Ru Complex Dye Research Articles

The impact of carboxylic acid anchoring groups on the optoelectronic and nonlinear optical properties of Ru complex dyes: A computational approach

In this study, density functional theory (DFT) and time-dependent DFT (TD-DFT) methods were used to analyze the effects of varying the number and positions of carboxylic acid anchoring groups attached to the bpy ligand of the [Ru(bpy)2(NCS)2] complex. Also the geometric structures, absorption geometry, electronic structures, optical properties, photovoltaic parameters, and nonlinear optical (NLO) properties of the designed [Ru(bpy)2(NCS)2] derivatives were investigated and compared with each other. The results indicate that the optoelectronic properties of these ruthenium (II) complexes are influenced by the number and positioning of carboxylic acid groups on the bipyridine moiety. Calculated values of ΔGinject and ΔGreg for the studied Ru(II) complexes suggest that the energy level alignment with the semiconductor and electrolyte satisfies the criteria. Furthermore, it was observed that the number and position of the anchoring carboxylic acid units is an effective approach to improve their NLO response. Overall, the structural modifications by the anchoring carboxylic acid groups on the bpy ligand of [Ru(bpy)2(NCS)2] complexes seem to fine-tune their DSSC performance and NLO response characteristics.

Effects of Anionic Polymer Modification of Dye‐Sensitized Niobate Photocatalysts on Solar‐Driven Z‐Scheme Overall Water Splitting

Pt‐intercalated calcium niobate nanosheets (Pt/HCa2Nb3O10) sensitized by a Ru(II) complex dye are good photocatalysts for producing H2 from aqueous solutions containing I− as a reversible electron donor. These materials are applicable to Z‐scheme overall water splitting in combination with a WO3‐based O2‐evolving photocatalyst under simulated sunlight. In this work, the effects of anionic polymer modification of the dye‐sensitized nanosheets are examined by adsorbing sodium poly(styrenesulfonate) (PSS), sodium polyacrylate, sodium polymethacrylate (PMA), or sodium poly(4‐styrenesulfonic‐co‐maleic acid) onto the dye‐sensitized nanosheet surface. For half‐cell H2‐evolution reaction in the presence of NaI, all of the polymers have a positive impact on the activity under visible light at lower light intensity, whereas only PMA is effective under high light‐intensity condition. For Z‐scheme overall water splitting with PtOx/H‐Cs‐WO3, PSS and PMA give almost the same solar‐to‐hydrogen energy conversion efficiencies (0.12% ± 0.01%) under optimized conditions. However, PMA operates better than PSS at relatively low and high NaI concentrations, which are in general disadvantageous for the H2‐ and O2‐evolving components of the Z‐scheme, respectively.

Water Reduction Photocathodes Based on Ru Complex Dyes Covered with a Conjugated Polymer Nanosheet

Water Reduction Photocathodes Based on Ru Complex Dyes Covered with a Conjugated Polymer Nanosheet

Diphenylcarbazone and tartrazine as sensitizer metal complex dyes for dye sensitized solar cells

Dye sensitized solar cells (DSSCs) are photovoltaic devices that produce electricity from the photon energy of sunlight using dyes. Dyes used DSSCs should have a broad absorption spectrum at the UV-Vis region and should be strongly bound to the photoanode surface. Dyes are used in DSSCs can be classified into three types: metal complex dyes, metal-free organic dyes and natural dyes. For metal complex dyes, ruthenium is usually used as metal centers. While most Ru complex dyes have high efficiency, Ru is a rare metal. To decrease the cost of Ru complex dyes, transition metals are widely investigated. In this work, diphenylcarbazone and tartrazine with different metal complexes were synthesized and investigated for their suitability for DSSCs. UV-Vis was used for the characterization of dyes and linear sweep voltammetry and electrochemical impedance spectroscopy were used to investigate the performance of DSSCs.

Toward Eco-Friendly Dye-Sensitized Solar Cells (DSSCs): Natural Dyes and Aqueous Electrolytes

Due to their low cost, facile fabrication, and high-power conversion efficiency (PCE), dye-sensitized solar cells (DSSCs) have attracted much attention. Ruthenium (Ru) complex dyes and organic solvent-based electrolytes are typically used in high-efficiency DSSCs. However, Ru dyes are expensive and require a complex synthesis process. Organic solvents are toxic, environmentally hazardous, and explosive, and can cause leakage problems due to their low surface tension. This review summarizes and discusses previous works to replace them with natural dyes and water-based electrolytes to fabricate low-cost, safe, biocompatible, and environmentally friendly DSSCs. Although the performance of “eco-friendly DSSCs” remains less than 1%, continuous efforts to improve the PCE can accelerate the development of more practical devices, such as designing novel redox couples and photosensitizers, interfacial engineering of photoanodes and electrolytes, and biomimetic approaches inspired by natural systems.

