Near-Infrared, Heavy Metal-Free Colloidal Giant Core/Shell Quantum Dots

Giant core/shell quantum dots (g-QDs) are a promising class of materials for future optoelectronic technologies due to their superior chemical- and photostability compared to bare QDs and core/thin shell QDs. However, inadequate light absorption in the visible and near-infrared (NIR) region and frequent use of toxic heavy metals (e.g., Cd and Pb) are still major challenges for most g-QDs (e.g., CdSe/CdS) synthesized to date. The synthesis of NIR, heavy metal-free, Zn-treated spherical CuInSe2/CuInS2 g-QDs is reported using the sequential cation exchange method. These g-QDs exhibit tunable NIR optical absorption and photoluminescence (PL) properties. Transient fluorescence spectroscopy shows prolonged lifetime with increasing shell thickness, indicating the formation of quasi type-II band alignment, which is further confirmed by simulations. As a proof-of-concept, as-synthesized g-QDs are used to sensitize TiO2 as a photoanode in a photoelectrochemical (PEC) cell, demonstrating an efficient and stable PEC system. These results pave the way toward synthesizing NIR heavy metal-free g-QDs, which are very promising components of future optoelectronic technologies.