Intriguing Photochemistry of the Additives in the Dye-Sensitized Solar Cells

Abstract

Over the years numerous mixes of chemical compounds have been tried in the electrolytes of dye-sensitized solar cells in efforts to improve their efficiency. How these chemicals interact with each other and the photoelectrode has received surprisingly little attention. Here we report results from a systematic study of two I-/I3electrolytes and their additives using infrared and Raman spectroscopy together with quantum chemical calculations. In the LiI electrolyte competing interactions between lithium cation and the solvent MPN and the additives TBP, NMBI and GuSCN were identified. These interactions could inhibit the interaction of lithium ions with the TiO2 surface. It was found that under Raman excitation of PMII solution in contact with the photoelectrode, efficient generation of I3takes place. For LiI solution, in addition, a Dye-I2 complex is formed. The results could be explained by diffusion limited build-up of I3and depletion of Iconcentrations in the focal area of the excitation beam and by reduction of I3via conduction band electrons of TiO2 beyond the focal region. To explain the formation of Dye-I2 complexes in the LiI electrolyte solutions a multi-step regeneration mechanism is proposed. It was found that GuSCN reduces the I3concentration in the electrolyte solutions studied, in the LiI electrolyte in addition it binds to lithium ions and nearly depletes the Dye-I2 complexes. From infrared spectra, it became clear that preventing water entering the DSCs during the preparation stages in ambient air is a demanding task. The identified interactions paint an intriguing new photochemical landscape of the function of the dye-sensitized solar cells giving guidelines for further development of the devices.

Demonstration of 12 Years Outdoor Working of Highly Durable Dye-Sensitized Solar Cell Modules Employing Hydrophobic Surface Passivation and Suppression of Biased Distribution of Iodine Ions

“…The dark-yellow electrolyte for the initial stage changed to reddish brown at the lower edge of the electrode, whereas the color changed to pale yellow at the upper edge. The Raman signal assigned to I 3 – , extremely weakened with a significant increase in the broadband luminescence at the upper edge. By contrast, there was no change in the I 3 – signal intensity and a slight increase in the luminescence at >2000 cm –1 at the lower edge.…”

Fabrication and characterization of novel hybrid nanocomposites with application in solar cells

“…The aforementioned observation is possibly attributed to the presence of the high amount of the hydrophilic KI in the polymer blend electrolyte samples. Finally, in the spectrum of the PVP/PEG blend-based polymer electrolyte employing TBP and GuSCN additives, a lowintensity peak at 2057 cm -1 appeared, which is attributed to the C-N stretching of SCN anion of GuSCN [527].…”

“…Moreover, there is a small broadening of the vibrational band of PVP at 1660 cm -1 that appeared in the PVP/PEG blend-based polymer electrolytes compared to the pure PVP/PEG polymer blend which could be due to PVP-I2 complexation, taking into account that KI:I2 wt% ratio was fixed at 10:1 [497]. The absorption peak at about 2057 cm -1 that appeared in all polymer blend electrolyte spectra is attributed to the C-N stretching of SCN anion of GuSCN [527]. By increasing the amount of BMII in the polymer blend electrolytes, some extra peaks and differences in their spectra appeared.…”