Influence of donor moiety in ruthenium sensitizers on the properties of dye-sensitized solar cells

Heteroleptic ruthenium complexes cis-[Ru(H2dcbpy)(L)(NCS)2], where H2dcbpy is 4,4'-dicarboxylic acid-2,2'-bipyridine and L is 4-(4-(N,N-di-(p-hexyloxyphenyl)-amino)styryl)-4'-methyl-2,2'-bipyridine (Rut-A) or 4-(4'-(3,6-dihexyloxycarbazole-9-yl)-styryl)-4'-methyl-2,2'-bipyridine (Rut-B), have been synthesized and characterized by NMR, UV-Vis spectroscopy, and cyclic voltammogram. The effect of different electron donors on the properties of dye-sensitized solar cells has been studied. The power conversion efficiency of DSSC based on Rut-B is 6.1% while Rut-A delivered a lower efficiency of 4.52% under the same device fabrication and measuring conditions. The better photovoltaic performance of Rut-B is mainly associated with enhanced dye absorptivity and charge recombination suppression.     

Photovoltaic performance of ruthenium complex dye associated with number and position of carboxyl groups on bipyridine ligands

A series of ruthenium complex dyes with different number and position of carboxyl groups on bipyridine ligands, such as Ru(4-carboxyl-4′-methyl-2,2′-bipyridine)(4,4′-dimethyl-2,2′- bipyridine)(NCS)₂ (denoted as Ru1A), Ru(4-carboxyl-4′-methyl-2,2′-bipyridine)₂(NCS)₂ (Ru11A), Ru(4,4′-dicarboxyl-2,2′-bipyridine)(4,4′-dimethyl-2,2′-bipyridine)(NCS)₂ (Ru2A), and Ru(4-carboxyl-4′-methyl-2,2′-bipyridine)(4,4′-dicarboxyl-2,2′-bipyridine)(NCS)₂ (Ru3A) were synthesized and compared with Ru(4,4′-dicarboxyl-2,2′-bipyridine)₂ (NCS)₂, commonly known as N3 dye for the adsorption behavior on the TiO₂ surface and photovoltaic properties of dye-sensitized solar cells. The experimental results show that the tilt angle of ruthenium dyes on the TiO₂ surface which is dependent on the number and position of their carboxyl groups strongly affected the photovoltaic performance.     

Novel DCM-based organic dye with a heteroleptic dual-electron donor for dye-sensitized solar cells

A new DCM-based organic dye with a heteroleptic dual electron donor was designed and its electronic and optical properties were investigated theoretically for dye-sensitized solar cells (DSSCs). In this study, heteroleptic Dab dye was compared with other homoleptic dyes (Daa and Dbb). To gain insight into the factors responsible for photovoltaic efficiency, density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations of these dyes were conducted. It showed that Dab dye is available as a photovoltaic device from the energy diagram for the TiO2 electrode and the iodide electrolyte. It also showed that although Dab dye produces slightly stronger absorption at above 600 nm, Dbb dye would show a better overall absorption property. Owing to the strong electron density and high proximity of its anchoring carboxylic group to LUMO + 1 and LUMO, however, it is expected that Dab dye with a heteroleptic dual donor will show a competitive performance compared to other dyes with homoleptic dual donors in the conversion efficiency for DSSCs.     

Efficient and Stable Solid‐State Dye‐Sensitized Solar Cells Based on a High‐Molar‐Extinction‐Coefficient Sensitizer

The high‐molar‐extinction‐coefficient heteroleptic ruthenium dye, cis‐Ru (4,4′‐bis(5‐octylthieno[3,2‐b] thiophen‐2‐yl)‐2,2′‐bipyridine) (4,4′‐dicarboxyl‐2,2′‐bipyridine) (NCS)₂, exhibits an AM 1.5 solar (100 mW cm^?2)‐to‐electric power‐conversion efficiency of 4.6% in a solid‐state dye‐sensitized solar cell (SSDSC) with 2,2′, 7,7′‐tetrakis‐(N,N‐di‐p‐methoxyphenylamine)9,9′‐spirobifluorene (spiro‐MeOTAD) as the organic hole‐transporting material. These SSDSC devices exhibit good durability during accelerated tests under visible‐light soaking for 1000 h at 60 °C. This demonstration elucidates a class of photovoltaic devices with potential for stable and low‐cost power generation. The electron recombination dynamics and charge collection that take place at the dye‐sensitized heterojunction are studied by means of impedance and transient photovoltage decay techniques.     

