Researchers at City University of Hong Kong have developed perovskite solar cells capable of maintaining stability at high temperatures. According to the researchers, the work paves the way to commercialization. Perovskite solar cells have been a promising frontier in solar energy due to their high power conversion efficiency, though they have been held back by their thermal instability. Left: Perovskite solar cells under high temperature aging. Right: Perovskite solar cells equipped with novel SAM. Courtesy of City University of Hong Kong. The researchers focused on the self-assembled monolayer (SAM), an essential part of these cells, which they envisioned as a heat-sensitive shield that needed reinforcement. “Despite their high power conversion efficiency, these solar cells are like a sports car that runs exceptionally well in cool weather but tends to overheat and underperform on a hot day. This was a significant roadblock preventing their widespread use,” said Zhu Zonglong, a professor in the Department of Chemistry. The researchers created a SAM that they anchored to a nickel oxide nanoparticle surface as a charge extraction layer. According to Zonglong, the cells retained greater than 90% of their efficiency, maintaining an efficiency rate of 25.6%, even after operating under 65 °C for more than 1000 hours. “We discovered that high-temperature exposure can cause the chemical bonds within SAM molecules to fracture, negatively impacting device performance. So, our solution was akin to adding a heat-resistant armor — a layer of nickel oxide nanoparticles, topped by a SAM, achieved through an integration of various experimental approaches and theoretical calculations,” Zonglong said. Molecular structure of the novel SAM, schematic illustration of SAM deposition method, and photovoltaic performance of SAM-based perovskite solar cells. Courtesy of City University of Hong Kong. Anchoring the SAM to an inherently stable nickel oxide surface enhanced the binding energy on the substrate. Additionally, the team synthesized a new SAM molecule of its own that promotes more efficient charge extraction in perovskite devices. “This breakthrough is pivotal as it addresses a major obstacle that previously impeded wider adoption of perovskite solar cells. Our findings could significantly broaden the utilization of these cells, pushing their application boundaries to environments and climates where high temperatures were a deterrent,” Zonglong said. Once commercialized, he said, the technology could help to decrease dependence on fossil fuels and contribute sustainably to combatting the global climate crisis. The research was published in Science (www.doi.org/10.1126/science.ade9637).