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Nature, News & Views

Photovoltaics

Harnessing leaf power

Nano Lett. 4, 1079-1083 (2004)

Could your laptop run on spinach? Perhaps. Das et al have isolated photosystem I, the central engine of photosynthesis, from chloroplasts of spinach leaves and tethered it to a thin film of gold deposited on a transparent, electrically conductive glass. They find that the photosystem generates an electric current in response to visible light, thereby acting as a photovoltaic cell.

The photosystem is a huge, many-molecule assembly, comprising 14 protein subunits and hundreds of chlorophylls, but it apparently remains functional when deposited on the substrate via a polyhistidine linker in the presence of peptide surfactants (which presumably surround the membrane-protein assembly to provide essential stabilization). The same trick works for the bacterial reaction centre from the photosynthetic purple bacterium Rhodobacter sphaeroides, a much simpler molecular assembly.

Das et al hope ultimately to achieve photovoltaic power conversion efficiencies of around 20%, which would be comparable to the best inorganic solar cells.

Philip Ball

CE&N June 14, 2004

Proteins that harvest light tapped for electronics

The remarkable light-harvesting ability of photosynthetic protein complexes in plants and certain bacteria can make the scientists who create photovoltaic devices turn green with envy. But using the complexes as photon-harvesting components in solid-state electronics has proven difficult: They aren't stable enough for practical use when removed from their native biological environs. Now, a group led by MIT electrical engineering professor Marc Baldo and Shuguang Zhang has developed a technique for integrating the light-harvesting complexes from Rhodobacter sphaeriodes and spinach's photosystem I into solid-state electronics [Nano Lett., 4, 1079 (2004)]. Using surfactant peptides, the team was able to stabilize the complexes so that their functionality wasn't diminished when incorporated into solid-state electronics. The researchers report that depositing an amorphous organic semiconductor between the photosynthetic complexes and the top metal contact was also crucial to successful integration. The technique preserves the complex's light-harvesting power for at least three weeks.