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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.

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.

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.

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.

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

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.

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.

Electrical transport properties of PVK (poly N-vinyl carbazole), a polymer exhibiting an intrinsic electroluminescence (EL) in blue region, have been investigated. In particular, resistivity and charge carrier mobility have been assessed by means of I–V measurements and by Field Effect (FET) doping, respectively. Dielectric constant has been also evaluated by means of C–V measurements performed on an ITO/PVK/Al single layer electroluminescent (EL) device. All electrical characterizations, carried out in different environmental conditions to deeply investigate PVK intrinsic conduction mechanisms, allowed to assess the good quality of spin coated PVK thin films. Electroluminescent measurements performed on ITO/PVK/Al and on ITO/PVK/Alq3/Al have been also performed. Finally, charge injection mechanisms from the electrodes to PVK have been investigated also as a function of the temperature. Experimental results have been compared with some well known theoretical models.

Amorphous and polycrystalline tin oxide (SnO x ) thin films were grown by ArF excimer laser-induced metal–organic chemical vapour deposition (L-MOCVD) from tetramethyltin (TMT) and oxygen as precursors. The films structure and composition were investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The deposition temperature and the ratio of the TMT and oxygen flow rates have been optimised in order to minimise the residual carbon content and to achieve stoichiometric SnO 2 films. The films deposited at room temperature were amorphous, strongly substoichiometric [O]:[Sn] = 1.3 and with a high residual carbon content depending on the TMT and oxygen ratio. Films grown at 300 °C were polycrystalline with [O]:[Sn] ratios up to 1.8 and with a much lower carbon content. The tin oxide films were subsequently used as sensing layers for gas detection. A satisfactory sensor performance was obtained for the oxidising NO 2 and the reducing N 2 O, CH 4 , SO 2 , CO, CO 2 , H 2 gases.

Polycrystalline silicon films have been grown from Si2H6 by low-pressure chemical vapour deposition at 800 K and in situ laser annealing (LA) on amorphous silicon seed layers deposited on a metallic Ti/Pd/Ag multilayer. The crystalline volume fraction in the seed layer was controlled by thermal annealing. According to the metal-induced crystallization effect, the presence of the metal induces a lower-temperature crystallization of silicon in the seed layers. X-ray diffraction and scanning electron microscopy data show that the formation of palladium silicides in the seed layer drives the growth of wire-like columns which are found to change morphology depending on the seed layer microstructure and LA parameters. It is suggested that superficial palladium was found to affect also the growth rate by enhancing the Si2H6 dissociation.

SiC thin films have been synthesised by combining low pressure chemical vapour deposition from Si 2 H 6 and C 2 H 2 at 520°C and in situ KrF-excimer laser annealing. Glancing incidence X-ray analysis showed the quantity of polycrystalline SiC in the laser-irradiated area depends on the mass-flow ratio of the precursor gases. In the region outside the laser spot where the films are amorphous, X-ray photoelectron spectroscopy measurements showed an increased SiC character for low disilane:acetylene mass-flow ratios.

P-type thin films of strontium–copper mixed oxide have been deposited by e-beam evaporation technique on glass and quartz substrates starting from SrCu 2 O 2 powders. A study of optical, electrical and structural properties was performed on the thin films, varying deposition parameters such as the substrate temperature and the oxygen partial pressure. For the first time, polycrystalline films of SrCu 2 O 2 were obtained using e-beam evaporation in O 2 atmosphere at relatively low temperature (350 °C) with transparency of over 60% in the visible light range and a high optical transmittance in near-infrared region. The optical band gap of thin film was estimated to be ∼3.12 eV. Seebeck and Hall effects measurements confirmed the p-type nature of semiconductors and conductivity as high as 5.3×10 −2 S/cm for non-intentionally doped materials was measured. Hole concentration and mobility at room temperature were 1.5×10 17 cm −3 and 2.2 cm 2 /Vs, respectively. X-Ray diffraction measurements revealed a polycrystalline structure of the films.

The growth of polycrystalline silicon on glass by laser-assisted chemical vapor deposition has been studied with the aim of identifying a light absorber layer for solar cells, with superior material quality compared to other technologies available for low-temperature substrates. One-dimensional calculations of the thermal wave produced by laser irradiation have been used to elucidate the complex interaction of the molten silicon surface layer with the substrate during the growth. The experiments show the relevant role played by the seed layer used as the growth initiator. The morphology of the laser-crystallized films has been analysed by scanning electron microscopy and X-ray diffraction. Polysilicon films, 2 μm thick, with a compact structure consisting of 1–2-μm grains that are almost monocrystalline, have been obtained.

Ni/Cu multilayers were grown by RF sputtering. The crystal orientation, the thickness of the elemental layers and the interface quality were analysed by X-ray diffraction in the θ –2 θ configuration. Magnetic anisotropy was investigated by both a static and a dynamic technique, namely magneto–optical Kerr effect (MOKE) and Brillouin light scattering (BLS). Longitudinal MOKE loops accounted for the in-plane orientation of the magnetization, while polar loops were used to determine the out-of-plane anisotropy fields, showing the existence of a minor second-order contribution in addition to the first-order one. BLS was then exploited to detect thermal excited spin waves through inelastic scattering of light. The out-of-plane anisotropy fields evaluated by this high-frequency dynamic technique compare well with the first-order values obtained by analysis of polar MOKE hysteresis cycles.

