In-situ analyses of triiodide formation in an iodine-free electrolyte for dye-sensitized solar cells using electro-diffuse-reflection spectroscopy (EDRS)

Abstract

An in-situ analysis of I3− formation in an iodine-free electrolyte is carried out using electro-diffuse-reflection spectroscopy (EDRS). Using EDRS, a monochromatic blue laser source irradiates the photo-anode at an incident angle of 45°. The intensity of scattered light is varied by modulating the cell potential. This novel EDRS method enables the detection of variations in I3− concentration in the vicinity of the TiO2 layer even without adding iodine into the electrolyte. Thus, the formation and existence of I3− in an iodine-free electrolyte is empirically revealed for the first time. Interestingly, EDRS results for NaI-free electrolytes show no significant peaks for the I3− formation, confirming electron transport occurs without forming I3− in the elelctrolyte. It is hypothesized that electrons directly propagate through the iodide media by forming diiodide radicals under the harsh electrolyte conditions in which no I2 or NaI are added. Additionally, J–V curves and a.c. impedance are measured to determine the effects of iodine concentration for the iodine-free electrolyte. In conclusion, the EDRS method is to be used for the development of alternative redox couples by examining their transport phenomena for future DSSCs.