Abstract

There is an urgent need to develop renewable energy technologies to replace depleting fossil fuel resources and provide a carbon neutral source of power. Solar energy is an abundant resource that represents an attractive target to supplement this requirement and the development of efficient solar cell systems to capture even a small fraction of this enormous reserve is currently an important scientific and engineering challenge. Some of the key benefits of using biological materials to reach this goal are that the photosensitive components are significantly cheaper than synthetic analogues (e.g. semi-conductors), are self-assembled and, in some cases, are capable of self-repair. A recently established multidisciplinary consortium of groups based in the University of Cambridge has proposed to develop, test and optimise a novel microbial fuel cell-inspired technology that exploits the photosynthetic machinery of intact micro-organisms (unicellular algae and cyanobacteria) for biological solar power and biofuel generation. Bio-photovoltaic (BPV) cells aspire to be the biological alternative to existing synthetic solar cell technologies. Several key electrochemical factors limiting performance efficiency, including the density of the photosynthetic catalyst, the electron carrier concentration and light intensity, have been investigated for optimising light-driven power outputs. Furthermore, biofilms grown from photosynthetic fresh water or marine microorganisms have demonstrated light-driven electrical power generation without the addition of an artificial electron carrier that persisted for several weeks and was highly sensitive to ambient light levels. When connected in series, four BPVs (each 110 cm2) generated enough power to run a commercial digital clock. The efficiencies achieved thus far indicate that BPV technology is a viable alternative to biomass-based photobioreactor systems for the harvesting of solar energy.