Perovskite solar cells become more durable – material retains 99 percent of its efficiency even after 1,450 hours of sunshine –

Promising development: Researchers have identified a perovskite material that can withstand intense lighting and heat. Installed in a solar cell, it retained around 99 of its efficiency in the test even after 1,450 operating hours. In practice, solar cells made from this perovskite could even last 20,000 hours, as the scientists report. That could make thinner and more powerful photovoltaic systems possible.

Perovskites are materials that have a specific crystal structure regardless of their individual components. In photovoltaics, they are considered the material of the future because perovskite semiconductors can convert sunlight into electricity, but are cheaper and more energy-efficient to manufacture than silicon cells. The crystalline thin films of these minerals can be produced by vapor deposition or deposition from solution.

Classic perovskite crystal structure. © Solid State/ CC-by-sa 3.0

Automated manhunt among perovskites

The problem, however, is that as soon as perovskite solar cells are exposed to UV radiation and heat, they have so far rapidly lost performance – the material decomposes. “The Achilles heel of perovskite solar cells is their low durability,” explains senior author Christoph Brabec from the Helmholtz Institute Erlangen-Nürnberg. While these solar cells lose their performance after days or weeks, the classic silicon solar cells last for more than 20 years.

Brabec and his team have therefore looked specifically for a more durable perovskite material. To do this, hundreds of different perovskite mixtures tested their lightfastness using an automated process. “Even if you only rely on tried and tested components, you come up with an enormous number of possible compositions that we can manufacture and test automatically with our processes,” explains first author Yicheng Zhao from the Helmholtz Institute.

New material and adapted cell structure

The scientists actually found what they were looking for: They identified a perovskite that showed hardly any light-induced degradation in the preliminary tests and used this as the basis for the construction of a solar cell. In doing so, they changed the structure of the cell in such a way that another source of degradation was avoided: the doped polymers or metal oxide nanoparticles otherwise used as contacts promote the corrosion of the perovskites at higher temperatures. Contact and electrical conductivity deteriorate early on.

“To improve the stability at the contact point, we packed the entire electrode in a kind of protective cover,” explains Zhao. A new double-layer polymer structure, the underside of which is undoped and the upper side is doped with a non-ionic element, protects against decomposition and ensures that the contact is maintained. The team then tested how well the perovskite solar cell constructed in this way held up in normal operation in a long-term exposure test at 65 degrees.

Durability confirmed in initial tests

The result: the perovskite solar cell remained stable and retained around 99 percent of its initial efficiency of 20.5 percent even after 1,450 hours of operation. “The values ​​are definitely among the best that have ever been measured for a planar perovskite solar cell in a long-term test,” says Brabec. The perovskite material also proved itself in an initial one-week field test under normal daylight and sunlight.

According to the research team, this perovskite, combined with the adapted solar cell structure, could open up new opportunities to produce perovskite solar cells and tandem solar cells with good durability. “It is always difficult to make a long-term forecast. But the perovskite solar cell that we have now developed could certainly be operated for over 20,000 operating hours under normal circumstances, ”estimates Brabec.

The researchers are aiming for further efficiency improvements in the future. “With an efficiency of 20.9 percent, the cell tested does not yet fully utilize its potential. 24 to 25 percent should be possible in the near future, ”explains Zhao. (Nature Energy, 2021; doi: 10.1038 / s41560-021-00953-z)

Source: Research Center Jülich

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