A team of researchers has unveiled a novel ligand exchange technique that enables the synthesis of organic cation-based perovskite quantum dots (PQDs), providing exceptional stability while suppressing internal defects in the photoactive layer of solar cells. The research findings could propel the development of an efficient quantum dot (QD) solar cell and thereby facilitate the commercialisation of next-generation solar cells.

Professor Sung-Yeon Jang, the lead researcher from UNIST, said the technology has achieved an 18.1% efficiency in QD solar cells. “This remarkable achievement represents the highest efficiency among quantum dot solar cells recognised by the prestigious National Renewable Energy Laboratory (NREL) in the United States,” Jang said.

QDs are semiconducting nanocrystals with typical dimensions ranging from several to tens of nanometres, capable of controlling photoelectric properties based on their particle size. PQDs, in particular, have garnered attention from researchers due to their outstanding photoelectric properties. Their manufacturing process involves simple spraying or application to a solvent, eliminating the need for the growth process on substrates. This approach allows for high-quality production in various manufacturing environments.

However, using QDs as solar cells requires a technology that reduces the distance between QDs through ligand exchange, a process that binds a large molecule, such as a ligand receptor, to the surface of a QD. Organic PQDs face challenges, including defects in their crystals and surfaces during the substitution process. As a result, inorganic PQDs with limited efficiency (of up to 16%) have predominantly been used as materials for solar cells.

The researchers used an alkyl ammonium iodide-based ligand exchange strategy, thereby substituting ligands for organic PQDs with excellent solar utilisation. This enabled the creation of a photoactive layer of QDs for solar cells with high substitution efficiency and controlled defects. As a result, the efficiency of the PQDs, which was previously limited to 13%, was improved to 18.1%. The solar cells also demonstrated stability, maintaining their performance after long-term storage for over two years. The new organic PQD solar cells exhibited high efficiency and stability simultaneously.

“This study presents a new direction for the ligand exchange method in organic PQDs, serving as a catalyst to revolutionise the field of QD solar cell material research in the future,” Jang said.

The research findings have been published online in Nature Energy.

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