Passivation enables high-efficiency perovskite solar cells

An international team of researchers has synthesised materials that were used for constructing a record-breaking perovskite solar module, with an efficiency of 21.4%. This was achieved through the passivation of the active solar cell layer, which increases the efficiency of the cell and significantly improves its stability. The team’s research was published in the journal Nature Communications.

Perovskite solar cells (PSCs) are one of the world’s fastest-growing solar cell technologies. These elements are thin-layered, lightweight, flexible and are made of low-cost materials. However, this type of solar cell still faces a major issue: quick degradation of perovskite material under environmental conditions.

Passivation is a simple but effective way to improve the stability of perovskite solar cells and has been considered as one of the most effective strategies for eliminating the defects of perovskite materials and their negative effects. The passivated perovskite surface becomes more resistant to ambient conditions as temperature or humidity, and more stable, extending the durability of the device.

Researchers from China, Italy, Lithuania, Switzerland and Luxembourg significantly improved the stability of perovskite solar cells using the passivation method. The perovskite surface becomes chemically inactive during passivation, thereby eliminating perovskite defects that occur during manufacture. The ensuing perovskite solar cells achieve an efficiency of 23.9% with long-term operational stability (over 1000 h).

“Passivation has been applied previously, but so far a two-dimensional (2D) layer of perovskite is being formed on the traditional three-dimensional (3D) perovskite light absorber, making it difficult for carriers to move, especially at higher temperatures,” said chief researcher Dr Kasparas Rakštys, from Kaunas University of Technology (KTU). “It is critical to avoid this because the solar cells become hot.”

To address this issue, the researchers conducted a study that estimated the minimum energy required to form 2D perovskites. The surface of the 3D perovskite layer was passivated by different isomers of phenylethylammonium iodide synthesised by KTU. These isomers have the same molecular formula but different arrangements of atoms in space, determining the probability of 2D perovskite formation.

Researchers from the Lausanne Federal Institute of Technology (EPFL) tested the materials in perovskite solar mini-modules with an active area over 300 times larger than typical, laboratory-scale perovskite solar cells. These mini-modules achieved a record solar energy conversion efficiency of 21.4%. The surface of the perovskite layer of the modules was coated with materials developed by KTU chemists.

“The study proved to be quite effective in preventing the negative effects of passivation on solar cells,” Dr Rakštys said. “It has been discovered that an isomer with the passivation groups closest to each other lead to the most efficient passivation due to the steric hindrance that avoids 2D perovskite formation. Interestingly, steric hindrance is also used as a tool in different areas of chemistry to prevent or slow down undesirable reactions.”

KTU researchers are now working with colleagues from other countries to produce functional, hole-transporting materials and new perovskite compositions.

Image courtesy of the study authors (cropped from the original) under CC BY 4.0

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