Tristan L. Temple

Optical properties of gold and aluminium nanoparticles for silicon solar cell applications

The optical properties of metal nanoparticles are explored as a function of lateral size, shape, aspect-ratio and metal type. Simulations based on the discrete dipole approximation are compared with experimental measurements of arrays of metal nanoparticles fabricated by electron-beam lithography. Careful selection of experimental parameters ensures minimization of far-field and near-field coupling, and inhomogeneous broadening, thus allowing comparison with single particle simulations. The optical properties of Au nanoparticles are compared with similar Al nanoparticles for each particle type. For solar cell light-trapping applications, we require metal nanoparticles that exhibit extinction peaks near the band-edge region of the absorbing material, as well as low absorption and large optical cross-sections. Al nanoparticles are shown to be of interest for amorphous silicon solar cells, but their applications for polycrystalline solar cells is limited by the presence of an interband region in the near-inf...

Role of the spacer layer in plasmonic antireflection coatings comprised of gold or silver nanoparticles

Abstract. Metal nanoparticles (NPs) can increase the absorption of light within semiconductors and hence improve the efficiency of solar cells. We experimentally investigate the effect that gold and silver NPs have on the reflectance of silicon wafers. The NPs are fabricated using the low cost, large area technique of thermal dewetting. We show that a dielectric spacer layer between the NPs and the semiconductor is required to achieve a net reduction of reflection. Furthermore, the optimum thickness of the spacer layer is found to be independent of NP size and metal type.

Tunable Low-loss Plasmonic Mirror for Diffuse Optical Scattering

The influence of driving field interference on light scattering is demonstrated for arrays of randomly arranged silver nanodiscs near a silver mirror. The peak driving field intensity is spectrally tuned by varying the separation distance between the nanodisc array and the mirror, while the plasmonic resonance position is tuned by modifying the nanodisc diameter. Scattering is maximized when the resonance position coincides with the peak driving field intensity. The optimized plasmonic mirror exhibits 60% diffuse reflectance at a wavelength of 950 nm with low (~10–12%) broadband absorption losses, for 6% surface coverage of 200-nm-diameter nanodiscs on 110 nm SiO2.

Improved fabrication of metal nanoparticles for photovoltaic applications

We demonstrate that ion beam milling and high temperature annealing can be used to modify the surface coverage and three-dimensional shape of metal nanoparticles, thus enabling optimization of the optical properties for solar cell applications.

Spectral Tunability of Plasmonic Scattering by Silver Nanodiscs near a Reflector

The scattering properties of a plasmonic array can be reinforced by placing the array near a planar reflector. Finite- Difference-Time-Domain (FDTD) simulations have been used to demonstrate the key design challenge of modulating the electric field that drives the plasmonic scattering, by varying the distance of a single Ag nanodisc from a Ag reflector. We show that the thickness of the dielectric separation layer plays a critical role in determining the spectral characteristics and the intensity of the power scattered by a Ag nanodisc near a reflector. A possible application of the designed structure as a plasmonic light-trap for thin Si solar cells is also experimentally demonstrated. Electron-beam lithography has been used to fabricate a pseudo-random array of 150nm plasmonic Ag nanodiscs on SiO2 on a Ag reflector substrate. The plasmonic reflector shows a high diffuse reflectance of ~54% in the near-infrared, near-bandgap 600-900nm wavelength region for thin Si solar cells, with a low broadband absorption loss of ~18%. Wavelength-angle resolved scattering measurements indicate an angular scattering range between 20° to 80° with maximum intensity of the scattered power in the 20° to 60° angular range.