Michele Manca

Durable Superhydrophobic and Antireflective Surfaces by Trimethylsilanized Silica Nanoparticles-Based Sol−Gel Processing

We present a robust and cost-effective coating method to fabricate long-term durable superhydrophobic andsimultaneouslyantireflective surfaces by a double-layer coating comprising trimethylsiloxane (TMS) surface-functionalized silica nanoparticles partially embedded into an organosilica binder matrix produced through a sol-gel process. A dense and homogeneous organosilica gel layer was first coated onto a glass substrate, and then, a trimethylsilanized nanospheres-based superhydrophobic layer was deposited onto it. After thermal curing, the two layers turned into a monolithic film, and the hydrophobic nanoparticles were permanently fixed to the glass substrate. Such treated surfaces showed a tremendous water repellency (contact angle = 168 degrees ) and stable self-cleaning effect during 2000 h of outdoor exposure. Besides this, nanotextured topology generated by the self-assembled nanoparticles-based top layer produced a fair antireflection effect consisting of more than a 3% increase in optical transmittance.

Superhydrophobicity Due to the Hierarchical Scale Roughness of PDMS Surfaces

Wettability control has been widely investigated in the last decades for technological applications such as microfluidic devices and self-cleaning surfaces by modifying both the chemical composition and the geometric structure of the surfaces. Inspired by the typical morphology of superhydrophobic leaves (such as lotus leaves), we have developed a dual-scale roughness, micro- and nanosized, on polydimethylsiloxane (PDMS) surfaces. By combining different geometric parameters and plasma treatment conditions, the structures were controlled hierarchically, at different independent length scales. Both the microsized replicated pillars and the nanosized etched posts tuned the wettability of the PDMS surfaces in a very simple way, up to contact angles of 170 degrees . Furthermore, changes in the influence of micro- and nanoscale geometrical structures were investigated. Hysteresis and contact angles of water droplets are evaluated as a combined effect of micropillars and a superimposed roughness, resulting in high advancing contact angles and low sliding angles.

Hyperbranched Anatase TiO2 Nanocrystals: Nonaqueous Synthesis, Growth Mechanism, and Exploitation in Dye-Sensitized Solar Cells

A colloidal crystal-splitting growth regime has been accessed, in which TiO(2) nanocrystals, selectively trapped in the metastable anatase phase, can evolve to anisotropic shapes with tunable hyperbranched topologies over a broad size interval. The synthetic strategy relies on a nonaqueous sol-gel route involving programmed activation of aminolysis and pyrolysis of titanium carboxylate complexes in hot surfactant media via a simple multi-injection reactant delivery technique. Detailed investigations indicate that the branched objects initially formed upon the aminolysis reaction possess a strained monocrystalline skeleton, while their corresponding larger derivatives grown in the subsequent pyrolysis stage accommodate additional arms crystallographically decoupled from the lattice underneath. The complex evolution of the nanoarchitectures is rationalized within the frame of complementary mechanistic arguments. Thermodynamic pathways, determined by the shape-directing effect of the anatase structure and free-energy changes accompanying branching and anisotropic development, are considered to interplay with kinetic processes, related to diffusion-limited, spatially inhomogeneous monomer fluxes, lattice symmetry breaking at transient Ti(5)O(5) domains, and surfactant-induced stabilization. Finally, as a proof of functionality, the fabrication of dye-sensitized solar cells based on thin-film photoelectrodes that incorporate networked branched nanocrystals with intact crystal structure and geometric features is demonstrated. An energy conversion efficiency of 6.2% has been achieved with standard device configuration, which significantly overcomes the best performance ever approached with previously documented prototypes of split TiO(2) nanostructures. Analysis of the relevant photovoltaic parameters reveals that the utilized branched building blocks indeed offer light-harvesting and charge-collecting properties that can overwhelm detrimental electron losses due to recombination and trapping events.

Influence of Chemistry and Topology Effects on Superhydrophobic CF4-Plasma-Treated Poly(dimethylsiloxane) (PDMS)

Superhydrophobic surfaces are gaining considerable interest in a lot of different applications, and nonetheless, precise control over the wettability properties of such surfaces is still a challenge due to difficulties when controlling the effects independently induced on superhydrophobicity by the chemical and topological surface characteristics. We have fabricated engineered superhydrophobic surfaces onto poly(dimethylsiloxane) (PDMS) substrates by means of suitable CF4-plasma treatments. These treatments allowed the modification of both the morphological properties of the PDMS surface, due to a preferential etching of certain components of its macromolecules, and the chemical ones, by the deposition of a fluorinated layer. Chemical effects were separated from topological ones by performing a double replica molding process of the CF4-plasma-treated surfaces. This allowed us to obtain positive copies of the structured surfaces without the overlaying fluorinated coating affecting the surface chemistry. Such replicated surfaces showed a decrease of the contact angle if compared to the treated ones and therefore evidenced chemistrys weight in superhydrophobicity effects. In particular, we found that, for highly dense columnar-like PDMS microstructures, the effect of the plasma-deposited fluorinated layer covering surfaces produces an enhancement of the contact angle of about 20 degrees .

Ultrathin TiO2(B) Nanorods with Superior Lithium-Ion Storage Performance

The peculiar architecture of a novel class of anisotropic TiO2(B) nanocrystals, which were synthesized by an surfactant-assisted nonaqueous sol-gel route, was profitably exploited to fabricate highly efficient mesoporous electrodes for Li storage. These electrodes are composed of a continuous spongy network of interconnected nanoscale units with a rod-shaped profile that terminates into one or two bulgelike or branch-shaped apexes spanning areas of about 5 × 10 nm(2). This architecture transcribes into a superior cycling performance (a charge capacitance of 222 mAh g(-1) was achieved by a carbon-free TiO2(B)-nanorods-based electrode vs 110 mAh g(-1) exhibited by a comparable TiO2-anatase electrode) and good chemical stability (more than 90% of the initial capacity remains after 100 charging/discharging cycles). Their outstanding lithiation/delithiation capabilities were also exploited to fabricate electrochromic devices that revealed an excellent coloration efficiency (130 cm(2) C(-1) at 800 nm) upon the application of 1.5 V as well as an extremely fast electrochromic switching (coloration time ∼5 s).