Enhanced performance of dye-sensitized solar cells by co-sensitization of metal-complex and organic dye

We systematically investigated a co-sensitized dye comprising of the Ru-complex (N719) dye blended with organic (Coomassie brilliant-blue R-250) as a novel photosensitizer for application in dye-sensitized solar cells (DSSCs). Compared with DSSCs made with the individual dyes, the power conversion efficiency of DSSC with co-sensitized dye is increased by 22 %, i.e., from 9.07 to 11 %. This enhancement results mainly from the significant increase in the open-circuit voltage (VOC) upon co-sensitization due to the upward movement of the conduction band edge and reduction in the charge recombination. Impedance spectroscopy analysis reveals higher charge recombination resistance and greater carrier lifetime for the co-sensitized dye-based DSSC, suggesting that the suppressed recombination due to improved morphology and reduced defects yields a high VOC. Moreover, co-sensitized DSSC exhibited enhanced short circuit current (JSC) and fill factor (FF). This strategy of using a co-sensitized dye as a photosensitizer in DSSCs could pave an effective way to approach high-performance, cost-effective DSSCs.

Interaction between dyes and iodide mediators in p-type dye-sensitized solar cells

The intermolecular interactions of a cyclometallated Ru-complex dye (1) and a diketopyrrolopyrrole-based organic dye (2) with iodine species (I3−, I2, and I2−) were investigated using density functional theory. The reduced dyes mainly interact with I3− via the reductive cleavage of the II bond, thus forming [I2−⋯Dye⋯I−]. The I2− interaction also involves II bond dissociation by single-electron transfer from the reduced dye to I2− to form a [I−⋯Dye⋯I−] complex. In most of the reduced dye–I2 complexes, single-electron transfer from the dye to I2 occurs without II bond breakage, thus forming [Dye⋯I2−]. These results suggest that both 1 and 2 can be completely regenerated in p-type dye-sensitized solar cells (DSSCs). The regeneration process involves one-electron transfer with an iodide–triiodide redox couple via three different mechanisms: by I3− via the transient intermediate [I2−⋯Dye⋯I−] complex yielding I2− and I−, by I2 via the [Dye⋯I2−] complex yielding I2−, or by I2− via the [I−⋯Dye⋯I−] complex yielding two I−.

Structural Effect of the Pendant Unit in Thiocyanate‐Free RuII Sensitizers on the Dye‐Sensitized Solar Cell Performance

A combination of Ru complex sensitizers and Co complex redox couples for dye‐sensitized solar cells (DSSCs) generally results in low power conversion efficiency. This has been suggested to be from undesired electron transfer due to strong intermolecular interactions between the dye and the redox couple. To retard the interactions, two thiocyanate‐free ruthenium (Ru) sensitizers were synthesized with a terpyridine attached that has a triphenylamine (TPA) unit with branched alkoxy chains. The main difference between the two dyes is the angle of the three phenyl rings in the TPA unit. The DSSCs using both the new dyes show higher short‐circuit currents and open‐circuit voltages in comparison with those using a Ru complex dye with nonbranched alkyl chains. The Ru sensitizer with a more twisted TPA unit displays relatively high power conversion efficiency without coadsorption of chenodeoxycholic acid, suggesting less intermolecular interaction among dyes and thus also with Co complex redox couples.

Effect of Adsorbed Water Molecules on Light Harvesting and Electron Injection Processes in Dye-Sensitized Nanocrystalline TiO2 Films

We studied the effects of adsorbed water molecules on light harvesting and electron injection processes in nanocrystalline TiO2 films sensitized with Ru-complex dyes. We found that the absorption spectra of adsorbed dyes containing SCN groups were sensitive to humidity (that is, the dyes exhibited vapochromism) and that the absorption spectra of dyes adsorbed on nanocrystalline films differed slightly from the spectra of the same dyes adsorbed on TiO2 single crystals, suggesting that the orientation of the dye molecules on the surface was affected by surface-adsorbed water molecules. The dynamics of electron injection from the excited dye molecules into the TiO2 were studied by transient absorption spectroscopy. Transient absorption signal intensities decreased with decreasing humidity, indicating that electron injection efficiency was reduced by loss of water molecules from the surface. IR spectroscopy indicated that only a small amount of physisorbed water was lost upon drying, and the use of an indicator dye showed that the proton concentration around the dye molecules on the surface was markedly increased by drying. On the basis of these findings, we discuss possible mechanisms for the vapochromism and for the reduction in electron injection efficiency caused by the loss of water molecules from the surface.

