Adsorption and electrochemical properties of photoelectrodes depending on TiO2 film thickness for dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) consist of a photoelectrode, electrolytes, and a counter electrode. In this work, we prepared the photo electrode using a commercial paste coated on F-doped SnO2 (FTO) glass substrates by the screen printing method; the thicknesses of the coated layers were 5, 9, and 14 μm. We developed an adsorption apparatus to understand the adsorption mechanism of dye molecules depending on TiO2 thin film thickness and to obtain precise adsorption amounts without involving a desorption step. Commercial N719 dye was employed to measure the adsorption data, which were then analyzed using the pseudo-first-order and pseudo-second-order models. The diffusion coefficient of the electrolyte containing the iodide/triiodide redox couple was determined by polarization measurements. Electrochemical properties in terms of electron harvesting and electron transport depending on film thickness were evaluated based on incident photon to current conversion efficiency, intensity-modulated photocurrent spectroscopy, and intensity-modulated photovoltage spectroscopy.