Novel phenothiazine-based organic dyes with a heteroleptic dual-electron-acceptor for dye-sensitized solar cells

We designed a novel organic dye with a heteroleptic dual-electron acceptor (cyanocrylic acid and rhodanine-acetic acid) on each side of a phenothiazine-based organic dye as a photosensitizer for dye-sensitized solar cells (DSSCs). Density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations were used to estimate the photovoltaic properties of the dyes, with the findings showing that the organic dyes when used in the heteroleptic dual-electron-acceptor type resulted in higher performance than their single electron-acceptor and homoleptic dual-electron-acceptor counterparts due to the higher molar extinction coefficients and the orientation of the adsorbed dye. It was attributed to relatively broad and intense absorption spectra in the visible region with the rhodanine-acetic acid moiety and abundant electronic coupling with TiO2 of the cyanoacrylic acid anchoring group.     

Organic photosensitizers with a heteroleptic dual donor for dye-sensitized solar cells

Using DFT and TDDFT calculations, we investigated the substitution effect in the electronic and optical properties of dye sensitizers with a dual donor composed of triphenylamine and/or indoline moieties. Due to replacement with the dual donor moieties, the HOMO levels were split into HOMO and HOMO - 1 levels, and the bandgaps between the HOMO and LUMO levels decreased, leading to the creation of bathochromically extended absorption spectra. Nearly degenerated splitting of the HOMO levels resulted from the similarity of the electronic structure between the HOMO and the HOMO - 1 levels, delocalized over both dual-donor moieties, when replacing the dual donors. It was shown that the additional electron-donating group creates an additional absorption band and causes a cascading two-electron process aiding the charge separation process. Owing to a more panchromatic attribute, easier energy transfer and feasible retardation of the recombination between the injected electrons and the electrolyte, it is expected that dyeTI will show better performance than the other dyes (dyeT dyeTT and dyeIT) as denoted here in terms of the conversion efficiency of dye-sensitized solar cells (DSSCs). This work presents the probable benefits of dye sensitizers with dual-donor moieties and provides insight into the development of more efficient dye sensitizers for DSSCs through modification of the Frontier molecular orbitals.     

Stable, high-efficiency ionic-liquid-based mesoscopic dye-sensitized solar cells

Efficient and stable mesoscopic dye-sensitized solar cells (DSCs) introducing a low-viscosity binary ionic liquid (1-propyl-3-methyl-imidazolium iodide (PMII) and 1-ethyl-3-methyl-imidazolium tetracyanoborate (EMIB(CN)(4))) electrolyte in combination with a new high-molar-extinction-coefficient ruthenium complex, Ru(2,2'-bipyridine-4,4'-dicarboxylic acid)(4,4'-bis(2-(4-tert-butyloxy -phenyl)ethenyl) -2,2'-bipyridine) (NCS)(2), are demonstrated. The dependence of photovoltaic performance, charge transport and electron lifetime on the composition of the binary ionic-liquid electrolyte with different ratios of PMII/EMIB(CN)(4) were investigated by electrochemical impedance and photovoltage transient techniques. A photovoltaic conversion efficiency of 7.6 % was obtained under simulated full sunlight illumination, which is a record for solvent-free DSCs. These devices exhibit excellent stability at 80 degrees C in the dark or under visible-light soaking at 60 degrees C during 1000 h of accelerated tests.     

Alkyl and fluoro-alkyl substituted squaraine dyes: A prospective approach towards development of novel NIR sensitizers

Alkyl and fluoroalkyl substituted symmetrical and unsymmetrical squaraine dyes have been synthesized for the fabrication of dye-sensitized solar cells (DSSC) based on nanoporous TiO₂. Results of DSSC performance clearly indicate that introduction of molecular asymmetry and increase in the alkyl chain length of the squaraine sensitizers leads to the enhancement in the photovoltaic performance. A perusal of photo-action spectra of squaraine sensitizer corroborates that introduction of molecular asymmetry and fluoroalkyl substitution leads to hampering of blue-shifted H-aggregate formation. Estimation of energy of HOMO and LUMO for these squaraine sensitizers used in the present investigation indicates that about 0.16 eV is sufficient for electron injection from photoexcited dye to TiO₂ conduction band and dye regeneration.     

