Dye-sensitized solar cells (DSCs) with cobalt-based mediators with efficiencies surpassing the record for DSCs with iodide-free electrolytes were developed by selecting a suitable combination of a cobalt polypyridine complex and an organic sensitizer. The effect of the steric properties of two triphenylamine-based organic sensitizers and a series of cobalt polypyridine redox mediators on the overall device performance in DSCs as well as on transport and recombination processes in these devices was compared. The recombination and mass-transport limitations that, previously, have been found to limit the performance of these mediators were avoided by matching the properties of the dye and the cobalt redox mediator. Organic dyes with higher extinction coefficients than the standard ruthenium sensitizers were employed in DSCs in combination with outer-sphere redox mediators, enabling thinner TiO(2) films to be used. Recombination was reduced further by introducing insulating butoxyl chains on the dye rather than on the cobalt redox mediator, enabling redox couples with higher diffusion coefficients and more suitable redox potential to be used, simultaneously improving the photocurrent and photovoltage of the device. Optimization of DSCs sensitized with a triphenylamine-based organic dye in combination with tris(2,2'-bipyridyl)cobalt(II/III) yielded solar cells with overall conversion efficiencies of 6.7% and open-circuit potentials of more than 0.9 V under 1000 W m(-2) AM1.5 G illumination. Excellent performance was also found under low light intensity indoor conditions.

Dye-sensitized solar cells (DSSCs) have attracted considerable interest as a low cost and renewable means of harnessing solar energy.[1] In order to make these devices competitive with other photovoltaic technologies, many attempts have been made to increase the photoconversion efficiency. One concept is to combine an n-type TiO 2 -based photoanode with a p-type NiO-based photocathode, in a tandem configuration in order to capture more of the solar spectrum and improve the open-circuit potential (V OC ). [2,3] Complementary to the photoanode, a photoexcited dye injects a hole into the valence band of the NiO cathode, which travels to the FTO charge collector. The reduced dye is oxidized by the redox couple in the electrolyte which diffuses to the photoanode (tandem-DSSC) or passive counter electrode (p-DSSC) where the redox cycle is completed ( Figure S1). Therefore, the development of an efficient photocathode is one of the key elements in achieving an effective tandem-DSSC. Here we describe a NiO-based p-DSSC giving 64% incident photon-to-current efficiency (IPCE) and a short circuit current (J SC ) of 5.48 mAcm À2

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Dye-sensitized solar cells (DSCs) are celebrating their 30th birthday and they are attracting a wealth of research efforts aimed at unleashing their full potential. Righteous font designed by Astigmatic and licensed under the Open Font License.

In tandem: Employing a molecular dyad and a cobalt-based electrolyte gives a threefold-increase in open-circuit voltage (V(OC)) for a p-type NiO device (V(OC) = 0.35 V), and a fourfold better energy conversion efficiency. Incorporating these improvements in a TiO(2)/NiO tandem dye-sensitized solar cell (TDSC), results in a TDSC with a V(OC) = 0.91 V (see figure; CB = conductance band, VB = valence band).

A series of donor−π−acceptor dyes with different electron-withdrawing groups were designed and synthesized for p-type dye-sensitized solar cells. The modification of dye structures shows significant influence on the photophysical, electrochemical, and photovoltaic performance of the dyes. DSSCs based on these dyes show maximum 63% and minimum 6% of incident monochromatic photon-to-current conversion efficiencies. The two dyes with the highest (P1) and lowest (P3) efficiencies were studied by femtosecond transient absorption spectroscopy, which shows a fast injection rate of more than (250 fs)−1 for both dyes. Such fast injection corresponds to more than 90% injection efficiency. The photoinduced absorption spectroscopy study of sensitized NiO films in the presence of electrolyte showed poor regeneration of P3 due to an insufficient driving force. This, together with aggregation of the dye on the NiO film, explained the poor solar cell performance.

We investigated a range of different mesoporous NiO electrodes prepared by different research groups and private firms in Europe to determine the parameters which influence good quality photoelectrochemical devices. This benchmarking study aims to solve some of the discrepancies in the literature regarding the performance of p-DSCs due to differences in the quality of the device fabrication. The information obtained will lay the foundation for future photocatalytic systems based on sensitized NiO so that new dyes and catalysts can be tested with a standardized material. The textural and electrochemical properties of the semiconducting material are key to the performance of photocathodes. We found that both commercial and non-commercial NiO gave promising solar cell and water-splitting devices. The NiO samples which had the two highest solar cell efficiency (0.145% and 0.089%) also gave the best overall theoretical H2 conversion.

Photoactive NiO electrodes for cathodic dye-sensitised solar cells (p-DSCs) have been prepared with thicknesses ranging between 0.43.0 µm by spray-depositing pre-formed NiO nanoparticles on fluorine-doped tin oxide (FTO) coated glass substrates. The larger thicknesses were obtained in sequential sintering steps using a conventional furnace (CS) and a newly developed rapid discharge sintering (RDS) method. The latter procedure is employed for the first time for the preparation of pDSCs. In particular, RDS represents a scalable procedure that is based on microwave-assisted plasma formation that allows the production in series of mesoporous NiO electrodes with large surface areas for p-type cell photocathodes. RDS possesses the unique feature of transmitting heat from the bulk of the system towards its outer interfaces with controlled confinement of the heating zone. The use of RDS results in a drastic reduction of processing times with respect to other deposition methods that involve heating/calcination steps with associated reduced costs in terms of energy. P1-dye sensitized NiO electrodes obtained via the RDS procedure have been tested in DSC devices and their performances have been analysed and compared with those of cathodic DSCs derived from CS-deposited samples. The largest conversion efficiencies (0.12 %) and incident photon-to-current conversion efficiencies, IPCEs, (50 %) were obtained with sintered NiO electrodes having thicknesses of ~1.5-2.0 μm. In all the devices, the photogenerated holes in NiO lived significantly longer ( h ~ 1 s) than has previously been reported for P1-sensitized NiO 2 photocathodes. In addition, P1-sensitised sintered electrodes give rise to relatively high photovoltages (up to 135 mV) when the triiodide-iodide redox couple is used.