Researchers at the Helmholtz-Zentrum Berlin (HZB) said that they have produced perovskite solar cells to achieve efficiencies of well above 24%, which are resistant to drop under rapid temperature fluctuations between -60 and +80 degrees Celsius over one hundred cycles.

The experiment findings correspond to about one year of outdoor use.

Perovskite semiconductors promise highly efficient and low-cost solar cells. However, the researchers said that the semi-organic material is very sensitive to temperature differences, which can quickly lead to fatigue damage in normal use.

The team of researchers identified that adding a dipolar polymer compound to the precursor perovskite solution helps to counteract this.

Additionally, the materials are cheap, can be processed into thin films with minimal energy input, and achieve significantly higher efficiencies than those of conventional silicon solar cells.

 “We optimized the device structure and process parameters, building upon previous results, and finally could achieve a decisive improvement with b-poly(1,1-difluoroethylene) or b-pV2F for short,” says Guixiang Li, a Ph.D. candidate.

b-pV2F molecules resemble a zigzag chain occupied by alternating dipoles.

Another researcher explained that this polymer wraps around the individual perovskite microcrystals in the thin film like a soft shell, creating a cushion against thermomechanical stress.

Scanning electron microscope images show that in the cells with b-pV2F, the tiny granules nestle a little closer.

In addition, the researchers informed that the dipole chain of b-pV2F improves the transport of charge carriers and thus increases the efficiency of the cell.

Solar modules are expected to provide stable output for at least 20 years in outdoor conditions while exposed to large temperature fluctuations. Silicon photovoltaics manage this efficiently, whereas the semi-organic perovskites lose performance relatively fast.

A researcher said that the sunlight could heat the inside of a photovoltaic cell to 80 degrees Celsius in the dark; the cell then cools down immediately to the outside temperature.

This triggers significant mechanical stresses in the thin layer of perovskite microcrystals, creating defects and even local phase transitions, so the thin film loses its quality.

The team, along with a few international partners, investigated a chemical variation that significantly improves the stability of the perovskite thin film in different solar cell architectures.

“Even under these extreme stresses, they still achieved 96 % efficiency in the end,” the researcher quoted above said.

If they can reduce the losses a little further, perovskite solar modules could still produce most of their original output after 20 years, a goal that is now coming within reach.

Recently, researchers at the Helmholtz-Zentrum Berlin (HZB) said they had achieved 32.5% conversion efficiency in tandem solar cells, the highest ever for this technology and a world record.

The teams from HZB had claimed to achieve a record value in late 2021 with an efficiency of 29.8% in a tandem solar cell made of perovskite and silicon. The result was certified by Fraunhofer ISE CalLab. The researchers improved upon their earlier conversion efficiency record of 29.15%.