Luisa De Marco

Italian Institute of Technology (IIT) , Genova, Liguria, Italy

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Publications (25)125.11 Total impact

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    ABSTRACT: This study deals with the synthesis and characterization of two π-extended organic sensitizers (G1 and G2) for applications in dye-sensitized solar cells. The materials are designed with a D–A–π–A structure constituted by i) a triarylamine group as the donor part, ii) a dithienyl-benzothiadiazole chromophore followed by iii) a further ethynylene-thiophene (G1) or ethynylene-benzene (G2) π-spacer and iv) a cyano-acrylic moiety as acceptor and anchoring part. An unusual structural extension of the π-bridge characterizes these structures. The so-configured sensitizers exhibit a broad absorption profile, the origin of which is supported by density functional theory. The absence of hypsochromic shifts as a consequence of deprotonation as well as notable optical and electrochemical stabilities are also observed. Concerning the performances in devices, electrochemical impedance spectroscopy indicates that the structural modification of the π-spacer mainly increases the electron lifetime of G2 with respect to G1. In devices, this feature translates into a superior power conversion efficiency of G2, reaching 8.1 %. These results are comparable to those recorded for N719 and are higher with respect to literature congeners, supporting further structural engineering of the π-bridge extension in the search for better performing π-extended organic sensitizers.
    ChemSusChem 07/2014; · 7.48 Impact Factor
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    ABSTRACT: Novel co-sensitizers have been structurally tailored and implemented in multi-sensitized devices demonstrating synergic efficiency enhancement attributable to improved light-harvesting as well as prevention of charge recombination.
    Chemical Communications 06/2014; · 6.38 Impact Factor
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    ABSTRACT: An explorative dye solar cell architecture based on the implementation of a 3D micro-patterned photoelectrode is disclosed here. An array of conical micro-pillars has been realized by laser micromachining of photosensitive glass which has been advantageously used as a substrate for deposition of a thin transparent conductive layer and a thick mesoporous TiO2 electrode. A significantly higher photocurrent density has been detected as an effect of the extended overall absorbing area of the micro-patterned photoelectrode with respect to a conventional 2D reference photoelectrode. This enhancement can also be partially imputable to a not negligible “waveguide effect” occurring within the glass micropillars.
    The Journal of Physical Chemistry C 05/2014; · 4.81 Impact Factor
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    ABSTRACT: We implemented a low-temperature approach to fabricate efficient photoanodes for Dye Sensitized Solar Cells which combines three different nano-architectures, namely a highly conductive and highly transparent AZO film, a thin TiO2-blocking layer and a mesoporous TiO2 nanorods-based working electrode. All the components were processed at T≤200°C. Both the AZO and TiO2 compact layers were deposited by reactive sputtering, whereas the TiO2 nanorods were synthesized by surfactant-assisted wet-chemical routes and processed into photoelectrodes in which the native geometric features assured uniform mesoporous structure with effective nanocrystal interconnectivity suitable to maximize light harvesting and electron diffusion. Due to the optimised structure of the TiO2-blocking/AZO bilayer as well as to the good adhesion of the TiO2 nanorods over it, a significant enhancement of the charge recombination resistance was demonstrated, this laying on the basis of the outstanding power conversion efficiency achievable through the use of this photoanode's architecture: a value of 4.6% (N719) was achieved with a 4m-thick electrode processed at T=200°C. This value noticeably overcomes the current literature limit got on AZO-based cells (N719) which instead use Nb-doped and thicker blocking layers, and thicker nanostructured photoanodes which have been even sintered at higher temperatures (450-500°C).
