59 research outputs found
Enhancing Dye-Sensitized Solar Cell Performances by Molecular Engineering: Highly Efficient Ï-Extended Organic Sensitizers
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Bis(1,10-phenanthroline) copper complexes with tailored molecular architecture: from electrochemical features to application as redox mediators in dye-sensitized solar cells
In the last few years, copper coordination compounds turned out to be effective competitors of cobalt complexes as redox mediators in the formulation of iodine-free electrolytes for dye-sensitized solar cells (DSSCs). However, the lack of a clear correlation between electrochemical signatures of copper complexes (i.e. half-wave potential and heterogeneous electron transfer rate) and photoelectrochemical performance of solar devices makes difficult the optimization of their coordination sphere. Therefore, to partially fill this gap and to elucidate the intrinsic correlation between the molecular architecture of these complexes and their electrochemical features, we prepared four Cu+/2+redox couples in which the copper center is coordinated by two 1,10-phenanthrolines bearing various substituents in position 2. These complexes were well characterized, from both electrochemical and spectroscopic point of view, and tested as electron shuttles in lab-scale photoelectrochemical cells sensitized with two efficient \ucf\u80-extended benzothiadiazole dyes. It appeared that 2-aryl-1,10-phenanthrolines effectively combine suitable optical and electrochemical properties. While a fast electron transfer kinetics generally positively affects the dye regeneration process, an optimal balance between dye regeneration efficiency, mass transport and heterogeneous electron transfer at both the counter electrode and at the TiO2interface, must be achieved in order to optimize DSSC performance. Within our series, the top performer was [Cu(2-tolyl-1,10-phenanthroline)2]+/2+which achieved a relative 20% and 15% improvement in power conversion efficiency (under 100 mW s\ue2\u88\u921simulated AM 1.5G illumination) with respect to control cells filled with [Co(bpy)3]2+/3+(bpy = 2,2\ue2\u80\ub2-bipyridine) and I\ue2\u88\u92/I3\ue2\u88\u92electrolytes, respectively
In Situ Formation of Zwitterionic Ligands: Changing the Passivation Paradigms of CsPbBr3 Nanocrystals
CsPbBr3 nanocrystals (NCs) passivated by conventional lipophilic capping ligands suffer from colloidal and optical instability under ambient conditions, commonly due to the surface rearrangements induced by the polar solvents used for the NC purification steps. To avoid onerous postsynthetic approaches, ascertained as the only viable stability-improvement strategy, the surface passivation paradigms of as-prepared CsPbBr3 NCs should be revisited. In this work, the addition of an extra halide source (8-bromooctanoic acid) to the typical CsPbBr3 synthesis precursors and surfactants leads to the in situ formation of a zwitterionic ligand already before cesium injection. As a result, CsPbBr3 NCs become insoluble in nonpolar hexane, with which they can be washed and purified, and form stable colloidal solutions in a relatively polar medium (dichloromethane), even when longly exposed to ambient conditions. The improved NC stability stems from the effective bidentate adsorption of the zwitterionic ligand on the perovskite surfaces, as supported by theoretical investigations. Furthermore, the bidentate functionalization of the zwitterionic ligand enables the obtainment of blue-emitting perovskite NCs with high PLQYs by UV-irradiation in dichloromethane, functioning as the photoinduced chlorine source.publishedVersionPeer reviewe
Surface and optical properties of phase-pure silver iodobismuthate nanocrystals
The study of surface defects is one of the forefronts of halide perovskite research. In the nanoscale regime, where the surface-to-volume ratio is high, the surface plays a key role in determining the electronic properties of perovskites. Perovskite-inspired silver iodobismuthates are promising photovoltaic absorbers. Herein, we demonstrate the colloidal synthesis of phase pure and highly crystalline AgBiI4 nanocrystals (NCs). Surface-sensitive spectroscopic techniques reveal the rich surface features of the NCs that enable their impressive long-term environmental and thermal stabilities. Notably, the surface termination and its passivation effects on the electronic properties of AgBiI4 are investigated. Our atomistic simulations suggest that a bismuth iodide-rich surface, as in the case of AgBiI4 NCs, does not introduce surface trap states within the band gap region of AgBiI4, unlike a silver iodide-rich surface. These findings may encourage the investigation of surfaces of other lead-free perovskite-inspired materials.publishedVersionPeer reviewe
