Stretchable solar cells retain high efficiency

Researchers from the King Abdullah University of Science and Technology (KAUST) have devised a way to turn rigid silicon into solar cells that can be stretched by 95%, while retaining high solar energy capture efficiency of 19%. Their work, published in the journal Advanced Energy Materials, shows that crystalline silicon solar panels could be just as effective when incorporated into stretchy wearable electronics or flexible robot skin as they are when used as rigid rooftop panels.

Although many new solar materials are being investigated, silicon remains by far the photovoltaic industry’s favourite. As explained by postdoctoral researcher Nazek El-Atab, “Monocrystalline silicon remains the material of choice in the PV industry due to its low cost, nontoxicity, excellent reliability, good efficiency and maturity of the manufacturing process.”

One drawback of silicon, for certain applications, is its rigidity, unlike some thin film solar cells. However, these flexible cells either consist of low-cost, low-efficiency organic materials or more efficient but very expensive inorganic materials. Laboratory head Muhammad Mustafa Hussain and his team have now taken a significant step towards overcoming this limitation by developing low-cost, high-efficiency, silicon-based stretchy solar cells.

The key was to take a commercially available rigid silicon panel and coat the back of the panel with a highly stretchable, inexpensive, biocompatible elastomer called ecoflex. The team then used a laser to cut the rigid cell into multiple silicon islands, which were held together by the elastomer backing. Each silicon island remained electrically connected to its neighbours via interdigitated back contacts that ran the length of the flexible solar cell.

The team initially made rectangle-shaped silicon islands that could be stretched to around 54%, according to Hussain. “Beyond this value, the strain of stretching led to diagonal cracks within the brittle silicon islands,” he said.

The team tried different designs to push the stretchability further, mindful that each slice of silicon they removed reduced the area available for light capture. The team tried a diamond pattern before settling on triangles, which saw them achieve “world-record stretchability and efficiency”, Hussain said.

Super flexible solar panels can be used effectively in moving robots. Image ©2019 KAUST; Heno Hwang.

The team now plans to incorporate the stretchy silicon solar material to power a multisensory artificial skin developed by Hussain’s lab. Making solar panels that stretch with even greater flexibility is also a target.

“The demonstrated solar cells can be mainly stretched in one direction — parallel to the interdigitated back contacts grid,” Hussain said. “We are working to improve the multidirectional stretching capability.”

Top image caption: Muhammad Mustafa Hussain (left) and Nazek El-Atab compare the flexibility of their solar cell with the rigid nature of a typical silicon solar cell. Image ©2019 KAUST.

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