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

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

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)

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

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

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

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)