Interfaces in nanoscale photovoltaics

This thesis deals with material interfaces in nanoscale photovoltaics. Interface properties between the absorbing semiconductor and other employed materials are crucial for an efficient solar cell. While the optical properties are largely unaffected by a few nanometer thin layer, the electronic properties can change tremendously: electrical passivation of surface defects or contact selectivity can turn a piece of black rock with two metal leads into a highly efficient solar cell.
On the nanoscale, highly useful properties emerge compared to wafer-based or even thin-film semiconductors. Most importantly, not only directly incident but also adjacent light can be absorbed by the single nanoscale element. As a result, an array of single nanoscale structures with much empty space in between can absorb as much light as a continuous thin-film. This effect leads to largely reduced material consumption and, depending on the growth method, even to a faster growth process for a fully absorbing layer. While this property is enormously beneficial for photovoltaics, another feature creates a great challenge: by nanostructuring semiconductors, the surface-to-volume ratio becomes much larger compared to thin-film or wafer-based solar cells. Consequently, the influence of surface and interface properties on the overall performance of the nanoscale photovoltaic elements increases substantially.
In this thesis, nanowires are therefore chosen as a sensitive platform to study the impact of those interface properties on the overall photovoltaic performance. Based on the findings, device designs for more efficient practical nanowire array solar cells and a highly promising manufacturing process are proposed.