Battery research Chinese scientists develop sandwich technology for laminated solar cells

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Flexible "tandem solar cells" are currently in demand, not only for smartwatches but also for other curved surfaces in e-cars or space technology. Chinese scientists have now achieved a breakthrough here: a sandwich technology for solar cells made from perovskite plus CIGS.

A team at "Westlake University" in Hangzhou has developed a new method to combine layers of perovskite and copper indium gallium diselenide (CIGS) while ensuring their stability. This has been the biggest hurdle in this technological route of battery research so far.

Solar module resembles a multi-layer cake

For more than a year, the team struggled to coat a CIGS layer with a perovskite layer that wasn't riddled with holes like Swiss cheese. It recently worked with a radically new coating method that they describe in a paper in the journal "Nature."

Their new solar module has a photovoltaic conversion efficiency of 23.4 percent, write the scientists led by Professor Wang Rui in Hangzhou. He compares his module, consisting of up to 15 layers, to a "multi-layer cake."

The solar cell is as thin as a hair

Each individual layer can "capture" sunlight of a different wavelength, according to Professor Wang. "This flexible and thin tandem solar cell is only as thick as a hair. It is realistic to assume that it will be used in the future in fields such as construction, automotive and aircraft manufacturing, and flexible wearables," Wang told the Chinese science newspaper Keji Ribao.

It is realistic to assume that it will be used in the future in fields such as construction, automotive and aircraft manufacturing, and flexible wearables.

Professor Wang Rui in Hangzhou

The paper in Nature is titled "Divalent cation replacement strategy stabilizes wide-bandgap perovskite for Cu(In,Ga)Se2 tandem solar cells." It states that the "stability and efficiency" of perovskite solar cells have been "substantially improved."

Giving up was not an option

The breakthrough is a typical example of how success in applied materials science often requires a combination of intelligence and simple yet admirable perseverance. Even after a year of unsuccessful attempts, a PhD student of Professor Wang named Tian Liuwen simply did not want to give up. He kept experimenting until one day the stable perovskite surface became visible under the electron microscope.

However, a certain stubbornness was also demonstrated by Professor Wang Rui, as the technological route "perovskite plus CIGS" had increasingly shrunk to a niche in battery research in recent years.

The combination of perovskite with perovskite or perovskite with silicon had been considered more promising for multi-layer sandwich constructions of thin-film solar modules. All the more surprising now is this breakthrough at the private Westlake University, founded by a prominent biophysicist.

Complicated but efficient

The high conversion rate of this invention can almost be compared to that of crystalline silicon solar cells. However, their construction—the successive application of the various layers—is a technically complex process. Each individual layer has its own specific requirements for thickness and uniformity. The comparison with "multi-layer cakes" that easily collapse fits quite well.

Problem of ion migration solved

Incidentally, the scientists in China have also solved the problem of "ion migration" with their new method, caused by "wandering" halogen ions in thin perovskite layers. These have now been tamed for the first time with the help of multivalent cations, the researchers report.

*Henrik Bork, long-time China correspondent for the Süddeutsche Zeitung and the Frankfurter Rundschau, is Managing Director at Asia Waypoint, a consulting agency specializing in China and based in Beijing. 
 

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