This thesis is a study of material blends involving organic semiconductors and their application
to opto-electronic devices, particularly photovoltaic diodes. Its principal aim is to examine
the microstructure of the blend, where microstructure is defined as molecular ordering and
spatial arrangement on the nanometer to micrometer scale. In general, each chapter of the
thesis presents a novel means by which to influence the microstructure of organic semiconductor
blends. These techniques are used as a means to understand how the photophysics of optoelectronic
devices is influenced by microstructure. We establish some general principles of how
microstructure relates to device performance and also find high performance in some entirely
novel device structures and architectures. It is hoped that understanding developed here will
lead to improvements in the performance of organic photovoltaic devices.