Anionic ancillary ligands in cyclometalated Ru(ii) complex sensitizers improve photovoltaic efficiency of dye-sensitized solar cells: insights from theoretical investigations

Comprehensive understanding of the impact of anionic ligands in Ru complex dyes on the performance of DSSCs by theoretical calculations.

Interfacial Charge Transfer in Dye-Sensitized Solar Cells Using SCN-Free Terpyridine-Coordinated Ru Complex Dye and Co Complex Redox Couples.

The efficiency of dye-sensitized solar cells (DSSCs) using Ru complex dyes and Co complex redox couples has been increased with a strategy to prevent charge recombination via the addition of bulky or lengthy peripheral units to the dyes. However, despite the efforts, most of the DSSCs are still suffering from nonunity quantum efficiency and fast recombination. We examine the effect of SCN ligand, which has been used for many Ru complex dyes and could attract positively charged Co complexes. We find that replacing the ligands with 2,6-bis(2'-(4'-trifluoromethyl)pyrazolyl)pyridine increases the quantum efficiency and electron lifetime. With the combination of the replacement of SCN ligands and the addition of bulky moiety, ∼80% external quantum efficiency is achieved. These suggest that not only the addition of a blocking effect but also the reduction of electrostatic and dispersion forces between dyes and Co complexes are essential to control the charge separation and recombination processes.

TiO2/graphene nanocomposite layers for improving the performances of dye-sensitized solar cells using a cobalt redox shuttle

Abstract Progresses in dye-sensitized solar cells (DSSCs) have revealed limitations due to I−/I3− redox shuttle and the necessity of its replacement. Cobalt-complexe redox species are the most promising alternatives for the application. In the present work, we have optimized the preparation of solar cells based on a Co-complex redox shuttle and Z907 Ru-complex dye. The system has been studied using pristine TiO2 and TiO2_single-layered graphene composite mesoporous layers for the electron transport. Our results on TiO2_graphene are promising since these cells, with the cobalt redox electrolyte, yielded to a power conversion efficiency close to that of a TiO2 photoelectrode combined with the iodine electrolyte. Using the nanocomposite layers permitted a significant increase in the photoelectrode specific surface area, dye loading and then cell short circuit current (Jsc). Moreover, the use of [Co(phen)3]2+/3+ improved the cell Voc due to a higher standard redox potential. However a limitation was found due to a shift of the TiO2 conduction band towards lower energy. Impedance spectroscopy study of the systems revealed a higher recombination rate for the Cobalt electrolyte and that the photoelectrode conductivity was slightly increased by adding graphene. It is shown that, even if improved in the presence of graphene, the charge collection efficiency was lower for the cobalt electrolyte compared to the iodide one. Globaly graphene improved the DSSC performance mainly due to the enlargement of the photoelectrode specific surface area and then of the dye loading.

Effects of 2-hexylthiophene on the performance of triphenylamine based organic dye for dye-sensitized solar cells

Inspired from the structure of Ru-complex dye C101, the 2-hexylthiophene moieties were introduced to the triphenylamine unit of dye L1 for dye L101as an attempt to enhance the donor capacity and achieve high overall power conversion efficiency (η). Finally, these two sensitizers were applied to Dye-sensitized solar cells(DSSCs), and their photovoltaic performance were further investigated through spectral, electrochemical, photovoltaic measurements. The η of L101 is 5.1% (Voc=724mV, Jsc=9.24mAcm−2, FF=0.76, εmaxabs=44.4×103M−1cm−1) which is higher than L1 (η=4.7%, Voc=712mV, Jsc=8.79mAcm−2, FF=0.75, εmaxabs=23.3×103M−1cm−1). This slight enhancement is mainly attributed to two reasons: firstly, the light-harvesting capacity is enhanced when introducing hexylthiophene moieties to the triphenylamine donor unit of L1 and contributed to a larger Jsc. Secondly, the introduced 2-hexylthiophene moieties improve the conduction band edge of TiO2 which result in the higher Voc of L101 than L1. These results demonstrate that the introduced 2-hexylthiophene moieties could help to achieve better performance.

