“Sunglasses for solar cells” improve their stability

The Smart Energy Materials group at the Adolphe Merkle Institute has achieved a significant breakthrough in perovskite solar cell technology by developing a strategy that can automatically adapt to changing light conditions. This could potentially solve one of the biggest challenges preventing the widespread adoption of next-generation solar devices: long-term stability.

This innovative approach uses bioinspired compounds that change their properties when exposed to sunlight, creating self-adjusting protective layers that enhance both efficiency and durability.

Prof. Jovana Milic and colleagues integrated photochromic materials into perovskite solar cells, creating devices that dynamically respond to environmental conditions. Perovskite devices have shown tremendous promise due to their exceptional efficiency and low manufacturing costs compared to traditional silicon cells. However, their tendency to degrade rapidly under real-world conditions has limited commercial deployment.

The breakthrough centers on a specialized compound termed SINO (4-(1,3,3-trimethylspiro[indoline-2,3'-naphtho[2,1-b]^[1][2]oxazin]-6'-yl)benzoic acid), which belongs to a class of materials known as photochromic compounds. Their response to light resembles sunglasses that become lighter or darker depending on light conditions. These materials reversibly change their molecular structure when exposed to light. When integrated into solar cells, SINO acts like a molecular switch that responds to sunlight by altering its configuration to better protect the underlying solar cell components by reversibly changing interfacial properties.

The researchers demonstrated that this photochromic layer transforms between two distinct states when exposed to light. In bright conditions, the material adopts a configuration that helps suppress unwanted ion migration within the perovskite crystal structure while simultaneously facilitating efficient charge extraction. This dual functionality addresses two critical challenges that have limited the practical deployment of perovskite solar technology.

The mechanism underlying these improvements involves sophisticated molecular interactions at the interface between the perovskite layer and the photochromic material. Advanced characterization methods showed that the material helps suppress unwanted ion migration, a primary cause of perovskite degradation, while simultaneously facilitating efficient charge extraction.

Laboratory testing also revealed photovoltaic performance improvements. Solar cells incorporating the SINO layer achieved power conversion efficiencies exceeding those of reference devices. More importantly for commercial viability, stability improved. Under simulated day-night cycling conditions that mimic real-world operation, SINO-treated cells maintained over 90% of their initial performance after 800 hours of testing, while conventional perovskite cells without the protective layer dropped to approximately 80% efficiency over the same period.

While the current laboratory devices show promise, scaling this technology requires addressing manufacturing integration challenges. The researchers estimate that industrial implementation could extend perovskite panel lifespans up to two years over the current five years in field conditions — a critical threshold for competing with silicon solar cells’ 25-year durability. Ongoing work focuses on optimizing deposition techniques to maintain the photochromic layer's responsiveness at scale, with pilot production trials anticipated by late 2026.

“This innovation represents a fundamental shift from traditional approaches that rely on static protective materials to dynamic, responsive interfaces that can adapt to changing operational conditions,” said Milic. “This approach, inspired by natural systems that respond to environmental stimuli, opens new possibilities for creating more resilient optoelectronic devices.”

Reference: Luo, W.; Castán, J. M. A.; Mirani, D.; Riquelme, A. J.; Sachan, A. K.; Kurman, O.; Kim, S.; Faini, F.; Zimmermann, P.; Hinderhofer, A.; Patel, Y.; Frei, A. T.; Moser, J.-E.; Ramirez, D.; Schreiber, F.; Maldivi, P.; Seo, J.-Y.; Tress, W.; Grancini, G.; Demadrille, R.; Milić, J. V. Photochromic Control in Hybrid Perovskite Photovoltaics. Advanced Materials 2025, 37 (20), 2420143.