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By the end of 2014, cumulative photovoltaic (PV) capacity globally reached about 178GW. The PV capacity growth curve is always positive. Traditionally dominated by silicon solar panels, researchers are under pressure to find better performing and cheaper materials and methods.
Researchers at the Cavendish Laboratory at the University of Cambridge are perfecting a method of artificial photosynthesis using a special chemical dye. The dye absorbs sunlight, affording it sufficient energy to inject one of its electrons into titanium dioxide nanoparticles to which the dye is attached. This process stimulates an electrical circuit which cycles many hundreds of times a second, creating a dye-sensitised solar cell, like a mini chemical engine.
Professor Jacqui Cole, head of the structure and dynamics group at the University of Cambridge, said: “The nature of the chemical dye is very important because it has to be able to absorb solar energy, providing the dye with sufficient energy, and then to release electrons into the nanoparticles to kick-start the electrical circuit.”
An exciting application of these solar cells is solar-powered ‘smart windows’ where the embedded cell is barely visibly in the glass. Such glass could power whole buildings in ‘smart cities’ independent of the electricity grid. There is therefore huge motivation for companies and researchers to find better chemical dyes that perform this dual process very well.
Perfecting this organic chemistry is difficult. Chemical computations are used to design synthetic molecules for optimum performance and help to validate the molecules quickly.
The National Service for Computational Chemistry Software at Imperial College, London (NSCCS) runs the computational models that test multiple molecule variants within a huge range of parameters to reveal the best design. The researchers’ understanding of how the molecules’ design can be verified is a vital consideration in proving the technology commercially, as is the cost and performance of the molecules. Cole said: “Researchers struggle to find the best chemical dyes in terms of stability, cost and performance.
“The economics of solar cell technology are governed by the price-to-performance ratio. It needs to be cheap compared with expensive silicon, but needs to raise its performance to get a better P/P ratio than silicon or other materials. We try to make better molecules that perform better – this is molecular engineering and it needs verification.”
The NSCCS has one of the few suites in the UK capable of the calculations used for this branch of organic chemistry, which need special Gaussian software and a high-performance processor.