Quantifying limits and losses in nanoscale photovoltaics

The conversion efficiency of a solar panel is the most important lever in the cost of electricity it produces. For photovoltaics to make a significant and lasting impact as a renewable energy resource, the electricity costs have to decrease, and the conversion efficiency therefore has to increase.
The field of nanophotonics aims to understand and manipulate the interaction of light and matter at the nanoscale. Since this interaction is at the heart of the photovoltaic energy conversion process, it is only natural that nanophotonics can play an important role in achieving high efficiencies.
This thesis brings together experimental and theoretical contributions aimed at deepening the understanding of how nanophotonics can enhance photovoltaic conversion efficiencies. In particular, we focus on the photovoltage that a nanoscale solar cell can generate, both in the ideal case and with practical limitations.
We study a number of nanophotonic mechanisms that can enhance the efficiency of a photovoltaic device: spectrum splitting, metal-semiconductor core-shell nanowires, directivity in absorption, and escape probability enhancements. We also present a new experimental technique to measure quantitatively the absorption cross section of a single nanostructure. Using our new experimental technique, we characterize the limits and performance losses of a nanoscale photovoltaic device in detail.
Overall, this thesis provides new fundamental insights into nanoscale photovoltaics. Our findings strengthen the role of nanophotonics in photovoltaics, and may also be applied in other optoelectronic devices such as light emitting diodes.