University of Bristol

Rapid urbanisation and a population predicted to increase by more than a billion people over the next 20 years places a huge strain on current global energy resources. Solar energy has long been a strong contender for clean energy production. With approximately 10^24 J reaching land each year, the potentially available energy is several thousand times larger than global usage. The challenge is harnessing this energy in a cheap, efficient way that is, preferably, compatible with existing infrastructure.

Photosynthetic organisms, like plants, have already perfected several aspects of solar energy capture. In particular, (almost) every photon that they absorb is successfully used to trigger the photosynthetic reaction cycle. In this respect, synthetic solar cells are less efficient as they waste a large proportion of absorbed photons as heat. However, they out-compete natural photosynthesis in other ways: they can absorb a larger fraction of the sunlight and do not have to use the energy they produce to rebuild damaged proteins. The aim of this proposal is to derive and apply a set of design principles for artificial photosynthetic devices that mimic natural organisms’ ability to efficiently use absorbed photons, without their other disadvantages.

Previous studies have focused on materials with a high degree of spatial and energetic ordering to efficiently transfer energy from the site of photon absorption to the ‘reaction centre’, where it is used to excite an electron. Such controlled set-ups can be hard to manufacture. However, recent research suggests that striking the right balance between naturally occurring disorder and molecular motion in a material may actually be the key to high efficiency in a more realistic model of the energy transfer. I will use computational models to explore the design implications of this new insight.

With an understanding of how to achieve the necessary balance and the extent to which contributing factors can be varied, I will then search for cheap, synthetic materials, such as polymer gels, that could optimally house isolated photosynthetic pigments. I will also explore the possibility of altering natural photosynthetic machinery to improve features such as protein stability without compromising efficiency.