Regulating ancillary ligands of Ru(ii) complexes with square-planar quadridentate ligands for more efficient sensitizers in dye-sensitized solar cells: insights from theoretical investigations

In this work, we designed three dyes (Ru1, Ru2, and Ru3) by modifying the square-planar quadridentate ligand of the experimental Ru(ii) complex K1, [RuL(trans-NCS)2] with L = dimethyl-6,60-bis(methyl-2-pyridylamino)-2,20-bipyridine-4,40-dicarboxylate, from a theoretical viewpoint. As is known, K1 shows obvious advantages over the famous dye N749 in light absorption ability because of its highly conjugated ancillary ligands. Density functional theory and time-dependent density functional theory methods were used to determine the geometrical structures, electronic structures and absorption spectra of the dye complexes. A quantum dynamics method in conjunction with extended Hückel theory was used to simulate the interfacial electron transfer process at the dye-TiO2 interface. The calculated results suggest that Ru1, which contains arylmethane groups, presents improved light absorption and efficient interfacial electron transfer compared with the reference dye K1. We also verified that the position of the anchoring carboxylic acid groups could largely guide the rate of interfacial electron transfer. Ru3, whose anchoring groups are attached to pyridine rings, would have significantly faster interfacial electron transfer than Ru2, whose anchoring groups are attached to the pyrrole ligands; this is because varying the position of the anchoring group results in a difference in the extent of electron donor-acceptor orbital interactions. We expect that the current study will provide some theoretical guidelines for the experimental synthesis of novel Ru(ii) complex dyes.

Isomer Dependence of Efficiency and Charge Recombination in Dye‐Sensitized Solar Cells Using Ru Complex Dyes Bearing Halogen Substituents

AbstractWe have synthesised Ru(H2‐dcbpy)(N,N′‐Y2‐bpy)(NCS)2 dyes (where N = 4, 5; Y = F, Cl, Br; N is the position on the bipyridyl ring where the halogen substituent is located) for dye‐sensitised solar cells. We show that careful consideration of the position of the substituent, in conjunction with the nature of the substituents, on a bpy ring is important to optimize the solar cells performance. Changing the position (from 4,4′ to 5,5′) along with the nature of the halogen (F, Cl, or Br) substituents were observed to cause changes in the electronic and spectroscopic properties of the dyes as well as influence the recombination rates at the TiO2–dyes–I–/I3– interface affecting the performance of the dyes in DSSCs.

Intermolecular interactions between a Ru complex and organic dyes in cosensitized solar cells: a computational study.

Intermolecular interactions in cyclometalated Ru complex dye (FT89) dimers, carbazole organic dye (MK-45 and MK-111) dimers, FT89-MK-45 complexes, and FT89-MK-111 complexes were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) to elucidate the improvement mechanism of dye-sensitized solar cell (DSSC) performance due to cosensitization with FT89 and MK dyes. All of the dimers and complexes form intermolecular cyclic hydrogen bonds via the carboxyl groups. The FT89 dimer and complexes with the TiO2Na model system promote intermolecular interactions with I2via the NCS ligand of the FT89 monomer. The computational results verify that MK-111 behaves not only as a sensitizer but also inhibits FT89 aggregation by effectively serving as a coadsorbent similar to deoxycholic acid (DCA) in the dye solution, suppressing recombination of the injected electrons in TiO2 with I2, improving DSSC performance.

Influence of Ionic Liquid on Recombination and Regeneration Kinetics in Dye-Sensitized Solar Cells

Nonvolatile electrolyte solutions are necessary for dye-sensitized solar cells (DSCs) with good long-term stability. Such electrolytes usually contain room-temperature ionic liquids (RTILs) and consequently possess higher viscosity and ionic strength than the volatile electrolytes used in current champion cells. In this study, we systematically investigated the effect of an RTIL additive on the performance of DSCs employing either a classical Ru-complex dye or a recently developed organic D-A-π-A dye, in combination with either I–/I3– or [Co(bpy)3]2+/3+ as redox mediator. Using impedance spectroscopy and transient absorption measurements under various background illumination intensities, recombination and regeneration kinetics were examined. Recombination is accelerated in the I–/I3– devices upon addition of RTIL, regardless of the dye used, but it is retarded in the [Co(bpy)3]2+/3+ devices. Addition of RTIL slowed regeneration in I–/I3– devices for both sensitizers, marginally accelerated it for [Co(bpy)...

