The behaviour of plasmonic metal nanoparticles (MNPs) placed in contact with a thin dielectric film on a high refractive index substrate is examined through finite-difference time domain simulations. The optical properties of this configuration are studied in the context of light trapping for thin-film amorphous silicon (a-Si) solar cells. We explore several different MNP configurations including both silver (Ag) and aluminium (Al) nanocubes along with traditional Ag nanospheres for reference. We demonstrate a large increase in the fraction of light coupled into the substrate (Fsubs), and consequently in the absorbed power, by spacing nanocubes away from the substrate. Further study concluded that blue-shifting the plasmonic resonances significantly reduced parasitic absorption in the visible spectrum and increased forward scattering by the MNPs. Transitioning to Al MNPs facilitated a large blue-shift in the plasmonic resonances allowing broadband enhancement in light absorption. For wavelengths less than the band-gap of a-Si, combining the effects of Al nanocubes on a 20 nm SiO2 spacer layer with a 25% surface coverage resulted in a 13.8% increase in solar power absorption over cells with optimally designed Ag nanocube and nanosphere arrays, and a 38.9% enhancement over a MNP free reference cell.

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We examine the enhancement effects of switching from traditional silver nanoparticles (NPs), which are resonant within the solar spectrum, to nonresonant aluminium NPs, which have surface plasmon resonances outside the solar spectrum, on light absorption in thin-film amorphous silicon (a-Si) solar cells. We show that the Al nanocube is an excellent choice for light trapping on a-Si, yielding a 13.8% increase in absorbed power over a cell with Ag nanocubes and a 38% increase over a bare cell.

©Copyright Ryan J. Veenkamp, 2014 The undersigned hereby recommends to the Faculty of Graduate and Postdoctoral Affairs acceptance of the thesis Light trapping in thin-film silicon solar cells via plasmonic metal nanoparticles submitted by Ryan J. Veenkamp, B.Sc. Engineering Abstract Cost cutting for solar cells in grid power applications is necessary in order to drive large-scale adoption and use of renewable solar energy. Despite the large recent cost reductions in crystalline silicon solar cells, thin-film solar cells also have a viable place in the market. These cells have several potential advantages over their thicker bulk crystalline silicon cousins including lower embodied energy and material costs, higher optical absorption rates and lower material purity requirements. The continuing issue with thin-film solar cells is the short optical path length through the absorbing layer and solving this whilst not increasing recombination rates requires the use of clever light trapping techniques. The purpose of this thesis is to investigate the effectiveness of plasmonic nanoparticles, in particular nanocubes, for light trapping in thin-film solar cells through numerical simulation and experimental demonstrations. We first investigate the optical properties of plasmonic metal nanoparticles (MNPs) based on the potential for scattering incident solar radiation into an absorbing substrate at large angles, significantly increasing optical path length. MNPs are then optimized in terms of shape, size, material and dielectric environment, and their effect on short circuit current (J sc ) enhancement is characterized. Al nanocubes are shown in simulation to obtain up to 40% J sc enhancement and subsequently demonstrated on a thin-film nanocrystalline silicon solar cell to be the most viable option for light trapping.iii