Perovskite solar cells reach new efficiency heights with novel additive

A small team of optical and solar cell specialists and electrical engineers affiliated with several institutions in China, and one in France, has found that adding pyrrodiazole to formamidinium iodide perovskite films can increase the efficiency of the solar cells made with them.

In their paper published in the journal Nature Communications, the group describes the process they used to find the additive, how it was added and how well a solar cell using the modified films worked when tested.

Over the past several years, silicon solar cells have become the standard. In more recent years, the price and availability of silicon have pushed researchers to look for other materials. One such promising material is the mineral perovskite. To date, its use has been limited by degradation and efficiency issues. In this new effort, the research team has worked to improve its efficiency.

The work by the team in this new effort was focused on the thin film used to make a perovskite solar cell—they mixed a small amount of pyrrodiazole with a formamidinium iodide perovskite sample to create the thin film. They did so, they note, to improve its stability during crystallization.

They found that doing so led to stronger bonds between PbI₂ and hydrogen due to the presence of the formamidinium iodide. It also led to improved uniformity as evidenced by reduced colloidal aggregation, which reduced overall defects. A reduction in defects, the team notes, reduces degradation.

The team then developed a full solar cell using the new films along with another innovation—slot-die coating in open air conditions. Such an innovation, they suggest, opens the door to large-scale production of their solar cells, a move that could lower costs, making them more competitive with cells based on silicon.

The researchers found the additive helped with efficiency. Their solar cells were tested at 21.5% peak efficiency and 20.3% certified efficiency. Both scores are among the highest ever achieved with perovskite solar cells. They also found that the cells demonstrated long-term stability, with a 94% efficiency rating after exposure to direct light for 1,000 hours, at 65% humidity. They also note that their testing results were verified by China’s National Institute of Measurement and Testing Technology.

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