Biohybrid solar cells: Fundamentals, progress, and challenges

Over the last two decades many reports have been published on diverse types of biohybrid electrodes utilizing components of the photosynthetic apparatus. Currently, the development of such devices does not extend beyond laboratory research. In the future, these electrodes could be used in biosensors, solar cells, and as a new technique to investigate photosynthetic pigment-protein complexes. Efficiency of light-to-current conversion is particularly important for solar cell applications. Selection of a suitable substrate for special pigment-protein complexes is a significant challenge for building an inexpensive and efficient device. Various combinations of pigment-protein complexes and substrates, as well as different measurement conditions make it difficult to directly compare performance of various solar cells. However, it has been shown, that one of the possible substrate materials, namely nanostructured TiO₂, is the most preferred material for the immobilization of pigment-protein complexes in terms of both cost and efficiency. The photocurrent values reaching several mA, were reported for TiO₂-based biohybrid electrodes. However, the efficiency of TiO₂-based biohybrid is still far from its potential maximum value due to fundamental challenges related to designing an optimum interface between TiO₂ nanostructure and pigment-protein complexes containing electron transferring cofactors. To date, counterproductive back reactions, also referred to as charge recombination, still dominate and lower internal quantum efficiency of these systems.