Chemical stoichiometry and gradient shell engineering for highly-efficient narrow near-band-edge emission in CuInS2 quantum dots

Copper indium sulfur-based quantum dots (CIS QDs) are classified as one of well-known ternary I-III-VI semiconductors, which have exciting promising applications in display and lighting devices, due to their unique merits such as non-toxicity, stability, and high photoluminescence quantum yield (PL QY). However, the emission full width at half maximum (FWHM) of CIS-based QDs typically extends to ∼140 ​nm, fundamentally limiting their use in high-color-purity light emitting. Herein, we report the rationally-designed CIS QDs with high efficiency and narrowband emission by chemical stoichiometry and gradient shell engineering, based on precisely controlling the dynamic growth and stoichiometric ratio. It is found that the accurate control on the growth kinetics and stoichiometry during the nucleation process of CIS QDs could enhance the crystallinity through gradual and organized crystalline growth, which effectively mitigates the formation of InCu substitutional and Cu vacancies, thus suppressing the defect emission. Furthermore, the introduced InSx/ZnxGa1-xS gradient shell on the surface of QDs cores could reduce the strain within interface, thereby eliminating the non-radiative recombination caused by the surface defects resulted from interface strain. As a result, a remarkable PLQY of 89% is achieved for the QDs. More importantly, their FWHM decreases to 70 ​nm, which is the narrowest one for CIS-based QDs ever reported, representing their bright future to be applied in high-definition display devices.