Efficiency of 21%! New material preparation for calcium-titanium ore batteries unveiled

In a collaboration between researchers at Monash University in Australia and Wuhan University of Technology in China, the pair say they were able to achieve a conversion efficiency of 21% using lead acetate as a precursor material for the manufacture of formamide-caesium chalcogenide solar cells.

The efficiency is said to be the best recorded result for a device made from a non-halide lead source. This could pave the way for the industrial manufacture of durable, high-efficiency chalcogenide photovoltaics.

Typically, most chalcogenide solar cell research uses lead halides, specifically a compound known as lead iodide. However, lead iodide must be 99.99% pure and is therefore expensive to use in cells.

To solve this problem, the team became the first to use lead acetate rather than lead iodide to create stable formamide-caesium chalcogenide solar cells.

The test devices showed great thermal stability, continuing to operate after 3300 hours at 65°C with no loss of efficiency.

A smaller prototype solar module using these cells achieved an efficiency of 18.8%. Large areas of chalcogenide layers were made by a single-step blade coating, demonstrating the potential feasibility of industrial manufacturing.

Lead author Jie Zhao, a PhD student at Monash University, said: "We have been able to use lead acetate in a one-step spin-coating process to obtain perfect, high-quality formamide-caesium chalcogenide films ...... As we don't need an anti-solvent, we can achieve this with large-scale techniques such as blade coating, which means the feasibility of industrial production is in place."

The secret ingredient ammonium

Compared to silicon, thin-film solar cells made from chalcogenide have the potential to transform the solar energy sector because they are cheap to manufacture, flexible and have a tunable band gap.

However, researchers are still grappling with reliability issues and must find a way to manufacture devices that can be commercially produced.

Due to their excellent stability, the researchers determined that chalcogenides fabricated using formamide and caesium were ideal commercial candidates. Previous attempts to synthesise them using lead acetate as a precursor had failed.

To investigate and solve this problem, the researchers investigated the underlying molecular mechanisms.

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

Contributing author Sebastian Fürer said, "The presence of ammonium serves to drive off residual acetic acid during the annealing process without the formation of unwanted by-products."

The chemical compound lead acetate is a very promising alternative precursor for creating smooth films with fewer defects than lead halide, the researchers said.

So far, lead acetate has only been used to make methylammonium or caesium-based chalcogenides, which are relatively unstable and unsuitable for practical applications.

Corresponding author Wenxin Mao said, "We provide the entire research community with a second method for fabricating high-quality chalcogenide solar cells."

Recently, researchers at the Helmholtz-Zentrum Berlin Centre said they had achieved a 32.5 per cent conversion efficiency in a stacked solar cell, the highest ever for this technology and a world record. The new laminated solar cell consists of a silicon cell on the bottom and a calcium titanite cell on the top.

In November, a research team from the Baden-Württemberg Centre for Solar Energy and Hydrogen Research in Stuttgart, Germany, combined chalcogenide with copper indium gallium selenide to create a stacked solar module with an efficiency of more than 21%.