With the recent development of foldable cell phone screens, research into foldable electronics has never been so intense. A particularly useful application of the foldable technology is in solar panels, according to a recently published Advanced Science study.
Current solar cells are limited to rigid, flat panels that are difficult to store in large numbers and incorporate into everyday devices. To be integrated into these elements, solar cells must be foldable – to bend repeatedly at will without breaking. Conventional conductive materials used in solar cells are not flexible enough, which is a major obstacle to the development of fully foldable cells. A key requirement for an efficient foldable ladder is the ability to withstand bending pressure within a very small radius while maintaining its integrity and other desirable properties. A thin, flexible, transparent and elastic conductor material is required.
“In contrast to purely flexible electronics, foldable devices with a folding radius of only 0.5 mm are subject to much greater deformation,” says Il Jeon, professor at Pusan National University in Korea. “This is not possible with conventional ultra-thin glass substrates and transparent metal oxide conductors, which can be made flexible but never completely foldable.”
Fortunately, an international team of researchers, including Jeon, has found a promising candidate to meet all of these requirements: single-walled carbon nanotube films (SWNT) due to their high transparency and mechanical strength. The only problem is that SWNTs have difficulty adhering to the substrate surface when subjected to force (e.g. bending) and require chemical doping. To address this problem, the scientists embedded the conductive layer in a polyimide (PI) substrate and filled the voids in the nanotubes.
The resulting prototype far exceeded the team's expectations. The composite film, which is just 7 micrometers thick, showed exceptional flexural strength, transparency of almost 80% and a power conversion efficiency of 15.2% – the highest value ever achieved in solar cells with carbon nanotube conductors, according to the study.
Photo: Pusan National University