A Korea Advanced Institute of Science and Technology led international research team has developed a new type of solar cell that can both withstand environmental hazards and is 26.7% efficient in power conversion.

Solar cells convert light into energy, but they can be inefficient and vulnerable to the environment, degrading with, ironically, too much light or other factors, including moisture and low temperature.

The team’s results have been published in Science.

The researchers, led by Byungha Shin, a professor from the Department of Materials Science and Engineering at KAIST, focused on developing a new class of light-absorbing material, called a wide bandgap perovskite.

Structure for the perovskite-Si tandem solar cell device. Image Credit: Korea Advanced Institute of Science and Technology. Click image for the largest view.

The material has a highly effective crystal structure that can process the power needs, but it can become problematic when exposed to environmental hazards, such as moisture. Researchers have made some progress increasing the efficiency of solar cells based on perovskite, but the material has greater potential than what has been previously achieved.

To achieve better performance, Shin and his team built a double layer solar cell, called a tandem, in which two or more light absorbers are stacked together to better utilize solar energy. To use perovskite in these tandem devices, the scientists modified the material’s optical property, which allows it to absorb a wider range of solar energy. Without the adjustment, the material is not as useful in achieving high performing tandem solar cells.

The modification of the optical property of perovskite, however, comes with a penalty – the material becomes hugely vulnerable to the environment, in particular, to light.

To counteract the wide bandgap perovskite’s delicate nature, the researchers engineered combinations of molecules composing a two-dimensional layer in the perovskite, stabilizing the solar cells.

Shin said, “We developed a high-quality wide bandgap perovskite material and, in combination with silicon solar cells, achieved world-class perovskite-silicon tandem cells.”

The development was only possible due to the engineering method, in which the mixing ratio of the molecules building the two-dimensional layer are carefully controlled. In this case, the perovskite material not only improved efficiency of the resulting solar cell but also gained durability, retaining 80% of its initial power conversion capability even after 1,000 hours of continuous illumination.

According to Shin this is the first time such a high efficiency has been achieved with a wide bandgap perovskite single layer alone.

“Such high-efficiency wide bandgap perovskite is an essential technology for achieving ultra-high efficiency of perovskite-silicon tandem (double layer) solar cells,” Shin said. “The results also show the importance of bandgap matching of upper and lower cells in these tandem solar cells.”

Now having stabilized the wide bandgap perovskite material, the researchers are focused on developing even more efficient tandem solar cells that are expected to have more than 30% of power conversion efficiency, something that no one has yet achieved.

Shin noted, “Our ultimate goal is to develop ultra-high-efficiency tandem solar cells that contribute to the increase of shared solar energy among all energy sources. We want to contribute to making the planet healthier.”

The tandem idea isn’t new but making it work well is quite unusual. Here it works and works with an fresh take on perovskite. Maybe this one has some legs to get out of the lab. By all means the research team has well earned congratulations!


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