioxide (TiO2) in pol- yethylenimine (PEI)/ethanol solutions with chemicophysi- cal properties suitable for the ink-jet printing process. In detail, we prepared suspensions by varying the concentra- tion of the polymeric dispersant to investigate the effect of the dispersant on the time stability and printability of the ink. Moreover, we printed the N-doped TiO2/PEI-based inks on different substrates and studied as the substrate temperature and the printing parameters influenced the printed product quality. Furthermore, the optical proper- ties and the morphology of the printed films were also investigated. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3630-3636, 2011

In this work, a simple approach to prepare luminescent poly(3-hexylthiophene)–CdS nanocomposites to be employed in organic light emitting devices (OLED) devices is reported. The nucleation and growth of CdS nanoparticles were obtained by the thermolysis of a single Cd and S precursor dispersed in the polymer at three different temperatures of annealing: 240, 265, and 300°C. In this way, it was possible to compare the properties of nanocomposites containing nanoparticles with different sizes. X-ray diffraction and transmission electron microscopy analyses confirmed the formation of CdS nanoparticles and gave information about the size, distribution, and morphology of the nanoparticles; monodispersive and very small nanoparticles with diameters below 2.5 nm were obtained at 240°C. The application of such nanocomposites as emitting layers in OLED devices is discussed. Enhanced electrooptical properties were observed for the device containing the nanocomposite annealed at 240°C with respect to the pure polymer based device. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

The inkjet printing (IJP) technique is gener- ally used as tool for positioning small quantities of a liquid material on a target substrate. An interesting application of IJP is inkjet etching that consists of the deposition of drops of solvent or solvent mixtures onto a soluble polymer layer. This technique allows one to structure the polymer film and to change the shape, from concave to convex, by varying the mixing ratio of the solvents. In this work, the structuring of some polymeric layers (polyimide and poly- styrene) by solvents (N-methyl-2-pyrrolidone (NMP) and toluene (TOL)) and a solvent mixture (TOL-NMP) at different mixing ratios were studied, and the effect of the printing parameters on the microstructural profile was investigated. Some applications in optoelectronic devices are described. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3637-3643, 2011

Transparent and conductive nanocomposite films were spin-coated with the use of undoped and di- methyl sulfoxide (DMSO)-doped polyaniline (PANI)- poly(styrene sulfonate) (PSS) dispersions. The prepared dispersions were investigated in terms of their nanopar- ticle size distributions, and the corresponding films were morphologically, optically, and electrically characterized. These films were used as hole-injection layers (HILs) in or- ganic light-emitting diode (OLEDs), and the device per- formances were compared to a reference device without an HIL. The device based on the PANI-PSS layer showed the best electrooptical characteristics, lowest switch-on voltage, and improved efficiency. In particular, the device efficiency grew about three times with the introduction of the PANI-PSS layer (1.20 Cd/A) and about two times with the introduction of the DMSO-doped PANI-PSS film (0.77 Cd/A) compared to an OLED without an HIL (0.4 Cd/A). These results indicate that the device with the undoped PANI-PSS was the more suitable one to be used as an HIL in an OLED device. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3618-3623, 2011

In order to assess the performance of solar micro-concentrators, specific methods and protocols need to be developed, tested, and applied. In detail, as in conventional concentration modules, one of the fundamental parameters to consider is the efficiency of optical concentrators. In fact, optical concentrators give fundamental information on the current potentially generated from solar microcells that receive the concentrated light radiation. To develop a measurement method for micrometer-size optical components, a suitable optical system was implemented and used. Moreover, the potential application of the printed microstructures in an optical system for solar micro-concentrators was demonstrated.

we report about the fabrication of organic light-emitting diodes (OLEDs) ink-jet printing a hole-transporting polymer (PF6, poly(9,9-dihexyl-9H-fluorene-2,7-diyl)) on flexible substrate (PET) and performing the other layers through vacuum thermal evaporation. The aim of the work is to employ the ink-jet printing (IJP) technology, familiar as a method for printing on paper, in optoelectronic applications and to determine how the deposition method affects the functional material film properties and hence the ultimate device performances. In this line of work, ink-jet printed polymer films are compared to same spin-coated polymer from the electro-optical point of view: both prepared materials are adopted as HTLs of electroluminescent devices. All manufactured OLEDs are characterized and their behaviours are investigated and analyzed with theoretical models. The results show differences in current density and optical behaviours between the devices fabricated by means of the above mentioned technologies which can be justified in terms of different trap distribution induced by impurity energy levels associated to each process.

The aim of this paper is to investigate the electrical and optical property modifications that can be related to the presence of a nanometric metallic layer at the interface between two organic emissive materials in a stacked structure. For purposes of comparison, reference devices have also been analyzed to emphasize the increase of electrical switching and hysteresis behaviors in current-voltage plots and spectral variations in electroluminescence. In this paper, we have tried to summarize the electrical effects of the floating nanometric thin metallic layer by extracting a small number of parameters which can represent the current state of the device.

In optoelectronics, inkjet printing (IJP) technology is being developed as an alternative to the traditional techniques for organic materials deposition. In this work, we report the fabrication of organic light-emitting diodes (OLEDs) on the flexible substrate by studying the effect of a surface chemical treatment on the inkjet printed polymer film morphology. The employed piranha treatment increases the substrate surface energy and improves the wettability, thus inducing a decrease in the IJ printed drop thickness. The IJ printed polymer (poly(9,9-dihexyl-9H-fluorene-2,7-diyl)) is the hole-transporting layer (HTL) of a hybrid structure in which the other layers are deposited by vacuum thermal evaporation. Furthermore, in order to determine the effect of the IJ deposition method on the manufactured OLED performances, we compare them to those of devices fabricated using standard technologies. With this aim, OLEDs with the same structure are fabricated by replacing the IJ printed polymer with a spin-coated ...

Carbon nanotube (CNT) and polymer composite materials were obtained using two manufacturing processes. The first method is dispersion of CNT in a solvent-doped poly(ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) solution. The composite retains high optical properties because of the polymeric system and shows improved electrical properties. The second method is in situ polymerization of ethylenedioxythiophene (EDOT) in the presence of CNT. This procedure assures a uniform CNT distribution in a highly conductive p-EDOT layer with reduced optical transmittance. The composites were analyzed for optical transmittance, surface energy, polarity, distribution, and resistivity, and then they were used as an anodic layer in organic light-emitting diode (OLED) manufacturing. The device performances were characterized and compared to that of conventional devices with an indium tin oxide anode. p-EDOT composite layers have shown conductivity and optical transmittance suitable to produce an OLED with a 10 cd...

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.