Effect of electrolyte bleaching on the stability and performance of dye solar cells

Degradation of dye solar cells (DSCs) under severe ageing conditions may lead to loss of the tri-iodide in the electrolyte - a phenomenon known as electrolyte bleaching. Monitoring changes in the tri-iodide concentration as a result of degradation mechanisms and understanding their causes and effects are fundamental for improving the long-term stability of DSCs. In this contribution a strongly accelerated ageing test (1 Sun visible light, 1.5 Suns UV light, T = 110 degrees C for 12 h) was performed on DSCs in a double-sealed masterplate configuration to purposely induce severe electrolyte bleaching, and its effects on the performance and stability of DSCs with different initial tri-iodide concentrations [I-3(-)](0) were investigated. The cells with low [I-3(-)](0) suffered a severe loss in short circuit current density J(SC) (up to 85%). Also a significant loss of open circuit voltage V-OC was observed and this loss was proportional to [I-3](0) with the highest V-OC drop observed with the highest [I-3(-)](0). Non-destructive analysis techniques based on the limited current density, JSC vs. light intensity, and photographic image analysis, were used to quantify the [I-3(-)] loss, which was found to be ca. 50 mM and independent of [I-3(-)](0). Quantitative model based V-OC analysis in terms of changing [I-3(-)] revealed that the degradation responsible for the V-OC drop was dominated by an unknown mechanism that is unrelated to [I-3(-)](0). The methods and results reported here help separating and identifying different degradation mechanisms related to electrolyte bleaching in DSCs.