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Copper-based metal complex redox mediators proved to be an efficient, futuristic electrolyte for dye-sensitized solar cell (DSC) applications addressing many critical issues of conventional iodide/triiodide electrolytes. However, copper redox mediators being bulkier than conventional iodine electrolytes impose movement restrictions contributing to unfavourable charge transfer processes. In the present manuscript, we analyzed the impact of TiO2 particle size (20 nm and 30 nm) on the photovoltaic parameters of DSCs using an organic D35 dye and an alternate copper redox mediator, Cu[(tmby)(2)](2+/1+). DSC photoanodes with 20 nm TiO2 particles realized a lower power conversion efficiency (PCE) of 6.32 +/- 0.07% in comparison to 7.36 +/- 0.12% efficiency achieved using DSCs made with 30 nm TiO2 particles. The improved PCE using 30 nm TiO2 particles is associated with the enhancement in short circuit current density (J(sc)), open-circuit potential (V-oc) and the fill factor (FF). Furthermore, comprehensive analysis of various charge transfer processes at discrete interfaces in these devices reveals collective enhancement in light-harvesting, dye regeneration and charge collection efficiency that ultimately contributed to achieving 16% improvement in PCE using 30 nm TiO2 particles.