A. De Girolamo Del Mauro

Optical properties of polystyrene-ZnO nanocomposite scattering layer to improve light extraction in organic light-emitting diode

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 radiativetransfer 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.

Microlens array manufactured by inkjet printing: study of the effects of the solvent and the polymer concentration on the microstructure shape

Recently, the inkjet printing (IJP) technology was advised as a direct method for the fabrication of high-quality and high-precision microlenses overcoming the drawbacks of the traditional techniques which usually require multiple complex processing steps making the fabrication costly. IJP has the great advantage to be extremely versatile in definition of the patterns of microstructures to be realized employing polymers with suitable optical transmission and thermo-mechanical properties. In the present work, we reported the manufacturing of microlenses by inkjet printing Poly(methyl methacrylate) (PMMA) solutions prepared with different solvents (toluene, N-Methyl-2-pyrrolidone, chlorobenzene, ortho-dichlorobenzene) and solvent mixtures at different mixing ratios and investigated the effects of these parameters on the shape and the geometry of the microstructures. These structures were analyzed by means of interferometric Mach- Zehnder technique in confocal configuration and the wave aberrations were evaluated. The results showed the feasibility of manufacturing microlenses via IJP with diameters ranging from 40 to 90 μm and focal lengths of the order of magnitude of hundred micron.

Improvement of the Inkjet Printed VOCs Sensor Performances through the Sensing Layer Geometry

Polymer nanocomposites (PNCs) are attractive as sensing materials in volatile organic compounds (VOCs) chemical sensors because they combine the simple processability of polymers together with the conductivity properties of nanoparticles dispersed in the insulating polymer matrix. Recently, these materials are easily processed by inkjet printing (IJP) technique whose patterning capability is one of its main advantages. In the present work, we fabricated PNCs chemical sensors inkjet printing a polystyrene (PS)/carbon black (CB) composite based ink. The sensor responses have been measured upon exposure to acetone organic vapors and analyzed as function of sensitive material geometry.

Solvent effects on spectral emission of PVK and PVK-Ir(ppy)3 based OLEDs

In this work we have compared the effect of using solvents with different boiling temperature on the spectroscopic emission proprieties of poly(n vinylcarbazole) (PVK) and PVK doped with Iridium complexes tris[2-phenylpyridinato-C2,N]iridium(III) (Ir(ppy)3) films, due to the different organization of the polymer on the substrate during the spin coating process. The modified molecular rearrangement affects the emission properties of the PVK material and the consequent energy transfer to the doping molecules. Both Static and dynamic emissions proprieties have been studied, for the case of pure PVK and PVK doped with different weight percentage of Ir(ppy)3. Different devices have been prepared to test the change in electroluminescence spectral shape and in electrical characteristic and the final efficiencies of the devices have been evaluated.

Inkjet Etching of Polymer Surfaces to Manufacture Microstructures for OLED Applications

A soluble polymer layer can be structured by means of solvent drops etching. The inkjet etching (IJE), innovative technique that consists of ejecting liquid material in controlled manner in terms of both volume amount (10–100 pL) and positioning on the substrate (μm resolution), allows to manufacture suitable shaped microstructures on top of polymer surfaces. In the present work we fabricated IJ etched polymer microstructures whose shape varies from concave to convex by employing a pure solvent or solvent mixtures with suitable mixing ratio of the solvents. The manufactured structure profile has been analyzed and the related geometrical parameters, i.e. depth, diameter and height, have been valuated as function of the drops number. Preliminary tests have been performed in order to employ the IJ etched polymer microstructures with the aim to improve the out‐coupling efficiency of organic light‐emitting diodes.

Inkjet Printed Chemical Sensors

Polymer nanocomposites (PNCs) represent a new class of sensing materials for volatile organic compounds (VOCs) detection. These materials can be simply processed by inkjet printing (IJP) technique, an emerging technology that has assumed a key role in the field of electronics wherever replacing conventional rigid substrates with flexible ones is required. In the present work, we fabricated PNCs chemical sensors inkjet printing a polystyrene (PS)/carbon black (CB) composite based ink on different substrates, flexible and not, such as polyethylene terephthalate (PET), glass and alumina. The sensors responses have been analyzed upon exposure to acetone organic vapors and compared in terms of sensitivity, response time and limit of detection.

TiO2/polymer nanocomposite based inks

We report the development and characterization of dielectric inks based on dispersions of TiO2 in poly(ethylenimine)/ethanol solutions having physicochemical properties suitable to ink‐jet printing process. In order to study the effect of polymer dispersant on the printability and stability of inks, we carried out dynamic light scattering analysis of different inks made with and without polymer. Moreover, we compare the curve of distribution of TiO2 particles size at different aging times. For TiO2polymerwe optimize the inkjet parameters (amplitude and duration of jetting impulse, jetting frequency, substrate velocity) to obtain thin lines based on TiO2/ poly(ethylenimine) nanocomposite on silicon substrate. Finally, the morphology of films was also investigated.

Effect of the Layer Geometry on Ink-Jet Sensor Device Perfomances

In this work, we report on ink-jet manufactured chemical sensors based on polymer carbon black composites. In particular, in order to study the correlation between ink-jet pattern geometry and device response sensors characterized by sensing layers consisting of polystyrene/carbon black composites lines of various shape and surfaces were fabricated. The morphology of films, the electrical characteristics and time stability of sensors were investigated.

ON THE FABRICATION PROCESS OF POLYMER-COMPOSITES BASED SENSORS

The results of investigations of the effects of two organic solvents of preparation, tetrahydrofuran (THF) and 1,1,1,3,3,3 Hexafluoro-2-propanol (HFIP), and of three different electrical geometry of devices on drop-coated poly (methyl-methacrylate)/ carbon black (PMMA/CB) composites gas sensors are presented. Using HFIP solvent, it is possible to obtain a good dispersion of the CB filler in the polymeric matrix but the thermodynamic responses of devices to acetone and ethanol vapours are independent from their morphology and from the geometry of devices. The highest sensor responses are to acetone vapor. This behavior could be probably attributed to the higher chemical affinity of less polar molecule as acetone towards PMMA. The filler dispersions, the current-voltage (I/V) characteristics and the stability of devices in the time were also studied and discussed.

ELECTRICAL AND OPTICAL CHARACTERIZATION OF POLYMER NANOCOMPOSITES SWELLING

In this work, polymer layers used in the fabrication of chemical sensors are characterized by means of an optical method based on white light interferometry. The study focuses on poly (hydroxy ethyl methacrylate) (PHEMA) and on nanocomposite Carbon black/PHEMA layers commonly used in chemical sensor technology for VOCs measurements. The response of nanocomposite PHEMA/CB layer upon exposure to vapour solvents is investigated in terms of film expansion and compared to the swelling properties of the PHEMA layer.