Surfactant-free synthesis of pure anatase TiO2 nanorods suitable for dye-sensitized solar cells

A non-aqueous, solvothermal method was applied to the synthesis of TiO2 nanorods in pure anatase crystal phase using Ti(IV)-isopropoxide. The use of benzyl alcohol as both solvent and reactant was investigated in combination with the addition of acetic acid to the reaction mixture. Various values of the AcOH : Ti(OiPr)4 molar ratio were realized in the synthesis and tested in order to obtain a significant dimensional and morphological control over the resulting TiO2 nanostructures, as well as to devise a simple and scalable synthetic protocol. On the basis of the experimental results, a substantially modified version of the well-established “benzyl alcohol route” was then designed and developed. X-ray diffractometry and transmission electron microscopy revealed that monodisperse anatase nanorods having a length of about 13–17 nm and a diameter of 5 nm can be obtained when AcOH and Ti(OiPr)4 are reacted in comparable proportions. Investigation of the characteristic parameters of dye-sensitized solar cells fabricated using the synthesized nanorods as photoanode revealed a power conversion efficiency of about 7.5% corresponding to an improvement of 28% with respect to a commercial spheroidal nanotitania (P25) based reference device.

NiO/MAPbI3-xClx/PCBM: A Model Case for an Improved Understanding of Inverted Mesoscopic Solar Cells

A spectroscopic investigation focusing on the charge generation and transport in inverted p-type perovskite-based mesoscopic (Ms) solar cells is provided in this report. Nanocrystalline nickel oxide and PCBM are employed respectively as hole transporting scaffold and hole blocking layer to sandwich a perovskite light harvester. An efficient hole transfer process from perovskite to nickel oxide is assessed, through time-resolved photoluminescence and photoinduced absorption analyses, for both the employed absorbing species, namely MAPbI3-xClx and MAPbI3. A striking relevant difference between p-type and n-type perovskite-based solar cells emerges from the study.

Flexible Carbon Nanotube-Based Composite Plates As Efficient Monolithic Counter Electrodes for Dye Solar Cells

We demonstrate a general approach to fabricate a novel low-cost, lightweight and flexible nanocomposite foil that can be effectively implemented as a monolithic counter-electrode in dye solar cells. The pivotal aim of this work was to replace not only the platinum catalyzer film, but even the underlying transparent conductive oxide-coated substrate, by means of a monolithic counter electrode based on carbonaceous materials. According to our approach, a proper dispersion of multiwalled carbon nanotubes (MWCNTs) has been added to a dilute polypropylene solution in toluene. The composite solution has been then adequately mixed and subsequently dried by means of a controlled solvent evaporation process; the resulting powder has been modeled by compression molding into thin plates. Four different series of plates have been realized by tuning the carbon nanotubes concentration from 5 wt % to 20 wt %. Finally, a specifically setup reactive ion etching treatment with oxygen plasma has been carried out onto the plate surface to remove the residual polymeric capping layer and allow the embedded CNTs to protrude on top of the surface. A fine-tuning of the morphological features has been made possible by adjusting the plasma etching conditions. For all the treated surfaces, the most meaningful electrochemical parameters have been quantitatively analyzed by means of both electrochemical impedance spectroscopy and cyclic voltammetry measurements. An as high as 13.8 mA/cm(2) photocurrent density, along with a solar conversion efficiency of 6.67%, has been measured for a dye solar cell mounting a counter-electrode based on a 20 wt % CNT nanocomposite.

Shape-tailored TiO2 nanocrystals with synergic peculiarities as building blocks for highly efficient multi-stack dye solar cells

An engineered photoelectrode for dye solar cells has been developed through the combination of three mesoporous stacks made of shape-tailored TiO2 anatase nanocrystals, which have been ad hoc synthesized by suitable colloidal routes. Optimization of light harvesting and charge collection efficiency allowed us to obtain a high power conversion efficiency of 10.26%.

Highly efficient smart photovoltachromic devices with tailored electrolyte composition

Driven by the tremendous opportunities offered by dye solar cells technology in terms of building integration, a new generation of smart multifunctional photoelectrochemical cells has the potential to attract the interest of a rapidly growing number of research institutions and industrial companies. Photovoltachromic devices are capable to produce a smart modulation of the optical transmittance and, at the same time, to generate electrical power by means of solar energy conversion. In this work, a specifically designed bifunctional counterelectrode has been realized by depositing a C-shaped platinum frame which bounds a square region occupied by a tungsten oxide (WO3) film onto a transparent conductive substrate. These two regions have been electrically separated to make possible distinct operations on one or both of the available circuits. Such an unconventional counterelectrode makes it possible to achieve a twofold outcome: a smart and fast-responsive control of the optical transmittance and a relatively high photovoltaic conversion efficiency. In particular we investigated the effect of the electrolyte composition on both photoelectrochromic and photovoltaic performances of such devices by systematically tuning the iodide content in the electrolyte. The best result was obtained by filling the cell with an iodine concentration of 0.005 M: a coloration efficiency of 61.10 cm2C−1 at a wavelength of 780 nm and, at the same time, a photovoltaic conversion efficiency of 6.55% have been reported.