IEEE Nanotechnology Symposium – Session 7 – Nano-Enabled Energy II

Here are the highlights from Session 7 – Nano-Enabled Energy II from day two of the IEEE San Francisco Bay Area Nanotechnology Council 6th Annual Symposium“Nanotechnology: State of the Art & Applications”

Presentation archive for talks not linked below. Updated as the council receives the presentations.

Dr. David Predergast, Lawrence Berkeley National Laboratory (LBNL) Molecular Foundry, “Nature of Nano-Scale Interfaces and Mechanisms for Solar Energy Conversion.”

  • 5 Department of Energy (DOE) “User Facilities” across the US.
  • LBNL has 6 departments – he’s in the Theory Facility.
  • Large computational resources there and throughout the DOE
  • His specialty is simulating X-ray spectroscopy from.  Using the first principles he builds models tries to predict & interpret X-ray absorption spectra from the Advanced Light Source (LBNL).

Dr. Ted Kamins, Department of Electrical Engineering, Stanford University, “Semiconductor Nanowires for Photovoltaic Solar Cells: Single Junction, Heterojunction, and Compositionally Graded Arrays.”

  • Reviewed limits of planar solar cells.
  • Nanowire growth using Vapor Liquid Solid (VLS) technique.  Best explanation of bottom-up fabrication of nanowires I’ve seen on slides 6 to 9.
  • To increase solar cell efficiency, there are two approaches:
    • Increase absorption of solar spectrum by changing material, thickness, and/or shape.
    • Increase collection of photogenerated carriers by changing material quality, and/or geometry.
  • Why use nanowires for solar cells?
    • Decrease reflectance (light trapping)
    • Increase junction area
    • Decrease distance between carrier generation and collection
    • Wider range of materials
    • Resonance effects
    • Less material used
  • Vertical aligned wires – can be built but require expensive Si wafer.  Caltech group figured out how to break nanowires off Si substrate for reuse a few times.
  • Random alignment wires – not as efficient as vertical but may be lower cost.  Need to decide between vertical & random wires on economics.
  • Methods to improve nanowire cells:
    • Build core shell structure so electron pair only needs to travel a short distance laterally.
    • Vertically stacked multi-junction solar cells (blue top, green middle, red bottom)
    • Ning @ ASU built different nanowires with different band gaps positioned along the substrate to increase efficiency.
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