Molecularly Engineered Ru(II) Sensitizers Compatible with Cobalt(II/III) Redox Mediators for Dye-Sensitized Solar Cells.

Thiocyanate-free isoquinazolylpyrazolate Ru(II) complexes were synthesized and applied as sensitizers in dye-sensitized solar cells (DSCs). Unlike most other successful Ru sensitizers, Co-based electrolytes were used, and resulting record efficiency of 9.53% was obtained under simulated sunlight with an intensity of 100 mW cm(-2).

Thiocyanate-free ruthenium(II) sensitizers for dye-sensitized solar cells based on the cobalt redox couple.

Two thiocyanate-free ruthenium(II) sensitizers, TFRS-41 and TFRS-42, with distinctive dialkoxyphenyl thienyl substituents were successfully prepared and tested for potential applications in making dye-sensitized solar cells (DSCs). Subsequent device fabrication was conducted by using a [Co(bpy)3 ](2+/3+) -based (bpy=2,2'-bipyridine) electrolyte, for which the best performance data, namely, JSC =13.11 mA cm(-2) , VOC =862 mV, fill factor=0.

A robust organic dye for dye sensitized solar cells based on iodine/iodide electrolytes combining high efficiency and outstanding stability.

Among the new photovoltaic technologies, the Dye-Sensitized Solar Cell (DSC) is becoming a realistic approach towards energy markets such as BIPV (Building Integrated PhotoVoltaics). In order to improve the performances of DSCs and to increase their commercial attractiveness, cheap, colourful, stable and highly efficient ruthenium-free dyes must be developed. Here we report the synthesis and complete characterization of a new purely organic sensitizer (RK1) that can be prepared and synthetically upscaled rapidly.

Highly efficient dye-sensitized solar cells based on panchromatic ruthenium sensitizers with quinolinylbipyridine anchors.

Panchromatic Ru(II) sensitizers TF-30-TF-33 bearing a new class of 6-quinolin-8-yl-2,2'-bipyridine anchor were synthesized and tested under AM1.5 G simulated solar irradiation. Their increased π conjugation relative to that of the traditional 2,2':6',2''-terpyridine-based anchor led to a remarkable improvement in absorptivity across the whole UV-Vis-NIR spectral regime.

Synergistic effect of ZnS outer layers and electrolyte methanol content on efficiency in TiO2/CdS/CdSe sensitized solar cells.

The effect of methanol content in water based polysulfide electrolytes in TiO(2)/CdS/CdSe quantum dot sensitized solar cells (QDSSCs) prepared by the SILAR method was studied. In addition, the effect of coating the mesoporous QD sensitized films with ZnS outer layers was investigated. Charge recombination reactions were measured using time resolved spectroscopic measurements.

Study of interface properties in CuPc based hybrid inorganic-organic solar cells.

Metal-substituted phthalocyanine thin films such as copper-phthalocyanine (CuPc) are often used as photo-active and hole transporting layers (HTLs) in fully organic photovoltaic devices. In this work, CuPc is vacuum sublimated on an electron acceptor layer of mesoporous titania (TiO(2)) for the formation of hybrid TiO(2):CuPc solar cell devices. The performance of these hybrid solar cell devices was demonstrated without and with dye sensitization at the TiO(2):CuPc interface.

Tailoring the interface using thiophene small molecules in TiO2/P3HT hybrid solar cells.

In this paper we focus on the effect of carboxylated thiophene small molecules as interface modifiers in TiO(2)/P3HT hybrid solar cells. Our results show that small differences in the chemical structure of these molecules, for example, the presence of the -CH(2)- group in the 2-thiopheneacetic acid (TAA), can greatly increase the TiO(2) surface wettability, improving the TiO(2)/polymer contact. This effect is important to enhance exciton splitting and charge separation.

Dye molecular structure device open-circuit voltage correlation in Ru(II) sensitizers with heteroleptic tridentate chelates for dye-sensitized solar cells.

Dicarboxyterpyridine chelates with π-conjugated pendant groups attached at the 5- or 6-position of the terminal pyridyl unit were synthesized. Together with 2,6-bis(5-pyrazolyl)pyridine, these were used successfully to prepare a series of novel heteroleptic, bis-tridentate Ru(II) sensitizers, denoted as TF-11-14. These dyes show excellent performance in dye-sensitized solar cells (DSCs) under AM1.

Sensitizer molecular structure-device efficiency relationship in dye sensitized solar cells.

In the Dye Sensitized Solar Cell (DSSC) the dye sensitizer carries out the light harvesting function and is therefore crucial in determining overall cell efficiency. In addition, the dye sensitizer can influence many of the key electron transfer processes occurring at the TiO(2)/dye/electrolyte interface which also determine efficiency. Dye structure can influence and drive forward electron injection into the conduction band of the TiO(2).

Electron transfer dynamics in dye-sensitized solar cells utilizing oligothienylvinylene derivates as organic sensitizers.

Two new organic dyes have been synthesized and used as efficient light-harvesting materials in molecular photovoltaic devices. These dyes are based on conjugated thienylvinylene units, with FL-4 consisting of a four-unit thienylvinylene oligomer and its homologue FL-7 which additionally incorporates the electron-donating triphenylamine unit (TPA) into its structure. Upon light excitation both dyes show efficient electron injection into the TiO2 conduction band and slow back electron transfer to the oxidized dye.

Synthesis, spectroscopy, crystal structure, electrochemistry, and quantum chemical and molecular dynamics calculations of a 3-anilino difluoroboron dipyrromethene dye.

