From identification of electrolyte degradation rates to lifetime estimations in dye solar cells with iodine and cobalt redox couples

Abstract

Degradation of dye solar cells is a major obstacle in their commercialization. Here we look into how much information on the degradation routes and rates one can extract from accessible measurements. Specifically we focus on tracking the color of the cell since all the main components of a dye solar cell have a specific color, and their color changes with degradation. Furthermore we look into extracting the degradation coefficients based on the specific color changes. One of the most vulnerable components of a dye solar cell is the electrolyte. Here we investigate the effect of two most interesting electrolyte compositions: 1) conventional iodine based electrolyte, which to date dominates the stability records of dye solar cells, and 2) cobalt complex electrolyte, which enables record high efficiencies. UV light is known to be highly detrimental as it destroys charge carriers – typically, a UV filter is recommended, but is it enough to prevent the loss of charge carriers? Here expectedly applying a UV filter improved the performance as the cells without a filter had only 4 ± 1 % of the initial efficiency left after a 1,000 hour light soaking test, whereas those with a filter maintained 90 ± 20 % of their initial efficiency. Applying a UV filter only hindered the loss of the charge carriers, but did not eliminate their degradation. From the color changes of the electrolyte, we could identify the degradation coefficient for these electrolytes. This analysis resulted in a highly relevant discovery: the loss rate of the charge carriers in iodine electrolyte was approximately double compared to cobalt electrolyte. Furthermore we could provide indicative estimates of future lifetimes of cells, which could be highly important in improving the lifetime of dye solar cells.