A new catalytic process developed by South Korean researchers could extend the lifespan of perovskite solar cells by preserving 95 percent of their initial efficiency after 1,000 hours of testing.
The technology was invented by a group of scientists at the Daejeon-based Korea Institute of Energy Research (KIER). The effort was led by SeJin Ahn, PhD, a faculty member and principal researcher at the institute. The team also collaborated with a group led by Dong-Seok Kim, PhD, at the Ulsan National Institute of Science and Technology (UNIST).
For the initiative, the cells were tested at temperatures of 185 degrees Fahrenheit (85 degrees Celsius) and 85 percent relative humidity. Still, even after 1,000 hours of exposure to extreme heat and humidity, they retained 95 percent of their initial power conversion efficiency.
According to the team, the new process could help perovskite solar cells compete with traditional silicon panels. “By solving the chronic lifetime issue, it will become an important milestone toward the commercialization of perovskite and tandem solar cells,” Ahn emphasized.
Longer-lasting solar cells
Perovskite solar cells are thin-film photovoltaic devices, which rely on perovskite materials to convert sunlight into electricity. They have attracted a great deal of attention in recent years because of their high energy conversion efficiency and potential for a low-cost manufacturing.
They are also cheap, easy to produce, and lightweight, which makes them suitable for flexible solar panels. But their lifespan is limited ranging from two to 10 years, compared with 25 to 30 years for silicon panels. They are also particularly vulnerable to heat and moisture, which can accelerate their degradation.
This reduces their long-term reliability, especially in hot and humid climates. The problem stems from lithium salts and additives in the hole transport layer. While these substances improve the cells’ efficiency, they also accelerate degradation.
In hot and humid conditions, the additives can evaporate, leaving tiny gaps in the thin film that reduce performance. At the same time, lithium ions can move freely inside the cell, and cause further damage and shortening its lifespan. Until now, researchers have struggled to eliminate these substances without compromising the cells’ ability to convert sunlight into electricity.
New catalytic process
To tackle the issue, the KIER team’s new catalytic process called the post-catalytic reaction filtering extraction process. The method removes harmful lithium ions and eliminates the need for additives while maintaining high power conversion efficiency.
The technology uses a nickel oxide (NiOx) catalyst. It attracts and removes lithium ions from the solution used to create the hole transport layer. When added to the solution, the nickel oxide powder undergoes a reaction that changes its surface properties, thus allowing it to attract lithium ions.
The reaction separates lithium ions from the salt without chemical additives. The released ions then attach to the nickel oxide particles. The researchers then use a physical filtration process to remove the powder from the solution. Because the nickel oxide particles are relatively large, they become trapped in the filter, and remove the attached lithium ions with them.
Credit: KIER
This results in a purified solution free of additives, residual lithium, and catalyst, which can be used to produce a defect-free hole transport layer. The catalyst is then removed. To evaluate the technology, the team tested solar cells made with the new process and compared them with conventional cells.
As outlined, the technology greatly preserve the cells’ performance. However, the new cells also achieved 25.24 percent efficiency, which is slightly higher than the 25.21 percent of conventional cells made with additives. According to the team, this findings could improve tandem solar cells.
“This work is significant in that it breaks away from the conventional framework for perovskite fabrication and presents a new process that catalytically induces only the necessary reactions and then filters out the root-cause substances,” Ahn concluded in a press release.
The study has been published in the journal Advanced Science.