ScienceDaily (Nov. 29, 2011) — Sometimes when people talk about solar energy, they tacitly assume that we're stuck with some version of the silicon solar cell and its technical and cost limitations. Not so.
Silicon solar cells have almost nothing to do with the biological photosystems in tree leaves and pond scum that use light energy to push electrons across a membrane -- and ultimately create sugars and other organic molecules.
At the time, nobody understood these complex assemblages of proteins and pigments well enough to exploit their secrets for the design of solar cells.
But things have changed
One team has just succeeded in making a crucial photosystem component -- a light-harvesting antenna -- from scratch. The new antenna is modeled on the chlorosome found in green bacteria
Testing for aggregation
The powdered pigments were carefully packaged and shipped by Fed Ex (because the Post Office won't ship chemicals) to Holten's lab at WUSTL and to David Bocian's lab at the University of California at Riverside.
Scientists in both labs made up green-tinctured solutions of each of the 30 molecules in small test tubes and then poked and prodded the solutions by means of analytical techniques to see whether the pigment had aggregated and, if so, how much had formed the assemblies. Holten's lab studied their absorption of light and their fluorescence (which indicated the presence of monomers, since assemblies don't normally fluoresce) and Bocian's lab studied their vibrational properties, which are determined by the network of bonds in the molecule or pigment aggregate as a whole.
In one crucial test Joseph Springer, a PhD student in Holten's lab, compared the absorption spectrum of a pigment in a polar solvent that would prevent it from self-assembling to the spectrum of the pigment in a nonpolar solvent that would allow the molecules to interact with one another and form assemblies.
"You can see them aggregate," Springer says. "A pigment that is totally in solution is clear, but colored a brilliant green. When it aggregates, the solution becomes a duller green and you can see tiny flecks in the liquid."