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SUMMARY:The bulk photovoltaic effect in polar oxides for robust and effici
 ent solar energy harvesting - Andrew M. Rappe (University of Pennsylvania)
DTSTART:20130626T100000Z
DTEND:20130626T110000Z
UID:TALK45980@talks.cam.ac.uk
CONTACT:Dr. Mike Towler
DESCRIPTION: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\ncl
 ass of materials for use in photovoltaic devices.  Their strong inversion 
 symmetry breaking due to spontaneous polarization allows for excited carri
 er separation by the bulk of the material and voltages\nhigher than the ba
 nd gap (Eg)\, which may allow efficiencies beyond the Shockley-Queisser li
 mit. Ferroelectric oxides are also robust and can be fabricated using low 
 cost methods such as sol-gel thin film deposition and sputtering.  Recent 
 work has shown how a decrease in ferroelectric layer thickness and judicio
 us engineering of domain structures and FE-electrode interfaces can dramat
 ically increase the\ncurrent harvested from FE absorber materials.  Furthe
 r improvements have been blocked by the wide band gaps (Eg =2.7-4 eV) of F
 E oxides\, which allow the use of only 8-20% of the solar spectrum and dra
 stically reduce the upper limit of photovoltaic efficiency.\n\nIn this tal
 k\, I will discuss new insight into the bulk photovoltaic effect\, and mat
 erials design to enhance the photovoltaic efficiency. We calculate from fi
 rst principles the current arising from the "shift\ncurrent" mechanism\, a
 nd demonstrate that it quantitatively explains the observed current.  Then
 \, we analyze the electronic features that lead to strong photovoltaic eff
 ects.  Finally\, we present new oxides\nthat are strongly polar yet have b
 and gaps in the visible range\, offering prospects for greatly enhanced bu
 lk photovoltaic effects.
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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