Use ultrafast lasers to probe the next-generation of solar cells

Researchers have been able to track the first fraction of a second after sunlight strikes solar cells.

Use ultrafast lasers to probe the next-generation of solar cells

Researchers have been able to track the first fraction of a second after sunlight strikes solar cells. This gives them insight into how they generate electricity.

Researchers could improve solar cells by probing the first moments of light conversion into electricity.

Researchers at Imperial College London developed the method using ultrafast lasers, X-rays, and radio waves to trigger a reaction, and measure the effects it has on the environment in just femtoseconds.

A team of researchers from Imperial University and Newcastle University have used this technique to study organic solar photovoltaic (OPV), materials that harness the sun's energy to generate electricity or water splitting.

OPV materials are being studied extensively as they offer cheaper renewable energy. Many of the current materials are inefficient or unstable because of the complex interaction between electrons excited by light.

A closer study of the fast interactions between electrons can provide valuable insight into the development of solar cells and catalysts.

More efficient devices

Professor Jon Marangos from Imperial's Department of Physics says that OPVs offer a cost-effective and flexible alternative to silicon-based solar photovoltaics and are therefore a promising option for future solar energy generation infrastructure.

"This work demonstrates how powerful our time-resolved Xray technique can be applied to a wider variety of materials. It may also provide insight that could lead to more efficient OPV devices."

The first step in solar energy conversion was probed by the team. This involved the reactions that occur when light strikes the material. To stimulate the reaction, they first fired a 15-femtosecond laser pulse at the material. Then, they followed that with an Xray pulse lasting only attoseconds (less then a millionth of a billionths of seconds), which measured the material's changes.

State that are rapidly changing

For the first time, the team was able to observe direct X-ray signatures showing the initial state of the material after electrons have been knocked out. This creates an "electron and hole" pair that can move through material.

In just 50 femtoseconds, the initial state transformed into a stable and new state. The observations were confirmed by calculations done at Newcastle University by Professor Tom Penfold, which showed that the initial state was determined by the distance between the molecules in the material.

Dr. Artem Bakulin from Imperial's Department of Chemistry says that this "sensitivity of the timeresolvedX-ray method directly to the initial electron dynamics occurring immediately after excitation of light opens the door for new insights into photophysics of a wide variety of organic optoelectronics and other materials."

Now, the team plans to investigate ultrafast charge dynamics within other organic semiconductor materials. This includes recently discovered materials that use different electron acceptor molecules, which have shown enhanced OPV efficiency.

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