A molecular tandem cell for efficient solar water splitting

Artificial photosynthesis provides a way to store solar energy in chemical bonds. Achieving water splitting without an applied external potential bias provides the key to artificial photosynthetic devices. We describe here a tandem photoelectrochemical cell design that combines a dye-sensitized photoelectrosynthesis cell (DSPEC) and an organic solar cell (OSC) in a photoanode for water oxidation. When combined with a Pt electrode for H₂ evolution, the electrode becomes part of a combined electrochemical cell for water splitting, 2H₂O → O₂ + 2H₂, by increasing the voltage of the photoanode sufficiently to drive bias-free reduction of H⁺ to H₂ The combined electrode gave a 1.5% solar conversion efficiency for water splitting with no external applied bias, providing a mimic for the tandem cell configuration of PSII in natural photosynthesis. The electrode provided sustained water splitting in the molecular photoelectrode with sustained photocurrent densities of 1.24 mA/cm² for 1 h under 1-sun illumination with no applied bias.