Photoelectric response mechanisms dependent on RuN3 and CuPc sensitized ZnO nanoparticles to oxygen gas

ZnO nanoparticles were synthesized by a simple mild solution method. Spectral sensitization of nanocrystalline ZnO was carried out with [Ru(dcbpy)(2)(NCS)(2) (dcbyp = 2,2'-bipyridyl-4,4'-dicarboxylate)] (RuN3) and CuPc. The electron transfer behaviours at the surface and interface in ZnO/RuN3 and ZnO/CuPc were investigated using a surface photocurrent technique. When exposed to oxygen gas, the surface photocurrent (I(SPC)) responses of ZnO/RuN3 and ZnO/CuPc decreased and increased, respectively. The results demonstrated through the adsorption of oxygen gas that there are different microscopic mechanisms for the surface charges. The microscopic processes of electron transfer between oxygen molecules and dye-sensitized ZnO are discussed in detail in this paper. Such research should be valuable for fundamental science and optoelectronic device application of ZnO nanoparticles.     

Natural dyes adsorbed on TiO2 nanowire for photovoltaic applications: enhanced light absorption and ultrafast electron injection

We investigate the electronic coupling between a TiO2 nanowire and a natural dye sensitizer, using state-of-the-art time-dependent first-principles calculations. The model dye molecule, cyanidin, is deprotonated into the quinonoidal form upon adsorption on the wire surface. This results in its highest occupied molecular orbital (HOMO) being located in the middle of the TiO2 bandgap and its lowest unoccupied molecular orbital (LUMO) being close to the TiO2 conduction band minimum (CBM), leading to greatly enhanced visible light absorption with two prominent peaks at 480 and 650 nm. We find that excited electrons are injected into the TiO2 conduction band within a time scale of 50 fs with negligible electron-hole recombination and energy dissipation, even though the dye LUMO is located 0.1-0.3 eV lower than the CBM of the TiO2 nanowire.     

用于太阳能电池的一种钌金属配合物

合成了一种钌金属配合物Ru-[bpy(COOEt) 2]2Cl2.利用1HNMR、MS、UV-Vis和元素分析等手段对其结构进行了表征.该金属配合物的DMF溶液在350～800nm的区域内有较强的光吸收;CV曲线表明,其HOMO与LUMO能级分别为-5.07和-3.16eV;TG曲线表明,其300℃以下具有较好的热稳定...     

Investigation of structural,morphological, electronic and photovoltaic properties of Co(II) complex with ligand

The dye sensitized solar cells (DSSCs) used as an alternative to inorganic semiconductor sensitized solar cells (ISSCs), have favorable ecological and economical properties. In our current study, Co(II) complex with 4,4′-methylene bis (2,6-diethyl) aniline-3,5-di-tert-butylsalicylaldimine ligand was used as a sensitizer in DSSC by growing on TiO₂ coated on FTO conductive glass substrate. Current density (J) versus voltage (V) measurement was applied to investigate the photovoltaic properties of the synthesized Co(II) complex with ligand. The calculated power conversion efficiency (η%) of the complex using the obtained current density (J) versus voltage (V) curve shows that this device can be used as a promising sensitizer in solar cell application. Furthermore, structural, morphological and electronic properties of Co(II) complex with ligand were characterized by x-ray diffraction, Fourier transform-infrared spectroscopy, scanning electron microscopy and electronic absorption measurements, respectively.     

Effect of electron-deficient linkers on the physical and photovoltaic properties of dithienopyrrole-based organic dyes

Organic sensitizers containing dithienopyrrole donor, benzotriazole or quinoxaline in the conjugation pathway, and cyanoacrylic acid acceptor featured in a donor–acceptor-π–acceptor configuration are reported. The effect of the nature of different conjugating bridges on photophysical, electrochemical and photovoltaic properties was systematically evaluated. The incorporation auxiliary acceptors broadened the absorption spectra and modulated the excited state energy levels. The DFT calculation unraveled a significant overlap of HOMO and LUMO orbitals in benzotriazole-containing dyes and the charge transfer character for the longer wavelength absorption. Among the dyes, a dye containing benzotriazole and thiophene in the conjugation pathway exhibited highest power conversion efficiency attributable to efficient electron injection and pronounced inhibition of electron recombination.     

Molecular orbital analysis of frontier orbitals for molecular electronics: a case study of unimolecular rectifier and photovoltaic cell

Recently, unimolecular devices have attracted significant attention as a ‘post-silicon technology’ to enable the fabrication of future nanoscale electronic devices. In this paper, we describe a candidate molecule for a rectifier function using porphyrin polymer and a photovoltaic cell using fullerene-based supramolecule. We have investigated the geometric and electronic structure of these organic molecules using an ab initio quantum mechanical calculation. These results for the porphyrin polymers show that the localization of the unoccupied orbital state on the acceptor moiety mostly depends on their structures. The calculated results for the electronic structure of a naphthalocyanine–fullerene supramolecule manifest that the HOMO’s were localized on the donor sub-unit and the LUMO’s were localized on theacceptor sub-unit.     

