Red-shifting the surface plasmon resonance of silver nanoparticles for light trapping in solar cells
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Red-shifting the surface plasmon resonance of silver nanoparticles for light trapping in solar cells Fiona Jean Beck1, and Kylie Catchpole2 1 Center for Sustainable Energy Systems, Australian National University, Room 216, Building #32, Acton, Canberra, 0200, Australia 2 AMOLF, Amsterdam, Netherlands ABSTRACT Surface plasmons in metallic nanoparticle arrays have been shown to increase the absorption of an underlying silicon substrate. This has wide ranging applications, not least in the photovoltaic industry. Incident light excites localised surface plasmons in the silver nanoparticles and is coupled into the silicon in trapped modes. The radiative behaviour of the nanoparticle film is changed by the proximity of a high refractive index surface, causing radiation to be directed into the silicon and providing a light-trapping layer. We investigate a simple and effective method of tuning the surface plasmon resonance frequency, and hence the spectral region at which the absorption enhancement is seen, by varying the underlying dielectric. The particle geometry and distribution are modified by the surface conditions provided by the dielectric layer, and both this and the change in refractive index alter the resonance position. Three common dielectrics used in the photovoltaic industry were investigated as surfaces on which to form arrays of self-assembled silver nanoparticles atmospheric pressure chemical vapour deposited titanium dioxide (APCVD TiO2), low pressure chemical vapour deposited silicon nitride (LPCVD Si3N4) and thermally grown silicon dioxide (SiO2). We show, by optical and electrical measurements, that the red-shifted resonances produced by nanoparticle films on APCVD TiO2, and LPCVD Si3N4 with relatively high refractive indices, correspond to an increase in optical absorption and external quantum efficiency in thin, crystalline solar cells at longer wavelengths
INTRODUCTION Solar energy has an important role to play in decreasing our reliance on fossil fuels for energy production. Technological improvements and the massive expansion in the photovoltaic (PV) industry in the last decade have reduced the cost of solar electricity to less than US 22 cents per kWh for large installations in favourable, sunny locations, as quoted by Solarbuzz LLC 1 for March 2008. Further decreases are necessary to make solar energy commercially competitive across a broad market. Thin-film silicon solar cells are a promising candidate to drive down the cost of solar energy generation. However, there are several intrinsic disadvantages with thin-film technology that need to be overcome. Current commercial thin-film cells have a lower efficiency than crystalline cells: up to 7% compared to 22% for wafer- based, monocrystalline cells in production2. One of the most important considerations is light trapping; since silicon is a poor absorber of long wavelength light it is desirable to confine the light within the active silicon layer for as long as possible to promote absorption. Traditional techniques such as surfa
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