Electrochemical Impedance Spectroscopy Study of the KI:EG Molar Ratio Effect on the Electrochemical and Interfacial Properties of KI:EG:I2 Deep Eutectic Electrolytes for Dye-Sensitized Solar Cells

Using electrochemical impedance spectroscopy (EIS), a technique that analyzes the electrical response of a system subjected to a sinusoidal disturbance in order to probe its physicochemical properties, this study determined an optimal molar ratio of 1:7 between ethylene glycol (EG) and potassium iodide (KI). This composition significantly improves the electrochemical performance of the KI, EG, and I2 electrolyte for photovoltaic applications. Four formulations with KI:EG molar ratios of 1:5, 1:7, 1:9, and 1:11 were synthesized. The amount of diiodine (I2) was fixed at 0.1 mol% relative to the amount of KI. These electrolytes were then characterized by EIS. The series resistance (Rs), charge transfer resistance (Rct), diffusion resistance (Rw), CPE (constant phase element) parameter, and exponent (n) were extracted and compared. The results show that the formulation with KI:EG = 1:7 has the lowest Rct (3.054 Ω) and Rw (7.296 Ω) values, indicating optimal redox kinetics and improved ion transport within the electrolyte. This molar ratio corresponds to a minimum Rs value (5.612 Ω), indicating reduced series resistance. The mechanisms of solvation, viscosity, and ion diffusion are examined. This work, based exclusively on screening by electrochemical impedance spectroscopy (EIS), highlights the decisive role of solvent composition in electrolyte performance. It identifies an optimal molar ratio window that strikes a balance between redox efficiency and ion mobility, with a view to improving DSSC performance.