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Title: Ultra-broadband antireflection coatings for multijunction solar cells using dielectric nanostructures
Author: Al Saleh, Yahya Husain Mohamed
ISNI:       0000 0004 6422 9453
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2017
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Optically excited geometrical Mie resonances in dielectric nanostructures can be utilised to directionally and strongly scatter light with zero loss over broadband ranges. The nanostructure (NS) shape, size, and surrounding dielectric environment affects the wavelength dependent scattering behaviour. If placed on a high index substrate the light is favourably scattered into the optically dense material. Nanostructures can also act as an optical impedance matching layer which can be utilised to design an ultra-broadband anti-reflection coating (ARC) which promises an enhanced performance for multi-junction solar cells. The challenge is to design structures that are strongly scattering with the appropriate modes to suppress reflection and leak any harvested light into the underlying substrate. In this thesis the design of dielectric nanostructures is investigated for application as an anti-reflection coating on high index substrates with the intent of application on four-junction multi-junction solar cells (4J-MJSC). By using three dimensional numerical modelling and Mie theory, materials suitable for this purpose are identified. Simulations are used to design the structures and optimise the properties of the ARC. The structures are found to be very good scatterers, however embedding them within current industry-standard coatings yield unfavourable results with higher reflections than their planar counterparts. A new design is tested and systematically varied from single planar layers to multi-layered nanostructures to investigate effects of increasing complexity of the structures. The developed coating is optimised by varying the shape, size, and pitch of structures. Multiple numerical modelling techniques are utilised and benchmarked against each other, namely: finite elements method (FEM), rigorously coupled wave analysis (RCWA), finite difference time domain (FDTD), layer optics, and Mie calculations where applicable. The new design offers low reflectivity over an ultra-broadband range that promises to improve the output of four-junction cells by up to 5.7%. Fabrication techniques are discussed and progress made towards a working sample is detailed.
Supervisor: Ekins-Daukes, Nicholas ; Maier, Stefan Sponsor: Wizārat al-Tarbiyah wa-al-Taʻlīm ; Oman
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral