Perovskite materials are quickly emerging as a promising candidate for solar cells, but one of their major downsides is that they can degrade in direct sunlight. Researchers at UCLA have now uncovered a root cause of the problem, and found a simple fix that can be applied during the manufacturing process.
Silicon has long reigned supreme in the world of solar cells, with no other material able to match its great combination of efficiency, durability and cost. But one contender is rapidly rising through the ranks – metal halide perovskites, which are approaching the efficiency of silicon but are cheaper, lighter and more flexible.
But of course there’s a catch. Perovskite materials tend to break down under direct sunlight, reducing their efficiency over time. That of course is a problem for devices designed to sit in direct sunlight. Past studies have tried to fix this durability issue by adding bulky molecules, old pigments, carbon nanodots made of hair, 2D additives, chili compounds or quantum dots.
In the new study, the UCLA researchers uncovered a mechanism for how this degradation occurs. Ironically, it stems from a surface treatment designed to correct defects and improve efficiency. This process involves coating the surface in a layer of organic ions, but the team found that doing so can create a kind of trap for energy-carrying electrons to gather on the surface. That in turn destabilizes the perovskite atoms’ arrangement, causing the breakdown over time.
So the team countered the issue by pairing positive and negative ions in the surface treatment. This worked to keep the surface neutral and stable, without interfering with the defect prevention of the original treatment.
To investigate how well the new treatment worked, the researchers tested solar cells under powerful lighting around the clock, to simulate accelerated aging conditions. Solar cells treated with the new technique kept 87 percent of their efficiency after more than 2,000 hours in these conditions – far better than the untreated cells, which dropped to 65 percent.
“Our perovskite solar cells are among the most stable in efficiency reported to date,” said Shaun Tan, co-first author of the study. “At the same time, we’ve also laid new foundational knowledge, on which the community can further develop and refine our versatile technique to design even more stable perovskite solar cells.”
The research was published in the journal Nature.
Source: UCLA