Chalcogenide-silicon tandem solar cells maintain 80% efficiency after one year

Researchers in Saudi Arabia claim they have improved the outdoor stability of calcium titanite-silicon tandem solar cells through proper encapsulation. At the end of the first year of operation, the cell's fill factor remained above 70%.

Chalcogenide-silicon tandem solar cells

Scientists at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia have conducted a year-long outdoor test of the calcium titanite-silicon tandem solar cell they are developing in 2020. They found that the device maintained more than 80% of its initial efficiency during the testing period from April 2021 to April 2022.

"We're not talking about 500 or 1,000 hours in a controlled laboratory environment, but real outdoor measurements over a sustained period of years." Researcher Maxime Babics told Photovoltaics magazine, noting that the tests have only just begun. "Now that the efficiency of solar tandem cells has exceeded 30 per cent, I think it's time to focus on stability, and we're aiming for a lifetime of at least 20 years."

The team recently described their findings in the article "One year of outdoor operation of a single chalcogenide/silicon tandem solar cell", published in the journal Cell Reported Matter Science. They point out that robust encapsulation is essential to minimise encapsulation-related failures.

These researchers soldered two metal wires on either side of the solar cell to extend the electrode joints. They then encapsulated the device between two layers of thermoplastic polyurethane (TPU) and glass before laminating the assembly.

They arranged the tandem solar cells at an angle of tilt of 25 degrees facing south. They then tested them at the KAUST test facility in Saudi Arabia at a global horizontal irradiance (GHI) of around 2240 kWh/m2.

The scientists said, "The combination of high irradiance, high temperature and high relative humidity at the test site created a challenging environment for the calcium titanite solar cells and is also most relevant for studying the outdoor toughness of photovoltaic technology."

The tandem installation's fill factor remained above 78% for the first four months and then gradually decreased to around 72% from August to December. At the end of the first year of operation, this value remained above 70%.

The researchers said, "As the fill factor is the parameter most likely to drop in outdoor conditions, results like this give us a lot of confidence in improving the stability of the series technology."

They note that the cell will still maintain more than 80 per cent of its initial efficiency by the end of April 2021.

Babics said, "This means we have made a big leap forward in outdoor stability, but it is clear that we have room for improvement. It's also important to note that this generation of tandem batteries was developed in our lab at the end of 2020, and I can say with great confidence that the next generation of tandem batteries we are currently developing will perform even better."