Photosystem I-​based Biophotovoltaics on Nanostructured Hematite

The electronic coupling between a robust red algal photosystem I (PSI) associated with its light harvesting antenna (LHCI) and nanocrystalline n-​type semiconductors, TiO2 and hematite (α-​Fe2O3) is utilized for fabrication of the biohybrid dye-​sensitized solar cells (DSSC)​. PSI-​LHCI is immobilized as a structured multilayer over both semiconductors organized as highly ordered nanocrystalline arrays, as evidenced by FE-​SEM and XRD spectroscopy. Of all the biohybrid DSSCs examined, α-​Fe2O3/PSI-​LHCI biophotoanode operates at a highest quantum efficiency and generates the largest open circuit photo-​current compared to the tandem system based on TiO2/PSI-​LHCI material. This is accomplished by immobilization of the PSI-​LHCI complex with its reducing side towards the hematite surface and nanostructuring of the PSI-​LHCI multilayer in which the subsequent layers of this complex are organized in the head-​to-​tail orientation. The biohybrid PSI-​LHCI-​DSSC is capable of sustained photoelectrochemical H2 production upon illumination with visible light above 590 nm. Although the solar conversion efficiency of the PSI-​LHCI​/hematite DSSC is currently below a practical use, the system provides a blueprint for a genuinely green solar cell that can be used for molecular hydrogen production at a rate of 744 μmoles H2 mg Chl-​1 h-​1, placing it amongst the best performing biohybrid solar-​to-​fuel nanodevices.