Cocoon Lets Next-Generation Solar Cells Pass Their Toughest Test

Professor Anita Ho-Baillie holds what could be the future of electricity production, a perovskite solar cell in a pressure-tight encasing that keeps it stable. Provided the challenges of making such cells larger can be overcome, they will produce electricity far more cheaply than any other source. UNSW

Perovskite solar cells wrapped in transparent blankets have achieved international stability standards for the first time, marking a major breakthrough in the quest for solar power so cheap other sources can't compete.

Silicon cells dominate the solar market but are reaching the limits of their capacity. We've barely scratched the surface of perovskite's potential, either on its own or in combination with silicon. However, perovskite cells are not very stable. Most decompose when exposed to moisture or heat. They've even been found to out-gas in a vacuum, usually made safer by the absence of reactive gasses.

Along with the loss of efficiency as they scale up in size, instability is a major obstacle to perovskite's mass production. That matters, because their thinness, cheap ingredients, and lack of expensive manufacturing processes mean if these problems can be solved, perovskite cells will become the cheapest (and cleanest) electricity source by far.

Professor Anita Ho-Baillie of the University of Sydney saw perovskites out-gassing in vacuums as a clue to their instability. She ran the escaping gasses through a mass spectrometer to understand what was going on. Then she wrapped cells in a polymer-glass blanket. The idea of encasing perovskites to keep out moisture is obvious and has already been met with some success, but by creating a pressure-tight seal, Ho-Baillie prevented the cells from releasing gasses and thereby stopped their breakdown.

In Science, Ho-Baillie has announced that cells encased in this way pass the International Electrotechnical Commission IEC61215:2016 standard for stability when cycled between extreme heat and cold, all while exposed to 85 percent humidity. “We have shown that we can drastically improve their thermal stability," Ho-Baillie said in a statement

Although other teams have made progress in improving perovskite stability, this test, originally designed to challenge silicon cells, has gone beyond them. Perovskite's properties depend on the metals they are doped with, and many teams are working to find the optimum combination to balance maximum electricity production with stability. Ho-Baillie's approach potentially resolves that, leaving the focus on capturing as much sunlight as possible.

Among perovskite cells' many advantages is that their thinness allows them to bend to suit the surface they are placed on, unlike silicon. Encasement could threaten this, but Ho-Baillie told IFLScience: “Thin glasses are out there, the trick is to find something that is also very thin and flexible” to wrap cells in.

Ho-Baillie acknowledged that while the encased cells have proven their capacity to survive heat and UV, she has yet to prove they can resist both at once.

Lead doping is common in laboratory perovskites, inspiring concerns about leakage and end-of-life disposal. Ho-Baillie noted the amounts of lead are small, and tin is increasingly used as a replacement. Nevertheless, she said the cocooning could address these fears.

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