    ACS Applied Materials & Interfaces 04/2014; · 5.01 Impact Factor
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    ABSTRACT: A photovoltachromic window can potentially act as a smart glass skin which generates electric energy as a common dye-sensitized solar cell and, at the same time, controls the incoming energy flux by reacting to even small modifications in the solar radiation intensity. We here report the successful implementation of a novel architecture of a photovoltachromic cell based on an engineered bi-functional counter electrode consisting of two physically separated platinum and tungsten oxide regions, which are arranged to form complementary comb-like patterns. Solar light is partially harvested by a dye-sensitized photoelectrode made on the front glass of the cell which fully overlaps a bi-functional counter electrode made on the back glass. When the cell is illuminated, the photovoltage drives electrons into the electrochromic stripes through the photoelectrochromic circuit and promotes the Li+ diffusion towards the WO3 film, which thus turns in its colored state: a photo-coloration efficiency of 17 cm2*min-1*W-1 at a wavelength of 650 nm under 1.0 sun was reported along with fast (coloration time < 2 sec and bleaching time < 5 sec) response. A fairly efficient photovoltaic functionality was also retained due to the co-presence of the independently switchable micro-patterned Platinum electrode.
    ACS Applied Materials & Interfaces 01/2014; · 5.01 Impact Factor
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    ABSTRACT: The peculiar architecture of a novel class of anisotropic TiO2(B) nanocrystals -which have been synthesized by an optimized surfactant-assisted nonaqueous sol-gel route- has been 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 rod-shaped profile which terminates into one or two bulge-like or branch-shaped apexes spanning areas of about 5 nm x 10 nm. This architecture transcribes into a superior cycling performance (a charge capacitance of 222 mAhg-1 was achieved by a carbon-free TiO2(B)-nanorods-based electrode versus 110 mAhg-1 exhibited by a comparable TiO2-anatase electrode) and good chemical stability (more than 90% of the initial capacity is kept after 100 charging/discharging cycles). Their outstanding lithiation/delithiation prerogatives have also been exploited to fabricate electrochromic devices which reveal an excellent coloration efficiency (130 cm2/C at 800 nm) upon the application of 1.5 V as well as an extremely fast electrochromic switching (coloration time ~ 5s).
    ACS Applied Materials & Interfaces 01/2014; · 5.01 Impact Factor
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    ABSTRACT: We have investigated the spectroscopic behavior of three different sensitizers adsorbed onto titania thin films in order to gain information both on the electron transfer process from dye to titania and on the anchorage of the chromophore onto the semiconductor. We have examined by UV-Vis and fluorescence spectroscopy the widely used ruthenium complex cis-di(thiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)ruthenium(II) (N719), the more recently developed organic molecular 3-(5-(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D5), and a push-pull zinc phthalocyanine sensitizer (ZnPc). Three type of titania films with different morphology, characterized by SEM and FT-IR measurement, were considered: a mesoporous transparent film deposited by spin-coating (TiMS), a semiopaque film deposited by doctor-blade from mesoporous titania (TiMS_DB) and a semiopaque film deposited by doctor-blade form commercial P25 titania (P25_DB). The use of TiMS is responsible for the adsorption of a higher amount of dye since the mesoporous structure allows increasing the interfacial area between dye and titania. Moreover, the fluorescence emission peak is weaker when the sensitizers are adsorbed onto TiMS. These findings suggest that mesostructured films could be considered the most promising substrates to realize photoanodes with a fast electron transfer process.
    International Journal of Photoenergy 10/2013; 2013. · 2.66 Impact Factor
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    ABSTRACT: An engineered bi-layered photoelectrode for dye solar cells has been developed which profitably employs two synergistic meso-ordered components, namely a thin meso-ordered TiO2 film and a main microparticles-based photoelectrode. The former has been deposited as an interfacial layer at the FTO-coated substrate and suppresses the back-transport reaction by blocking direct contact between the electrolyte and conductive oxide. The latter is made of hierarchical micro- and nano-structured building blocks prepared by template synthesis, which permits efficient light scattering without sacrificing the internal surface area. The optimization of light harvesting and charge recombination dynamics allowed us to achieve as high energy conversion efficiency as 9.7%.
