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Title: Enhancing the efficiency of thin-film solar cells using rear-electrode plasmonic gratings
Author: Wincott, Matthew
ISNI:       0000 0004 6495 978X
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2016
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This work describes an investigation into optical methods to improve the optical absorption properties of thin-film organic solar cells. The focus lies on the incorporation of nano-scaled gratings into the rear metallic electrode of the cell. Finite Difference Time Domain simulations are used to explore the absorption of light within the solar cell structure, building on similar work by Abass et al. and Sefunc et al. Planar devices can be optimised by altering the layer thicknesses to achieve optimal absorption within the photoactive region. When gratings are incorporated, they are found to have significant effects on the absorption within the active layer, due to the excitation of surface plasmons, total internal reflection, and shifts in interference within the multilayer stack. The enhancements are analysed in greater detail by comparing with dispersion plots generated both theoretically and using further simulations, and provide a useful reference for future device design. Devices incorporating triangular, rectangular, and sinusoidal gratings, using both silver and aluminium electrodes, are investigated and demonstrate enhancements compared to optimised planar devices of up to 10% and 4.5% respectively using a triangular grating. Aluminium is therefore shown to be a useful material in the design of plasmonic solar cells incorporating gratings. Rectangular and sinusoidal gratings are also shown to provide enhancements of up to 6.5% and 8% respectively for silver gratings. Devices incorporating 2D gratings are shown to have similar enhancements and are insensitive to incident polarisation. Devices incorporating gratings display broad intolerance to grating parameters and good insensitivity to the angle of incidence up to around 15°. Factors that influence absorption in practical devices incorporating gratings such as illumination conditions and choice of substrate are discussed. Alternative active layer materials are discussed in terms of their likely impact on featured devices, including the effect of the introduction of additional layers. Practical steps towards the fabrication of experimental devices are described, including a demonstration of the use of a Focussed Ion Beam technique to generate ridges with periodicity down to 300 nm. Transfer to a soft intermediate polymer. PDMS is also demonstrated through a simple method with very high fidelity.
Supervisor: Assender, Hazel ; Smith, Jason ; Watt, Andrew Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available