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 lightharvesting 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.