Characteristics of the Iodide/Triiodide Redox Mediator in Dye-Sensitized Solar Cells
21 Oct 2009-Accounts of Chemical Research (American Chemical Society)-Vol. 42, Iss: 11, pp 1819-1826
TL;DR: The iodide/triiodide redox couple has good solubility, does not absorb too much light, has a suitable redox potential, and provides rapid dye regeneration, and it is expected that overall efficiencies above 15% might be achieved if half of this internal potential loss could be gained.
Abstract: Dye-sensitized solar cells (DSCs) have gained widespread interest because of their potential for low-cost solar energy conversion. Currently, the certified record efficiency of these solar cells is 11.1%, and measurements of their durability and stability suggest lifetimes exceeding 10 years under operational conditions. The DSC is a photoelectrochemical system: a monolayer of sensitizing dye is adsorbed onto a mesoporous TiO2 electrode, and the electrode is sandwiched together with a counter electrode. An electrolyte containing a redox couple fills the gap between the electrodes. The redox couple is a key component of the DSC. The reduced part of the couple regenerates the photo-oxidized dye. The formed oxidized species diffuses to the counter electrode, where it is reduced. The photovoltage of the device depends on the redox couple because it sets the electrochemical potential at the counter electrode. The redox couple also affects the electrochemical potential of the TiO2 electrode through the recombin...
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TL;DR: Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency as mentioned in this paper, and many DSC research groups have been established around the world.
Abstract: Dye-sensitized solar cells (DSCs) offer the possibilities to design solar cells with a large flexibility in shape, color, and transparency. DSC research groups have been established around the worl ...
8,707 citations
TL;DR: In this article, a Co(II/III)tris(bipyridyl)-based redox electrolyte was used in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8).
Abstract: The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co(II/III)tris(bipyridyl)–based redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight.
5,462 citations
Journal Article•
TL;DR: Mesoscopic solar cells that incorporate a Co(II/III)tris(bipyridyl)–based redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer are reported, enabling attainment of strikingly high photovoltages approaching 1 volt.
Abstract: Simultaneous modification of the dye and redox shuttle boosts the efficiency of a dye-sensitized solar cell. The iodide/triiodide redox shuttle has limited the efficiencies accessible in dye-sensitized solar cells. Here, we report mesoscopic solar cells that incorporate a Co(II/III)tris(bipyridyl)–based redox electrolyte in conjunction with a custom synthesized donor-π-bridge-acceptor zinc porphyrin dye as sensitizer (designated YD2-o-C8). The specific molecular design of YD2-o-C8 greatly retards the rate of interfacial back electron transfer from the conduction band of the nanocrystalline titanium dioxide film to the oxidized cobalt mediator, which enables attainment of strikingly high photovoltages approaching 1 volt. Because the YD2-o-C8 porphyrin harvests sunlight across the visible spectrum, large photocurrents are generated. Cosensitization of YD2-o-C8 with another organic dye further enhances the performance of the device, leading to a measured power conversion efficiency of 12.3% under simulated air mass 1.5 global sunlight.
5,385 citations
TL;DR: O'Regan and Gratzel demonstrated that a film of titania nanoparticles deposited on a DSC would act as a mesoporous n-type photoanode and thereby increase the available surface area for dye attachment by a factor of more than a thousand.
Abstract: Dye-sensitized solar cells (DSCs) are attractive because they are made from cheap materials that do not need to be highly purified and can be printed at low cost 1 . DSCs are unique compared with almost all other kinds of solar cells in that electron transport, light absorption and hole transport are each handled by different materials in the cell 2,3 . The sensitizing dye in a DSC is anchored to a wide-bandgap semiconductor such as TiO2, SnO2 or ZnO. When the dye absorbs light, the photoexcited electron rapidly transfers to the conduction band of the semiconductor, which carries the electron to one of the electrodes 4 . A redox couple, usually comprised of iodide/triiodide (I – /I3 – ), then reduces the oxidized dye back to its neutral state and transports the positive charge to the platinized counter-electrode 5 . In 1991, O’Regan and Gratzel demonstrated that a film of titania (TiO2) nanoparticles deposited on a DSC would act as a mesoporous n-type photoanode and thereby increase the available surface area for dye attachment by a factor of more than a thousand 1 . This approach dramatically improved light absorption and brought power-conversion efficiencies into a range that allowed the DSC to be viewed as a serious competitor to other solar cell technologies 6 . A schematic and energy level diagram showing the operation of a typical DSC is shown in Fig. 1. During the 1990s and the early 2000s, researchers found that organometallic complexes based on ruthenium provided the highest power-conversion efficiencies 7,8
1,215 citations
Cites background from "Characteristics of the Iodide/Triio..."
...The iodide/triiodide system has been particularly successful in DSCs because of the slow recombination kinetics between electrons in the titania with the oxidized dye and the triiodide in the electrolyte, which leads to long-lived electron lifetimes (between 1 ms and 1 s...
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TL;DR: It is demonstrated that a functionalized graphene sheet based ink can serve as a catalytic, flexible, electrically conductive counter electrode material and a new electrochemical impedance spectroscopy equivalent circuit is proposed that matches the observed spectra features to the appropriate phenomena.
