Electrochemical impedance analysis on the additional layers for the enhancement on the performance of dye-sensitized solar cell

A dye-sensitized solar cell is one of the representative photochemical solar cells. It has been actively studied and its performance has been much enhanced so far. For better performance, various additional layers such as compact, barrier, and light scattering layers have been applied. Compact and barrier layers suppress the charge recombination with redox electrolyte and light scattering layer improves the light harvesting. Although it was confirmed that these layers were clearly effective for the performance enhancement, there is still a variety of opinions concerning their electrochemical impedance analyses. Therefore, this work tried to analyze their effect on the internal impedance using electrochemical impedance spectroscopy. The most widely used materials were employed for the fabrication of additional layers. TiCl ₄ and Zn(NO₃)₂â̂™6H ₂O aqueous solutions, and a 400 nm sized TiO₂ were used for compact, barrier, and light scattering layers, respectively. The photovoltaic characteristics confirmed their effect on the performance and their impedance spectra were analyzed according to high, middle, and low frequency bands. As a result, these layers mainly affected the impedance in the middle frequency range because the change of TiO₂/dye/electrolyte interface was significantly associated with this impedance. Finally, all three layers were applied to a single cell and the performance was considerably increased with reduced charge recombination and improved light harvesting.