Photosystem I (PSI) has drawn widespread interest for use in biomimetically inspired energy conversion devices upon extracting it from plants or cyanobacteria and assembling it at electrode surfaces. We report that ~1 micron thick films of PSI on gold electrodes provide an order-of-magnitude improvement in photo-generated current over that of a PSI monolayer although only one layer of PSI is in contact with the electrode in each case. We have investigated the mechanism for this dramatic improvement by monitoring the effect of PSI film thickness and electrochemical mediator on photoinduced current. The partitioning of hydrophobic mediators into the moderately hydrophobic PSI film creates an elevated concentration of electron acceptors to rapidly draw current from the interfacial, bound PSI layer as well as electron donors to turn over the P700 reaction centers dispersed throughout the film. We will also discuss design considerations in the fabrication of a photoelectrochemical cell that contains these thin films of PSI. At present, these prototype cells can be used to power simple devices such as calculators.