Douglas Detert EE235 Prof. Connie Chang March 2, 2009
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A brief overview ofPlasmonic Nanostructure Design for Efficient Light Coupling into Solar Cells
V.E. Ferry, L.A. Sweatlock, D. Pacifici, and H.A. Atwater, Nano Letters, 8 4391
Douglas DetertEE235Prof. Connie Chang
March 2, 2009
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Douglas Detert — EE235 — March 2, 2009
Solar Cell Design/Material Considerations
• Conventional solar cells (e.g. Silicon) require thick absorption layers for complete absorption
• Thin film solar cells (e.g. CdTe, CIGS) decrease bulk recombination effects and allow for higher quality absorber materials
• Problem: Thin film cells are limited by decreased absorption, carrier excitation, and photocurrent
• Solution: Texture top/bottom surfaces to enhance light absorption
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Douglas Detert — EE235 — March 2, 2009
Surface Plasmon Polariton Enhanced Solar Cells
• Surface Plasmon Polaritons (SPPs) are collective oscillations of free electrons at metal/dielectric boundaries
• SPPs are highly localized to interfaces and propagate easily for microns. Energy in SPP modes enhances absorption
• Momentum mismatch between incident light and SPPs does not allow for direct excitation of SPPs
• Goal: Design a nanostructure back contact that scatters light into SPP mode
Barnes. J Opt A-Pure Appl Op 8 S87-S93 (2006)
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Douglas Detert — EE235 — March 2, 2009
Scattering From a Single Groove
• Light energy is scattered into two key modes
• Photonic (~semiconductor)
• SPP (~interface)
• Both enhance photoabsorption, but photonic modes are not supported in extremely thin structures
Hy
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Douglas Detert — EE235 — March 2, 2009
Results: Scattering From a Single Groove
• Finite-difference time-domain (FDTD) simulations paired with modal decomposition analysis
• Three physical effects involved in incoupling efficiencies:
• Fabry-Pérot resonance of thin film
• Photonic mode excitation at SPP resonance wavelength
• Polarization resonance of scatterer
• Film thickness and scatterer geometry affect above properties
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Douglas Detert — EE235 — March 2, 2009
Effect of Groove Dimensions
• Groove width: SPP modes break down at large groove sizes, photonic mode flattens out
• Groove depth has little effect on incoupling efficiency
• Ridge-like structure: enhances photonic mode
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Douglas Detert — EE235 — March 2, 2009
Conclusion & Outlook
• Groove-like nanostructures improve photoabsorption in thin film solar cells by coupling light to various modes, including interfacial SPP modes.
• Incoupling to SPP modes allows for enhancement in thin film solar cells
• To date, solar cells enhanced by SPPs have been fabricated with only top-layer patterning.
Pillai et al. JAP 101 093105 (2007)