The study, which is published in the Science journal, demonstrates a “molecular glue” that keeps a key interface inside cells from degrading. The treatment dramatically increases cells’ stability and reliability over time, while also improving the efficiency with which they convert sunlight into electricity. This will improve the long term reliability of the solar technology and bring perovskite one step closer to commercial viability.
“There have been great strides in increasing the power-conversion efficiency of perovskite solar cells,” said Nitin Padture, a professor of engineering at Brown University and senior author of the new research. “But the final hurdle to be cleared before the technology can be widely available is reliability — making cells that maintain their performance over time. That’s one of the things my research group has been working on, and we’re happy to report some important progress.”
While the efficiency improvements in perovskites have been remarkable, Padture says, making the cells more stable and reliable has remained challenging. Part of the problem has to do with the layering required to make a functioning cell. The layers, made from different materials, respond differently to external forces, creating mechanical stress and compromising performance.
The weakest of those layer interfaces is the one between the perovskite film used to absorb light and the electron transport layer, which keeps current flowing through the cell. It is this interface that the research team has focused on in order to boost the functional life of the perovskite cells.
The experiment
Padture and his colleagues began experimenting with compounds known as self-assembled monolayers or SAMs. “This is a large class of compounds,” Padture said. “When you deposit these on a surface, the molecules assemble themselves in a single layer and stand up like short hairs. By using the right formulation, you can form strong bonds between these compounds and all kinds of different surfaces.”
Padture and his team found that a formulation of SAM with silicon atom on one side, and iodine atom on the other, could form strong bonds with both the election transport layer (which is usually made of tin oxide) and the perovskite light-absorbing layer.
Testing of solar cell function showed that the SAMs dramatically increased the functional life of the perovskite cells. Non-SAM cells prepared for the study retained 80% of their peak efficiency for around 700 hours of lab testing. Meanwhile, the SAM cells were still going strong after 1,300 hours of testing. Based on those experiments, the researchers project the 80%-efficiency-life of the SAM cells to be about 4,000 hours.
