Thin films for silicon-based tandem photovoltaics 1=Energy 2=Solar Technology

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More than 90% of photovoltaic solar cells are made from crystalline silicon, and this market share is increasing as worldwide installations approach the terawatt level. The best single-junction silicon cells have efficiencies of up to 26.7%, and record cells are closing in on silicon's maximum efficiency of 29.4%. This limit can be exceeded by depositing or mounting a wider bandgap semiconductor on top of the silicon-based solar cell to form a tandem configuration, which are capable of exceeding efficiencies of 35%. Such device architectures are very timely, and if successful will have a significant impact on global energy production through renewable sources.Much attention has focused on placing a variety of thin film semiconductors onto silicon (e.g. perovskites, CdTe, CIGS), but less attention has been paid on the interface with the silicon. This PhD project will address the fundamental science underpinning the interface between the silicon and the thin film semiconductor to accelerate the development of tandem cells. The aim is to develop ultra-thin passivation films (< 1 nm) using atomic layer deposition (ALD), which exhibit excellent thermal and electrical stability when applied to semiconductor surfaces. The objective will be to develop a fundamental understanding of the passivation mechanism at the atomic scale and how processes can be manipulated in order to achieve optimal long-term thermal and electrical properties. The films developed will then be applied in a range of contexts; mainly silicon photovoltaics (with a focus on tandems), but also on other applications such lithium ion battery anodes.