Silicon Nanocrystals Embedded in Silicon Carbide for Tandem Solar Cell Applications

This thesis presents work on silicon nanocrystals (Si NCs) embedded in silicon carbide (SiC), which are expected to have a higher bandgap than bulk Si due to quantum confinement, with a view to using them in the top cell of a multijunction solar cell. It discusses photoluminescence, carrier transport, and dopant diffusion in SiC-embedded Si NCs, as well as the preparation and characterisation of Si NC-based multijunction solar cells.

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Tandem solar cells consist of multiple individual solar cells stacked in order of increasing bandgap, with the cell with highest bandgap towards the incident light. This allows photons to be absorbed in the cell that will convert them to electricity with the greatest efficiency, and is the only solar cell concept to surpass the theoretical efficiency limit of a conventional solar cell so far.
This work is concerned with the development of silicon nanocrystals (Si NCs) embedded in silicon carbide, which are expected to have a higher bandgap than bulk Si due to quantum confinement, for use in the top cell of a two-junction tandem cell. Charge carrier transport and recombination were investigated as a function of various parameters. Distortion of luminescence spectra by optical interference was highlighted and a robust model to describe transport of majority carriers was developed. Furthermore, a range of processing steps required to produce a Si NC-based tandem cell were studied, culminating in the preparation of the first Si NC-based tandem cells. The resulting cells exhibited open-circuit voltages of 900 mV, demonstrating tandem cell functionality.