My dissertation focuses on organic light emitting diodes (OLEDs) and photovoltaic cells. OLEDs are used in many commercial displays, and solar cells are one of the most promising technologies for renewable energy production. In particular my work has focused on the question how magnetic fields affect the optical and electronic properties of the devices. My goals have been twofold: to understand the detailed scientific mechanism behind magnetic field effects, and to improve the performance of the devices in the presence of magnetic fields.