Study of Electron Injection Efficiency of N719/TiO2 System in Different Room Temperature Ionic Liquid (IL) Environments By Using Femtosecond Transient Absorption Spectroscopy: Effect of Varying Viscosity

Introduction: Use of room temperature ionic liquid (RTIL) instead of conventional solvents in dye sensitized solar cells (DSSCs) has attracted many attentions among scientific as well as technical communities because of its negligible vapor pressure, high boiling points, low flammability, high ionic conductivity and electrochemical stability. Electron injection efficiency from excited state dye to the conduction band (CB) of semiconductor nanoparticles is one of the important elementary steps to determine the overall cell efficiency. Experimental: In this work, a series of room temperature ionic liquids (ILs) of varying viscosity have been employed as an environment for Ru-complex dye (N719) sensitized TiO2 system to study electron injection efficiency using femtosecond transient absorption spectroscopy. The investigated ILs are (Figure 1): i) with [EMIm]+ cation and [TCB]-, [SCN]-, [TCM]-, [DCA]-, [FSA]-, [BF3CF3]-, [TFSA]- and [TfO]- as different anionic counterparts and ii) with [DMEIm]+ cation and [TFSA]- anion (DTFSA) . These ILs are categorized as –CN ([TCB]-, [SCN]-, [TCM]- and [DCA]-) and –F ([FSA]-, [BF3CF3]-, [TFSA]- and [TfO]-and DTFSA) containing ILs. The details of the experimental procedure are described elsewhere [1]. Results adn discussions: Figure 2 shows the transient time profiles of adsorbed N719/TiO2 system in -CN and -F containing IL environments using 532 nm excitation femtosecond laser pulse and probed at 800 nm, which is the absorption band of the oxidized dye molecules (N719+). The trend of absorbance (ΔOD) value of N719/TiO2in –CN containing IL environments at 1ns delay time is [TCB]>[SCN]>[TCM]>[DCA] which reflects the electron injection efficiency (Figure 2a). For –F containing IL environments, the trend of absorbance value (ΔOD) at 1ns delay is [FSA]>[BF3CF3]>[TFSA]>[TfO]>[DTFSA] (Figure 2b) which also reflects the electron injection efficiecny trends. It intrigues us that the trend of electron injection efficiency is completely different with respect to viscosity of these –CN and –F containing IL environments. It is observed that the electron injection efficiency increases with increasing viscosity for –CN containing IL environments, however reverse trend is found for -F containing IL environments (Figure. 3). Modulation of CB edge energy is the main factor for influencing the electron injection efficiency for –CN containing ILs [1] whereas orientation of the dye moleucles along TiO2 nanoparticles changes the electronic coupling between the excited state of the dye moleucles and CB of TiO2for -F containing ILs of N719/TiO2 system. Acknowledgement: This work is supported by NEDO Japan

Carbazole dye with phosphonic acid anchoring groups for long-term heat stability of dye-sensitized solar cells

In dye-sensitized solar cells (DSSCs), the binding strength between the dye and TiO2 surface may affect the heat stability of the DSSCs. Carboxylic acids have generally been used as the anchoring groups for the adsorption of dyes on TiO2 surfaces. However, a phosphonic acid anchor is expected to effect more stable bonding to a TiO2 surface because of its tridentate binding capability. In this study, we developed a new carbazole dye that employed a phosphonic acid anchor, MK-94. We studied the effect of the dye anchoring group on the heat stability of DSSCs by comparing MK-94, MK-2 (a carbazole dye with a carboxylic acid anchoring group), and Z-907 (a well-known, robust Ru complex dye with a carboxylic acid anchoring group).In the initial performance assessment, the DSSC with MK-94 exhibited a lower short circuit current (jsc) but a higher open circuit voltage (ΔVoc) than MK-2. With respect to heat stability, decreases in jsc and ΔVoc were suppressed with MK-94, and the drop of the power conversion efficiency (PCE) was kept within 6% after 504h of heating. In addition, MK-94 demonstrated the longest electron lifetime and largest charge transfer resistance than the other dyes during the stability test. In contrast, the PCE decreased 27% from the initial value in the DSSC with MK-2. Thus, the phosphonic acid anchor was effective in extending the long-term heat stability of the DSSCs.

Improvement in Photovoltaic Performance of Dye-sensitized Solar Cells by Cosensitization with an Organometal Halide Perovskite

Abstract The possibility of an organometal halide perovskite, CH3NH3PbBr3, was investigated as a cosensitizer to a Ru-complex dye and an alkoxysilylcoumarin dye in dye-sensitized solar cells. The perovskite was found to work as the cosensitizer effectively, and the light-to-electric energy conversion efficiencies of the cells were improved more than 10% by the cosensitization under the present test conditions.