Femtosecond Optical Probes of Mesoscopic Materials for Photovoltaics

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There is growing evidence that our increasing consumption of fossil fuels is leading to a change in climate. Such predictions have brought new urgency to the development of clean, renewable sources of energy that will permit the current level of world economic growth to continue without damage to our ecosystem. Photovoltaic cells based on organic or organic/inorganic hybrid materials have shown rapid improvements over the past decade, comparing favourably with existing inorganic semiconductor technology on energy, scalability and cost associated with manufacture. The most promising materials for organic or hybrid photovoltaics are based on blends of two components at whose interface light-generated excitations dissociate into charges contributing to a photocurrent. Blend morphology on the meso-scale plays a crucial role in these systems, with efficient photovoltaic operation requiring both large interfacial area and existence of carrier percolation paths to the electrodes. The proposed work will establish how both aims can be achieved, using a powerful new combination of non-contact femtosecond time-resolved techniques to examine a range of novel mesoscopic blends. This methodology will allow the simultaneous examination of exciton diffusion and dissociation, charge-carrier generation, recombination and conductivity, providing direct clues to the optimisation of materials for photovoltaics. Collaborations with researchers working on making photovoltaic devices will ensure that knowledge gained from these non-contact material probes will directly feed into enhancing device performance. This combined approach will allow the UK's exceptionally high expertise in the area of organic electronics to contribute effectively to its current goal of reducing harmful greenhouse gas emission.