Abstract: When applied on the counter electrode of a dye-sensitized solar cell, functionalized graphene sheets with oxygen-containing sites perform comparably to platinum (conversion efficiencies of 5.0 and 5.5%, respectively, at 100 mW cm−2 AM1.5G simulated light). To interpret the catalytic activity of functionalized graphene sheets toward the reduction of triiodide, we propose a new electrochemical impedance spectroscopy equivalent circuit that matches the observed spectra features to the appropriate phenomena. Using cyclic voltammetry, we also show that tuning our material by increasing the amount of oxygen-containing functional groups can improve its apparent catalytic activity. Furthermore, we demonstrate that a functionalized graphene sheet based ink can serve as a catalytic, flexible, electrically conductive counter electrode material.
1,040 citations
References
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TL;DR: In this article, the authors describe a photovoltaic cell, created from low-to medium-purity materials through low-cost processes, which exhibits a commercially realistic energy-conversion efficiency.
Abstract: THE large-scale use of photovoltaic devices for electricity generation is prohibitively expensive at present: generation from existing commercial devices costs about ten times more than conventional methods1. Here we describe a photovoltaic cell, created from low-to medium-purity materials through low-cost processes, which exhibits a commercially realistic energy-conversion efficiency. The device is based on a 10-µm-thick, optically transparent film of titanium dioxide particles a few nanometres in size, coated with a monolayer of a charge-transfer dye to sensitize the film for light harvesting. Because of the high surface area of the semiconductor film and the ideal spectral characteristics of the dye, the device harvests a high proportion of the incident solar energy flux (46%) and shows exceptionally high efficiencies for the conversion of incident photons to electrical current (more than 80%). The overall light-to-electric energy conversion yield is 7.1-7.9% in simulated solar light and 12% in diffuse daylight. The large current densities (greater than 12 mA cm-2) and exceptional stability (sustaining at least five million turnovers without decomposition), as well as the low cost, make practical applications feasible.
26,457 citations
TL;DR: Cis-X 2 Bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) complexes were prepared and characterized with respct to their absorption, luminescence, and redox behavior.
Abstract: cis-X 2 Bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) complexes (X=Cl - , Br, I - , CN - , and SCN - ) were prepared and characterized with respct to their absorption, luminescence, and redox behavior. They act as efficient charge-transfer sensitizers for nanocrystalline TiO 2 films (thickness 8-12 μm) of very high internal surface area (roughness factor ca. 1000), prepared by sintering of 15-30-nm colloidal titania particles on a conducting glass support. The performance of cis-di(thiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) (1) was found to be outstanding and is unmatched by any other known sensitizer
5,785 citations
TL;DR: A dye-sensitized heterojunction of TiO2 with the amorphous organic hole-transport material 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene (OMeTAD) was described in this article.
Abstract: Solar cells based on dye-sensitized mesoporous films of TiO2 arelow-cost alternatives to conventional solid-state devices1. Impressive solar-to-electrical energy conversion efficiencies have been achieved with such films when used in conjunction with liquid electrolytes2. Practical advantages may be gained by the replacement of the liquid electrolyte with a solid charge-transport material. Inorganic p-type semiconductors3,4 and organic materials5,6,7,8,9 have been tested in this regard, but in all cases the incident monochromatic photon-to-electron conversion efficiency remained low. Here we describe a dye-sensitized heterojunction of TiO2 with the amorphous organic hole-transport material 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene (OMeTAD; refs. 10 and 11). Photoinduced charge-carrier generation at the heterojunction is very efficient. A solar cell based on OMeTAD converts photons to electric current with a high yield of 33%.
3,386 citations
TL;DR: In this article, the incident photon to current efficiency (IPCE) of DSCs increases with increase in the haze of the TiO2 electrodes, especially in the near infrared wavelength region.
Abstract: Dye-sensitized solar cells (DSCs) using titanium dioxide (TiO2) electrodes with different haze were investigated. It was found that the incident photon to current efficiency (IPCE) of DSCs increases with increase in the haze of the TiO2 electrodes, especially in the near infrared wavelength region. Conversion efficiency of 11.1%, measured by a public test center, was achieved using high haze TiO2 electrodes. This indicates that raising the haze of TiO2 electrodes is an effective technique for improvement of conversion efficiency.
1,844 citations
TL;DR: A new powerful tool to study the electron lifetime in dye solar cells as a function of the photovoltage (Voc) ; the open-circuit voltage-decay (OCVD) technique is developed and has certain advantages over frequenIn summary, the temperature effect on the arrangement of stilbenoid dendrimers on HOPG is presented in this work.
Abstract: Recently, a new class of photoelectrochemical cells based on nanoscaled porous metal oxide semiconductors (dye-sensitized solar cell) has promoted intense research due to the prospects of cheap and efficient conversion of visible light into electricity and of new applications such as transparent solar cells. It is widely agreed that the electron-transfer kinetics play a major role in determining the energy conversion efficiency of dye-sensitized solar cells. 3] Herein, we develop a new powerful tool to study the electron lifetime in dye solar cells as a function of the photovoltage (Voc) ; the open-circuit voltage-decay (OCVD) technique. This technique has certain advantages over frequenIn summary, the temperature effect on the arrangement of stilbenoid dendrimers on HOPG is presented in this work. It is seen that SD12 molecules form well-ordered hexagonal nanostructures at 16 C. However, if the adlayer is annealed at 65 C, the adlayer structure is changed into a well-ordered parallelogram nanostructure in a close-packed arrangement with a higher surface coverage. The phenomenon described here supports the earlier reports on two liquid-crystalline phases for SD12. The results in this research are useful in understanding the phase transition of SD12 as well as metastable complex systems with temperature.
1,156 citations