The study of photosynthetic organisms has resulted in a molecular-level understanding of the design features allowing efficient, robust conversion of solar to chemical energy by complexes of antennae and reaction center proteins embedded in a membrane. Bio-inspired systems have successfully recreated individual elements of the photosynthetic apparatus. However, it has proved difficult to self-assemble the pieces with the right spatial separations while making a conductive, stable interface with electrodes. Designed proteins offer unique advantages: (A) they comprise a stable, polar matrix which can readily be designed on an atomic scale to constrain these components at any desired separation and orientation. (B) They can be designed to dock to specific binding sites to assemble modular multi-functional arrays. (C) Proteins are inherently non-toxic, and their production has become both inexpensive and environmentally benign in comparison to their synthetic counterparts. Taken together, these advantages compose a strong argument for using designed proteins in any supermolecular chemical endeavor.

We are developing a biologically inspired protein-based photovoltaic device in which the protein serves as a self-assembling ‘smart matrix’ which incorporates synthetic cofactors tailored for the purposes of photon absorption, charge separation and directional charge/hole spatial transfer (see the above figure). The proteins form the central element of the photovoltaic device. Synthetic phthalocyanine cofactors absorb light and synthetic porphyrins provide the active elements for charge separation and electron/hole transfer. The assembled device will be a robust supermolecular structure that self-assembles between transparent electrodes and efficiently generates a photocurrent. This approach combines the best aspects of biological macromolecules and synthetic molecular design to create a device that is 'green', robust, and has high light conversion efficiency.