    Physical Chemistry Chemical Physics 09/2013; · 3.83 Impact Factor
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    ABSTRACT: This study deals with the synthesis and characterization of two new di-anchoring dyes for applications in dye-sensitized solar cells. The materials were designed with a branched D(-π-A)2 structure containing (i) a rigid alkyl-functionalized carbazole core as the donor part, (ii) one (DYE1) or two (DYE2) thiophene units as the π-bridge and (iii) a cyano-acrylic moiety as acceptor and anchoring part. Electrochemical impedance spectroscopy indicated that the injected electron lifetime is higher in the case of DYE2, probably due to the length of the π-spacer that, in combination with the alkyl chain on the carbazole unit, hampers the charge recombination with the electrolyte. Stability tests on TiO2-sensitized films revealed that the di-anchoring remarkably slows down the desorption process, which conversely is evident for classic reference dyes. The highest power conversion efficiency reaches 5.01% in the case of DYE2 with a photovoltage of 0.70 V and a photocurrent of 10.52 mA cm−2, substantially deriving from a broader absorption with respect to DYE1, as also confirmed by IPCE measurements. These results support the efforts aimed at the structural engineering of D(-π-A)2 dyes to design new, more efficient and stable organic sensitizers.
    Dyes and Pigments 08/2013; 98(2):221–231. · 3.53 Impact Factor
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    ABSTRACT: 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%.
    Energy & Environmental Science 05/2013; 6(6):1791-1795. · 11.65 Impact Factor
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    ABSTRACT: Three families of linear shaped TiO2 anatase nanocrystals with variable aspect ratio (4, 8, 16) and two sets of branched TiO2 anatase nanocrystals (in the form of open-framework sheaf-like nanorods and compact braid-like nanorod bundles, respectively) were employed to fabricate high-quality mesoporous photoelectrodes and then implemented into dye-sensitized solar cells to elucidate the intrinsic correlation holding between the photovoltaic performances and the structure of the nanocrystal building blocks. To this aim, the chemical capacitance and the charge-transfer resistance of the photoelectrodes were extrapolated from electrochemical impedance spectroscopy measurements and used to draw a quantitative energy diagram of the dye-sensitized solar cells realized, on the basis of which their photovoltaic performances have been discussed. It has thus been revealed that photoanodes made from braid-like branched-nanorod bundles exhibited the most favorable conditions to minimize recombination at the interface with the electrolyte due to their deep distribution of trap states, whereas linear-shaped nanorods with higher aspect-ratios result in more remarkable downshift of the conduction band edge.
    The Journal of Physical Chemistry C 01/2013; 117(6):2574–2583. · 4.81 Impact Factor
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    ABSTRACT: Novel triphenylamine (TPA)-based organic dyes were synthesized and assessed for their performance in dye-sensitized solar cells (DSSCs). In the dyes considered the TPA group and the cyanoacetic acid have the role of electron-donor and -acceptor, respectively, whereas a thienyl–fluoro-phenyl-substituted was introduced as π-linker to improve the dye performance in DSSCs. Experimental characterizations empasize that the presence of electron withdrawing substituents in the linker close to the electron-acceptor moiety leads to a more efficient intramolecular photoinduced charge transfer. In fact, photovoltaic experiments reveal that the DSSCs based on the thienyl–o-fluoro-phenyl substituted dyes yield a better solar-energy-to-electricity conversion efficiency.
    Journal of Materials Chemistry A. 01/2013; 1:11909.
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    ABSTRACT: Four different species of ionically conductive polymers were synthesized and successfully implemented to formulate novel quasi-solid electrolytes for dye solar cells. A power conversion efficiency superior to 85% of the correspondent liquid electrolyte as well as an excellent cell's stability was demonstrated after 500 days of storage.
