UC San Diego nanostructures will raise thin-film solar cell ...( Thanks to nanostructures that scatte...)

Thanks to nanostructures that scatter and channel light, University of California, San Diego electrical engineers are working toward thin-film single junction solar cells with the potential for nearly 45 percent sunlight-to-electricity conversion efficiencies. This UC San Diego effort to break the theoretical limit of 31 percent efficiency for conventional single junction cells recently received a big funding boost from the U.S. Department of Energys Solar America program.

In November 2007, a team of Jacobs School electrical engineers led by professor Edward Yu won an $885,000 grant from the U.S. DOE to further develop their thin-film and nanowire solar cell devices that incorporate nanostructures, including semiconductor quantum wells and photon-scattering nanoparticles.

The new devices could lead to big gains in thin-film solar cell efficiency by increasing both the number of photons thin-film solar cells absorb and the number of excited electrons the same devices collect.

The most recent estimate of the maximum power conversion efficiency under normal illumination conditions that one can expect with our new thin-film solar cell approach is approximately 45 percent. This is a very large improvement over the 31 percent maximum theoretical efficiency for todays solar cells with classic p-n junctions, said Edward Yu, the Principal Investigator on the three-year DOE grant.

Electrical engineering professors Paul Yu and Deli Wang are co-PIs on the project.

From the outside, the optimized devices behave just like traditional thin-film solar cells. But inside, the nanostructures enable the solar cells to circumvent an important tradeoff that has stymied past attempts to incorporate quantum wells into thin-film solar cells in order to boost device efficiency. Quantum wells can increase solar cell efficiency by raising photon absorption by lowering the energy band gap.

In the past, engineers have tried to a
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