X-Ray diffraction and X-ray texture analysis have been carried out on RF magnetron sputtered ITO (indium tin oxide) thin films on glass substrates in order to understand their crystal growth behaviour. Films deposited at various deposition rates and gas compositions were subjected to investigation. X-Ray diffraction analysis revealed the polycrystalline structure of the films with a difference in crystallographic orientation without any change in the BCC (Body Centred Cubic) structure. Both the increase in deposition rate and gas composition reflects the change in crystallographic orientation. X-Ray texture analysis on the grown films revealed also a difference in film texturization following the change in crystallographic orientation. Strong orientation of crystallites perpendicular to the substrate were observed for films grown with (400) preferential plane.

Amorphous WO3 films have been deposited by E-beam evaporation technique at a substrate temperature of 80°C using different base pressure values. The best results have been obtained starting from a mild base pressure (1×10−5 Torr) probably due to the presence of water and oxidative atmosphere in the evaporation chamber. TEM investigations have shown that thermally evaporated WO3 films have an amorphous metastable structure, which subjected to energetic solicitations changes towards a nanocrystalline phase. The amorphous material subsequently annealed at a temperature of 500°C exhibits a fully crystalline structure. Also, in this case good electrochromic properties have been observed. Afterwards a WO3 double layer structure has been realised depositing an amorphous film upon a crystalline layer. The amorphous/crystalline structure properties have been compared with the amorphous and crystalline single layer ones. The colouration response and the transmittance asymptotic value during the bleaching phase have been better for the double layer.

Cu/Ni/Cu heterostructures have been in situ deposited on the 7×7 reconstructed Si(111) surface. A number of complementary techniques, such as in situ low-energy, medium-energy and Kikuchi electron diffraction and ex situ X-ray diffraction, were used in order to characterise the growth process and the structural properties of the films. It is found that the growth mode of metallic films is characterised by the presence of twinned islands induced by the 7×7 reconstruction of the Si(111) substrate. This work can stimulate further application of the metal–metal epitaxy on silicon to grow high quality ultrathin magnetic films to be integrated in microelectronic devices.

Polysilicon thin films have been obtained by Laser Induced Crystallization utilizing a Q-switched diode pumped, frequency-doubled Nd:YLF laser at 523-nm wavelength. Intrinsic and n-doped amorphous materials, of different thickness, have been deposited on Corning 1737 by LPCVD technique. The irradiation conditions have been varied in order to study their influence on crystallized material properties. Electrical and optical properties of as-deposited and crystallized films have been determined. Structural characterization has been performed to evaluate average grain size and distribution. Larger grain size has been observed in intrinsic materials compared to n-doped materials and the largest grain size (≈1 μm) has been obtained on materials having thickness of 50 nm. Critical role of doping in the crystallization process has been pointed out.

Amorphous and crystalline WO3 films show electrochromic properties by means of double injection of cations and electrons. At low substrate temperature thermal evaporation technique produces an amorphous material mixed to a nanocrystalline phase. When this material is annealed at temperatures higher than 400°C a fully crystalline structure is obtained. Different absorption mechanisms are responsible for colored amorphous and crystalline WO3 layers, small polaron transitions and Drude-like free electron scattering, respectively. Furthermore, both O/W ratio and crystalline structure affect electrochromic efficiency of a WO3 film. It has been confirmed that a hydrogen tungsten bronze structure appears when the material is colored. Finally, a self-bleaching process occurs when a colored WO3 film is exposed to an oxidative environment.

Epitaxial Cu/Fe/Cu trilayers with Fe film thickness between 4 and 110 A have been deposited on the 7×7 reconstructed surface of Si(111) single crystal. The structural and chemical characterization of Fe films was accomplished by in situ low energy electron diffraction, Kikuchi electron diffraction and Auger electron spectroscopy. As the Fe thickness exceeds about 6–8 A, a fcc–bcc phase transition occurs by the appearance of bcc(110) domains in the Kurdjumov–Sachs orientation. The structural transformation is also confirmed by ex situ X-ray diffraction experiments in the θ–2θ configuration. The evolution of the magnetic properties with the Fe film thickness has been studied by means of surface magneto-optic Kerr effect. Hysteresis loops measurements in the longitudinal configuration show a marked increase of the saturation signal which can be associated with the structural fcc–bcc phase transition of Fe.

We have studied the light degradation process of a-Si:H at different temperatures monitoring the defect density and the photoconductivity. Our data are not in complete agreement with the predictions of the two most widely accepted models (the recombination induced bond breaking model and the stretched exponential one). We show that our experiments can be well interpreted by a model in which the creation rate is proportional to the square of the photoconductivity and in which the annealing rate is computed considering a distribution of energy barriers and it is enhanced by the degradation light.