A team from the Korea Institute of Energy Research (KIER) has achieved a groundbreaking power conversion efficiency of 23.64% for ultra-lightweight, flexible perovskite/CIGS tandem solar cells. Their findings were published in the March 2025 edition of Joule, marking the highest reported efficiency for this class of solar cells to date.
While perovskite/silicon tandem cells have reached efficiencies of up to 34.6%, their bulk and fragility make them less suitable for applications where flexibility and lightness are key—such as in vehicles, aircraft, satellites, and wearable technology.
Flexible thin-film perovskite/CIGS tandem cells offer a compelling alternative due to their adaptability and low weight, ideal for integration on curved or mobile surfaces. However, their commercial adoption has been limited by relatively lower efficiency and complex manufacturing processes.
To address these challenges, the KIER team introduced a simplified lift-off fabrication method that not only improves manufacturability but also enhances cell performance. This technique involves depositing a polyimide (PI) layer onto a soda-lime glass (SLG) substrate, building the tandem solar cell on top, and then detaching it from the glass. This method allows for more stable and uniform fabrication than approaches that use flexible substrates directly.
The team also tackled performance loss caused by potassium diffusion during manufacturing. Potassium atoms, originating from the glass substrate, can create defects in the CIGS absorber layer, hindering charge movement and efficiency. By using the PI layer as a diffusion barrier, the researchers successfully minimized these defects, boosting the cell’s performance well beyond the previous record of 18.1%.
Durability tests confirmed the robustness of the design. Even after 100,000 bending cycles, the cells retained 97.7% of their original efficiency, highlighting their suitability for long-term use in flexible applications.
Lead researcher Inyoung Jeong emphasized the significance of the achievement: “This milestone demonstrates the commercial viability of next-generation flexible solar cells, paving the way toward future devices with 30% efficiency.”
Principal investigator Kihwan Kim added that the power-to-weight ratio of their cells is approximately 10 times higher than that of perovskite/silicon tandems, making them ideal for building-integrated photovoltaics, transportation, and aerospace sectors. “With improvements in large-area processing and stability, we aim to boost industrial competitiveness and accelerate the shift to renewable energy,” he said.
