Biological photovoltaic systems that employ whole organisms are the most robust type, and lifetimes of multiple months have been observed.[9] The insulating outer membranes of whole cells impedes electron transfer from the sites of electron generation inside the cell to the anode.[3] As a result, conversion efficiencies are low unless lipid-soluble redox mediators are included in the system.[10] Cyanobacteria are typically used in these systems because their relatively simple arrangement of intracellular membranes compared to eukaryotic algae facilitates electron export.