Unlike traditional crystalline silicon-based cells, which are widely used due to cost efficiency and scalability, the new tandem design leverages thin-film technologies for enhanced adaptability. Silicon-perovskite tandems have reached up to 34.6 percent efficiency, but their weight and fragility restrict usage in weight-sensitive sectors such as aerospace and automotive. To address these challenges, KIER researchers turned to combining perovskite with copper indium gallium selenide (CIGS), a semiconductor known for its flexibility and suitability for curved surfaces.
CIGS thin-film solar cells can be fabricated on substrates like polyimide and metal foils, making them ideal for integration into non-flat surfaces. However, these cells have historically faced obstacles in efficiency and ease of production. KIER's innovation lies in both its materials engineering and a novel lift-off fabrication technique.
The team introduced a process in which a glass base is first coated with a polyimide layer. The tandem solar cell is then constructed atop this foundation and subsequently detached from the glass, producing a freestanding, flexible device. This method offers stability during fabrication and improves layer uniformity, which enhances performance and consistency.
Another breakthrough came from managing alkali metal diffusion. During fabrication, potassium atoms from the glass substrate can penetrate the CIGS layer, creating defects that impair charge mobility. Using computational modeling, KIER scientists showed that the polyimide coating effectively suppresses this unwanted diffusion, resulting in fewer structural flaws and better performance.
The culmination of these innovations was a solar cell that not only surpassed the previous efficiency benchmark of 18.1 percent for flexible perovskite/CIGS tandems but also maintained 97.7 percent of its output after 100,000 flexing cycles, confirming its mechanical resilience.
"This research is a key achievement that demonstrates the commercial potential of next-generation high-efficiency solar cell technology with flexibility and lightness," said Dr. Inyoung Jeong. "It serves as an important milestone toward realizing ultralight, flexible solar cells with 30 percent efficiency in the future."
Dr. Kihwan Kim, principal investigator of the project, added, "The power-to-weight ratio of the fabricated solar cell is approximately 10 times higher than that of perovskite/silicon tandem solar cells, making it highly promising for applications in fields that require ultralight solar modules, such as building exteriors, vehicles, and aerospace."
The study, published in the March issue of Joule (Impact Factor: 38.6), was conducted with support from KIER's R and D Program and in collaboration with Professor Tae Kyung Lee of Gyeongsang National University and Professor Hae-Jin Kim of Yonsei University.
Research Report:Flexible and lightweight perovskite/Cu(In,Ga)Se2 tandem solar cells
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