In a new study, researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) have demonstrated that creating one of the raw materials necessary for perovskites – a relatively new-to-science material – in a different way could be key to the success of these cells.

The findings have been published in the journal Nano Energy under the paper titled ‘Removal of residual compositions by powder engineering for high-efficiency formamidinium-based perovskite solar cells with operation lifetime over 2000 hours.’ The work was supported by the OIST Technology Development and Innovation Center’s Proof-of-Concept Program.

Led by Professor Yabing Qi, researchers attached to OIST’s Energy Materials and Surface Sciences Unit synthesized the crystalline powder in perovskites called FAPbI3 using a more precise powder engineering method.

“The crystalline powder in perovskites – FAPbI3 – forms the perovskite’s absorber layer,” explained one of the lead authors, Dr. Guoqing Tong, a postdoctoral scholar in the Unit. “Previously, this layer was fabricated by combining two materials – PbI2 and FAI. The reaction that takes place produces FAPbI3. But this method is far from perfect. There are often leftovers of one or both of the original materials, which can impede the efficiency of the solar cell,” Tong explained.

The researchers pointed out that another benefit of this method was that the perovskite’s stability increased across different temperatures. The researchers noted that when the perovskite’s absorber layer was formed from the original reaction, at room temperature, it turned from brown to yellow, which wasn’t ideal for absorbing light. The synthesized version was brown even at room temperature.

In the past, researchers have created a perovskite-based solar cell with more than 25% efficiency, which is comparable to silicon-based solar cells. But, to move these new solar cells beyond the lab, an upscale in size and long-term stability is necessary, feel the scientists.

Using the synthesized crystalline perovskite powder, Dr. Tong, and his team achieved a conversion efficiency of over 23% in their solar cell, but the lifespan was more than 2,000 hours. Even after scaling up to solar modules of 5x5cm2, the team still achieved over 14% efficiency. As a proof-of-concept, the researchers fabricated a device that used a perovskite solar module to charge a lithium-ion battery.

The experts feel that the results represent a crucial step towards efficient and stable perovskite-based solar cells and modules that could be used outside of the lab. “Our next step is to make a solar module that is 15x15cm2 and has an efficiency of more than 15%,” said Dr. Tong. Dr. Tong is hopeful that further progress in the field would allow them to power a building at OIST with their solar modules.

The emerging field of perovskite solar cells has opened new doors for researchers, slowly gaining popularity and acceptance among solar technologies.

Earlier this year, Oxford PV, an Oxford University spin-off company, announced a new record efficiency of 29.52% for its perovskite silicon tandem solar cell.

Last year, a team of researchers at the Hebrew University of Jerusalem came up with a new method to produce recyclable perovskite used in solar cells. The process is expected to have a lasting impact on the solar sector. The solar cells prepared using this structure demonstrated a power conversion efficiency of 11.08% with a high open-circuit voltage of 0.988 V.