"There is great interest in organic materials with semiconducting electronic properties. This arises from both a scientific point of view (how can a plastic be a semiconductor?) and a technological point of view as these materials can be used to make light-emitting diodes, lasers and solar cells. The performance of all these devices is strongly affected by exciton diffusion, a process that is little studied or understood (particularly compared with charge transport) largely because of the lack of reliable measurement techniques. The purpose of this proposal is to make a breakthrough in the measurement, understanding and control of exciton diffusion in organic semiconductors, and so create a new generation of materials and devices with enhanced performance due to control of exciton diffusion. The key elements of the study are first to develop and validate advanced measurements of exciton diffusion. This will open up the whole topic of exciton “transport” and provide the tools for us (and others) to explore the physics of exciton diffusion and how it is affected by a range of factors relating to the structure of the materials and how they are processed. The following phase of work will use information about the main factors affecting exciton diffusion to develop strategies for controlling it. A particular challenge is to increase exciton diffusion which will then lead to improved efficiency of organic solar cells. We aim to address this both by applying the structure-property relations we develop and by developing directional exciton transfer, including quantum coherent energy transfer. This is an unconventional approach to improving organic solar cells, which could not only improve their efficiency, but also greatly simplify their structure, leading to a breakthrough in their manufacturability. Control of exciton diffusion arising from the proposed research will also lead to strategies for increasing the efficiency of organic light-emitting diodes and lasers."