Stanford Researchers Mimic Structure Of Insects Eyes To Make Perovskite Solar Cells More Durable

By  on Clean Technica, 3 Sept 2017

The single most important factor driving the installation of more solar panels worldwide is cost. As solar panels get cheaper, the decision to build solar power plants instead of conventional coal, natural gas, or nuclear power plants gets easier.

Perovskites — a class of materials whose structure is similar to that of table salt — are cheaper to manufacture than conventional solar cells made from silicon. That’s the good news. The bad news is that they are not as efficient at turning sunlight into electricity as silicon solar cells are and they are far less durable. Time is a significant factor when determining the cost of something. If a new product costs half what a conventional product does but only lasts a tenth as long, it is more expensive in the long run even though it cost less initially.

Researchers have been slowly making progress on the efficiency of perovskite solar cells. Some are now the equal of conventional solar cells made of silicon. But they still are far less durable. They are negatively affected by heat and humidity and are extremely fragile. “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. He is the senior author of an article published recently by Energy & Environmental Science

“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.”

Nicholas Rolston is a graduate student working with Dauskardt and a co-author of the study. “Perovskites are the most fragile materials ever tested in the history of our lab,” said Rolston. “This fragility is related to the brittle, salt-like crystal structure of perovskite, which has mechanical properties similar to table salt.”

Image via Thomas Shahan/Creative Commons

The researchers think they may have found a solution to the short durability of perovskites in the structure of insect eyes. “We were inspired by the compound eye of the fly, which consists of hundreds of tiny segmented eyes,” Dauskardt explains. “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.”

The researchers constructed a 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.”

perovskite compound solar cell

“Scaffolds in a compound solar cell filled with perovskite after fracture testing.” Image via Dauskardt Lab/Stanford University

Tests 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 [conventional] solar cell,” Dauskardt says. “So we achieved a huge increase in fracture resistance with no penalty for efficiency.”

So far, so good. But how would the less brittle persovskite solar cells hold up to the heat and humidity normally experienced by rooftop solar panels? To find out, the researchers exposed them to temperatures of 185 degrees Fahrenheit and 85% relative humidity for six weeks. Despite these extreme 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. “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.”

The usual disclaimers apply. This study is based on results in a laboratory. Commercial applications could be years or even decades away. But the research is encouraging. It wasn’t that long ago that solar panels were less than 1% efficient. Today, 20% is realistic and some have reached 30% efficiency or more under laboratory conditions. Solar panels make with perovskite solar cells may not be available at Home Depot or Northern Tool just yet, but they are on their way.

Top chart by CleanTechnica, data via Lazard