Energy Focus: Electronic bucket brigade could boost solar-cell voltages
- PDF / 1,198,174 Bytes
- 4 Pages / 585 x 783 pts Page_size
- 98 Downloads / 178 Views
ergy Focus Electronic bucket brigade could boost solar-cell voltages
I
f solar cells could generate higher voltages when sunlight falls on them, they would produce electrical power more efficiently than is currently possible. Now a team of researchers at Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California–Berkeley (UCB) has studied bismuth ferrite, or BFO, to determine how the photovoltaic process occurs in materials known as ferroelectrics, known for developing very high voltages under illumination. The researchers reported their findings in the September 16 issue of Physical Review Letters (DOI: 10.1103/PhysRevLett.107.126805). “We worked with very thin films of bismuth ferrite, or BFO, grown in the laboratory of our colleague Ramamoorthy Ramesh,” said Joel Ager of Berkeley Lab’s Materials Sciences Division (MSD), who led the research effort. “These thin films have regions—called domains—where the electrical polarization points in different directions. Ramesh’s group is able to make film with exquisite control over this domain structure.” Because BFO has a range of unusual properties, the group led by Ramesh, who is a member of MSD and a professor of materials sciences, engineering, and physics at UCB, has long studied
with respect to the substrate. As shown in the figure, relatively large defect-free regions of graphene monolayer were grown on the Au(111) surface. These findings were supported by low-energy electron diffraction measurements and Auger spectroscopy and confirmed the macroscopic formation of graphene on the Au(111) surface. The properties of the graphene/ metal contact were also investigated and were shown to be weaker than in any previously reported graphene/metal system. The Fermi wave vector, estimated from low-bias STM images, where standing
waves coming from the Au(111) surface are observed through the graphene layer, is in perfect agreement with the value for pristine Au(111). The minimum around the Fermi level observed in differential conductance plots, as obtained with STM, is associated with the Dirac point of the graphene’s electronic structure— an indication of the lack of doping for this system. The researchers said, “Our new method paves the way to extend the range of possible substrates for the epitaxial growth of graphene to other low reactivity metals.” Steven Trohalaki
its characteristics by building custom devices made from the material. The BFO films studied by Ager and his colleagues have a unique periodic domain pattern extending over distances of hundreds of micrometers. The domains form in stripes, each measuring 50–300 nm across, separated by domain walls 2 nm thick. In each of these stripes the electrical polarization is opposite from that of its neighbors. Because of the wide extent and highly periodic domain structure of the BFO thin films, the research team avoided the problems faced by groups who had tried to understand photovoltaic effects in other ferroelectrics, whose differences in polarity were thought to surround impurity atoms
Data Loading...
