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

Abstract

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 °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 [I₃⁻]₀ were investigated. The cells with low [I₃⁻]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 [I₃⁻]₀ with the highest V_OC drop observed with the highest [I₃⁻]₀. Non-destructive analysis techniques based on the limited current density, J_SCvs. light intensity, and photographic image analysis, were used to quantify the [I₃⁻] loss, which was found to be ca. 50 mM and independent of [I₃⁻]₀. Quantitative model based V_OC analysis in terms of changing [I₃⁻] revealed that the degradation responsible for the V_OC drop was dominated by an unknown mechanism that is unrelated to [I₃⁻]₀. The methods and results reported here help separating and identifying different degradation mechanisms related to electrolyte bleaching in DSCs.