Bug-eye design makes perovskite solar cells more durable

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Packing tiny solar cells together like the micro-lenses in the compound eye of an insect could pave the way for perovskite solar panels.

For a new study, researchers used the insect-inspired design to protect the fragile photovoltaic material from deteriorating when exposed to heat, moisture, and mechanical stress.

“Perovskites are the most fragile materials ever tested in the history of our lab.”

“Perovskites are promising, low-cost materials that convert sunlight to electricity as efficiently as conventional solar cells made of silicon,” says Reinhold Dauskardt, a professor of materials science and engineering at Stanford University. “The problem is that perovskites are extremely unstable and mechanically fragile. They would barely survive the manufacturing process, let alone be durable long term in the environment.”

Most solar devices, like rooftop panels, use a flat, or planar, design. But that approach doesn’t work well with perovskite.

“Perovskites are the most fragile materials ever tested in the history of our lab,” says graduate student Nicholas Rolston, a co-lead author of the study that appears in Energy & Environmental Science. “This fragility is related to the brittle, salt-like crystal structure of perovskite, which has mechanical properties similar to table salt.”

To address the durability challenge, scientists turned to nature.

“We were inspired by the compound eye of the fly, which consists of hundreds of tiny segmented eyes,” Dauskardt says. “It has a beautiful honeycomb shape with built-in redundancy: If you lose one segment, hundreds of others will operate. Each segment is very fragile, but it’s shielded by a scaffold wall around it.”

Using the compound eye as a model, the researchers created a compound solar cell consisting of a vast honeycomb of perovskite microcells, each encapsulated in a hexagon-shaped scaffold just 0.02 inches (500 microns) wide.

“The scaffold is made of an inexpensive epoxy resin widely used in the microelectronics industry,” Rolston says “It’s resilient to mechanical stresses and thus far more resistant to fracture.”

Tests conducted during the study show that the scaffolding had little effect on how efficiently perovskite converted light into electricity.

“We got nearly the same power-conversion efficiencies out of each little perovskite cell that we would get from a planar solar cell,” Dauskardt says. “So we achieved a huge increase in fracture resistance with no penalty for efficiency.”

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But could the new device withstand the kind of heat and humidity that conventional rooftop solar panels endure?

To find out, researchers exposed encapsulated perovskite cells to temperatures of 185 F (85 C) and 85 percent relative humidity for six weeks. Despite these extreme conditions, the cells continued to generate electricity at relatively high rates of efficiency.

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Dauskardt and colleagues have filed a provisional patent for the new technology. To improve efficiency, they are studying new ways to scatter light from the scaffold into the perovskite core of each cell.

“We are very excited about these results,” he says. “It’s a new way of thinking about designing solar cells. These scaffold cells also look really cool, so there are some interesting aesthetic possibilities for real-world applications.”

Postdoctoral scholars Brian Watson and Adam Printz and also co-lead authors of the work. The National Science Foundation and a grant from the Stanford Precourt Institute for Energy provided funding.

Source: Stanford University