The Bulk Photovoltaic Efect in Polar Oxides for Robust and Eficient Solar Energy Harvesting

Andrew Rappe^a

^aUniversity of Pennsylvania, 200 South 33rd Street, Philadelphia, 19104, United States

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe September Meeting 2015 (NFM15)

Santiago de Compostela, Spain, 2015 September 6th - 15th

Invited Speaker, Andrew Rappe, presentation 105
Publication date: 8th June 2015

Solar energy is the most promising source of renewable, clean energy to replace the current reliance on fossil fuels. Ferroelectric (FE) materials have recently attracted increased attention as a candidate class of materials for use in photovoltaic devices. Their strong inversion symmetry breaking due to spontaneous polarization allows for excited carrier separation by the bulk of the material and voltages higher than the band gap (Eg), which may allow eciencies beyond the Shockley-Queisser limit. Ferroelectric oxides are also robust and can be fabricated using low cost methods such as sol-gel thin lm deposition and sputtering. Recent work has shown how a decrease in ferroelectric layer thickness and judicious engineering of domain structures and FE-electrode interfaces can dramatically increase the current harvested from FE absorber materials. Further improvements have been blocked by the wide band gaps (Eg =2.7{4 eV) of FE oxides, which allow the use of only 8-20% of the solar spectrum and drastically reduce the upper limit of photovoltaic eciency. In this talk, I will discuss new insight into the bulk photovoltaic eect, and materials design to enhance the photovoltaic eciency. We calculate from rst principles the current arising from the \shift current" mechanism, and demonstrate that it quantitatively explains the observed current. Then, we analyze the electronic features that lead to strong photovoltaic eects. Finally, we present new oxides that are strongly polar yet have band gaps in the visible range, oering prospects for greatly enhanced bulk photovoltaic eects.

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