Maria Grazia Lobello

Engineering of thiocyanate-free Ru(II) sensitizers for high efficiency dye-sensitized solar cells

We synthesized a series of Ru(II) metal complexes TFRS-1, -2, -4, -21, -22 and -24 with a single 4,4′-dicarboxylic acid-2,2′-bipyridine together with two functionalized pyridyl azolate ancillary ligands consisting of pyrazolate or triazolate groups. Both photophysical measurements and DFT/TDDFT calculations were conducted to gain insight into their electronic and optical properties. The triazolate series of sensitizers TFRS-21, -22 and -24 showed an enlarged optical band gap with respect to their pyrazolate counterparts TFRS-1, -2 and -4. When employed in dye sensitized solar cells (DSCs), the triazolate sensitizers show slightly inferior JSC values due to the poor incident photon-to-current conversion efficiencies recorded compared to the pyrazolate series. Moreover, the endowed 5-(hexylthio)thiophen-2-yl substituents exert a notable hyperchromic effect and bathochromic shift in the absorption spectra, which then improves the short circuit current JSC to 18.7 and 15.5 mA cm−2 and the overall conversion efficiency to η = 10.2% and 8.25% for TFRS-4 and TFRS-24, respectively. For the evaluation of VOC, transient photocurrent and photovoltage decay measurements were carried out to compare the rates of interfacial recombination of electrons from the TiO2 conduction band to electrolyte.

Thiocyanate-Free Ruthenium(II) Sensitizer with a Pyrid-2-yltetrazolate Ligand for Dye-Sensitized Solar Cells

The synthesis of the new complex [Ru(Tetrazpy)(dcbpy)2]Cl is reported, along with its spectroscopical, electrochemical, and theoretical characterization. The first dye-sensitized solar cell device with this complex has been prepared, leading to a 3% of conversion efficiency, promising data considering the simplicity of the Tetrazpy ligand.

A Simple Synthetic Route to Obtain Pure Trans‐Ruthenium(II) Complexes for Dye‐Sensitized Solar Cell Applications

We report a facile synthetic route to obtain functionalized quaterpyridine ligand and its trans-dithiocyanato ruthenium complex, based on a microwave-assisted procedure. The ruthenium complex has been purified using a silica chromatographic column by protecting carboxylic acid groups as iso-butyl ester, which are subsequently hydrolyzed. The highly pure complex exhibits panchromatic response throughout the visible region. DFT/time-dependent DFT calculations have been performed on the ruthenium complex in solution and adsorbed onto TiO2 to analyze relative electronic and optical properties. The ruthenium complex endowed with the functionalized quaterpyridine ligand was used as a sensitizer in dye-sensitized solar cell yielding a short-circuit photocurrent density of more than 19 mA cm(-2) with a broad incident photon to current conversion efficiency spectra ranging from 400 to 900 nm, exceeding 80 % at 700 nm.

Tuning the Dipolar Second‐Order Nonlinear Optical Properties of Cyclometalated Platinum(II) Complexes with Tridentate N^C^N Binding Ligands

Appropriate functionalization of the cyclometalated ligand, L, and the choice of the ancillary ligand, X, allows the dipolar second-order nonlinear optical response of luminescent [PtLX] complexes--in which L is an N^C^N-coordinated 1,3-di(2-pyridyl)benzene ligand and X is a monodentate halide or acetylide ligand--to be controlled. The complementary use of electric-field-induced second-harmonic (EFISH) generation and harmonic light scattering (HLS) measurements demonstrates how the quadratic hyperpolarizability of this appealing family of multifunctional chromophores, characterized by a good transparency throughout much of the visible region, is dominated by an octupolar contribution.

An Integrated Experimental and Theoretical Approach to the Spectroscopy of Organic‐Dye‐Sensitized TiO2 Heterointerfaces: Disentangling the Effects of Aggregation, Solvation, and Surface Protonation

We report a joint experimental and computational study into the spectroscopic properties of a prototypical D5 organic dye, both in solution and adsorbed on a TiO2 surface, with the aim of modeling and quantifying the UV/Vis spectral shifts that occur in the different explored environments. Going from the dye in solution to dye-sensitized TiO2, various factors may shift the position of the UV/Vis absorption maximum, both towards longer and shorter wavelengths. Here we have focused on the effect of dye aggregation on TiO2, surface protonation, and solvent effects. The D5 dye forms stable aggregates on the TiO2 surface that cause spectral blueshifts. We used different sensitization conditions to vary the dye loading and thus the extent of dye aggregation. For each sensitization condition, we explored protonated and native TiO2 films. Computational modeling of different dimeric aggregates with increasing intermolecular interactions and simulation of the associated optical responses also confirm the observed spectral blueshifts. Our results show that both the presence of surface protons and solvent stabilize the excited state of the adsorbed dye molecules, which causes a marked redshift in the absorption maximum and thus moves in the opposite direction to the shift due to the increase in the surface coverage.