Scientists: Nature teaches green, efficient sunlight harvesting

Posted Sep 26, 2011 by Elizabeth Cunningham Perkins
Solar power cells are not advanced enough to match human energy needs, but an international team of scientists wrote that new studies of natural, clean, solar-powered complex systems already hint how to capture, transfer and store sunlight efficiently.
Scientists have studied natural sunlight harvesting circuits more more than a century  to learn how ...
Scientists have studied natural sunlight harvesting circuits more more than a century, to learn how to build clean, efficient solar energy technology.
John Davey (S. John Davey)/
In an article published September 23 in the journal Nature Chemistry, collaborating chemists from universities in the United States, Canada, the UK and the Netherlands detailed their survey of the most recent studies of natural sunlight-harvesting antenna complexes in plants and microorganisms, and summarized the lessons learned from photosynthesis into plans and recommendations to guide scientists and engineers designing future solar energy technologies, which the team expects will be capable of plugging into ever-abundant sunlight, converting and storing its energy and flowing the power over long distances, within vast arrays of microscopic energy grids, ScienceDaily reported.
University of Toronto chemist Greg Scholes explained how natural photosynthesis inspired the team's vision of developing and demonstrating human-made molecular energy circuits to capture, regulate, amplify and direct raw solar energy:
"More than 10 million billion photons of light strike a leaf each second. Of these, almost every red-coloured photon is captured by chlorophyll pigments which feed plant growth."
According to the researchers, a primary challenge is routing the energy from sunlight that is captured and stored for only a billionth of a second by colored dye or pigment molecules, called chromophores, before it is lost:
Though scientists have been studying photosynthesis for more than 100 years, replicating the design principles involved in this complex natural process will require overhauling many currently practiced chemical synthesis procedures; new approaches will be needed to mimic the way nature's chromophores are organized and the way natural molecular excitation energy is tuned to optimize light-harvesting within solar antenna complexes in leaves and algae.
Mimicking artificially the quantum coherence the team discovered is involved in electronic excitation transport in nature might present the biggest chemical dynamics challenge, according to the scientists.
Yet a clear framework for the design and synthesis of working molecular-scale artificial photosynthesizing antenna units and systems can be discerned from recent findings, and developed for the future through deeper research into several key how-to questions, the team claimed.
The plan recommended in their paper includes: engineering artificial chromophores with large absorption capacity; arranging these pigment molecules in optimal patterns on the antennas; taking advantage of the light-absorbing molecules' collective properties, including exploiting quantum mechanical principals; identifying environmental factors taking place in the classical physics realm that affect quantum coherence and the transport of electric excitation energy in photosynthesis; and integrating regulatory mechanisms to ensure excess energy dissipates without causing damage.
UC Berkeley physical chemist Graham Fleming asserted, "Solar energy is forecasted to provide a significant fraction of the world's energy needs over the next century, as sunlight is the most abundant source of energy we have at our disposal. However, to utilize solar energy harvested from sun¬light efficiently we must understand and improve both the effective capture of photons and the transfer of electronic excitation energy."