Photosynthesis, the conversion of solar energy into chemical energy, fuels our increasing energy consumption through the use of fossil fuels derived from ancient organic matter. However, the associated greenhouse gas emissions have resulted in several problems such as climate change and environmental pollution. As a result of the increasing demand for alternative energy sources, decades of research have been dedicated to mimicking photosynthesis in artificial bio-hybrid devices. Photosynthesis is powered by two key proteins, Photosystem II (PSII) and Photosystem I (PSI), that act in series as biological pseudo-photodiodes. Both proteins can be extracted from a wide variety of plant materials and have the potential to be implemented on a global scale for low-cost solar energy conversion.

Photosystem I (PSI), in particular, is ideal for use in solar cells due to its innate ability to photoexcite electrons with a quantum efficiency approaching unity. In vivo, these electrons are then mediated to the water-soluble redox protein called ferrodoxin; in artificial biohybrid devices, these electron acceptor proteins must be replaced with electrodes and electrochemical mediators. In this work, novel PSI-based solar cells were prepared by using polyviologens as the electron-transport layer between the PSI protein and the indium tin oxide (ITO) anode. Redox polymer-modified electrodes are increasingly used as electron-transfer catalysts in electrochemical applications. Polyviologens are a unique class of organic polycationic polymers, which can rapidly accept excited state electrons from a primary donor such as PSI and subsequently donate them to a secondary acceptor. Our device is a unique example of the direct use of extracted PSI protein to create photoactive biohybrid electrodes and represents one of few reported methods for incorporating PSI into a solid-state device, eliminating the problems associated with wet photoelectrochemical cells, such as corrosion and leaks.