With the recent development of foldable mobile phone screens, research on foldable electronics has never been so intensive. One particularly useful application of the foldable technology is in solar panels, according to a recently published Advanced Science study.
Current solar cells are restricted to rigid, flat panels which are difficult to store in large numbers and integrate into everyday appliances. To be integrated into these items, solar cells need to be foldable – to bend at will repeatedly without breaking. Traditional conducting materials used in solar cells lack flexibility, creating a huge obstacle in developing fully foldable cells. A key requirement for an efficient foldable conductor is the ability to withstand the pressure of bending within a very small radius while maintaining its integrity and other desirable properties. A thin, flexible, transparent and resilient conductor material is needed.
“Unlike merely flexible electronics, foldable devices are subject to much harsher deformations, with folding radii as small as 0.5 mm,” says Il Jeon, a professor at Pusan National University, Korea. “This is not possible with conventional ultra-thin glass substrates and metal oxide transparent conductors, which can be made flexible but never fully foldable.”
Fortunately, an international team of researchers, including Jeon, identified a promising candidate to answer all of these requirements: single-walled carbon nanotube (SWNT) films, owing to their high transparency and mechanical resilience. The only problem is that SWNTs struggle to adhere to the substrate surface when force is applied (such as bending) and requires chemical doping. To address this problem, the scientists embedded the conducting layer into a polyimide (PI) substrate, filling the void spaces in the nanotubes.
Their resulting prototype far exceeded the team’s expectations. Only 7 micrometers thick, the composite film exhibited exceptional resistance to bending, almost 80% transparency and a power conversion efficiency of 15.2% – the most ever achieved in solar cells using carbon nanotube conductors, notes the study.
Photo: Pusan National University