COMPARATIVE ANALYSIS OF POLYSULFIDE ELECTROLYTE SYSTEMS FOR THE PERFORMANCE ENHANCEMENT IN CdS QUANTUM DOT-SENSITIZED SOLAR CELLS

Abstract

This study has focused on improving the performance and stability of TiO2 /CdS quantum dot sensitized solar cells by investigating two electrolyte optimization methods. One method has focused on solvent effects, and the other method is on redox chemistry optimization. In the first method, this study investigated the impact of the solvent, which consisted of pure methanol, pure deionized water, and a methanol-water mixture (7:3v/v). Among the three solvents, pure methanol produced the highest power output due to its low viscosity and high polarity, this is due to an enhancement in the ion mobility and redox kinetics, However, it seems to have a drawback due to high volatility compromising long-term stability. Although pure water has provided lower efficiency due to its limited ionic conductivity, the methanol-water mixture demonstrated a favorable balance between performance and stability in a specific ratio. Method two has focused on varying the molar concentration of Na₂ S. For this purpose, this work tested different concentrations ranges in 0.5 M to 2.5 M to identify the best ratio that illustrates the highest performance of photocurrent and efficiency. The optimal composition (2.5 M Na₂ S + 3.5 M S) achieved the highest efficiency, lower charge transfer resistance (Rp), and enhanced Incident Photon-to-Current Efficiency (IPCE) response. However, further increasing of Na₂ S to 3M reduced the performance because of the viscosity and side reactions. Overall, combining an optimized redox couple with a stable methanol-water solvent system resulted in a high-performing, reproducible, and practically viable electrolyte formulation. Both of these optimization approaches offer a promising route toward the development of more efficient and stable QDSCs, contributing to their future implementation in solar energy technologies.