What happens when light hits solar cells? Scientists just observed the first moments

Zooming in on the first step of solar energy conversion

The researchers’ unique technique employs ultrafast lasers and x-rays to initiate a response and then analyze the changes it creates in just femtoseconds, which is quadrillionths of a second, according to a study published in Nature Communications.

The team investigated the first moments of solar energy conversion, which are the reactions in the material generated by light striking. To start the reaction, they fired a 15-femtosecond laser pulse at the substance. They then used an x-ray pulse that lasted only attoseconds (less than millionths of a billionth of a second) to measure the resulting changes in the material.

For the first time, the researchers observed direct x-ray traces of the material's initial state when electrons are knocked out of position, which results in the formation of an electron and "hole" pair that can move through the substance. In about 50 femtoseconds, this initial state rapidly changed into a new, more stable form. 

Making more efficient OPV devices

Moreover, calculations by Newcastle University's Tom Penfold, who was a part of the study, were aligned with the observations. They proved that the initial state was determined by the distance between chains of molecules in the material.

“This sensitivity of the time-resolved x-ray method to the initial electron dynamics occurring directly after excitation by light paves the way for new insights into the photophysics of a wide range of organic optoelectronic and other materials,” Artem Bakulin, a researcher from the Department of Chemistry at Imperial, said, in a press release.

After illuminating the first moments of light inside a solar cell, the team now intends to investigate the ultrafast charge dynamics in other organic semiconductor materials, such as ones that use different molecules as electron acceptors and exhibit increased OPV efficiency. As cheap and flexible alternatives to silicon-based photovoltaics, OPVs are regarded as an excellent prospect for use in future solar energy generation infrastructure, which makes this study even the more exciting.

“This work demonstrates the power of our new time-resolved x-ray technique, which can now be applied to a wider range of materials and may provide the understanding needed for making more efficient OPV devices,” Professor Jon Marangos from the Department of Physics at Imperial, said.