Ulsan National Institute of Science and Technology (UNIST) researchers have developed solar cells using narrow bandgap organic cation-based perovskite-based quantum dots (PQDs) and demonstrated substantially higher efficiency compared with their inorganic counterparts.
The team stressed that research to this point has predominantly focused on inorganic cation PQDs despite the fact that organic cation PQDs have more favorable bandgaps. However, the recent study unveiled a novel ligand exchange technique, that enables the synthesis of organic cation-based PQDs, ensuring exceptional stability while suppressing internal defects in the photoactive layer of solar cells.
This novel approach enabled the fabrication of a device that demonstrated exceptional performance, retaining efficiency even after long-term storage. “Our developed technology has achieved an impressive 18.1% efficiency in QD solar cells,” stated Professor Sung-Yeon Jang from the School of Energy and Chemical Engineering at UNIST. “This remarkable achievement represents the highest efficiency among quantum dot solar cells recognized by the prestigious National Renewable Energy Laboratory (NREL) in the United States.”
QDs are semiconducting nanocrystals with typical dimensions ranging from several to tens of nanometers, capable of controlling photoelectric properties based on their particle size. PQDs, in particular, have garnered significant attention from researchers due to their outstanding photoelectric properties.
Furthermore, their manufacturing process involves simple spraying or application to a solvent, eliminating the need for the growth process on substrates. This streamlined approach allows for high-quality production in various manufacturing environments.
However, the practical use of QDs in solar cells necessitates 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 notable 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 been predominantly utilized as materials for solar cells.
In this study, the research team employed an alkyl ammonium iodide-based ligand exchange strategy, effectively substituting ligands for organic PQDs with excellent solar utilization. This breakthrough enables the creation of a photoactive layer of QDs for solar cells with high substitution efficiency and controlled defects.
Consequently, the efficiency of organic PQDs, previously limited to 13% using existing ligand substitution technology, has been significantly improved to 18.1%. Moreover, these solar cells demonstrate exceptional stability, maintaining their performance even after long-term storage for over two years. The newly-developed organic PQD solar cells exhibit both high efficiency and stability simultaneously.
Through this study, the scientists addressed the challenges associated with organic PQDs, which have proven difficult to utilize, so this study may present a new direction for the ligand exchange method in organic PQDs, serving as a catalyst to revolutionize the field of QD solar cell material research.
