Australian researchers have made a discovery that could influence the future of solar cell material design.

A team, led by Professor Timothy Schmidt at UNSW, has been looking at ways to capture the energy of visible light that is currently wasted due to the limitations of silicon, which is only able to access approximately 25 per cent of the solar spectrum.

One of the ways to reduce this waste is through the design of materials that can be coated on top of silicon to capture some of the energy of light that silicon cannot.

By incorporating singlet exciton fission, a process that generates two excitons from a single photon, it is hoped that silicon solar cell efficiencies can be boosted beyond 30 per cent.

The work, published in Nature Chemistry, examines the role of a short-lived (~8 billionths of a second), excited molecular complex called an excimer in singlet exciton fission.

 It overturns previous thinking by demonstrating that these singlet fission materials must avoid excimer formation to reach full potential in enhancing photovoltaic energy conversion.

“As we look to find ways to bring down the cost of solar energy harvesting, we should be designing materials that avoid excimer formation,” Professor Schmidt explains.

“Singlet exciton fission has enormous promise for improving the efficiency of solar cells, but its dynamics are complex and not well understood.”

By comparing the fission process when it is run both forwards and in reverse, the researchers were able to perform a simple test of theories for the mechanism of exciton fission.

The result suggests that what had previously been considered as an intermediate in the fission process may in fact be a source of loss.

With this understanding the team was able to propose an important new direction in the search for materials to be used in higher efficiency solar cells.