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April 14, 2007

3D solar cells boost efficiency and a separate quantum understanding of photosynthesis

Unique three-dimensional solar cells that capture nearly all of the light that strikes them could boost the efficiency of photovoltaic (PV) systems while reducing their size, weight and mechanical complexity.

the blades of grass like design has resulted in a big jump in current generated. Ready said the three-dimensional panels produce about 60 times more current than traditional solar cells. But current is only half the equation. To generate electricity, a cell has to churn out voltage as well. And so far, that's where Ready's invention has fallen short. There's still too much resistance within the cell to produce the type of electricity that's needed. But he said he'll now focus on reworking the interface to smooth out the kinks.

In a separate development, In a paper entitled, Evidence for wavelike energy transfer through quantum coherence in photosynthetic systems, researchers report the detection of “quantum beating” signals, coherent electronic oscillations in both donor and acceptor molecules, generated by light-induced energy excitations, like the ripples formed when stones are tossed into a pond.


Sunlight absorbed by bacteriochlorophyll (green) within the FMO protein (gray) generates a wavelike motion of excitation energy whose quantum mechanical properties can be mapped through the use of two-dimensional electronic spectroscopy. Credit: Image courtesy of Greg Engel, Lawrence Berkeley National Laboratory, Physical Biosciences Division


Electronic spectroscopy measurements made on a femtosecond (millionths of a billionth of a second) time-scale showed these oscillations meeting and interfering constructively, forming wavelike motions of energy (superposition states) that can explore all potential energy pathways simultaneously and reversibly, meaning they can retreat from wrong pathways with no penalty. This finding contradicts the classical description of the photosynthetic energy transfer process as one in which excitation energy hops from light-capturing pigment molecules to reaction center molecules step-by-step down the molecular energy ladder.

"The classical hopping description of the energy transfer process is both inadequate and inaccurate," said Fleming. "It gives the wrong picture of how the process actually works, and misses a crucial aspect of the reason for the wonderful efficiency."

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