Researchers from the École polytechnique fédérale de Lausanne (EPFL) have discovered a way of using phosphate salt to mitigate the dangerous impact of lead in perovskite solar cells.
The core element of perovskite solar cells is lead, which is dissoluble in water. Halide perovskite solubility is generally a big advantage, as it means building these solar panels is simpler and far more cost cost–effective. However, it can pose both an environmental threat and a health hazard when the panel breaks or gets wet, for example, when it rains.
Perovskite solar cells offer the greatest efficiency but pose a threat
“The solar energy-to-electricity conversion of perovskite solar cells is unbelievably high, around 25%, which is now approaching the performance of the best silicon solar cells,” explained Professor László Forró at EPFL’s School of Basic Sciences. “But their central element is lead, which is a poison; if the solar panel fails, it can wash out into the soil, get into the food chain, and cause serious diseases.”
Due to the poisonous and dangerous nature of lead, it is essential for it to be captured before it is able to reach the soil, and it must be possible to recycle it.
This challenge has led to extensive research efforts as it is the core barrier standing in front of regulatory authorities authorising the development of perovskite solar cells on a sizable, commercial scale.
However, efforts to synthesise non-water-soluble and lead-free perovskites have thus far yielded inadequate performance.
Using phosphate salt to mitigate the impact of lead
Now, Forró’s team have developed a promising and effective resolution to this challenge, which entails the utilisation of transparent phosphate salt, which does not block solar light, so it does not impact performance.
Moreover, if the solar panel ceases to work, the phosphate salt instantaneously reacts with lead to form a water-insoluble compound that cannot leak out to the soil and can also be recycled.
This novel research has been published in ACS Applied Materials & Interfaces.
“A few years ago, we discovered that cheap and transparent phosphate salt crystals, like those in soil fertilisers, can be incorporated into various parts of the sandwich-like lead halide perovskite devices, like photodetectors, LEDs or solar cells,” commented Endre Horváth, the first author of the study.
“These salts instantaneously react with lead ions in the presence of water and precipitate them into extremely non-water-soluble lead phosphates.”
“The ‘fail-safe’ chemistry keeps lead ions from leaching out and can render perovskite devices safer to use in the environment or close to humans,” explained Márton Kollár, the chemist responsible for the growth of perovskite crystals.
“We show that this approach can be used to build functional photodetectors, and we suggest that the broad community of researchers and R&D centres working on various devices like solar cells and light-emitting diodes implements it in their respective prototypes,” added Pavao Andričevic, who characterised the sensitive photodetectors.
“This is an extremely important study – I would say, a central one – for large-scale commercialisation of perovskite-based solar cells,” Forró concluded.