A simple electrode assembly consisting of mixed 2D J-Aggregates organized on aminothiolate-modified Au (111), when placed in Fe²⁺/Fe³⁺ (Malonic acid) redox solution, generated a large cathodic photocurrent with quantum yield easily exceeding 20%, despite the close proximity of the J-aggregate to the metal surface that generally causes strong quenching of the excited J-aggregate. The relationship between the photocurrent quantum yield and dye mixing ratio revealed a distinct super additive effect of dye mixing closely related to the dye supersensitization in silver halide imaging system. The results have been analyzed to obtain new insights into the supersensitization mechanism such as the hole-trapping model, the exciton-trapping model, etc. as previously proposed.