Imine-linked receptors decorated ZnO-based dye-sensitized solar cells

This study reports the synthesis, characterization and photophysical properties of imine-linked receptors decorated ZnO nanoparticles using wet precipitation method. Initially, polymer dye 3 was synthesized using condensation reaction between 2-furancarboxaldehyde 1 and polyethylenimine 2. The decoration of imine-linked receptors on ZnO nanoparticles (sample A) was characterized and investigated by X-ray diffraction, scanning electron microscope and dynamic light scattering spectroscopic studies. Further, polymer dye 3 was added to ruthenium chloride (RuCl₃) to form a polymer–ruthenium-based composite dye-capped ZnO nanoparticles (sample B). The optical properties of sample A were evaluated by fluorescence and UV–Vis spectroscopy. The samples A and B were further processed to dye-sensitized solar cells using wet precipitation method. The results of observations revealed that the addition of ruthenium–polymer dye molecules increased the light harvesting capacity of ZnO-based DSSCs. A maximum solar power to electricity conversion efficiency (η) of 3.83% was recorded for sample B-based DSSCs with ruthenium–metal complex dye as a good photosensitizer. The recorded photovoltaic efficiency of sample B-based DSSCs was enhanced by 1.36% compared to sample A-based DSSCs.

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Ion coordinating sensitizer for high efficiency mesoscopic dye-sensitized solar cells: influence of lithium ions on the photovoltaic performance of liquid and solid-state cells

A Li+ coordinating sensitizer, NaRu(4-carboxylic acid-4'-carboxylate)(4,4'-bis[(triethylene glycol methyl ether) methyl ether]-2,2'-bipyridine)(NCS)2 (coded as K51), has been synthesized, and the effect of Li+ coordination on its performance in mesoscopic titanium dioxide dye-sensitized solar cells has been investigated. Fourier transform infrared spectra suggest that Li+ coordinates to the triethylene oxide methyl ether side chains on the dye molecules. With the addition of Li+ to a nonvolatile liquid electrolyte, we observe a significant increase in the photocurrent density, with only a small decrease in the open-circuit voltage, contrary to a non ion coordinating dye which displays a large drop in potential with the addition of Li+. For a solar cell incorporating an organic hole-transporter, we find the potential rises with increasing the Li+ concentration in the hole-transporter matrix. For the liquid electrolyte and solid-state cells, we obtain power conversion efficiencies of 7.8% and 3.8%, respectively, under simulated sunlight.     

Quantum mechanical modeling of self-assembly and photoinduced electron transfer in PNA-based artificial living organisms

In order to support the creation of both artificial living organisms in the USA LANL "Protocell Assembly" project and programmable nano-biorobots in the EU "Programmable Artificial Cell Evolution" project, we used quantum mechanical (QM), density functional theory (DFT), the semiempirical PM3 method, and molecular mechanics (MM) software to investigate various complex photosynthetic systems based on peptide nucleic acid (PNA) in a water environment. Quantum mechanical DFT PBEPBE simulations, including electron correlations, confirm that water molecules that surround all the photosynthetic complex of the LANL protoorganism are main constructing factors and stabilize this system consisting of: PNA fragment attached by covalent bond sensitizer 1,4-bis(N,N-dimethylamino)naphthalene molecule, lipid precursor molecule and fragment of lipid molecules mono layer. The absorption spectrum shift to the red wavelengths in the complex artificial protocell photosynthetic center might be used as the measure of the complexity of this system. The electron pi-pi* transitions in the first and third excited states are from HOMO and HOMO-1 located on the conjugated water molecules and sensitizer 1,4-bis(N,N-dimethylamino)naphthalene molecule to the LUMO of the lipid precursor molecule as calculated using the time dependent (TD) PBEPBE/6-31G model. Electron charge tunneling in the first and third excited states should induce metabolic photodissociation of the lipid precursor molecule because of localization of the transferred electron cloud on the head (waste) of the lipid precursor molecule. TD electron correlation PBEPBE/6-31G calculations show that in the different energies of excitation, the charge transfer tunneling is from sensitizer to lipid precursor and cytosine molecules. One should note that in a water solvent, the electron charge transfer pi-pi* transition in the fifth and sixth excited state is from the HOMO and HOMO-1 located on the sensitizer 1,4-bis(N,N-dimethylamino)naphthalene molecule to the LUMO+2 located on the cytosine-PNA fragment molecule. Investigation results indicate that strong back electron tunneling from the sensitizer 1,4-bis(N,N-dimethylamino)naphthalene molecule to the cytosine molecule in the LANL artificial photosynthetic system exists.     

