Understanding the physics of the light-matter interaction in materials with the perovskite crystal structure is an extremely active and exciting topic at present. Inorganic-organic hybrid perovskites have provided an entirely new class of optoelectronic materials with excellent photovoltaic performance (over 22% solar power conversion efficiency), and have further potential for use in light emitters. However, the physics of what happens after light is absorbed in these compounds is poorly understood: some studies have concluded that free, mobile charges are created directly, while other work has reported the formation of excitons - bound electron-hole pairs. In this PhD project the student will investigate how free charges and excitons are created and subsequently move, using ultrafast terahertz spectroscopy. This is an advanced experimental method that probes the conductivity of materials as they respond to pulses of light with <1ps duration.