Nanoscale interface engineering for silicon-based tandem photovoltaics 1=Energy 2=Solar Technology

Worldwide installations of photovoltaic solar cells are rapidly reaching the terawatt level. Crystalline silicon is used for more than 90% of these, and this market share is growing. 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 placing a wider bandgap semiconductor on top of the silicon base cell to form a tandem configuration. This could enable solar cells to have efficiencies of 35% or higher. The key to the success of such an approach is to ensure the incremental cost of the top cell is realistic in the context of the relatively low cost of the silicon base cell. Recent advances in wider bandgap low-cost manufacturable top cells (such as perovskites) make such tandem architectures extremely timely. If these are successful they will have a significant impact on global energy production by renewable sources.

The interface between the silicon and the wider bandgap material is the key topic to address at present. This PhD project will address the fundamental materials science of the interface between the silicon and the top cell to accelerate the development of tandem cells. Ultra-thin passivation films (< 1 nm) will be produced using atomic layer deposition (ALD), and these 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 may then be applied to a selection of silicon-based tandem photovoltaic architectures.