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A brief overview of Plasmonic 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 Detert EE235 Prof. Connie Chang March 2, 2009. Solar Cell Design/Material Considerations.
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A brief overview ofPlasmonic Nanostructure Design for Efficient Light Coupling into Solar CellsV.E. Ferry, L.A. Sweatlock, D. Pacifici, and H.A. Atwater, Nano Letters, 8 4391 • Douglas Detert • EE235 • Prof. Connie Chang • 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
Barnes. J Opt A-Pure Appl Op 8 S87-S93 (2006) 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
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
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
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
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. JAP101 093105 (2007)