This thesis explores the manner in which light interacts with matter, and the subsequent control of photogenerated charge. Firstly, we consider the nature of photogenerated charge in the context of mixed ionic electronic conductors. We introduce a new interpretation of surface photovoltage measurements for these materials and demonstrate control over transport of charge throughout the material.

Thereafter, we explore the physical implications of concentrating light. We present a theoretical study detailing it may be possible to concentrate light without the loss of energy by the generation of entropy through photon multiplication. In the context of silicon photovoltaics, we analyse the achievable benefits of light concentration in real world environments. Experimentally, we outline how the effectiveness of concentrating devices may be measured using spatially resolved photoluminescence measurements.

Finally, we conduct an extensive ultrafast spectroscopic study exploring the nature of light and charge in a cell. The mathematical basis and workflow is initially introduced, before outlining how ultrafast measurements of live cells can rich information on photoexcited dynamics of living systems.