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Above-bandgap voltages from ferroelectric photovoltaic devices


In conventional solid-state photovoltaics, electron–hole pairs are created by light absorption in a semiconductor and separated by the electric field spaning a micrometre-thick depletion region. The maximum voltage these devices can produce is equal to the semiconductor electronic bandgap. Here, we report the discovery of a fundamentally different mechanism for photovoltaic charge separation, which operates over a distance of 1–2 nm and produces voltages that are significantly higher than the bandgap. The separation happens at previously unobserved nanoscale steps of the electrostatic potential that naturally occur at ferroelectric domain walls in the complex oxide BiFeO3. Electric-field control over domain structure allows the photovoltaic effect to be reversed in polarity or turned off. This new degree of control, and the high voltages produced, may find application in optoelectronic devices.

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Figure 1: Model domain-wall architectures.
Figure 2: Light and dark IV measurements.
Figure 3: Role of domain-walls in the photovoltaic response.
Figure 4: Band structure in dark conditions and under illumination.
Figure 5: Domain-wall switching effect.


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The work at Berkeley was performed within the Helios Solar Energy Research Center, which is supported by the Director, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division, of the US Department of Energy under contract no. DE-AC02-05CH11231. J.S. acknowledges support from the Alexander von Humboldt Foundation. Y.H.C. would like to acknowledge the support of the National Science Council, R.O.C., under contract no. NSC 98-2119-M-009-016.

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S.Y.Y. and J.S. conceived and designed the experiments. S.Y.Y., J.S. and S.J.B. performed the experiments. P.S., C.H.Y., M.D.R., P.Y., Y.-H.C. and J.W.A. contributed material and analysis. S.Y.Y., J.S., S.J.B., J.F.S., L.W.M. and R.R. co-wrote the paper.

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Correspondence to S. Y. Yang.

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Yang, S., Seidel, J., Byrnes, S. et al. Above-bandgap voltages from ferroelectric photovoltaic devices. Nature Nanotech 5, 143–147 (2010).

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