Researchers from Monash University, Australia, in collaboration with the Wuhan University of Technology in China, said they were able to use lead acetate as a precursor in making formamidinium-caesium perovskite solar cells with a conversion efficiency of 21%.

The efficiency is claimed to be the best-recorded result for a device made from a non-halide lead source. This can pave the way for creating durable, efficient perovskite photovoltaics at an industrial scale.

Typically, most perovskite solar cell research uses lead halides, particularly a chemical compound called lead iodide. But lead iodide must be 99.99% pure and thus are expensive to use in cells.

To address the issue, the team became the first to make stable formamidinium-cesium perovskite solar cells using lead acetate rather than lead iodide.

The test devices showed strong thermal stability, continuing to function with no efficiency loss after 3,300 hours running at 65°C.

A smaller prototype solar panel featuring these cells achieved 18.8% efficiency. The large-area perovskite layer was fabricated in an ambient atmosphere and was made via a single-step blade coating, demonstrating potential viability for industrial-scale manufacturing.

“We’ve been able to use lead acetate in a one-step, spin-coating process to get the perfect, high-quality formamidinium-caesium perovskite thin film…and because we don’t need an anti-solvent agent, we can do this via large-scale techniques, such as blade coating, which means it’s viable at industrial scale,” said lead author Jie Zhao, a Ph.D. student at Monash University.

Secret Ingredient Ammonium 

 Thin film solar cells made from perovskites have the potential to change the solar energy sector owing to their low manufacturing cost, flexibility, and tunable band gap when compared to silicon.

However, researchers still struggle to solve reliability issues and must find a way to create devices at a viable commercial scale.

The researchers identified an ideal candidate for commercial use in perovskites made using formamidinium and caesium because of their superior stability. Previous attempts to synthesize them using lead acetate as the precursor failed.

 To investigate and solve this issue, the researchers examined the underlying molecular mechanisms.

The researchers identified the need to use ammonium as a volatile cation (positively charged ion) at a critical stage through X-ray diffraction and nuclear magnetic resonance spectroscopy.

Contributing author Sebastian Fürer said: “The presence of ammonium served to drive away the residual acetate during annealing, without forming unwanted side products.”

The researchers said that the chemical compound lead acetate emerged as a promising alternative precursor because it can create smooth thin films with fewer defects than lead halides.

Until now, lead acetate had only been used to make methylammonium or caesium-based perovskites, which are relatively unstable and unsuitable for real-world applications.

“We have provided the entire research community a second way to make high-quality perovskite solar cells,” corresponding author Wenxin Mao said.

Recently, researchers at the Helmholtz-Zentrum Berlin said they had achieved 32.5% conversion efficiency in tandem solar cells, the highest ever for this technology and a world record. The new tandem solar cell consists of a silicon bottom cell and a perovskite top cell.

In November, a team of researchers from the Centre for Solar Energy and Hydrogen Research Baden-Württemberg in Stuttgart, Germany, combined perovskite with copper indium gallium selenide to build a tandem solar module with an efficiency of 21% and above.

Image: Australian Research Council