Insights into the limitations of solar cells sensitized with ruthenium dyes revealed in time-resolved spectroscopy studies

Abstract

The substitution of iodide electrolytes with cobalt ones has led to the current champion laboratory efficiencies for dye-sensitized solar cells (DSSCs). However, unlike with organic dyes, this strategy does not work with classical ruthenium dyes. Therefore, we compare DSSCs sensitized with a popular Ru dye (N719) using both types of electrolytes by exploring the electron dynamics occurring from sub-ps to seconds. An important limitation in the photocurrent of cobalt-based cells is revealed to be due to electron recombination between titania and oxidized Ru dyes, which is much higher than that in iodide-based cells and occurs on the time scale of tens and hundreds of ps. Electron recombination between titania and the electrolyte, taking place on the millisecond time scale, is responsible for further lowering of the photovoltage and fill factor of cobalt-based cells. Ruthenium dyes also exhibit lower absorption coefficients with respect to their organic counterparts. For this reason, we also investigate the effect of the changes in the titania layer thickness, addition of scattering nanoparticles and modifications in the TiCl treatment on DSSC performance.

Interplay between Ruthenium Sensitizer and Ruthenium Catalyst in Photoelectrochemical Cells with Different Water-Based Electrolytes

“…This wavelength is close to the maximum of the phosphorescence spectrum recorded for RuP in the dye-sensitized solar cell . Therefore, similar to our previous works, , we ascribed the rise of this signal to the decay of the stimulated emission from the RuP triplet state, which is due to the electron injection to TiO 2 . Furthermore, the complementary global fit obtained for the transient absorption data recorded in NIR also shows a ∼100 ps time component.…”

The Effect of Chloride Anions on Charge Transfer in Dye-Sensitized Photoanodes for Water Splitting

“…Finally, they were heated again at 150 °C for 5 min, 300 °C for 5 min, and 450 °C for 30 min. The thickness of the prepared mesoporous titania layer was about 2–3 μm [18]. The prepared photoanodes were immersed in one of the following solutions: (i) 0.3 mM ethanol solution of RuP dye (DN-S02, Dyenamo) or (ii) saturated ethanol solution of RuOEC catalyst (DN-S07, Dyenamo) at room temperature for about 16 h. In order to prepare the photoanode consisting of both RuP and RuOEC, sensitization of TiO 2 was performed as described elsewhere [13] allowing 1 h for RuP and then 16 h for RuOEC.…”

Synergistic Effect of Alkyl Chain Barriers on Heteroleptic Ruthenium Dyes and Co3+/2+ Complex Mediators for Reduced Charge Recombination in Dye-Sensitized Solar Cells

“…The enhanced recombination was assumed to arise from the interaction of Ru dye cation with Co 3+/2+ cations, affecting the interaction of injected electrons and dye cations. 41 (ii) Lack of electron injection from the triplet excited state of the Ru dye. 42 (iii) Charge separation loss due to electron transfer from the photoexcited Ru dye to Co 3+ redox species, leading to fever electrons injected into the TiO 2 .…”