O(2)-responsive chemical sensors based on hybrid xerogels that contain fluorinated precursors

We report the development and analytical figures of merit associated with several new O(2)-responsive sensor materials. These new sensing materials are formed by sequestering the luminophore tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) ([Ru(dpp)(3)](2+)) within hybrid xerogels that are composed of two of the following methoxysilanes: tetramethoxysilane, n-propyl-trimethoxysilane, 3,3,3-trifluoropropyl-trimethoxysilane, phenethyl-trimethoxysilane, and pentafluorophenylpropyl-trimethoxysilane. Steady-state and time-resolved luminescence measurements are used to investigate these hybrid xerogel-based sensor materials and elucidate the underlying reasons for the observed performance. The results show that many of the [Ru(dpp)(3)](2+)-doped composites form visually uniform, crack-free xerogel films that can be used to construct O(2) sensors that have linear calibration curves and excellent long-term stability. To the best of our knowledge, the [Ru(dpp)(3)](2+)-doped fluorinated hybrid xerogels also exhibit the highest O(2) sensitivity of any reported [Ru(dpp)(3)](2+)-based sensor platform.     

A stable quasi-solid-state dye-sensitized solar cell with an amphiphilic ruthenium sensitizer and polymer gel electrolyte

Dye-sensitized nanocrystalline solar cells (DSC) have received considerable attention as a cost-effective alternative to conventional solar cells. One of the main factors that has hampered widespread practical use of DSC is the poor thermostability encountered so far with these devices. Here we show a DSC with unprecedented stable performance under both thermal stress and soaking with light, matching the durability criteria applied to silicon solar cells for outdoor applications. The cell uses the amphiphilic ruthenium sensitizer cis-RuLL'(SCN)(2) (L = 4,4'-dicarboxylic acid-2,2'-bipyridine, L' = 4,4'-dinonyl-2,2'-bipyridine) in conjunction with a quasi-solid-state polymer gel electrolyte, reaching an efficiency of >6% in full sunlight (air mass 1.5, 100 mW cm(-2)). A convenient and versatile new route is reported for the synthesis of the heteroleptic ruthenium complex, which plays a key role in achieving the high-temperature stability. Ultramicroelectrode voltammetric measurements show that the triiodide/iodide couple can perform charge transport freely in the polymer gel. The cell sustained heating for 1,000 h at 80 degrees C, maintaining 94% of its initial performance. The device also showed excellent stability under light soaking at 55 degrees C for 1,000 h in a solar simulator (100 mW cm(-2)) equipped with a ultraviolet filter. The present findings should foster widespread practical application of dye-sensitized solar cells.     

Ab-initio and DFT methodologies for computing hyperpolarizabilities and susceptibilities of highly conjugated organic compounds for nonlinear optical applications

In this talk, after a short introduction on the methodologies used for computing dipole polarizability (α), second and third-order hyperpolarizability and susceptibility; the results of theoretical studies performed on density functional theory (DFT) and ab-initio quantum mechanical calculations of nonlinear optical (NLO) properties for a few selected organic compounds and polymers will be explained. The electric dipole moments (μ) and dispersion-free first hyperpolarizabilities (β) for a family of azo-azulenes and a styrylquinolinium dye have been determined by DFT at B3LYP level. To reveal the frequency-dependent NLO behavior, the dynamic α, second hyperpolarizabilities (γ), second (χ⁽²⁾) and third-order (χ⁽³⁾) susceptibilites have been evaluated using time-dependent HartreeFock (TDHF) procedure. To provide an insight into the third-order NLO phenomena of a series of pyrrolo-tetrathiafulvalene-based molecules and pushpull azobenzene polymers, two-photon absorption (TPA) characterizations have been also investigated by means of TDHF. All computed results of the examined compounds are compared with their previous experimental findings and the measured data for similar structures in the literature. The one-photon absorption (OPA) characterizations of the title molecules have been theoretically obtained by configuration interaction (CI) method. The highest occupied molecular orbitals (HOMO), the lowest unoccupied molecular orbitals (LUMO) and the HOMO–LUMO band gaps have been revealed by DFT at B3LYP level for azo-azulenes, styrylquinolinium dye, push–pull azobenzene polymers and by parametrization method 6 (PM6) for pyrrolo-tetrathiafulvalene-based molecules.