Biohybrid Photoprotein-Semiconductor Cells with Deep-Lying Redox Shuttles Achieve a 0.7 V Photovoltage

Photosynthetic proteins transduce sunlight into biologically useful forms of energy through a photochemical charge separation that has a close to 100% quantum efficiency, and there is increasing interest in their use as sustainable materials in biohybrid devices for solar energy harvesting. This work explores a new strategy for boosting the open circuit voltage of photoelectrochemical cells based on a bacterial photosynthetic pigment-protein by employing highly oxidizing redox electrolytes in conjunction with an n-type silicon anode. Illumination generates electron-hole pairs in both the protein and the silicon electrode, the two being connected by the electrolyte which transfers electrons from the reducing terminal of the protein to photogenerated holes in the silicon valence band. A high open circuit voltage of 0.6 V is achieved with the most oxidizing electrolyte 2,2,6,6-tetramethyl-1-piperidinyloxy, and this is further improved to 0.7 V on surface modification of the silicon electrode to increase its surface area and reduce reflection of incident light. The photovoltages produced by these biohybrid protein/silicon cells are comparable to those typical of silicon heterojunction and dye-sensitized solar cells.