Augmenting Photocurrent Using Photoproteins of Complementary Optical Characteristics

Research on solar energy conversion by photosynthetic proteins in a device setting has been primarily directed toward optimising charge separation and mediation, with much less attention paid to manipulating the absorption cross-section of the light harvesting proteins to boost current output. This chapter explores the benefits of incorporating optically-complementary variants of a photosynthetic protein in a stacked, tandem solar cell architecture that utilises a conductive polymer, poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), as a transparent electrode material. Two naturally-occurring red and green versions of a bacterial reaction centre/light harvesting 1 protein were used that vary only in the type of light harvesting carotenoid that feeds the central reaction centre module with excited state energy. In green/red tandem cells assembled with optically-complementary layers, a photocurrent was obtained that was consistently up to ≈20% stronger than could be obtained from tandem cells assembled with two optically-identical layers or cells in which the two types of protein were simply mixed. In addition, the use of PEDOT:PSS as an electrode material resulted in a 12-fold enhancement in photocurrent density compared to that achievable with platinum. The findings provide insights into the design of cost-effective photo-bioelectrochemical cells with superior photoelectric performance that exploit the diversity of naturally occurring photosynthetic pigments in an optimised manner.