Researchers from Henan University, Southeast University, HZB, EPFL, Queen Mary University of London, Chinese Academy of Sciences, University of Stuttgart, Cardiff University, University of the Basque Country UPV/EHU, University of Cambridge, Xiamen University and The Hong Kong Polytechnic University have developed a method for enhancing both the efficiency and environmental resilience of perovskite solar cells.
"We have recently achieved significant advances in protecting perovskite solar cells against light, heat, moisture, and mechanical stress. But operating them reliably under changing environmental conditions is still a challenge," says Prof. Michael Saliba, head of the Institute for Photovoltaics (IPV) at the University of Stuttgart.
The study focuses on triple-cation lead halide perovskites, composed of methylammonium (MA), formamidinium (FA), and cesium (Cs) ions. “Triple-cation perovskites are considered by many experts a gold standard because they combine high efficiency with long-term stability while being reproducible,” explains Saliba, who pioneered their development in 2016. The synergy of these cations provides robust structural tolerance and energy-level alignment, allowing precise tuning of bandgap and material stability under operational stress.
However, a long-standing challenge remains: the vulnerability of grain boundaries (GBs) - the microscopic interfaces between perovskite crystals - which act as channels for ion migration and stress accumulation. These defects accelerate degradation when devices are exposed to fluctuating light, humidity, and temperature conditions.
"Further advances are required to commercialize these perovskites and establish them as a reliable alternative to silicon semiconductors,” says Saliba. "To achieve this, we apply minor adjustments that produce major effects." The international team introduced photoswitchable organic molecules, known as isomeric compounds (specifically, Ca-Abz), at the perovskite grain boundaries. These molecules reversibly switch between trans (E) and cis (Z) conformations under UV-containing light, functioning as dynamic “stress buffers.”
This light-triggered switching allows the molecular network to absorb and release lattice strain during operation. The mechanism effectively prevents the rupture of perovskite lattice bonds and suppresses the accumulation of structural defects during repeated light cycling. As co-author Dr. Weiwei Zuo notes, “Stabilizing the grain boundaries stabilizes the entire solar cell.”
To test their approach, the researchers subjected the modified perovskite solar cells (PSCs) to stringent environmental stress simulations mimicking day–night operation and outdoor exposure. Under 2,000 hours of continuous UV-containing light cycling at 65 °C and 500–600 temperature cycles between –40 °C and +85 °C, the devices retained over 95% of their initial power conversion efficiency (PCE).
The optimized devices achieved a certified PCE of 26.9% (maximum 27.2%, with an MPPT-certified efficiency of 26.7%), placing them among the most efficient and stable perovskite devices reported to date. The combination of triple-cation composition and photoswitchable grain-boundary passivation allows simultaneous enhancement of efficiency, structural durability, and photostability.
Light-cycling tests and atomistic modeling confirmed that the photoswitchable isomers mitigate grain-boundary fragmentation and prevent light-induced lattice expansion - key degradation pathways limiting perovskite performance. Beyond mechanical stabilization, the light-active molecules also convert part of the high-energy UV radiation into less damaging wavelengths, further protecting the perovskite lattice.
“Our new material design increases the operational stability and lifespan of perovskite solar cells while maintaining competitive performance, making them even more suitable for practical applications,” explain Saliba and Zuo. This dynamic, self-adjusting grain-boundary regulation marks a step forward toward commercially viable perovskite photovoltaics capable of enduring real-world light and temperature cycling without sacrificing power output.
