Tapping the energy-conversion potential of visible and near-infrared light
Tapping the energy-conversion potential of visible and near-infrared light lead image
The development of sustainable energy conversion technologies has long been a global imperative. Much attention has been focused on solar cells and photocatalysts, which expedite water and organic compound decomposition by generating electron-hole pairs upon irradiation. Most of these rely primarily on ultraviolet and visible light, which comprise less than half of the solar spectrum.
Yoshiki Niihori and Masaaki Mitsui highlighted recent advances in converting visible and near-infrared light through triplet-triplet annihilation photon upconversion (TTA-UC).
“While the name is a bit long, the concept is powerful,” said Mitsui. “Whereas many materials can’t absorb low-energy light efficiently, TTA-UC can actually convert low-energy photons into higher-energy ones.”
The researchers focused on ligand-protected metal clusters (LMCs), arrays of inorganic-organic nanoparticles used to initiate the upconversion process. The ultra-small metal particles behave more like molecules than bulk materials and can be fine-tuned to their excited states.
“LMCs offer remarkable tunability,” said Mitsui. “By changing the metal composition or modifying the surrounding organic ligands, we can precisely adjust their performance. This kind of control is very difficult to achieve with conventional sensitizers.”
Niihori and Mitsui reviewed both experimental and theoretical advances, noting that one of the most exciting developments is the deeper understanding of why certain modifications improve performance. Also, with so many LMC types available, they believe that customizing for specific applications is a realistic possibility.
“One of the remaining challenges is to develop systems that work efficiently in the solid state and under low-light conditions — key for real-world solar applications,” said Mitsui. “But LMCs definitely represent a highly versatile platform for developing next-generation light-conversion materials for applications from solar energy harvesting to optoelectronics and biophotonics.”
Source: “Harnessing metal cluster sensitizers for triplet-triplet annihilation photon upconversion: Strategies for performance enhancement,” by Yoshiki Niihori and Masaaki Mitsui, Chemical Physics Reviews (2025). The article can be accessed at https://doi.org/10.1063/5.0273181 .
