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 ...

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Dye-Sensitized Solar Cells

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.

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Porphyrin-Sensitized Solar Cells with Cobalt (II/III)–Based Redox Electrolyte Exceed 12 Percent Efficiency

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.

Porphyrin-sensitized solar cells with cobalt (II/III)-based redox electrolyte exceed 12 percent efficiency (vol 334, pg 629, 2011)

Perhaps the largest challenge for our global society is to find ways to replace the slowly but inevitably vanishing fossil fuel supplies by renewable resources and, at the same time, avoid negative effects from the current energy system on climate, environment, and health. The quality of human life to a large degree depends upon the availability of clean energy sources. The worldwide power consumption is expected to double in the next 3 decades because of the increase in world population and the rising demand of energy in the developing countries. This implies enhanced depletion of fossil fuel reserves, leading to further aggravation of the environmental pollution. As a consequence of dwindling resources, a huge power supply gap of 14 terawatts is expected to open up by year 2050 equaling today’s entire consumption, thus threatening to create a planetary emergency of gigantic dimensions. Solar energy is expected to play a crucial role as a future energy source. The sun provides about 120 000 terawatts to ...

Recent advances in sensitized mesoscopic solar cells.

The dye-sensitized solar cell (DSC) provides a technically and economically credible alternative concept to present day p–n junction photovoltaic devices. In contrast to the conventional silicon systems, where the semiconductor assumes both the task of light absorption and charge carrier transport the two functions are separated here. Light is absorbed by a sensitizer, which is anchored to the surface of a wide band gap oxide semiconductor. Charge separation takes place at the interface via photo-induced electron injection from the dye into the conduction band of the solid. Carriers are transported in the conduction band of the semiconductor to the charge collector. The use of sensitizers having a broad absorption band in conjunction with oxide films of nanocrystalline morphology permits to harvest a large fraction of sunlight. Nearly quantitative conversion of incident photon into electric current is achieved over a large spectral range extending from the UV to the near IR region. Overall solar (standard AM 1.5) to current conversion efficiencies of 10.6% have been reached. New electrolytes based on ionic liquids have been developed that show excellent stability both under prolonged light soaking and high temperature stress. There are good prospects to produce these cells at lower cost than conventional devices. Here we present the current state of the field, and discuss the importance of mastering the interface of the mesoporous films by assisting the self-assembly of the sensitizer at the surface of the oxide nanocrystals.

Conversion of sunlight to electric power by nanocrystalline dye-sensitized solar cells

Transient absorption spectroscopy was employed to study charge-transfer dynamics in dye-sensitized nanocrystalline solar cells (DSSC) containing a new one-electron redox mediator, cobalt(II)-bis[2,6-bis(1‘-butylbenzimidazol-2‘-yl)pyridine] Photovoltaic cells incorporating this relay have yielded light-to-electricity power conversion efficiencies of up to 52% This rivals the performance of the tri-iodide/iodide couple that is currently almost exclusively used in DSSC Interception of the dye oxidized state by electron transfer from the Co(II) complex in diluted electrolyte was found to follow a first-order kinetics with a rate constant of km = 5 × 105 s-1 Above a threshold of 10-2 M, under which the cationic relay is essentially adsorbed onto the negatively charged particle surface, larger concentrations of the reduced mediator resulted in a linear increase of the apparent rate, yielding a second-order rate constant of km‘‘ = 29 × 106 M-1 s-1 Dynamics of the recombination reaction between injected co

CoII(dbbip)22+ Complex Rivals Tri-iodide/Iodide Redox Mediator in Dye-Sensitized Photovoltaic Cells

A series of new cobalt complexes [Co(LLL)(2)X(2)] were synthesized and evaluated as redox mediators for dye-sensitized nanocrystalline TiO(2) solar cells. The structure of the ligand and the nature of the counterions were found to influence the photovoltaic performance. The one-electron-transfer redox mediator [Co(dbbip)(2)](ClO(4))(2) (dbbip = 2,6-bis(1'-butylbenzimidazol-2'-yl)pyridine) performed best among the compounds investigated. Photovoltaic cells incorporating this redox mediator yielded incident photon-to-current conversion efficiencies (IPCE) of up to 80%. The overall yield of light-to-electric power conversion reached 8 % under simulated AM1.5 sunlight at 100 W m(-2) intensity and more than 4% at 1000 W m(-2). Photoelectrodes coated with a 2 microm thick nanoporous layer and a 4 microm thick light-scattering layer, sensitized with a hydrophobic ruthenium dye, gave the best results.

Hervé Nusbaumer

Papers

CoII(dbbip)22+ Complex Rivals Tri-iodide/Iodide Redox Mediator in Dye-Sensitized Photovoltaic Cells

An alternative efficient redox couple for the dye-sensitized solar cell system.