The increase in demand for energy has made Photosystem I (PSI), which can convert solar energy into a charge separation with an efficiency near unity, a topic of great research interest. Redox mediators play an important role in the optimization of PSI based electrode systems. Profound understanding about how these mediators impact the photo-induced current of these bio-hybrid systems is necessary. Here we report the investigation of various mediators with formal potentials (E-0') that span the two electron transfer (ET) sites of PSI (E-0' from 0.48 to 0.65 V vs. Ag/AgCl). The present results have demonstrated that mediators with more positive formal potentials produced larger photocurrents. Ferricyanide was found to be the most effective mediator in this system at equilibrium potential, with a photocurrent density of 900 nA/cm(2). Additionally, the effects of the mediators' light absorbance and concentration properties have been studied. The mediators with light absorbance that overlap with the Qy band were found to have a more significant effect on photocurrent generation than mediators with absorbance overlap with the Soret band. This thorough study of these mediators facilitates PSI based applications, and offers a method to optimize bio-circuit devices that involve redox mediators. (C) 2013 The Electrochemical Society. All rights reserved.