Role of alkyl groups regulating recombination and mass transport at cobalt electrolyte-dye interface in dye sensitized solar cells

•Probing cobalt redox mediators' selectivity as a function of structural variations in dyes.•Recombination and mass transport explored using small and large perturbation techniques.•Introducing alkyl chains on both dye and electrolyte to arrest recombination at the TiO2-dye-electrolyte interface.•Establishing new design rules for organic metal-free dyes to make them compatible with alternate redox mediators.