Homoleptic, di- and trivalent transition metal complexes with monoanionic N,N,O-heteroscorpionate ligands: Potential redox mediators for dye-sensitized solar cells? (original) (raw)
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Corrosiveness is one of the main drawbacks of using the iodide/triiodide redox couple in dye-sensitized solar cells (DSSCs). Alternative redox couples including transition metal complexes have been investigated where surprisingly high efficiencies for the conversion of solar to electrical energy have been achieved. In this paper, we examined the development of a DSSC using an electrolyte based on square pyramidal oxidovanadium(IV/V) complexes. The oxidovanadium(IV) complex (Ph4P)2[VIVO(hybeb)] was combined with its oxidized analogue (Ph4P)- [VVO(hybeb)] {where hybeb4− is the tetradentate diamidodiphenolate ligand [1-(2-hydroxybenzamido)-2-(2-pyridinecarboxamido)benzenato}and applied as a redox couple in the electrolyte of DSSCs. The complexes exhibit large electron exchange and transfer rates, which are evident from electron paramagnetic resonance spectroscopy and electrochemistry, rendering the oxidovanadium(IV/V) compounds suitable for redox mediators in DSSCs. The very large self-exchange rate constant offered an insight into the mechanism of the exchange reaction most likely mediated through an outer-sphere exchange mechanism. The [VIVO(hybeb)]2−/[VVO(hybeb)]− redox potential and the energy of highest occupied molecular orbital (HOMO) of the sensitizing dye N719 and the HOMO of [VIVO(hybeb)]2− were calculated by means of density functional theory electronic structure calculation methods. The complexes were applied as a new redox mediator in DSSCs, while the cell performance was studied in terms of the concentration of the reduced and oxidized form of the complexes. These studies were performed with the commercial Ru-based sensitizer N719 absorbed on a TiO2 semiconducting film in the DSSC. Maximum energy conversion efficiencies of 2% at simulated solar light (AM 1.5; 1000 W m−2) with an open circuit voltage of 660 mV, a short-circuit current of 5.2 mA cm−2, and a fill factor of 0.58 were recorded without the presence of any additives in the electrolyte.
Metal Coordination Complexes as Redox Mediators in Regenerative Dye-Sensitized Solar Cells
Inorganics, 2019
Dye-sensitized solar cells (DSSCs) have attracted a substantial interest in the last 30 years for the conversion of solar power to electricity. An important component is the redox mediator effecting the transport of charge between the photoelectrode and the dark counter electrode (CE). Among the possible mediators, metal coordination complexes play a prominent role and at present are incorporated in several types of devices with a power conversion efficiency exceeding 10%. The present review, after a brief introduction to the operation of DSSCs, discusses at first the requirements for a successful mediator. Subsequently, the properties of various classes of inorganic coordination complexes functioning as mediators relevant to DSSC operation are presented and the operational characteristics of DSSC devices analyzed. Particular emphasis is paid to the two main classes of efficient redox mediators, the coordination complexes of cobalt and copper; however other less efficient but promis...
The role of transition metal complexes in dye sensitized solar devices
Coordination Chemistry Reviews, 2013
This article focuses on the progress obtained in the design of metal complexes which find application as sensitizers for dye-sensitized solar cells, DSSCs, and as electron shuttles in substitution of the triiodide/iodide redox couple. Coupling of sterically hindered dyes with mobile shuttles, based on a transition metal complex, represents the most advanced innovation which has allowed to reach on a single device the record efficiency of 12%. Issues which require further research are also discussed.
Physical Chemistry Chemical Physics, 2014
We report a combined experimental and computational study of polynuclear [Run(TPPZ)n+1] 2n+ complexes, of interest in the field of photoactive polymers. The complexes with n ) 1, 2, 3 and n > 5 have been synthesized and spectroscopically characterized. A red-shift of the visible band maximum from 2.59 to 2.03 eV is observed going from the monomer to the longer oligomeric species (n > 5). To characterize the geometries, electronic structure, and excited states of these complexes, density functional theory (DFT) and time-dependent DFT calculations on the [Run(TPPZ)n+1] 2n+ series with n ) 1-4 in solution have been performed. The agreement between experimental and calculated spectra is good, both in terms of absorption maximum energies and relative intensities for different values of n. For all the investigated complexes, we assign the main band in the visible region as a metal-to-metal plus ligand charge transfer (MMLCT) transition. The resulting excited states are delocalized throughout the entire complexes, as they originate from a superposition of π*(TPPZ)-t2g(Ru) states. The low-energy shoulder of the main visible absorption band, present in the experimental spectra for n > 1, is proposed to arise from spin-forbidden singlet-triplet transitions of similar MMLCT character, consistent with the observed enhancement of this feature in the spectra of the corresponding Os oligomers.
Promising Dye Sensitizer on Solar Cell From Complexes of Metal and Rhodamine B
International Journal of Renewable Energy Research, 2015
Herein a series of complexes from metals (Fe, Co, Ni) and rhodamine B as ligand were synthesized, characterized and applied as promising dye sensitizer on solar cell. Complexes were obtained from the reaction of Fe(II), Co(II), Ni(II) salts and rhodamine B with mole ratio 1:3. UV-Visible spectroscopy confirms all of complexes showing Metal Ligand Charge Transfer (MLCT) absorption band at 258 nm and stability constant (log K) of complexes were 23.47 for Fe-Rb and Ni-Rb and 23.76 for Co-Rb. Infrared spectroscopy confirms metal-ligand coordination through carbonyl (CO) and methoxy (CH 3 O) groups. Electrical conductivity analysis indicates that all of complexes are ionic complexes. All of complexes can be utilized as promising dye sensitizer with efficiency 2.03% (Fe), 0.59% (Co), and 0.12% (Ni). Goal of this research is to help solve dye waste problem and energy crisis.
Copper Complexes as Alternative Redox Mediators in Dye-Sensitized Solar Cells
Molecules, 2021
Thirty years ago, dye-sensitized solar cells (DSSCs) emerged as a method for harnessing the sun’s energy and converting it into electricity. Since then, a lot of work has been dedicated to improving their global photovoltaic efficiency and their eco-sustainability. Recently, various articles showed the great potential of copper complexes as a convenient and cheap alternative to the traditional ruthenium dyes. In addition, copper complexes demonstrate that they can act as redox mediators for DSSCs, thus being an answer to the problems related to the I3−/I− redox couple. The aim of this review is to report on the most recent impact made by copper complexes as alternative redox mediators. The coverage, mainly from 2016 up to now, is not exhaustive, but allows us to understand the great role played by copper complexes in the design of eco-sustainable DSSCs.
A simple copper(I) complex and its application in efficient dye sensitized solar cells
Inorganica Chimica Acta, 2013
A novel copper(I) complex bearing two 6,6 0-dimethyl-2,2 0-bipyridine-4,4 0-dibenzoic acid ligands was prepared along with related deprotonated derivatives with Na + or NBu 4 + as counterion. Their performance as photosensitizer in dye sensitized solar cells was studied as a function of the anchoring group and the electrolyte composition, comparing it with that of the known copper(I) complex bearing two 6,6 0-dimethyl-2,2 0-bipyridine-4,4 0-dicarboxylic acid ligands and the ruthenium benchmark N719. Interestingly, the novel protonated complex is characterized by the best overall power conversion efficiency (3.0%) reported up to now for a copper(I) complex.
Journal of the American Chemical Society, 2012
Dye-sensitized solar cells (DSCs) are an attractive renewable energy technology currently under intense investigation. In recent years, one area of major interest has been the exploration of alternatives to the classical iodide/ triiodide redox shuttle, with particular attention focused on cobalt complexes with the general formula [Co(L) n ] 2+/3+. We introduce a new approach to designing redox mediators that involves the application of [Co(PY5Me 2)(MeCN)] 2+/3+ complexes, where PY5Me 2 is the pentadentate ligand, 2,6bis(1,1-bis(2-pyridyl)ethyl)pyridine. It is shown, by X-ray crystallography, that the axial acetonitrile (MeCN) ligand can be replaced by more strongly coordinating Lewis bases (B) to give complexes with the general formula [Co(PY5Me 2)(B)] 2+/3+ , where B = 4-tert-butylpyridine (tBP) or N-methylbenzimidazole (NMBI). These commonly applied DSC electrolyte components are used for the first time to fine-tune the potential of the redox couple to the requirements of the dye through coordinative interactions with the Co II/III centers. Application of electrolytes based on the [Co(PY5Me 2)(NMBI)] 2+/3+ complex in combination with a commercially available organic sensitizer has enabled us to attain DSC efficiencies of 8.4% and 9.2% at a simulated light intensity of 100% sun (1000 W m −2 AM1.5 G) and at 10% sun, respectively, higher than analogous devices applying the [Co(bpy) 3 ] 2+/3+ redox couple, and an open circuit voltage (V oc) of almost 1.0 V at 100% sun for devices constructed with the tBP complex.