Dye Regeneration Kinetics in Dye-Sensitized Solar Cells

The ideal driving force for dye regeneration is an important parameter for the design of efficient dye-sensitized solar cells. Here, nanosecond laser transient absorption spectroscopy was used to measure the rates of regeneration of six organic carbazole-based dyes by nine ferrocene derivatives whose redox potentials vary by 0.85 V, resulting in 54 different driving-force conditions. It was found that the reaction follows the behavior expected for the Marcus normal region for driving forces below 29 kJ mol^–1 (Δ<i>E</i> = 0.30 V). Driving forces of 29–101 kJ mol^–1 (Δ<i>E</i> = 0.30–1.05 V) resulted in similar reaction rates, indicating that dye regeneration is diffusion controlled. Quantitative dye regeneration (theoretical regeneration yield 99.9%) can be achieved with a driving force of 20–25 kJ mol^–1 (Δ<i>E</i> ≈ 0.20–0.25 V)