Enhanced Stability Key for Perovskite Solar Cells to Rival Silicon

An international team comprising researchers from the University of Toronto’s Faculty of Applied Science & Engineering has achieved a significant breakthrough in the development of perovskite solar cells. Their latest design can withstand high temperatures for more than 1,500 hours, bringing this emerging technology closer to commercial viability.

The team’s groundbreaking findings have been published in the prestigious journal Science.

According to Ted Sargent, a University Professor in the Edward S. Rogers Sr. Department of Electrical and Computer Engineering and recent addition to the departments of Chemistry and Electrical and Computer Engineering at Northwestern University, “Perovskite solar cells offer new avenues to overcome the efficiency limitations of traditional silicon-based technology, which currently dominates the industry. However, silicon still holds certain advantages, such as stability, due to its decades-long head start. Our study demonstrates how we can bridge that gap.”

Conventional solar cells are made from energy-intensive, high-purity silicon wafers and have limited capacity to absorb specific segments of the solar spectrum.

In contrast, perovskite solar cells consist of nanoscale crystal layers, making them more adaptable to cost-effective manufacturing techniques. Researchers can also manipulate the size and composition of these crystals to tune the wavelengths of light they can capture.

Moreover, perovskite layers can be deposited on top of each other or even on top of silicon solar cells, enabling broader utilization of the solar spectrum and further enhancing overall efficiency.

In recent years, advances from Sargent’s lab and other research groups have brought the efficiency of perovskite solar cells within the range of silicon-based cells. However, the issue of stability has received comparatively less attention.

So Min Park, a postdoctoral fellow in Sargent’s lab and one of the co-lead authors of the study, explains, “We specifically aimed to investigate high-temperature and high-humidity conditions as these would reveal the components most prone to failure and guide improvement efforts. Leveraging our expertise in materials discovery, spectroscopy, and device fabrication, we developed and characterized a new surface coating for perovskites. Our data indicate that this coating, composed of fluorinated ammonium ligands, significantly enhances the cell’s stability.”

A typical perovskite solar cell contains a passivation layer that surrounds the light-absorbing perovskite layer and facilitates the movement of electrons into the surrounding circuit.

However, depending on its composition and exposure to heat and humidity, the passivation layer can deform in ways that impede electron flow.

Mingyang Wei, a Ph.D. graduate from the Department of Electrical and Computer Engineering and current postdoctoral fellow at École Polytechnique Fédérale de Lausanne, who is also a co-lead author, explains, “Many research groups employ passivation layers made with large ammonium ions, which are organic nitrogen-containing molecules. Although these layers exhibit stable 2D structures at room temperature, they can degrade at elevated temperatures due to their interaction with the underlying perovskites. We have replaced conventional ammonium ions with 3,4,5-trifluoroanilinium ions. This novel passivation layer does not intercalate into the perovskite crystal structure, ensuring thermal stability.”

The team then conducted performance tests on the cells, subjecting them to continuous measurements at 85 degrees Celsius, 50 percent relative humidity, maximum power-point tracking, and illumination equivalent to full sunlight. The study reports a T85 value, which represents the time taken for the cell’s performance to degrade to 85 percent of its original value, of 1,560 hours.

Park adds, “Typically, a perovskite cell of this nature would last around 500 hours. While some research teams have reported measurements of over 1,000 hours, they did not test the cells at temperatures as high as ours. Our design signifies a significant advancement, and we were thrilled to see its outstanding performance.”

Park believes that combining the team’s passivation layer with other innovative approaches, such as double- or triple-junction designs, can further enhance perovskite solar cell performance.

She concludes, “We still have a long way to go before achieving parity with silicon’s performance, but the progress in this field has been remarkable in recent years. We’re heading in the right direction, and we hope that this study will inspire further breakthroughs.”

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