Lightweight and bendy solar cells that are just as efficient as conventional ones could massively expand the use of solar power.
Most solar cells in use today are crystal silicon-based, thanks to their high efficiency and ease of manufacture, but they can only be placed on flat, static surfaces because they crack under stress. Existing bendy solar cells made from other materials offer an alternative, but at the cost of much lower energy efficiency.
Now, Wenzhu Liu at the Chinese Academy of Sciences in Shanghai and his colleagues have developed a thin, lightweight silicon-based cell that is so flexible it can wrap around itself without losing any efficiency.
The team created the cell by first thinning a photovoltaic silicon wafer by more than 60 per cent, which makes it as bendy as paper, but also reflective and so less efficient. Chemically treating the surface to create microscopic, pyramid-shaped bumps restores this efficiency, but makes it brittle when bent – until Liu had an idea to fix that.
“One day, when I tore a plastic food bag, the small notch on the bag’s edge inspired me to ask whether the tendency of silicon cells to fragment with mechanical stress is caused by sharp notches on the edges of the wafers,” he says.
After filming the treated cells snapping in slow motion, Liu and his team realised that the cracks would start at the edge of a cell in channels between the pyramids. When they softened these channels and tried bending a cell, they found that lots of tiny, superficial cracks accumulated but the cell didn’t break, and it retained its efficiency.
The bendy cells can be easily fabricated using existing silicon wafer techniques and, because they are 95 per cent lighter than rigid cells, could be used on walls without compromising building integrity. Liu and his team tested the cells in extreme environments – such as at the South Pole, on a drone flying at an altitude of 20 kilometres and on a balloon in high wind – and found they worked as well and sometimes better than rigid solar cells.
Kyle Frohna at the University of Cambridge says the work is very impressive. “It opens silicon up to a whole other class of applications, some of which we’ve thought of and some of which we probably haven’t even thought of yet.”