Wrinkles and deep folds as photonic structures in photovoltaics


Some of the simplest light-harvesting systems in nature rely on the presence of surface structures to increase internal light scattering. We have extended this concept to increase the efficiencies of man-made solar energy harvesting systems. Specifically, we exploit the wrinkles and deep folds that form on polymer surfaces when subjected to mechanical stress to guide and retain light within the photo-active regions of photovoltaics. Devices constructed on such surfaces show substantial improvements in light harvesting efficiencies, particularly in the near-infrared region where light absorption is otherwise minimal. We report a vast increase in the external quantum efficiency of polymer photovoltaics by more than 600% in the near-infrared, where the useful range of solar energy conversion is extended by more than 200 nm. This method of exploiting elastic instabilities of thin, layered materials is straightforward and represents an economical route to patterning photonic structures over large areas to improve the performance of optoelectronics.

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Figure 1: Morphological evolution of wrinkles to folds.
Figure 2: Photovoltaic performance of polymer solar cells.
Figure 3: Photon flux diagrams of the optical stacks on flat, wrinkled and composite surfaces.
Figure 4: Flexible polymer solar cells constructed on flat and wrinkled surfaces.


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This work was supported by a grant from the Photovoltaics Program at ONR (N00014-11-10328) to J.B.K and Y.-L.L. J.B.K., Y.-L.L., P.K. and H.A.S. also acknowledge funding through the Princeton Center for Complex Materials, an NSF-sponsored MRSEC (DMR-0819860). N.C.P. and J.W.F. acknowledge the support of the Air Force Office of Scientific Research (US-AFOSR). S.J.O. and C.R.K. acknowledge the support of the NSF CBET programme (CBET-0854226). The authors would also like to thank B. Rand of IMEC for extensive discussions.

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J.B.K. fabricated and tested the polymer solar cells on rigid and flexible substrates. P.K. constructed the surfaces with wrinkles and folds. N.C.P. performed optical simulations and theory. J.B.K. and S.O. carried out local photocurrent mapping. All authors were involved in extensive discussions and data analyses. J.B.K. and Y.-L.L. wrote the manuscript with input from the other authors.

Correspondence to Yueh-Lin Loo.

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Kim, J., Kim, P., Pégard, N. et al. Wrinkles and deep folds as photonic structures in photovoltaics. Nature Photon 6, 327–332 (2012) doi:10.1038/nphoton.2012.70

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