Chemical analysis of cesium lead-halide perovskite nanocrystals by total-reflection X-ray fluorescence spectroscopy
Cesium lead-halide perovskite nanocrystals are an emerging class of materials which potentially have different applications due to the several physical properties they exhibit. These properties are strongly dependent on the elemental composition of the nanocrystals and, to date, only few methods are available for their chemical analysis, such as scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX). The present work aims at establishing a new, fast and simple method for the elemental analysis of cesium lead-halide perovskite nanocrystals exploiting total-reflection x-ray fluorescence (TXRF) spectroscopy. The method was validated using a synthetized set of samples and comparing the TXRF results with SEM-EDX data. The sample preparation consisted in suspending the perovskites in 2.0 ml of hexane and sampling 10 ÎŒl of the suspension for deposition on a preheated quartz carrier. The element recovery ranged between 82% and 118% for mixed-halide perovskites, while for single halide perovskites it improved to 86%â105%. The present method can be implemented and used also for the elemental characterization of other types of perovskite nanocrystals
Impact of Precatalyst Activation on Suzuki-Miyaura Catalyst-Transfer Polymerizations: New Mechanistic Scenarios for Pre-transmetalation Events
The
relevance of L<sub>n</sub>PdX<sub>2</sub> precatalyst activation
on the Suzuki-Miyaura reaction course was investigated in the case
of catalyst-transfer polymerizations. A catalytic study, backed up
by theoretical calculations, allowed to ascertain the coexistence
of a neutral and an anionic mechanistic pathways in the precatalyst
activation, in which the bulky <sup><i>t</i></sup>Bu<sub>3</sub>P external ligand plays a crucial role. The fine-tuning of
the catalytic conditions can steer the activation step toward the
anionic pathway, leading to the full control over the polymerization
course. While providing insights and perspectives into the catalyst-transfer
polymerizations, these results uncover unexplored scenarios for the
pre-transmetalation events of Suzuki-Miyaura reactions contributing
to its full understanding
Molecular engineering of largely Ï-extended metal-free sensitizers containing benzothiadiazole units: Approaching 10% efficiency dye-sensitized solar cells using iodine-based electrolytes
none4Grisorio, Roberto; De Marco, Luisa; Giannuzzi, Roberto; Gigli, Giuseppe; Suranna, Gian PaoloGrisorio, Roberto; De Marco, Luisa; Giannuzzi, Roberto; Gigli, Giuseppe; Suranna, Gian Paol
Implementation of Sustainable Solvents in Green Polymerization Approaches
In modern polymer chemistry directed toward the synthesis of conjugated
materials, the synthetic routes devised to achieve the process sustainability
are based on CH bond activation. This prerequisite distinguishes
both the tandem SuzukiâHeck as well as the direct arylation polymerizations
(DArP); however, their compatibility with environmentally benign solvents
still represents a challenge. In this paper, the implementation of sustainable
solvents for the synthesis of poly(9,9-dioctylfluorenylene-vinylene) by using
the traditional Pd(AcO)2/P(o-Tol)3/NEt3 catalytic system is described. It is
assessed that selected green solvents (i.e., anisole and propylene carbonate)
constitute the ideal media for the tandem SuzukiâHeck polymerization.
Furthermore, by modulating medium polarity using mixtures of these green
solvents and changing the reaction temperature, a suitable compromise
between high molecular weights and regioregularity of the resulting polymers
is reached. Conversely, the presence of propylene carbonate is deleterious
for the DArP of 2-bromo-3-hexylthiophene, while it is found that catalyst
performances in anisole strictly depend on the palladium source used. The
best conditions are obtained using PdCl2(PPh3)2 as the precatalyst, affording
a highly regioregular (93%) poly(3-hexylthiophene) in quantitative yields and
high molecular weights (26.7 kg molâ1)
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