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.