"Colloidal quantum dots (CQDs) have recently attracted significant attention as a candidate material for optoelectronic devices, and in particular photodetectors and solar cells. These materials can be manufactured in the solution phase and spin-cast onto a variety of substrates, significantly reducing the cost of device fabrication. Additionally, the bandgap of CQD films can be tuned to allow absorption of specific wavelength regions by varying the diameter of the CQDs, due to the quantum confinement size effect. To maintain efficient charge extraction in these devices, the thickness of the CQD layer is restricted, resulting in devices that are limited by non-complete absorption. To improve efficiencies it is necessary to decouple the optical thickness from the electrical thickness by employing novel light-trapping schemes. Plasmonics offers the opportunity to confine light in sub-wavelength volumes, increasing the absorption in thin films. Discrete metal particles can be fabricated on a glass substrate, by simple self assembly or by nano-fabrication techniques, before the CQD are spin cast thus allowing plasmonic scattering structures to be incorporated into the cells without significantly increasing the complexity or cost of cell fabrication. By integrating plasmonic light trapping based on sub wavelength scattering structures with CQD devices, we will aim to dramatically increase the absorption, while maintaining good electrical characteristics, and hence achieve gains in overall performance and efficiency. Additionally, we will study the physical mechanisms behind plasmonic enhancement by employing FDTD simulations to investigate the scattering behaviour of single particles and periodic arrays embedded in CQD films, and combine this with simple conceptual models to design optimal scattering structures. These will be fabricated on CQD devices with the aim of providing the maximal absorption enhancement possible with plasmonic structures."
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