An asymmetrically substituted fluorescent difluoroboron dipyrromethene (BODIPY) dye, with a phenylamino group at the 3-position of the BODIPY chromophore, has been synthesized by nucleophilic substitution of 3,5-dichloro-8-(4-tolyl)-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene. The solvent-dependent spectroscopic and photophysical properties have been investigated by means of UV-vis spectrophotometry and steady-state and time-resolved fluorometry and reflect the large effect of the anilino substituent on the fluorescence characteristics. The compound has a low fluorescence quantum yield in all but the apolar solvents cyclohexane, toluene, and chloroform.

Boron dipyrromethene analogs with phenyl, styryl, and ethynylphenyl substituents: synthesis, photophysics, electrochemistry, and quantum-chemical calculations.

Seven fluorescent boradiazaindacene-based compounds with one or two phenyl, ethenylphenyl, and ethynylphenyl substituents at the 3- (or 3,5-) position(s) were synthesized via palladium-catalyzed coupling reactions with the appropriate 3,5-dichloroBODIPY derivative. The effect of the various substituents at the 3- (or 3,5-) position(s) on the spectroscopic and photophysical properties were studied as a function of solvent by means of UV/vis absorption, steady-state, and time-resolved fluorometry, and theoretical modeling. The emission maxima of the symmetrically 3,5-disubstituted dyes are shifted to longer wavelengths (by 30 to 60 nm) relative to the related asymmetrically 3,5-disubstituted ones.

Fluorescence of single molecules in polymer films: sensitivity of blinking to local environment.

The single-molecule fluorescence blinking behavior of the organic dye Atto647N in various polymer matrixes such as Zeonex, PVK, and PVA as well as aqueous media was investigated. Fluorescence blinking with off-times in the millisecond to second time range is assigned to dye radical ions formed by photoinduced electron transfer reactions from or to the environment. In Zeonex and PVK, the measured off-time distributions show power law dependence, whereas, in PVA, no such dependence is observed.

Structure-dependent photoinduced electron transfer in fullerodendrimers with light-harvesting oligophenylenevinylene terminals.

Oligophenylenevinylene (OPV)-terminated phenylenevinylene dendrons G1-G4 with one, two, four, and eight "side-arms", respectively, were prepared and attached to C60 by a 1,3-dipolar cycloaddition of azomethine ylides generated in situ from dendritic aldehydes and N-methylglycine. The relative electronic absorption of the OPV moiety increases progressively along the fullerodendrimer family C60G1-C60G4, reaching a 99:1 ratio for C60G4 (antenna effect). UV/Vis and near-IR luminescence and transient absorption spectroscopy was used to elucidate photoinduced energy and electron transfer in C60G1-C60G4 as a function of OPV moiety size and solvent polarity (toluene, dichloromethane, benzonitrile), taking into account the fact that the free-energy change for electron transfer is the same along the series owing to the invariability of the donor-acceptor couple.

Photoinduced energy and electron transfer in fullerene-oligophenyleneethynylene systems: dependence on the substituents of the oligomer unit.

The photophysical properties of fullerene hybrid systems in which disymmetrically substituted linear oligophenyleneethynylene (OPE) substituents have been attached to C(60) through a pyrrolidine ring are discussed. These hybrid systems differ in both the length of the conjugated OPE backbone and in the type of terminating groups employed, i.e.

Multistep electron transfer processes on dye co-sensitized nanocrystalline TiO2 films.

We report a method for achieving multilayer co-sensitization of nanocrystalline TiO2 films. The method is based upon an aluminum isopropoxide treatment of the monosensitized film prior to deposition of a second sensitizer. Appropriate selection of sensitizer dyes allows vectorial, multistep, electron transfer processes, resulting in a suppression of interfacial charge recombination and a significantly improved photovoltaic device performance relative to single-layer co-sensitization devices.

Molecular control of recombination dynamics in dye-sensitized nanocrystalline TiO2 films: free energy vs distance dependence.

In this paper we address the dependence of the charge recombination dynamics in dye-sensitized, nanocrystalline TiO2 films upon the properties of the sensitizer dye employed. In particular we focus upon dependence of the charge recombination kinetics upon the dye oxidation potential E0(D+/D), determined electrochemically, and the spatial separation r of the dye cation HOMO orbital from the metal oxide surface, determined by semiempirical calculations. Our studies employed a series of ruthenium bipyridyl dyes in addition to porphyrin and phthalocyanine dyes.

Control of charge recombination dynamics in dye sensitized solar cells by the use of conformally deposited metal oxide blocking layers.

We report herein a methodology for conformally coating nanocrystalline TiO2 films with a thin overlayer of a second metal oxide. SiO2, Al2O3, and ZrO2 overlayers were fabricated by dipping mesoporous, nanocrystalline TiO2 films in organic solutions of their respective alkoxides, followed by sintering at 435 degrees C. These three metal oxide overlayers are shown in all cases to act as barrier layers for interfacial electron transfer processes.

Slow charge recombination in dye-sensitised solar cells (DSSC) using Al2O3 coated nanoporous TiO2 films.

The conformal growth of an overlayer of Al2O3 on a nanocrystalline TiO2 film is shown to result in a 4-fold retardation of interfacial charge recombination, and a 30% improvement in photovoltaic device efficiency.

Molecular control of recombination dynamics in dye sensitised nanocrystalline TiO2 films.

Modification of the structure of a porphyrin dye shows a significant change in the rate of charge recombination between injected electrons in the TiO2 and the oxidized dye anchored to it following optical excitation, offering an insight into fundamental understanding of processes occurring at the dye/semiconductor interface.