Nanosociety Meeting Friday @ 12pm, McCullough 115: Tuning the shape of Semiconductor Nanowires for Advanced Photovoltaics

Brian E Hardin bhardin at stanford.edu
Thu Nov 12 15:45:05 PST 2009


Jia Zhu (Cui Group) will be presenting his latest research on making
efficient nanostructured amorphous silicon solar cells at 12pm in McCullough
115. Pizza will be served.


Tuning the shape of Semiconductor Nanowires for Advanced Photovoltaics

*Jia Zhu*

Department of Electrical Engineering

Cui Group



*Tuning the shape of nanostructures can have a strong effect on photon
management and charge carrier collection for photovoltaics. Here we
demonstrate two examples of nanowire shape designing: nanocones and branched
nanowires.*

*Compared to uniform diameter nanowires, nanocones have been shown for
absorbing light with much reduced reflection due to near perfect impedance
match. One step further, we demonstrate a new concept of nanodome solar
cells, with nanocone arrays as the center piece of this design. The nanodome
solar cells will not only greatly reduce light reflection, but also
efficiently couple light into propagating wave, which dramatically enhance
light travelling path. This new design provides another approach to decouple
the direction of light absorption and charge collection, but with much
reduced surface area and material usage, compared to nanowire radial p-n
junction structure.** Amorphous Si solar cell was used as a demonstration of
concept. Nanodome solar cells can absorb 46% more sunlight than flat film
devices with the same thickness. We demonstrate nanodome devices with a
power efficiency of 5.9%, which is 25% higher than flat film one. This
nanodome design can be applied to a variety of other solar cell
technologies. *

*PbSe nanocrystals have shown greatly enhanced multi exciton generation
(MEG) effect, one important step toward third generation solar cells.
However, it is difficult o extract generated carriers from nanocrystals
without good transport pathways. Three dimensional branched nanowire, with
strong quantum confinement within two dimensions, and the connected third
dimension as an efficient charge carrier pathway, can be ideal for enhanced
MEG effect, light absorption, and carrier collection. We demonstrate
successfully a large area growth of PbSe Hyperbranced and Chiral Branched
Nanowires on a variety of substrates. More interestingly, Chiral Branched
Nanowires reveal a new nanowire growth mechanism, dislocation driven growth,
which can be applied to a variety of materials.*

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