Materials that stand on edge increase efficiency in solar cells

Studies by researchers from Lund University in Sweden and Fudan University in China have shown increased efficiency in solar cells thanks to perovskite’s ability to self-organise by standing on edge.

In its regular form, perovskite is very sensitive to moisture. It dissolves when it comes into contact with water, and even normal humidity deteriorates the material within hours or minutes. Now the researchers appear to have overcome that problem.

Tönu Pullerits, professor of chemical physics at Lund University, said: “We have succeeded in producing thin sheets with a water-repelling surface, making the whole construction much more stable. In addition, we have succeeded in orienting the sheets so as to obtain acceptable solar cells, with an efficiency of 10%.”

The researchers not only built thin sheets out of perovskite to achieve water-repelling surfaces but also discovered that the sheets self-organised in a way that clearly increased efficiency.

Since the sheets are so thin, many need to be layered on top of each other in order for sufficient absorption of sunlight. A problem arises at this point in that the water-repelling surfaces do not allow electrons to circulate freely within the material. It becomes difficult for the electrons to jump from one sheet to another, which reduces efficiency in the solar cells.

The researchers first tested two different water-repelling surfaces. They expected one version to give better results, enabling the electrons to jump more easily from one sheet to another. Instead, the outcome was the opposite - the second version gave much better results. This surprised the researchers, who then started new experiments to understand why.

"Here, our laser experiments were crucial. We could show that the sheets with the second surface material self-organised in such a way as to stand on edge instead of lying flat against one another", explained Prof Pullerits.

He sees the result as an important step on the way to constructing stable and efficient solar cells out of perovskite. Thanks to the self-organising structure of the sheets, the electrons were able to move freely between the contacts, considerably increasing the efficiency of converting the solar energy to electricity.

Author
Tom Austin-Morgan

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