Wet suit rubber makes solar cells stretchy and efficient

Solar cells made of organic molecules offer many advantages over their silicon cousins. They are thin, lightweight, flexible, and printable on large areas. But make the devices bendy, and their ability to convert light to electricity plummets.

Researchers have now overcome this trade-off between efficiency and flexibility by adding chloroprene rubber—aka neoprene, the stuff of wet suits—to organic photovoltaic materials (Joule 2025, DOI: 10.1016/j.joule.2025.101996). Organic solar cells containing a mass fraction of 5% neoprene have an efficiency of 17%, which matches the current efficiency of other organic solar cells while being much more stretchable than others reported so far; by comparison, today’s best rigid devices convert 20% of light into electricity.

The new cells should be easier to print on rolls and last longer in wearable devices than rubber-free ones, says Tobin J. Marks, a chemist at Northwestern University. Marks developed the devices with Antonio Facchetti of the Georgia Institute of Technology; Yifan Wang, Yahui Liu, and Zhishan Bo of Qingdao University; Hongxiang Li of Peking University; and other colleagues.

Organic solar cells use two types of molecules: one absorbs light and releases electrons, and another soaks up the electrons. Separating these two types of molecules is necessary to boost their interactions and, in turn, device efficiency, Facchetti says.

Typically, small, chlorinated molecules are added to the organic light-converting material for this separation, but the chlorinated molecules are volatile and escape during processing. In the new work, the researchers used chloroprene rubber for a twofer; the nonvolatile solid makes the photovoltaic layer stretchy, while the chlorine atoms and double bonds on the neoprene structure enhance electron flow between the organic molecules.

Neoprene could, in principle, be added to any organic photovoltaic material, Marks says. “I imagine people saying, ‘Gee, chloroprene rubber, I can buy that at a hardware store; let me put that in my solar cell.’”

A slight trade-off between efficiency and bendability does remain. The device efficiency fell to 15.6% when the researchers added a mass fraction of 20% chloroprene rubber. But the cells retain almost 90% of this initial efficiency even after they are stretched by 50% of their original size 5,000 times.

This efficiency maintenance even at high chloroprene loading is impressive, says Brendan O’Connor, a mechanical and aerospace engineer at North Carolina State University who was not involved in the work. “An optimization of mechanical demands and power generation will need to be weighed [for applications].”

The use of a simple, commercially available additive is elegant, says Justin Hodgkiss, a chemist at Victoria University of Wellington who was not involved in the work. “These devices are right up there with the very best reported devices in terms of efficiency, flexibility, and stability, all at once,” he says.