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

: Seo, S.J.; Bialecka, K.A.; Kang, M.S.; Hinsch, A.; Moon, S.H.


Journal of power sources 275 (2015), pp.675-680
ISSN: 0378-7753
Journal Article
Fraunhofer ISE ()

An in-situ analysis of I-3(-) 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 degrees. The intensity of scattered light is varied by modulating the cell potential. This novel EDRS method enables the detection of variations in I-3(-) concentration in the vicinity of the TiO2 layer even without adding iodine into the electrolyte. Thus, the formation and existence of I-3(-) 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 I-3(-) formation, confirming electron transport occurs without forming I-3(-) 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 I-2 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.