    Chemical Communications 02/2012; 48(25):3109-11. · 6.38 Impact Factor
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    ABSTRACT: We report on a novel approach to integrate colloidal anatase TiO(2) nanorods as key functional components into polymer bulk heterojunction (BHJ) photovoltaic devices by means of mild, all-solution-based processing techniques. The successful integration of colloidal nanoparticles in organic solar cells relies on the ability to remove the long chain insulating ligands, which indeed severely reduces the charge transport. To this aim we have exploited the concomitant mechanisms of UV-light-driven photocatalytic removal of adsorbed capping ligands and hydrophilicization of TiO(2) surfaces in both solid-state and liquid-phase conditions. We have demonstrated the successful integration of the UV-irradiated films and colloidal solutions of TiO(2) nanorods in inverted and conventional solar cell geometries, respectively. The inverted devices show a power conversion efficiency of 2.3% that is a ca. three times improvement over their corresponding cell counterparts incorporating untreated TiO(2), demonstrating the excellent electron-collecting property of the UV-irradiated TiO(2) films. The integration of UV-treated TiO(2) solutions in conventional devices results in doubled power conversion efficiency for the thinner active layer and in maximum power conversion efficiency of 2.8% for 110 nm thick devices. In addition, we have demonstrated, with the support of device characterizations and optical simulations, that the TiO(2) nanocrystal buffer layer acts both as electron-transporting/hole-blocking material and optical spacer.
    Physical Chemistry Chemical Physics 02/2012; 14(11):3987-95. · 3.83 Impact Factor
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    ABSTRACT: The following values have no corresponding Zotero field: PB - WILEY-VCH Verlag
    Berichte der deutschen chemischen Gesellschaft 01/2012; · 2.94 Impact Factor
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    ABSTRACT: 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.
    Journal of the American Chemical Society 11/2011; 133(47):19216-39. · 10.68 Impact Factor
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    ABSTRACT: 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.
    ACS Applied Materials & Interfaces 08/2011; 3(9):3625-32. · 5.01 Impact Factor
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    ABSTRACT: We demonstrate a general approach by which colloidal anatase TiO2nanocrystals with anisotropically tailored linear and branched shapes can safely be processed into high-quality mesoporous photoelectrodes for dye-sensitized solar cells (DSSCs). A detailed study has been carried out to elucidate how the nanoscale architecture underlying the photoelectrodes impacts their ultimate performances. From the analysis of the most relevant electrochemical parameters, an intrinsic correlation between the photovoltaic performances and the structure of the nanocrystal building blocks has been deduced and explained on the basis of relative contributions of the electron transport and light-harvesting properties of the photoelectrodes. Depending on the nanocrystals incorporated, these devices can exhibit an energy conversion efficiency of 5.2% to 7.8%, which ranks 38% to 53% higher than that achievable with corresponding cells based on reference spherical nanoparticles. It has been ascertained that DSSCs based on high aspect-ratio linear nanorods allow for a remarkable improvement in the charge-collection efficiency due to minimization of detrimental charge-recombination processes at the photoelectrode/electrolyte interface. On the other hand, DSSCs fabricated from branched nanocrystals with a peculiar bundle-like configuration are characterized by a drastic reduction of undesired charge-trapping phenomena. These findings can be useful in the design and fabrication of future generations of high-performing DSSCs based on colloidal nanocrystals with properly engineered size and shape parameters.
    Journal of Materials Chemistry 08/2011; 21(35):13371-13379. · 5.97 Impact Factor
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    ABSTRACT: Extremely lightweight plates made of an engineered PMMA-based composite material loaded with hollow glass micro-sized spheres, nano-sized silica particles and aluminum hydroxide prismatic micro-flakes were realized by cast molding. Their interesting bulk mechanical properties were combined to properly tailored surface topography compatible with the achievement of a superhydrophobic behavior after the deposition of a specifically designed hydrophobic coating. With this aim, we synthesized two different species of fluoromethacrylic polymers functionalized with methoxysilane anchoring groups to be covalently grafted onto the surface protruding inorganic fillers. By modulating the feed composition of the reacting monomers, it was possible to combine the hydrophobic character of the polymer with an high adhesion strength to the substrate and hence to maximize both the water contact angle (up to 157°) and the durability of the easy-to-clean effect (up to 2000 h long outdoor exposure).
    Journal of Colloid and Interface Science 08/2011; 363(2):668-75. · 3.17 Impact Factor
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    ABSTRACT: 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 cm2 C−1 at a wavelength of 780 nm and, at the same time, a photovoltaic conversion efficiency of 6.55% have been reported.
    Energy & Environmental Science 07/2011; 4(7):2567-2574. · 11.65 Impact Factor