Insect eyes offer insight into manufacture of perovskites

Scientists at Stanford University have taken inspiration from the compound eyes of insects to improve the viability of perovskites, a promising photovoltaic material that presents manufacturing challenges.

Compound eyes
(Image credit: Thomas Shahan/Creative Commons)

According to Reinhold Dauskardt, a professor of materials science and engineering at Stanford, perovskites are promising, low-cost materials that convert sunlight to electricity as efficiently as conventional solar cells made of silicon. Despite their promise, they are also prone to deteriorating when exposed to heat, moisture or mechanical stress.

“They would barely survive the manufacturing process, let alone be durable long-term in the environment,” said Dauskardt, lead author of a study detailing the research team’s results in Energy & Environmental Science (E&ES).

Most commercial solar devices use a planar design, which doesn’t work well with perovskite solar cells.

“Perovskites are the most fragile materials ever tested in the history of our lab,” said graduate student Nicholas Rolston, a co-lead author of the E&ES study. “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, the Stanford team turned to nature.

“We were inspired by the compound eye of the fly, which consists of hundreds of tiny segmented eyes,” said Dauskardt. “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 are said to have created a compound solar cell consisting of a vast honeycomb of perovskite microcells, each encapsulated in a hexagon-shaped scaffold 500 microns wide.

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

Tests conducted during the study revealed that the scaffolding had little effect on the perovskite’s ability to convert 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 said. “So we achieved a huge increase in fracture resistance with no penalty for efficiency.”

To test the new device, the researchers exposed encapsulated perovskite cells to temperatures of 85 degrees Celsius and 85 per cent relative humidity for six weeks. Despite these conditions, the cells continued to generate electricity at relatively high rates of efficiency.

Dauskardt and his 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.