Optimising photochemical solar energy conversion in natural and artificial molecular systems.

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The underlying processes that convert solar photons into chemical or electrical energy in organic solar cells and in natural photosynthetic systems have many features in common [1,2]. In both cases, solar photons are absorbed by an assembly of molecules, followed by diffusion of the photogenerated exciton, dissociation into separated charges and separation of the charges across the device or membrane. Natural photosystems achieve charge separation with high quantum efficiency and with low apparent energy losses, suggesting that aspects of the structure of photosystems could be beneficial for artificial systems like solar cells. Thanks to their well understood structure they provide appealing model systems in which to study the process of photoinduced charge separation. For both photosystems and solar cells, the light emitted by the system when illuminated or subject to applied bias (i.e. luminescence), carries information about the different processes involved in the photochemical process and is key to understanding behaviour [3].The aim of this project is to develop a physics-based model of photochemical solar energy conversion that can be applied in parallel to photosystems and molecular solar cell structures, and use it along with experimental data to better understand the function of photosystems and optimise the design of solar cells. The project has the following objectives:1) To develop an existing model of the quantum dynamics of excitations in molecular systems to simulate the process of solar photochemical energy conversion in either photosystems or molecular solar cells.2) To use experimental measurements of light absorption and emission in such systems along with the model to identify the factors limiting energy conversion efficiency and suggest improved designs.3) To apply the methods to recently discovered varieties of photosystem in order to understand how they manage to drive photochemical reactions with light of lower energy than standard photosytems without loss in quantum efficiency [4].4) To use the understanding gained to suggest new arrangements of molecules in organic solar cells that could lead to improvements in the conversion efficiency by reducing non-radiative energy losses [3].